CN117795029A

CN117795029A - Adhesive composition and adhesive sheet

Info

Publication number: CN117795029A
Application number: CN202280053747.6A
Authority: CN
Inventors: 野依慎太郎; 笹原一辉; 形见普史; 藤田昌邦; 片冈贤一; 西野智哉
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2021-08-03
Filing date: 2022-07-19
Publication date: 2024-03-29

Abstract

The present invention provides an adhesive composition capable of forming an adhesive having both a high refractive index and a low elastic modulus. The present invention provides an adhesive composition comprising an acrylic polymer and a plasticizer. The monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1). The plasticizer is a compound having two or more double bond-containing rings and being liquid at 30 ℃.

Description

Adhesive composition and adhesive sheet

Technical Field

The present invention relates to an adhesive composition and an adhesive sheet.

The present application claims priority based on japanese patent application No. 2021-127817 filed on month 8 and 3 of 2021 and japanese patent application No. 2022-061160 filed on month 3 and 31 of 2022, which are incorporated herein by reference in their entirety.

Background

In general, an adhesive (also referred to as a pressure-sensitive adhesive; hereinafter, the same applies) exhibits a soft solid (viscoelastic body) state in a temperature range around room temperature, and has a property of being easily adhered to an adherend by pressure. By utilizing such properties, adhesives are widely used for joining or fixing, protecting, etc. purposes in various industrial fields of household electric products to automobiles, various machines, electric appliances, electronic appliances, etc. Examples of applications of the adhesive include applications in which a polarizing film, a retardation film, a cover window member, and other various light-transmitting members are bonded to other members in display devices such as liquid crystal display devices and organic EL display devices. Patent documents 1 and 2 are examples of technical documents related to an adhesive for an optical member.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2014-169382

Patent document 2: japanese patent application laid-open No. 2017-128732

Disclosure of Invention

Problems to be solved by the invention

Patent documents 1 and 2 disclose an adhesive composition containing a (meth) acrylate polymer having a monomer having a plurality of aromatic rings as a monomer unit as a main component and an adhesive formed by crosslinking the adhesive composition, and propose an adhesive having a refractive index of 1.50 or more, particularly preferably 1.51 or more, by using a monomer having a plurality of aromatic rings. For example, there is a material having a high refractive index as a material for attaching an adhesive such as an optical member, and it is known that when a normal acrylic adhesive is used for bonding such a high refractive index material, reflection occurs at an interface due to a refractive index difference between the two materials. The use of an adhesive having a high refractive index as an adhesive for bonding or the like of the high refractive material can prevent or suppress the interfacial reflection. The refractive index of the acrylic adhesive is generally about 1.47.

Incidentally, an adhesive having good flexibility can be preferably used depending on the application site and the manner of use of the adhesive. For example, in recent years, as a display such as an organic EL display device used in electronic equipment such as a smart phone, a foldable display and a rollable display have been put into practical use, and an adhesive used in the above applications is also required to have flexibility following an adherend that is repeatedly bent. The adhesive having excellent flexibility is suitable for electronic devices having a curved surface shape, because it is easy to follow and adhere to the surface of the curved surface shape such as a three-dimensional shape. Even for an adhesive having a high refractive index, if the flexibility can be improved, the adhesive can be applied to a use requiring the flexibility. However, the high refractive index material used as a monomer component of the adhesive polymer and an additive for an adhesive has a tendency to have a high glass transition temperature due to aromatic rings and the like, and an adhesive formed using the high refractive index material has a tendency to have a high elastic modulus. In the design of adhesives, there is a trade-off between high refractive index and low elastic modulus, and it would be practically beneficial if an adhesive that can be achieved that is compatible with both.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an adhesive composition capable of forming an adhesive having both a high refractive index and a low elastic modulus. Another object of the present invention is to provide an adhesive sheet comprising an adhesive layer formed of the above adhesive composition.

Means for solving the problems

According to the present specification, an adhesive composition containing an acrylic polymer and a plasticizer is provided. The monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1). The plasticizer is a compound having two or more double bond-containing rings and being liquid at 30 ℃. The pressure-sensitive adhesive composition having the above-described structure is suitable for forming a pressure-sensitive adhesive having a high refractive index because the monomer component constituting the acrylic polymer contains the aromatic ring-containing monomer (A1). In addition, since the adhesive composition contains a compound having two or more double bond-containing rings and being liquid at 30 ℃ as a plasticizer, an adhesive having a high refractive index and low elastic modulus can be formed.

In some preferred embodiments, the compound is a compound that is liquid at 20 ℃. By using a compound that is liquid at 20 ℃ as a plasticizer, a low elastic modulus adhesive is easily formed.

In some preferred embodiments, the adhesive composition contains greater than 15 parts by weight of the plasticizer relative to 100 parts by weight of the acrylic polymer. In some embodiments, the adhesive composition contains greater than 30 parts by weight of the plasticizer relative to 100 parts by weight of the acrylic polymer. According to the adhesive composition having the above-described composition, an adhesive having both a high refractive index and a low elastic modulus can be satisfactorily formed.

In some preferred embodiments, the plasticizer has at least one ring selected from aromatic rings and heterocyclic rings as the double bond-containing ring. By using a compound having the above chemical structure as a plasticizer, an adhesive that combines a high refractive index and a low elastic modulus can be easily obtained.

In some preferred embodiments, the plasticizer has a first double bond-containing ring and a second double bond-containing ring. The first double bond-containing ring and the second double bond-containing ring are connected via a linking group having 1 to 5 atoms. Such a plasticizer has a linking group between two or more double bond-containing rings, and thus tends to have a high refractive index and to easily lower the elastic modulus of the adhesive. By using the plasticizer having such a structure, both the high refractive index and the low elastic modulus can be more uniformly achieved.

In some embodiments, the plasticizer has a molecular weight in the range of 100 to 2000. Plasticizers having a molecular weight in the above range are easily compatible with adhesives and easily exert plasticizing effects.

In some embodiments, the monomer component constituting the acrylic polymer contains a monomer (A2) in addition to the aromatic ring-containing monomer (A1), and the monomer (A2) is a monomer having at least one of a hydroxyl group and a carboxyl group. By using an acrylic polymer having such a monomer composition, a high refractive index adhesive that combines flexibility and good cohesive force can be satisfactorily obtained.

In some embodiments, the aromatic ring-containing monomer (A1) is contained in the monomer component in an amount of 60 wt% or more. By using an acrylic polymer having a polymerization ratio of 60% by weight or more of the aromatic ring-containing monomer (A1), an adhesive having a high refractive index can be easily obtained.

In some embodiments, 50% by weight or more of the aromatic ring-containing monomer (A1) is a monomer having a homopolymer glass transition temperature of 10 ℃ or lower. Thus, even if the polymerization ratio of the aromatic ring-containing monomer (A1) is increased, both the high refractive index and the low elastic modulus can be balanced.

The adhesive compositions disclosed herein preferably also contain a crosslinking agent. By using a crosslinking agent to impart moderate cohesiveness to the adhesive, the workability of the adhesive sheet in manufacturing, processing, storage, adhesion to an adherend, and the like can be improved.

In addition, according to the present specification, there is provided an adhesive sheet comprising an adhesive layer comprising any of the adhesives disclosed herein (which may be an adhesive formed from any of the adhesive compositions disclosed herein). The adhesive disclosed herein can achieve both a high refractive index and a low elastic modulus, and therefore, the adhesive sheet comprising the adhesive is preferably used for joining, fixing, protecting, etc. in applications where a high refractive index is desired and flexibility that can withstand repeated bending operations is required, such as foldable display applications.

The present invention is not limited to the above-described embodiments, and various modifications, variations, and other modifications may be made without departing from the scope of the present invention.

Drawings

Fig. 1 is a cross-sectional view schematically showing the structure of an adhesive sheet according to an embodiment.

Fig. 2 is a cross-sectional view schematically showing the structure of an adhesive sheet according to another embodiment.

Fig. 3 is a cross-sectional view schematically showing the structure of an adhesive sheet according to another embodiment.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described. Matters necessary for the practice of the present invention other than those specifically mentioned in the present specification may be understood by those skilled in the art based on the teachings of the present invention and technical knowledge at the time of application as described in the present specification. The present invention may be implemented based on the disclosure in the present specification and technical knowledge in the art.

In the following drawings, members and portions that perform the same function may be denoted by the same reference numerals, and repeated description may be omitted or simplified. In addition, the embodiments described in the drawings are schematically illustrated for the sake of clarity of explanation of the present invention, and are not necessarily intended to represent the dimensions and scale of the product actually provided.

In the present specification, the "base polymer" of the adhesive means the main component of the rubbery polymer contained in the adhesive. The rubbery polymer is a polymer exhibiting rubber elasticity in a temperature range around room temperature. In the present specification, unless otherwise specified, "main component" means a component having a content of more than 50% by weight.

In the present specification, the "acrylic polymer" refers to a polymer containing a monomer unit derived from a monomer having at least one (meth) acryloyl group in one molecule as a monomer unit constituting the polymer. Hereinafter, a monomer having at least one (meth) acryloyl group in one molecule is also referred to as an "acrylic monomer". Thus, an acrylic polymer in this specification is defined as a polymer containing monomer units derived from acrylic monomers. Typical examples of the acrylic polymer include acrylic polymers in which more than 50% by weight (preferably more than 70% by weight, for example, more than 90% by weight) of the monomer components constituting the polymer are acrylic monomers.

In addition, in the present specification, "acrylic monomer" means a monomer having at least one (meth) acryloyl group in one molecule. Here, "(meth) acryl" means a meaning that generally indicates acryl and methacryl. Therefore, the term "acrylic monomer" as used herein may include both a monomer having an acryl group (acrylic monomer) and a monomer having a methacryl group (methacrylic monomer). Also, in the present specification, "(meth) acrylic acid" means acrylic acid and methacrylic acid in total, and "(meth) acrylic acid ester" means acrylic acid ester and methacrylic acid ester in total. Other similar terms are also the same.

< adhesive composition >

The adhesive composition disclosed herein is not particularly limited in form as long as it is a composition capable of forming an adhesive containing an acrylic polymer (preferably an adhesive containing the acrylic polymer as a base polymer). The adhesive composition may be in various forms, for example: a solvent-type adhesive composition comprising an adhesive-forming component in an organic solvent; an active energy ray-curable adhesive composition prepared by curing an active energy ray such as ultraviolet rays or radiation rays to form an adhesive; a water-dispersible adhesive composition in which an adhesive-forming component is dispersed in water; and hot melt adhesive compositions which form an adhesive when applied in a heated and melted state and cooled to around room temperature. Although not particularly limited, the techniques disclosed herein may be satisfactorily implemented using solvent-based adhesive compositions. In the method having the solvent-based adhesive layer formed of the solvent-based adhesive composition, both the high refractive index and the low elastic modulus can be satisfactorily achieved.

The adhesive composition disclosed herein contains an aromatic ring-containing monomer (A1) as a monomer component constituting the above acrylic polymer. In the present specification, the term "monomer component constituting the acrylic polymer" refers to a monomer constituting a repeating unit of the acrylic polymer in an adhesive formed from the adhesive composition, regardless of whether the monomer component is contained in the adhesive composition in the form of a preformed polymer (which may be an oligomer) or in the form of an unpolymerized monomer. That is, the monomer component constituting the acrylic polymer may be contained in the adhesive composition in any of a polymer, an unpolymerized state, and a partially polymerized state. From the viewpoint of ease of preparation of the adhesive composition, in some embodiments, it is preferable that the adhesive composition contains substantially all (for example, 95% by weight or more, preferably 99% by weight or more) of the monomer components in the form of a polymer.

(monomer (A1))

As the monomer (A1), a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule is used. As the monomer (A1), one kind or a combination of two or more kinds of the compounds may be used alone.

Examples of the above-mentioned ethylenically unsaturated group include a (meth) acryloyl group, a vinyl group, and a (meth) allyl group. The (meth) acryl group is preferable from the viewpoint of polymerization reactivity, and the acryl group is more preferable from the viewpoints of flexibility and adhesion. From the viewpoint of suppressing the decrease in flexibility of the adhesive, it is preferable to use, as the monomer (A1), a compound having 1 number of ethylenically unsaturated groups contained in one molecule (i.e., a monofunctional monomer).

The number of aromatic rings contained in one molecule of the compound used as the monomer (A1) may be 1 or 2 or more. The upper limit of the number of the aromatic rings is not particularly limited, and may be, for example, 16 or less. In some embodiments, the number of aromatic rings may be, for example, 12 or less, preferably 8 or less, more preferably 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less from the viewpoint of easy preparation of the adhesive composition, transparency of the adhesive, and the like.

The aromatic ring of the compound used as the monomer (A1) may be a carbocyclic ring such as a benzene ring (may be a benzene ring constituting a part of a biphenyl structure, a fluorene structure); condensed rings of naphthalene, indene, azulene, anthracene, phenanthrene, etc., and may also be heterocyclic (hetero element rings), such as pyridine, pyrimidine, pyridazine, pyrazine, triazine, pyrrole, pyrazole, imidazole, triazole, pyridine, pyrimidine, triazine, and the like,Azole ring, iso->An azole ring, a thiazole ring, a thiophene ring, and the like. The hetero atom contained as a ring constituent atom in the above-mentioned heterocyclic ring may be, for example, one or two or more selected from the group consisting of nitrogen, sulfur and oxygen. In some embodiments, the heteroatoms comprising the heterocyclic ring may be one or both of nitrogen and sulfur. The monomer (A1) may have a structure in which one or more carbocycles and one or more heterocycles are condensed, for example, as in a dinaphthiophene structure.

The aromatic ring (preferably, a carbocycle) may have one or more substituents on the ring constituting atoms, or may have no substituents. In the case of having a substituent, examples of the substituent include an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidoxy group, and the like, but are not limited thereto. In the substituent containing a carbon atom, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be 1 or 2, for example. In some embodiments, the aromatic ring may be an aromatic ring having no substituent on a ring constituent atom or an aromatic ring having one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen atom (e.g., a bromine atom) on a ring constituent atom. The aromatic ring of the monomer (A1) has a substituent on its ring constituting atom means that the aromatic ring has a substituent other than a substituent having an ethylenically unsaturated group.

The aromatic ring and the ethylenically unsaturated group may be bonded directly or via a linking group. The linking group may be, for example, a group having one or two or more structures selected from alkylene, oxyalkylene, poly (oxyalkylene) groups, phenyl groups, alkylphenyl groups, alkoxyphenyl groups, groups having a structure in which one or two or more hydrogen atoms of these groups are substituted with hydroxyl groups (for example, hydroxyalkylene groups), oxy groups (-O-groups), and thiooxy groups (-S-groups), and the like. In some embodiments, aromatic ring-containing monomers having a structure in which an aromatic ring is directly bonded to an ethylenically unsaturated group or bonded via a linking group selected from the group consisting of an alkylene group, an oxyalkylene group, and a poly (oxyalkylene) group may be preferably employed. The number of carbon atoms in the alkylene group and the oxyalkylene group is preferably 1 to 4, more preferably 1 to 3, and may be 1 or 2, for example. The repeating number of the oxyalkylene unit in the above-mentioned poly (oxyalkylene) group may be, for example, 2 to 3.

Examples of the compound which can be preferably used as the monomer (A1) include aromatic ring-containing (meth) acrylates and aromatic ring-containing vinyl compounds. The aromatic ring-containing (meth) acrylate and the aromatic ring-containing vinyl compound may be used singly or in combination of two or more. One or more aromatic ring-containing (meth) acrylates may be used in combination with one or more aromatic ring-containing vinyl compounds.

In some embodiments, as the monomer (A1), a monomer having two or more aromatic rings (preferably, carbocycles) in one molecule may be preferably used from the viewpoint of easily obtaining a high refractive index effect. Examples of the monomer having two or more aromatic rings in one molecule (monomer containing a plurality of aromatic rings) include: a monomer having a structure in which two or more non-condensed aromatic rings are bonded via a linking group, a monomer having a structure in which two or more non-condensed aromatic rings are directly (i.e., not via other atoms) chemically bonded, a monomer having a condensed aromatic ring structure, a monomer having a fluorene structure, a monomer having a dinaphthiophene structure, a monomer having a dibenzothiophene structure, or the like. The monomer containing a plurality of aromatic rings may be used singly or in combination of two or more.

The linking group may be, for example, an oxy group (-O-): thiooxy (-S-), oxyalkylene (e.g. -O- (CH) ₂ ) _n -a radical, where n is 1 to 3, preferably 1), a thiooxyalkylene radical (e.g. -S- (CH) ₂ ) _n -a radical, where n is 1 to 3, preferably 1), a linear alkylene radical (i.e. - (CH) ₂ ) _n -a group, wherein n is 1 to 6, preferably 1 to 3), a group obtained by partially or completely halogenating the alkylene group in the above-mentioned oxyalkylene group, the above-mentioned thiooxyalkylene group and the above-mentioned linear alkylene group, and the like. Preferable examples of the linking group include, from the viewpoint of flexibility of the adhesive, the following: oxy, thiooxy, oxyalkylene and linear alkylene groups. Specific examples of the monomer having a structure in which two or more non-condensed aromatic rings are bonded via a linking group include: phenoxybenzyl (meth) acrylate (e.g., m-phenoxybenzyl (meth) acrylate), thiophenoxybenzyl (meth) acrylate, benzyl (meth) acrylate, and the like.

The monomer having a structure in which two or more non-condensed aromatic rings are directly chemically bonded may be, for example, (meth) acrylate having a biphenyl structure, (meth) acrylate having a triphenyl structure, biphenyl having a vinyl group, or the like. Specific examples thereof include o-phenylphenol (meth) acrylate and biphenyl methyl (meth) acrylate.

Examples of the monomer having a condensed aromatic ring structure include: naphthalene ring-containing (meth) acrylates, anthracycline-containing (meth) acrylates, vinyl-containing naphthalenes, vinyl-containing anthracenes, and the like. As specific examples, there may be mentioned: 1-naphthylmethyl (meth) acrylate (otherwise known as 1-naphthylmethyl (meth) acrylate), hydroxyethylated β -naphthol acrylate, 2-naphthylethyl (meth) acrylate, 2-naphthyloxyethyl acrylate, 2- (4-methoxy-1-naphthyloxyethyl (meth) acrylate, and the like.

Specific examples of the monomer having a fluorene structure include: 9, 9-bis (4-hydroxyphenyl) fluorene (meth) acrylate, 9-bis [4- (2-hydroxyethoxy) phenyl ] fluorene (meth) acrylate, and the like. The monomer having a fluorene structure includes a structural portion obtained by directly chemically bonding two benzene rings, and thus is included in the concept of the monomer having a structure obtained by directly chemically bonding two or more non-condensed aromatic rings.

Examples of the monomer having a dinaphthiophene structure include: and (meth) acryl-containing dinaphthothiophenes, vinyl-containing dinaphthothiophenes, (meth) allyl-containing dinaphthothiophenes, and the like. As specific examples, there may be mentioned: (meth) acryloyloxymethyl dinaphthiophene (e.g. CH bonded at the 5-or 6-position of the dinaphthiophene ring) ₂ CH(R ¹ )C(O)OCH ₂ -a compound of structure. Here, R is ¹ Is a hydrogen atom or a methyl group. ) (meth) acryloyloxyethyl dinaphthiophene (e.g., CH bonded at the 5-or 6-position of the dinaphthiophene ring) ₂ CH(R ¹ )C(O)OCH(CH ₃ ) -or CH ₂ CH(R ¹ )C(O)OCH ₂ CH ₂ -a compound of structure. Here, R is ¹ Is a hydrogen atom or a methyl group. ) Vinyl dinaphthiophene (for example, a compound having a structure in which a vinyl group is bonded to the 5-or 6-position of a naphthothiophene ring), and (meth) allyloxydinaphthiophene. The monomer having a dinaphthiophene structure includes a naphthalene structure, and a structure in which a thiophene ring is fused to two naphthalene structures, and therefore is included in the concept of the monomer having a fused aromatic ring structure.

Examples of the monomer having a dibenzothiophene structure include: dibenzothiophene containing a (meth) acryloyl group, dibenzothiophene containing a vinyl group, and the like. The monomer having a dibenzothiophene structure has a structure in which a thiophene ring and two benzene rings are fused, and thus is included in the concept of the monomer having a fused aromatic ring structure described above.

The dinaphthiophene structure and the dibenzothiophene structure do not belong to a structure in which two or more non-condensed aromatic rings are directly chemically bonded.

In some preferred embodiments, as the monomer (A1), a monomer having one aromatic ring (preferably a carbocycle) in one molecule may be used. The monomer having one aromatic ring in one molecule (monomer containing a single aromatic ring) can contribute to, for example, improvement of flexibility of an adhesive, adjustment of adhesive characteristics, improvement of transparency, and the like. The monomer containing a single aromatic ring may be used singly or in combination of two or more. In some embodiments, from the viewpoint of increasing the refractive index of the adhesive, a monomer having one aromatic ring in one molecule is preferably used in combination with a monomer containing a plurality of aromatic rings.

As examples of the monomer having one aromatic ring in one molecule, there can be cited: benzyl (meth) acrylate, methoxybenzyl (meth) acrylate, phenyl (meth) acrylate, ethoxylated phenol (meth) acrylate, phenoxypropyl (meth) acrylate, phenoxybutyl (meth) acrylate, methylphenyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, chlorobenzyl (meth) acrylate and other aromatic ring-containing (meth) acrylates; bromine-substituted aromatic ring-containing (meth) acrylates such as 2- (4, 6-dibromo-2-sec-butylphenoxy) ethyl (meth) acrylate, 2- (4, 6-dibromo-2-isopropylphenoxy) ethyl (meth) acrylate, 6- (4, 6-dibromo-2-sec-butylphenoxy) hexyl (meth) acrylate, 6- (4, 6-dibromo-2-isopropylphenoxy) hexyl (meth) acrylate, 2, 6-dibromo-4-nonylphenyl acrylate, and 2, 6-dibromo-4-dodecylphenyl acrylate; aromatic ring-containing vinyl compounds such as styrene, α -methylstyrene, vinyltoluene, and t-butylstyrene; n-vinylpyridine, N-vinylpyrzine and N Vinyl pyrrole, N-vinylimidazole, N-vinylCompounds having vinyl substituents on the heteroaromatic ring such as oxazoles; etc.

As the monomer (A1), a monomer having a structure in which an oxyethylene chain is interposed between an ethylenically unsaturated group and an aromatic ring in the above-described various aromatic ring-containing monomers can be used. Monomers having an oxyethylene chain sandwiched between an ethylenically unsaturated group and an aromatic ring in this way can be regarded as ethoxylates of the original monomers. The oxyethylene units (-CH) in the above oxyethylene chain ₂ CH ₂ The number of repetitions of O-) is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, for example 1. As specific examples of the ethoxylated aromatic ring-containing monomer, there may be mentioned: ethoxylated ortho-phenylphenol (meth) acrylates, ethoxylated nonylphenol (meth) acrylates, ethoxylated cresol (meth) acrylates, phenoxyethyl (meth) acrylate, phenoxydiethylene glycol di (meth) acrylate, and the like.

The content of the monomer (A1) containing a plurality of aromatic rings is not particularly limited, and may be, for example, 5 wt% or more, 25 wt% or more, or 40 wt% or more. In some embodiments, the content of the monomer (A1) containing a plurality of aromatic rings may be, for example, 50% by weight or more, and from the viewpoint of easily obtaining a higher refractive index, it is preferably 70% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomer (A1) may be a monomer having a plurality of aromatic rings. That is, as the monomer (A1), only one or two or more kinds of monomers having a plurality of aromatic rings may be used. In some embodiments, the content of the monomer (A1) containing a plurality of aromatic rings may be less than 100 wt%, may be 98 wt% or less, may be 90 wt% or less, may be 80 wt% or less, may be 70 wt% or less, may be 65 wt% or less, may be 50 wt% or less, and may be 10 wt% or less, for example, in consideration of the balance between the high refractive index and the low elastic modulus, and the balance with the adhesive force if necessary. The technology disclosed herein may be carried out in such a manner that the content of the monomer containing a plurality of aromatic rings in the monomer (A1) is less than 5% by weight. Monomers containing multiple aromatic rings may not be used.

The content of the monomer containing a plurality of aromatic rings in the monomer component constituting the acrylic polymer is not particularly limited, and may be set so that a binder having a desired refractive index and elastic modulus can be obtained. The content of the monomer containing a plurality of aromatic rings in the monomer component may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, the content of the monomer containing a plurality of aromatic rings in the above-mentioned monomer component may be, for example, more than 35% by weight, advantageously more than 50% by weight, preferably more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, may be 91% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more, 95% by weight or more, 96% by weight or more, 97% by weight or more, 98% by weight or 99% by weight or more, from the viewpoint of facilitating realization of an adhesive having a higher refractive index. The content of the monomer containing a plurality of aromatic rings in the above-mentioned monomer component is favorably about 99% by weight or less, more favorably 98% by weight or less, still more favorably 96% by weight or less, yet still more favorably 93% by weight or less, yet still more favorably 90% by weight or less, yet still more favorably 85% by weight or less, yet still more favorably 80% by weight or less, yet still more favorably 75% by weight, in view of the balance between the high refractive index and the low elastic modulus and, if necessary, the balance with the adhesive force. In some embodiments, the content of the monomer containing a plurality of aromatic rings in the monomer component may be 70 wt% or less, 60 wt% or less, 50 wt% or less, 40 wt% or less, 25 wt% or less, 15 wt% or less, or 5 wt% or less, from the viewpoint of facilitating higher adhesive properties and/or optical properties (e.g., transparency). The technology disclosed herein can also be implemented such that the content of the monomer containing a plurality of aromatic rings in the above-described monomer component is less than 3% by weight.

The content of the monomer (A1) containing a single aromatic ring is not particularly limited, and may be, for example, 5 wt% or more, 25 wt% or more, or 40 wt% or more. In some embodiments, the content of the monomer containing a single aromatic ring in the monomer (A1) may be, for example, 50% by weight or more, and from the viewpoint of easily obtaining a higher refractive index, it is preferably 70% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. It may be that substantially 100% by weight of the monomer (A1) is a monomer containing a single aromatic ring. That is, as the monomer (A1), only one or two or more monomers having a single aromatic ring may be used. In some embodiments, the content of the monomer containing a single aromatic ring in the monomer (A1) may be less than 100 wt%, may be 98 wt% or less, may be 90 wt% or less, may be 80 wt% or less, may be 70 wt% or less, may be 65 wt% or less, may be 50 wt% or less, or may be 10 wt% or less, for example, in view of the balance between the high refractive index and the low elastic modulus, and the balance with the adhesive force if necessary. The technology disclosed herein can also be implemented in such a manner that the content of the monomer containing a single aromatic ring in the monomer (A1) is less than 5% by weight. Monomers containing a single aromatic ring may not be used.

The content of the monomer containing a single aromatic ring in the monomer component constituting the acrylic polymer is not particularly limited, and may be set so that a binder having a desired refractive index and elastic modulus can be obtained. The content of the monomer containing a single aromatic ring in the monomer component may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, the content of the monomer containing a single aromatic ring in the above-mentioned monomer component may be, for example, more than 35% by weight, advantageously more than 50% by weight, preferably 60% by weight or more, more preferably more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, may be 95% by weight or more, and may be 98% by weight or more, from the viewpoint of facilitating realization of an adhesive having a higher refractive index. The content of the monomer containing a single aromatic ring in the above-mentioned monomer component may be about 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less, in view of the balance between the high refractive index and the low elastic modulus, and if necessary, the balance with the adhesive force. In some embodiments, the content of the monomer containing a single aromatic ring in the above-described monomer component may be 70% by weight or less, 60% by weight or less, 50% by weight or less, 40% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight from the viewpoint of facilitating higher adhesive properties and/or optical properties (e.g., transparency). The technology disclosed herein can also be implemented in such a manner that the content of the single aromatic ring-containing monomer in the above-described monomer component is less than 3% by weight.

In some aspects of the technology disclosed herein, it may be preferable to employ a high refractive index monomer as at least a portion of monomer (A1). The "high refractive index monomer" herein means a monomer having a refractive index of, for example, about 1.510 or more, preferably about 1.530 or more, and more preferably about 1.550 or more. The upper limit of the refractive index of the high refractive index monomer is not particularly limited, and is, for example, 3.000 or less, 2.500 or less, 2.000 or less, 1.900 or less, 1.800 or less, or 1.700 or less from the viewpoint of ease of preparation of the adhesive composition and ease of compatibility with flexibility suitable as an adhesive. The high refractive index monomer may be used singly or in combination of two or more.

The refractive index of the monomer was measured using an Abbe refractometer under conditions of a measurement wavelength of 589nm and a measurement temperature of 25 ℃. As the Abbe refractometer, the model "DR-M4" manufactured by the company ATAGO or its equivalent may be used. This nominal value of the refractive index at 25 ℃ may be used in the case where it is provided by the manufacturer or the like.

As the high refractive index monomer, a compound having a refractive index matching the concept of the aromatic ring-containing monomer (A1) disclosed herein (for example, the above-exemplified compound and group of compounds) can be suitably used. As specific examples, there may be mentioned: m-phenoxybenzyl acrylate (refractive index: 1.566, tg of homopolymer: -35 ℃), 1-naphthylmethyl acrylate (refractive index: 1.595, tg of homopolymer: 31 ℃), ethoxylated o-phenylphenol acrylate (repeat number of oxyethylene units: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD 20): 1.519, tg of homopolymer: 6 ℃), phenoxyethyl acrylate (refractive index (nD 20): 1.517, tg of homopolymer: 2 ℃), phenoxydiglycol acrylate (refractive index: 1.510, tg of homopolymer: -35 ℃), 6-acryloxymethyldinaphthiophene (6 MDNTA, refractive index: 1.75), 6-methacryloxymethyldinaphthiophene (6 MDNTMA, refractive index: 1.726), 5-acryloxyethyldinaphthiophene (5 EDNTA, refractive index: 1.786), 6-acryloxyethyldinaphthiothiophene (6 NTA, refractive index: 1.722), 6-vinyldinaphthiophene (VD6: 62, refractive index: 5, etc., but not limited to these materials.

The content of the high refractive index monomer (i.e., the aromatic ring-containing monomer having a refractive index of about 1.510 or more, preferably about 1.530 or more, more preferably about 1.550 or more) in the monomer (A1) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, 35% by weight or more, or 40% by weight or more. In some embodiments, the content of the high refractive index monomer in the monomer (A1) may be, for example, 50% by weight or more, preferably 70% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more, from the viewpoint of facilitating higher refractive index. It may be that substantially 100% by weight of the monomer (A1) is a high refractive index monomer. In some embodiments, the content of the high refractive index monomer in the monomer (A1) may be less than 100 wt%, may be 98 wt% or less, may be 90 wt% or less, may be 80 wt% or less, or may be 65 wt% or less, for example, from the viewpoint of balancing both the high refractive index and the low elastic modulus, and if necessary, the adhesive strength.

The content of the high refractive index monomer in the monomer component constituting the acrylic polymer is not particularly limited, and may be set so that a binder having a desired refractive index and elastic modulus can be achieved. If necessary, the composition may be further set in consideration of both adhesive properties (for example, adhesive strength) and optical properties (for example, total light transmittance, haze value, etc.). The content of the high refractive index monomer in the monomer component may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, the content of the high refractive index monomer in the monomer component constituting the acrylic polymer may be, for example, more than 35% by weight, and from the viewpoint of easily obtaining a higher refractive index, more than 50% by weight is advantageous, and more than 70% by weight is preferable, and it may be 75% by weight or more, 85% by weight or more, 90% by weight or more, and 95% by weight or more. The content of the high refractive index monomer in the above-mentioned monomer component is preferably 99% by weight or less, more preferably 98% by weight or less, still more preferably 96% by weight or less, and may be 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less, from the viewpoint of balancing both the high refractive index and the low elastic modulus and, if necessary, the adhesive strength.

In some preferred embodiments, an aromatic ring-containing monomer having a homopolymer Tg of 10 ℃ or less (hereinafter, sometimes referred to as "monomer L") is employed as at least a part of the monomer (A1). When the content of the aromatic ring-containing monomer (A1) (particularly, the aromatic ring-containing monomer (A1) corresponding to at least one of the above-mentioned aromatic ring-containing monomers, single aromatic ring-containing monomers, and high refractive index monomers) in the monomer component is increased, the storage modulus G 'of the adhesive generally tends to increase, and by using the monomer L as a part or all of the monomer (A1), the increase in the storage modulus G' can be suppressed. This can improve the refractive index while maintaining a low elastic modulus more favorably. The Tg of the monomer L may be, for example, 5℃or less, 0℃or less, 10℃or less, 20℃or less, or 25℃or less. The lower limit of Tg of the monomer L is not particularly limited. In some embodiments, the Tg of the monomer L may be, for example, -70℃or higher, may be-55℃or higher, or may be-45℃or higher, in view of the balance with the effect of improving the refractive index. In other embodiments, the Tg of the monomer L may be, for example, -30℃or higher, may be-10℃or higher, may be 0℃or higher, or may be 3℃or higher. The monomers L may be used singly or in combination of two or more.

As the monomer L, a substance having such Tg can be suitably used from among compounds (for example, the above-exemplified compounds and compound groups) included in the concept of the aromatic ring-containing monomer (A1) disclosed herein. As preferable examples of the aromatic ring-containing monomer which can be used as the monomer L, there can be mentioned: m-phenoxybenzyl acrylate (Tg of homopolymer: -35 ℃), benzyl acrylate (Tg of homopolymer: 6 ℃), phenoxyethyl acrylate (Tg of homopolymer: 2 ℃), phenoxydiethylene glycol acrylate (Tg of homopolymer: -35 ℃).

The content of the monomer L in the monomer (A1) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, the content of the monomer L in the monomer (A1) may be, for example, 50% by weight or more, preferably 60% by weight or more, 70% by weight or more, 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more, from the viewpoint of easily obtaining an adhesive having a high refractive index and a low elastic modulus at a higher level. It may be that substantially 100% by weight of the monomer (A1) is the monomer L. In some embodiments, the content of the monomer L in the monomer (A1) may be less than 100 wt%, may be 98 wt% or less, may be 90 wt% or less, may be 80 wt% or less, or may be 65 wt% or less, for example, from the viewpoint of balancing both a high refractive index and a low elastic modulus, and if necessary, balancing the adhesive strength.

The content of the monomer L in the monomer component constituting the acrylic polymer may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, the content of the monomer L in the monomer component may be, for example, more than 35% by weight, and from the viewpoint of improving the refractive index, more than 50% by weight is advantageous, and preferably more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more, from the viewpoint of easily obtaining an adhesive having a high refractive index and a low elastic modulus at a higher level. The content of the monomer L in the above-mentioned monomer component is preferably about 99% by weight or less, more preferably about 98% by weight or less, and still more preferably about 96% by weight or less, and may be 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less, from the viewpoint of achieving both a high refractive index and a low elastic modulus and, if necessary, an adhesive strength.

In some embodiments, from the viewpoint of low modulus of elasticity, the glass transition temperature Tg based on the composition of the monomer (A1) _A1 The temperature is suitably about 20℃or less, preferably 10℃or less, for example, 5℃or less, 0℃or less, 10℃or less, 20℃or less, or 25℃or less. Glass transition temperature Tg _A1 The lower limit of (2) is not particularly limited. In some ways, the glass transition temperature Tg is given a balance with the effect of increasing the refractive index _A1 For example, the temperature may be-70℃or higher, may be-55℃or higher, or may be-45℃or higher. The technology disclosed herein is also capable of having a glass transition temperature Tg _A1 For example, -40 ℃ or higher, -35 ℃ or higher, -33 ℃ or higher, -30 ℃ or higher or-25 ℃ or higher. In other embodiments, the glass transition temperature Tg _A1 For example, the temperature may be-10℃or higher, 0℃or higher, or 3℃or higher.

Here, the glass transition temperature Tg based on the composition of the monomer (A1) _A1 The Tg is determined by the Fox equation described below based on the composition of the monomer (A1) alone in the monomer components constituting the acrylic polymer.Glass transition temperature Tg _A1 The Fox equation can be applied only for the monomer (A1) in the monomer components constituting the acrylic polymer, and is calculated from the glass transition temperature of each aromatic ring-containing monomer used as the monomer (A1) and the weight fraction of each aromatic ring-containing monomer in the total amount of the monomer (A1). In the case where only one monomer is used as the monomer (A1), the Tg of the homopolymer of the monomer is equal to the Tg of the glass transition temperature Tg _A1 And consistent.

In some embodiments, as the aromatic ring-containing monomer (A1), a combination of a monomer L (i.e., an aromatic ring-containing monomer having a homopolymer Tg of 10 ℃ or less) and a monomer H having a Tg of more than 10 ℃ may be used. The Tg of the monomers H may be, for example, greater than 10℃or greater than 15℃or greater than 20 ℃. By using the monomer L and the monomer H in combination, the binder having a large content of the aromatic ring-containing monomer (A1) in the monomer component can achieve both a higher refractive index of the binder and flexibility suitable for adhesion to an adherend at a higher level. The ratio of the amount of the monomer L to the amount of the monomer H to be used is not particularly limited, and may be set so as to exhibit the effect appropriately. For example, it is preferable to satisfy any one of the glass transition temperatures Tg _A1 The amount ratio of the monomer L to the monomer H is set in the manner of (a) and (b).

In some embodiments, the aromatic ring-containing monomer (A1) may preferably be selected from compounds that do not contain a structure (e.g., biphenyl structure) obtained by direct chemical bonding of two or more non-condensed aromatic rings. For example, an acrylic polymer composed of a monomer component having a composition in which a compound having a structure in which two or more non-condensed aromatic rings are directly chemically bonded is contained in an amount of less than 5% by weight (more preferably, less than 3% by weight, and may be 0% by weight). The amount of the compound having a structure in which two or more non-condensed aromatic rings are directly chemically bonded is limited in this way, and is advantageous from the viewpoint of achieving an adhesive that combines a high refractive index and a low elastic modulus more uniformly, and if necessary, also combines adhesive strength more uniformly.

The content of the monomer (A1) in the monomer component constituting the acrylic polymer is not particularly limited, and may be set so that an adhesive agent having a desired refractive index and elastic modulus, and adhesive properties (for example, adhesive strength) and/or optical properties (for example, total light transmittance, haze value, etc.) can be obtained. In some embodiments, the content of the monomer (A1) in the monomer component may be, for example, 30% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more, and may be 70% by weight or more. In some preferred embodiments, the content of the monomer (A1) in the monomer component constituting the acrylic polymer may be, for example, more than 70% by weight, preferably at least 75% by weight, and from the viewpoint of easily obtaining a higher refractive index, preferably at least 80% by weight, at least 85% by weight, at least 90% by weight, at least 91% by weight, at least 92% by weight, at least 93% by weight, at least 94% by weight, at least 95% by weight, at least 96% by weight, at least 97% by weight, at least 98% by weight, or at least 99% by weight. The content of the monomer (A1) in the monomer component is typically less than 100% by weight, and is preferably about 99% by weight or less, more preferably 98% by weight or less, even more preferably 96% by weight or less, and may be 93% by weight or less, or 90% by weight or less, from the viewpoint of achieving both a high refractive index and a low elastic modulus and, if necessary, an adhesive strength. In some embodiments, the content of the monomer (A1) in the above-mentioned monomer component may be less than 90% by weight, may be less than 85% by weight, or may be less than 80% by weight, from the viewpoint of facilitating higher adhesive properties and/or optical properties (e.g., transparency).

(monomer (A2))

In some preferred embodiments, the monomer component constituting the acrylic polymer may contain the monomer (A2) in addition to the monomer (A1) described above. The monomer (A2) is a monomer corresponding to at least one of a monomer having a hydroxyl group (hydroxyl group-containing monomer) and a monomer having a carboxyl group (carboxyl group-containing monomer). The hydroxyl group-containing monomer is a compound having at least one hydroxyl group and at least one ethylenically unsaturated group in one molecule. The above carboxyl group-containing monomer is a compound containing at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. The monomer (A2) can contribute to the introduction of crosslinking points into the acrylic polymer or impart moderate cohesiveness to the adhesive. The monomer (A2) may be used singly or in combination of two or more. The monomer (A2) is typically a monomer containing no aromatic ring.

Examples of the ethylenically unsaturated group contained in the monomer (A2) include: (meth) acryl, vinyl, (meth) allyl, and the like. The (meth) acryl group is preferable from the viewpoint of polymerization reactivity, and the acryl group is more preferable from the viewpoints of low modulus of elasticity and adhesion. From the viewpoint of low modulus of elasticity of the adhesive, as the monomer (A2), a compound having 1 number of ethylenically unsaturated groups contained in one molecule (i.e., a monofunctional monomer) is preferably used.

In some embodiments, as the monomer (A2), a monomer having a relatively long distance between an ethylenically unsaturated group (e.g., a (meth) acryloyl group) and a hydroxyl group and/or a carboxyl group may be used. In this way, in the above-described mode in which the hydroxyl group and/or the carboxyl group is used for the crosslinking reaction, a crosslinked structure having high flexibility is easily obtained. For example, a compound having 3 or more atoms (typically carbon atoms, oxygen atoms) constituting a chain (connecting chain) connecting the above-mentioned ethylenically unsaturated group and the hydroxyl group and/or carboxyl group(s) may be used as the monomer (A2), for example, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, 15 or more, 16 or more, 17 or more, 18 or 19 or more. The upper limit of the number of constituent atoms of the connecting chain is, for example, 45 or less, and may be 20 or less (for example, 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, 10 or less, 9 or 8 or less). The number of the connecting chain constituting atoms connecting the ethylenically unsaturated group and the hydroxyl group and/or the carboxyl group means the minimum number of atoms required to reach the hydroxyl group or the carboxyl group from the ethylenically unsaturated group. For example, the above-mentioned linking chain is formed of a linear alkylene group (i.e., - (CH) ₂ ) _n -groups) the number of n is the number of atoms constituting the above-mentioned connecting chain. In addition, for example, the above-mentioned linking chain is an oxyethylene group (i.e., - (C) ₂ H ₄ O) _n -group), the number of carbon atoms constituting the oxyethylene group is 2 and the number of oxygen atoms is 1The product (3 n) of the sum of 3 and n is the number of atoms constituting the connecting chain. The monomer (A2) is not particularly limited, but may be a monomer having a structure represented by- (CH) between the above-mentioned ethylenically unsaturated group and the above-mentioned hydroxyl group and/or carboxyl group ₂ ) _n -an alkylene unit represented by- (C) _m H _2m O) -a monomer of at least one of the oxyalkylene units represented by the formula (e.g., an oxyethylene unit wherein m is 2, an oxypropylene unit wherein m is 3, and an oxybutylene unit wherein m is 4). The number of the alkylene units and the oxyalkylene units is not particularly limited, but may be 1 or more (for example, 1 to 15 or 1 to 10 or 2 to 6 or 2 to 4). In the formula representing the alkylene unit, n is an integer of 1 to 10, for example, and may be 2 or more, 3 or more, 4 or more, or 6 or less, or 5 or less. M in the formula representing the oxyalkylene unit is an integer of 2 or more, for example, an integer of 2 to 4. The monomer (A2) may be a monomer containing an ester bond, an ether bond, a thioether bond, an aromatic ring, an aliphatic ring, or a heterocyclic ring (for example, a ring containing a nitrogen atom (N) or an oxygen atom (O) or a sulfur atom (S)) in addition to the above-mentioned ethylenically unsaturated group, hydroxyl group and/or carboxyl group, alkylene unit, and/or oxyalkylene unit. The alkylene unit and the oxyalkylene unit may have a substituent.

Examples of the hydroxyl group-containing monomer include: hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, and (4-hydroxymethylcyclohexyl) methyl (meth) acrylate are not limited thereto. Examples of the hydroxyl group-containing monomer that can be preferably used include: 4-hydroxybutyl acrylate (Tg: -40 ℃) and 2-hydroxyethyl acrylate (Tg: -15 ℃). From the viewpoint of improving flexibility in the room temperature region, 4-hydroxybutyl acrylate having a lower Tg is more preferable. In the case of using a hydroxyalkyl (meth) acrylate as the hydroxyl-containing monomer and using the hydroxyl group for the crosslinking reaction, a hydroxyalkyl (meth) acrylate (e.g., 4-hydroxybutyl acrylate) having 3 or more (e.g., 3 to 12, preferably 4 to 10) carbon atoms, such as a monomer having a large number of carbon atoms of the hydroxyalkyl group in the hydroxyalkyl (meth) acrylate, is preferably used from the viewpoint of obtaining a crosslinked structure having high flexibility. In a preferred embodiment, 50% by weight or more (for example, more than 50% by weight, more than 70% by weight or more than 85% by weight) of the monomer (A2) may be 4-hydroxybutyl acrylate. The hydroxyl group-containing monomer may be used singly or in combination of two or more.

In some modes of using a hydroxyl group-containing monomer as the monomer (A2), the above hydroxyl group-containing monomer may be one or two or more selected from compounds having no methacryloyl group. Preferable examples of the hydroxyl group-containing monomer having no methacryloyl group include various hydroxyalkyl acrylates mentioned above. For example, it is preferable that more than 50 wt%, more than 70 wt% or more than 85 wt% of the hydroxyl group-containing monomers used as the monomer (A2) are hydroxyalkyl acrylates. By using the hydroxyalkyl acrylate, a hydroxyl group which contributes to providing a crosslinking point and imparting moderate cohesiveness can be introduced into the acrylic polymer, and an adhesive having excellent flexibility and adhesiveness in the room temperature region can be easily obtained as compared with the case where only the corresponding hydroxyalkyl methacrylate is used.

Examples of the carboxyl group-containing monomer include, but are not limited to, acrylic monomers such as (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, and itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Examples of the carboxyl group-containing monomer that can be preferably used include acrylic acid and methacrylic acid. In some embodiments, from the viewpoint of reducing the elastic modulus of the adhesive, it is preferable to use, as the carboxyl group-containing monomer, a compound represented by the following formula (1), for example.

CH ₂ ＝CR ¹ -COO-R ² -OCO-R ³ -COOH (1)

Here, R in the above formula (1) ¹ Is hydrogen or methyl.R ² And R is ³ The divalent linking groups (specifically, organic groups having 1 to 20 carbon atoms (for example, 2 to 10, preferably 2 to 5)) may be the same or different from each other. R in the above formula (1) ² And R is ³ For example, a divalent aliphatic hydrocarbon group, an aromatic hydrocarbon group, or an alicyclic hydrocarbon group may be used. For example, R is as described above ² And R is ³ An alkylene group having 2 to 5 carbon atoms is used. Specific examples of the carboxyl group-containing monomer represented by the above formula (1) include: 2- (meth) acryloyloxyethyl hexahydrophthalic acid, 2- (meth) acryloyloxyethyl-phthalic acid, 2- (meth) acryloyloxyethyl-2-hydroxyethyl-phthalic acid, 2- (meth) acryloyloxyethyl-succinic acid, 2- (meth) acryloyloxypropyl hexahydrophthalic acid hydrogen ester, 2- (meth) acryloyloxypropyl tetraphthalic acid hydrogen ester, and the like. The carboxyl group-containing monomer may be used singly or in combination of two or more. It is also possible to use both hydroxyl-containing monomers and carboxyl-containing monomers.

The content of the monomer (A2) in the monomer component constituting the acrylic polymer is not particularly limited, and may be set according to the purpose. In some embodiments, the content of the monomer (A2) may be, for example, 0.01 wt% or more, 0.1 wt% or more, or 0.5 wt% or more. From the viewpoint of obtaining a higher use effect, the content of the monomer (A2) is preferably 1% by weight or more, and may be 2% by weight or more, or may be 4% by weight or more in some embodiments. The upper limit of the content of the monomer (A2) in the monomer component is set so that the total of the content of the monomer (A1) is not more than 100% by weight. In some embodiments, the content of the monomer (A2) is, for example, preferably 30 wt% or less or 25 wt% or less, and is preferably 20 wt% or less, more preferably 15 wt% or less, and may be less than 12 wt%, may be less than 10 wt%, or may be less than 7 wt% from the viewpoint of facilitating a higher refractive index by relatively increasing the content of the monomer (A1). In some preferred embodiments, the content of the monomer (A2) is less than 5 wt%, more preferably less than 3 wt%, and may be 1.5 wt% or less from the viewpoint of imparting low elastic modulus to the adhesive.

The total content of the monomer (A1) and the monomer (A2) in the monomer component constituting the acrylic polymer may be, for example, 31% by weight or more, preferably 51% by weight or more, 61% by weight or more, or 71% by weight or more. In some embodiments, the total content of the monomer (A1) and the monomer (A2) in the monomer components constituting the acrylic polymer may be, for example, 76% by weight or more, preferably 81% by weight or more, 86% by weight or more, 91% by weight or more, 96% by weight or more, 99% by weight or more, or substantially 100% by weight, from the viewpoint of easily and appropriately exhibiting the effect of these monomers.

(monomer A3)

In some preferred embodiments, the monomer component constituting the acrylic polymer may contain an alkyl (meth) acrylate (hereinafter, also referred to as "monomer (A3)") in addition to the above-described monomer (A1). The monomer (A3) can contribute to lowering the elastic modulus of the adhesive. In addition, it is also possible to contribute to improvement of the compatibility of additives in the adhesive, the adhesive property such as the adhesive strength, and the like. The monomer (A3) may be used singly or in combination of two or more.

As the monomer (A3), a monomer having 1 to 20 carbon atoms at the ester end (i.e., C _1-20 Alkyl (meth) acrylates of straight-chain or branched alkyl groups. As (meth) acrylic acid C _1-20 Specific examples of alkyl esters include: methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylateTetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, nonadecyl (meth) acrylate, eicosyl (meth) acrylate, and the like, but are not limited thereto.

In some embodiments, it may be preferable to employ as at least a portion of monomer (A3) an alkyl (meth) acrylate having a homopolymer Tg of-20deg.C or less (more preferably-40deg.C or less, for example-50deg.C or less). Such low Tg alkyl (meth) acrylates can contribute to low elastic modulus of the adhesive. In addition, such a low Tg alkyl (meth) acrylate contributes to improvement of adhesion characteristics such as adhesive strength. The lower limit of Tg of the alkyl (meth) acrylate is not particularly limited, and may be, for example, at least-85℃and at least-75℃and at least-65℃and at least-60 ℃. Specific examples of the low Tg alkyl (meth) acrylate include: n-Butyl Acrylate (BA), 2-ethylhexyl acrylate (2 EHA), heptyl acrylate, octyl acrylate, isononyl acrylate (iNA), and the like. In other embodiments, alkyl (meth) acrylates having homopolymers with Tg greater than-20deg.C (e.g., greater than-10deg.C) may be employed as at least a portion of monomer (A3). The upper limit of Tg of the alkyl (meth) acrylate is, for example, 10℃or lower, and may be 5℃or lower, or may be 0℃or lower. Alkyl (meth) acrylates having a Tg in this range can help to adjust the elastic modulus of the adhesive. Although not particularly limited, the alkyl (meth) acrylate having the Tg described above is preferably used in combination with the low Tg alkyl (meth) acrylate described above. Specific examples of the alkyl (meth) acrylate having the Tg include Lauryl Acrylate (LA).

In some modes using the monomer (A3), it is preferable to use C (meth) acrylic acid _4-8 Alkyl esters as monomers (A3). Among them, acrylic acid C is more preferably used _4-8 Alkyl esters. (meth) acrylic acid C _4-8 The alkyl esters may be used singly or in combination of two or more. By using (meth) acrylic acid C _4-8 Alkyl esters havingThe elastic modulus of the adhesive is easily reduced, and good adhesive properties (adhesive strength, etc.) tend to be easily obtained. In using (meth) acrylic acid C _4-8 In the embodiment of the alkyl ester as the monomer (A3), among the alkyl (meth) acrylate contained in the monomer component, C (meth) acrylic acid _4-8 The proportion of the alkyl ester is preferably 30% by weight or more, more preferably 50% by weight or more, still more preferably 70% by weight or more, still more preferably 90% by weight or more, and may be substantially 100% by weight.

In some modes using the monomer (A3), it may be preferable to use C (meth) acrylic acid _1-6 Alkyl esters as monomers (A3). By using (meth) acrylic acid C _1-6 Alkyl esters, which are capable of adjusting the storage modulus for each temperature range. For example, the storage modulus in the high temperature region can be set relatively high or the difference in storage modulus between the low temperature region and the high temperature region can be suppressed from becoming large. In addition, (meth) acrylic acid C _1-6 The alkyl ester tends to have excellent copolymerizability with the monomer (A1). (meth) acrylic acid C _1-6 The alkyl esters may be used singly or in combination of two or more. As (meth) acrylic acid C _1-6 Alkyl esters, preferably acrylic acid C _1-6 Alkyl esters, more preferably acrylic acid C _2-6 Alkyl esters, more preferably acrylic acid C _4-6 Alkyl esters. In other embodiments, (meth) acrylic acid C _1-6 The alkyl ester is preferably (meth) acrylic acid C _1-4 Alkyl esters, more preferably C (meth) acrylic acid _2-4 Alkyl esters, more preferably acrylic acid C _2-4 Alkyl esters. As (meth) acrylic acid C _1-6 Preferred examples of alkyl esters include BA.

(meth) acrylic acid C in the monomer component constituting the acrylic polymer _1-6 The content of the alkyl ester may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. In some embodiments, the above (meth) acrylic acid C is from the viewpoints of low modulus of elasticity, adhesive strength, etc _1-6 The content of the alkyl ester may be 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or moreMore than wt% (e.g., more than 30 wt%). (meth) acrylic acid C in the monomer component _1-6 The upper limit of the content of the alkyl ester is, for example, less than 50% by weight, and may be less than 35% by weight. In some embodiments, from the viewpoint of maintaining a high refractive index, the above (meth) acrylic acid C _1-6 The content of the alkyl ester is, for example, 24 wt% or less, preferably less than 20 wt%, more preferably less than 17 wt%, and may be less than 12 wt%, and may be less than 7 wt%, and may be less than 3 wt%, and may be less than 1 wt%. The technology disclosed herein may be used substantially without (meth) acrylic acid C _1-6 Alkyl esters.

In other modes using the monomer (A3), it may be preferable to use (meth) acrylic acid C _7-12 Alkyl esters as monomers (A3). By using (meth) acrylic acid C _7-12 Alkyl esters, which preferably reduce the storage modulus. (meth) acrylic acid C _7-12 The alkyl esters may be used singly or in combination of two or more. As (meth) acrylic acid C _7-12 Alkyl esters, preferably acrylic acid C _7-10 Alkyl esters, more preferably acrylic acid C _7-9 Alkyl esters, more preferably acrylic acid C ₈ Alkyl esters. As (meth) acrylic acid C _7-12 Examples of alkyl esters include 2EHA, iNA, LA, and preferred examples include 2EHA.

(meth) acrylic acid C in the monomer component constituting the acrylic polymer _7-12 The content of the alkyl ester may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. In some embodiments, the above (meth) acrylic acid C is from the viewpoints of low modulus of elasticity, adhesive strength, etc _7-12 The content of the alkyl ester may be 10 wt% or more, 15 wt% or more, 20 wt% or more, or 25 wt% or more (for example, 30 wt% or more). (meth) acrylic acid C in the monomer component _7-12 The upper limit of the content of the alkyl ester is, for example, less than 50% by weight, and may be less than 35% by weight. In some embodiments, from the viewpoint of maintaining a high refractive index, the above (meth) acrylic acid C _7-12 The content of alkyl esters is, for exampleThe content of the organic compound is 24 wt% or less, preferably less than 20 wt%, more preferably less than 17 wt%, and may be less than 12 wt%, and may be less than 7 wt%, and may be less than 3 wt%, and may be less than 1 wt%. The technology disclosed herein can also be used without substantial use of (meth) acrylic acid C _7-12 Alkyl esters.

In some embodiments using the monomer (A3), at least a part of the monomer (A3) is preferably an alkyl acrylate from the viewpoint of low modulus of elasticity. The use of alkyl acrylate is advantageous from the viewpoint of adhesion properties such as adhesive strength. For example, 50 wt% or more of the monomer (A3) is preferably an alkyl acrylate, and the proportion of the alkyl acrylate in the monomer (A3) is more preferably 75 wt% or more, further preferably 90 wt% or more, or substantially 100 wt% of the monomer (A3) is an alkyl acrylate. There may be employed a method in which only one or two or more kinds of alkyl acrylate are used as the monomer (A3) instead of alkyl methacrylate.

In the case where the monomer component contains the monomer (A3) ((meth) acrylic acid alkyl ester), the content thereof may be set so as to appropriately exert the effect of use of the (meth) acrylic acid alkyl ester in the monomer component. In some embodiments, the content of the alkyl (meth) acrylate may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. The upper limit of the content of the monomer (A3) in the monomer component may be set so that the total of the content of the monomers (A1) and (A2) is not more than 100% by weight, for example, less than 50% by weight, or less than 35% by weight. In some embodiments, the content of the monomer (A3) may be, for example, 24 wt% or less. Since the refractive index of the alkyl (meth) acrylate is generally low, it is advantageous to limit the content of the monomer (A3) in the monomer component and to relatively increase the content of the monomer (A1) in order to increase the refractive index. From this viewpoint, the content of the monomer (A3) is suitably less than 23% by weight of the monomer component, preferably less than 20% by weight, more preferably less than 17% by weight, and may be less than 12% by weight, and may be less than 7% by weight, and may be less than 3% by weight, and may be less than 1% by weight. The technology disclosed herein may be preferably practiced in such a manner that substantially no monomer (A3) is used.

(other monomers)

The monomer component constituting the acrylic polymer may contain a monomer other than the above-mentioned monomers (A1), (A2), and (A3) (hereinafter referred to as "other monomer") as required. The other monomers mentioned above may be used, for example, for the purpose of Tg adjustment of the acrylic polymer, adjustment of adhesive property, improvement of compatibility in the adhesive layer, and the like. The above other monomers may be used singly or in combination of two or more.

Examples of the other monomer include monomers having a functional group other than a hydroxyl group and a carboxyl group (functional group-containing monomers). For example, examples of other monomers that can improve the cohesive force and heat resistance of the adhesive include: sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, cyano group-containing monomers, and the like. Examples of the monomer that can introduce a functional group that can be a crosslinking base point into the acrylic polymer or that can contribute to improvement of adhesion to an adherend and compatibility in an adhesive include: an amide group-containing monomer (e.g., (meth) acrylamide, N-methylol (meth) acrylamide, etc.), an amino group-containing monomer (e.g., aminoethyl (meth) acrylate, N-dimethylaminoethyl (meth) acrylate, etc.), a monomer having a ring containing a nitrogen atom (e.g., N-vinyl-2-pyrrolidone, N- (meth) acryloylmorpholine, etc.), an imide group-containing monomer, an epoxy group-containing monomer, a ketone group-containing monomer, an isocyanate group-containing monomer, an alkoxysilyl group-containing monomer, etc. Among the monomers having a ring containing a nitrogen atom, there are, for example, N-vinyl-2-pyrrolidone, which is also an amide group-containing monomer. The relationship between the monomer having a nitrogen atom-containing ring and the amino group-containing monomer is also the same.

Examples of other monomers that can be used in addition to the functional group-containing monomers include: vinyl ester monomers such as vinyl acetate; non-aromatic ring-containing (meth) acrylates such as cyclohexyl (meth) acrylate and isobornyl (meth) acrylate; olefin monomers such as ethylene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride; alkoxy group-containing monomers such as methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, and ethoxyethoxyethyl (meth) acrylate; vinyl ether monomers such as methyl vinyl ether; etc. As a preferable example of other monomers which can be used for the purpose of improving the flexibility of the adhesive, etc., ethoxyethoxyethyl acrylate (otherwise known as ethyl carbitol acrylate, tg of homopolymer: -67 ℃ C.) can be cited.

In the case of using the above-mentioned other monomers, the amount to be used is not particularly limited, and may be appropriately set within a range in which the total amount of the monomer components is not more than 100% by weight. The content of the other monomer in the monomer component may be, for example, about 35 wt% or less (for example, 0 wt% to 25 wt%) or less, suitably about 20 wt% or less (for example, 0 wt% to 20 wt%), or about 10 wt% or less (for example, 0 wt% to 10 wt%) or less, preferably about 5 wt% or less, for example, about 1 wt% or less, from the viewpoint of easily exhibiting the refractive index improving effect by the use of the monomer (A1). The techniques disclosed herein may preferably be practiced in such a way that the monomer components do not substantially contain other monomers as described above.

In some embodiments, the monomer component constituting the acrylic polymer may have a composition in which the amount of the methacryloyl group-containing monomer used is suppressed to a predetermined level or less. The amount of the methacryloyl group-containing monomer used in the monomer component may be, for example, less than 5% by weight, less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. From the viewpoint of achieving an adhesive that combines flexibility, adhesiveness and high refractive index in a balanced manner, it is advantageous to limit the amount of the methacryloyl group-containing monomer used in this way. The monomer component constituting the acrylic polymer may be a composition not containing a methacryloyl group-containing monomer (e.g., a composition containing only an acryl group-containing monomer).

In some embodiments, the amount of the carboxyl group-containing monomer used is limited from the viewpoint of suppressing coloring or discoloration (e.g., yellowing) of the binder among the monomer components constituting the acrylic polymer. The amount of the carboxyl group-containing monomer used in the monomer component may be, for example, less than 1% by weight, less than 0.5% by weight, less than 0.3% by weight, less than 0.1% by weight, or less than 0.05% by weight. Such a limitation of the amount of the carboxyl group-containing monomer used is advantageous from the viewpoint of suppressing corrosion of metal materials (e.g., metal wiring, metal film, etc., which may be present on an adherend) that may contact or come close to the adhesive disclosed herein. The technology disclosed herein may be practiced in such a manner that the monomer components constituting the acrylic polymer do not contain a carboxyl group-containing monomer.

For the same reason, in some embodiments, it is preferable to limit the amount of the monomer having an acidic functional group (including a sulfonic acid group, a phosphoric acid group, and the like in addition to a carboxyl group) in the monomer component constituting the acrylic polymer. The preferable amount of the carboxyl group-containing monomer can be used as the amount of the acid functional group-containing monomer in the monomer component of this embodiment. The technology disclosed herein can be preferably carried out in such a manner that the above-mentioned monomer component does not contain an acid group-containing monomer (i.e., such a manner that the acrylic polymer is acid-free).

(glass transition temperature Tg) _T )

The monomer component constituting the acrylic polymer preferably has a glass transition temperature Tg based on the composition of the monomer component _T Is a composition below about 15 deg.c. In some embodiments, the glass transition temperature Tg _T Preferably 10℃or lower, more preferably 5℃or lower, still more preferably 1℃or lower, and may be 0℃or lower. In other embodiments, the glass transition temperature Tg _T The temperature may be-10deg.C or lower, may be-20deg.C or lower, may be-25deg.C or lower, may be-30deg.C or lower, or may be-35deg.C or lower. From the viewpoint of low elastic modulus of the adhesive, the glass transition temperature Tg _T Low is advantageous. In addition, glass transition temperature Tg _T For example, the temperature may be at least-60 ℃, and from the viewpoint of easily increasing the refractive index of the adhesive, it is preferably at least-50 ℃, more preferably at least-45 ℃, and still more preferably at least-40 ℃. In some preferred embodiments, the glass transition temperature Tg _T Can be above-30deg.C, above-20deg.C, above-10deg.C, above-5deg.C. By using a glass transition temperature Tg having the above range _T The acrylic polymer of the composition of (a) can satisfactorily form an adhesive that combines a high refractive index with a low elastic modulus.

The glass transition temperature Tg is not particularly specified here _T The glass transition temperature is determined by Fox formula based on the composition of the above monomer components. The Fox equation is shown below, and is a relation between Tg of the copolymer and glass transition temperature Tgi of a homopolymer obtained by homopolymerizing monomers constituting the copolymer.

1/Tg＝Σ(Wi/Tgi)

In the above Fox formula, tg represents the glass transition temperature (unit: K) of the copolymer, wi represents the weight fraction (copolymerization ratio based on weight) of the monomer i in the copolymer, and Tgi represents the glass transition temperature (unit: K) of the homopolymer of the monomer i.

As the glass transition temperature of the homopolymer used for calculation of Tg, the values described in the publicly known materials such as "Polymer handbook" (3 rd edition, john Wiley & Sons, inc., 1989) are used. For the monomers described in the above polymer handbook, the highest value was used. In the case where Tg of the homopolymer is not described in the known material, a value obtained by the measurement method described in JP-A2007-51271 is used.

(Process for producing acrylic Polymer)

In the technology disclosed herein, the method for obtaining an acrylic polymer composed of such monomer components is not particularly limited, and various polymerization methods known as a synthetic method of an acrylic polymer, such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, and a photopolymerization method, can be suitably employed. For example, a solution polymerization method can be preferably employed. The polymerization temperature in the solution polymerization can be appropriately selected depending on the kind of the monomer and solvent used, the kind of the polymerization initiator, and the like, and may be, for example, about 20 to about 170 ℃ (typically about 40 to about 140 ℃).

The solvent (polymerization solvent) used for the solution polymerization may be appropriately selected from conventionally known organic solvents. For example, an aromatic compound (typically an aromatic hydrocarbon) selected from toluene and the like; acetate esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1, 2-dichloroethane; lower alcohols such as isopropyl alcohol (for example, monohydric alcohols having 1 to 4 carbon atoms); ethers such as t-butyl methyl ether; ketones such as methyl ethyl ketone; and the like, or a mixed solvent of two or more thereof.

The initiator used for the polymerization may be appropriately selected from conventionally known polymerization initiators depending on the kind of the polymerization method. For example, one or two or more azo polymerization initiators such as 2,2' -Azobisisobutyronitrile (AIBN) may be preferably used. As other examples of the polymerization initiator, there may be mentioned: persulfates such as potassium persulfate; peroxide initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane initiators such as phenyl substituted ethane; an aromatic carbonyl compound; etc. As still another example of the polymerization initiator, a redox initiator based on a combination of a peroxide and a reducing agent can be cited. The polymerization initiator may be used singly or in combination of two or more. The amount of the polymerization initiator to be used may be a usual amount, and for example, may be selected from the range of about 0.005 to about 1 part by weight (typically about 0.01 to about 1 part by weight) relative to 100 parts by weight of the monomer component.

In the above polymerization, various conventionally known chain transfer agents may be used as needed. For example, thiols such as n-dodecyl mercaptan, t-dodecyl mercaptan, thioglycollic acid, and α -thioglycerol can be used. Alternatively, a chain transfer agent (non-sulfur-based chain transfer agent) having no sulfur atom may be used. Examples of the non-sulfur chain transfer agent include: anilines such as N, N-dimethylaniline and N, N-diethylaniline; terpenes such as alpha-pinene and terpinolene; styrenes such as α -methylstyrene and α -methylstyrene dimer; etc. The chain transfer agent may be used singly or in combination of two or more. In the case of using the chain transfer agent, the amount of the chain transfer agent to be used may be, for example, about 0.01 to about 1 part by weight based on 100 parts by weight of the monomer component.

The weight average molecular weight (Mw) of the acrylic polymer is not particularly limited, and is, for example, about 30X 10 ⁴ Above, about 50×10 ⁴ The above is suitable and may be about 70X 10 ⁴ Above, may be about 80×10 ⁴ The above. By using an acrylic polymer having a Mw of a predetermined value or more, a proper cohesive force that can exhibit desired adhesive properties can be easily obtained. In addition, additives such as plasticizers may be contained in a larger amount, and the desired elastic modulus tends to be easily achieved. In addition, the Mw of the acrylic polymer has an upper limit of, for example, about 500X 10 ⁴ From the viewpoint of adhesion properties, it is preferably about 400X 10 ⁴ The following (more preferably about 150X 10) ⁴ Hereinafter, for example, about 130×10 ⁴ The following) are included.

The Mw of the acrylic polymer can be determined by polystyrene conversion by Gel Permeation Chromatography (GPC). Specifically, the measurement was performed under the following conditions using the trade name "HLC-8220GPC" (manufactured by Tosoh corporation) as a GPC measurement apparatus.

[ measurement conditions of GPC ]

Sample concentration: 0.2 wt% (tetrahydrofuran solution)

Sample injection amount: 10 mu L

Eluent: tetrahydrofuran (THF)

Flow (flow rate): 0.6 mL/min

Column temperature (measurement temperature): 40 DEG C

Column:

sample column: trade name "TSKguardcolumn SuperHZ-H"1 root+trade name "TSKgel SuperHZM-H"2 root (manufactured by Tosoh Co., ltd.)

Reference column: trade name "TSKgel SuperH-RC"1 root (manufactured by Tosoh Co., ltd.)

A detector: differential Refractometer (RI)

Standard sample: polystyrene

(plasticizer)

The adhesive composition disclosed herein is characterized by containing a plasticizer in addition to the acrylic polymer. By using a plasticizer, the elastic modulus of the adhesive can be reduced. In addition, in the form of the adhesive sheet, flexibility and follow-up property against deformation can be improved. As the plasticizer disclosed herein, a cyclic unsaturated organic compound having two or more double bond rings can be used. In other words, the plasticizer is a compound having two or more double bond rings in one molecule. Thus, the plasticizer has at least a first double bond-containing ring and a second double bond-containing ring. By having two or more double bond-containing rings, the refractive index of the adhesive is not impaired or the low elastic modulus of the adhesive can be facilitated while maintaining the refractive index. The number of the double bond ring-containing groups included in the plasticizer is preferably 6 or less, and may be 4 or less, or 3 or less, from the viewpoint of exhibiting a plasticizing effect. The plasticizer may be used singly or in combination of two or more.

In addition, the plasticizers used in the techniques disclosed herein are compounds that are liquid at 30 ℃. In the present specification, "liquid" means that fluidity is exhibited, and a state of a substance means liquid. The compound comprises a compound with a melting point of 30 ℃ or lower. The plasticizer is in a liquid state at 30 ℃, so that the plasticizer can exhibit a plasticizing effect appropriately and can effectively realize a low elastic modulus of the adhesive. The plasticizer is preferably a compound which is liquid at 25 ℃, more preferably a compound which is liquid at 20 ℃. As the plasticizer, a compound having two or more double bond-containing rings and being liquid at 30 ℃ is used, whereby an adhesive having both a high refractive index and a low elastic modulus can be formed.

The double bond-containing ring of the plasticizer disclosed herein may be a conjugated double bond-containing ring (typically an aromatic ring), or may be any of non-conjugated double bond-containing rings. The plasticizer may have at least one ring selected from aromatic rings and heterocyclic rings (hetero element rings) as a double bond-containing ring. The heterocycle may have a structure contained in an aromatic ring, or may have a double bond-containing heterocycle structure different from the aromatic ring. The plasticizer may have a double bond-containing ring (typically an aromatic ring) and may be a carbocyclic ring such as a benzene ring (optionally The benzene ring is a part of biphenyl structure and fluorene structure. ) The method comprises the steps of carrying out a first treatment on the surface of the Condensed rings of naphthalene ring, indene ring, azulene ring, anthracene ring, phenanthrene ring, etc., and may be heterocyclic rings such as pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, pyrrole ring, pyrazole ring, imidazole ring, triazole ring,Azole ring, iso->An azole ring, a thiazole ring, a thiophene ring, and the like. The hetero atom contained as the ring constituting atom in the above-mentioned hetero ring may be, for example, one or two or more selected from the group consisting of nitrogen, sulfur and oxygen. In some embodiments, the heteroatoms comprising the heterocyclic ring may be one or both of nitrogen and sulfur. The plasticizer may have a structure obtained by condensing one or more carbocycles such as a dinaphthiophene structure with one or more heterocyclic rings.

The above-mentioned double bond-containing ring (typically aromatic ring, preferably carbocycle) may have one or more substituents on the ring constituting atoms, or may have no substituents. In the case of having a substituent, examples of the substituent include: alkyl, alkoxy, aryloxy, hydroxy, halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), hydroxyalkyl, hydroxyalkyloxy, glycidoxy, etc., but are not limited to these substituents. In the substituent containing a carbon atom, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be 1 or 2, for example. In some embodiments, the above-mentioned double bond-containing ring may be an aromatic ring having no substituent on the ring constituting atom or having one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, an ethylenically unsaturated group (e.g., a (meth) acryloyloxy group, a hydroxyl group and a hydroxyalkyl group.

In some embodiments, it may be preferable to use compounds without ethylenically unsaturated groups as plasticizers. This can suppress deterioration of the adhesive composition due to heat and light (deterioration of leveling property due to progress of gelation and increase of viscosity), and can improve storage stability. In order to suppress the change in elastic modulus, dimensional change or deformation (warpage, undulation, etc.), the occurrence of optical distortion, etc. caused by the reaction of the ethylenically unsaturated groups in the adhesive sheet having the adhesive layer containing the plasticizer, it is preferable to use a plasticizer having no ethylenically unsaturated groups.

As the plasticizer, a high refractive index plasticizer having a refractive index of about 1.50 or more can be preferably used. By using a high refractive index plasticizer, both a high refractive index and a low elastic modulus can be achieved at a higher level. The refractive index of the plasticizer is preferably about 1.51 or more, more preferably about 1.53 or more, still more preferably about 1.55 or more, and may be about 1.56 or more, may be about 1.58 or more, may be about 1.60 or more, or may be about 1.62 or more, from the viewpoint of maintaining and increasing the refractive index of the adhesive while performing low elastic modulus. In some embodiments, the plasticizer preferably has a refractive index of 2.50 or less, more preferably 2.00 or less, and still more preferably 1.90 or less, still more preferably 1.80 or less, still more preferably 1.70 or less, from the viewpoints of ease of preparation of the adhesive composition, compatibility in the adhesive, and the like.

The refractive index of the plasticizer was measured using an Abbe refractometer under conditions of a measurement wavelength of 589nm and a measurement temperature of 25℃in the same manner as the refractive index of the monomer. This nominal value may be employed in the case where the nominal value of the refractive index at 25 ℃ is provided by the manufacturer or the like.

The molecular weight of the plasticizer is not particularly limited, but a plasticizer having a molecular weight smaller than that of the above acrylic polymer is generally used. The molecular weight of the plasticizer is suitably 30000 or less, advantageously 25000 or less, and may be less than 10000 (e.g., less than 5000) or less than 3000, from the viewpoint of easily exhibiting plasticizing effect. In some embodiments, the molecular weight of the plasticizer is preferably 2000 or less, more preferably 1200 or less, and even more preferably 900 or less, and may be 600 or less, 500 or less, 400 or less, 300 or less, or 250 or less (e.g., 220 or less). The molecular weight of the plasticizer is not excessively large, which is advantageous from the viewpoint of improving the compatibility in the adhesive layer and the like. In addition, the molecular weight of the plasticizer is preferably 100 or more, more preferably 130 or more, still more preferably 150 or more, and may be 170 or more, 200 or more, 220 or more, or 250 or more, from the viewpoint of easily exerting a sufficient plasticizing effect. The molecular weight of the plasticizer is preferably not low from the viewpoints of heat resistance of the pressure-sensitive adhesive sheet and suppression of contamination of the adherend. In some embodiments, the molecular weight of the plasticizer is, for example, 300 or more, preferably 315 or more, and may be 350 or more. Since the plasticizer having a large molecular weight is not easily gasified, it is easy to obtain an adhesive that can exhibit stable characteristics by using the plasticizer having a large molecular weight in the adhesive. In addition, plasticizers with large molecular weights do not migrate easily within the adhesive. Therefore, for example, migration of the plasticizer to the adhesive surface and the like are less likely to occur, thereby affecting the adhesive property. The molecular weight of the plasticizer is more preferably 400 or more, still more preferably 450 or more, particularly preferably 500 or more, and may be 530 or more.

As the molecular weight of the plasticizer, a molecular weight calculated based on a chemical structure is used. In the case where the nominal value of the molecular weight is provided by the manufacturer or the like, the nominal value may be employed.

In some embodiments, as the plasticizer, one or more selected from a compound having a structure in which two or more non-condensed double bond-containing rings (typically aromatic rings) are bonded via a linking group, a compound having a structure in which two or more non-condensed double bond-containing rings (typically aromatic rings) are directly (i.e., not via other atoms) chemically bonded, a compound having a condensed double bond-containing ring (typically aromatic rings) structure, a compound having a fluorene structure, a compound having a dinaphthiophene structure, a compound having a dibenzothiophene structure, and the like and a compound that is in a liquid state at 30 ℃ (e.g., 25 ℃ or 20 ℃) may be used.

In the case of using a compound having a structure in which two or more non-condensed double bond-containing rings are bonded via a linking group as an augmentationIn the manner of the plasticizer, the linking group may be, for example, an oxy group (-O-): thiooxy (-S-), oxyalkylene (e.g., -O- (CH) ₂ ) _n -a radical, where n is 1 to 3, preferably 1), a thiooxyalkylene radical (for example-S- (CH) ₂ ) _n -a radical, where n is 1 to 3, preferably 1), a linear alkylene radical (i.e. - (CH) ₂ ) _n -a group, where n is 1 to 6, preferably 1 to 3), a group obtained by partially or completely halogenating the alkylene group in the above-mentioned oxyalkylene group, the above-mentioned thiooxyalkylene group and the above-mentioned linear alkylene group, and the like. The linking group may have a siloxane bond (-SiOR-) or an ester bond. In the plasticizer, the linking group linking the first double bond-containing ring (non-condensed ring) and the second double bond-containing ring (non-condensed ring) may be selected from the same groups as the linking groups described above. Preferred examples of the linking group include an oxy group, a thiooxy group, an oxyalkylene group and a linear alkylene group from the viewpoint of low modulus of elasticity of the adhesive. The number of atoms of the linking group is not particularly limited, and may be, for example, 1 to 30, 1 to 25, 1 to 20, 1 to 18, preferably 1 to 12, more preferably 1 to 10, still more preferably 1 to 8, particularly preferably 1 to 5, 1 to 3, or 1 or 2. The number of atoms of the linking group means the minimum number of atoms required to reach from one non-condensed double bond-containing ring to another non-condensed double bond-containing ring. For example, when the linking group is formed from a linear alkylene group (i.e., - (CH) ₂ ) _n -groups) the number of n is the number of atoms of the linking group. In addition, for example, when the linking group is an oxyethylene group (i.e., - (C) ₂ H ₄ O) _n -group), the product of the sum of the number of carbon atoms 2 and the number of oxygen atoms 1, 3 and n (3 n) constituting the oxyethylene group is the number of atoms of the linking group. Preferable examples of the above-mentioned compound include a compound having a phenoxybenzyl group. Examples of the above-mentioned compounds include: phenoxybenzyl (meth) acrylates (e.g., m-phenoxybenzyl (meth) acrylate, phenoxybenzyl alcohol, oxybis [ (alkoxyalkyl) benzene)](e.g., 4' -oxybis [ (methoxymethyl) benzene)]) Etc. Other examples of the above-mentioned compounds include polysiloxane plasticizers (specificallyIs a siloxane compound).

The compound having a structure in which two or more double bond-containing rings (non-condensed rings) are directly chemically bonded may be, for example, a compound having a biphenyl structure, a compound having a triphenyl structure, or the like. Examples of the compound having a condensed double bond-containing ring structure include: naphthalene ring-containing compounds, anthracene ring-containing compounds, and the like. Specific examples thereof include 1-naphthacenedione and the like. The above-mentioned compound having a fluorene structure includes a structural moiety obtained by directly chemically bonding two benzene rings, and therefore is included in the concept of the above-mentioned compound having a structure obtained by directly chemically bonding two or more double bond-containing rings (non-condensed rings). The compound having a dinaphthiophene structure includes a naphthalene structure, and a structure obtained by condensing a thiophene ring with two naphthalene structures is also included in the concept of the compound having a condensed double bond ring structure. The above-mentioned compound having a dibenzothiophene structure has a structure in which a thiophene ring is condensed with two benzene rings, and is therefore included in the concept of the above-mentioned compound having a condensed double bond ring structure.

In some embodiments, as the plasticizer, a polysiloxane-based plasticizer may be used. By using a polysiloxane plasticizer, a stable plasticizing effect is easily obtained, and a high adhesive strength is easily obtained, so that the refractive index, flexibility, and adhesive strength of the adhesive can be improved in a balanced manner. As the polysiloxane plasticizer, a compound having two or more double bond-containing rings and being liquid at 30 ℃ can be used without particular limitation. The polysiloxane plasticizer is specifically a siloxane compound having 1 or more (typically 2 or more) Si atoms, and the upper limit thereof is not particularly limited and may be, for example, about 10 or less. In one molecule of the polysiloxane plasticizer, the Si atom and the double bond ring may or may not be directly bonded. Preferably, at least one of the above Si atoms is directly bonded to at least one ring containing a double bond. The polysiloxane plasticizer may be used singly or in combination of two or more.

In some embodiments, as the polysiloxane plasticizer, a polysiloxane plasticizer containing a siloxane compound having 2 to 5 Si atoms and having two or more double bond rings bonded to at least one of the Si atoms may be used. A polysiloxane plasticizer containing a siloxane compound having such a structure can exert a plasticizing effect based on the flexibility of the siloxane structure, and by having at least one Si atom having 2 or more and 5 or less Si atoms and having two or more double bond rings bonded thereto, ease of matching with or compatibility with a material to be plasticized and stability of the plasticizing effect (for example, a low increase rate of elastic modulus for storage under humid heat) can be achieved in a balanced manner. From the viewpoint of chemical stability, the above-mentioned siloxane compound preferably does not have a hydrogen atom bonded to a Si atom. That is, a silicone compound having no Si-H bond is preferable.

In the case where the number of Si atoms of the siloxane compound is 3 or more, the siloxane compound may be chain-shaped or cyclic, and is preferably a chain-shaped siloxane compound from the viewpoint of suppressing volatilization. The linear siloxane compound having 3 or more Si atoms may be linear or branched, and is preferably linear from the viewpoint of obtaining a higher plasticizing effect. Hereinafter, unless otherwise specified, a silicone compound having 3 or more Si atoms refers to a chain (typically straight) silicone compound having 3 or more Si atoms.

Each double bond-containing ring of the polysiloxane plasticizer may be a ring containing a conjugated double bond (typically an aromatic ring) or a ring not containing a conjugated double bond. The plasticizer may have at least one ring selected from aromatic rings and heterocyclic rings (hetero element rings) as a double bond-containing ring. The heterocycle may have a structure contained in an aromatic ring, or may have a double bond-containing heterocycle structure different from the aromatic ring. The plasticizer may have a double bond-containing ring (typically an aromatic ring), and may be a carbocycle such as a benzene ring or a naphthalene ring, or may be a pyridine ring, an imidazole ring, a triazole ring, Heterocyclic rings such as an azole ring, a thiazole ring, and a thiophene ring. The hetero atom contained as the ring constituent atom in the above-mentioned heterocyclic ring may be, for example, one or two or more selected from the group consisting of nitrogen, sulfur and oxygen. In some embodiments, the heteroatoms comprising the heterocyclic ring may be one or both of nitrogen and sulfur.

The above-mentioned double bond-containing ring (typically aromatic ring, preferably carbocycle) may have one or more substituents on the ring constituting atoms, or may have no substituents. In the case of having a substituent, examples of the substituent include: alkyl, alkoxy, hydroxyl, halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), hydroxyalkyl, hydroxyalkyloxy, glycidoxy, etc., but are not limited thereto. In the substituent containing a carbon atom, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be 1 or 2, for example. In some embodiments, each double bond-containing ring included in the polysiloxane plasticizer is independently selected from the group consisting of an aromatic ring having no substituent on a ring constituent atom and an aromatic ring having one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, a hydroxyl group, and a hydroxyalkyl group (preferably, the group consisting of an alkyl group and an alkoxy group). For example, each double bond-containing ring of the polysiloxane plasticizer is independently selected from aromatic rings (preferably carbocycles) having no substituent on the ring constituting atoms. In some preferred embodiments, each double bond-containing ring that the polysiloxane plasticizer has is a benzene ring.

The number of Si atoms of the silicone compound is preferably 3 or more from the viewpoints of easy volatility of plasticizing effect and stability thereof (for example, suppression of an increase in elastic modulus due to volatilization and dissipation of the plasticizer from a plasticizer-blended material). In addition, the number of Si atoms of the silicone compound is preferably 4 or less, more preferably 3 or less, from the viewpoint of compatibility in the adhesive agent, and the like. Among them, a polysiloxane plasticizer having 3 Si atoms of the above siloxane compound, that is, a polysiloxane plasticizer containing a trisiloxane compound is preferable.

The number of the double bond rings (for example, having a substituent or not having a benzene ring) included in the silicone compound is at least 2, and is preferably 3 or more, more preferably 4 or more, and may be 5 or more from the viewpoint of heat resistance (for example, a low increase rate of elastic modulus for storage under moist heat) of plasticizing effect. When the number of Si atoms in the siloxane compound is n, the number of double bond-containing rings in the siloxane compound is typically 2n+2 or less, and 2n+1 or less is preferable, and 2n or less, 2n-1 or less, or 2n-2 or less is preferable from the viewpoint of improving the plasticizing effect. For example, in the case where the silicone compound is a trisiloxane compound, the number of double bond-containing rings included in the trisiloxane compound is typically 8 or less, and may be, for example, 2 or more and 7 or less, 3 or more and 7 or less, or 4 or more and 7 or less. Among them, trisiloxane compounds having a double bond ring (for example, unsubstituted benzene ring) number of 4 or more and 6 or less (for example, 4 or 5) are preferable.

In some embodiments, at least one of Si atoms (typically Si atoms constituting a siloxane chain) contained in the siloxane compound is a Si atom having two or more double bond rings bonded thereto. In the above-mentioned silicone compound, the number of Si atoms having two or more double bond rings bonded thereto may be two or more from the viewpoint of improving the stability of the plasticizing effect. In the siloxane compound having 3 or more Si atoms, the number of Si atoms having two or more double bond rings bonded thereto may be 2 or more and 3 or more, and when n is the number of Si atoms of the siloxane compound, n may be n or less, n-1 or less, or n-2 or less. In some embodiments, from the viewpoint of improving the plasticizing effect, the number of double bond-containing rings bonded to at least one of Si atoms contained in the above-mentioned silicone compound (preferably a silicone compound having 3 or more Si atoms) is 1 or 0. For example, a linear siloxane compound having 3 or more and 5 or less Si atoms is preferable, and Si atoms at both ends each independently have two or three (preferably two) double bond-containing rings, and Si atoms other than both ends each independently have one double bond-containing ring or no double bond-containing ring structure.

The siloxane compound may contain a Si atom to which a group other than the double bond-containing ring is bonded. Examples of the groups other than the double bond-containing ring include: alkyl, aralkyl, alkoxy, halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), fluoroalkyl, hydroxyl, hydroxyalkyl, hydroxyalkyloxy, epoxy, glycidoxy, amino, monoalkylamino, dialkylamino, carboxyl, carboxyalkyl, mercapto, etc., are not limited to these groups. In the substituent containing a carbon atom, the number of carbon atoms contained in the substituent is, for example, 1 to 8, preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. The groups other than the double bond-containing ring bonded to the respective Si atoms contained in the siloxane compound may each be independently selected from the group consisting of the above-exemplified groups.

In some embodiments, the above siloxane compounds preferably do not have ethylenically unsaturated groups (including groups where the double bond in the double bond-containing ring is an olefinic double bond). A silicone plasticizer containing a silicone compound having no ethylenically unsaturated group is advantageous from the viewpoint of stability of plasticizing effect by the plasticizer, and is also preferable from the viewpoint of storage stability of an adhesive sheet having an adhesive layer containing the above-described silicone plasticizer, and from the viewpoint of suppressing changes in elastic modulus, dimensional changes or deformations (warpage, undulation, etc.), generation of optical distortion, etc. caused by reaction of ethylenically unsaturated groups.

In some embodiments of the polysiloxane plasticizer disclosed herein, from the viewpoint of improving the plasticizing effect, at least one of Si atoms (at least two in the siloxane compound having 3 or more Si atoms) contained in the siloxane compound preferably has at least one methyl group on the Si atom. For example, it is preferable that Si atoms at both ends of the siloxane chain each independently have one or two (more preferably one) methyl groups. In some preferred embodiments, each Si atom contained in the above-described siloxane compound independently has one or two methyl groups. According to the silicone plasticizer containing the siloxane compound having such a structure, the plasticizing effect due to the flexibility of the siloxane structure and the stability of the plasticizing effect due to the structure having two or more double bond rings bonded to at least one Si atom can be balanced.

In some embodiments, when the number of Si atoms contained in the siloxane compound is n, a value obtained by adding up the number of substituents bonded to the Si atoms (hereinafter, also referred to as a total number of substituents) is typically 2n+2, at least two of which are double bond-containing rings. In some embodiments, the proportion SR of the number of double bond-containing rings (preferably aromatic carbocycles, e.g., benzene rings) to the total number of substituents in the polysiloxane plasticizer is at least 16%, and may be 20% or more, or may be 25% or more. When the ratio SR is higher, the heat resistance of the polysiloxane plasticizer and the stability of the plasticizing effect by the polysiloxane plasticizer generally tend to be improved. In some embodiments, the ratio SR is favorably 33% or more, preferably 40% or more, more preferably 50% or more (e.g., 60% or more), and may be 65% or more, or may be 75% or more. The ratio SR may be 100%, and is preferably 85% or less, more preferably 80% or less, and may be 75% or less, 65% or less, or 60% or less (for example, 50% or less) from the viewpoint of ease of blending and compatibility.

In some embodiments, the molecular weight of the polysiloxane plasticizer (specifically, the silicone compound) is preferably 400 or more, more preferably 430 or more, more preferably 460 or more, and may be 490 or more, or 520 or more, from the viewpoint of stability of plasticizing effect. In addition, the molecular weight of the silicone compound is preferably 900 or less, more preferably 700 or less, still more preferably 650 or less, 600 or less, 560 or less, 540 or less, or 500 or less, from the viewpoint of plasticizing effect, ease of compounding, compatibility, and the like.

As the molecular weight of the siloxane compound, a molecular weight calculated based on a chemical structure or a measurement value obtained by using matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) can be used. In the case where the nominal value of the molecular weight is provided by the manufacturer or the like, the nominal value may be employed.

The refractive index of the polysiloxane plasticizer disclosed herein is not particularly limited, and may be, for example, in the range of about 1.30 to about 1.80. From the viewpoint of suppressing a decrease in refractive index of a material (for example, an adhesive) to which the plasticizer is blended and achieving a low modulus of elasticity, it is preferable that the refractive index of the polysiloxane plasticizer in some embodiments is 1.45 or more, preferably 1.50 or more, more preferably 1.52 or more (for example, 1.53 or more or 1.54 or more), and still more preferably 1.55 or more (for example, 1.56 or more or 1.57 or more). In addition, the refractive index of the polysiloxane plasticizer may be, for example, 1.70 or less, 1.65 or less, or 1.60 or less from the viewpoint of ease of compounding, compatibility, and the like.

In some embodiments, ethylene glycol compounds having two or more double bond rings in one molecule may be used as the plasticizer. The oxyethylene unit (i.e., - (C) ₂ H ₄ O) -units) are, for example, 1 to 10, can be 1 to 6 or 2 to 4. The ethylene glycol compound may have a structure in which two or more non-condensed double bond-containing rings are bonded via an oxyethylene unit (for example, 1 to 10, preferably 1 to 6, and typically 2 to 4 oxyethylene units) as a linking group. The compound may be a compound having one or more ester groups. Examples of the ethylene glycol compound include a compound having a structure in which two or more benzoic acids are linked to ethylene glycol, diethylene glycol, triethylene glycol or polyethylene glycol through an ester bond.

The technology disclosed herein can be carried out without using the above-mentioned glycol compound as a plasticizer or with limiting the amount of the glycol compound used. For example, the content of the ethylene glycol compound in the plasticizer contained in the adhesive composition may be set to less than 90% by weight. The content of the ethylene glycol compound in the plasticizer may be less than 50% by weight, may be less than 10% by weight, may be less than 3% by weight, may be less than 1% by weight, and the adhesive composition may be substantially free of the ethylene glycol compound as a plasticizer. Similarly, the amount of the ethylene glycol compound used in the adhesive composition may be set to less than 0.5 parts by weight or less than 0.1 parts by weight based on 100 parts by weight of the acrylic polymer.

In other embodiments, liquid rosin such as liquid rosin esters may be used as plasticizers. The liquid rosin (e.g., liquid rosin ester) may correspond to the compound having a condensed double bond ring structure.

The amount of plasticizer used is not particularly limited and may be set according to the purpose. The plasticizer may be used in an amount of, for example, 1 part by weight or more, or 10 parts by weight or more based on 100 parts by weight of the acrylic polymer from the viewpoint of reducing the elastic modulus of the adhesive. In some preferred embodiments, the plasticizer may be used in an amount of more than 15 parts by weight, or 20 parts by weight or more, or 30 parts by weight or more (for example, more than 30 parts by weight), more preferably 40 parts by weight or more, still more preferably 50 parts by weight or more, particularly preferably 60 parts by weight or more, or 75 parts by weight or more, or 90 parts by weight or more, based on 100 parts by weight of the acrylic polymer. For example, when the above-mentioned ethylene glycol compound is used as a plasticizer, it is preferable to use more than 30 parts by weight (for example, 40 parts by weight or more, further 50 parts by weight or more) per 100 parts by weight of the acrylic polymer. In addition, from the viewpoint of achieving both the high refractive index and the low elastic modulus of the adhesive in a balanced manner, the amount of the plasticizer to be used is preferably about 200 parts by weight or less, more preferably 150 parts by weight or less, still more preferably 120 parts by weight or less, and may be 100 parts by weight or less, 80 parts by weight or less, or 70 parts by weight or less, based on 100 parts by weight of the acrylic polymer. In some embodiments where the adhesive property is more important, the plasticizer may be used in an amount of 45 parts by weight or less or 35 parts by weight or less based on 100 parts by weight of the acrylic polymer.

(additive (H) _RO ))

Herein disclosedThe adhesive composition may contain an organic material having a refractive index larger than that of the acrylic polymer as an additive to be used as desired. Hereinafter, such an organic material may be described as "additive (H) _RO ) ". Here, the above-mentioned "H _RO "means an Organic material (Organic material) having a high refractive index (High Refractive index). By using the additive (H) in combination _RO ) An adhesive agent which can achieve more appropriate combination of refractive index and adhesive properties (peel strength, flexibility, etc.) with an acrylic polymer can be realized. As additive (H) _RO ) The organic material of (2) may be a polymer or a non-polymer. In addition, the polymerizable functional group may be present or absent. In the present specification, the additive (H _RO ) Defined as an additive different from the compound used as the plasticizer described above. Thus, the additive (H _RO ) In particular not in a liquid state (liquid) at 30 ℃ (e.g. 25 ℃ or 20 ℃). Additive (H) _RO ) One kind or two or more kinds may be used singly or in combination.

Additive (H) _RO ) The refractive index of (2) may be set to an appropriate range according to the relative relation with the refractive index of the acrylic polymer, and is therefore not limited to a specific range. Additive (H) _RO ) The refractive index of (c) may be selected from, for example, a range of refractive indices greater than 1.55, greater than 1.56, or greater than 1.57 and greater than that of the acrylic polymer. From the viewpoint of increasing the refractive index of the adhesive, in some embodiments, the additive (H _RO ) The refractive index of (2) is favorably 1.58 or more, preferably 1.60 or more, more preferably 1.63 or more, but may be 1.65 or more, 1.70 or more, or 1.75 or more. By means of additives of higher refractive index (H _RO ) Even when a smaller amount of additive (H _RO ) The target refractive index can also be achieved. This is preferable from the viewpoint of suppressing the decrease in the adhesive property and the optical property. Additive (H) _RO ) The upper limit of the refractive index of (2) is not particularly limited, but is, for example, 3.000 or less, 2.500 or less, or less from the viewpoints of compatibility in the adhesive, high refractive index, and easiness of flexibility suitable as an adhesiveThe content is 2.000 or less, may be 1.950 or less, may be 1.900 or less, or may be 1.850 or less.

The additive (H _RO ) The refractive index of (2) was measured using an Abbe refractometer under conditions of a measurement wavelength of 589nm and a measurement temperature of 25℃in the same manner as the refractive index of the monomer. This nominal value of the refractive index at 25 ℃ may be employed in the case where it is provided by the manufacturer or the like.

Additive (H) _RO ) Refractive index n of (2) _b Refractive index n with acrylic Polymer _a The difference, n _b -n _a (hereinafter also referred to as "Δn _A ". ) Set to be greater than 0. In some aspects, an _A For example, the ratio is 0.02 or more, may be 0.05 or more, may be 0.07 or more, may be 0.10 or more, may be 0.15 or more, may be 0.20 or more, or may be 0.25 or more. By passing delta n _A Greater choice of acrylic polymer and additive (H _RO ) Has a composition comprising a catalyst comprising an additive (H _RO ) The effect of increasing the refractive index tends to be high. In addition, from the additives (H) _RO ) From the standpoint of compatibility of (a), in some embodiments, an _A For example, the content may be 0.70 or less, 0.60 or less, 0.50 or less, or 0.40 or less or 0.35 or less.

In some embodiments, the additive (H _RO ) Refractive index n of (2) _b And an additive (H) containing the same _RO ) Refractive index n of the binder of (2) _T The difference, n _b -n _T (hereinafter, also referred to as "Δn _B ". ) May be set to be greater than 0. In some aspects, an _B For example, the ratio is 0.02 or more, may be 0.05 or more, may be 0.07 or more, may be 0.10 or more, may be 0.15 or more, may be 0.20 or more, or may be 0.25 or more. By passing delta n _B The composition of the binder and the additives (H _RO ) Has a composition comprising a catalyst comprising an additive (H _RO ) The effect of increasing the refractive index tends to be high. In addition, from the viewpoint of compatibility in the adhesive, transparency of the adhesive, and the like, in some embodiments, Δn _B For example, it may be 0.70 or less,may be 0.60 or less, may be 0.50 or less, may be 0.40 or less, or may be 0.35 or less.

As additive (H) _RO ) The molecular weight of the organic material used is not particularly limited and may be selected according to the purpose. From the standpoint of balancing the effect of the high refractive index with other characteristics (e.g., optical characteristics suitable for the adhesive such as softness and haze), in some embodiments, the additive (H _RO ) A molecular weight of less than about 10000 is suitable, preferably less than 5000, more preferably less than 3000 (e.g., less than 1000), may be less than 800, may be less than 600, may be less than 500, and may be less than 400. From the viewpoint of improving the compatibility in the adhesive, the additive (H _RO ) It is advantageous that the molecular weight of (2) is not excessive. In addition, additive (H) _RO ) The molecular weight of (2) may be 130 or more, or 150 or more, for example. In some embodiments, the additive (H _RO ) From the viewpoint of increasing the refractive index of (a) the additive (H _RO ) The molecular weight of (2) is preferably 170 or more, more preferably 200 or more, and may be 230 or more, 250 or more, 270 or more, 500 or more, 1000 or more, or 2000 or more. In some embodiments, polymers having a molecular weight of about 1000 to about 10000 (e.g., 1000 or more and less than 5000) may be used as additives (H _RO )。

As additive (H) _RO ) For polymers of non-polymers or low degree of polymerization (e.g., about dimer to about pentamer), the molecular weight calculated based on chemical structure or the measured value obtained by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) may be used. In the additive (H) _RO ) In the case of a polymer having a higher polymerization degree, a weight average molecular weight (Mw) based on GPC performed under appropriate conditions can be used. This nominal value of molecular weight may be employed in the case where it is provided by the manufacturer or the like.

Can be used as additive (H) _RO ) Examples of the organic material of the option (a) include an organic compound having an aromatic ring and a heterocyclic ring (which may be an aromatic ring or a non-aromatic heterocyclic ring). ) An organic compound of (C) or the like,but are not limited to these.

As additive (H) _RO ) The above-mentioned organic compound having an aromatic ring (hereinafter also referred to as "aromatic ring-containing compound") is used. ) The aromatic ring may be selected from the same aromatic rings as those of the compound used as the monomer (A1).

The aromatic ring may have one or more substituents on the ring constituting atoms, or may have no substituents. In the case of having a substituent, examples of the substituent include: alkyl, alkoxy, aryloxy, hydroxy, halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), hydroxyalkyl, hydroxyalkyloxy, glycidoxy, etc., but are not limited thereto. Among the substituents containing carbon atoms, the number of carbon atoms contained in the substituent is, for example, from 1 to 10, advantageously from 1 to 6, preferably from 1 to 4, more preferably from 1 to 3, and may be, for example, 1 or 2. In some embodiments, the aromatic ring may be an aromatic ring having no substituent on a ring constituting atom or an aromatic ring having one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen atom (e.g., a bromine atom).

As additive (H) _RO ) Examples of the aromatic ring-containing compound of (a) include: a compound useful as the monomer (A1); an oligomer comprising a compound usable as the monomer (A1) as a monomer unit; a compound having a structure in which a group having an ethylenically unsaturated group (which may be a substituent bonded to a ring constituting atom) or a portion constituting an ethylenically unsaturated group in the group is removed from the compound usable as the monomer (A1) and replaced with a hydrogen atom or a group having no ethylenically unsaturated group (for example, a hydroxyl group, an amino group, a halogen atom, an alkyl group, an alkoxy group, a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidoxy group or the like); examples of the plasticizer include, but are not limited to, compounds other than the plasticizers disclosed herein.

In some embodiments, as an additive (H _RO ) From the viewpoint of easily obtaining a high refractive index effect, it is preferable to use an organic compound having two or more aromatic rings in one moleculeHereinafter, the "compound having a plurality of aromatic rings" is also referred to as "compound having a plurality of aromatic rings". ). The compound having a plurality of aromatic rings may or may not have a polymerizable functional group such as an ethylenically unsaturated group. The compound having a plurality of aromatic rings may be a polymer or a non-polymer. The polymer may be an oligomer (preferably an oligomer having a molecular weight of about 5000 or less, more preferably about 1000 or less, for example, an oligomer of about dimer to about pentamer) containing a monomer having a plurality of aromatic rings as monomer units. The oligomer may be, for example: homopolymers of monomers containing multiple aromatic rings; copolymers of two or more monomers containing multiple aromatic rings; copolymers of one or more monomers containing multiple aromatic rings with other monomers; etc. The other monomer may be an aromatic ring-containing monomer other than a monomer containing a plurality of aromatic rings, a monomer having no aromatic ring, or a combination thereof.

As non-limiting examples of the compound containing a plurality of aromatic rings, there may be mentioned: a compound having a structure in which two or more non-condensed aromatic rings are bonded via a linking group, a compound having a structure in which two or more non-condensed aromatic rings are directly (i.e., not via another atom) chemically bonded, a compound having a condensed aromatic ring structure, a compound having a fluorene structure, a compound having a dinaphthiophene structure, a compound having a dibenzothiophene structure, or the like. The compound having a plurality of aromatic rings may be used singly or in combination of two or more.

As an additive (H) _RO ) An organic compound having a heterocycle (hereinafter also referred to as a heterocycle-containing organic compound) of the options (a). ) Examples of (a) include a thioepoxy compound and a compound having a triazine ring. Examples of the thioepoxy compound include bis (2, 3-cyclothiopropyl) disulfide and a polymer thereof (refractive index 1.74) described in japanese patent No. 3712653. Examples of the compound having a triazine ring include compounds having at least one triazine ring (for example, 3 to 40, preferably 5 to 20) in one molecule. The triazine ring has aromatic character and therefore has a triazine ring The term "compound having a plurality of triazine rings" includes the term "compound having an aromatic ring" as used herein, and the term "compound having a plurality of triazine rings" includes the term "compound having an aromatic ring.

In some embodiments, as an additive (H _RO ) Compounds without ethylenically unsaturated groups may be preferably employed. This can suppress deterioration of the adhesive composition due to heat and light (deterioration of leveling property due to progress of gelation and increase of viscosity), and improve storage stability. From the combination of the additive (H _RO ) In the pressure-sensitive adhesive sheet of the pressure-sensitive adhesive layer (a), it is preferable to use an additive (H) having no ethylenically unsaturated group from the viewpoints of suppressing dimensional change, deformation (warpage, waviness, etc.), generation of optical distortion, etc. caused by the reaction of the ethylenically unsaturated group _RO )。

In the case of using an oligomer as an additive (H _RO ) In the embodiment (a), the oligomer can be obtained by polymerizing the corresponding monomer component by a known method. In the case of producing the oligomer by radical polymerization, a polymerization initiator, a chain transfer agent, an emulsifier, and the like for radical polymerization may be appropriately added to the monomer component to perform polymerization. The polymerization initiator, chain transfer agent, emulsifier, etc. for radical polymerization are not particularly limited, and may be appropriately selected and used. The weight average molecular weight of the oligomer can be controlled by the amount of the polymerization initiator, the amount of the chain transfer agent, and the reaction conditions, and the amount thereof can be appropriately adjusted according to the kind of the initiator and the chain transfer agent.

Examples of the chain transfer agent include: lauryl mercaptan, glycidyl mercaptan, thioglycollic acid, 2-mercaptoethanol, alpha-thioglycerol, thioglycollic acid, 2-ethylhexyl thioglycolate, 2, 3-dimercapto-1-propanol, and the like. The chain transfer agent may be used alone or in combination of two or more. The amount of the chain transfer agent to be used may be set so as to obtain an oligomer having a desired weight average molecular weight, depending on the composition of the monomer component used for the synthesis of the oligomer, the kind of the chain transfer agent, and the like. In some embodiments, the chain transfer agent is suitably used in an amount of about 15 parts by weight or less, may be 10 parts by weight or less, or may be about 5 parts by weight or less, relative to 100 parts by weight of the total amount of monomers used in the synthesis of the oligomer. The lower limit of the amount of the chain transfer agent to be used is not particularly limited, and may be, for example, 0.01 parts by weight or more, 0.1 parts by weight or more, 0.5 parts by weight or more, or 1 part by weight or more, based on 100 parts by weight of the total amount of the monomers used for the synthesis of the oligomer.

Additive (H) _RO ) The amount of the compound (in the case of using a plurality of compounds, the total amount thereof) used is not particularly limited as long as it is more than 0 parts by weight relative to 100 parts by weight of the acrylic polymer, and may be set according to the purpose. In some embodiments, the additive (H _RO ) The amount of the acrylic polymer to be used may be, for example, 80 parts by weight or less, and 60 parts by weight or less is advantageous from the viewpoint of achieving a balanced combination of an increase in refractive index of the adhesive and suppression of a decrease in adhesive properties and optical properties, and preferably 45 parts by weight or less. In some modes where more importance is attached to the adhesive property and the optical property, the additive (H _RO ) The amount of the acrylic polymer may be, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less based on 100 parts by weight of the acrylic polymer. In addition, from the viewpoint of increasing the refractive index of the adhesive, the additive (H _RO ) The amount of the acrylic polymer used may be, for example, 1 part by weight or more, advantageously 3 parts by weight or more, preferably 5 parts by weight or more, 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or 20 parts by weight or more, based on 100 parts by weight of the acrylic polymer.

(crosslinking agent)

The adhesive composition disclosed herein may contain a crosslinking agent as needed for the purpose of adjusting the cohesive force of the adhesive. As a cross-linking agent, can use isocyanate cross-linking agent, epoxy cross-linking agent, aziridine cross-linking agent, Oxazoline cross-linking agent, melamine resin and metal chelate compound cross-linking agentCross-linking agents and the like are well known in the art of adhesives. Among them, isocyanate-based crosslinking agents and epoxy-based crosslinking agents can be preferably used. As other examples of the crosslinking agent, there may be mentioned a monomer having two or more ethylenically unsaturated groups in one molecule, namely, a polyfunctional monomer. The crosslinking agent may be used singly or in combination of two or more.

As the isocyanate-based crosslinking agent, isocyanate compounds having 2 or more functions can be used, and examples thereof include: aliphatic polyisocyanates such as trimethylene diisocyanate, butylene diisocyanate, pentamethylene Diisocyanate (PDI), hexamethylene Diisocyanate (HDI), and dimer acid diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), and 1, 3-bis (isocyanatomethyl) cyclohexane; aromatic isocyanates such as 2, 4-toluene diisocyanate, 4' -diphenylmethane diisocyanate, and Xylylene Diisocyanate (XDI); by means of allophanate bonds, biuret bonds, isocyanurate bonds, uretdione bonds, urea bonds, carbodiimide bonds, ketoimine bonds, and, A polyisocyanate modified product (for example, an isocyanurate form of HDI, an allophanate form of HDI, etc.) obtained by modifying the isocyanate compound with a diazinetrione bond or the like; etc. Examples of commercial products include: trade names Takenate 300S, takenate, takenate 600, takenate D165N, takenate D178NL (manufactured by Sanchiku chemical Co., ltd.), sumidur T80, sumidur L, desmodur N3400 (manufactured by Kagaku Bayer polyurethane Co., ltd.), milliconate MR, milliconate MT, coronate L, coronate HL, coronate HX, coronate 2770 (manufactured by Tosoh Co., ltd.), trade name Duranate A201H (manufactured by Asahi chemical Co., ltd.), and the like. The isocyanate compound may be used singly or in combination of two or more. It is also possible to use a combination of a difunctional isocyanate compound and a trifunctional or higher isocyanate compound.

Examples of the epoxy-based crosslinking agent include: bisphenol A, epichlorohydrin type epoxy resins, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerol triglycidyl ether, 1, 6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diamine glycidyl amine, N, N, N ', N ' -tetraglycidyl m-xylylenediamine, 1, 3-bis (N, N ' -diglycidyl aminomethyl) cyclohexane, and the like. These may be used singly or in combination of two or more.

Examples of the polyfunctional monomer include: ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ethylene glycol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, 1, 12-dodecanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, allyl (meth) acrylate, vinyl (meth) acrylate, divinylbenzene, bisphenol a di (meth) acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, butanediol (meth) acrylate, hexanediol di (meth) acrylate, and the like. The polyfunctional monomer may be used singly or in combination of two or more.

In some embodiments, at least a portion of the crosslinker may use a difunctional crosslinker having two crosslinking reactive groups (e.g., isocyanate groups) per molecule. By using a bifunctional crosslinking agent, a soft crosslinked structure is easily formed. The bifunctional crosslinking agent may be used singly or in combination of two or more. In addition, a bifunctional crosslinking agent may be used in combination with a trifunctional or higher crosslinking agent.

In some embodiments, as the crosslinking agent, an acyclic crosslinking agent (also referred to as a chain crosslinking agent) having no ring structure such as an aromatic ring or an aliphatic ring can be preferably used. For example, among the isocyanate-based crosslinking agents, isocyanate-based compounds having no ring structure such as an aromatic ring and an isocyanurate ring are preferably used. By using an acyclic isocyanate compound as a crosslinking agent, a crosslinking agent having high flexibility can be easily formed. Specific examples of the acyclic isocyanate include: aliphatic isocyanate compounds (for example, PDI and HDI), and modified products of aliphatic isocyanate compounds (for example, modified products of polyisocyanates obtained by modifying PDI and HDI with allophanate bonds, biuret bonds, urea bonds, and carbodiimide bonds). The acyclic crosslinking agent may be used singly or in combination of two or more. In some preferred embodiments, a non-cyclic difunctional crosslinker may be used as the crosslinker.

In some embodiments, as the crosslinking agent, a crosslinking agent having a relatively long distance between one crosslinking reactive group (for example, an isocyanate group) and another crosslinking reactive group in one molecule may be used. Thereby forming a flexible crosslinked structure having a predetermined length or more. For example, in one molecule of the crosslinking agent, a compound having 10 or more (for example, 12 or more or 14 or more) atoms constituting a connecting chain connecting one crosslinking reactive group with other crosslinking reactive groups may be used as the crosslinking agent. The upper limit of the number of the connecting chain constituent atoms is not particularly limited, and may be 2000 or less, 1000 or less, 500 or less, 100 or less, 50 or less, 30 or less, or 20 or less, for example, since the upper limit may be prepared by polymerization or the like depending on the purpose. The number of connecting chain constituting atoms connecting the crosslinking reactive groups means the minimum number of atoms required for one molecule of the crosslinking agent to reach another crosslinking reactive group (in the case of three or more crosslinking reactive groups, the crosslinking reactive group closest to the one crosslinking reactive group). The above-mentioned crosslinking agents having a connecting chain may be used singly or in combination of two or more. In some preferred embodiments, a non-cyclic difunctional crosslinker may be used as the crosslinker. Examples of the commercial products of the crosslinking agent include: trade name Coronate 2770 (manufactured by Tosoh corporation), trade name Takenate D178NL (manufactured by Sanjing chemical corporation), trade name Duranate A201H (manufactured by Asahi Kabushiki Kaisha Co., ltd.), and the like.

The amount of the crosslinking agent (which may be a polyfunctional monomer) used is not particularly limited, and may be, for example, in the range of about 0.001 parts by weight to about 5.0 parts by weight relative to 100 parts by weight of the above monomer components. In some embodiments, the amount of the crosslinking agent used is preferably 3.0 parts by weight or less, more preferably 2.0 parts by weight or less, and may be 1.0 parts by weight or less, 0.5 parts by weight or less, or 0.2 parts by weight or less, based on 100 parts by weight of the monomer component, from the viewpoint of improving the adhesion to the adherend. In some embodiments, the amount of the crosslinking agent used may be, for example, 0.005 parts by weight or more, 0.01 parts by weight or more, 0.05 parts by weight or more, 0.08 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, or 0.4 parts by weight or more, based on 100 parts by weight of the monomer component, from the viewpoint of appropriately exhibiting the effect of the crosslinking agent used.

In order to more effectively perform the crosslinking reaction, a crosslinking catalyst may be used. Examples of the crosslinking catalyst include: metal crosslinking catalysts such as tetra-n-butyl titanate, tetra-isopropyl titanate, zirconium tetra-acetylacetonate, iron acetylacetonate, butyltin oxide, and dioctyltin dilaurate. Among them, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferable. The amount of the crosslinking catalyst used is not particularly limited. In view of the balance between the rate of the crosslinking reaction and the length of the lifetime of the adhesive composition, the amount of the crosslinking catalyst used may be, for example, in the range of about 0.0001 parts by weight or more and 1 part by weight or less, preferably in the range of 0.001 parts by weight or more and 0.5 parts by weight or less, relative to 100 parts by weight of the monomer component.

Compounds that can undergo keto-enol tautomerism can be included in the adhesive composition as crosslinking retarders. This can achieve the effect of extending the lifetime of the adhesive composition. For example, in an adhesive composition containing an isocyanate-based crosslinking agent, a compound that can undergo keto-enol tautomerism can be preferably used. As the compound in which keto-enol tautomerism can occur, various β -dicarbonyl compounds can be used. For example, β -diketones (acetylacetone, 2, 4-hexanedione, etc.), acetoacetates (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably used. The compounds which can undergo keto-enol tautomerism may be used singly or in combination of two or more. The amount of the compound capable of undergoing keto-enol tautomerism may be, for example, 0.1 to 20 parts by weight, 0.5 to 10 parts by weight, or 1 to 5 parts by weight based on 100 parts by weight of the monomer component.

(tackifier)

Tackifiers may be included in the adhesive compositions disclosed herein. As the tackifier, known tackifying resins such as rosin-based tackifying resins, terpene-based tackifying resins, phenol-based tackifying resins, hydrocarbon-based tackifying resins, ketone-based tackifying resins, polyamide-based tackifying resins, epoxy-based tackifying resins, and elastomer-based tackifying resins can be used. These resins may be used singly or in combination of two or more. The amount of the tackifier resin used is not particularly limited, and may be set according to the purpose or use so as to exhibit an appropriate adhesive property. In some embodiments, the amount of the tackifier is preferably 30 parts by weight or less, more preferably 10 parts by weight or less, and still more preferably 5 parts by weight or less, based on 100 parts by weight of the monomer component, from the viewpoints of refractive index and transparency. The techniques disclosed herein may preferably be practiced without the use of tackifiers.

(leveling agent)

In some embodiments, a leveling agent may be contained in the adhesive composition as needed for the purpose of improving the appearance (for example, improving the uniformity of thickness) of the adhesive layer formed from the composition, improving the coatability of the adhesive composition, and the like. As non-limiting examples of leveling agents, mention may be made of: acrylic leveling agents, fluorine-containing leveling agents, silicone leveling agents, and the like. The leveling agent may be, for example, an appropriate one selected from commercially available leveling agents and used by a conventional method.

In some embodiments, as the leveling agent, a polymer (hereinafter also referred to as "polymer (B)") which is a polymer including a monomer having a polyorganosiloxane skeleton (hereinafter also referred to as "monomer S1") and a monomer raw material of an acrylic monomer (hereinafter also referred to as "monomer raw material B") may be preferably used. The polymer (B) may be a copolymer of the monomer S1 and an acrylic monomer. The polymer (B) may be used singly or in combination of two or more.

The monomer S1 is not particularly limited, and any monomer containing a polyorganosiloxane skeleton may be used. As the monomer S1, a monomer having a structure with a polymerizable reactive group at one end can be preferably used. Among them, the monomer S1 having a structure having a polymerizable reactive group at one end and having no functional group at the other end which reacts with the acrylic polymer by crosslinking can be preferably used. Examples of the commercial products include: single-terminal reactive silicone oils (e.g., type X-22-174ASX, X-22-2426, X-22-2475, KF-2012, etc.) manufactured by Xinyue chemical industries, inc. The monomers S1 may be used singly or in combination of two or more.

The functional group equivalent of the monomer S1 may be, for example, about 100 g/mol to about 30000 g/mol. In some preferred embodiments, the functional group equivalent is, for example, 500 g/mol or more, 800 g/mol or more, 1500 g/mol or more, or 2000 g/mol or more. The functional group equivalent may be 20000 g/mol or less, may be less than 10000 g/mol, may be 7000 g/mol or less, or may be 5500 g/mol or less, for example. When the functional group equivalent of the monomer S1 is within the above range, a good leveling effect is easily exhibited.

In the case of using two or more types of monomers having different functional group equivalents as the monomer S1, the sum of the products of the functional group equivalents of the respective monomers and the weight fractions of the monomers may be used as the functional group equivalent of the monomer S1.

Herein, "functional group equivalent" refers to the weight of the main skeleton (e.g., polydimethylsiloxane) to which each functional group is bonded. The labeling unit g/mol is converted to 1 mol of functional group. The functional equivalent of the monomer S1 can be determined, for example, on the basis of Nuclear Magnetic Resonance (NMR) ¹ H-NMR(Proton NMR) spectrum intensity. Based on ¹ The calculation of the functional group equivalent (g/mol) of the monomer S1 of the spectral intensity of H-NMR can be based on ¹ A general structure analysis method in H-NMR spectroscopy is carried out by referring to Japanese patent No. 5951153, if necessary. The functional group equivalent of the monomer S1 refers to a polymerizable functional group (for example, an ethylenically unsaturated group such as a (meth) acryl group, a vinyl group, an allyl group, or the like).

The content of the monomer S1 in the monomer raw material B may take an appropriate value within a range where the desired effect is exhibited by using the monomer S1, and is not limited to a specific range. In some embodiments, the content of the monomer S1 in the monomer raw material B may be, for example, 5 to 60 wt%, 10 to 50 wt%, or 15 to 40 wt%.

The monomer raw material B contains, in addition to the monomer S1, an acrylic monomer copolymerizable with the monomer S1. Thereby, the compatibility of the polymer (B) in the adhesive layer can be improved. Examples of the acrylic monomer that can be used as the monomer raw material B include alkyl acrylates. The term "alkyl" as used herein refers to a chain (including straight chain and branched) alkyl (group) and does not include an alicyclic hydrocarbon group as described below. In some embodiments, monomer feed B may comprise (meth) acrylic acid C _4-12 Alkyl esters (preferably C (meth) acrylic acid) _4-10 Alkyl esters, e.g. C (meth) acrylic acid _6-10 Alkyl esters). In other embodiments, monomer feed B may comprise methacrylic acid C _1-18 Alkyl esters (preferably methacrylic acid C _1-14 Alkyl esters, e.g. methacrylic acid C _1-10 Alkyl esters). The monomer raw material B may contain, for example, one or two or more selected from Methyl Methacrylate (MMA), n-Butyl Methacrylate (BMA), and 2-ethylhexyl methacrylate (2 EHMA) as acrylic monomers.

As other examples of the acrylic monomer, there may be mentioned (meth) acrylic esters having alicyclic hydrocarbon groups. For example, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, tetrahydrodicyclopentadiene (meth) acrylate, 1-adamantyl (meth) acrylate, and the like can be used. (meth) acrylic esters having alicyclic hydrocarbon groups may not be used.

The content of the alkyl (meth) acrylate and the alicyclic hydrocarbon group-containing (meth) acrylate in the monomer raw material B may be, for example, 10% by weight or more and 95% by weight or less, 20% by weight or more and 95% by weight or less, 30% by weight or more and 90% by weight or less, 40% by weight or more and 90% by weight or less, or 50% by weight or more and 85% by weight or less.

As other examples of the monomer that can be contained in the monomer raw material B together with the monomer S1, there are listed: examples of the monomers that can be used in the acrylic polymer include carboxyl group-containing monomers, anhydride group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, amide group-containing monomers, monomers having a nitrogen atom-containing ring, aminoalkyl (meth) acrylates, vinyl esters, vinyl ethers, olefins, (meth) acrylates having an aromatic hydrocarbon group, and (meth) acrylates having a halogen atom.

The Mw of the polymer (B) may be, for example, 5000 or more, preferably 10000 or more, or 15000 or more. The Mw of the polymer (B) may be 200000 or less, preferably 100000 or less, 50000 or less, or 30000 or less, for example. By setting the Mw of the polymer (B) to an appropriate range, appropriate compatibility and leveling property can be exhibited.

The polymer (B) can be produced by polymerizing the above-mentioned monomer by a known method such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, or a photopolymerization method.

In order to adjust the molecular weight of the polymer (B), a chain transfer agent may be used as needed. Examples of the chain transfer agent used include: mercapto compounds such as t-dodecyl mercaptan, mercaptoethanol, and α -thioglycerol; thioglycolates such as thioglycollic acid and methyl thioglycolate; alpha-methylstyrene dimer; etc. The amount of the chain transfer agent to be used is not particularly limited, and may be appropriately set so as to obtain the polymer (B) having a desired molecular weight. In some embodiments, the chain transfer agent may be used in an amount of, for example, 0.1 to 5 parts by weight, 0.2 to 3 parts by weight, or 0.5 to 2 parts by weight, based on 100 parts by weight of the monomer.

The amount of the polymer (B) used may be, for example, 0.001 parts by weight or more, or 0.01 parts by weight or more, or 0.03 parts by weight or more, based on 100 parts by weight of the acrylic polymer, from the viewpoint of obtaining a higher effect of use. The amount of the polymer (B) used may be, for example, 3 parts by weight or less, and is preferably 1 part by weight or less, or may be 0.5 part by weight or less, or may be 0.1 part by weight or less, from the viewpoint of reducing the influence on the refractive index. The techniques disclosed herein can be practiced in such a way that the adhesive composition is substantially free of polymer (B).

(high refractive index particles)

High refractive index particles may be included as optional ingredients in the adhesive compositions disclosed herein. The high refractive index particles herein mean particles that can increase the refractive index of the binder by being contained in the binder. Hereinafter, the high refractive index particles may be referred to as "particles P _HRI ". HRI refers to high refractive index (high refractive index).

As particles P _HRI For example, one or two or more kinds of particles composed of a material having a refractive index of 1.60 or more, preferably 1.70 or more (may be 1.80 or more, may be 1.90 or more, and may be 2.00 or more) may be used. Constituting particles P _HRI The upper limit of the refractive index of the material is not particularly limited, and may be 3.00 or less, 2.80 or less, 2.50 or less, 2.20 or less, or 2.00 or less, for example. Constituting particles P _HRI The refractive index of the material (a film thickness capable of measuring refractive index) was measured using a commercially available ellipsometer at a measurement wavelength of 589nm and a measurement temperature of 25 ℃. As an ellipsometer, for example, a product can be usedThe product name "EC-400" (manufactured by JA. Woolam corporation) or an equivalent thereof.

Particles P _HRI The type of (c) is not particularly limited, and one or two or more materials capable of increasing the refractive index of the binder may be selected from metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. As particles P _HRI Among inorganic oxides (e.g., metal oxides), inorganic oxides that can increase the refractive index of the adhesive sheet can be preferably used. As constituent particles P _HRI Preferable examples of the material of (a) may be listed as follows: titanium dioxide (titanium oxide, tiO) ₂ ) Zirconium dioxide (zirconium oxide, zrO ₂ ) Aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, niobium oxide (Nb) ₂ O ₅ Etc.) and the like, and specifically, a metal oxide. The particles containing these inorganic oxides (e.g., metal oxides) may be used singly or in combination of two or more. Among them, particles containing titanium dioxide and zirconium dioxide are preferable, and particles containing zirconium dioxide are particularly preferable. In addition, as the metal particles, for example, an iron-containing material, a zinc-containing material, a tungsten-containing material, a platinum-containing material may have a high refractive index. The organic particles include particles of a resin such as a styrene resin, a phenol resin, a polyester resin, and a polycarbonate resin, and have a relatively high refractive index. Examples of the organic-inorganic composite particles include a composite of the above-mentioned inorganic material and an organic material, and a material obtained by coating the inorganic particles with an organic material such as a resin. As particles P _HRI From the viewpoint of compatibility with the binder component, particles obtained by surface-treating the organic particles and the inorganic particles with a surface-treating agent can be used.

Particles P _HRI The average particle diameter of (2) is not particularly limited, and particles of an appropriate size that can achieve a desired increase in refractive index by being contained in the binder can be used. Particles P _HRI For example, the average particle diameter of (C) may be about 1nm or more, and about 5nm or more is suitable. From the viewpoint of improving refractive index, handleability, and the like, the particles P _HRI The average particle diameter of (C) is preferably about 10nm or more, and may be about 20nm or moreAnd may be about 30nm or more. The upper limit of the average particle diameter is, for example, about 300nm or less, preferably about 100nm or less, more preferably about 70nm or less, still more preferably about 50nm or less, and may be about 35nm or less (for example, about 25nm or less) from the viewpoint of maintaining the adhesive property or the like.

The particles P _HRI The average particle diameter of (a) means a volume average particle diameter, specifically, a particle P using a particle size distribution measuring apparatus based on a laser scattering/diffraction method _HRI Particle diameter (50% volume average particle diameter; hereinafter, sometimes abbreviated as D) at 50% cumulative value in particle size distribution measured by the dispersion liquid ₅₀ . ). As the measuring device, for example, the product name "Microtrac MT3000II" manufactured by Microtrac Bell corporation or an equivalent thereof may be used.

Particles P in adhesive layer _HRI The content of (2) is not particularly limited. The above particles P _HRI The content of (c) may be different depending on the refractive index of the target adhesive sheet. For example, for the above particle P _HRI The content of (2) may be appropriately set so as to achieve a refractive index equal to or higher than a predetermined value in consideration of the required adhesive property and the like. In some embodiments, in an adhesive formed from the adhesive composition, particles P in the adhesive composition _HRI The content of (c) may be, for example, about 75% by weight or less, and the particles P in the adhesive composition may be from the viewpoints of adhesive properties and transparency _HRI The content of (2) may be about 50 wt% or less, or about 30 wt% or less. Particles P _HRI The lower limit of the content of (c) is not particularly limited, and may be, for example, more than 0% by weight, 1% by weight or more, or 5% by weight or more. In other embodiments, in the adhesive formed from the adhesive composition, particles P in the adhesive composition _HRI For example, the content of (c) is less than 10 wt%, may be less than 1 wt%, or may be less than 0.1 wt%. The technology disclosed herein is capable of being substantially free of particles P with an adhesive composition _HRI Is carried out by way of example.

Particles P in binder _HRI Can be contained in rootDetermined according to the relative relationship with the amount of acrylic polymer contained in the adhesive. Particles P with respect to 100 parts by weight of the acrylic polymer _HRI The content of (c) may be, for example, about 100 parts by weight or less, and from the viewpoints of adhesion properties and transparency, about 60 parts by weight or less, or about 40 parts by weight or less. Particles P _HRI The lower limit of the content of (b) is not particularly limited, and may be, for example, more than 0 part by weight, 1 part by weight or more, or 5 parts by weight or more based on 100 parts by weight of the acrylic polymer. In some embodiments, particle P is present in an amount of 100 parts by weight relative to the acrylic polymer _HRI The content of (2) is, for example, less than 30 parts by weight, may be less than 10 parts by weight, may be less than 1 part by weight, or may be less than 0.1 part by weight.

(other additives)

The adhesive composition disclosed herein may contain, as necessary, known additives that can be used in the adhesive composition, such as softeners, colorants (dyes, pigments, etc.), fillers, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, and preservatives, within a range that does not significantly hinder the effects of the present invention. In addition to the plasticizer disclosed herein, one or more of known plasticizers (for example, phthalates, terephthalates, adipates, and glycol benzoate) and plasticizing materials such as liquid camphene phenol may be contained. The conventional additives can be used by a conventional method, and the features of the present invention are not particularly imparted thereto, so that detailed description thereof will be omitted.

< adhesive >

The adhesives disclosed herein may be formed, for example, using any of the adhesive compositions described above. The adhesive may be a cured product of an adhesive composition formed by curing a solvent-type, active energy ray-curable, water-dispersible, hot-melt-type or other adhesive composition by drying, crosslinking, polymerization, cooling or the like. The curing method (e.g., drying, crosslinking, polymerization, cooling, etc.) of the adhesive composition may be applied only in one kind, and two or more kinds may be applied simultaneously or in multiple steps. For solvent borne adhesive compositions, the composition may typically be dried (preferably further crosslinked) to form an adhesive. In the case of an active energy ray-curable adhesive composition, an adhesive can be typically formed by irradiation of active energy rays to cause polymerization and/or crosslinking. When the active energy ray-curable adhesive composition is required to be dried, the active energy ray may be irradiated after the drying.

(refractive index)

The refractive index of the adhesive formed from the adhesive composition disclosed herein is higher than that of conventional general acrylic adhesives. According to the technology disclosed herein, it is possible to provide an adhesive having a refractive index of, for example, 1.55 or more, an adhesive composition capable of forming the adhesive, and an adhesive sheet containing the adhesive. The refractive index of the adhesive is suitably 1.560 or more, preferably more than 1.570. In some embodiments, the refractive index of the adhesive may be 1.575 or more, 1.580 or more, or 1.585 or more. According to the adhesive having such a refractive index, light reflection at the interface with the adherend can be appropriately suppressed in the use mode of the adhesive attached to the material having a high refractive index. The preferable upper limit of the refractive index of the adhesive varies depending on the refractive index of the adherend or the like, and thus is not limited to a specific range, and may be, for example, 1.700 or less, 1.670 or less, 1.650 or less, 1.620 or less, or 1.600 or less.

The refractive index of the adhesive can be adjusted by, for example, the composition of the adhesive (e.g., the composition of the monomer components constituting the acrylic polymer). Specifically, the composition comprises an acrylic polymer having a high content of the monomer (A1) in the monomer component, and an additive (H _RO ) It is possible to prepare an adhesive exhibiting a refractive index of a prescribed or higher.

In the present specification, the refractive index of the adhesive means the refractive index of the surface (adhesive surface) of the adhesive. The refractive index of the adhesive can be measured using a commercially available refractive index measuring device (Abbe refractometer) under the conditions of a measurement wavelength of 589nm and a measurement temperature of 25 ℃. As the Abbe refractometer, for example, the model "DR-M4" manufactured by the company ATAGO or its equivalent can be used. As the measurement sample, an adhesive layer containing an adhesive to be evaluated can be used. Specifically, the refractive index of the adhesive can be measured by the method described in examples described later.

(storage modulus G')

According to the technology disclosed herein, low elastic modulus of the adhesive can be achieved while having a high refractive index. Although not limited to a specific range, the storage modulus G' (0 ℃) of the adhesive at 0℃may be, for example, less than 1.0X10 ⁸ Pa, may be less than 5.0X10 ⁷ Pa, may be less than 1.0X10 ⁷ Pa, may be less than 5.0X10 ⁶ Pa. The pressure-sensitive adhesive having the storage modulus G' (0 ℃) has moderate flexibility in a temperature range from around 0 ℃ to above, and can adhere well to an adherend, for example. The lower limit of the storage modulus G' (0 ℃) is not particularly limited, and is, for example, 1.0X10 ² Pa or more, may be 1.0X10 ³ Pa or more. When the storage modulus G' (0 ℃) is equal to or higher than a predetermined value, the adhesive is likely to have a moderate cohesive force in a range from normal temperature to high temperature, for example. In some preferred embodiments, the adhesive has a storage modulus G' (0 ℃) of 1.0X10 ⁶ Pa or less, more preferably 5.0X10 ⁵ Pa or less, may be 2.0X10 ⁵ Pa or less, may be 1.0X10 ⁵ Pa or less, may be 7.0X10 ⁴ Pa or less, may be 5.0X10 ⁴ Pa or less, or 3.0X10 s ⁴ Pa or below. The storage modulus G' (0 ℃) is preferably 1.0X10 ⁴ Pa or more, more preferably 2.0X10 ⁴ Pa or more, more preferably 4.0X10 ⁴ Pa or more, may be 6.0X10 ⁴ Pa or more, or 1.0X10 g ⁵ Pa or more. An adhesive having the storage modulus G' (0 ℃) in the above range can be an adhesive that combines a high refractive index and flexibility and has flexibility that can withstand repeated bending operations.

The storage modulus G' (80 ℃) at 80℃of the adhesive disclosed herein is not particularly limitedMade, e.g. less than 1.0X10 ⁵ Pa is suitable, preferably less than 5.0X10 ⁴ Pa, more preferably less than 3.0X10 ⁴ Pa, may be less than 1.0X10 ⁴ Pa, may be less than 5.0X10 ³ Pa or below. The adhesive, which limits the storage modulus G' (80 ℃) as described above, has good flexibility in a high temperature region. The lower limit of the storage modulus G' (80 ℃) is not particularly limited, and is, for example, 1.0X10 ² Pa or more, 5.0X10 ² Pa or more is suitable, preferably 1.0X10 ³ Pa or more, more preferably 3.0X10 ³ Pa or more, or 5.0X10 s ³ Pa or more. The pressure-sensitive adhesive having the storage modulus G' (80 ℃) has a moderate cohesive force in a high temperature region and tends to be excellent in heat resistance, and is preferable.

The storage modulus G' (-10 ℃) at-10℃of the binders disclosed herein is not particularly limited and may be, for example, less than 1.0X10% ⁹ Pa, may be less than 1.0X10 ⁸ Pa, less than 1.0X10 ⁷ Pa is suitably, preferably 5.0X10 ⁶ Pa or less, may be 1.0X10 ⁶ Pa or less, may be 5.0X10 ⁵ Pa or less, may be 1.0X10 ⁵ Pa or below. The adhesive having the storage modulus G' (-10 ℃) limited as described above can be an adhesive having more excellent flexibility. For example, the adhesive can be a flexible adhesive having excellent flexibility in a low temperature range and having flexibility capable of withstanding repeated bending operations in a wide temperature range including a low temperature range. The lower limit of the storage modulus G' (-10 ℃) is not particularly limited, and is, for example, 1.0X10 ² Pa or more, 1.0X10 ³ Pa or more is suitable, preferably 5.0X10 ³ Pa or more, more preferably 1.0X10 ⁴ Pa or more, may be 5.0X10 ⁴ Pa or more, may be 1.0X10 ⁵ Pa or more, or 5.0X10 s ⁵ Pa or more. The adhesive having the storage modulus G' (-10 ℃) can be an adhesive having flexibility and moderate cohesive force. In addition, the adhesive having the storage modulus G' (-10 ℃) tends to have a high refractive index and flexibility even in a low temperature region.

The storage modulus G' (-20 ℃) at-20℃of the binders disclosed herein is not particularly limited and may be, for example, less than 1.0X10% ¹⁰ Pa, may be less than 1.0X10 ⁹ Pa, 5.0X10 g ⁸ Pa or less is suitably 1.0X10 s ⁸ Pa or less, may be 5.0X10 ⁷ Pa or less, may be 1.0X10 ⁷ Pa or less, may be 5.0X10 ⁶ Pa or less, may be 1.0X10 ⁶ Pa or less, or 5.0X10 s ⁵ Pa or below. The adhesive having the storage modulus G' (-20 ℃) limited as described above can be an adhesive having particularly excellent flexibility. For example, the adhesive can be made to have excellent flexibility in a lower temperature range and flexibility capable of withstanding repeated bending operations in a wide temperature range including a low temperature range. The lower limit of the storage modulus G' (-20 ℃) is not particularly limited, and is, for example, 1.0X10 ² Pa or more, 1.0X10 ³ Pa or more is suitable, preferably 1.0X10 ⁴ Pa or more, more preferably 1.0X10 ⁵ Pa or more, may be 5.0X10 ⁵ Pa or more, or 1.0X10 g ⁶ Pa or more. The adhesive having the storage modulus G' (-20 ℃) can be an adhesive having flexibility and moderate cohesive force. In addition, the adhesive having the storage modulus G' (-20 ℃) tends to have a high refractive index and flexibility even in a low temperature region.

(storage modulus ratio)

In some embodiments, as the binder, a binder having a ratio (G '(0 ℃) to G' (80 ℃) of storage modulus G '(0 ℃) at 0 ℃ to storage modulus G' (80 ℃) at 80 ℃ in a range of 1 to 1000 may be used. According to the adhesive satisfying the above characteristics, since the change in elastic modulus is suppressed in a wide temperature range from 0 ℃ to a high temperature range, stable characteristics (flexibility and the like) are easily exhibited against temperature changes. The ratio (G '(0 ℃ C.)/G' (80 ℃ C.)) is preferably 300 or less, more preferably 100 or less, still more preferably 50 or less, and may be 25 or less, 10 or less, or 5 or less. The lower limit of the ratio (G '(0 ℃ C.)/G' (80 ℃ C.)) may be, for example, 2 or more, or 3 or more.

In some embodiments, as the binder, a binder having a ratio (G '(-10 ℃ C.)/G' (80 ℃ C.) of storage modulus G '(-10 ℃ C.)) at-10 ℃ C., relative to storage modulus G' (80 ℃ C.) at 80 ℃ C.) in the range of 1 to 1000 may be used. According to the adhesive satisfying the above characteristics, since the change in elastic modulus is suppressed in a wide temperature range from a low temperature region to a high temperature region, it is preferable that the adhesive easily exhibits stable characteristics (such as flexibility) against temperature change. The ratio (G '(-10 ℃ C.)/G' (80 ℃ C.) is preferably 300 or less, more preferably 150 or less, still more preferably 100 or less, and may be 50 or less, 30 or less, 20 or less, or 10 or less. The lower limit of the ratio (G '(-10 ℃ C.)/G' (80 ℃ C.) may be, for example, 2 or more, or 3 or more.

In some embodiments, as the binder, a binder having a ratio (G '(-20 ℃ C.)/G' (80 ℃ C.) of storage modulus G '(-20 ℃ C.)) at-20 ℃ C., relative to storage modulus G' (80 ℃ C.) at 80 ℃ C.) in the range of 1 to 1000 may be used. According to the adhesive satisfying the above characteristics, since the change in the elastic modulus is suppressed in a wide temperature range from a lower temperature range to a high temperature range, stable characteristics (flexibility and the like) can be easily exhibited against temperature changes. The ratio (G '(-20 ℃ C.)/G' (80 ℃ C.) may be 500 or less, 300 or less, 150 or less, 100 or less, 50 or less, or 30 or less. The lower limit of the ratio (G '(-20 ℃ C.)/G' (80 ℃ C.)) may be, for example, 5 or more, 10 or more, 50 or more, or 100 or more.

The glass transition temperature (Tg) of the adhesive is not particularly limited, and may be set in consideration of flexibility in a low temperature region and cohesion (heat resistance, etc.) in a high temperature region. In some embodiments, the adhesive has a Tg of, for example, 30℃or less, and may be 15℃or less, or may be 5℃or less. In some preferred embodiments, the Tg of the binder is 0℃or less, more preferably-5℃or less, still more preferably-10℃or less, and may be-15℃or less (e.g., -20 ℃) or less from the viewpoint of flexibility. The lower the Tg of the adhesive, the more excellent the adhesion properties such as adhesion to an adherend tend to be. In addition, by setting the Tg of the adhesive to be low, a change in the elastic modulus in a temperature region higher than the Tg can be suppressed. The lower limit of Tg of the binder is, for example, -50℃or higher, preferably-40℃or higher, and may be-30℃or higher. The adhesive having the Tg tends to easily obtain a moderate cohesive force. In addition, there is a tendency that an adhesive agent having both a high refractive index and a low elastic modulus is easily formed.

The storage modulus G' of the binder and the glass transition temperature Tg of the binder at the respective temperatures can be measured by the method described in examples described later, and from the results, the respective storage modulus ratios can be calculated. The storage modulus G', the storage modulus ratio, and the glass transition temperature Tg of the adhesive can be adjusted by, for example, selecting the composition of the monomer components constituting the acrylic polymer (for example, selecting the type and content of the monomer (A1)), selecting the type of plasticizer, the amount of plasticizer used, the presence or absence of the crosslinking agent used, the type and amount of the plasticizer used, the presence or absence of the additive used, the type and amount of the monomer used, and the like.

< adhesive sheet >

According to this specification, an adhesive sheet having an adhesive layer is provided. The adhesive constituting the adhesive layer may be an adhesive formed from any of the adhesive compositions disclosed herein (e.g., a cured product of the adhesive composition).

The pressure-sensitive adhesive sheet may be a pressure-sensitive adhesive sheet with a base material having the pressure-sensitive adhesive layer on one side or both sides of a non-releasable base material (supporting base material), or may be a pressure-sensitive adhesive sheet without a base material having the pressure-sensitive adhesive layer held by a release liner or the like (i.e., a pressure-sensitive adhesive sheet without a non-releasable base material. Typically, a pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer). The term "adhesive sheet" as used herein may include an object called an adhesive tape, an adhesive label, an adhesive film, or the like. The pressure-sensitive adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, the pressure-sensitive adhesive sheet may be further processed into various shapes.

Fig. 1 and 2 show an example of a structure of a double-sided adhesive type base-less adhesive sheet (base-less double-sided adhesive sheet). The pressure-sensitive adhesive sheet 1 shown in fig. 1 has a structure in which both sides 21A and 21B of a pressure-sensitive adhesive layer 21 without a base material are protected by release liners 31 and 32, respectively, at least on the pressure-sensitive adhesive layer side of which is a release surface. The pressure-sensitive adhesive sheet 2 shown in fig. 2 has a structure in which one surface (pressure-sensitive adhesive surface) 21A of the pressure-sensitive adhesive layer 21 without a base material is protected by a release liner 31 having both surfaces as release surfaces, and when the pressure-sensitive adhesive sheet is wound, the other surface (pressure-sensitive adhesive surface) 21B of the pressure-sensitive adhesive layer 21 contacts the back surface of the release liner 31, whereby the other surface 21B is also protected by the release liner 31. The technology disclosed herein is preferably implemented in the form of a base-free pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer, from the viewpoint of being able to follow the flexibility of an adherend to be repeatedly folded. The above-mentioned base-free adhesive sheet is preferable from the viewpoints of, for example, reducing the thickness of the adhesive sheet and improving the transparency of the adhesive sheet.

The adhesive sheet disclosed herein may have, for example, a cross-sectional structure schematically shown in fig. 3. The adhesive sheet 3 shown in fig. 3 has a support substrate 10, and a first adhesive layer 21 and a second adhesive layer 22 supported by the first face 10A and the second face 10B of the support substrate 10, respectively. The first surface 10A and the second surface 10B are both non-releasable surfaces (non-releasable surfaces). The pressure-sensitive adhesive sheet 3 is used by attaching the surface (first pressure-sensitive adhesive surface) 21A of the first pressure-sensitive adhesive layer 21 and the surface (second pressure-sensitive adhesive surface) 22A of the second pressure-sensitive adhesive layer 22 to an adherend, respectively. That is, the pressure-sensitive adhesive sheet 3 is configured as a double-sided pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet). The adhesive sheet 3 before use has the following constitution: the first adhesive surface 21A and the second adhesive surface 22A are protected by release liners 31 and 32, respectively, at least on the adhesive surface side of which is a surface (release surface) having releasability. Alternatively, the following constitution may be adopted: the release liner 32 is omitted, and a release liner having both surfaces serving as release surfaces is used as the release liner 31, and the second adhesive surface 22A is also protected by the release liner 31 by bringing the second adhesive surface 22A into contact with the back surface of the release liner 31 by winding the adhesive sheet 3.

The technology disclosed herein can be preferably implemented in the form of the above-described base-free or base-equipped double-sided adhesive sheet for fixing and joining members (e.g., optical members). Alternatively, although not particularly shown, the pressure-sensitive adhesive sheet disclosed herein may be in the form of a single-sided pressure-sensitive adhesive sheet with a base material having a pressure-sensitive adhesive layer on only one side of a non-releasable base material (supporting base material). As an example of the form of the single-sided adhesive sheet, a form in which either the first adhesive layer 21 or the second adhesive layer 22 is not provided in the configuration shown in fig. 3 is exemplified.

(adhesive layer)

The adhesive layer of the adhesive sheet disclosed herein may be formed by applying (e.g., coating) an adhesive composition on an appropriate surface and then curing the composition. The application of the adhesive composition can be performed using a conventional coater such as a gravure roll coater, a reverse roll coater, a contact roll coater, a dip roll coater, a bar coater, a blade coater, or a spray coater.

The thickness of the adhesive layer is not particularly limited, and may be 3 μm or more, for example. In some embodiments, the thickness of the adhesive layer is, for example, preferably 5 μm or more, and may be 10 μm or more, 15 μm or more, 20 μm or more, 30 μm or more, 50 μm or more, 70 μm or more, or 85 μm or more. By increasing the thickness of the adhesive layer, there is a tendency for the adhesive force to increase. In some embodiments, the thickness of the adhesive layer may be 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 120 μm or less, for example. In some preferred embodiments, the thickness of the adhesive layer is 100 μm or less, more preferably 75 μm or less, still more preferably 70 μm or less, and may be 50 μm or less, or may be 30 μm or less. From the viewpoint of thinning of the adhesive sheet, etc., it is advantageous that the thickness of the adhesive layer is not excessively large. In addition, the pressure-sensitive adhesive layer having a small thickness tends to have excellent followability to an adherend. The technology disclosed herein can be preferably performed such that the thickness of the adhesive layer is in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm), for example. In the case of an adhesive sheet having a first adhesive layer and a second adhesive layer on a first surface and a second surface of a base material, the thickness of the adhesive layer may be applied to at least the thickness of the first adhesive layer. The thickness of the second adhesive layer may be selected from the same range. In the case of the pressure-sensitive adhesive sheet without a base material, the thickness of the pressure-sensitive adhesive sheet corresponds to the thickness of the pressure-sensitive adhesive layer.

In some embodiments, the adhesive has a storage modulus G' (0 ℃) Pa at 0 ℃]Thickness T [ mu ] m of adhesive layer]The product (G' (0 ℃ C.). Times.T) is, for example, 5.0X10 ⁴ ～7.5×10 ⁷ Is suitable in the range of 5.0X10, preferably ⁴ ～5.0×10 ⁷ Within a range of (2). In the adhesive layer having a small thickness, even if having a relatively high elastic modulus, good flexibility is easily obtained by having the product (G' (0 ℃) x T) in the above range. Further, by limiting the product (G '(0 ℃) x T) to a predetermined value or less, the thickness of the pressure-sensitive adhesive layer and the upper limit of the storage modulus G' (0 ℃) are limited, whereby excellent flexibility can be easily obtained. In some preferred embodiments, the product (G' (0 ℃ C.) times T) may be 1.0X10 ⁵ The above may be 2.0X10 ⁵ The above may be 8.0X10 ⁵ The above. The product (G' (0 ℃ C.) times T) may be 2.0X10 ⁷ Hereinafter, it may be 1.0X10 ⁷ Hereinafter, the ratio may be 6.0X10 ⁶ The following is given.

(haze value)

In some embodiments, the haze value of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet may be, for example, 5.0% or less, preferably 3.0% or less, more preferably 2.0% or less, further preferably 1.0% or less, and may be 0.9% or less, and may be 0.8% or less, and may be 0.5% or less, and may be 0.3% or less. The pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer with high transparency as described above can be preferably used in applications requiring high light transmittance (for example, optical applications) and applications requiring good visual recognition of the performance of an adherend by the pressure-sensitive adhesive sheet, in a configuration having a base material or a configuration not having a base material. The lower limit of the haze value of the adhesive layer is not particularly limited, and from the viewpoint of improving transparency, the smaller the haze value is, the more preferable. On the other hand, in some embodiments, the haze value may be, for example, 0.05% or more, or 0.1% or more, in view of refractive index and adhesive property. These haze values related to the adhesive layer can be preferably applied to haze values of an adhesive sheet in the case where the technology disclosed herein is implemented in the form of a base-material-free adhesive sheet (typically an adhesive sheet composed of an adhesive layer).

The "haze value" herein refers to the ratio of diffuse transmitted light to total transmitted light when visible light is irradiated to a measurement object. Also known as turbidity. The haze value can be expressed by the following formula.

Th(％)＝Td/Tt×100

In the above formula, th is a haze value (%), td is a scattered light transmittance, and Tt is a total light transmittance. The haze value can be measured by the method described in examples described below. The haze value of the adhesive layer can be adjusted by, for example, selecting the composition, thickness, and the like of the adhesive layer.

In some embodiments, the haze value of the pressure-sensitive adhesive sheet may be, for example, 5.0% or less, preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less, may be 0.9% or less, may be 0.8% or less, may be 0.5% or less, or may be 0.3% or less. The pressure-sensitive adhesive sheet having such high transparency can be preferably used for applications requiring high light transmittance (for example, optical applications) and applications requiring good visibility of an adherend by the pressure-sensitive adhesive sheet. The lower limit of the haze value of the pressure-sensitive adhesive sheet is not particularly limited, and from the viewpoint of improving transparency, the smaller the haze value is, the more preferable. On the other hand, in some embodiments, the haze value may be, for example, 0.05% or more and may be 0.10% or more in view of refractive index and adhesive property. The haze value of the pressure-sensitive adhesive sheet can be measured by the same method as that for the above-mentioned pressure-sensitive adhesive layer. The haze value of the pressure-sensitive adhesive sheet can be obtained by selecting the type of substrate and the thickness of the substrate in the composition having the substrate, such as the composition of the pressure-sensitive adhesive layer.

In some embodiments, the total light transmittance of the adhesive layer is preferably 85.0% or more (e.g., 88.0% or more, 90.0% or more, or greater than 90.0%). The pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer with high transparency as described above can be preferably used in applications (for example, optical applications) requiring high light transmittance and applications requiring good visibility of an adherend by the pressure-sensitive adhesive sheet, in a structure having a base material or a structure not having a base material. The upper limit of the total light transmittance may be about 98% or less, about 96% or less, or about 95% or less, for example, in practical use. In some embodiments, the adhesive layer may have a total light transmittance of about 94% or less, about 93% or less, or about 92% or less, in view of refractive index and adhesive properties. Total light transmittance according to JIS K7136:2000, the measurement was performed using a commercially available transmittance meter. As the transmittance meter, the trade name "HAZEMETER HM-150" manufactured by Country color technical research or an equivalent thereof can be used. The total light transmittance can be measured by the method described in examples described below. The total light transmittance of the adhesive layer can be adjusted by selecting the composition, thickness, and the like of the adhesive layer, for example.

In some embodiments, the adhesive sheet preferably has a total light transmittance of 85.0% or more (e.g., 88.0% or more, 90.0% or more, or greater than 90.0%). The pressure-sensitive adhesive sheet having such high transparency can be preferably used for applications requiring high light transmittance (for example, optical applications) and applications requiring good visibility of an adherend by the pressure-sensitive adhesive sheet. The upper limit of the total light transmittance may be about 98% or less, about 96% or less, or about 95% or less, for example, in practical use. In some embodiments, the adhesive sheet may have a total light transmittance of about 94% or less, about 93% or less, or about 92% or less, in view of refractive index and adhesive properties. The total light transmittance of the adhesive sheet can be measured by the same method as that for the measurement of the total light transmittance of the adhesive layer. The total light transmittance of the pressure-sensitive adhesive sheet can be obtained by selecting the composition of the pressure-sensitive adhesive layer, the type of the substrate, and the thickness of the substrate in the composition having the substrate.

(peel Strength)

The peel strength of the adhesive sheet to the glass plate is not particularly limited. In some embodiments, the peel strength of the adhesive sheet to the glass plate is, for example, 0.1N/25mm or more, and may be 0.5N/25mm or more. In some preferred embodiments, the peel strength of the glass sheet is 1.0N/25mm or more, more preferably 1.5N/25mm or more, still more preferably 2.0N/25mm or more, and may be 3.0N/25mm or more, or may be 5.0N/25mm or more, or may be 10N/25mm or more. The pressure-sensitive adhesive sheet having a peel strength to a glass plate of a predetermined value or more is suitable for joining and fixing, for example, glass members. The upper limit of the peel strength is not particularly limited, and may be, for example, 30N/25mm or less, 25N/25mm or less, or 20N/25mm or less.

Here, the peel strength can be grasped by the following operations: the resulting mixture was pressed against an alkali glass plate as an adherend, left to stand at 23℃for 30 minutes in an atmosphere of 50% RH, and then the peel strength was measured under conditions of 180℃for peel angle and 300 mm/min for pulling speed. In the measurement, an appropriate lining material (for example, a polyethylene terephthalate (PET) film having a thickness of about 25 μm to about 50 μm) may be attached to the pressure-sensitive adhesive sheet to be measured as needed for reinforcement. The peel strength can be more specifically measured by the method described in examples described below.

(thickness of adhesive sheet)

The thickness of the pressure-sensitive adhesive sheet (substrate-less pressure-sensitive adhesive sheet or pressure-sensitive adhesive sheet with a substrate) disclosed herein may be 1000 μm or less, 350 μm or less, 200 μm or less, 120 μm or less, 75 μm or less, or 50 μm or less, for example. From the viewpoint of handleability, the thickness of the pressure-sensitive adhesive sheet may be, for example, 5 μm or more, 10 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more.

The thickness of the pressure-sensitive adhesive sheet refers to the thickness of the portion to be adhered to the adherend. For example, the pressure-sensitive adhesive sheet 3 having the structure shown in fig. 3 is the thickness from the first pressure-sensitive adhesive surface 21A to the second pressure-sensitive adhesive surface 22A, and does not include the thickness of the release liners 31 and 32.

< support substrate >)

The pressure-sensitive adhesive sheet of some embodiments may be in the form of a pressure-sensitive adhesive sheet with a substrate having a pressure-sensitive adhesive layer on one or both sides of the support substrate. The material of the support base is not particularly limited, and may be appropriately selected depending on the purpose, mode of use, and the like of the adhesive sheet. As non-limiting examples of substrates that can be used, mention may be made of: plastic films such as polyolefin films mainly composed of polyolefin such as polypropylene (PP) and ethylene-propylene copolymer, polyester films mainly composed of polyester such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and polyethylene naphthalate (PEN), and polyvinyl chloride films mainly composed of polyvinyl chloride; foam sheets formed from foams such as polyurethane foam, polyethylene (PE) foam, polychloroprene foam, and the like; woven and nonwoven fabrics obtained by using various fibrous materials (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semisynthetic fibers such as acetate) alone or in combination; paper such as japanese paper, high-quality paper, kraft paper, crepe paper, etc.; metal foils such as aluminum foil and copper foil; etc. The substrate may be a composite substrate. Examples of such a composite substrate include: a base material having a structure in which a metal foil and the plastic film are laminated, a plastic base material having a structure in which inorganic fibers such as glass cloth are reinforced, and the like.

In some embodiments, various film substrates may be preferred. The film substrate may be a porous substrate such as a foam film or a nonwoven fabric sheet, a non-porous substrate, or a substrate having a structure in which a porous layer and a non-porous layer are laminated. In some embodiments, as the film base material, a base material including a (self-supporting or independent) resin film capable of independently maintaining a shape may be preferably used. Here, "resin film" refers to a resin film that is of a non-porous structure, typically substantially bubble-free (void-free). Therefore, the resin film is a concept different from a foam film and a nonwoven fabric. As the resin film, a film (self-supporting or independent) capable of independently maintaining a shape can be preferably used. The resin film may have a single-layer structure or a multilayer structure (for example, a three-layer structure) of two or more layers.

As the resin material constituting the resin film, for example, it is possible to use: a polyester; a polyolefin; polycycloolefins derived from monomers having an aliphatic ring structure such as a norbornene structure; polyamide (PA) such as nylon 6, nylon 66, and partially aromatic polyamide; polyimide (PI) such as transparent polyimide (CPI); polyamideimide (PAI); polyetheretherketone (PEEK); polyethersulfone (PES); polyphenylene Sulfide (PPS); polycarbonate (PC); polyurethane (PU); ethylene vinyl acetate copolymer (EVA); fluororesins such as Polytetrafluoroethylene (PTFE); an acrylic resin; cellulose polymers such as triacetyl cellulose (TAC); polyarylate; a polystyrene; polyvinyl chloride; polyvinylidene chloride; and the like.

The resin film may be a film formed using a resin material containing one kind of such a resin alone, or may be a film formed using a resin material obtained by blending two or more kinds of such resins. The resin film may be unstretched or stretched (for example, uniaxially stretched or biaxially stretched). For example, a PET film, a PBT film, a PEN film, an unstretched polypropylene (CPP) film, a biaxially stretched polypropylene (OPP) film, a Low Density Polyethylene (LDPE) film, a Linear Low Density Polyethylene (LLDPE) film, a PP/PE blend film, a cycloolefin polymer (COP) film, a CPI film, a TAC film, or the like can be preferably used. Examples of the resin film that is preferable from the viewpoints of strength and dimensional stability include PET film, PEN film, PPS film, and PEEK film. From the viewpoint of availability and the like, particularly preferred are PET films and PPS films, and among them, PET films are preferred.

To the resin film, known additives such as a light stabilizer, an antioxidant, an antistatic agent, a colorant (dye, pigment, etc.), a filler, a slip agent, and an antiblocking agent may be blended as necessary within a range that does not significantly inhibit the effect of the present invention. The blending amount of the additive is not particularly limited and may be appropriately set according to the use of the adhesive sheet and the like.

The method for producing the resin film is not particularly limited. For example, conventionally known general resin film molding methods such as extrusion molding, inflation molding, T-die casting, and calender roll molding can be suitably employed.

The substrate may consist essentially of such a base film. Alternatively, the base material may include an auxiliary layer in addition to the base film. Examples of the auxiliary layer include an optical property adjusting layer (e.g., a coloring layer or an antireflection layer), a printed layer for imparting a desired appearance to a substrate, a laminate layer, an antistatic layer, an undercoat layer, and a surface treatment layer such as a release layer.

In some embodiments, a substrate having light transmittance (hereinafter also referred to as a light-transmitting substrate) can be preferably used as the support substrate. Thus, the pressure-sensitive adhesive sheet with a base material having light transmittance can be formed. The total light transmittance of the light-transmitting substrate may be, for example, greater than 50% or 70% or more. In some preferred embodiments, the total light transmittance of the support substrate is 80% or more, more preferably 90% or more, and may be 95% or more (e.g., 95% to 100%). The total light transmittance was in accordance with JIS K7136: 2000, the measurement was performed using a commercially available transmittance meter. As the transmittance meter, the trade name "HAZEMETER HM-150" manufactured by Country color technical research or an equivalent thereof was used. A preferable example of the light-transmitting base material is a resin film having light-transmitting properties. The light-transmitting substrate may be an optical film.

The thickness of the base material is not particularly limited, and may be selected according to the purpose, mode of use, and the like of the adhesive sheet. The thickness of the base material may be, for example, 500 μm or less, and from the viewpoint of handling and workability of the adhesive sheet, it is preferably 300 μm or less, 150 μm or less, 100 μm or less, 50 μm or less, 25 μm or less, or 10 μm or less. When the thickness of the base material is reduced, the following property to the surface shape of the adherend tends to be improved. From the viewpoint of handleability, workability, and the like, the thickness of the base material may be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

The surface of the substrate on the side on which the adhesive layer is laminated may be subjected to conventionally known surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, formation of an undercoat layer by application of a primer (primer), and the like, as required. Such a surface treatment may be a treatment for improving the anchoring property of the adhesive layer to the substrate. The composition of the primer used for forming the undercoat layer is not particularly limited, and may be appropriately selected from known compositions. The thickness of the undercoat layer is not particularly limited, and is generally from about 0.01 μm to about 1 μm, preferably from about 0.1 μm to about 1 μm. Examples of other treatments that may be applied to the substrate as needed include antistatic layer formation treatment, coloring layer formation treatment, printing treatment, and the like. These treatments may be applied singly or in combination.

< pressure-sensitive adhesive sheet with Release liner >

The pressure-sensitive adhesive sheet disclosed herein may be in the form of a pressure-sensitive adhesive article obtained by bringing the surface (pressure-sensitive adhesive surface) of the pressure-sensitive adhesive layer into contact with the release surface of the release liner. Thus, according to the present specification, there is provided an adhesive sheet (adhesive article) with a release liner, comprising: any of the adhesive sheets disclosed herein and a release liner having a release surface in contact with the adhesive surface of the adhesive sheet.

As the release liner, there is no particular limitation, and for example, it is possible to use: a release liner having a release layer on the surface of a liner substrate such as a resin film or paper (which may be a paper laminated with a resin such as polyethylene); a release liner comprising a resin film formed of a low-tackiness material such as a fluorine-containing polymer (polytetrafluoroethylene or the like) or a polyolefin resin (polyethylene, polypropylene or the like). From the viewpoint of excellent surface smoothness, a release liner having a release layer on the surface of a resin film as a liner base material, and a release liner containing a resin film formed of a low-tackiness material can be preferably used. The resin film is not particularly limited as long as it can protect the pressure-sensitive adhesive layer, and examples thereof include: polyethylene (PE) film, polypropylene (PP) film, polybutylene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyester film (PET film, PBT film, etc.), polyurethane film, ethylene-vinyl acetate copolymer film, etc. For forming the release layer, for example, a known release agent such as a silicone release agent, a long-chain alkyl release agent, an olefin release agent, a fluorine-containing release agent, a fatty acid amide release agent, molybdenum sulfide, or silica powder can be used.

< usage >

The pressure-sensitive adhesive sheet disclosed herein is not limited in its use and can be used for various purposes. The pressure-sensitive adhesive sheet disclosed herein has a pressure-sensitive adhesive agent having both a high refractive index and a low elastic modulus, and therefore can be used for various applications requiring a high refractive index and flexibility by utilizing the characteristics thereof. For example, in electronic devices such as portable electronic devices, they are suitable as display devices (image display devices) such as liquid crystal display devices, organic EL (electroluminescence) display devices, PDP (plasma display panel), and electronic paper; devices (optical devices) such as input devices such as touch panels are particularly suitable as pressure-sensitive adhesive sheets for foldable displays and rollable displays. For example, in a foldable display or a rollable display, the foldable display is preferably used as a method for joining or fixing or protecting a member having a high refractive index. The pressure-sensitive adhesive sheet disclosed herein has a high refractive index and is flexible enough to withstand repeated bending operations, and therefore can satisfactorily follow an adherend (foldable display or the like) that is repeatedly bent while being attached to the foldable display or the rollable display. Examples of the object to be adhered in this mode of use include glass members such as window glass and cover glass used in foldable displays and rollable displays. The pressure-sensitive adhesive sheet disclosed herein is also suitable for use in electronic devices having a curved surface shape, for example, a three-dimensional shape of a portable electronic device, because it is easy to follow and adhere to the curved surface shape. In addition, in some preferred embodiments, the adhesive may be an adhesive having excellent heat resistance in addition to having a high refractive index and a low elastic modulus. The above-mentioned portable electronic device is sometimes used in a high-temperature environment, and the advantage of using the above-mentioned heat-resistant adhesive sheet is great because the internal space thereof is heated by heat generated from the electronic component.

Examples of the above-described portable electronic device include, for example: a mobile phone, a smart phone, a tablet personal computer, a notebook personal computer, various wearable devices (for example, wrist wearing type worn on a wrist such as a wristwatch, modularized type worn on a part of a body with a clip, a band, or the like, eye wearing (eye wearing) type including glasses type (monocular type, binocular type, helmet type is also included), clothing type worn on a shirt, socks, hat, or the like in the form of, for example, ornaments, ear wearing type worn on an ear such as an earphone, or the like), a digital camera, a digital video camera, an acoustic device (portable music player, recording pen, or the like), a calculator (desktop calculator, or the like), a portable game device, an electronic dictionary, an electronic notepad, an electronic book, a vehicle-mounted information device, a portable radio, a portable television, a portable printer, a portable scanner, a portable modem, or the like. It should be noted that "portable" in this specification is interpreted as being insufficient to be portable only, and it is actually portable at a level that an individual (standard adult) can relatively easily carry.

The material (adherend material) to which the pressure-sensitive adhesive sheet disclosed herein is attached is not particularly limited, and examples thereof include: examples of the metal material include metal materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, zinc, and an alloy containing two or more of them, and various resin materials (typically, plastic materials) such as polyimide resins, acrylic resins, polyether nitrile resins, polyether sulfone resins, polyester resins (PET resins, polyethylene naphthalate resins, and the like), polyvinyl chloride resins, polyphenylene sulfide resins, polyether ether ketone resins, polyamide resins (so-called aramid resins, and the like), polyarylate resins, polycarbonate resins, diacetyl cellulose, and triacetyl cellulose, polyvinyl butyral polymers, and liquid crystal polymers, and inorganic materials such as alumina, zirconia, alkali glass, alkali-free glass, quartz glass, and carbon. The adhesive sheet disclosed herein can be used by being stuck to a member (for example, an optical member) composed of the above-described materials.

The member or material to be adhered (at least one adherend in the double-sided adhesive sheet) of the adhesive sheet disclosed herein may be a member or material containing a material having a higher refractive index than that of a general acrylic adhesive. The refractive index of the adherend is, for example, 1.50 or more, and there are also adherend materials having a refractive index of 1.55 or more or 1.58 or more, and there are also adherend materials having a refractive index of 1.62 or more (for example, about 1.66). Such an adherend material of high refractive index is typically a resin material. More specifically, the resin may be a polyester resin such as PET, a polyimide resin, an aromatic polyamide resin, a polyphenylene sulfide resin, a polycarbonate resin, or the like. With respect to such a material, the effect (suppression of reflection of light due to a refractive index difference) brought about by the use of the adhesive sheet disclosed herein can be preferably exerted. The upper limit of the refractive index of the adherend material is, for example, 1.80 or less, and may be 1.70 or less. The pressure-sensitive adhesive sheet disclosed herein can be preferably used in such a manner as to be stuck to an adherend (e.g., a member) having a high refractive index as described above. Preferable examples of such an adherend include a resin film having a refractive index of 1.50 to 1.80 (preferably 1.55 to 1.75, for example 1.60 to 1.70). The refractive index can be measured by the same method as that of the adhesive.

The member or material to be adhered to the pressure-sensitive adhesive sheet (at least one adherend in the double-sided pressure-sensitive adhesive sheet) may be a member or material having light transmittance. Such an adherend can easily obtain the advantage of the effect (suppression of light reflection at the interface between the adherend and the adhesive sheet) by the technique disclosed herein. The total light transmittance of the adherend is, for example, more than 50%, and preferably 70% or more. In some preferred embodiments, the total light transmittance of the adherend is 80% or more, more preferably 90% or more, and may be 95% or more (for example, 95% to 100%). The pressure-sensitive adhesive sheet disclosed herein can be preferably used so as to be attached to an adherend (for example, an optical member) having a total light transmittance of a predetermined value or more. The total light transmittance described above was in accordance with JIS K7136: 2000 was measured using a commercially available transmittance meter. As the transmittance meter, the trade name "HAZEMETER HM-150" manufactured by Country color technical research or an equivalent thereof can be used.

In some preferred embodiments, the adherend (e.g., member) to which the adhesive sheet is attached may be an adherend having the above-described refractive index and having the above-described total light transmittance. Specifically, the pressure-sensitive adhesive sheet disclosed herein can be preferably used as a pressure-sensitive adhesive material, for example, a member, which is stuck to an adherend having a refractive index of 1.50 or more (for example, about 1.55 or more, about 1.58 or more, about 1.62 or more, about 1.66 or the like) and a total light transmittance of more than 50% (for example, 70% or more, preferably 80% or more, more preferably 90% or more, and still 95% or more). In such a manner of adhering to the member, the effects of the techniques disclosed herein can be particularly preferably exerted.

As an example of the preferred application, an optical application is given. More specifically, for example, the pressure-sensitive adhesive sheet disclosed herein can be preferably used for applications for bonding optical members (for bonding optical members), for manufacturing applications of products (optical products) using the optical members, and the like.

The optical member is a member having optical characteristics (for example, polarization, light refraction, light scattering, light reflection, light transmittance, light absorption, light diffraction, optical rotation, visibility, and the like). The optical member is not particularly limited as long as it has optical characteristics, and examples thereof include a member constituting a device (optical device) such as a display device (image display device) and an input device, and a member used in such a device, and examples thereof include: polarizing plates, wave plates, phase difference plates, optical compensation films, brightness enhancement films, light guide plates, reflection films, antireflection films, hard Coat (HC) films, impact absorption films, antifouling films, photochromic films, light modulation films, transparent conductive films (ITO films), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates; a member in which these films are further laminated (these may be collectively referred to as "functional film"), and the like. The "plate" and the "film" include plate-like, film-like, sheet-like, and other forms, and for example, "polarizing film" includes "polarizing plate", and "light guide plate" includes "light guide film", "light guide sheet", and the like. In addition, the "polarizing plate" includes a circular polarizing plate.

Examples of the display device include: liquid crystal display devices, organic EL display devices, micro LEDs (μled), mini LEDs (miniLED), PDPs, electronic papers, and the like. The input device may be a touch panel.

The optical member is not particularly limited, and examples thereof include members (e.g., sheet-like, film-like, plate-like members) including glass, acrylic resin, polycarbonate, PET, and metal film. The term "optical member" in the present specification includes a member (such as a design film, a decorative film, or a surface protective film) that plays a role of decoration and protection while maintaining visibility of a display device or an input device.

The technology disclosed herein can be preferably used for bonding an optical film such as a film having one or two or more functions of light transmission, reflection, diffusion, waveguide, light collection, diffraction, and the like, a fluorescent film, and the like, to another optical member (other optical film may be used). Among them, in the bonding of an optical film having at least one of the functions of light guiding, light collecting and light diffracting, it is preferable that the entire bonding layer has a high refractive index, and this is a preferable application object of the technology disclosed herein.

The adhesive disclosed herein can be preferably used for bonding optical films such as light guide films, diffusion films, fluorescent films, toner films, prism sheets, lenticular films, and microlens array films, for example. In these applications, from the viewpoint of downsizing and higher performance of the optical member, improvement in thickness and light extraction efficiency is demanded. As an adhesive that can cope with this demand, the adhesive disclosed herein can be preferably used. More specifically, for example, in joining a light guide film and a diffusion film, the thickness can be reduced by adjusting the refractive index (for example, increasing the refractive index) of an adhesive layer as a joining layer. In the bonding of the fluorescent film, the light extraction efficiency (also referred to as luminous efficiency) can be improved by appropriately adjusting the refractive index difference between the fluorescent light-emitting body and the binder. In the bonding of the color matching film, the refractive index of the binder is appropriately adjusted so as to reduce the refractive index difference from the color matching pigment, thereby contributing to the reduction of the scattering component and the improvement of the light transmittance. In joining of prism sheets, lenticular films, microlens array films, and the like, by appropriately adjusting the refractive index of the adhesive, it is possible to contribute to control of diffraction of light, enhancement of brightness, and/or viewing angle.

The pressure-sensitive adhesive sheet disclosed herein is preferably used so as to be stuck to an adherend of high refractive index (may be a layer or member of high refractive index), and can suppress interfacial reflection with the adherend. As described above, the pressure-sensitive adhesive sheet used in this manner preferably has a small refractive index difference from the adherend and high adhesion to the interface with the adherend. In addition, from the viewpoint of improving the uniformity of appearance, the pressure-sensitive adhesive layer is preferably high in uniformity of thickness, for example, the surface smoothness of the pressure-sensitive adhesive surface is preferably high. In the case where the thickness of the adherend of high refractive index is small (for example, in the case of 5 μm or less, 4 μm or less, or 2 μm or less), it is particularly interesting to suppress reflection at the interface from the viewpoint of suppressing coloration or color unevenness caused by interference of reflected light. As an example of such a use method, there is given: in a polarizing plate with a retardation layer comprising a polarizer, a first retardation layer and a second retardation layer in this order, a means for joining the polarizer to the first retardation layer and/or joining the first retardation layer to the second retardation layer is provided.

The pressure-sensitive adhesive sheet disclosed herein is suitable for increasing the refractive index, and therefore, can be preferably used so as to be adhered to a light-emitting layer (for example, a light-emitting layer having high refractive index mainly composed of an inorganic material) of an optical semiconductor or the like. By reducing the refractive index difference between the light-emitting layer and the adhesive layer, reflection at their interface can be suppressed, and light extraction efficiency can be improved. The adhesive sheet used in this manner preferably has an adhesive layer with a high refractive index. From the viewpoint of improving the brightness, the pressure-sensitive adhesive sheet is preferably low in coloring. This is advantageous from the viewpoint of suppressing unintentional coloration caused by the adhesive sheet.

In the present specification, a self-light emitting element means a light emitting element capable of controlling light emission luminance by a value of a current flowing. The self-luminous element may be formed of a single body or may be formed of an aggregate. Specific examples of the self-light emitting element include a Light Emitting Diode (LED) and an organic EL, but are not limited to these elements. In this specification, a light-emitting device refers to a device including such a self-light-emitting element as a constituent element. Examples of the light-emitting device include a light source module device (for example, a planar light-emitting module) used as illumination, and a display device formed with pixels, but are not limited to these devices.

The adhesive disclosed herein can be used preferably as a coating layer for covering a lens surface, a joining layer for a member opposing the lens surface (e.g., a member having a surface shape corresponding to a lens surface), a filling layer filled between the lens surface and the member, or the like, among microlenses used as constituent members of cameras, light-emitting devices, and the like, and other lens members (e.g., microlens constituting a microlens array film, microlens for cameras, and the like). The adhesive disclosed herein is suitable for increasing the refractive index, and therefore, even in the case of a lens having a high refractive index (for example, a lens made of a high refractive index resin or a lens having a surface layer made of a high refractive index resin), the refractive index difference from the lens can be reduced. This is advantageous from the viewpoint of thinning of the lens and the product having the lens, and contributes to suppression of aberration and improvement of abbe number. The adhesive disclosed herein can be used as a lens resin by itself, for example, in a form of filling in a recess or a void of an appropriate transparent member.

The method of bonding the optical members using the pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and may be, for example, (1) a method of bonding the optical members to each other using the pressure-sensitive adhesive sheet disclosed herein, (2) a method of bonding the optical members to members other than the optical members using the pressure-sensitive adhesive sheet disclosed herein, or (3) a method of bonding the pressure-sensitive adhesive sheet disclosed herein to the optical members or to members other than the optical members in a form including the optical members. In the aspect (3), the pressure-sensitive adhesive sheet including the form of the optical member may be, for example, a pressure-sensitive adhesive sheet in which the support is an optical member (for example, an optical film). The pressure-sensitive adhesive sheet having such a form including an optical member as a support can be understood as a pressure-sensitive adhesive optical member (for example, pressure-sensitive adhesive optical film). In addition, when the adhesive sheet disclosed herein is of the type having a support and the functional film is used as the support, the adhesive sheet disclosed herein may be understood as "adhesive functional film" having the adhesive layer disclosed herein on at least one side of the functional film.

As described above, according to the technology disclosed herein, a laminate having the adhesive sheet disclosed herein and a member to which the adhesive sheet is attached is provided. The member to which the adhesive sheet is attached may be a member having the refractive index of the adherend material described above. The difference (refractive index difference) between the refractive index of the pressure-sensitive adhesive sheet and the refractive index of the member may be the refractive index difference between the adherend and the pressure-sensitive adhesive sheet. The members constituting the laminate are described as the above-described members, materials, and adherends, and thus, the description thereof will not be repeated.

As will be understood from the above description and the following examples, the matters disclosed by the present specification include the following matters.

[1] An adhesive composition, wherein the adhesive composition comprises an acrylic polymer and a plasticizer,

the monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1),

the plasticizer is a compound having two or more double bond-containing rings and being liquid at 30 ℃.

[2] The adhesive composition according to the above [1], wherein the compound is a compound which is liquid at 20 ℃.

[3] The adhesive composition according to the above [1] or [2], wherein the adhesive composition contains more than 15 parts by weight of the plasticizer relative to 100 parts by weight of the acrylic polymer.

[4] The adhesive composition according to any one of the above [1] to [3], wherein the adhesive composition contains more than 30 parts by weight of the plasticizer with respect to 100 parts by weight of the acrylic polymer.

[5] The adhesive composition according to any one of the above [1] to [4], wherein the plasticizer has at least one ring selected from aromatic rings and heterocyclic rings as the double bond-containing ring.

[6] The adhesive composition according to any one of the above [1] to [5], wherein the plasticizer has a first double bond-containing ring and a second double bond-containing ring, and the first double bond-containing ring and the second double bond-containing ring are connected via a linking group having 1 to 5 atoms.

[7] The adhesive composition according to any one of the above [1] to [6], wherein the molecular weight of the plasticizer is in the range of 100 to 2000.

[8] The adhesive composition according to any one of the above [1] to [7], wherein the monomer component constituting the acrylic polymer contains a monomer (A2) in addition to the aromatic ring-containing monomer (A1), and the monomer (A2) has at least one of a hydroxyl group and a carboxyl group.

[9] The adhesive composition according to any one of [1] to [8], wherein the aromatic ring-containing monomer (A1) is contained in the monomer component in an amount of 60% by weight or more.

[10] The adhesive composition according to any one of the above [1] to [9], wherein 50% by weight or more of the aromatic ring-containing monomer (A1) is a monomer having a homopolymer glass transition temperature of 10℃or lower.

[11] An adhesive, wherein the adhesive is formed from the adhesive composition described in any one of [1] to [9] above.

[12]As described above [11]]The adhesive has a refractive index of 1.55 or more, and a storage modulus G' (0 ℃) at 0 ℃ of 1.0X10 ⁴ Pa～1.0×10 ⁶ Pa.

[13] The adhesive according to the above [11] or [12], wherein the glass transition temperature of the adhesive is in the range of-50℃to 0 ℃.

[14] The adhesive according to any one of the above [11] to [13], wherein a ratio (G ' (0 ℃) of the storage modulus G ' (0 ℃) to the storage modulus G ' (80 ℃) at 80 ℃ of the adhesive (G ' (0 ℃) to G ' (80 ℃) is in a range of 1 to 1000.

[15] The adhesive according to any one of the above [11] to [14], wherein the ratio (G '(-10 ℃ C.)/G' (80 ℃ C.) of the storage modulus G '(-10 ℃ C.) at-10 ℃ C.) to the storage modulus G' (80 ℃ C.) at 80 ℃ C.) of the adhesive is in the range of 1 to 1000.

[16] An adhesive sheet comprising an adhesive layer formed of the adhesive composition according to any one of [1] to [10] above.

[17] An adhesive sheet comprising an adhesive layer comprising the adhesive of any one of [11] to [15 ].

[18] The adhesive sheet according to the above [16] or [17], wherein the thickness of the adhesive layer is in the range of 5 μm to 75. Mu.m.

[19]As described above [16]]～[18]The adhesive sheet according to any one of, wherein the adhesive sheet has a storage modulus G' (0 ℃) Pa at 0 ℃ of the adhesive]Thickness T [ mu ] m of adhesive layer]The product (G' (0 ℃ C.). Times.T) was 5.0X10 ⁴ ～5.0×10 ⁷ Within a range of (2).

[20] The adhesive sheet according to any one of [16] to [19], wherein the adhesive sheet has a total light transmittance of 85% or more.

[21] The adhesive sheet according to any one of [16] to [20], wherein the adhesive sheet has a haze value of 3% or less.

[22] The adhesive sheet according to any one of [16] to [21], wherein the adhesive sheet has a peel strength to a glass plate of 0.1N/25mm or more.

Examples

Some embodiments of the present invention are described below, but the present invention is not intended to be limited to what is shown in these specific examples. In the following description, unless otherwise specified, "parts" and "%" of the amount and content used are weight basis.

< example 1 >

(preparation of acrylic Polymer solution)

Into ase:Sub>A four-necked flask equipped with ase:Sub>A stirring blade, ase:Sub>A thermometer, ase:Sub>A nitrogen inlet tube and ase:Sub>A cooler, 95 parts of m-phenoxybenzyl acrylate (trade name "Light Acrylate POB-A", manufactured by Kyowase:Sub>A chemical Co., ltd., refractive index: 1.566, tg of homopolymer: -35 ℃ C. Or less, described as "POB-A.) and 5 parts of 4-hydroxybutyl acrylate (4 HBA), 0.2 part of 2,2' -azobisisobutyronitrile as ase:Sub>A polymerization initiator, and 150 parts of ethyl acetate as ase:Sub>A polymerization solvent were charged, and nitrogen was slowly introduced while stirring, and the liquid temperature in the flask was maintained at about 60 ℃ C. And polymerization was carried out for 6 hours, thereby preparing ase:Sub>A solution (40%) of acrylic polymer P1. The Mw of the acrylic polymer P1 was 50 ten thousand.

(preparation of adhesive composition)

The acrylic adhesive composition of this example was prepared by diluting the solution (40%) of the acrylic polymer P1 to 20% with ethyl acetate, adding 10 parts (nonvolatile content 0.1 parts) of an isocyanurate of hexamethylene diisocyanate (trade name "Coronate HX", manufactured by eason corporation) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (nonvolatile content 0.01 parts) of a 1% ethyl acetate solution of iron acetylacetonate as a crosslinking catalyst to 500 parts (nonvolatile content 100 parts) of the solution, and mixing them with stirring.

(production of adhesive sheet)

The acrylic adhesive composition prepared above was coated on a silicone-treated surface of a polyethylene terephthalate (PET) film R1 (thickness 50 μm) having one surface subjected to silicone treatment, and heated at 130 ℃ for 2 minutes, thereby forming an adhesive layer having a thickness of 20 μm. Next, a silicone-treated surface of a PET film R2 (thickness 25 μm) having one surface subjected to silicone treatment was bonded to the surface of the pressure-sensitive adhesive layer. A substrate-free double-sided adhesive sheet containing the above adhesive layer was obtained by the above operation. The double-sided of the adhesive sheet is protected by PET films (release liners) R1, R2.

< example 2 >

(preparation of acrylic Polymer solution)

Into a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet pipe, and a cooler, 99 parts of benzyl acrylate (trade name "Viscoat #160", manufactured by osaka organic chemical industry Co., ltd., refractive index: 1.519, tg of homopolymer: 6 ℃ or less, described as "BZA") as a monomer component, 1 part of 4HBA, 0.2 part of 2,2' -azobisisobutyronitrile as a polymerization initiator, and 100 parts of ethyl acetate as a polymerization solvent were charged, and nitrogen was introduced while slowly stirring, and polymerization was carried out for 6 hours while maintaining the liquid temperature in the flask at about 60 ℃. The Mw of the acrylic polymer P2 was 100 tens of thousands.

(preparation of adhesive composition)

The solution of the acrylic polymer P2 (polymer concentration: 50%) was diluted to a polymer concentration of 30% with ethyl acetate, and to 334 parts (nonvolatile matter: 100 parts) of this solution, 10 parts (nonvolatile matter: 0.1 part) of an isocyanurate of hexamethylene diisocyanate (trade name "cornate HX", manufactured by eason corporation, trifunctional isocyanate compound) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (nonvolatile matter: 0.01 part) of a 1% ethyl acetate solution of iron acetylacetonate as a crosslinking catalyst were added and stirred and mixed to prepare an acrylic adhesive composition of this example.

(production of adhesive sheet)

Using the obtained acrylic pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet (a base-free double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) of this example was produced in the same manner as in example 1.

< examples 3 to 5 >

In the preparation of the acrylic pressure-sensitive adhesive composition of example 2, acrylic pressure-sensitive adhesive compositions of each example were prepared in the same manner as in the preparation of the acrylic pressure-sensitive adhesive composition of example 2 except that 30 parts (example 3), 45 parts (example 4) or 60 parts (example 5) of POB-ase:Sub>A (trade name "Light Acrylate POB-ase:Sub>A", manufactured by co-glong chemical company, m-phenoxybenzyl acrylate, refractive index: 1.566, liquid at 20 ℃) were added to 100 parts of the nonvolatile component contained in the solution of the acrylic polymer P2. Adhesive sheets of each example (substrate-free double-sided adhesive sheets composed of an adhesive layer) were produced in the same manner as in the production of the adhesive sheet of example 1, except that the obtained acrylic adhesive compositions were used.

< example 6 >

A solution of an acrylic polymer P3 was prepared in the same manner as in the preparation of the acrylic polymer solution of example 2 except that the composition of the monomer components was changed to 99 parts of phenoxyethyl acrylate (trade name "Viscoat #192", manufactured by osaka organic chemical industry co., ltd., refractive index: 1.517, tg of the homopolymer: 2 ℃ C. Or below, described as "PEA") and 1 part of 4 HBA. The Mw of the acrylic polymer P3 was 100 tens of thousands.

An acrylic pressure-sensitive adhesive composition of this example was prepared in the same manner as in the preparation of the acrylic pressure-sensitive adhesive composition of example 2 except that the solution of the acrylic polymer P3 was used instead of the solution of the acrylic polymer P2, and a pressure-sensitive adhesive sheet (a base-free double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) of this example was prepared in the same manner as in example 1 using the obtained acrylic pressure-sensitive adhesive composition.

< example 7 >

In the preparation of the acrylic adhesive composition in example 3, a solution of acrylic polymer P3 was used instead of a solution of acrylic polymer P2. An acrylic pressure-sensitive adhesive composition of this example was prepared in the same manner as in the preparation of the acrylic pressure-sensitive adhesive composition of example 3, and a pressure-sensitive adhesive sheet (a base-free double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) of this example was produced in the same manner as in example 1 using the obtained acrylic pressure-sensitive adhesive composition.

< example 8 >

A solution of acrylic polymer P4 was prepared in the same manner as in the preparation of the acrylic polymer solution in example 2, except that the composition of the monomer components was changed to 99 parts BZA and 1 part Acrylic Acid (AA). The Mw of the acrylic polymer P4 was 100 tens of thousands.

The solution of the acrylic polymer P4 (polymer concentration: 50%) was diluted to a polymer concentration of 30% with ethyl acetate, and 0.1 part of an epoxy-based crosslinking agent (trade name "tetra C", manufactured by mitsubishi gas chemical company, 1, 3-bis (N, -diglycidyl aminomethyl) cyclohexane) was added to 334 parts (nonvolatile matter: 100 parts) of the solution and stirred and mixed, thereby preparing the acrylic adhesive composition of this example.

An adhesive sheet of this example (a base-free double-sided adhesive sheet composed of an adhesive layer) was produced in the same manner as in the production of the adhesive sheet of example 1, except that the obtained acrylic adhesive composition was used.

< examples 9 to 12 >, respectively

In the preparation of the acrylic adhesive composition of example 8, 60 parts of POB-ase:Sub>A (example 9) as plasticizer A1, 60 parts of 4,4' -oxybis [ (methoxymethyl) benzene ] (manufactured by tokyo chemical industry company, refractive index: 1.56, liquid at 20 ℃) and 60 parts of 3-phenoxybenzyl alcohol (manufactured by tokyo chemical industry company, refractive index: 1.591, liquid at 20 ℃) as plasticizer ase:Sub>A 3 were further added to 100 parts of the nonvolatile component contained in the solution of acrylic polymer P4 (example 11) or 60 parts of 1-naphtalenethione (manufactured by tokyo chemical industry company, refractive index: 1.63, liquid at 20 ℃) as plasticizer ase:Sub>A 4, respectively, the acrylic adhesive compositions of examples were prepared in the same manner as the preparation of the acrylic adhesive composition of example 8. Adhesive sheets of each example (substrate-free double-sided adhesive sheets composed of an adhesive layer) were produced in the same manner as in the production of the adhesive sheet of example 1, except that the obtained acrylic adhesive compositions were used.

< example 13 >

A solution of acrylic polymer P5 was prepared in the same manner as in the preparation of the acrylic polymer solution in example 2, except that the composition of the monomer components was changed to 90 parts BZA, 9 parts n-Butyl Acrylate (BA) and 1 part AA. The Mw of the acrylic polymer P5 was 100 ten thousand.

The acrylic pressure-sensitive adhesive composition of this example was prepared by diluting a solution of the acrylic polymer P5 (polymer concentration: 50%) to a polymer concentration of 30% with ethyl acetate, adding 60 parts of the plasticizer A3 (POB-AL) and 0.1 part of the epoxy-based crosslinking agent to 334 parts (nonvolatile matter: 100 parts) of the solution, and mixing with stirring.

< example 14 >

An acrylic adhesive composition of this example was prepared in the same manner as in the preparation of the acrylic adhesive composition of example 13 except that 15 parts by solid content of biscresolfluorene (9, 9-bis (4-hydroxy-3-methylphenyl) fluorene manufactured by osaka gas chemical company, refractive index: 1.68. Or below, sometimes referred to as "BCF") was further added as an additive to 100 parts by weight of the nonvolatile component contained in the solution of acrylic polymer P5. The above additives were added in the form of a 10% ethyl acetate solution.

< examples 15 to 16 >, respectively

A solution of acrylic polymer P6 was prepared in the same manner as in the preparation of the acrylic polymer solution in example 2, except that the composition of the monomer components was changed to 90 parts BZA, 9 parts 2-ethylhexyl acrylate (2 EHA), and 1 part AA. The Mw of the acrylic polymer P6 was 100 ten thousand.

In the preparation of the acrylic adhesive compositions in examples 13 to 14, a solution of the acrylic polymer P6 was used instead of the solution of the acrylic polymer P5. The acrylic pressure-sensitive adhesive compositions of examples 15 to 16 were prepared in the same manner as in the preparation of the acrylic pressure-sensitive adhesive compositions of examples 13 to 14, and pressure-sensitive adhesive sheets (base-free double-sided pressure-sensitive adhesive sheets composed of a pressure-sensitive adhesive layer) of examples were prepared using the obtained acrylic pressure-sensitive adhesive compositions in the same manner as in example 1.

< examples 17 to 18 >

A solution of acrylic polymer P7 was prepared in the same manner as in the preparation of the acrylic polymer solution in example 2, except that the composition of the monomer components was changed to 80 parts BZA, 19 parts BA and 1 part AA. In addition, a solution of acrylic polymer P8 was prepared in the same manner as in the preparation of the acrylic polymer solution in example 2, except that the composition of the monomer components was changed to 66 parts BZA, 33 parts BA and 1 part AA. The Mw of the acrylic polymers P7, P8 was 100 tens of thousands.

In the preparation of the acrylic adhesive composition in example 13, a solution of acrylic polymer P7 (example 17) or P8 (example 18) was used instead of the solution of acrylic polymer P5. The acrylic pressure-sensitive adhesive compositions of examples 17 to 18 were prepared in the same manner as in the preparation of the acrylic pressure-sensitive adhesive composition of example 13, and pressure-sensitive adhesive sheets (base-free double-sided pressure-sensitive adhesive sheets composed of a pressure-sensitive adhesive layer) of examples were prepared in the same manner as in example 1 using the obtained acrylic pressure-sensitive adhesive compositions.

< example 19 >

In addition to changing the composition of the monomer components to 85 parts POB-A, 14 parts BA, and 1 part AA, a solution of acrylic polymer P9 was prepared by the same operation as the preparation of acrylic polymer solution in Example 2. The Mw of acrylic polymer P9 is 1 million.

In the preparation of the acrylic adhesive composition in example 13, a solution of acrylic polymer P9 was used instead of a solution of acrylic polymer P5. An acrylic pressure-sensitive adhesive composition of this example was prepared in the same manner as in the preparation of the acrylic pressure-sensitive adhesive composition of example 13, and a pressure-sensitive adhesive sheet (a base-free double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) of this example was prepared in the same manner as in example 1 using the obtained acrylic pressure-sensitive adhesive composition.

< example 20 >

In the preparation of the acrylic pressure-sensitive adhesive composition in example 19, 23 parts of 6-acryloxymethyldinaphthiophene (trade name "6MDNTA" manufactured by SUGAI chemical industry co., and dinaphthiophene-6-methyl acrylate, refractive index 1.75. Hereinafter, sometimes referred to as "6 MDNTA") was further added as an additive to 100 parts of the nonvolatile component contained in the solution of the acrylic polymer P9. An acrylic pressure-sensitive adhesive composition of this example was prepared in the same manner as in the preparation of the acrylic pressure-sensitive adhesive composition of example 19, and a pressure-sensitive adhesive sheet (a base-free double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) of this example was prepared in the same manner as in example 1 using the obtained acrylic pressure-sensitive adhesive composition. The above additives were added in the form of a 10% ethyl acetate solution.

< examples 21 to 22 >, respectively

In addition to changing the composition of the monomer components to 80 parts POB-A, 19 parts BA, and 1 part AA, a solution of acrylic polymer P10 was prepared by the same operation as the preparation of acrylic polymer solution in Example 2. The Mw of acrylic polymer P10 is 1 million.

In the preparation of the acrylic adhesive composition in example 13, a solution of acrylic polymer P10 was used instead of a solution of acrylic polymer P5. The acrylic adhesive composition of example 21 was prepared in the same manner as the preparation of the acrylic adhesive composition of example 13. In addition, in the preparation of the acrylic adhesive composition of example 21, the amount of the epoxy-based crosslinking agent used was changed to 0.5 part per 100 parts of the nonvolatile component contained in the solution of the acrylic polymer P10, thereby preparing the acrylic adhesive composition of example 22.

Using the obtained acrylic pressure-sensitive adhesive compositions, pressure-sensitive adhesive sheets (base-free double-sided pressure-sensitive adhesive sheets composed of a pressure-sensitive adhesive layer) of each example were produced in the same manner as in example 1.

< example 23 >

An acrylic polymer P11 solution was prepared in the same manner as in example 1 except that the composition of the monomer components was changed to 99 parts of POB-A and 1 part of 2-acryloyloxyethyl succinic acid (trade name "HOA-MS (N)", hereinafter referred to as "HOA-MS"). The Mw of the acrylic polymer P11 was 50 ten thousand.

To 334 parts (nonvolatile matter 100 parts) of this solution, 40 parts of the plasticizer A3 (POB-AL), 20 parts of trimethylpentaphenyl trisiloxane (trade name "HIVACF-5", manufactured by the shin-Etsu chemical industry Co., ltd., molecular weight: 546, refractive index: 1.575, liquid at 20 ℃) and 0.3 part of the epoxy-based crosslinking agent (hereinafter, also referred to as a crosslinking agent C1.) were added and mixed with stirring, thereby preparing an acrylic adhesive composition of this example.

< example 24 >

In addition to changing the composition of the monomer components to 95 parts POB-A, 2 parts lauryl acrylate (LA), 2 parts 2EHA, and 1 part 4HBA, the solution of acrylic polymer P12 was prepared by the same operation as the preparation of acrylic polymer solution in Example 23. The Mw of acrylic polymer P12 is 500000.

The acrylic adhesive composition of this example was prepared by diluting a solution of the acrylic polymer P12 to a polymer concentration of 30% with ethyl acetate, adding 40 parts of the plasticizer A3 (POB-AL), 20 parts of the plasticizer A5 (HIVAC F-5), 0.3 part of a non-cyclic difunctional isocyanate-based crosslinking agent (trade name "Coronate2770", manufactured by eason corporation), hexamethylene Diisocyanate (HDI) allophanate), 2 parts of acetylacetone as a crosslinking retarder, and 1 part (nonvolatile 0.01 part) of a 1% ethyl acetate solution of iron acetylacetonate as a crosslinking catalyst to 334 parts of the solution (nonvolatile 100 parts) and mixing them with stirring.

< example 25 >

In addition to changing the composition of the monomer components to 90 parts POB-A, 9 parts 2EHA, and 1 part 4HBA, a solution of acrylic polymer P13 was prepared by the same operation as the preparation of acrylic polymer solution in Example 23. The Mw of acrylic polymer P13 is 500000.

The acrylic adhesive composition of this example was prepared by diluting a solution of the acrylic polymer P13 to a polymer concentration of 30% with ethyl acetate, adding 80 parts of the plasticizer A5 (HIVAC F-5), 0.5 part of the crosslinking agent C2 (corona 2770), 2 parts of acetylacetone as a crosslinking retarder, and 1 part (nonvolatile content 0.01 part) of a 1% ethyl acetate solution of iron acetylacetonate as a crosslinking catalyst to 334 parts (nonvolatile content 100 parts) of the solution, and mixing with stirring.

< examples 26 to 28 >

Solutions of acrylic polymers P14 and P15 were prepared respectively in the same manner as in the preparation of the acrylic polymer solution in example 23, except that the composition of the monomer components was changed as shown in table 3. The Mw of acrylic polymers P14 and P15 were 50 ten thousand, respectively.

The acrylic adhesive compositions of each example were prepared by diluting a solution of the acrylic polymer P11, P14 or P15 to a polymer concentration of 30% with ethyl acetate, adding the plasticizer A3 and the crosslinking agent C1 or C2 as shown in table 3 to 334 parts (nonvolatile matter 100 parts), further adding 2 parts of acetylacetone as a crosslinking retarder to examples 26 and 28, and 1 part (nonvolatile matter 0.01 part) of a 1% ethyl acetate solution of iron acetylacetonate as a crosslinking catalyst, and mixing with stirring.

Adhesive sheets of each example (substrate-free double-sided adhesive sheets composed of an adhesive layer) were produced in the same manner as in the production of the adhesive sheet of example 1, except that the obtained acrylic adhesive composition was used.

< evaluation method >)

(refractive index)

For each adhesive layer (substrate-free double-sided adhesive sheet), the refractive index was measured using an Abbe refractometer (model "DR-M4" manufactured by ATAGO Co., ltd.) at a measurement wavelength of 589nm and a measurement temperature of 25 ℃.

(storage modulus G' and glass transition temperature)

The adhesive layers of each example were laminated to prepare a laminate having a thickness of about 1.5mm as a sample for measurement. Dynamic viscoelasticity was measured using "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific company under the following conditions. The storage modulus G' [ Pa ] of the adhesive at each temperature (-20 ℃, -10 ℃, 0 ℃ and 80 ℃) was determined from the measurement results. The temperature corresponding to the peak top temperature of the loss tangent tan δ (loss modulus G "/storage modulus G') in the dynamic viscoelasticity measurement was obtained as the glass transition temperature (Tg) [ °c ] of the adhesive.

[ measurement conditions ]

Deformation mode: torsion

Measuring frequency: 1Hz

Temperature range: -50-150 DEG C

Heating rate: 5 ℃/min

Shape: parallel plates 7.9mm phi

(total light transmittance and haze)

The total light transmittance and haze of the test pieces were measured using a haze meter (HM-150 manufactured by color technology research, village) in a measuring environment at 23℃using test pieces obtained by bonding the adhesive layers of each example to alkali-free glass (thickness: 0.8mm to 1.0mm, total light transmittance: 92%, and haze: 0.4%). The total transmittance and haze of the alkali-free glass were subtracted from the measured values to obtain the total transmittance [% ] and haze [% ] of the adhesive (layer). For the substrate-less adhesive sheet composed of the above adhesive layer, the total light transmittance [% ] and the haze [% ] of the adhesive layer are the total light transmittance [% ] and the haze [% ] of the adhesive sheet.

(peel Strength to glass plate)

The release liner was peeled off from one surface of the pressure-sensitive adhesive sheet at 23℃under a measurement environment of 50% RH, and a PET film having a thickness of 50 μm was bonded to the release liner and was backed, followed by cutting into a size of 25mm in width and 100mm in length, and the resulting film was used as a test piece. The other release liner was peeled off from the test piece, and the test piece was pressed against the surface of an alkali glass plate (manufactured by Song Nitro industries Co., ltd., thickness: 1.35mm, green plate edge polished) as an adherend by reciprocating a 2kg roller 1 time. It was left under this environment for 30 minutes, and then, using a universal tensile compression tester, it was prepared according to JIS Z0237: 2000, peel strength (adhesive strength) [ N/25mm ] was measured under conditions of a pulling speed of 300 mm/min and a peeling angle of 180 degrees. As a universal tensile compression tester, "tensile compression tester, TG-1kN" manufactured by Meibuya Co., ltd. In the case of the single-sided adhesive sheet with a substrate, the backing of the PET film is not essential.

(bending test)

The pressure-sensitive adhesive sheets with release liners of each example were cut into a rectangular shape of 2cm×10cm, and test pieces for measurement were obtained. A cylindrical rod of 4mm in diameter was fixed at a height sufficient for measurement, and the test piece obtained above was placed on the rod and bent. Specifically, the test piece was formed into an inverted U shape by hanging the center portion in the longitudinal direction on a rod. Then, both ends located below the test piece were fixed with clamps (13 g), and a 60g weight was suspended and fixed on the clamps with a 1cm long wire, thereby applying a load to the bent portion of the test piece. In this state, the test piece was kept at a prescribed temperature environment (-20 ℃, -10 ℃ or 0 ℃) for 1 minute, and then the test piece was removed from the rod. Then, the test piece was allowed to stand on a horizontal plane in such a manner that the convex side of the bent portion thereof was downward in this temperature environment for 10 minutes. The time until the end (short side end) of the test piece after standing for 10 minutes was brought into contact with the horizontal surface was measured. The tests were carried out at-20 ℃, -10 ℃ and 0 ℃ respectively, and softness was evaluated according to the following criteria.

E (Excellent excelent): in all temperature conditions (-20 ℃, -10 ℃ and 0 ℃) of the bending test, the end of the test piece was in contact with the horizontal plane within 10 minutes.

G (Good): in the bending test at-10 ℃ and 0 ℃, the end of the test piece is in contact with the horizontal plane within 10 minutes.

A (Acceptable accept): in a bending test under a temperature condition of 0 ℃, the end of the test piece is in contact with a horizontal plane within 10 minutes.

P (difference pool): in the bending test under all temperature conditions, the end of the test piece was not in contact with the horizontal plane or the adhesive layer was peeled from the release liner within 10 minutes.

The summary and evaluation results of the adhesives of each example are shown in tables 1 to 3.

As shown in tables 1 to 3, examples 3 to 5, example 7, and examples 9 to 28 were able to form a polymer having a refractive index of 1.55 or more and a storage modulus G' (0 ℃ C.) of 1.0X10 ⁶ An adhesive having Pa or less, that is, an adhesive having a high refractive index and a low modulus of elasticity, examples 3 to 5, 7, and 9 to 28 used an adhesive composition comprising an acrylic polymer obtained by polymerization using the aromatic ring-containing monomer (A1) and a compound having two or more double bond rings as a plasticizer and being liquid at 30 ℃. The adhesive sheets of these examples were all acceptable in the results of the bending test (A or more). On the other hand, in examples 1 to 2, examples 6 and 8, an adhesive having a high refractive index can be formed by using an acrylic polymer comprising the aromatic ring-containing monomer (A1) as a monomer unit, but the storage modulus G' (0 ℃) is more than 1.0X10 ⁶ Pa, does not have a low elastic modulus. The adhesive sheets of these examples were found to be unacceptable (P) as a result of the bending test.

More specifically, as is clear from the results of examples 3 to 5, by increasing the amount of the plasticizer, it is possible to produce an adhesive having a lower elastic modulus with a lower storage modulus G' at each temperature while maintaining a high refractive index. From these results, examples 9 to 12 show that the use of a compound having two or more double bond-containing rings and being liquid at 30 ℃ as a plasticizer can achieve both high refractive index and low elastic modulus. Examples 13 to 16 and example 20 are the results of investigation of additives, and it is found that higher refractive index can be achieved by using various additives. Further, as is clear from a comparison of examples 13 and 15, by selecting the type of the alkyl (meth) acrylate as the monomer component, it is possible to adjust the adhesive such as to increase the storage modulus G' in a high temperature region while making the adhesive low in elastic modulus. Examples 17 to 18 are examples in which the use ratio of the aromatic ring-containing monomer (A1) was changed, and it was found that the refractive index could be maintained high even if the amount of the aromatic ring-containing monomer (A1) used was limited. In examples 17 to 18, the difference in storage modulus G' between the low temperature region and the high temperature region was more suppressed. It is considered that the aromatic ring-containing monomer (A1) is reduced and increased, and the alkyl (meth) acrylate (specifically BA) is increased. Examples 21 to 22 are examples in which the amount of the crosslinking agent was changed, and it was found that the storage modulus G' could be improved by increasing the amount of the crosslinking agent. Examples 23 to 28 are examples in which the monomer composition of the polymer, the type of plasticizer, the type of crosslinking agent, and/or the use ratio of each component are changed, and it is known that the storage modulus of the adhesive can be adjusted to a desired range while maintaining a high refractive index by adjusting the monomer composition of the acrylic polymer, selecting the type of plasticizer, adjusting the amount of plasticizer used, and the like to design the adhesive composition.

Specific examples of the present invention have been described in detail above, but they are merely illustrative, and do not limit the claims. The technology described in the claims includes various modifications and changes to the specific examples illustrated above.

Description of the reference numerals

1. 2, 3 pressure-sensitive adhesive sheet

10. Support substrate

10A first side

10B second side

21. An adhesive layer, a first adhesive layer

21A adhesive side, first adhesive side

21B adhesive surface

22. Second adhesive layer

22A second adhesive side

31. 32 release liner

Claims

1. An adhesive composition, wherein the adhesive composition comprises an acrylic polymer and a plasticizer,

2. The adhesive composition of claim 1, wherein the compound is a compound that is liquid at 20 ℃.

3. The adhesive composition according to claim 1 or 2, wherein the adhesive composition contains more than 15 parts by weight of the plasticizer with respect to 100 parts by weight of the acrylic polymer.

4. The adhesive composition according to any one of claims 1 to 3, wherein the adhesive composition contains more than 30 parts by weight of the plasticizer with respect to 100 parts by weight of the acrylic polymer.

5. The adhesive composition according to any one of claims 1 to 4, wherein the plasticizer has at least one ring selected from aromatic rings and heterocyclic rings as the double bond-containing ring.

6. The adhesive composition of any of claims 1-5, wherein the plasticizer has a first double bond-containing ring and a second double bond-containing ring, the first double bond-containing ring and the second double bond-containing ring being connected via a linking group having 1-5 atoms.

7. The adhesive composition of any of claims 1-6, wherein the plasticizer has a molecular weight in the range of 100-2000.

8. The adhesive composition according to any one of claims 1 to 7, wherein a monomer component constituting the acrylic polymer contains a monomer (A2) in addition to the aromatic ring-containing monomer (A1), the monomer (A2) having at least one of a hydroxyl group and a carboxyl group.

9. The adhesive composition according to any one of claims 1 to 8, wherein the aromatic ring-containing monomer (A1) is contained in the monomer component in an amount of 60% by weight or more.

10. An adhesive sheet, wherein the adhesive sheet comprises an adhesive layer formed of the adhesive composition according to any one of claims 1 to 9.