JP7426608B2 - photocurable composition - Google Patents

Description

The present invention relates to photocurable compositions.

Optically transparent adhesives are used for bonding constituent members such as cover lenses of displays, for example, for the purpose of improving the visibility of display devices such as liquid crystal displays and organic EL displays. In recent years, there has been an increasing trend in the use of not only conventional flat displays but also curved displays, particularly in in-vehicle displays and digital signage, due to their design characteristics. Furthermore, for the curved member, resin materials such as polycarbonate and acrylic are likely to be used instead of glass, which has been widely used in the past, due to ease of processing. These resin materials have a large difference in thermal expansion compared to glass substrates used in liquid crystal display panels. Therefore, the adhesive for bonding the resin material and the glass substrate is required to have enough flexibility to absorb the stress applied to the base material due to the difference in thermal expansion between them.

As adhesives having such transparency, there are compositions that use radical species as reactive species, which have been widely used in the past, but compositions that use anion species as reactive species are attracting attention. The reasons for this are that compositions containing anionic species as reactive species shrink less during curing than compositions containing cationic species as reactive species, do not inhibit curing due to oxygen or moisture, and cure. One example of this is that corrosion and yellowing caused by the reaction initiator are less likely to occur on objects and surrounding components.

For example, the display encapsulant described in Patent Document 1 is used as an adhesive for electronic components that can be applied to flexible displays and curved displays.

JP2019-82598A

However, the cured product obtained by curing the display sealant described in Patent Document 1 has a high elastic modulus of 74 MPa to 565 MPa. For this reason, it is not possible to follow the difference in thermal expansion between the resin material and the glass substrate of the display, which may cause peeling or cracking. In addition, heating at 120° C. is required for curing, making it difficult to apply to bonding resin materials with low heat resistance. As described above, the composition is required to have excellent curability, have a low elastic modulus, and form a flexible cured product.

An object of the present invention is to provide a photocurable composition that has excellent curability and can form a cured product with excellent flexibility.

The photocurable composition of the present invention is
(A) Component: (meth)acrylic acid ester copolymer having an epoxy group in the copolymer structure,
(B) component: a compound having two or more thiol groups in one molecule,
(C) component: a photobase generator, and (D) component: containing a reactive diluent,
The copolymer is a polymer obtained by polymerizing two or more types of (meth)acrylic acid ester compounds, and the two or more types of (meth)acrylic acid ester compounds are the two or more types of (meth)acrylic acid ester compounds. Contains 3 to 10 parts by mass of a (meth)acrylic acid ester compound having an epoxy group in the side chain based on 100 parts by mass of the ester compound,
The epoxy equivalent of the copolymer is 1,000 g/eq to 3,000 g/eq,
The weight average molecular weight of the copolymer is 5,000 to 500,000,
It is characterized by containing 2 to 7 parts by mass of the component (C) based on a total of 100 parts by mass of the component (A), the component (B), the component (C), and the component (D).

The photocurable composition of the present invention has excellent curability and can form a cured product with excellent flexibility.

Embodiments of the present invention will be specifically described below. The present invention is not limited to such embodiments. The present invention can be implemented with appropriate modifications within the scope of the purpose of the present invention.
The photocurable composition will be described in detail below.

<Photocurable composition>
The photocurable composition according to the embodiment of the present invention is
(A) Component: (meth)acrylic acid ester copolymer having an epoxy group in the copolymer structure,
(B) component: a compound having two or more thiol groups in one molecule,
(C) component: a photobase generator, and (D) component: containing a reactive diluent,
The copolymer is a polymer obtained by polymerizing two or more types of (meth)acrylic acid ester compounds, and the two or more types of (meth)acrylic acid ester compounds are the two or more types of (meth)acrylic acid ester compounds. Contains 3 to 10 parts by mass of a (meth)acrylic acid ester compound having an epoxy group in the side chain based on 100 parts by mass of the ester compound,
The epoxy equivalent of the copolymer is 1,000 g/eq to 3,000 g/eq,
The weight average molecular weight of the copolymer is 5,000 to 500,000,
It is characterized by containing 2 to 7 parts by mass of the component (C) based on a total of 100 parts by mass of the component (A), the component (B), the component (C), and the component (D).
In addition to the above-mentioned (A) component, (B) component, (C) component, and (D) component, the photocurable composition according to the present embodiment also has the curability of the photocurable composition and the cured product thereof. Other components such as various additives may be blended within a range that does not impair flexibility. Examples of additives include antioxidants and the like.

The photocurable composition according to this embodiment can form a cured product with excellent curability and flexibility. The reason for this is thought to be as follows. When the photocurable composition is irradiated with active energy rays, component (C) decomposes and a base is generated. The generated base reacts with the thiol group of component (B). This reaction produces reactive species (thiolate anions) derived from the thiol group of component (B). The reactive species (thiolate anion) reacts with the epoxy group of component (A). A cured product is obtained by this reaction. In the photocurable composition according to the present embodiment, since the component (A) is a (meth)acrylic acid ester copolymer having a flexible structure, the components (A) and (B) are resistant to active energy rays. Flexibility can be imparted to a cured product obtained by reacting with a base generated by decomposition of component (C) by irradiation as a reaction initiator. Note that the flexibility of the cured product can be confirmed by the storage modulus of the cured product. A method for measuring the storage modulus of a cured product will be explained in Examples.

Examples of active energy rays include ultraviolet rays (UV), electron beams, alpha rays, and beta rays, and specifically ultraviolet rays.

Irradiation with active energy rays is not particularly limited, and may be performed, for example, at a temperature of 20° C. or higher and 30° C. or lower.

The curing reaction after irradiation with active energy rays is not particularly limited, but can be performed, for example, at room temperature or higher, specifically at 20°C or higher and 80°C or lower, more specifically at 40°C or higher and 60°C or lower. obtain.

Each component will be explained in detail below.
[Component (A): (meth)acrylic acid ester copolymer containing epoxy groups in the copolymer structure]
The compound of component (A) is a copolymer of two or more types of (meth)acrylic acid ester compounds. The copolymer contains repeating units derived from two or more types of (meth)acrylic ester compounds, and a certain proportion of repeating units derived from (meth)acrylic ester compounds having an epoxy group in the side chain (hereinafter referred to as " (sometimes referred to as "side chain repeating unit"). That is, the copolymer has a side chain structure derived from a (meth)acrylic acid ester compound having an epoxy group in the side chain. The side chain repeating unit has the general formula (1):
-[ _CH2 -C( ^R2 )(COO- ^R1 )]-...(1)
[In general formula (1), R ¹ represents an epoxy group, and R ² represents a hydrogen atom or a methyl group]
It can be expressed as In this way, in the side chain repeating unit, the epoxy group is bonded to the ether oxygen of the part derived from the (meth)acryloxy group.

The above-mentioned fixed ratio is described in terms of the weight ratio of the monomers forming the copolymer. Specifically, the two or more types of (meth)acrylic ester compounds include a (meth)acrylic ester compound having an epoxy group in the side chain based on 100 parts by mass of the two or more types of (meth)acrylic ester compounds. It contains 3 to 10 parts by weight, preferably 5 to 10 parts by weight. The weight ratio of the monomers can be calculated from the blending ratio (weight ratio) of the monomers used to synthesize the copolymer. Alternatively, the (meth)acrylic material blended into the photocurable composition as a photocurable material (that is, the copolymer of component (A) contained in the photocurable composition) is determined by nuclear magnetic resonance spectroscopy. It can also be calculated from the ratio of the number of protons derived from the ester side chains of the acid ester compound.
The above-mentioned fixed proportions can also be described in molar ratios of repeating units. That is, it contains 3 to 13 moles, preferably 7 to 13 moles, of side chain repeating units per 100 moles of repeating units derived from two or more types of (meth)acrylic acid ester compounds.

When the weight ratio of the compound of component (A) is within the above range, it is possible to achieve both good curability and flexibility. On the other hand, if the weight ratio is too small (for example, less than 3 parts by mass), the photocurable composition will not be cured or will take an extremely long time, for example 2 hours or more, to cure. In other words, the curability of the photocurable composition decreases. Moreover, when the weight ratio is too large (for example, when it exceeds 10 parts by mass), specifically, the structure of the copolymer becomes rigid, and the flexibility of the copolymer itself decreases. As a result, the flexibility of the cured product obtained from the photocurable composition decreases.

The compound of component (A) has at least one member selected from the group consisting of an aliphatic structure and an aromatic structure bonded to the side chain, in addition to the (meth)acrylic acid ester compound having an epoxy group in the side chain. The monomer may be a (meth)acrylic acid ester compound having the above structure, styrene, (meth)acrylic acid amide, or maleimide. More preferably, it has a structure in which at least one selected from the group consisting of an aliphatic structure and an aromatic structure is bonded to a side chain.

The above-mentioned "(meth)acrylic acid ester compound having an epoxy group in the side chain" is not particularly limited, and examples thereof include glycidyl acrylate, glycidyl methacrylate, and 4-hydroxybutyl acrylate glycidyl ether.

The above-mentioned "aliphatic structure" is not particularly limited, but includes, for example, an aliphatic hydrocarbon group and an aliphatic ether group.

Examples of the above-mentioned "aliphatic hydrocarbon group" include hydrocarbon groups having 1 to 20 carbon atoms, specifically, 5 to 20 carbon atoms. In this specification, the term "hydrocarbon group" refers to a hydrocarbon group consisting of carbon atoms and hydrogen atoms, and refers to a group obtained by removing one or more hydrogen atoms from a hydrocarbon.

The above-mentioned "aliphatic ether group" is a structure having an oxygen atom within the structure or at the end of the aliphatic hydrocarbon group. Examples of the aliphatic ether group include a structure having an ethylene oxide group within the structure of an aliphatic hydrocarbon group or at a terminal portion thereof. The number of the ethylene oxide groups contained in the aliphatic ether group is, for example, 1 or more and 14 or less, specifically 1 or more and 9 or less.

The above-mentioned "aromatic structure" is not particularly limited as long as it contains an aromatic ring (more specifically, a benzene ring, etc.), and examples thereof include benzyl, phenoxyethyl, and phenoxydiethylene glycol.

The weight average molecular weight (Mw) of the copolymer is 5,000 to 500,000, preferably 10,000 to 300,000, more preferably 100,000 to 250,000. When the weight average molecular weight of the copolymer is within the above range, the photocurable composition according to this embodiment can have an appropriate viscosity. On the other hand, if the weight average molecular weight of the copolymer is too small (for example, less than 5,000), the resulting cured product will have reduced flexibility. In addition, if the weight average molecular weight of the copolymer is too large (for example, exceeding 500,000), the viscosity of the photocurable composition becomes too high, or the component (A) takes a gel-like form. The compatibility between component (A) and other components deteriorates.

The epoxy equivalent of the copolymer is 1,000 g/eq to 3,000 g/eq, preferably 1,200 g/eq to 3,000 g/eq, more preferably 1,400 g/eq to 2,900 g /eq. On the other hand, if the epoxy equivalent of the copolymer is too small (for example, less than 1,000 g/eq), the proportion of epoxy groups contained in the copolymer of component (A) is high, resulting in a high crosslinking density. , the resulting cured product becomes rigid and has reduced flexibility. In addition, if the epoxy equivalent of the copolymer is too large (for example, exceeding 3,000 g/eq), the proportion of epoxy groups contained in the copolymer of component (A) is small, making it difficult to crosslink and photocuring. The curability of the composition decreases. The epoxy equivalent of the copolymer can be measured using an automatic titrator ("COM-1750" manufactured by Hiranuma Sangyo Co., Ltd.) according to the method described in Japanese Industrial Standards (JIS) K7236:2001.

The photocurable composition according to the present embodiment preferably contains 10 parts by mass or more of component (A) based on 100 parts of the total mass of component (A), component (B), component (C), and component (D). It may be contained in a range of less than 60 parts by mass, more preferably 20 parts by mass or more and less than 50 parts by mass.

By containing component (A) in the above range, in the photocurable composition, a cured product of the photocurable composition obtained after irradiating the photocurable composition with an active energy ray and heating it can have flexibility. Note that "flexibility" means a state in which the cured product does not break even when it is bent or stretched, and can be quantitatively evaluated by measuring the viscoelasticity of the cured product.

[Component (B): compound having two or more thiol groups in one molecule]
The compound of component (B) is a compound that reacts by anionic polymerization, and is a compound that can contribute to curing of the photocurable composition. The compound of component (B) is not particularly limited as long as it has a thiol group in one molecule.

The compound of component (B) has, for example, 2 or more thiol groups in one molecule, preferably 2 to 6 thiol groups, more preferably 3 to 6 thiol groups, and still more preferably 3 to 4 thiol groups. .

The compound of component (B) preferably contains a thiol group in its molecular structure and further contains an ester bond in its molecular structure.

The compound (B) which further contains an ester bond in its molecular structure is not particularly limited, but includes, for example, pentaerythritol tetrakis (3-mercaptobutyrate), 1,4-bis(3-mercaptobutyrate), -mercaptobutyryloxy)butane, and 1,3,5-tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinane-2,4,6-trione.

In the compound of component (B), the thiol group is preferably a secondary thiol group. A secondary thiol group refers to a structure in which a thiol group is bonded to a secondary carbon atom, and specifically refers to CH ₃ CH(SH)-.

Among the compounds of component (B), from the viewpoint of improving reactivity, pentaerythritol tetrakis (3-mercaptobutyrate) and 1,4-bis(3-mercaptobutyryloxy)butane are preferably used.

In the photocurable composition according to this embodiment, preferably 15 parts of component (B) is added to 100 parts by mass of the total mass of component (A), component (B), component (C), and component (D). It is contained in a range of at least 20 parts by mass and less than 37 parts by mass, more preferably at least 20 parts by mass and less than 37 parts by mass.

By containing component (B) in the above range, the photocurable composition can be cured better.

If the content of component (B) becomes too large, unreacted thiol groups or unreacted component (B) may remain in the cured product obtained by curing the photocurable composition. In such a case, the cured product may deteriorate over time or unreacted component (B) may ooze out.

[Component (C): Photobase generator]
Component (C) is a compound that decomposes and generates a base upon irradiation with active energy rays. The base generated from component (C) extracts hydrogen from the compound of component (B), specifically the thiol group contained in component (B), and reacts with the epoxy group contained in the compound of component (A). .

The component (C) is latent to active energy rays (e.g., light, specifically, ultraviolet rays), that is, it irradiates with active energy rays (e.g., light, specifically, ultraviolet rays). It is a compound that generates a base when activated, and it is a compound that does not generate an anion in the absence of active energy. By using such a compound, the polymerization reaction does not proceed during storage, and the viscosity of the photocurable composition is less likely to increase.

Component (C) may preferably contain at least one selected from the group consisting of a carboxylate having either a xanthone skeleton or a ketoprofen skeleton, a salt containing a borate anion, and a carbamate compound.

Examples of carboxylic acid salts having a xanthone skeleton include 2-(9-oxoxanthen-2-yl)propionic acid 1,5,7-triazabicyclo[4.4.0]dec-5-ene, and -(9-oxoxanthene-2-yl)propionic acid 1,8-diazabicyclo[5.4.0]undec-7-ene and the like.

Examples of carboxylic acid salts having a ketoprofen skeleton include 1,2-disopropyl-3-[bis(dimethylamino)methylene]guanidinium 2-(3-benzoylphenyl)propinate, and 1,8-diazabicyclo[5.4. 0]undec-7-ene 2-(3-benzoylphenyl)propinate and the like.

Examples of the salt containing a borate anion include 1,2-dicyclohexyl-4,4,5,5-tetramethyldiguadium n-butyltriphenylborate. Examples of carbamate compounds include (2-nitrophenyl)methyl 4-(methacryloyloxy)piperidine-1-carboxylate and 2-nitrobenzyl cyclohexylcarbamate.

In one embodiment, component (C) contains one or more of a carboxylate having a xanthone skeleton, a carboxylate having a ketoprofen skeleton, and a salt containing a borate anion.
In the above embodiment, it is preferable to use a compound capable of generating a strong base such as amidine, guanidine, or phosphazene base as component (C). When such a compound is used, hydrogen is extracted from the compound of component (B) by the base generated by the decomposition of component (C), and reacts with the epoxy group derived from the compound of component (A). Because the base generated is a strong base, the above reaction can proceed particularly quickly. As a result, the photocurable composition can be cured particularly well.

As the component (C), for example, (2-(9-oxoanthene-2-yl)propionic acid 1,5,7-triazabicyclo[4,4,0]dec-5-ene)), 2- (9-oxoxanthen-2-yl)propionic acid 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,2-dicyclohexyl-4,4,5,5-tetramethyldiguadium n -butyltriphenylborate, 1,2-disopropyl-3-[bis(dimethylamino)methylene]guanidium 2-(3-benzoylphenyl)propinate, and the like. Since the base generated by these compounds is a strong base, the curing reaction of the photocurable composition can proceed favorably.

In the photocurable composition according to the present embodiment, preferably 1 part of component (C) is added to 100 parts by mass of the total mass of component (A), component (B), component (C), and component (D). It is contained in a range of at least 3 parts by mass and less than 10 parts by mass, more preferably at least 3 parts by mass and less than 7 parts by mass.

By containing component (C) in the above range, the curing reaction of the photocurable composition can proceed favorably. If the content of component (C) is too low, the amount of base generated by light irradiation may be small and may be insufficient to cure the photocurable composition.

If the content of component (C) becomes too high, a large amount of free base may be present in the photocurable composition. In such a case, the storage stability of the photocurable composition may be impaired. Moreover, when component (C) is solid, specifically powdered, it may not dissolve in components other than component (C).

[Component (D): Reactive diluent]
The compound of component (D) is a compound that reacts with an anion generated from a thiol group through a reaction with a base generated by decomposition of component (C) by irradiation with active energy rays, and is useful for adjusting the viscosity of a photocurable composition. It is a compound that can contribute. The compound of component (D) is not particularly limited as long as it is a compound having an epoxy group, vinyl group or acryloyl group in one molecule.

The compound of component (D) has, for example, one to two, preferably one, epoxy group or vinyl group in one molecule.

The compound of component (D) preferably does not contain a hydroxyl group or a carboxylic acid group in its molecular structure.

The compound of component (D) is not particularly limited, but includes, for example, aliphatic glycidyl ether, aliphatic glycidyl ester, and aliphatic vinyl ether.

Examples of the aliphatic glycidyl ether include butyl glycidyl ether, 2-ethylhexyl glycidyl ether, and lauryl glycidyl ether.

Examples of the aliphatic vinyl ether include butyl vinyl ether, isopropyl vinyl ether, and cyclohexyl vinyl ether.
The photocurable composition according to the present embodiment preferably contains 15 parts by mass of component (D) based on 100 parts by mass of the total mass of component (A), component (B), component (C), and component (D). It is contained in a range of at least 20 parts by mass and less than 40 parts by mass, more preferably at least 20 parts by mass and less than 40 parts by mass.

By containing component (D) in the above range, the photocurable composition can have an appropriate viscosity. Thereby, the photocurable composition has good coating properties. Furthermore, since the proportion of component (A) in the photocurable composition is relatively large, the obtained cured product has excellent flexibility.

In addition to the (A) component, (B) component, (C) component, and (D) component, the photocurable composition of the present embodiment also includes various resins, as long as the curability and flexibility are not impaired. Any components such as additives may be blended.

The photocurable composition according to this embodiment is prepared by weighing component (A), component (B), and component (C) so that the mass ratio is within the above-mentioned range, and further adding other components as necessary. It can be prepared by adding and thoroughly mixing each component. The mixing method is not particularly limited. For example, mixing may be performed using a mixing device or the like known to those skilled in the art.

The photocurable composition according to the embodiment of the present invention has component (A), component (B), component (C), and component (D) blended so that the mass ratio is within the above-mentioned range, and ( By adjusting the amount of the (meth)acrylic acid ester compound containing an epoxy group constituting the copolymer of component A), it is possible to control the flexibility of the cured product. Therefore, the photocurable composition of the present invention can be usefully used as a flexible adhesive.
The photocurable composition of the present invention can be used to bond adherends made of different materials, for example members with a large difference in thermal expansion, such as a resin material and glass.

Hereinafter, the present invention will be described in more detail using Examples. Note that the present invention is not limited in any way by the following examples. Further, unless otherwise specified, parts and percentages in the examples are based on mass.

(Example 1)
Example 1 will be described in detail below. (Preparation of components (A) to (D))
As component (A), a (meth)acrylic acid ester copolymer containing an epoxy group in the copolymer structure; as component (B), pentaerythritol tetrakis (3-mercapto) having four thiol groups in one molecule; 1,2-disopropyl-3-[bis(dimethylamino)methylene]guanidium 2-(3 -benzoylphenyl) propinate ("WPBG-266" manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.); and a vinyl ether compound cyclohexyl vinyl ether ("CHVE" manufactured by Nippon Carbide Industries Co., Ltd.) were used as component (D).

(Preparation of photocurable composition)
First, 7.6 g of component (A) and 5.7 g of component (D) were uniformly mixed using a rotation-revolution defoaming stirrer so that the total blending amount of components (A) to (D) was 20 g. Mix to form a solution. 1.0 g of powdered component (C) was added thereto. The above mixture was thoroughly mixed and dissolved using a rotation/revolution defoaming stirrer. Thereafter, 5.7 g of component (B) was added and thoroughly mixed and dissolved using the rotation/revolution defoaming stirrer again to prepare photocurable composition 1.

Table 1 shows the blending amounts of components (A) to (D) in photocurable composition 1 of Example 1. The left column in the column of Example 1 shows the blending amount [unit: g], and the right column shows the amount of any of the components (A) to (D) in the total blending amount of the components (A) to (D). It shows the proportion of the amount [unit: mass %]. Moreover, (A) component No. The physical properties of No. 1 (weight ratio, polymerization average molecular weight, and epoxy equivalent) are shown in Table 2. Here, the weight ratio is the total amount of the (meth)acrylic acid ester compound forming the copolymer of component (A). It is the ratio (weight ratio) of the amount of (meth)acrylic acid ester compound having an epoxy group in the side chain to

[Examples 2 to 4 and Comparative Examples 1 to 4]
Photocurable compositions 2 to 4 and C1 to C4 were prepared in the same manner as in Example 1, except that the blending amounts of components (A) to (D) shown in Table 1 were changed. However, in Comparative Example 2, component (C) was not dissolved and a uniformly mixed photocurable composition C2 could not be prepared. For this reason, a photocured product could not be produced, and the curability evaluation and flexibility evaluation described below could not be performed.

[Evaluation method]
The curability and flexibility of photocured products produced from photocurable compositions were evaluated by the following evaluation methods. Table 1 shows the evaluation results.
Note that "-" in the curability and flexibility rows of Table 1 indicates that the evaluation could not be made. The numerical value in parentheses in the flexibility evaluation indicates the storage modulus [unit: kPa] used in the flexibility evaluation.

(Evaluation of curability of photocured material)
The curability of the photocured product was evaluated by the degree of curing in the coating film 2 hours after UV irradiation.
First, the storage modulus and loss modulus of the coating film were measured. The photocurable composition was applied to a transparent stage of a UV irradiation rheometer ("DHR-2" manufactured by TA Instruments Co., Ltd.) to form a coating film. Next, the coating film was irradiated with ultraviolet rays using a high-pressure mercury lamp as a light source with a gap of 100 μm. The UV irradiation conditions were such that the UV irradiation amount at 254 nm was 1500 mJ/cm ² . After UV irradiation, the temperature of the coated film was raised to 50°C at a heating rate of 42°C/min, and then kept at 50°C. In addition, the storage modulus and loss modulus of the coating film were measured using a UV irradiation rheometer for 2 hours from the start of UV irradiation to the coating film. The time from the start of UV irradiation to the time when the storage modulus and the loss modulus intersect is defined as the intersection of the storage modulus and the loss modulus as the timing of gelation, and the time until this intersection occurs (as described above) The determined time) was taken as the curing time. In actual measurements, the storage modulus and loss modulus could not be measured unless the coating film was cured to some extent.

The cured state of the coating film 2 hours after UV irradiation was visually observed, and the degree of cure (cured or uncured) was determined based on the observation results and curing time based on the following evaluation criteria. 〇 was considered a pass.
(Evaluation criteria)
〇 (curing): The curing time is less than 2 hours, and the coating film after 2 hours of UV irradiation is in a non-flowable state (that is, a state in which the storage modulus is higher than the loss modulus) ×( Uncured): The curing time is 2 hours or more, and the coating film has fluidity after 2 hours of UV irradiation.

(Evaluation of flexibility of photocured material)
The flexibility of the photocured product was evaluated using the storage modulus of the photocured product obtained by curing the photocurable composition. The storage modulus can be continuously measured by measuring the curing time in the above-mentioned curability evaluation. Specifically, after measuring the curing time (that is, after the intersection of the storage modulus and the loss modulus occurred), the photocured product was further kept at 50° C. until there was no change in the storage modulus. Here, the storage elastic modulus at the time when there was no change was determined. The flexibility of the photocured material was evaluated from the obtained storage modulus based on the following evaluation criteria. 〇 was considered a pass.
(Evaluation criteria)
〇 (Good): The storage modulus of the photocured product is less than 100 kPa. × (Bad): The storage modulus of the photocured product is 100 kPa or more.

(comprehensive evaluation)
Based on the results of the above curability evaluation and flexibility evaluation, a comprehensive evaluation of the photocured product was performed based on the following evaluation criteria.
(Evaluation criteria)
〇 (Good): 〇 (cured) in curability evaluation, and 〇 (good) in flexibility evaluation × (bad): × (uncured) in curability evaluation, and/or flexibility evaluation It is × (bad) in

As shown in Tables 1 and 2, the photocurable compositions (1) to (4) of Examples 1 to 4 contained components (A) to (D). In photocurable compositions (1) to (4), a (meth)acrylic ester having an epoxy group in the side chain is added to a total of 100 parts by mass of the (meth)acrylic ester compound constituting component (A). It contained 3 to 10 parts by mass of the compound. Further, the epoxy equivalent of the copolymer of component (A) was 5,000 to 500,000. Further, the component (C) was contained in an amount of 2 to 7 parts by mass based on a total of 100 parts by mass of the components (A) to (D).

As shown in Table 1, for the photocurable compositions (1) to (4) of Examples 1 to 4, the curability evaluation and flexibility evaluation were all 0, and the overall evaluation was also 0.

As shown in Tables 1 and 2, in the photocurable compositions C1 and C2 of Comparative Examples 1 and 2, the component (C) was 2 parts by mass relative to the total of 100 parts by mass of the components (A) to (D). or more than 7 parts by mass. In addition, photocurable compositions C3 and C4 of Comparative Examples 3 and 4 had an epoxy group in the side chain (meth ) Contained less than 3 parts by mass or more than 10 parts by mass of an acrylic ester compound. Further, the epoxy equivalent of the copolymer of component (A) of the photocurable compositions C3 to C4 of Comparative Examples 3 to 4 was less than 5,000 or more than 500,000.

As shown in Table 1, the curability evaluation of Comparative Example 1 was x (uncured). This is because the proportion of component (C) is small, and the amount of base generated by decomposition of component (C) by irradiation with active energy rays is small, which slows down the curing reaction. Furthermore, in Comparative Example 2, a photocured product could not be produced and the curability could not be evaluated. This is because component (C) was not dissolved in components (A), (B), and (D), and a photocurable composition in which the components were uniformly mixed could not be prepared. Moreover, the curability evaluation of Comparative Example 4 was × (uncured). This is because the proportion of epoxy groups contained in the copolymer of component (A) is small, so that the reaction time with the thiol group of component (B) becomes long.

As shown in Table 1, in Comparative Examples 1 and 4, the storage modulus could not be measured because the photocurable compositions C1 and C4 were not cured and a photocured product could not be produced. In Comparative Example 2, a photocured product could not be produced as described above, so flexibility could not be evaluated. The flexibility evaluation of Comparative Example 3 was ×. This is because the proportion of epoxy groups contained in the copolymer of component (A) is high, so the structure of the cured product is rigid, that is, the crosslinking density is high.

From the above, the photocurable compositions of Examples 1 to 4 can produce photocured products with excellent curability and flexibility compared to the photocurable compositions of Comparative Examples 1 to 4.

Since the cured product of the photocurable composition of the present invention has flexibility, the photocurable composition of the present invention can be used to bond members with a large difference in coefficient of thermal expansion, such as plastic materials and glass. Can be used together.

Claims (3)

(A) Component: (meth)acrylic acid ester copolymer having an epoxy group in the copolymer structure,
(B) component: a compound having two or more thiol groups in one molecule,
(C) component: a photobase generator, and (D) component: containing a reactive diluent,
The copolymer is a polymer obtained by polymerizing two or more types of (meth)acrylic acid ester compounds, and the two or more types of (meth)acrylic acid ester compounds are the two or more types of (meth)acrylic acid ester compounds. Contains 3 to 10 parts by mass of a (meth)acrylic acid ester compound having an epoxy group in the side chain based on 100 parts by mass of the ester compound,
The epoxy equivalent of the copolymer is 1,000 g/eq to 3,000 g/eq,
The weight average molecular weight of the copolymer is 5,000 to 500,000,
Photocuring characterized by containing 2 to 7 parts by mass of the component (C) based on a total of 100 parts by mass of the component (A), the component (B), the component (C), and the component (D). sexual composition. The photocurable composition according to claim 1, wherein the compound of the component (B) has 2 or more and 6 or less thiol groups in one molecule. Component (C) contains at least one selected from the group consisting of a carboxylate having either a xanthone skeleton or a ketoprofen skeleton, a salt containing a borate anion, a quaternary ammonium salt, and a carbamate compound. Item 2. Photocurable composition according to item 1 or 2.