WO2024143457A1 - Adhesive composition, adhesive sheet, multilayer body, and display provided with said multilayer body - Google Patents

Abstract

The present invention addresses the problem of providing: an adhesive composition which has adhesive force, heat resistance, resistance to wet heat whitening, outgas resistance, light resistance, low dielectric constant and metal corrosion resistance even in cases where a biological material is used therefor; an adhesive sheet which uses this adhesive composition; a multilayer body; and a display. The problem is solved by an adhesive composition which contains: (A) an acrylic polymer that is a copolymer of a monomer mixture that contains specific amounts of (a1) a (meth)acrylate ester monomer having an alicyclic structure (excluding (a3) monomers), (a2) an alkyl (meth)acrylate ester monomer having a linear alkyl group with 8 to 18 carbon atoms, and (a3) a (meth)acrylate ester monomer having a carboxy group and/or a (meth)acrylate ester monomer having a hydroxy group; and (B) a curing agent.

Description

Pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet, laminate, and display including said laminate

The present disclosure relates to an adhesive composition, an adhesive sheet, a laminate, and a display including the laminate.

Adhesive sheets with an adhesive layer formed from an adhesive are easy to handle and are therefore used in a wide range of fields, including label and medical applications. Among these, adhesives used in applications where long-term use is expected, such as marking films, window films, automotive parts, and optical displays, are required to have durability, including heat resistance, moist heat resistance, weather resistance, and light resistance. For this reason, there has been active research in recent years into ways to improve the durability of adhesives.

Various optical displays, such as liquid crystal displays (LCDs) and organic electroluminescence displays (OLEDs), are widely used as display devices. In addition to being used as display devices, optical displays are also used as input devices such as touch panels. A cover panel is installed on the touch panel to protect the surface. Usually, the components that make up these optical displays are bonded together via an adhesive layer.

As mentioned above, adhesives for optical displays, which are expected to be used for a long time, are required to have high durability, such as not lifting or peeling off from the adherend in high temperature and high humidity environments (peel resistance), not discoloring the adhesive layer itself to white (humid heat whitening resistance), and not discoloring the adhesive layer itself to yellow (yellowing resistance). In addition to the above durability, adhesives used to fix cover panels made of transparent plastic materials such as polycarbonate (PC) and polymethyl methacrylate (PMMA) are required to not cause appearance defects due to gases generated from the transparent plastic (outgassing resistance). Furthermore, if the dielectric constant of the adhesive used around the capacitive touch panel is high, it tends to cause malfunctions when the display is touched, so there is a demand for adhesives that can form adhesive layers with low dielectric constants. In addition, there is also a demand for properties that do not corrode such metal materials, assuming that they will be used for transparent electrodes.

In terms of durability, displays, especially those for in-vehicle use, require high durability. In particular, due to revolutionary advances in information technology in recent years, such as the 5th generation mobile communication system (5G), the Internet of Things (IoT), and artificial intelligence (AI), the development of automobiles equipped with electrification and external displays is progressing. Accordingly, the required performance is becoming more stringent, such as the need for heat resistance at higher temperatures, such as 120°C (previously around 85-105°C). Therefore, it has been a major challenge to develop an adhesive that meets all of the requirements, such as heat resistance at higher temperatures and the continued resistance to moist heat whitening and outgassing that have been required up until now.

Many studies have been conducted so far to satisfy the durability required for adhesives for optical displays. The adhesive described in Patent Document 1 uses an acrylic adhesive in which a hydroxyl-containing acrylic ester and a nitrogen-containing acrylic ester are copolymerized in order to impart resistance to wet heat whitening and outgassing, but the heat resistance and light resistance at 120°C are sometimes insufficient.
In addition, the adhesive described in Patent Document 2 uses an acrylic adhesive obtained by copolymerizing an acrylic acid alkyl ester having 4 to 8 carbon atoms and N-(2-hydroxyethyl)acrylamide as monomers in order to suppress display unevenness. However, this adhesive sometimes has insufficient heat resistance at 120° C., resistance to moist heat whitening, resistance to outgassing, and adhesion.

In addition to the increasing performance requirements, the depletion of petroleum resources and carbon dioxide emissions from the combustion of petroleum-derived products are becoming issues in the industries in which pressure-sensitive adhesive sheets are used. As a result, attempts are being made to conserve petroleum resources by using bio-derived materials instead of petroleum-derived materials in a variety of industries, starting with the packaging materials sector, as well as the optical and semiconductor sectors.

In adhesives that mainly contain acrylic polymers, one method for increasing the ratio of biologically derived materials is to obtain an acrylic polymer by copolymerizing a monomer mixture containing a linear alkyl alcohol produced from an organism and a (meth)acrylic acid alkyl ester monomer obtained by esterifying (meth)acrylic acid. Biologically derived linear alcohols are currently available in stable quantities at relatively low cost, making them suitable for industrial use. Patent Document 3 discloses an adhesive obtained by copolymerizing a monomer mixture containing a biomass-derived acrylate with an alkyl group having 12 to 24 carbon atoms, but the conditions for the heat resistance retention test are low temperature and short time, and even if the test is passed, the heat resistance may be insufficient.

JP 2017-106000 A JP 2007-264092 A JP 2020-105308 A

The problem that this disclosure aims to solve is to provide an adhesive composition that has adhesive strength, heat resistance, resistance to moist heat whitening, resistance to outgassing, light resistance, low dielectric constant, and resistance to metal corrosion, even when a biologically derived material is used, and an adhesive sheet, laminate, and display that use the same.

As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved in the following aspect, and have completed the present disclosure.
That is, the present disclosure relates to a pressure-sensitive adhesive composition comprising an acrylic polymer (A) and a curing agent (B), wherein the acrylic polymer (A) is a copolymer of a monomer mixture comprising the following (a1), (a2) and (a3):
The pressure-sensitive adhesive composition comprises, relative to 100 mass% of the monomer mixture, 2.5 to 20 mass% of (a1), 30 to 80 mass% of (a2), and 0.1 to 20 mass% of (a3).
(a1) a (meth)acrylic acid ester monomer having an alicyclic structure (excluding (a3)),
(a2) a (meth)acrylic acid alkyl ester monomer having a linear alkyl group having 8 to 18 carbon atoms;
(a3) A (meth)acrylic acid ester monomer having a carboxy group and/or a (meth)acrylic acid ester monomer having a hydroxy group.

The present disclosure also relates to the above pressure-sensitive adhesive composition, characterized in that (a3) contains a (meth)acrylic acid ester monomer having a hydroxy group.

The present disclosure also relates to the above-mentioned adhesive composition, characterized in that the monomer mixture further contains (a4) a (meth)acrylic acid alkyl ester monomer having an alkyl group having 1 to 4 carbon atoms.

The present disclosure also relates to the above pressure-sensitive adhesive composition, further comprising a silane coupling agent (C).

The present disclosure also relates to the above pressure-sensitive adhesive composition, characterized in that the curing agent (B) contains an isocyanate-based curing agent or a blocked form thereof.

The present disclosure also relates to an adhesive sheet having an adhesive layer made of the above-mentioned adhesive composition.

The present disclosure also relates to a laminate comprising the above-mentioned pressure-sensitive adhesive sheet and a light-transmitting substrate.

The present disclosure also relates to a display comprising the laminate, a polarizing plate, and an optical element.

The present disclosure provides an adhesive composition that has adhesive strength, heat resistance, resistance to moist heat whitening, resistance to outgassing, light resistance, low dielectric constant, and resistance to metal corrosion, even when a biologically derived material is used, and an adhesive sheet, laminate, and display that use the same.

FIG. 2 is a schematic cross-sectional view partially illustrating an example of a laminate according to the present embodiment. FIG. 2 is a schematic cross-sectional view partially illustrating a display, which is an example of the use of the laminate of the present embodiment. FIG. 2 is a schematic cross-sectional view of a dielectric constant measurement sample.

The pressure-sensitive adhesive composition according to the present disclosure (also referred to as the present pressure-sensitive adhesive composition), pressure-sensitive adhesive sheet, laminate and display will be described below, but are not limited thereto.
In this specification, the term "(meth)acrylic acid ester" includes acrylic acid ester and methacrylic acid ester, and means either or both of an acrylic acid ester and a methacrylic acid ester. The monomers (a1) to (a4) described below refer to monomers having an ethylenically unsaturated group.
In this specification, the monomers (a1) to (a4) may be simply referred to as (a1) to (a4), respectively.
In addition, in this specification, a numerical range specified using "to" is intended to include the numerical values before and after "to" as the lower and upper limit values of the range.
In the numerical ranges described in this specification, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in another stepwise manner. In addition, in the numerical ranges described in this specification, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.
In addition, the terms "film" and "sheet" are not differentiated by thickness. In other words, the term "sheet" in this specification includes thin film-like objects, and the term "film" in this specification includes thick sheet-like objects.
Furthermore, the adherend refers to an object (counterpart) to which the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is attached.
Unless otherwise noted, the various components appearing in this specification may be used independently as a single type, or as a combination of two or more types.

<<Adhesive composition>>
The pressure-sensitive adhesive composition according to the present disclosure contains an acrylic polymer (A) and a curing agent (B).

<Acrylic polymer (A)>
The acrylic polymer (A) is a copolymer of a monomer mixture containing the monomers (a1), (a2) and (a3) described below. The acrylic polymer (A) contains 2.5 to 20 mass% (a1) (in total), 30 to 80 mass% (a2) (in total), and 0.1 to 20 mass% (a3) (in total) in 100 mass% of the monomer mixture. When two or more of the monomer components (a1) to (a3) are used, the content ratio of these monomers means the total content ratio of the monomer components used. For example, when a (meth)acrylic acid ester monomer having a carboxy group and a (meth)acrylic acid ester monomer having a hydroxy group are used in combination as the monomer (a3), the total content ratio of these is the content ratio of (a3).

[Monomer (a1)]
(a1) is a (meth)acrylic acid ester monomer having an alicyclic structure. However, in this specification, a (meth)acrylic acid ester monomer having a carboxy group or a hydroxy group is considered to be monomer (a3) even if it has an alicyclic structure.
Examples of the alicyclic structure include a cycloalkane structure, a cycloalkene structure, and an alicyclic ether structure. From the viewpoint of yellowing resistance, a cycloalkane structure or an alicyclic ether structure having no unsaturated bond in the ring is preferred.

Examples of monomer (a1) include isobornyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, (5-ethyl-1,3-dioxane-5-yl)methyl (meth)acrylate, etc. Among these, from the viewpoint of outgassing resistance and increasing the proportion of biologically derived materials, it is even more preferable to use isobornyl (meth)acrylate and tetrahydrofurfuryl (meth)acrylate as (a1), which can be produced from alcohol available as a biomass raw material.

The (total) content of (a1) is 2.5 to 20 mass% in 100 mass% of the monomer mixture, preferably 5 to 15 mass%, and more preferably 7 to 13 mass%. If the content of (a1) is less than 2.5 mass%, the cohesive strength of the adhesive layer decreases, and the adhesive strength, heat resistance, and light resistance are insufficient. If the content of (a1) is more than 20 mass%, the tack of the adhesive layer decreases, and the adhesive strength, heat resistance, and light resistance are insufficient.

[Monomer (a2)]
(a2) is a (meth)acrylic acid alkyl ester monomer having a linear alkyl group having 8 to 18 carbon atoms. Since (meth)acrylic acid alkyl ester monomers having such a carbon number are available as biologically derived materials, the ratio of biologically derived materials can be increased by using these. Furthermore, by including this monomer, the polarity of the entire adhesive layer can be reduced, and therefore the dielectric constant can be reduced. Furthermore, since the alkyl group is linear, it can be partially crystallized in the adhesive layer, thereby increasing heat resistance.

Examples of monomer (a2) include normal octyl (meth)acrylate, normal nonyl (meth)acrylate, normal decyl (meth)acrylate, normal undecyl (meth)acrylate, normal dodecyl (meth)acrylate, normal tridecyl (meth)acrylate, normal tetradecyl (meth)acrylate, normal pentadecyl (meth)acrylate, normal hexadecyl (meth)acrylate, normal heptadecyl (meth)acrylate, and normal octadecyl (meth)acrylate.

The (total) content of (a2) is 30-80% by mass, preferably 30-78% by mass, more preferably 40-70% by mass, even more preferably 42-68% by mass, even more preferably 45-68% by mass, and most preferably 50-60% by mass, based on 100% by mass of the monomer mixture. If the content of (a2) is less than 30% by mass, sufficient biological material cannot be used in the adhesive or adhesive layer, and the dielectric constant becomes too high to be used in electronic devices with high-frequency signal transmission functions. If the content of (a2) exceeds 80% by mass, the cohesive strength of the adhesive layer decreases, and the adhesive strength, heat resistance, and light resistance become insufficient.

In 100% by mass of (a2), the content of (meth)acrylic acid alkyl ester monomers having a linear alkyl group with 8 to 14 carbon atoms is preferably 70% by mass or more. By using such a ratio, it is easy to obtain a higher adhesive strength.

In 100% by mass of (a2), the ratio of acrylate to methacrylate is preferably 50:50 to 100:0, more preferably 60:40 to 100:0, even more preferably 70:30 to 100:0, even more preferably 80:20 to 100:0, and most preferably 90:10 to 100:0. By using such a ratio, it is easy to obtain a higher adhesive strength.

[Monomer (a3)]
(a3) is a (meth)acrylic acid ester monomer having a carboxy group and/or a (meth)acrylic acid ester monomer having a hydroxy group. In other words, (a3) is either one or both of a (meth)acrylic acid ester monomer having a carboxy group and a (meth)acrylic acid ester monomer having a hydroxy group. In addition, it is preferable to use a (meth)acrylic acid ester monomer having a carboxy group and a (meth)acrylic acid ester monomer having a hydroxy group in combination as (a3). By using these in combination in the pressure-sensitive adhesive composition, it becomes easier to impart excellent heat resistance, light resistance, and metal corrosion resistance.

The (total) content of (a3) is 0.1 to 20 mass% in 100 mass% of the monomer mixture, preferably 0.1 to 15 mass%, more preferably 0.5 to 10 mass%, and most preferably 1 to 5 mass%. By making the content of (a3) 0.1 mass% or more, it is possible to ensure resistance to moist heat, and by making it 20 mass% or less, it is possible to reduce outgassing and lower the dielectric constant.

There are no limitations on the (meth)acrylic acid ester monomer having a carboxy group, so long as it is a monomer having a carboxy group in the molecule. Specific examples of such monomers include (meth)acrylic acid, p-carboxybenzyl acrylate, β-carboxyethyl acrylate, maleic acid, monoethyl maleic acid, itaconic acid, citraconic acid, and fumaric acid. Of these, (meth)acrylic acid is preferred from the standpoint of adhesive strength.

The content of the (meth)acrylic acid ester monomer having a carboxy group is preferably more than 0% by mass and not more than 5% by mass in 100% by mass of the monomer mixture, more preferably 0.1 to 4% by mass, even more preferably 0.2 to 2% by mass, and most preferably 0.4 to 1% by mass. By keeping it in this range, it is possible to reduce metal corrosiveness in a configuration in which the adhesive layer is in contact with metals such as a transparent conductive layer, and to lower the dielectric constant.

The (meth)acrylic acid ester monomer having a hydroxy group is not limited as long as it is a monomer having a hydroxy group in the molecule, and specific examples of the monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.
Of these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred from the viewpoints of adhesive strength and resistance to moist heat.

The content of the (meth)acrylic acid ester monomer having a hydroxyl group is preferably 0.1 to 20 mass% in 100 mass% of the monomer mixture, more preferably 0.1 to 15 mass%, even more preferably 0.5 to 10 mass%, even more preferably 1 to 5 mass%, and most preferably 2 to 4 mass%. By making it 0.1 mass% or more, it is easy to ensure resistance to moist heat, and by making it 20 mass% or less, it is easy to reduce outgassing and the dielectric constant can be easily lowered.

[Monomer (a4)]
The monomer mixture serving as the raw material for the acrylic polymer (A) preferably further contains a (meth)acrylic acid alkyl ester monomer (a4) having an alkyl group having 1 to 4 carbon atoms. Here, the monomer (a4) can be contained in an amount of, for example, 0.1% by mass or more, or 1% by mass or more, based on 100% by mass of the monomer mixture. By containing (a4), it becomes easier to achieve both adhesive strength, heat resistance, and moist heat resistance.

Examples of monomer (a4) include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, and tert-butyl (meth)acrylate.
Of these, from the viewpoint of ease of molecular weight adjustment, it is preferable to use an acrylic acid alkyl ester monomer as (a4).

The preferred (total) content of (a4) is 10 to 42% by mass, and more preferably 20 to 40% by mass, in 100% by mass of the monomer mixture. By making it 10% by mass or more, it becomes easier to achieve both adhesive strength, heat resistance, and moist heat resistance, and by making it 42% by mass or less, the dielectric constant can be made lower. In order to ensure tack, the ratio of acrylate to methacrylate in 100% by mass of (a4) is preferably 80:20 to 100:0, and more preferably 90:10 to 100:0.

[Other monomers]
The monomer mixture serving as the raw material of the acrylic polymer (A) may contain other monomers other than the above (a1) to (a4) as optional components. Examples of other monomers include (meth)acrylic acid alkyl ester monomers having a branched alkyl group, nitrogen-containing (meth)acrylic acid esters such as acrylamide, alkoxy-based (meth)acrylic acid esters such as methoxyethyl acrylate, vinyl-based monomers such as vinyl acetate and styrene, and monomers having a glycidyl group such as glycidyl (meth)acrylate.
The (total) content of other monomers is preferably 35% by mass or less, more preferably 25% by mass or less, even more preferably 15% by mass or less, and most preferably 5% by mass or less, based on 100% by mass of the monomer mixture.

(Production of Acrylic Polymer (A))
The acrylic polymer (A) can be produced by polymerizing the above-mentioned monomer mixture.
The polymerization can be carried out by a known polymerization method such as solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, etc., but solution polymerization is preferred. The solvent used in the solution polymerization is preferably, for example, acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, cyclohexanone, etc. The polymerization temperature is preferably a boiling point reaction at 60 to 120°C. The polymerization time is preferably about 5 to 12 hours.

The polymerization initiator used in the polymerization is preferably a radical polymerization initiator, and the radical polymerization initiator is generally a peroxide or an azo compound.
Examples of the peroxide include dialkyl peroxides such as di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, and 2,5-di(t-butylperoxy)hexyne-3;
Peroxyesters such as t-butyl peroxybenzoate, t-butyl peroxyacetate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane;
Ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide;
Peroxyketals such as 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and n-butyl-4,4-bis(t-butylperoxy)valerate;
Hydroperoxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, and 2,5-dimethylcyclohexane-2,5-dihydroperoxide;
Diacyl peroxides such as benzoyl peroxide, decanoyl peroxide, lauroyl peroxide, and 2,4-dichlorobenzoyl peroxide;
Examples of the peroxydicarbonate include peroxydicarbonates such as bis(t-butylcyclohexyl)peroxydicarbonate.

Examples of the azo compound include 2,2'-azobisbutyronitrile such as 2,2'-azobisisobutyronitrile (abbreviation: AIBN) and 2,2'-azobis(2-methylbutyronitrile);
2,2'-azobisvaleronitrile such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile);
2,2'-azobispropionitrile such as 2,2'-azobis(2-hydroxymethylpropionitrile);
Examples of the compound include 1,1'-azobis-1-alkanenitriles such as 1,1'-azobis(cyclohexane-1-carbonitrile).

The polymerization initiator is preferably used in an amount of 0.01 to 10 parts by mass, more preferably 0.1 to 2 parts by mass, per 100 parts by mass of the monomer mixture.

(Weight average molecular weight (Mw))
The weight average molecular weight of the acrylic polymer (A) is preferably 500,000 to 1,500,000, and more preferably 600,000 to 1,200,000. By setting the weight average molecular weight within the above range, peel resistance, outgas resistance, and light resistance in high temperature and high humidity environments are further improved. The weight average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

<Curing Agent (B)>
The adhesive composition according to the present disclosure includes a curing agent (B). The curing agent (B) to be blended in the adhesive composition is preferably one that reacts with the carboxyl group and the hydroxyl group of the monomer (a3) by heat or the like to form bonds. The blending of the curing agent (B) improves the cohesive strength of the adhesive layer, and improves the adhesive strength, heat resistance, and light resistance.

As the curing agent (B), one or more types can be appropriately selected from known crosslinking agents such as isocyanate-based curing agents, epoxy-based curing agents, oxazoline-based curing agents, aziridine-based curing agents, carbodiimide-based curing agents, metal chelate-based curing agents, and melamine-based curing agents, taking into consideration the reactivity with the functional groups of the polymer in the adhesive composition. However, from the viewpoints of adhesive strength, heat resistance, and light resistance, it is preferable that the curing agent (B) contains an isocyanate-based curing agent or a block thereof.

The isocyanate-based curing agent is an isocyanate having two or more isocyanate groups or a block thereof. As the isocyanate, for example, aromatic (poly)isocyanates, aliphatic (poly)isocyanates, araliphatic (poly)isocyanates, alicyclic (poly)isocyanates, and their biuret forms, nurate forms, and adduct forms are preferred, and from the viewpoint of yellowing resistance, aliphatic isocyanates, alicyclic isocyanates, and their biuret forms, nurate forms, and adduct forms are even more preferred.

Examples of aliphatic isocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (also known as HMDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

Examples of alicyclic isocyanates include 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI, isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanatomethyl)cyclohexane.

Examples of aromatic isocyanates include 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4',4"-triphenylmethane triisocyanate, etc.

Examples of aromatic aliphatic isocyanates include ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate.

The biuret compound is a self-condensation product having a biuret bond formed by the self-condensation of an isocyanate monomer. An example of the biuret compound is the biuret compound of hexamethylene diisocyanate.

The nurate is a trimer of an isocyanate monomer. Examples include a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, and a trimer of tolylene diisocyanate.

The adduct is a bifunctional or higher isocyanate compound formed by reacting an isocyanate monomer with a bifunctional or higher low-molecular-weight active hydrogen-containing compound. Examples of the adduct include a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with tolylene diisocyanate, a compound obtained by reacting trimethylolpropane with xylylene diisocyanate, a compound obtained by reacting trimethylolpropane with isophorone diisocyanate, and a compound obtained by reacting 1,6-hexanediol with hexamethylene diisocyanate.

From the viewpoint of forming a sufficient crosslinked structure, the isocyanate compound is preferably a trifunctional isocyanate compound. The isocyanate compound is more preferably an adduct or nurate, which is a reaction product between an isocyanate monomer and a trifunctional low-molecular-weight active hydrogen-containing compound. The isocyanate compound is preferably a trimethylolpropane adduct of hexamethylene diisocyanate, a nurate of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, a nurate of tolylene diisocyanate, a trimethylolpropane adduct of isophorone diisocyanate, or a nurate of isophorone diisocyanate, and more preferably a trimethylolpropane adduct of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, or a trimethylolpropane adduct of isophorone diisocyanate.

Examples of epoxy curing agents (epoxy compounds) include glycerin diglycidyl ether, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidylaminophenylmethane.

Examples of aziridine-based curing agents (aziridine compounds) include N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxite), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, and 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane.

The carbodiimide-based curing agent (carbodiimide compound) is preferably a high molecular weight polycarbodiimide produced by a decarboxylation condensation reaction of a diisocyanate compound in the presence of a carbodiimide catalyst. The commercially available high molecular weight polycarbodiimide is preferably the Carbodilite series from Nisshinbo Industries. Among these, Carbodilite V-03, 07, and 09 (all trade names) are preferred because of their excellent compatibility with organic solvents.

The metal chelate curing agent is preferably a coordination compound of a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, or zirconium with acetylacetone or ethyl acetoacetate. Examples of metal chelate curing agents include aluminum ethyl acetoacetate diisopropylate, aluminum trisacetylacetonate, aluminum bisethyl acetoacetate monoacetylacetonate, and aluminum alkyl acetoacetate diisopropylate.

Oxazoline-based hardeners have two or more oxazoline groups in the molecule and may be low molecular weight compounds or polymers. Examples of low molecular weight compounds of oxazoline-based hardeners include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2,2'-bis-(2-oxazoline), 2,2'-methylene-bis-(2-oxazoline), 2,2'-ethylene-bis-(2-oxazoline), 2,2'-trimethylene-bis-(2-oxazoline), and 2,2'-tetramethylene-bis-(2-oxazoline). , 2,2'-hexamethylene-bis-(2-oxazoline), 2,2'-octamethylene-bis-(2-oxazoline), 2,2'-ethylene-bis-(4,4'-dimethyl-2-oxazoline), 2,2'-p-phenylene-bis-(2-oxazoline), 2,2'-m-phenylene-bis-(2-oxazoline), 2,2'-m-phenylene-bis-(4,4'-dimethyl-2-oxazoline), 2,2'-(1,3-phenylene)-bis-(2-oxazoline), bis-(2-oxazolinylcyclohexane)sulfide, bis-(2-oxazolinylnorbornane)sulfide, etc. Examples of the oxazoline-based curing agent of a polymer include a polymer having an addition polymerizable oxazoline as an essential component. Examples of the addition-polymerizable oxazoline include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

Typical examples of melamine-based hardeners include fully alkyl etherified melamine resins, methylol group-type melamine resins, and imino group-type melamine resins that contain some imino groups.

The curing agent (B) is preferably contained in an amount of 0.02 to 4 parts by mass, and more preferably 0.04 to 1 part by mass, per 100 parts by mass of the acrylic polymer (A) in the adhesive composition. If the content is 0.02 parts by mass or more, the cohesive strength is further improved, and if it is 4 parts by mass or less, it becomes easier to achieve both cohesive strength and flexibility, making it easier to obtain sufficient adhesive strength, heat resistance, and light resistance.

<Silane Coupling Agent (C)>
The pressure-sensitive adhesive composition preferably contains a silane coupling agent (C). By containing the silane coupling agent (C), the adhesive strength, heat resistance, wet heat whitening resistance, and light resistance can be further improved. The silane coupling agent (C) is preferably contained in an amount of 0.05 to 0.2 parts by mass per 100 parts by mass of the acrylic polymer (A). By containing the silane coupling agent (C) in an amount of 0.05 to 0.2 parts by mass, excellent heat resistance, outgassing resistance, and light resistance can be easily imparted.

Examples of the silane coupling agent (C) include an alkoxysilane compound having a (meth)acryloxy group, an alkoxysilane compound having a vinyl group, an alkoxysilane compound having an amino group, an alkoxysilane compound having a mercapto group, and an alkoxysilane compound having an epoxy group.
Specific examples of commercially available products include KBM-403 (3-glycidoxypropyltrimethoxysilane), KBE-403 (3-glycidoxypropyltriethoxysilane), KBM-303 (2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane) (all trade names, manufactured by Shin-Etsu Chemical Co., Ltd.), BYK-325N (polyether-modified polymethylalkylsiloxane) (trade name, manufactured by BYK Japan KK), and the like.

The adhesive composition may contain various resins, chlorinated polyolefins (described below), oils, softeners, dyes, pigments, antioxidants, and UV absorbers as optional components, so long as the problem can be solved.

Examples of chlorinated polyolefins include chlorinated polypropylene, acid-modified chlorinated polypropylene, acrylic-modified chlorinated polypropylene, chlorinated polyethylene, chlorinated ethylene-vinyl acetate copolymer, etc. Here, chlorinated polypropylene or chlorinated ethylene-vinyl acetate copolymer is preferred from the viewpoints of good compatibility with acrylic polymers and the like and effective reduction in polarity.
Specific examples of commercially available products include Superchlorine 390S (chlorinated polypropylene, chlorine content 36%) and Superchlorine BX (chlorinated EVA, chlorine content 18%) (both trade names, manufactured by Nippon Paper Industries Co., Ltd.).

Adhesive sheet
The pressure-sensitive adhesive sheet according to the present disclosure (also referred to as the present pressure-sensitive adhesive sheet) comprises a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition according to the present disclosure.

The adhesive sheet has either a configuration in which a release film is formed on both sides of an adhesive layer, or a configuration in which a release film is formed on one side of an adhesive layer and a light-transmitting substrate is provided on the other side of the adhesive, and the adhesive layer is an adhesive layer formed from the adhesive composition.

<Release film>
The release film is not particularly limited, but a transparent plastic substrate can be suitably used. Examples of the material of the transparent plastic substrate include polyesters such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), and plastic materials such as polycarbonate, triacetyl cellulose, polysulfone, polyarylate, and polycycloolefin. The plastic materials can be used alone or in combination of two or more kinds.

Among the transparent plastic substrates mentioned above, a transparent plastic substrate with excellent heat resistance, i.e., a transparent plastic substrate in which deformation is suppressed or prevented under harsh conditions such as high temperature or high temperature and high humidity, can be preferably used as the release film. PET films or sheets are particularly suitable as transparent plastic substrates.

<Light-transmitting substrate>
A transparent plastic substrate is used as the light-transmitting substrate. Examples of the material of such a light-transmitting substrate include acrylic resins such as polyethylene terephthalate (PET), polyethylene naphthalate, and polymethyl methacrylate (PMMA), and plastic materials such as polycarbonate (PC), polycycloolefin, polyimide, polyphenylene ether, polysulfone, polyethersulfone, polystyrene, and polypropylene. In particular, a PET film or PC is preferable, and PC is more preferable in terms of durability.
The plastic materials may be used alone or in combination of two or more kinds.
The light-transmitting substrate may be subjected to an appropriate surface treatment, for example, a physical treatment such as a corona discharge treatment or a plasma treatment, or a chemical treatment such as an undercoat treatment.

This adhesive sheet has excellent adhesion, heat resistance, resistance to wet and hot whitening, resistance to outgassing, light resistance, low dielectric constant, and resistance to metal corrosion. For this reason, it is suitable as an adhesive for forming optical display components such as display devices such as LCDs and OLEDs and input devices such as touch panels, and for bonding these components together. Optical components are not particularly limited, and include PET films, polarizing plates, retardation plates, elliptical polarizing plates, optical compensation films, brightness improvement films, infrared/electromagnetic wave cut films, front anti-reflection films, surface protection films, films with an ITO (indium tin oxide) layer, films with a zinc oxide (ZnO) layer, films obtained by coating or printing metal nanoparticles, films obtained by coating or printing a dispersion containing carbon nanotubes, films obtained by coating or printing a dispersion containing graphene, films obtained by coating or printing a dispersion containing conductive polymers, metal plates formed of SUS, metal meshes, and even laminates of these.

The thickness of the transparent plastic substrate is not particularly limited, but is preferably 10 to 200 μm, and more preferably 25 to 150 μm, for example.

When applying the adhesive composition, the viscosity can be adjusted by adding an appropriate liquid medium. Specific examples include hydrocarbon solvents such as toluene, xylene, hexane, and heptane; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as acetone and methyl ethyl ketone; halogenated hydrocarbon solvents such as dichloromethane and chloroform; ether solvents such as diethyl ether, methoxytoluene, and dioxane, and other hydrocarbon solvents. However, water and alcohol must be used with caution, as they may inhibit the reaction between the acrylic polymer (A) and the isocyanate curing agent (B).

There are no particular limitations on the coating method, and various coating methods can be used, such as with a Mayer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, and spin coater. There are also no particular limitations on the drying and curing method, and examples include hot air drying, infrared rays, reduced pressure methods, and methods using active energy rays. However, from the perspective of outgassing resistance, hot air or steam heating at 60 to 180°C is preferred as the drying and curing method.

The thickness of the adhesive layer is preferably 2 to 1000 μm, and more preferably 5 to 500 μm. The adhesive layer may be in either a single layer or a laminate of two or more layers.

<Laminate>
The laminate includes a light-transmitting substrate and a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer is formed using the pressure-sensitive adhesive sheet according to the present disclosure. Specifically, for example, the laminate can be formed by peeling the release film from the pressure-sensitive adhesive sheet and attaching the pressure-sensitive adhesive layer to the light-transmitting substrate.
The laminate according to the present disclosure has a structure of, for example, a light-transmitting substrate/a pressure-sensitive adhesive layer/a polarizing plate. In this case, it is preferable to provide the light-transmitting substrate, the pressure-sensitive adhesive layer, and the polarizing plate in this order. This makes it possible to obtain a laminate with excellent transparency.

FIG. 1 shows an example of a schematic cross-sectional view partially illustrating a laminate according to the present disclosure. In FIG. 1, reference numeral 3 denotes a light-transmitting substrate (cover panel), reference numeral 1 denotes an adhesive layer, and reference numeral 4 denotes a polarizing plate.

In the laminate shown in FIG. 1, a light-transmitting substrate (cover panel) 3 is attached to a polarizing plate 4 via an adhesive layer 1.

<Production of Laminate for Display>
In the method for producing a laminate according to the present disclosure, for example, a laminate can be formed by peeling off a release film from a pressure-sensitive adhesive sheet having a release film on both sides of a pressure-sensitive adhesive layer, and attaching the pressure-sensitive adhesive layer to an adherend such as a light-transmitting flexible substrate or a polarizing plate. Alternatively, a pressure-sensitive adhesive layer can be directly formed on a light-transmitting flexible substrate, and then an adherend or a pressure-sensitive adhesive layer provided on another pressure-sensitive adhesive sheet can be attached to the pressure-sensitive adhesive layer to form a laminate.

"display"
A display preferably includes the laminate according to the present disclosure, a polarizing plate, and an optical element, thereby providing the display according to the present disclosure with excellent flexibility and visibility.
The optical element is not particularly limited, and examples thereof include a liquid crystal element and an organic EL element.

FIG. 2 shows an example of a schematic cross-sectional view partially illustrating a display, which is an example of the use of this adhesive sheet. In FIG. 2, reference numeral 3 denotes a light-transmitting substrate (cover panel), reference numeral 2 denotes a release film, reference numeral 1 denotes a first adhesive layer, reference numeral 4 denotes a polarizing plate, reference numeral 5 denotes a second adhesive layer, reference numeral 6 denotes a barrier layer such as silicon nitride, reference numeral 7 denotes an organic EL layer, reference numeral 8 denotes a support such as polyimide, and reference numeral 9 denotes an organic EL cell. Note that the configuration of the display according to the present disclosure is not limited to that shown in FIG. 2.

In the display shown in Fig. 2, a light-transmitting substrate (cover panel) 1 is attached to a polarizing plate 4 via a pressure-sensitive adhesive layer (first pressure-sensitive adhesive layer 1) according to the present disclosure, and is further attached to an organic EL cell 9 via a pressure-sensitive adhesive layer for a polarizing plate (second pressure-sensitive adhesive layer 5). In this way, the pressure-sensitive adhesive sheet can be used in a form in which a transparent pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition is attached to a light-transmitting substrate (cover panel) 3 and a polarizing plate 4, and the laminate is further attached to an organic EL cell 9 via a pressure-sensitive adhesive layer for a polarizing plate.
For example, in FIG. 2, the present pressure-sensitive adhesive layer can be used as either the first pressure-sensitive adhesive layer 1 or the second pressure-sensitive adhesive layer 5 .
Generally, when comparing the first pressure-sensitive adhesive layer 1 and the second pressure-sensitive adhesive layer 5, the quality required for the pressure-sensitive adhesive layer is higher for the first pressure-sensitive adhesive layer 1. That is, since the pressure-sensitive adhesive composition has good adhesion and bonding properties to the substrate, it is preferably used for the first pressure-sensitive adhesive layer 1. In this case, the pressure-sensitive adhesive for forming the second pressure-sensitive adhesive layer 5 may be the pressure-sensitive adhesive composition according to the present disclosure, or a conventionally known pressure-sensitive adhesive may be used.

　There are no particular limitations on how the displays can be used, but examples include OLED televisions, OLED smartphones, OLED tablets, and OLED smartwatches.

The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples. In the examples, unless otherwise specified, "parts" refers to "parts by mass" and "%" refers to "% by mass". The blending amounts in the tables are parts by mass, and the amounts other than the solvent are calculated as non-volatile contents. The blank spaces in the blending amounts of each component in the tables indicate that the component is not blended.
The method for measuring the weight average molecular weight of the acrylic polymer (A) is as follows.

<Measurement of weight average molecular weight (Mw)>
The weight average molecular weight (Mw) was measured by gel permeation chromatography (GPC). The equipment used was a GPC equipment manufactured by Shimadzu Corporation: LC-GPC system "Prominence". The column used was a TSKgel α-M manufactured by Tosoh Corporation, two of which were connected in series. The eluent was N,N-dimethylformamide (DMF), and the measurement was performed at 40°C. The Mw was determined by conversion using polystyrene with a known Mw as the standard substance.

The materials used in the examples and comparative examples are listed below.
<Curing Agent (B)>
[Isocyanate-based hardener]
B-1: (Product name "NP-1200", manufactured by Mitsui Chemicals, Inc., biuret form of hexamethylene diisocyanate)
B-2: (Product name "D-172N", manufactured by Mitsui Chemicals, Inc., nurate form of hexamethylene diisocyanate)
B-3: (Product name "D-160N", manufactured by Mitsui Chemicals, Inc., trimethylolpropane modified hexamethylene diisocyanate)
B-4: (Product name "Desmodur 2565", manufactured by Covestro, nurate form of isophorone diisocyanate)
B-5: (Product name "Coronate L", manufactured by Tosoh Corporation, trimethylolpropane-modified tolylene diisocyanate)
[Other hardeners]
B-6: Zirconium tetraacetylacetonate: (product name "Orgatics ZC-700", manufactured by Matsumoto Fine Chemical Co., Ltd.)
B-7: N,N,N',N'-tetraglycidyl-m-xylylenediamine (TETRAD-X)

<Silane Coupling Agent (C)>
KBM-303: (trade name, [2-(3,4-epoxycyclohexyl)ethyl]trimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.)
KBE-403: (product name, 3-glycidoxypropyltriethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.)

<Production Example of Acrylic Polymer>
(Acrylic Polymer (A-1))
Using a reaction apparatus equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping tube, 11 parts of isobornyl acrylate (IBXA) as monomer (a1), 56.5 parts of octyl acrylate (OA) as monomer (a2), 2 parts of 2-hydroxyethyl acrylate (HEA) and 0.5 parts of acrylic acid (AA) as monomer (a3), and 30 parts of methyl acrylate (MA) as monomer (a4), each half of the monomer mixture, 0.2 parts of azobisisobutyronitrile as an initiator, and 60 parts of ethyl acetate as a solvent were charged into a reaction vessel, and the remaining half of the monomer mixture and 60 parts of ethyl acetate and 0.2 parts of azobisisobutyronitrile were added and mixed, and the solution was dropped from the dropping tube over about 2 hours, and polymerized for 6 hours at about 80 ° C. under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled and diluted with ethyl acetate to obtain an acrylic polymer solution with a non-volatile content of 30%. Here, the obtained acrylic polymer is designated as (A-1). The weight average molecular weight (Mw) of the resulting acrylic polymer is shown in Table 1.

(Acrylic Polymers (A-2 to 57, A'-1 to 10))
Acrylic polymers (A-2 to 57, A'-1 to 10) were synthesized in the same manner as for the production of acrylic polymer (A-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Tables 1 to 5. The weight average molecular weights of the obtained acrylic polymers are shown in Tables 1 to 5.

The abbreviations are as follows:
IBXA: Isobornyl acrylate THFA: Tetrahydrofurfuryl acrylate TMCHA: 3,3,5-trimethylcyclohexyl acrylate CHA: Cyclohexyl acrylate IBXMA: Isobornyl methacrylate CTFA: (5-ethyl-1,3-dioxane-5-yl)methyl acrylate BZA: Benzyl acrylate PEA: Phenoxyethyl acrylate OA: Normal octyl acrylate (alkyl group carbon number: 8)
OMA: normal octyl methacrylate (alkyl group carbon number: 8)
DA: normal decyl acrylate (alkyl group carbon number: 10)
DMA: normal decyl methacrylate (alkyl group has 10 carbon atoms)
DDA: normal dodecyl acrylate (alkyl group has 12 carbon atoms)
DDMA: normal dodecyl methacrylate (alkyl group has 12 carbon atoms)
TrDA: normal tridecyl acrylate (alkyl group carbon number: 13)
TrDMA: normal tridecyl methacrylate (alkyl group carbon number: 13)
TeDA: normal tetradecyl acrylate (alkyl group carbon number: 14)
TeDMA: normal tetradecyl methacrylate (alkyl group carbon number: 14)
HDA: normal hexadecyl acrylate (alkyl group carbon number: 16)
HDMA: normal hexadecyl methacrylate (alkyl group carbon number: 16)
ODA: normal octadecyl acrylate (alkyl group carbon number: 18)
ODMA: normal octadecyl methacrylate (alkyl group carbon number: 18)
2EHA: 2-ethylhexyl acrylate iDA: isodecyl acrylate iDMA: isodecyl methacrylate HEA: hydroxyethyl 4HBA: 4-hydroxy-normal butyl AA: acrylic acid MAA: methacrylic acid MA: methyl acrylate EMA: ethyl methacrylate BA: normal butyl acrylate

Example 1
A pressure-sensitive adhesive composition was obtained by blending 100 parts of the acrylic polymer (A-1) with 0.4 parts of "NP-1200" (trade name, manufactured by Mitsui Chemicals, Inc., biuret form of hexamethylene diisocyanate) as the isocyanate curing agent (B) and 0.1 parts of KBE-403 (trade name, 3-glycidoxypropyltriethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) as the silane coupling agent (C).
The obtained pressure-sensitive adhesive composition was applied using a comma coater onto a 38 μm-thick release liner (product name SP-PET-O1-BU: manufactured by Mitsui Chemicals Tocello Co., Ltd.) as a release sheet so that the thickness after drying would be 100 μm, and dried for 3 minutes at 110° C. Thereafter, a 75 μm-thick release liner (product name SP-PET-O3-B3: manufactured by Mitsui Chemicals Tocello Co., Ltd.) as a release sheet was bonded to the pressure-sensitive adhesive layer, and aging was carried out in this state for 7 days at 23° C. to obtain a pressure-sensitive adhesive sheet.

<Examples 2 to 69 and Comparative Examples 1 to 11>
As shown in Tables 6 to 8, pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets were obtained in the same manner as in Example 1, except that the types and amounts of the acrylic polymer, curing agent, and silane coupling agent were changed.

<<Physical properties and evaluation of pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet>>
The adhesive strength, heat resistance (peeling, yellowing), humidity and heat whitening resistance, outgassing resistance, light resistance (peeling, yellowing), and metal corrosion resistance of the obtained adhesive composition and adhesive sheet were evaluated and the dielectric constant was measured by the following methods. The results are shown in Tables 9 to 11.

<Adhesive strength>
The 38 μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was attached to a substrate PET film (manufactured by Toyobo Co., Ltd., product name: Cosmoshine A-4360, thickness 100 μm), and cut into a size of 25 mm wide x 100 mm long to prepare a test adhesive sheet. The other 75 μm release liner of this test adhesive sheet was peeled off, and the adhesive layer was attached to a glass plate in an atmosphere of 23 ° C.-relative humidity 50% (50% RH), and further pressure-bonded with a roll in accordance with JIS Z-0237. After 24 hours from pressure bonding, the peel strength (peel angle 180 °, peel speed 300 mm / min; unit N / 25 mm width) was measured with a tensile tester (Tensilon: manufactured by Orientec Co., Ltd.).
[Evaluation criteria]
A+: Peel strength is 25N/25mm or more. Excellent.
A: The peel strength is 21 N/25 mm or more and less than 25 N/25 mm. Good.
B: Peel strength is 18 N/25 mm or more and less than 21 N/25 mm. Fairly good.
C: Peel strength is 15 N/25 mm or more and less than 18 N/25 mm. Practical use is possible.
D: Peel strength is less than 15 N/25 mm. Not practical.

<Heat resistance (peeling)>
The 38 μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was attached to a 0.5 mm thick polycarbonate (PC) plate (product name: Iupilon NF2000: manufactured by Mitsubishi Gas Chemical Co., Ltd.) using a laminator in an atmosphere of 23 ° C.-50% RH. Next, the other 75 μm release liner of the adhesive sheet was peeled off, and the adhesive layer was attached to a glass plate using a laminator as described above. The test piece was prepared by applying a pressure of 0.5 MPa and holding it for 20 minutes in an atmosphere of 50 ° C., and laminated in the order of PC plate/adhesive layer/glass plate, and was left in an environment of 120 ° C. for 1000 hours. After cooling it at 23 ° C.-50% RH for 24 hours, the degree of peeling of the test piece was visually evaluated.
[Evaluation criteria]
A+: Peeled area is less than 5% of the whole area. Excellent.
A: The peeled area is 5% or more and less than 15% of the entire area. Good.
B: The peeled area is 15% or more and less than 30% of the total area. Fairly good.
C: Peeled area is 30% or more and less than 50% of the total area. Practical use is possible.
D: Peeling area is 50% or more of the whole. Not practical.

<Heat resistance (yellowing)>
The 38 μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was laminated to a glass plate using a laminator in an atmosphere of 23 ° C.-50% RH. Next, the other 75 μm release liner of the adhesive sheet was peeled off, and the adhesive layer was laminated to a glass plate using a laminator as described above. The test piece was prepared by laminating the glass plate/adhesive layer/glass plate in this order by applying a pressure of 0.5 MPa and holding it for 20 minutes in an atmosphere of 50 ° C., and was left in an environment of 120 ° C. for 1000 hours. After cooling it at 23 ° C.-50% RH for 1 hour, the b value was measured, and the difference Δb from the b value before the heat resistance test was calculated. The b value was measured using a spectrophotometer SE6000 manufactured by Nippon Denshoku Kogyo Co., Ltd. under the conditions of a D65 light source and a viewing angle of 2 °.
[Evaluation criteria]
A+: Δb is less than 0.8. Excellent.
A: Δb is 0.8 or more and less than 1.3. Good.
B: Δb is 1.3 or more and less than 2.0. Fairly good.
C: Δb is 2.0 or more and less than 3.0. Practical use is possible.
D: Δb is 3.0 or more. Not practical.

<Wet and heat whitening resistance (glass composition)>
The 38 μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was laminated to a glass plate using a laminator in an atmosphere of 23 ° C.-50% RH. Next, the other 75 μm release liner of the adhesive sheet was peeled off, and the adhesive layer was laminated to a glass plate using a laminator as described above. The test piece was prepared by laminating the glass plate/adhesive layer/glass plate in this order by applying a pressure of 0.5 MPa and holding it for 20 minutes in an atmosphere of 50 ° C., and was left for 1000 hours in an environment of 85 ° C.-85% RH. After cooling it for 1 hour at 23 ° C.-50% RH, the HAZE was measured. The HAZE was measured using a Turbidimeter NDH5000W manufactured by Nippon Denshoku Kogyo Co., Ltd.
[Evaluation criteria]
A+: HAZE is less than 1.0. Excellent.
A: HAZE is 1.0 or more and less than 2.0. Good.
B: HAZE is 2.0 or more and less than 3.5. Fairly good.
C: HAZE is 3.5 or more and less than 5.0. Practical use is possible.
D: HAZE is 5.0 or more. Not suitable for practical use.

<Wet and heat whitening resistance (PC composition)>
The 38 μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was attached to a PET film (manufactured by Toyobo Co., Ltd., product name: A-4300, thickness 100 μm), and cut to a size of 40 mm wide x 60 mm long to prepare a test adhesive sheet. Next, the other 75 μm release liner of the test adhesive sheet was peeled off, and the sheet was attached to a 0.5 mm thick polycarbonate (PC) plate (product name Iupilon NF2000: manufactured by Mitsubishi Gas Chemical Co., Ltd.). This was held for 20 minutes under a pressure of 0.5 MPa in an atmosphere of 50° C. to prepare a test piece laminated in the order of PET film/adhesive layer/PC plate, and left in an environment of 85° C.-85% RH for 240 hours. This was cooled at 23° C.-50% RH for 1 hour, and then HAZE was measured. The haze was measured using a Turbidimeter NDH5000W manufactured by Nippon Denshoku Industries Co., Ltd.
[Evaluation criteria]
A+: HAZE is less than 1.5. Excellent.
A: HAZE is 1.5 or more and less than 2.5. Good.
B: HAZE is 2.5 or more and less than 4.0. Fairly good.
C: HAZE is 4.0 or more and less than 5.5. Practical use is possible.
D: HAZE is 5.5 or more. Not practical.

<Outgassing resistance>
Test pieces were prepared in the same manner as in the evaluation of wet heat whitening resistance (PC structure), and then left for 72 hours in an environment of 85°C and 85% RH. After leaving the test pieces for 1 hour in an atmosphere of 23°C and 50% RH, the appearance of the test pieces was visually observed.
[Evaluation criteria]
A+: No bubbles or floating. Excellent.
A: There are very few air bubbles or lifting of the adhesive layer (1 to less than 5 air bubbles, and the lifting area is less than 3% of the total). Good.
B: There are a few air bubbles or lifting of the adhesive layer (5 to less than 15 air bubbles, and 3% to less than 5% of the total lifted area). Fairly good.
C: Air bubbles or lifting of the adhesive layer are observed (15 to less than 30 air bubbles, and lifting of the adhesive layer accounts for 5% to less than 10% of the total area).
D: There are many air bubbles or lifted adhesive layers (30 or more air bubbles, or lifted areas of 10% or more of the total surface area). Not suitable for practical use.

<Light resistance (peeling)>
A coating liquid was prepared by mixing 10 parts of D-172N as a curing agent with 100 parts of a surface protective coating agent (manufactured by Toyo Ink Co., Ltd., product name: YL454UR, acrylic varnish), and applying the mixture to a 0.5 mm thick polycarbonate (PC) plate (product name: Iupilon NF2000: manufactured by Mitsubishi Gas Chemical Co., Ltd.) using a bar coater. The mixture was then aged at 40°C for 72 hours to prepare a PC plate having a surface protective layer. A test piece was prepared in the same manner as in the evaluation of heat resistance (peeling), except that a PC plate having the above-mentioned surface protective layer was used instead of Iupilon NF2000, and then irradiated with light for 500 hours using a xenon weathering tester manufactured by Q-Lab Co., Ltd. under conditions of a black panel temperature of 83°C and an illuminance of 60 W/m2. The test piece was cooled for 24 hours at 23°C-50% RH, and the degree of peeling of the test piece was evaluated visually.
[Evaluation criteria]
A+: Peeled area is less than 5% of the whole area. Excellent.
A: The peeled area is 5% or more and less than 15% of the entire area. Good.
B: The peeled area is 15% or more and less than 25% of the total area. Fairly good.
C: Peeled area is 25% or more and less than 50% of the total area. Practical use is possible.
D: Peeling area is 50% or more of the whole. Not practical.

<Light resistance (yellowing)>
After preparing a test piece in the same procedure as the evaluation of heat resistance (yellowing), the test piece was irradiated with light for 1000 hours under the conditions of a black panel temperature of 63°C and an illuminance of 85 W/m2 using a Q-Lab xenon weathering tester. After cooling for 1 hour at 23°C-50% RH, the b value was measured, and the difference Δb from the b value before the light resistance test was calculated. The b value was measured using a spectrophotometer SE6000 (product name) manufactured by Nippon Denshoku Industries Co., Ltd., under the conditions of a D65 light source and a viewing angle of 2°.
[Evaluation criteria]
A+: Δb is less than 1.0. Excellent.
A: Δb is 1.0 or more and less than 2.0. Good.
B: Δb is 2.0 or more and less than 3.5. Fairly good.
C: Δb is 3.5 or more and less than 5.0. Practical use is possible.
D: Δb is 5.0 or more. Not practical.

<Metal corrosion resistance>
The 38 μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was attached to a PET film (manufactured by Toyobo Co., Ltd., product name: A-4300, thickness 100 μm), and cut to a size of 40 mm wide x 60 mm long to prepare a test adhesive sheet. Next, the other 75 μm release liner of the test adhesive sheet was peeled off, and the exposed adhesive layer was attached using a laminator to a transparent conductive film of a PET film with a width of 40 mm and a length of 160 mm on which a transparent conductive film was formed by ITO in an atmosphere of 23° C.-50% RH to obtain a laminate, and its resistance value was measured using Loresta GP (model number MCP-T600, manufactured by Mitsubishi Chemical Corporation).
Next, the laminate was left in an environment of 85° C. and 90% RH for 1000 hours, and the resistance was then measured again. The rate of change in resistance before and after the leaving was calculated to evaluate the corrosion resistance of the transparent conductive film.
[Evaluation criteria]
A+: The rate of change in resistance value is less than 120%. Excellent.
A: The rate of change in resistance value is 120% or more and less than 130%. Good.
B: The rate of change in resistance value is 130% or more and less than 140%. Fairly good.
C: The rate of change in resistance value is 140% or more and less than 150%. Practical use is possible.
D: The rate of change in resistance value is 150% or more. Not practical.

<Dielectric constant>
The method for measuring the dielectric constant will be described with reference to FIG. 3. The obtained adhesive sheet was prepared to a size of 100 mm wide x 100 mm long to prepare a test adhesive sheet. The 38 μm release liner of the test adhesive sheet was peeled off, and the exposed adhesive layer 4 was attached to the aluminum vapor deposition layer 3C formed on the glass plate 6. Next, the other 75 μm release liner of the test adhesive sheet was peeled off, and aluminum vapor deposition layers 3A and 3B were formed on the surface of the exposed adhesive layer 4 that was not in contact with the aluminum vapor deposition layer 3C, thereby obtaining a dielectric constant measurement sample 1. Next, the connection terminal (measurement terminal 2A) of the measurement device 7 was connected to the measurement terminal joint portion 5 of the dielectric constant measurement sample 1, and the connection terminal (measurement terminal 2B) was connected to the aluminum vapor deposition layer 3A. The dielectric constant was then measured under the following conditions. The evaluation criteria are as follows.

Measuring device: 1260 impedance measuring instrument manufactured by Solartron, UK Amplifier: 1296 model manufactured by Solartron, UK Dielectric constant measurement interface Electrode configuration: 21 mmΦ, 40 nm thick aluminum vapor deposition layer Counter electrode: 21 mmΦ, 40 nm thick aluminum vapor deposition layer AC current: 100 mV
Terminal: Pin probe Frequency: 100kHz
Measurement environment: 23°C - 50% RH
Sample thickness: 25 μm

[Evaluation criteria]
A+: Dielectric constant is 3.0 or less. Excellent.
A: The dielectric constant is greater than 3.0 and equal to or less than 3.1. Good.
B: The dielectric constant is more than 3.1 and 3.3 or less. Fairly good.
C: Dielectric constant is more than 3.3 and 3.5 or less. Practical use is possible.
D: The dielectric constant exceeds 3.5. Not practical.

As shown in Tables 9 and 10, the pressure-sensitive adhesive compositions according to the present disclosure exhibited excellent results in adhesion, heat resistance, wet heat whitening resistance, outgassing resistance, light resistance, low dielectric constant, and metal corrosion resistance. On the other hand, as shown in Table 11, the pressure-sensitive adhesive compositions of the comparative examples did not satisfy all of the adhesion, heat resistance, wet heat whitening resistance, outgassing resistance, light resistance, low dielectric constant, and metal corrosion resistance.
From these results, it can be said that the pressure-sensitive adhesive composition according to the present disclosure can be suitably used for bonding optical members.

This application claims priority based on Japanese Patent Application No. 2022-209352, filed on December 27, 2022, the entire disclosure of which is incorporated herein by reference.

The symbols in FIG. 1 and FIG. 2 will be explained below.
1: First pressure-sensitive adhesive layer 2: Release film 3: Light-transmitting substrate (cover panel)
4 Polarizing plate 5 Second adhesive layer 6 Barrier layer 7 Organic EL layer 8 Support 9 Organic EL cell

The symbols in FIG. 3 are explained below.
Reference Signs List 1 Dielectric constant measurement sample 2A Measurement terminal 2B Measurement terminal 3A Aluminum vapor deposition layer 3B Aluminum vapor deposition layer 3C Aluminum vapor deposition layer 4 Adhesive layer 5 Measurement terminal joint portion 6 Glass plate 7 Measurement device

Claims (8)

1. A pressure-sensitive adhesive composition comprising an acrylic polymer (A) and a curing agent (B),
   The acrylic polymer (A) is a copolymer of a monomer mixture containing the following (a1), (a2), and (a3):
   The pressure-sensitive adhesive composition contains 2.5 to 20 mass% of (a1), 30 to 80 mass% of (a2), and 0.1 to 20 mass% of (a3) relative to 100 mass% of the monomer mixture.
   (a1) a (meth)acrylic acid ester monomer having an alicyclic structure (excluding (a3)),
   (a2) a (meth)acrylic acid alkyl ester monomer having a linear alkyl group having 8 to 18 carbon atoms;
   (a3) A (meth)acrylic acid ester monomer having a carboxy group and/or a (meth)acrylic acid ester monomer having a hydroxy group.
2. The pressure-sensitive adhesive composition according to claim 1, characterized in that (a3) contains a (meth)acrylic acid ester monomer having a hydroxy group.
3. The adhesive composition according to claim 1, characterized in that the monomer mixture further contains (a4) a (meth)acrylic acid alkyl ester monomer having an alkyl group having 1 to 4 carbon atoms.
4. The pressure-sensitive adhesive composition according to claim 1, further comprising a silane coupling agent (C).
5. The adhesive composition according to claim 1, characterized in that the curing agent (B) contains an isocyanate-based curing agent or a blocked product thereof.
6. An adhesive sheet having an adhesive layer made of the adhesive composition according to any one of claims 1 to 5.
7. A laminate comprising the adhesive sheet according to claim 6 and a light-transmitting substrate.
8. A display comprising the laminate of claim 7, a polarizing plate, and an optical element.

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