Adhesive composition, and adhesive sheet and laminate using said adhesive composition

Abstract

Provided is an adhesive composition containing: an acrylic polymer (A) which is a copolymer of a monomer mixture containing a hydroxyl group-containing monomer (a1); and a curing agent (B), wherein the adhesive composition contains 5-50 mass% of the hydroxyl group-containing monomer (a1), 20-80 mass% of an alkyl acrylate ester monomer (a2) having an alkyl group with 4-8 carbon atoms, and 15-65 mass% of methyl acrylate (a3) in 100 mass% of the monomer mixture, the weight average molecular weight of the acrylic polymer (A) is 400,000-1,200,000, the weight average molecular weight of the curing agent (B) is 3,000-20,000, and the average number of functional groups of the curing agent (B) is 1.8-2.5 inclusive.

Description

Pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet and laminate using said pressure-sensitive adhesive composition

[0001] The present disclosure relates to a pressure-sensitive adhesive composition, and a pressure-sensitive adhesive sheet and laminate using the pressure-sensitive adhesive composition.

[0002] Adhesive sheets having an adhesive layer formed from an adhesive are easy to handle and are used in a wide range of fields, from general-purpose fields such as labels and masking tapes to medical and optical fields. Among these, adhesives used in applications where long-term use is expected, such as optical displays, require durability such as heat resistance and moist heat resistance, and have been actively studied in recent years.

[0003] In recent years, various optical displays, including image display devices such as liquid crystal displays and organic EL displays, have become widespread. Optical displays are also used as input devices, such as touch panels, in addition to display devices. Touch panels are provided with cover panels to protect their surfaces. Components constituting an optical display are usually bonded together via an adhesive layer.

[0004] As described above, adhesives for optical displays intended for long-term use are required to have high durability, such as not discoloring the adhesive layer itself white under high humidity conditions (humid heat whitening resistance), not causing cohesive failure of the adhesive itself under long-term high temperature environments (heat resistance), and not causing lifting or peeling from the adherend under high temperature environments (heat peel resistance), in addition to the basic adhesive properties such as thick film coating ability and initial adhesion. Furthermore, adhesives used to fix cover panels made of transparent plastic materials such as polycarbonate (PC) and polymethyl methacrylate (PMMA) are required to not only have the above durability but also not cause lifting and / or foaming due to gas generated from the transparent plastic (outgassing resistance).

[0005] Among optical displays, high durability is particularly required for in-vehicle applications. In recent years, technological innovations such as fifth-generation mobile communication systems (5G), Internet of Things (IOT), artificial intelligence (AI), and autonomous driving technology have led to active development of automotive electrification and vehicles equipped with interior and exterior displays. As a result, the required performance has become even more stringent, with heat resistance at temperatures as high as 120°C now being required, in addition to the conventional heat resistance of 80 to 100°C. Therefore, providing a pressure-sensitive adhesive that satisfies the heat resistance at higher temperatures and the continued requirements for humidity and heat whitening resistance and outgassing resistance has been a major challenge.

[0006] Many studies have been conducted to date to achieve the durability required for pressure-sensitive adhesives for optical displays. For example, the pressure-sensitive adhesive described in Patent Document 1 uses an acrylic pressure-sensitive adhesive obtained by copolymerizing a hydroxyl group-containing acrylic ester and a nitrogen-containing acrylic ester to impart resistance to moist heat whitening and outgassing, but the heat-resistance peeling property is insufficient at 120°C. The pressure-sensitive adhesive described in Patent Document 2 uses an acrylic pressure-sensitive adhesive obtained by copolymerizing an alkyl acrylate ester having 4 to 8 carbon atoms with N-(2-hydroxyethyl)acrylamide as a monomer to suppress display unevenness, but the heat resistance, moist heat whitening resistance, outgassing resistance, and adhesiveness at 120°C are insufficient.

[0007] JP 2017-106000 A JP 2007-264092 A

[0008] The problem to be solved by the present disclosure is to provide a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet that have thick-film coating properties, initial adhesion, resistance to wet heat whitening, heat resistance, heat-resistant peelability, and outgassing resistance.

[0009] The present inventors have conducted extensive research to solve the above problems and have completed the present invention.

[0010] That is, an embodiment of the present disclosure relates to a pressure-sensitive adhesive composition comprising an acrylic polymer (A) and an isocyanate-based curing agent (B), wherein the acrylic polymer (A) is a copolymer of a monomer mixture containing a hydroxyl group-containing monomer (a1), an acrylic acid alkyl ester monomer (a2) having an alkyl group having 4 to 8 carbon atoms, and methyl acrylate (a3), wherein the monomer mixture contains 5 to 50 mass% of the hydroxyl group-containing monomer (a1), 20 to 80 mass% of the acrylic acid alkyl ester monomer (a2) having an alkyl group having 4 to 8 carbon atoms, and 15 to 65 mass% of the methyl acrylate (a3), relative to 100 mass% of the monomer mixture; the weight-average molecular weight of the acrylic polymer (A) is 400,000 to 1,200,000; the weight-average molecular weight of the isocyanate-based curing agent (B) is 3,000 to 20,000; and the average number of functional groups of the isocyanate-based curing agent (B) is 1.8 to 2.5.

[0011] An embodiment of the present disclosure also relates to the above pressure-sensitive adhesive composition, wherein the acrylic polymer (A) contains 0.3 mass% or less of the (meth)acrylic acid ester monomer (a4) having a carboxyl group in 100 mass% of the monomer mixture.

[0012] Moreover, an embodiment of the present disclosure relates to the above pressure-sensitive adhesive composition, which further contains a silane coupling agent.

[0013] An embodiment of the present disclosure also relates to a pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition and a release film.

[0014] An embodiment of the present disclosure also relates to the pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer has a gel fraction of 40 to 80 mass %.

[0015] An embodiment of the present disclosure also relates to a laminate including a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition and a light-transmitting substrate.

[0016] The present disclosure makes it possible to provide a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet that are excellent in thick-film coating properties, initial adhesion, resistance to wet heat whitening, heat resistance, heat-resistant peelability, and outgassing resistance.

[0017] The pressure-sensitive adhesive, pressure-sensitive adhesive sheet, and laminate of the present disclosure will be described below, but are not limited thereto. In this specification, unless otherwise specified, the terms "(meth)acrylic," "(meth)acryloyl," "(meth)acrylic acid," and "(meth)acrylate" represent "acrylic or methacrylic," "acryloyl or methacryloyl," "acrylic acid or methacrylic acid," and "acrylate or methacrylate," respectively.

[0018] In this specification, the isocyanate-based curing agent (B) may be abbreviated as "curing agent (B)", the hydroxyl group-containing monomer (a1) as "monomer (a1)", the acrylic acid alkyl ester monomer (a2) having an alkyl group with 4 to 8 carbon atoms as "monomer (a2)", and the (meth)acrylic acid ester monomer (a4) having a carboxyl group as "monomer (a4)".

[0019] In this specification, a monomer refers to a monomer having an ethylenically unsaturated group. In addition, in this specification, "parts" and "%" represent "parts by mass" and "% by mass," respectively, unless otherwise specified. In this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the lower and upper limit ranges. Furthermore, "film" and "sheet" are not distinguished by thickness. Furthermore, an adherend refers to the surface to which the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is attached.

[0020] [Adhesive Composition] The adhesive composition of the present disclosure contains an acrylic polymer (A) and an isocyanate-based curing agent (B). The isocyanate-based curing agent (B) is preferably contained in an amount of 0.2 to 2.0 parts by mass, more preferably 0.4 to 1.0 parts by mass, per 100 parts by mass of the acrylic polymer (A). When the amount of the isocyanate-based curing agent (B) is within the above range, both heat resistance and heat-resistant peelability can be achieved.

[0021] <Acrylic Polymer (A)> The acrylic polymer (A) used in the present disclosure is a copolymer of a monomer mixture containing a hydroxyl group-containing monomer (a1), an acrylic acid alkyl ester monomer (a2) having an alkyl group containing 4 to 8 carbon atoms, and methyl acrylate (a3). The monomer mixture contains 5 to 50 mass% of the hydroxyl group-containing monomer (a1), 20 to 80 mass% of the acrylic acid alkyl ester monomer (a2) having an alkyl group containing 4 to 8 carbon atoms, and 15 to 65 mass% of the methyl acrylate (a3) ​​per 100 mass% of the monomer mixture. If the content of monomer (a1) exceeds 50 mass%, the thermal crosslinking reaction caused by the hydroxyl groups in the acrylic polymer (A) proceeds under high temperature conditions, resulting in over-crosslinking of the pressure-sensitive adhesive composition, which makes it impossible to relieve stress generated by thermal shrinkage of the substrate or adherend, resulting in reduced heat peel resistance. Furthermore, if the content of monomer (a1) is less than 5 mass%, whitening of the adhesive layer under high temperature and high humidity conditions cannot be suppressed. If the content of monomer (a2) is less than 20% by mass, sufficient initial adhesive strength cannot be obtained. If it exceeds 80% by mass, cohesive strength decreases and heat resistance becomes insufficient. If the content of methyl acrylate (a3) ​​is less than 15% by mass, outgassing resistance decreases. If the content of methyl acrylate (a3) ​​is more than 65% by mass, initial adhesive strength decreases.

[0022] The monomer (a1) is not limited as long as it is a monomer having a hydroxyl group in the molecule. Specific examples include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl acrylamide. Of these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred from the viewpoints of adhesive strength and moist heat resistance.

[0023] The content of the monomer (a1) is preferably 10 to 40% by mass, and more preferably 15 to 25% by mass, relative to 100% by mass of the monomer mixture. By having the content of the monomer (a1) be 10 to 40% by mass relative to 100% by mass of the monomer mixture, the wet heat whitening property and heat peel resistance under high temperature and high humidity environments are improved.

[0024] Examples of (meth)acrylic acid alkyl ester monomers (a2) having an alkyl group having 4 to 8 carbon atoms include butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, etc. However, in this specification, (meth)acrylic acid ester monomers having a hydroxyl group or a carboxyl group are referred to as (a1) or (a4), respectively, even if they have an alkyl group having 4 to 8 carbon atoms.

[0025] The upper limit of the content of monomer (a2) is preferably 75% by mass, more preferably 70% by mass, and most preferably 65% ​​by mass. The lower limit of the content of monomer (a2) is preferably 25% by mass, more preferably 30% by mass. For example, it may be 25 to 70% by mass, 30 to 70% by mass, 25 to 65% by mass, or 30 to 65% by mass. When the content of monomer (a2) is 25 to 75% by mass relative to 100% by mass of the monomer mixture, initial adhesion and outgassing resistance are improved.

[0026] The monomer mixture further contains methyl acrylate (a3), and may contain a (meth)acrylic acid ester monomer (a4) having a carboxyl group and other monomers, as necessary.

[0027] The content of methyl acrylate (a3) ​​is preferably 25 to 60 mass% and more preferably 30 to 55 mass% in 100 mass% of the monomer mixture. When the content of methyl acrylate in 100 mass% of the monomer mixture is 25 to 60 mass%, adhesive strength and outgassing resistance are improved.

[0028] The (meth)acrylic acid ester monomer (a4) having a carboxyl group is not limited as long as it is a monomer having a carboxyl group in the molecule, and specific examples include (meth)acrylic acid, p-carboxybenzyl acrylate, β-carboxyethyl acrylate, etc. Among these, (meth)acrylic acid is preferred from the viewpoint of adhesive strength, and acrylic acid is more preferred.

[0029] From the viewpoint of metal corrosiveness, it is preferable that the monomer mixture does not contain the monomer (a4), but if the monomer (a4) is contained, it is preferable that the amount of the monomer (a4) is 0.3 mass% or less relative to 100 mass% of the monomer mixture, since metal corrosiveness can be suppressed if the amount is 0.3 mass% or less.

[0030] The other monomer may be any monomer other than the above (a1) to (a4), and examples thereof include (meth)acrylic acid alkyl ester monomers having an alicyclic structure, (meth)acrylic acid ester monomers such as ethyl (meth)acrylate having an alkyl group with 3 or less carbon atoms, (meth)acrylic acid ester monomers such as lauryl (meth)acrylate having an alkyl group with 9 or more carbon atoms, alkoxy-based (meth)acrylic acid esters such as methoxyethyl (meth)acrylate, and nitrogen atom-containing monomers such as N-vinyl-2-pyrrolidone.

[0031] (Production of Acrylic Polymer (A)) The acrylic polymer (A) can be produced by polymerizing the monomer mixture. Although known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization are possible, solution polymerization is preferred. Preferred solvents used in solution polymerization include, for example, acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, and cyclohexanone. The polymerization temperature is preferably a boiling point reaction at 60 to 120°C. The polymerization time is preferably about 3 to 8 hours.

[0032] The polymerization initiator used in the polymerization is preferably a radical polymerization initiator. Radical polymerization initiators are generally azo compounds and peroxides. Examples of azo compounds include 2,2'-azobisbutyronitriles such as 2,2'-azobisisobutyronitrile (AIBN) and 2,2'-azobis(2-methylbutyronitrile); 2,2'-azobisvaleronitriles such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile); 2,2'-azobispropionitriles such as 2,2'-azobis(2-hydroxymethylpropionitrile); and 1,1'-azobis-1-alkanenitriles such as 1,1'-azobis(cyclohexane-1-carbonitrile).

[0033] Examples of peroxides 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; peroxy esters 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; Examples of the peroxyketals include 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; and peroxydicarbonates such as bis(t-butylcyclohexyl)peroxydicarbonate.

[0034] The amount of the polymerization initiator is preferably 0.01 to 3 parts by mass, more preferably 0.04 to 1.5 parts by mass, based on 100 parts by mass of the monomer mixture.

[0035] (Weight Average Molecular Weight (Mw)) The weight average molecular weight (Mw) of the acrylic polymer (A) is 400,000 to 1,200,000. If the weight average molecular weight is below 400,000, the cohesive strength decreases and heat resistance is insufficient. If the molecular weight exceeds 1,200,000, the operability during thick film coating of 100 μm or more and the appearance after coating and drying are insufficient. The weight average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). From the viewpoint of achieving both thick film coatability and heat resistance, the weight average molecular weight of the acrylic polymer (A) is preferably 500,000 to 1,000,000, and most preferably 600,000 to 900,000.

[0036] <Isocyanate-Based Curing Agent (B)> The curing agent (B) used in the present disclosure has a weight-average molecular weight of 3,000 to 20,000 and an average number of functional groups of 1.8 to 2.5. If the weight-average molecular weight of the curing agent (B) exceeds 20,000, the cohesive strength of the adhesive layer itself decreases, resulting in reduced heat resistance. If it is less than 3,000, the relaxation property decreases, making it impossible to relieve stress due to thermal shrinkage of the substrate, resulting in substrate lift and reduced heat-resistant peelability. Having an average number of functional groups of 1.8 to 2.5 can impart heat resistance and flexibility to the adhesive composition, thereby alleviating stress from the substrate or adherend and improving heat-resistant peelability. The weight-average molecular weight of the curing agent (B) is preferably 4,500 to 17,000, and most preferably 6,000 to 15,000. Furthermore, an average number of functional groups of 1.9 to 2.3 is more preferable. When the weight average molecular weight of the curing agent (B) is 4,500 to 17,000, heat resistance and heat-resistant peelability can be imparted, and when the average number of functional groups is 1.9 to 2.3, stress from the substrate or adherend can be further alleviated, and heat-resistant peelability can be improved.

[0037] The average functionality of the curing agent (B) is calculated using the number average molecular weight measured by light scattering detection and the NCO value calculated based on the NCO content determined by titration. The detailed calculation method is shown in the examples.

[0038] The isocyanate curing agent refers to an isocyanate having two or more isocyanate groups or a block product thereof. Examples include biuret, nurate, adduct, and allophanate products of aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and araliphatic polyisocyanates, as well as polyurethane polyisocyanates having terminal isocyanate groups, which are reaction products of the above polyisocyanates and polymer polyols. Polyurethane polyisocyanates having terminal isocyanate groups are preferred in terms of their high reactivity with the hydroxyl groups in the acrylic polymer (A) and their adhesiveness and heat resistance.

[0039] Examples of aromatic polyisocyanates 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, and 4,4',4"-triphenylmethane triisocyanate.

[0040] Examples of aliphatic polyisocyanates 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.

[0041] Examples of the aromatic aliphatic polyisocyanate 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.

[0042] Examples of alicyclic polyisocyanates include 3-isocyanatemethyl-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(isocyanatemethyl)cyclohexane.

[0043] The biuret compound is a self-condensation product having a biuret bond formed by self-condensation of an isocyanate monomer, such as a biuret compound of hexamethylene diisocyanate.

[0044] The nurate derivative is a trimer of an isocyanate monomer, such as a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, or a trimer of tolylene diisocyanate.

[0045] The adduct is a bifunctional or higher isocyanate compound formed by the reaction of an isocyanate monomer with a low molecular weight compound having two or more active hydrogen groups in the molecule. The isocyanate monomer may be a biuret, nurate, adduct, or allophanate formed from the aromatic polyisocyanate, aliphatic polyisocyanate, alicyclic polyisocyanate, or araliphatic polyisocyanate. Examples of low molecular weight compounds having two or more active hydrogen groups in the molecule include low molecular weight polyols and low molecular weight polyamines. The term "low molecular weight compound" refers to a monomer that does not have a polymerization unit. 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.

[0046] The allophanate compound is a bifunctional or higher isocyanate compound obtained by reacting a monoalcohol with an excess amount of isocyanate in the presence of an allophanate catalyst. Examples of the allophanate compound include a compound obtained by reacting a monofunctional butanol with hexamethylene diisocyanate, a compound obtained by reacting a dodecanol with hexamethylene diisocyanate, and a compound obtained by reacting polyoxypropylene with 2-ethylhexyl ether.

[0047] The polyurethane polyisocyanate having terminal isocyanate groups is a reaction product of one or more polymer polyols and isocyanate. The isocyanate may be a biuret, nurate, adduct, or allophanate of the aromatic polyisocyanate, aliphatic polyisocyanate, alicyclic polyisocyanate, or araliphatic polyisocyanate. The polymer polyol is not limited as long as it is a polymer compound having two or more hydroxyl groups. Examples include polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol, and polyisoprene polyol. The polymer compound refers to a compound having polymerization units.

[0048] Examples of polyurethane polyisocyanates having a terminal isocyanate group include a compound obtained by reacting polypropylene glycol with hexamethylene diisocyanate, a compound obtained by reacting polyethylene glycol with hexamethylene diisocyanate, and a compound obtained by reacting polyethylene glycol, polypropylene glycol as a polyol, and hexamethylene diisocyanate.

[0049] The method for producing a polyurethane polyisocyanate having terminal isocyanate groups is not particularly limited, but examples include a method in which a polymer polyol and an isocyanate are urethane-converted in the presence of a urethane-converting catalyst. A specific example is a production method in which a reaction vessel is charged with polypropylene glycol, hexamethylene diisocyanate, ethyl acetate, and dioctyltin as a urethane-converting catalyst, and the mixture is reacted in a nitrogen atmosphere at approximately 70°C for 6 hours to form a urethane. The molar ratio of the hydroxyl groups of the polymer polyol to the isocyanate groups of the isocyanate (NCO / OH ratio) is preferably 1.10 to 1.65. An NCO / OH ratio of 1.10 to 1.60 allows for stable production of a polyurethane polyisocyanate having terminal isocyanate groups and reduces unreacted isocyanate, thereby stabilizing the gel fraction of the pressure-sensitive adhesive layer after aging.

[0050] The pressure-sensitive adhesive composition of the present disclosure can use a known curing agent in addition to the curing agent (B), and examples of known curing agents include epoxy-based curing agents, aziridine-based curing agents, carbodiimide-based curing agents, etc. From the viewpoint of adhesiveness and heat resistance, it is preferable to use the isocyanate-based curing agent (B) alone.

[0051] <Silane Coupling Agent (C)> The pressure-sensitive adhesive composition of the present disclosure preferably further contains a silane coupling agent (C). By containing the silane coupling agent (C), it is possible to improve adhesive strength, heat resistance, and resistance to wet heat whitening. 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 using an amount of 0.05 to 0.2 parts by mass, it becomes easy to achieve both heat resistance and outgassing resistance.

[0052] Examples of the silane coupling agent (C) include alkoxysilane compounds having a (meth)acryloxy group, alkoxysilane compounds having a vinyl group, alkoxysilane compounds having an amino group, alkoxysilane compounds having a mercapto group, and alkoxysilane compounds having an epoxy group. Specific examples of commercially available products include KBM-403 (3-glycidoxypropyltrimethoxysilane), KBE-403 (3-glycidoxypropyltriethoxysilane), and KBM-303 (2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane) (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0053] The pressure-sensitive adhesive composition of the present disclosure may contain chlorinated polyolefin, a plasticizer such as oil, a pigment, a dye, an antioxidant, an ultraviolet absorber, and the like, as long as the problem can be solved.

[0054] [Adhesive Sheet] The adhesive sheet of the present disclosure refers to one comprising an adhesive layer formed from the adhesive composition and a release film. The adhesive layer is formed by curing the adhesive composition. The adhesive sheet of the present disclosure may have a configuration in which the release film is provided on both sides of the adhesive layer, or a configuration in which the release film is provided on one side of the adhesive layer.

[0055] (Release Film) The release film is not particularly limited, but it is preferable to use a plastic substrate. Examples of materials for the plastic substrate include polyesters such as PET and acrylics such as PMMA.

[0056] The thickness of the plastic substrate is not particularly limited, but is preferably, for example, 10 to 5,000 μm, and more preferably 25 to 3,000 μm.

[0057] When applying the pressure-sensitive adhesive composition, the viscosity may be adjusted by adding a suitable solvent. Examples of suitable solvents 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 alcohols should be avoided because they may inhibit the reaction between the hydroxyl groups in the acrylic polymer (A) and the isocyanate curing agent (B).

[0058] The coating method is not particularly limited, and examples thereof include various coating methods using a Mayer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, spin coater, etc. The drying and curing method is also not particularly limited, and examples thereof include hot air drying, infrared rays, reduced pressure methods, and methods using active energy rays, but hot air or steam heating at 60 to 180°C is preferred from the viewpoint of outgassing resistance.

[0059] The thickness of the adhesive layer is preferably 10 to 1,000 μm, more preferably 20 to 500 μm. The adhesive layer may be in the form of a single layer or a laminate of two or more layers.

[0060] The gel fraction of the pressure-sensitive adhesive layer is preferably 40 to 80% by mass, more preferably 50 to 75% by mass, and even more preferably 55 to 70% by mass. A gel fraction of 40% by mass or more can improve heat resistance, and a gel fraction of 80% by mass or less can impart stress relaxation properties to the pressure-sensitive adhesive layer and improve heat-resistant peelability.

[0061] The gel fraction of the pressure-sensitive adhesive layer was determined by the following method. The pressure-sensitive adhesive composition was applied to a 75 μm-thick release film (SP-PET-O3-B3, manufactured by Mitsui Chemicals Tohcello Inc.) to a thickness of 100 μm, dried at 50°C for 3 minutes, and then dried at 100°C for 3 minutes. After drying, a 38 μm-thick release liner (SP-PET-O1-BU, manufactured by Mitsui Chemicals Tohcello Inc.) was attached to the pressure-sensitive adhesive layer as a release film, and aging was carried out in this state at 40°C for 4 days to obtain a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer made of a cured product in which a peak derived from isocyanate groups (near 2270 cm-1) was not observed by FT-IR (the peak derived from isocyanate groups had disappeared). The adhesive tape was cut to a predetermined size, attached to a SUS200 mesh (mesh opening: 0.077 mm, wire diameter: 0.05 mm), immersed in ethyl acetate, extracted at 50°C for 24 hours, and then dried at 100°C for 30 minutes. The gel fraction was calculated using the following formula: Gel fraction (mass%) = (G2 / G1) x 100, where G1 is the mass of the adhesive layer before extraction with ethyl acetate and G2 is the mass of the adhesive layer after extraction with ethyl acetate and drying.

[0062] The pressure-sensitive adhesive sheet of the present disclosure has excellent adhesiveness, resistance to moist heat whitening, outgassing resistance, and heat resistance, and is therefore suitable for forming display components such as display devices such as LCDs and OLEDs, and input devices such as touch panels, or for bonding components together. In particular, it is suitable for use in fixing a cover panel to an optical display component. By using the pressure-sensitive adhesive of the present disclosure to fix a cover panel to an optical display component, it is possible to satisfy various durability requirements, such as heat resistance, resistance to moist heat whitening, outgassing resistance, and light resistance.

[0063] (Cover Panel) Examples of materials for the cover panel include polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polycarbonate (PC), polyimide, polycycloolefin, and glass.

[0064] [Laminate] The laminate of the present disclosure includes a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition and a light-transmitting substrate. The method for producing the laminate is not particularly limited, but for example, the laminate can be formed by peeling off one release film from the pressure-sensitive adhesive sheet of the present disclosure and attaching the pressure-sensitive adhesive layer to the light-transmitting substrate.

[0065] As the light-transmitting substrate, glass or a transparent plastic substrate is used. Examples of the transparent plastic substrate include plastic materials such as polyethylene terephthalate (PET), polyethylene naphthalate, polymethyl methacrylate (PMMA), polycycloolefin, polyimide, and polycarbonate (PC). In particular, PET or PC is preferred, and PC is even more preferred in terms of durability. In addition, the light-transmitting substrate may be appropriately subjected to surface treatment such as physical treatment such as corona discharge treatment or plasma treatment, or chemical treatment such as primer treatment, in order to improve adhesion between the substrate and the pressure-sensitive adhesive layer. In addition, the light-transmitting substrate may have a coating layer on the side opposite to the pressure-sensitive adhesive layer.

[0066] The present disclosure will be explained in more detail below using examples, but the present disclosure is not limited to these examples. In the examples, unless otherwise specified, "parts" means "parts by mass," "%" means "% by mass," and "RH" means "relative humidity." The amounts in the tables are in parts by mass, and all amounts other than the solvent are calculated as non-volatile components. Blank spaces in the tables indicate that no components are added. The methods for measuring the weight average molecular weight and average number of functional groups of the acrylic polymer (A) and curing agent (B) are as follows:

[0067] <Measurement of Weight Average Molecular Weight (Mw)> The weight average molecular weight (Mw) was measured by gel permeation chromatography (GPC). For the measurement of the acrylic polymer (A), a GPC apparatus manufactured by Shimadzu Corporation: LC-GPC system "Prominence" was used, and for the column, a TSKgel α-M manufactured by Tosoh Corporation was used, two of which were connected in series. For the measurement of the isocyanate-based curing agent (B), a GPC apparatus manufactured by Shimadzu Corporation: LC-GPC system "Prominence" connected to a multi-angle light scattering detector DAWN HELEOS II manufactured by Wyatt Technology was used. For the column, a SHODEX LF-804 manufactured by Resonac Holdings Inc. was used, and three of which were connected in series. For each measurement, N,N-dimethylformamide (DMF) was used as the eluent, and measurements were performed at 40 ° C. The Mw was determined by conversion using polystyrene with a known Mw as the standard substance.

[0068] <Average Number of Functional Groups of Curing Agent (B)> In the above GPC measurement, the number average molecular weight (Mn) of the curing agent (B) was further calculated using analysis software ASTRA from Wyatt Technology. Furthermore, the NCO content (mass%) was determined using the method described in JIS K 6806:2003, and the NCO value of the curing agent (B) was calculated using the following formula: NCO value = (NCO content × 56100) ÷ (42 × 1000) The average number of functional groups was calculated from the obtained number average molecular weight (Mn) and NCO value using the following formula: Average number of functional groups = (Mn × NCO value) ÷ 56100

[0069] <Acrylic Polymer Production Example> (Acrylic Polymer (A-1)) Using a reaction apparatus equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping tube, 10 parts of 2-hydroxyethyl acrylate (HEA) as monomer (a1), 15 parts of butyl acrylate (BA) as monomer (a2), and 25 parts of methyl acrylate (MA) as monomer (a3), 0.2 parts of azobisisobutyronitrile as an initiator, and 60 parts of ethyl acetate as a solvent were charged into a reaction vessel, and a solution obtained by mixing 10 parts of HEA, 15 parts of BA, and 25 parts of MA with 60 parts of ethyl acetate and 0.2 parts of azobisisobutyronitrile was added dropwise from the dropping tube over about 2 hours, and polymerization was carried out for 6 hours at about 80 ° C. under a nitrogen atmosphere. After completion of the reaction, the mixture was cooled and diluted with ethyl acetate to produce an acrylic polymer having a weight average molecular weight (Mw) of 760,000.

[0070] (Acrylic Copolymers (A-2 to A-23, A25-A-28, A'-1 to A'-13)) Copolymers (A-2 to A-23, A25-A-28, A'-1 to A'-13) were synthesized in the same manner as in the production of acrylic copolymer (A-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Tables 1 to 4. The weight-average molecular weights of the obtained acrylic copolymers are shown in Tables 1 to 4.

[0071]

[0072]

[0073]

[0074]

[0075] The abbreviations for the materials used in producing the acrylic polymer are explained below. [Monomer (a1)] HEA: 2-hydroxyethyl acrylate HBA: 4-hydroxybutyl acrylate [Monomer (a2)] BA: butyl acrylate (alkyl group carbon number: 4) 2EHA: 2-ethylhexyl butyl acrylate (alkyl group carbon number: 8) [Monomer (a3)] MA: methyl acrylate [Monomer (a4)] AA: acrylic acid [Other monomers] EA: ethyl acrylate (alkyl group carbon number: 2) DA: dodecyl acrylate (alkyl group carbon number: 12) MMA: methyl methacrylate CHA: cyclohexyl methacrylate

[0076] <Production Example of Isocyanate-Based Curing Agent> (Isocyanate-Based Curing Agent (B-1)) Using a reaction apparatus equipped with a stirrer, a reflux condenser, a nitrogen inlet pipe, a thermometer, and a dropping tube, 100 parts of PPG1000 (polypropylene glycol (number average molecular weight (Mn): 1000)) as a polymer polyol, 100 parts of ethyl acetate, and 0.02 parts of dioctyltin (manufactured by Nitto Kasei Co., Ltd., trade name "Neostan U-810") as a urethanization catalyst were charged into a reaction vessel, and 20 parts of hexamethylene diisocyanate (HDI) and 80 parts of ethyl acetate were added dropwise over 4 hours at about 70°C under a nitrogen atmosphere in the reaction vessel, and the reaction was allowed to proceed for 3 hours after completion of the dropwise addition. After cooling, the mixture was diluted with ethyl acetate to produce an isocyanate-based curing agent (B-1) having a weight average molecular weight (Mw) of 14,000 and an average functionality of 2.01.

[0077] (Isocyanate-based curing agents (B-2 to B-20, B'-1 to B'-3) B-2 to B-20 and B'-1 to B'-3 were produced in the same manner as in the production of isocyanate-based curing agent (B-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Tables 5 and 6. The weight-average molecular weights (Mw) of the obtained isocyanate-based curing agents are shown in Tables 5 and 6.

[0078]

[0079]

[0080] The abbreviations used in Tables 5 to 7 are as follows: [High polymer polyols] PPG200: Polypropylene glycol (functional groups: 2, number average molecular weight: 200) PPG400: Polypropylene glycol (functional groups: 2, number average molecular weight: 400) PPG600: Polypropylene glycol (functional groups: 2, number average molecular weight: 600) PPG1000: Polypropylene glycol (functional groups: 2, number average molecular weight: 1,000) PPG2000: Polypropylene glycol (functional groups: 2, number average molecular weight: 2,000) PPG5000: Polypropylene glycol (functional groups: 2, number average molecular weight: 5,000) PEG200: Polyethylene glycol (functional groups: 2, number average molecular weight: 200) PEG600: Polyethylene glycol (functional groups: 2, number average molecular weight: 600) P-510: Polyester polyol (functionality 2, number average molecular weight 500, manufactured by Kuraray Co., Ltd., product name "Kuraray Polyol P-510") P-1010: Polyester polyol (functionality 2, number average molecular weight 1,000, manufactured by Kuraray Co., Ltd., product name "Kuraray Polyol P-1010") [Low molecular weight polyols] EG: Ethylene glycol (functionality 2, number average molecular weight 62.07) TMP: Trimethylolpropane [Isocyanates] HDI: Hexamethylene diisocyanate (functionality 2, number average molecular weight 168.2) D-1: Allophanate-modified polyisocyanate (functionality 2, number average molecular weight 620)

[0081] (Polyisocyanate Compound (D-1)) Using a reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, and a thermometer, 100 parts of HDI and 8 parts of 2-ethylhexanol were charged into a reaction vessel, and a urethane reaction was carried out under a nitrogen atmosphere at about 90°C for 2 hours. After that, the temperature was raised to 120°C, and 0.05 parts of a 20% solids solution of 2-ethylhexanoic acid zirconium in mineral spirits was added as an allophanate catalyst, and after 1.5 hours, 0.05 parts of pyrophosphoric acid was added to stop the reaction. The reaction solution was filtered, and then the unreacted hexamethylene diisocyanate was removed using a falling thin-film distillation apparatus, first at 160°C (27 Pa) and then at 150°C (13 Pa), to thereby purify polyisocyanate compound (D-1).

[0082] (Isocyanate-based curing agent (B-21)) 100 parts of the polyisocyanate compound (D-1) obtained above and 117 parts of PPG1000 (polypropylene glycol (number of functional groups: 2, number average molecular weight (Mn): 1,000)) were charged into a reaction vessel and subjected to urethane formation at about 120°C for 6 hours under a nitrogen atmosphere to produce an isocyanate-based curing agent (B-21) having a weight average molecular weight (Mw) of 8,900 and an average number of functional groups of 2.01.

[0083] (Isocyanate-based curing agent (B'-6)) In the same apparatus as for isocyanate-based curing agent B-21, 7 parts of trimethylolpropane and 250 parts of HDI were charged into a reaction vessel, and urethane formation was carried out for 4 hours at about 120°C under a nitrogen atmosphere. After that, unreacted hexamethylene diisocyanate was removed in the same manner as for B-21, to produce an isocyanate-based curing agent (B'-6) having a weight average molecular weight (Mw) of 700 and an average number of functional groups of 3.

[0084] (Isocyanate-based curing agents (B-22, 23, B'-4, B'-5)) B-22, B-23, B'-4, and B'-5 were produced in the same manner as in the production of isocyanate-based curing agent (B-21), except for changing the composition and blending amounts (parts by mass) to those shown in Table 7. The weight-average molecular weights (Mw) of the obtained isocyanate-based curing agents are shown in Table 7.

[0085]

[0086] Example 1 A pressure-sensitive adhesive composition was obtained by blending 0.3 parts of a curing agent (B-1) and 0.1 parts of KBE-403 (3-glycidoxypropyltriethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) as a silane coupling agent (C) with 100 parts of an acrylic polymer (A-1). The obtained pressure-sensitive adhesive composition was applied using a comma coater to a 75 μm thick release liner (SP-PET-O3-B3: manufactured by Mitsui Chemicals Tocello Co., Ltd.) as a release film to a thickness of 100 μm after drying, and then dried at 50°C for 3 minutes, followed by further drying at 100°C for 3 minutes. After drying, a 38 μm thick release liner (SP-PET-O1-BU: manufactured by Mitsui Chemicals Tocello Co., Ltd.) as a release film was bonded to the pressure-sensitive adhesive layer, and aging was carried out in this state at 40°C for 4 days to obtain a pressure-sensitive adhesive sheet.

[0087] <Examples 2 to 25, 27 to 53, Comparative Examples 1 to 19> As shown in Tables 8 to 10, pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets were obtained in the same manner as in Example 1, except that the types and blending amounts of the acrylic polymer, curing agent, and silane coupling agent were changed.

[0088] <Physical properties and evaluation of pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet> The thick-film coating property of the pressure-sensitive adhesive composition of the present disclosure and the initial adhesion, humidity and heat whitening resistance, heat resistance, heat-resistant peelability, and outgassing resistance of the pressure-sensitive adhesive sheet were measured using the following methods. The results are shown in Tables 8 to 10.

[0089] <Thick Film Coatability> Using a comma coater, the obtained pressure-sensitive adhesive composition was coated onto a 75 μm thick release liner (SP-PET-O3-B3: manufactured by Mitsui Chemicals Tocello Co., Ltd.) as a release film to a dry thickness of 100 μm, and then dried at 50°C for 3 minutes, followed by another 3 minutes at 100°C. The appearance of the dried coating film was evaluated visually. ⊚: No bubbles or wrinkles. Excellent. ○: Very slight bubbles and / or wrinkles (if bubbles, 1 to less than 5, and if wrinkles, the wrinkle area is less than 1% of the total). Good. △: Slight bubbles and / or wrinkles (if bubbles, 5 to less than 10, and if wrinkles, the wrinkle area is 1% to less than 3% of the total). Fairly good. ▲: Bubbles and / or wrinkles (if bubbles, 10 to less than 30, and if wrinkles, the wrinkle area is 3% to less than 10% of the total). Acceptable for practical use. ×: Numerous bubbles and / or wrinkles (more than 30 bubbles, or more than 10% of the total wrinkle area). Not suitable for practical use. However, if both bubbles and wrinkles occur at the same time, the worse evaluation criterion for bubbles or wrinkles will be used.

[0090] <Initial Adhesion> The 38 μm release film was peeled off from the obtained pressure-sensitive adhesive sheet and bonded to a 188 μm thick PET film (A-4300: manufactured by Toyobo Co., Ltd.). Next, the other 75 μm release film was peeled off from the pressure-sensitive adhesive sheet, and the sheet was bonded to a glass plate using a laminator as described above, and then pressed with a roll in accordance with JIS Z-0237. After 20 minutes and 24 hours had elapsed since bonding, the peel strength (peel angle 180°, peel rate 300 mm / min; unit N / 25 mm width) was measured using a tensile tester (Tensilon: manufactured by Orientec Co., Ltd.), and the ratio P (%) of the peel strength after 20 minutes to the peel strength after 24 hours was calculated using the following formula: P (%) = (X / Y) × 100 X: peel strength after 20 minutes (N / 25 mm) Y: peel strength after 24 hours (N / 25 mm) [Evaluation Criteria] ⊚: P is 85% or more. Excellent. ○: P is 78% or more and less than 85%. Good. △: P is 70% or more and less than 78%. Fairly good. ▲: P is 60% or more and less than 70%. Suitable for practical use. ×: P is less than 60%. Not suitable for practical use.

[0091] <Heat and Humidity Whitening> The 38 μm release liner was peeled off from the obtained pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive layer was bonded to a glass plate using a laminator in an atmosphere of 23°C and 50% RH. Next, the other 75 μm release liner was peeled off from the pressure-sensitive adhesive sheet, and the sheet was bonded to a glass plate using a laminator in the same manner as above. 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 glass plate / pressure-sensitive adhesive layer / glass plate, and this was left in an environment of 85°C and 85% RH for 1000 hours. After cooling at 23°C and 50% RH for 1 hour, the haze was measured. The haze was measured using a Turbidimeter NDH5000W manufactured by Nippon Denshoku Industries Co., Ltd. [Evaluation Criteria] ⊚: haze is less than 1.0. Excellent. ○: haze is 1.0 or more but less than 2.0. Good. △: Haze is 2.0 or more and less than 3.5. Fairly good. ▲: Haze is 3.5 or more and less than 5.0. Suitable for practical use. ×: Haze is 5.0 or more. Not suitable for practical use.

[0092] <Heat Resistance> The obtained pressure-sensitive adhesive sheet was cut to a size of 25 mm wide and 100 mm long to prepare a test piece. The 38 μm release liner was then peeled off from the test piece in an atmosphere of 23°C and 50% RH, and the test piece was pressed against a glass surface by moving a 2 kg hand roller back and forth once so that the applied area was 25 mm wide x 40 mm long. After leaving the test piece in an atmosphere of 23°C and 50% RH for 24 hours, a 500 g load was applied and the test piece was left in an 80°C environment for 10 hours. After 10 hours, the slippage of the test piece was evaluated using a microscope. ◎: The test piece slippage was less than 0.1 mm. Excellent. ○: The test piece slippage was 0.1 mm or more and less than 0.3 mm. Good. △: The test piece slippage was 0.3 mm or more and less than 0.5 mm. Fairly good. ▲: The test piece slippage was 0.5 mm or more and less than 0.7 mm. Acceptable for practical use. ×: The test piece slippage was 0.7 mm or more and not suitable for practical use.

[0093] <Heat Resistance Peelability> The 38 μm release liner was peeled off from the obtained pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive layer was bonded to a 0.5 mm thick polycarbonate (PC) plate (Iupilon NF2000: manufactured by Mitsubishi Gas Chemical Company, Inc.) using a laminator in an atmosphere of 23°C and 50% RH. Next, the other 75 μm release liner was peeled off from the pressure-sensitive adhesive sheet, and the sheet was bonded to a glass plate using a laminator in the same manner as above. 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 PC plate / pressure-sensitive adhesive layer / glass plate, and this was left in an environment of 120°C for 1000 hours. After cooling for 24 hours at 23°C and 50% RH, the degree of peeling of the test piece was visually evaluated. ⊚: Peeling area was less than 5% of the total. Excellent. ○: Peeling area was 5% or more but less than 15% of the total. Good. △: Peeled area is 15% or more and less than 30% of the total. Fairly good. ▲: Peeled area is 30% or more and less than 50% of the total. Suitable for practical use. ×: Peeled area is 50% or more of the total. Not suitable for practical use.

[0094] <Outgassing> Test pieces were prepared using the same procedure as in the evaluation of heat and humidity whitening resistance (PC composition), and then left for 72 hours in environments of 85°C and 85% RH and 90°C and 85% RH, respectively. After leaving them in an atmosphere of 23°C and 50% RH for 1 hour, the appearance of each test piece was visually observed. [Evaluation Criteria] ◎: No bubbles or lifting. Excellent. ○: Very few bubbles and / or lifting of the adhesive layer were observed (1 to less than 5 bubbles, and if lifting, the lifted area was less than 3% of the total). Good. △: Slight bubbles and / or lifting of the adhesive layer were observed (5 to less than 15 bubbles, and if lifting, the lifted area was 3% to less than 5% of the total). Fairly good. ▲: Bubbles and / or lifting of the adhesive layer were observed (15 to less than 30 bubbles, and if lifting, the lifted area was 5% to less than 10% of the total). Acceptable for practical use. ×: There are many bubbles and / or lifted adhesive layer (30 or more bubbles, or lifted area of ​​10% or more of the total). Not suitable for practical use. However, if bubbles and wrinkles occur simultaneously, the worse evaluation criterion for bubbles or wrinkles will be used.

[0095]

[0096]

[0097]

[0098] Although the present invention has been described with reference to the above-mentioned several embodiments, the present invention is not limited to these several embodiments. Various modifications can be made to the configuration and details of the present invention within the scope of the present invention.

[0099] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-188424 filed on November 2, 2023, and the subject matter described in Japanese Patent Application No. 2024-165866 filed on September 25, 2024, the entire disclosures of which are incorporated herein by reference.

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic polymer (A) and an isocyanate-based curing agent (B), wherein the acrylic polymer (A) is a copolymer of a monomer mixture containing a hydroxyl group-containing monomer (a1), an acrylic acid alkyl ester monomer (a2) having an alkyl group with 4 to 8 carbon atoms, and methyl acrylate (a3), wherein the hydroxyl group-containing monomer (a1) is 5 to 50 mass%, the acrylic acid alkyl ester monomer (a2) having an alkyl group with 4 to 8 carbon atoms is 20 to 80 mass%, and the methyl acrylate (a3) ​​is 15 to 65 mass%, based on 100 mass% of the monomer mixture; the weight-average molecular weight of the acrylic polymer (A) is 400,000 to 1,200,000; the weight-average molecular weight of the isocyanate-based curing agent (B) is 3,000 to 20,000; and the average number of functional groups of the isocyanate-based curing agent (B) is 1.8 to 2.

5.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic polymer (A) contains 0.3 mass% or less of the (meth)acrylic acid ester monomer (a4) having a carboxyl group in 100 mass% of the monomer mixture.

3. The pressure-sensitive adhesive composition according to claim 1, further comprising a silane coupling agent.

4. An adhesive sheet comprising an adhesive layer formed from the adhesive composition according to any one of claims 1 to 3, and a release film.

5. The pressure-sensitive adhesive sheet according to claim 4, wherein the gel fraction of the pressure-sensitive adhesive layer is 40 to 80% by mass.

6. A laminate comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 3 and a light-transmitting substrate.

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