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

Abstract

To provide an adhesive agent and adhesive sheet having thick film coating property, initial adhesion, moisture-heat whitening resistance, heat resistance, thermal peeling resistance and outgas resistance, in combination.SOLUTION: An adhesive composition comprising an acrylic polymer (A) that is a copolymer of a monomer mixture containing hydroxyl group-containing monomer (a1) and a curing agent (B), wherein the monomer mixture of 100 mass% contains 5 to 50 mass% of the hydroxyl group-containing monomer (a1), 20 to 80 mass% of an alkyl acrylate monomer (a2) having an alkyl group with 4 to 8 carbon atoms, and 15 to 65 mass% of methyl acrylate (a3); the weight average molecular weight of the acrylic polymer (A) is 400,000 to 1,200,000, the weight average molecular weight of the curing agent (B) is 3,000 to 20,000, and the average number of functional groups of the curing agent (B) is 1.8 to 2.5. This describes an adhesive composition solved by the above characteristics.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Adhesive sheets with 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 tape to the 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 electroluminescence (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 equipped with cover panels to protect their surfaces. Usually, the components constituting an optical display are bonded together via an adhesive layer.

[0004] As mentioned above, adhesives for optical displays, which are expected to be used for long periods of time, must meet basic adhesive performance requirements such as thick-film coating ability and initial adhesion, as well as high durability, such as preventing the adhesive layer itself from turning white under high humidity conditions (humid heat whitening resistance), preventing cohesive failure of the adhesive itself under long-term high-temperature conditions (heat resistance), and preventing lifting or peeling from the adherend under high-temperature conditions (heat peel resistance). Furthermore, adhesives used to secure cover panels made of transparent plastic materials such as polycarbonate (PC) and polymethyl methacrylate (PMMA) must not only meet the above durability requirements, but also prevent lifting or foaming due to gases generated by the transparent plastic (outgassing resistance).

[0005] Optical displays, especially those for automotive applications, require high durability. In recent years, technological innovations such as fifth-generation mobile communication systems (5G), the 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. This has resulted in even stricter performance requirements, with heat resistance at temperatures as high as 120°C now required, in addition to the conventional heat resistance of 80-100°C. Therefore, providing adhesives that can withstand higher temperatures while also satisfying the traditional requirements for resistance to moist heat whitening and outgassing has been a major challenge.

[0006] Many studies have been conducted to date to achieve the durability required for adhesives for optical displays. For example, the adhesive described in Patent Document 1 uses an acrylic 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 peel resistance at 120°C is insufficient. The adhesive described in Patent Document 2 uses an acrylic 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. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-106000 A [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-264092 Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention 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 invention 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 with 4 to 8 carbon atoms, and methyl acrylate (a3), wherein the hydroxyl group-containing monomer (a1) accounts for 5 to 50 mass%, the acrylic acid alkyl ester monomer (a2) having an alkyl group with 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] Another embodiment of the present invention 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] Another embodiment of the present invention relates to the above pressure-sensitive adhesive composition, which further contains a silane coupling agent.

[0013] Another embodiment of the present invention 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] Another embodiment of the present invention relates to the above pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer has a gel fraction of 40 to 80 mass %.

[0015] The present invention also relates to a laminate comprising a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition and a light-transmitting substrate. [Effects of the Invention]

[0016] The present invention 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. DETAILED DESCRIPTION OF THE INVENTION

[0017] The pressure-sensitive adhesive, pressure-sensitive adhesive sheet, and laminate of the present invention will be described below, but the present invention is not limited thereto. In this specification, unless otherwise specified, the terms "(meth)acrylic", "(meth)acryloyl", "(meth)acrylic acid", and "(meth)acrylate" mean "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, the term "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. Furthermore, in this specification, a numerical range specified using "to" is intended to include the numerical values ​​before and after "to" as the range's lower and upper limits. Furthermore, the terms "film" and "sheet" are not distinguished by thickness. Furthermore, the adherend refers to the other side to which the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is attached.

[0020] [Adhesive composition] The pressure-sensitive adhesive composition of the present invention 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 weight of the acrylic polymer (A). When the amount of the isocyanate-based curing agent (B) added 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 invention 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), and 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 with 4 to 8 carbon atoms, and 15 to 65 mass% of the methyl acrylate (a3) ​​based on 100 mass% of the monomer mixture. If the content of monomer (a1) exceeds 50% by mass, the thermal crosslinking reaction due to the hydroxyl groups in the acrylic polymer (A) proceeds in a high-temperature environment, causing the pressure-sensitive adhesive composition to over-crosslink, which makes it impossible to relieve stress caused by thermal shrinkage of the substrate or adherend, resulting in a decrease in heat-resistance peelability. Furthermore, if the content of monomer (a1) is less than 5% by mass, it is impossible to prevent the pressure-sensitive adhesive layer from whitening in a high-temperature, high-humidity environment. If the content of the monomer (a2) is less than 20% by mass, sufficient initial adhesiveness cannot be obtained, whereas if it exceeds 80% by mass, the cohesive strength decreases and heat resistance becomes insufficient. If the content of methyl acrylate (a3) ​​is less than 15% by mass, the outgassing resistance decreases, and if the content of methyl acrylate (a3) ​​is more than 65% by mass, the initial adhesive strength decreases.

[0022] Monomer (a1) is not limited as long as it has a hydroxyl group in the molecule, and specific examples thereof include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethylacrylamide. Of these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred from the viewpoint of adhesive strength and resistance to moist heat.

[0023] The content of the monomer (a1) is preferably 10 to 40% by mass, more preferably 15 to 25% by mass, based on 100% by mass of the monomer mixture. By having the content of the monomer (a1) be 10 to 40% by mass based on 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 the (meth)acrylic acid alkyl ester monomer (a2) having an alkyl group with 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, a (meth)acrylic acid ester monomer having a hydroxyl group or a carboxyl group is referred to as (a1) or (a4), respectively, even if it has an alkyl group with 4 to 8 carbon atoms.

[0025] The upper limit of the content of monomer (a2) is preferably 75 mass%, more preferably 70 mass%, and most preferably 65 mass%. The lower limit of the content of monomer (a2) is preferably 25 mass%, more preferably 30 mass%. When the content of monomer (a2) is 25 to 75 mass% in 100 mass% of the monomer mixture, initial adhesiveness 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, and if it is 0.3 mass% or less, metal corrosiveness can be suppressed.

[0030] The other monomers may be any monomers 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 above-mentioned monomer mixture. Although known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization are possible, solution polymerization is preferred. Solvents used in solution polymerization are preferably, 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 for the polymerization is preferably a radical polymerization initiator, and the radical polymerization initiator is generally an azo compound or a peroxide. 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'-azobispropionitriles such as 2,2'-azobis(2-hydroxymethylpropionitrile); Examples include 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; 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 include 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, relative to 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 coating of a thick film 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 coating properties 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 invention 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 will decrease, and heat resistance will decrease. If it is less than 3,000, the relaxation property will decrease and stress caused by thermal shrinkage of the substrate will not be alleviated, causing the substrate to lift and decreasing heat resistance peeling property. When the average number of functional groups is 1.8 to 2.5, heat resistance and flexibility can be imparted to the pressure-sensitive adhesive composition, stress from the substrate or adherend can be alleviated, and heat-resistant peelability can be improved. 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, and the average number of functional groups is more preferably 1.9 to 2.3. 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, thereby improving heat-resistant peelability.

[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 polymeric 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 of 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, low molecular weight polyamines, etc. The low molecular weight compounds refer to monomers that do not have polymerization units. 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 polyisocyanates having terminal isocyanate groups are the reaction products of one or more polymeric polyols and isocyanates. As the isocyanate, biuret, nurate, adduct and allophanate forms of the above-mentioned aromatic polyisocyanate, aliphatic polyisocyanate, alicyclic polyisocyanate and araliphatic polyisocyanate can be used. The polymer polyol is not limited in any way 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-formed in the presence of a urethane-formation catalyst. A specific example is a production method in which polypropylene glycol, hexamethylene diisocyanate, ethyl acetate, and dioctyltin as a urethane-formation catalyst are charged into a reaction vessel and reacted for 6 hours at approximately 70°C under a nitrogen atmosphere 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] In addition to the curing agent (B), the pressure-sensitive adhesive composition of the present invention can also contain a known curing agent. Examples of known curing agents include epoxy-based curing agents, aziridine-based curing agents, and carbodiimide-based curing agents. 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 invention preferably further contains a silane coupling agent (C). By containing the silane coupling agent (C), adhesive strength, heat resistance, and resistance to wet heat whitening can be 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 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 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), 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 invention may contain chlorinated polyolefin, a plasticizer such as oil, a pigment, a dye, an antioxidant, an ultraviolet absorber, etc., as long as the problem can be solved.

[0054] [Adhesive sheet] The pressure-sensitive adhesive sheet of the present invention includes a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition and a release film. The pressure-sensitive adhesive layer is formed by curing the pressure-sensitive adhesive composition. The pressure-sensitive adhesive sheet of the present invention may have a configuration in which the release film is provided on both sides of the pressure-sensitive adhesive layer or a configuration in which the release film is provided on one side of the pressure-sensitive adhesive layer.

[0055] (Release film) The release film is not particularly limited, but it is preferable to use a plastic substrate, for example, a polyester such as PET, or an acrylic such as PMMA.

[0056] The thickness of the plastic substrate is not particularly limited, and 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 an appropriate 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 is a value determined by the following method. The adhesive composition was coated onto a 75 μm-thick release film (SP-PET-O3-B3, manufactured by Mitsui Chemicals Tohcello) 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) was attached to the adhesive layer as a release film. This was then aged at 40°C for 4 days to obtain an adhesive tape with an adhesive layer made of a cured product in which the peak attributable to isocyanate groups (near 2270 cm-1) was not observed by FT-IR (the peak attributable to isocyanate groups had disappeared). The adhesive tape was cut to a specified 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 viscosity was then calculated using the following formula: Gel fraction (mass%) = (G2 / G1) × 100 G1: Mass of the adhesive layer before extraction with ethyl acetate G2: Mass of adhesive layer after extraction with ethyl acetate and drying

[0062] The pressure-sensitive adhesive sheet of the present invention 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, and 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 invention 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 the cover panel material include polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polycarbonate (PC), polyimide, polycycloolefin, and glass.

[0064] [Laminate] The laminate of the present invention 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 invention and attaching the pressure-sensitive adhesive layer to the light-transmitting substrate.

[0065] The light-transmitting substrate may be glass or a transparent plastic substrate. 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. Furthermore, the light-transmitting substrate may be appropriately subjected to a surface treatment such as a physical treatment such as a corona discharge treatment or a plasma treatment, or a chemical treatment such as a primer treatment, in order to improve the adhesion between the substrate and the pressure-sensitive adhesive layer. Furthermore, the light-transmitting substrate may have a coating layer on the side opposite to the pressure-sensitive adhesive layer. [Example]

[0066] The present invention will be explained in more detail below with reference to examples, but the present invention 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 blending amounts in the tables are in parts by mass, and all amounts other than the solvent are calculated as non-volatile content. Blank spaces in the tables indicate that no blending was performed. The weight average molecular weight and average number of functional groups of the acrylic polymer (A) and the curing agent (B) are measured by the following methods.

[0067] <Measurement of weight average molecular weight (Mw)> The weight-average molecular weight (Mw) was measured by gel permeation chromatography (GPC). The acrylic polymer (A) was measured using a Shimadzu Corporation LC-GPC system "Prominence" GPC apparatus and a Tosoh Corporation TSKgel α-M column, two of which were connected in series. The isocyanate curing agent (B) was measured using a Shimadzu Corporation LC-GPC system "Prominence" GPC apparatus connected to a Wyatte Technology DAWN HELEOS II multi-angle light scattering detector. Resonac Holdings Inc. SHODEX LF-804 columns were used, three of which were connected in series. N,N-dimethylformamide (DMF) was used as the eluent for each measurement, and measurements were performed at 40°C. 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 GPC measurement, the number average molecular weight (Mn) of the curing agent (B) was further calculated using the analysis software ASTRA from Wyatt Technology Corp. 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 functionality = (Mn × NCO value) ÷ 56100

[0069] <Production example of acrylic polymer> (Acrylic polymer (A-1)) A reactor equipped with a stirrer, reflux condenser, nitrogen inlet, thermometer, and dropping tube was charged with 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 initiator, and 60 parts of ethyl acetate as solvent. A solution of 10 parts of HEA, 15 parts of BA, and 25 parts of MA, 60 parts of ethyl acetate, and 0.2 parts of azobisisobutyronitrile was added dropwise from the dropping tube over approximately 2 hours and polymerized for 6 hours at approximately 80°C under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled and diluted with ethyl acetate to produce an acrylic polymer with a weight-average molecular weight (Mw) of 760,000.

[0070] (Acrylic copolymers (A-2 to A-28, A'-1 to A'-13)) Copolymers (A-2 to A-28, A'-1 to A'-13) were synthesized in the same manner as in the production of the 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] [Table 1]

[0072] [Table 2]

[0073] [Table 3]

[0074] [Table 4]

[0075] The abbreviations for the materials used in the production of 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 curing agent> (Isocyanate-based curing agent (B-1)) Using a reactor equipped with a stirrer, reflux condenser, nitrogen inlet pipe, thermometer, and dropping tube, 100 parts of PPG1000 (polypropylene glycol (number average molecular weight (Mn): 1000)) as a high molecular weight polyol, 100 parts of ethyl acetate, and 0.02 parts of dioctyltin (manufactured by Nitto Kasei Co., Ltd., product name "Neostan U-810") as a urethanization catalyst were charged into a reactor, and 20 parts of hexamethylene diisocyanate (HDI) and 80 parts of ethyl acetate were added dropwise over 4 hours at approximately 70°C under a nitrogen atmosphere. After completion of the addition, the mixture was allowed to react for 3 hours. After cooling, the mixture was diluted with ethyl acetate to produce an isocyanate-based curing agent (B-1) with 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 the isocyanate-based curing agent (B-1), except for the compositions and blending amounts (parts by mass) 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] [Table 5]

[0079] [Table 6]

[0080] The abbreviations used in Tables 5 to 7 are as follows: [High molecular weight polyol] 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 (functional group number 2, number average molecular weight 500, manufactured by Kuraray Co., Ltd., product name "Kuraray Polyol P-510") P-1010: Polyester polyol (functional group number 2, number average molecular weight 1,000, manufactured by Kuraray Co., Ltd., product name "Kuraray Polyol P-1010") [Low molecular weight polyol] EG: Ethylene glycol (functional groups: 2, number average molecular weight: 62.07) TMP: Trimethylolpropane [Isocyanate] HDI: Hexamethylene diisocyanate (functional groups: 2, number average molecular weight: 168.2) D-1: Allophanate-modified polyisocyanate (functional groups 2, number average molecular weight 620)

[0081] (Polyisocyanate compound (D-1)) Using a reactor equipped with a stirrer, reflux condenser, nitrogen inlet, and thermometer, 100 parts of HDI and 8 parts of 2-ethylhexanol were charged into a reactor and the urethane reaction was carried out under a nitrogen atmosphere at approximately 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. After 1.5 hours, 0.05 parts of pyrophosphoric acid was added to stop the reaction. The reaction solution was filtered and then purified using a falling thin-film distillation apparatus, with unreacted hexamethylene diisocyanate removed at 160°C (27 Pa) and 150°C (13 Pa) to obtain the 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 (functionality: 2, number average molecular weight (Mn): 1,000)) were charged into a reaction vessel and subjected to urethane formation at approximately 120°C for 6 hours under a nitrogen atmosphere, producing an isocyanate-based curing agent (B-21) with a weight average molecular weight (Mw) of 8,900 and an average functionality 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 approximately 120°C under a nitrogen atmosphere. After that, unreacted hexamethylene diisocyanate was removed using the same procedures as for B-21, to produce an isocyanate-based curing agent (B'-6) with 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 the production of the isocyanate-based curing agent (B-21), except for the compositions and blending amounts (parts by mass) shown in Table 7. The weight-average molecular weights (Mw) of the obtained isocyanate-based curing agents are shown in Table 7.

[0085] [Table 7]

[0086] Example 1 A pressure-sensitive adhesive composition was obtained by blending 100 parts of the acrylic polymer (A-1) with 0.3 parts of the 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). The obtained pressure-sensitive adhesive composition was coated using a comma coater onto a 75 μm thick release liner (SP-PET-O3-B3: manufactured by Mitsui Chemicals Tocello Inc.) as a release film so that the dried thickness would be 100 μm, and the coating was 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 Tocello Inc.) as a release film was attached 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 53 and 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 amounts of the acrylic polymer, curing agent, and silane coupling agent were changed.

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

[0089] <Thick film coating ability> The obtained pressure-sensitive adhesive composition was applied using a comma coater onto a 75 μm-thick release liner (SP-PET-O3-B3, manufactured by Mitsui Chemicals Tocello Co., Ltd.) as a release film so that the thickness after drying would be 100 μm, and the coating was dried at 50° C. for 3 minutes, and then dried at 100° C. for 3 minutes. The appearance of the coating film after drying was evaluated visually. ◎: No foaming or wrinkles. Excellent. ○: There is very little foaming and / or wrinkles (if there are foaming, there are 1 or more and less than 5, and if there are wrinkles, the wrinkled area is less than 1% of the whole). Good. △: There is slight foaming and / or wrinkles (5 to less than 10 foaming spots, 1% to less than 3% of the total wrinkles). Fairly good. ▲: There are bubbles and / or wrinkles (if there are bubbles, there are 10 to less than 30 bubbles; if there are wrinkles, there are 3 to less than 10% of the total). Suitable for use. ×: There are many bubbles and / or wrinkles (more than 30 bubbles, or more than 10% of the total wrinkle area). Not suitable for practical use. However, if bubbling and wrinkles occur at the same time, the evaluation criterion for either bubbling or wrinkles, whichever results in the worse evaluation, is used.

[0090] <Initial adhesion> The 38 μm release film was peeled off from the resulting pressure-sensitive adhesive sheet, and the sheet was then attached to a 188 μm thick PET film (A-4300: manufactured by Toyobo Co., Ltd.). The other 75 μm release film was then peeled off from the pressure-sensitive adhesive sheet, and the sheet was attached to a glass plate using a laminator in the same manner as above, and then pressed with a roll in accordance with JIS Z-0237. After 20 minutes and 24 hours had elapsed since the sheet was pressed, 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 / 25mm) Y: Peel strength after 24 hours (N / 25mm) [Evaluation criteria] ◎: P is 85% or more. Excellent. ○: P is 78% or more and less than 85%. Good. △: P is 70% or more but less than 78%. Fairly good. ▲: P is 60% or more and less than 70%. Practical use possible ×: P is less than 60%. Not practical.

[0091] <Heat and humidity whitening> The 38 μm release liner was peeled off from the resulting adhesive sheet, 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 was peeled off from the adhesive sheet, and the adhesive layer was laminated to a glass plate using a laminator as described 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 of glass plate / adhesive layer / glass plate, and then left in an environment of 85 ° C - 85% RH for 1000 hours. After cooling at 23 ° C - 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 and 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 practical.

[0092] <Heat resistance> The resulting adhesive sheet was cut to a width of 25 mm and a length of 100 mm 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 onto a glass surface with a 2 kg hand roller, moving it back and forth once to obtain an adhesive area of ​​25 mm width x 40 mm length. 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 test piece was evaluated for displacement using a microscope. ◎: The deviation of the test piece is less than 0.1 mm. Excellent. ○: The deviation of the test piece is 0.1 mm or more and less than 0.3 mm. Good. △: The deviation of the test piece is 0.3 mm or more and less than 0.5 mm. Fairly good. ▲: The deviation of the test piece is 0.5 mm or more but less than 0.7 mm. Practical use is possible. ×: The deviation of the test piece is 0.7 mm or more, and it is not practical.

[0093] <Heat-resistant peelability> The 38 μm release liner was peeled off from the resulting 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 Co., Inc.) using a laminator in an atmosphere of 23 ° C - 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 of PC plate / pressure-sensitive adhesive layer / glass plate, and then left in an environment of 120 ° C for 1000 hours. After cooling for 24 hours at 23 ° C - 50% RH, the degree of peeling of the test piece was evaluated visually. ◎: Peeling area is less than 5% of the total. Excellent. ○: Peeled area is 5% or more and less than 15% of the whole. Good. △: Peeled area is 15% or more and less than 30% of the total. Fairly good. ▲: Peeling area is 30% or more but less than 50% of the total. Practical use possible. ×: Peeling area is 50% or more of the whole. Not practical.

[0094] <Outgassing> Test pieces were prepared using the same procedure as for 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 floating. Excellent. Good: There are very few bubbles and / or lifted adhesive layer (1 to less than 5 bubbles, and lifted area is less than 3% of the total). △: There are a few bubbles and / or lifted adhesive layer (5 to less than 15 bubbles, and 3% to less than 5% of the total lifted area). Fairly good. ▲: Air bubbles and / or lifted adhesive layer present (15 to less than 30 air bubbles, or lifted area of ​​5 to less than 10% of the total). Suitable for use. ×: There are many bubbles and / or raised areas of the adhesive layer (30 or more bubbles, or raised areas that account for 10% or more of the total area). Not suitable for practical use. However, if bubbling and wrinkles occur at the same time, the evaluation criterion for either bubbling or wrinkles, whichever results in the worse evaluation, is used.

[0095] [Table 8]

[0096] [Table 9]

[0097] [Table 10]

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic polymer (A) and an isocyanate-based curing agent (B), 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); The monomer mixture contains, based on 100% by mass, 5 to 50% by mass of a hydroxyl group-containing monomer (a1), 20 to 80% by mass of an acrylic acid alkyl ester monomer (a2) having an alkyl group having 4 to 8 carbon atoms, and 15 to 65% by mass of methyl acrylate (a3), 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; A pressure-sensitive adhesive composition, characterized in that the isocyanate-based curing agent (B) has an average number of functional groups of 1.8 to 2.

5.

2. 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. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 3 and a release film.

5. 5. The pressure-sensitive adhesive sheet according to claim 4, wherein the pressure-sensitive adhesive layer has a gel fraction of 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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