Adhesive composition, adhesive sheet using the adhesive composition and laminate

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 a 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 tapes to the medical and optical fields. Among them, 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, such as image display devices such as liquid crystal displays and organic electroluminescence displays, have become widespread. In addition to being used as display devices, optical displays are also used as input devices such as touch panels. A cover panel is installed on the touch panel to protect the surface. Usually, the components constituting the optical display are bonded together via an adhesive layer.

[0004] As mentioned above, adhesives for optical displays, which are expected to be used for a long time, require high durability, such as the adhesive layer itself not turning white under high humidity conditions (humid heat whitening resistance), the adhesive itself not undergoing cohesive failure under long-term high temperature environments (heat resistance), and not lifting or peeling off from the adherend under high temperature environments (heat peel resistance), in addition to the basic adhesive performance such as thick film coating ability and initial adhesion. Also, adhesives used to fasten cover panels made of transparent plastic materials such as polycarbonate (PC) and polymethyl methacrylate (PMMA) need to not lift or foam due to gas generated from the transparent plastic in addition to the above durability (outgassing resistance).

[0005] Among optical displays, high durability is required, especially for in-vehicle applications. In recent years, technological innovations such as the fifth generation mobile communication system (5G), Internet of Things (IOT), artificial intelligence (AI), and autonomous driving technology have led to active development of automobile electrification and vehicles equipped with interior and exterior displays. The heat resistance required up to 120°C is now required, in addition to the heat resistance required up to 80-100°C in the past, and the required performance has become even stricter. Therefore, it has been a major challenge to provide an adhesive that satisfies the heat resistance at higher temperatures and the continued requirements for moisture and heat whitening resistance and outgassing resistance.

[0006] Many studies have been conducted so far to meet 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-containing acrylic ester and a nitrogen-containing acrylic ester in order to impart resistance to moist heat whitening and outgassing, but the heat-resistant peeling property is insufficient under the condition of 120°C. The adhesive described in Patent Document 2 uses an acrylic adhesive obtained by copolymerizing an acrylic acid alkyl ester having 4 to 8 carbon atoms and N-(2-hydroxyethyl)acrylamide as monomers in order to suppress display unevenness, but the heat resistance, moist heat whitening resistance, outgassing resistance, and adhesion at 120°C are insufficient. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-106000 A [Patent Document 2] JP 2007-264092 A Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to provide an adhesive and an adhesive sheet which have thick-film coatability, 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 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] 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, further comprising 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% by 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. Effect 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 coatability, initial adhesion, resistance to wet heat whitening, heat resistance, heat-resistant peelability, and outgassing resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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" respectively mean "acrylic or methacrylic", "acryloyl or methacryloyl", "acrylic acid or methacrylic acid", and "acrylate or methacrylate".

[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 monomer is a monomer having an ethylenically unsaturated group. In this specification, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass", respectively. Furthermore, in this specification, a numerical range specified using "to" is intended to include the numerical values ​​before and after "to" as the lower and upper limit values ​​of the range. Furthermore, the terms "film" and "sheet" are not differentiated 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 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 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 group in the acrylic polymer (A) proceeds in a high-temperature environment, causing the pressure-sensitive adhesive composition to be overcrosslinked, which makes it impossible to relieve the stress generated by the thermal shrinkage of the substrate or adherend, resulting in a decrease in heat-resistance peelability. If the content of monomer (a1) is less than 5% by mass, it is impossible to suppress whitening of the pressure-sensitive adhesive layer in a high-temperature and high-humidity environment. If the content of the monomer (a2) is less than 20% by mass, sufficient initial adhesion 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] The monomer (a1) is not limited as long as it has 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-hydroxyethylacrylamide. Of these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred from the viewpoints of adhesive strength and resistance to moist heat.

[0023] The content of monomer (a1) is preferably 10 to 40 mass% and more preferably 15 to 25 mass% in 100 mass% of the monomer mixture. When the content of monomer (a1) is 10 to 40 mass% in 100 mass% of the monomer mixture, the wet heat whitening property and heat peeling resistance in a high temperature and high humidity environment are improved.

[0024] Examples of the (meth)acrylic acid alkyl ester monomer (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, a (meth)acrylic acid ester monomer having a hydroxyl group or a carboxyl group is considered to be (a1) or (a4), respectively, even if it has an alkyl group having 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, the 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%, 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%, the 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 thereof 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 mixture contains the monomer (a4), it is preferable that the amount of the monomer (a4) is 0.3 mass% or less based on 100 mass% of the monomer mixture. If the amount is 0.3 mass% or less, metal corrosiveness can be suppressed.

[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 having 3 or less carbon atoms, (meth)acrylic acid ester monomers such as lauryl (meth)acrylate having an alkyl group having 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. The polymerization method may be a known method such as solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, etc., but solution polymerization is preferred. The solvent used in solution polymerization is preferably, for example, acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, cyclohexanone, etc. The polymerization temperature is preferably a boiling point reaction at 60 to 120°C. The polymerization time is preferably about 3 to 8 hours.

[0032] The polymerization initiator used in 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 the peroxide include dialkyl peroxides such as di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, and 2,5-di(t-butylperoxy)hexyne-3; Peroxyesters such as t-butyl peroxybenzoate, t-butyl peroxyacetate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; Peroxyketals such as 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and n-butyl-4,4-bis(t-butylperoxy)valerate; Hydroperoxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, and 2,5-dimethylcyclohexane-2,5-dihydroperoxide; Diacyl peroxides such as benzoyl peroxide, decanoyl peroxide, lauroyl peroxide, and 2,4-dichlorobenzoyl peroxide; Examples include peroxydicarbonates such as bis(t-butylcyclohexyl) peroxydicarbonate.

[0034] The amount of the polymerization initiator is preferably 0.01 to 3 parts by mass, and 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 less than 400,000, the cohesive force decreases and the 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 coatability and heat resistance, the weight-average molecular weight of the acrylic polymer (A) is preferably from 500,000 to 1,000,000, and most preferably from 600,000 to 900,000.

[0036] <Isocyanate-based hardener (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 decreases, and the heat resistance decreases. If it is less than 3,000, the relaxivity decreases and the stress due to the thermal shrinkage of the substrate cannot be relaxed, causing the substrate to lift off and decreasing the heat resistance of the peeling. 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, and stress from the substrate or adherend can be alleviated, resulting in improved 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. 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, and heat-resistant peelability can be improved.

[0037] The average number of functional groups 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 obtained by titration. A detailed calculation method is shown in the examples.

[0038] The isocyanate-based curing agent refers to an isocyanate having two or more isocyanate groups or a block thereof. Examples include biuret, nurate, adduct and allophanate forms of aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates and aromatic aliphatic polyisocyanates, and polyurethane polyisocyanates having terminal isocyanate groups which are reaction products of the polyisocyanates and polymer polyols. Polyurethane polyisocyanates having terminal isocyanate groups are preferred because they have good reactivity with the hydroxyl groups in the acrylic polymer (A) and have good adhesion 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 form is a self-condensation product having a biuret bond formed by self-condensation of an isocyanate monomer, for example, a biuret form of hexamethylene diisocyanate.

[0044] The nurate form 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 obtained by reacting 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 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 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 product of one or more polymeric polyols and an isocyanate. As the isocyanate, biuret, nurate, adduct and allophanate forms of the above-mentioned aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates and araliphatic polyisocyanates can be used. The polymer polyol is not limited as long as it is a polymer compound having two or more hydroxyl groups. Examples of the polymer polyol include polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol, and polyisoprene polyol. The polymer compound refers to a compound having a polymerization unit.

[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, and hexamethylene diisocyanate as a polyol.

[0049] The method for producing polyurethane polyisocyanate having terminal isocyanate groups is not particularly limited, and examples thereof include a method of urethane-forming polymer polyol and isocyanate in the presence of a urethane-forming catalyst. A specific example is a production method in which polypropylene glycol, hexamethylene diisocyanate, ethyl acetate, and dioctyl tin as a urethane-forming catalyst are charged into a reaction vessel and reacted at about 70°C for 6 hours under a nitrogen atmosphere to form a urethane. The molar ratio (NCO / OH ratio) of the hydroxyl group of the polymer polyol to the isocyanate group of the isocyanate is preferably 1.10 to 1.65. By having an NCO / OH ratio of 1.10 to 1.60, polyurethane polyisocyanate having terminal isocyanate groups can be stably produced, and unreacted isocyanate can be reduced, so that the gel fraction of the pressure-sensitive adhesive layer after aging can be stabilized.

[0050] In the pressure-sensitive adhesive composition of the present invention, in addition to the curing agent (B), a known curing agent can be used in combination. Examples of known curing agents include epoxy-based curing agents, aziridine-based curing agents, and carbodiimide-based curing agents. From the viewpoint of adhesion and heat resistance, it is preferred 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), the adhesive strength, heat resistance, and wet heat whitening resistance 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 making it 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 polyolefins, plasticizers such as oils, pigments, dyes, antioxidants, ultraviolet absorbers, etc., as long as the problem can be solved.

[0054] [Adhesive sheet] The pressure-sensitive adhesive sheet of the present invention refers to a sheet including 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 release film on both sides of the pressure-sensitive adhesive layer or a release film 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, for example, preferably from 10 to 5,000 μm, and more preferably from 25 to 3,000 μm.

[0057] When applying the adhesive composition, the viscosity may be adjusted by adding a suitable solvent. For example, hydrocarbon solvents such as toluene, xylene, hexane, heptane, etc.; ester solvents such as ethyl acetate, butyl acetate, etc.; ketone solvents such as acetone, methyl ethyl ketone, etc.; halogenated hydrocarbon solvents such as dichloromethane, chloroform, etc.; ether solvents such as diethyl ether, methoxytoluene, dioxane, etc., or other hydrocarbon solvents, etc. are included. However, water and alcohol should be avoided because they may inhibit the reaction between the hydroxyl group in the acrylic polymer (A) and the isocyanate curing agent (B).

[0058] The coating method is not particularly limited, and various coating methods can be used, such as a Mayer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, spin coater, etc. In addition, the drying and curing method is not particularly limited, and examples thereof include hot air drying, infrared rays, reduced pressure methods, and 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 pressure-sensitive adhesive layer is preferably 10 to 1,000 μm, more preferably 20 to 500 μm. The pressure-sensitive 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 applied to a 75 μm-thick release film (SP-PET-O3-B3: manufactured by Mitsui Chemicals Tohcello Co., Ltd.) 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 Co., Ltd.) was attached to the adhesive layer as a release film, and aged at 40 ° C for 4 days in this state to obtain an adhesive tape having an adhesive layer made of a cured product in which a peak derived from an isocyanate group (near 2270 cm-1) was not observed by FT-IR (the peak derived from an isocyanate group disappeared). The adhesive tape was cut to a predetermined size, attached to a SUS200 mesh (opening: 0.077 mm, line diameter: 0.05 mm), immersed in ethyl acetate, extracted at 50 ° C for 24 hours, dried at 100 ° C for 30 minutes, and then calculated using the following formula. Gel fraction (mass%) = (G2 / G1) x 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 adhesion, resistance to moist heat whitening, resistance to outgassing, and heat resistance, and is therefore suitable for forming display members such as display devices such as LCDs and OLEDs, and input devices such as touch panels, and for bonding members together. In particular, it is suitable for use in fixing a cover panel to an optical display member. By using the pressure-sensitive adhesive of the present invention to fix a cover panel to an optical display member, it is possible to satisfy various durability requirements such as heat resistance, resistance to moist heat whitening, resistance to outgassing, 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 side of the 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. In order to increase the adhesion between the substrate and the pressure-sensitive adhesive layer, 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 an undercoat treatment. The light-transmitting substrate may have a coating layer on the side opposite to the pressure-sensitive adhesive layer. EXAMPLES

[0066] The present invention will be described 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 the amounts other than the solvent are calculated as non-volatile contents. The blanks in the tables indicate that no blending was performed. The methods for measuring the weight average molecular weight and the average number of functional groups of the acrylic polymer (A) and the curing agent (B) are as follows.

[0067] <Measurement of weight average molecular weight (Mw)> Weight average molecular weight (Mw) was measured by gel permeation chromatography (GPC). For the measurement of acrylic polymer (A), Shimadzu Corporation's GPC device: LC-GPC system "Prominence" and Tosoh Corporation's TSKgel α-M were used as columns, two of which were connected in series. For the measurement of isocyanate-based curing agent (B), Shimadzu Corporation's GPC device: LC-GPC system "Prominence" connected to Wyatte Technology's multi-angle light scattering detector DAWN HELEOS II were used. For the column, Resonaq Holdings Inc.'s SHODEX LF-804 was 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 above GPC measurement, the number average molecular weight (Mn) of the curing agent (B) was further calculated using analysis software ASTRA from Wyatt Technology Co., Ltd. The NCO content (mass%) was determined by 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 x 56100) ÷ (42 x 1000) The average functionality 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)) 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 adding 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 dropped 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 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. Moreover, 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 preparation of the acrylic polymers 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, reflux condenser, nitrogen inlet tube, thermometer, and 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., product name "Neostan U-810") as a urethane catalyst were charged into a reaction tank, and 20 parts of hexamethylene diisocyanate (HDI) and 80 parts of ethyl acetate were dropped into the reaction tank at about 70 ° C. under a nitrogen atmosphere over 4 hours, and the reaction was allowed to proceed for 3 hours after the end of the dropping. 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 functional group number of 2.01.

[0077] (Isocyanate-based hardeners (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 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. [Polymer polyol] PPG200: Polypropylene glycol (functional groups: 2, number average molecular weight: 200) PPG400: Polypropylene glycol (functional group number 2, number average molecular weight 400) PPG600: Polypropylene glycol (functional group number 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 group number 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 group number 2, number average molecular weight 62.07) ·TMP: Trimethylolpropane [Isocyanate] HDI: Hexamethylene diisocyanate (functional group number 2, number average molecular weight 168.2) D-1: Allophanate-modified polyisocyanate (functional group 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 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 was added as an allophanate catalyst, and 1.5 hours later, 0.05 parts of pyrophosphoric acid was added to stop the reaction. After filtering the reaction liquid, a falling thin film distillation apparatus was used to remove unreacted hexamethylene diisocyanate at 160°C (27 Pa) for the first time and 150°C (13 Pa) for the second time, and the polyisocyanate compound (D-1) was purified.

[0082] (Isocyanate-based hardener (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 tank and subjected to urethane formation at about 120°C for 6 hours under a nitrogen atmosphere, producing an isocyanate-based curing agent (B-21) having a weight average molecular weight (Mw) of 8,900 and an average functionality of 2.01.

[0083] (Isocyanate-based hardener (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 tank and urethane-formation was carried out for 4 hours at about 120°C under a nitrogen atmosphere. After that, the unreacted hexamethylene diisocyanate was removed in the same manner as for B-21, and 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 was produced.

[0084] (Isocyanate-based hardeners (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 the isocyanate-based curing agent (B-21), except for the composition 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 the silane coupling agent (C) KBE-403 (3-glycidoxypropyltriethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.). The obtained adhesive composition was coated using a comma coater onto a 75 μm-thick release liner (SP-PET-O3-B3: manufactured by Mitsui Chemicals Tocello) 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. After drying, a 38 μm-thick release liner (SP-PET-O1-BU: manufactured by Mitsui Chemicals Tocello) was attached to the adhesive layer as a release film, and aged in this state at 40° C. for 4 days to obtain an 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 composition and pressure-sensitive adhesive sheet> The thick-film coating property of the pressure-sensitive adhesive composition of the present invention, and the initial adhesion, humidity and heat whitening resistance, heat resistance, heat peel resistance, and outgassing resistance of the pressure-sensitive adhesive sheet were evaluated and measured by the following methods. 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 (1 to less than 5 foaming, and the wrinkled area is less than 1% of the total). Good. △: There is a small amount of foaming and / or wrinkles (5 to less than 10 foaming, 1% to less than 3% of the total wrinkles). Fairly good. ▲: There is foaming and / or wrinkles (10 to less than 30 foaming, 3% to less than 10% wrinkles). Usable. ×: There are many bubbles and / or wrinkles (more than 30 bubbles, or wrinkles that account for more than 10% of the total surface area). Not suitable for practical use. However, when bubbling and wrinkling occur at the same time, the worse evaluation criterion of bubbling or wrinkling is used.

[0090] <Initial adhesion> The 38 μm release film of the obtained adhesive sheet was peeled off, and the sheet was attached to a 188 μm thick PET film (A-4300: manufactured by Toyobo Co., Ltd.). Next, the other 75 μm release film of the adhesive sheet was peeled off, and the sheet was attached 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 the pressing, the peel strength (peel angle 180°, peel speed 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] <Wet heat whitening> The 38 μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was laminated to a glass plate using a laminator in an atmosphere of 23 ° C-50% RH. Next, the other 75 μm release liner of the adhesive sheet was peeled off, and the adhesive layer was laminated to a glass plate using a laminator as described above. The laminate was held for 20 minutes under a pressure of 0.5 MPa in an atmosphere of 50 ° C to prepare a test piece in which the glass plate / adhesive layer / glass plate were laminated in this order, and the test piece was left in an environment of 85 ° C-85% RH for 1000 hours. The test piece was cooled at 23 ° C-50% RH for 1 hour, and then the haze was measured. The haze was measured using a Turbidimeter NDH5000W manufactured by Nippon Denshoku Kogyo 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. Practical use is possible. ×: Haze is 5.0 or more. Not practical.

[0092] <Heat resistance> The obtained adhesive sheet was cut into a test piece having a width of 25 mm and a length of 100 mm, and then the 38 μm release liner of the test piece was peeled off in an atmosphere of 23°C-50% RH, and the test piece was pressed against a glass surface by rolling it back and forth once with a 2 kg hand roller so that the applied area was 25 mm wide x 40 mm long. After leaving it for 24 hours in an atmosphere of 23°C-50% RH, a load of 500 g was applied and it was left for 10 hours in an environment of 80°C. After 10 hours, the deviation of the test piece was evaluated 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 between 0.5mm and 0.7mm. Practical use is possible. ×: The test piece is displaced by 0.7 mm or more, and is not suitable for practical use.

[0093] <Heat resistance> The 38 μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was attached to a 0.5 mm thick polycarbonate (PC) plate (Iupilon NF2000: manufactured by Mitsubishi Gas Chemical Co., Ltd.) using a laminator in an atmosphere of 23 ° C-50% RH. Next, the other 75 μm release liner of the adhesive sheet was peeled off, and the adhesive layer was attached to a glass plate using a laminator as described above. The test piece was prepared by applying a pressure of 0.5 MPa and holding it for 20 minutes in an atmosphere of 50 ° C, and laminated in the order of PC plate / adhesive layer / glass plate, and was left in an environment of 120 ° C for 1000 hours. The test piece was cooled at 23 ° C-50% RH for 24 hours, and then the degree of peeling of the test piece was visually evaluated. ◎: Peeling area is less than 5% of the whole. Excellent. ○: Peeling area is 5% or more and less than 15% of the whole area. Good. △: Peeling area is 15% or more and less than 30% of the total area. Fairly good. ▲: Peeling area is 30% or more and less than 50% of the total area. Practical use is possible. ×: Peeling area is 50% or more of the whole. Not practical.

[0094] <Outgassing> Test pieces were prepared in the same manner as in the evaluation of heat and humidity whitening resistance (PC composition), and then left for 72 hours in environments of 85°C-85% RH and 90°C-85% RH, respectively. After leaving them in an atmosphere of 23°C-50% RH for 1 hour, the appearance of each test piece was visually observed. [Evaluation Criteria] ◎: No bubbles or floating. Excellent. ◯: There are very few air bubbles and / or lifted adhesive layer (1 to less than 5 air bubbles, and the lifted area is less than 3% of the total). Good. △: There are a few air bubbles and / or lifted adhesive layer (5 to less than 15 air bubbles, and lifted area is 3% to less than 5% of the total). Fairly good. ▲: Air bubbles and / or lifted adhesive layer are present (15 to less than 30 air bubbles, and lifted area is 5 to less than 10% of the total). Practical use is possible. ×: There are many air bubbles and / or raised areas of the adhesive layer (30 or more air bubbles, or 10% or more of the raised area). Not suitable for practical use. However, when bubbling and wrinkling occur at the same time, the worse evaluation criterion of bubbling or wrinkling 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 functional group number 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. 4. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to claim 1, 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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