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

Abstract

The present invention provides an adhesive composition containing an acrylic polymer (A) which is a copolymer of a monomer mixture containing a hydroxyl group-containing monomer (a1), and a curing agent (B), the adhesive composition containing 5-50% by mass of the hydroxyl group-containing monomer (a1), 20-80% by mass of an alkyl acrylate monomer (a2) having a C4-8 alkyl group, and 15-65% by mass of methyl acrylate (a3) per 100% by 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 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.

Description

Technical Field

[0001] This disclosure relates to adhesive compositions, adhesive sheets and laminates using the adhesive compositions. Background Technology

[0002] Adhesive sheets with adhesive layers formed by adhesives are easy to handle and are therefore used in a wide range of fields, from general applications such as labels and masking tapes to medical / optical applications. Adhesives used in applications intended for long-term use, such as optical displays, require durability such as heat resistance and resistance to damp heat, and have been extensively studied in recent years.

[0003] In recent years, various optical displays, such as liquid crystal displays (LCDs) and organic EL displays, have become widely used. In addition to being used as display devices, optical displays are also used as input devices, such as touch panels. Touch panels have cover plates for surface protection. Typically, the components of an optical display are bonded together using adhesive layers.

[0004] As mentioned above, adhesives intended for long-term use in optical displays require not only basic properties such as thick-film coating and initial adhesion, but also high durability, including the adhesive layer remaining white under high humidity conditions (resistance to damp heat whitening), preventing coagulation and degradation of the adhesive itself under prolonged high temperatures (heat resistance), and preventing detachment or peeling from the adhered material under high temperatures (heat peel resistance). Furthermore, adhesives used to fix covers made of transparent plastic materials such as polycarbonate (PC) and polymethyl methacrylate (PMMA) require, in addition to the aforementioned durability, the absence of detachment and / or foaming caused by gases emitted from the transparent plastic (resistance to gas release).

[0005] High durability is required in optical displays, especially for automotive applications. In recent years, with technological innovations such as 5G, the Internet of Things (IoT), Artificial Intelligence (AI), and autonomous driving, the electrification of automobiles and the development of in-vehicle displays are actively underway. Previously, heat resistance of 80-100°C was required; now, heat resistance up to 120°C is demanded, making performance requirements even more stringent. Therefore, providing adhesives that meet the requirements for higher temperature resistance as well as the long-standing demands for resistance to damp heat whitening and gas release has become a major challenge.

[0006] To date, much research has been conducted to meet the durability requirements of adhesives for optical displays. For example, in the adhesive described in Patent Document 1, an acrylic adhesive obtained by copolymerizing hydroxyl-containing acrylates with nitrogen-containing acrylates is used to impart resistance to damp heat whitening and gas release. However, its heat-resistant peeling properties at 120°C are insufficient. In the adhesive described in Patent Document 2, an acrylic adhesive obtained by copolymerizing alkyl acrylates with 4 to 8 carbon atoms with N-(2-hydroxyethyl)acrylamide is used to suppress display unevenness. However, its heat resistance, resistance to damp heat whitening, gas release resistance, and adhesion at 120°C are insufficient.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2017-106000

[0010] Patent Document 2: Japanese Patent Application Publication No. 2007-264092 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] The problem to be solved by this disclosure is to provide an adhesive and adhesive sheet that combines thick film coating properties, initial adhesion, resistance to damp heat whitening, heat resistance, heat peeling resistance, and gas release resistance.

[0013] Methods for solving problems

[0014] The inventors conducted repeated research to solve the above-mentioned problems, and as a result, completed this invention.

[0015] Specifically, the embodiments of this disclosure relate to an adhesive composition comprising an acrylic polymer (A) and an isocyanate curing agent (B); wherein the acrylic polymer (A) is a copolymer comprising a monomer mixture comprising a hydroxyl-containing monomer (a1), an alkyl acrylate monomer having 4 to 8 carbon atoms (a2), and methyl acrylate (a3), wherein 100% by mass of the monomer mixture contains 5 to 50% by mass of the hydroxyl-containing monomer (a1), 20 to 80% by mass of the alkyl acrylate monomer having 4 to 8 carbon atoms (a2), and 15 to 65% by mass of methyl acrylate (a3), the acrylic polymer (A) having a weight-average molecular weight of 400,000 to 1,200,000; the isocyanate curing agent (B) having a weight-average molecular weight of 3,000 to 20,000, and the isocyanate curing agent (B) having an average number of functional groups of 1.8 to 2.5.

[0016] Furthermore, embodiments of this disclosure relate to the above-described adhesive composition, wherein the content of a carboxyl-containing (meth)acrylate monomer (a4) in 100% by mass of the monomer mixture of the acrylic polymer (A) is 0.3% by mass or less.

[0017] Furthermore, embodiments of this disclosure relate to the above-described adhesive compositions containing silane coupling agents.

[0018] Furthermore, embodiments of this disclosure relate to adhesive sheets having an adhesive layer and a release film formed from the above-described adhesive composition.

[0019] Furthermore, embodiments of this disclosure relate to the above-mentioned adhesive sheet, wherein the gel fraction of the adhesive layer is 40 to 80 by mass.

[0020] Furthermore, embodiments of this disclosure relate to a laminate comprising an adhesive layer formed from the above-described adhesive composition and a light-transmitting substrate.

[0021] Invention Effects

[0022] According to this disclosure, adhesives and adhesive sheets with excellent thick film coating properties, initial adhesion, resistance to damp heat whitening, heat resistance, heat peel resistance, and gas release resistance can be provided. Detailed Implementation

[0023] The adhesives, adhesive sheets, and laminates disclosed herein will be described below, but are not limited thereto.

[0024] It should be noted that in this specification, when marked as "(meth)acrylic", "(meth)acryloyl", "(meth)acrylic", or "(meth)acrylate", unless otherwise specified, they respectively represent "acrylic or methacrylic", "acryloyl or methacryloyl", "acrylic or methacrylic", or "acrylate or methacrylate".

[0025] In this specification, isocyanate-based curing agents (B) are sometimes referred to as "curing agent (B)", hydroxyl-containing monomers (a1) are referred to as "monomers (a1)", alkyl acrylate monomers (a2) having 4 to 8 carbon atoms are referred to as "monomers (a2)", and (meth)acrylate monomers (a4) having carboxyl groups are referred to as "monomers (a4)".

[0026] In this specification, monomer refers to a monomer having an olefinic unsaturated group.

[0027] In addition, unless otherwise specified, "parts" and "%" in this specification refer to "parts by mass" and "% by mass," respectively.

[0028] In addition, in this specification, the numerical range defined by “~” includes the range of values ​​recorded before and after “~” as the lower and upper limits.

[0029] In addition, "film" and "sheet" are not distinguished based on thickness.

[0030] Furthermore, the adhered object refers to the object to which the adhesive layer of the adhesive sheet is attached.

[0031] [Adhesive Composition]

[0032] The adhesive composition disclosed herein comprises an acrylic polymer (A) and an isocyanate-based curing agent (B). Preferably, the composition contains 0.2 to 2.0 parts by weight of the isocyanate-based curing agent (B) relative to 100 parts by weight of the acrylic polymer (A), and more preferably, 0.4 to 1.0 parts by weight. By adjusting the amount of isocyanate-based curing agent (B) to the above range, both heat resistance and heat-resistant peeling properties can be achieved.

[0033] <Acrylic Polymer (A)>

[0034] The acrylic polymer (A) used in this disclosure is a copolymer comprising a monomer mixture including a hydroxyl-containing monomer (a1), an alkyl acrylate monomer having 4 to 8 carbon atoms (a2), and methyl acrylate (a3), wherein 100% by mass of the monomer mixture contains 5 to 50% by mass of the hydroxyl-containing monomer (a1), 20 to 80% by mass of the alkyl acrylate monomer having 4 to 8 carbon atoms (a2), and 15 to 65% by mass of the methyl acrylate (a3).

[0035] If the monomer (a1) content exceeds 50% by mass, the thermal cross-linking reaction caused by the hydroxyl groups in the acrylic polymer (A) will progress under high temperature conditions, resulting in over-cross-linking of the adhesive composition. Consequently, it will be unable to mitigate the stress caused by the thermal shrinkage of the substrate and adherend, leading to reduced heat-resistant peeling. Furthermore, if the monomer (a1) content is less than 5% by mass, it will be unable to suppress the whitening of the adhesive layer under high temperature and high humidity conditions.

[0036] If the content of monomer (a2) is less than 20% by mass, sufficient initial adhesion cannot be obtained. In addition, if it exceeds 80% by mass, the cohesiveness decreases and the heat resistance is insufficient.

[0037] If the content of methyl acrylate (a3) ​​is less than 15% by mass, the gas release resistance decreases. Furthermore, if the content of methyl acrylate (a3) ​​exceeds 65% by mass, the initial adhesion decreases.

[0038] There are no restrictions on monomers (a1) as long as they contain hydroxyl groups within the molecule. Specifically, examples include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethylacrylamide.

[0039] From the perspective of adhesion and resistance to damp heat, 2-hydroxyethyl methacrylate and 4-hydroxybutyl methacrylate are preferred.

[0040] Regarding the content of monomer (a1), it is preferably 10 to 40% by mass in 100% by mass of the monomer mixture, more preferably 15 to 25% by mass. By making the content of monomer (a1) in 100% by mass of the monomer mixture 10 to 40% by mass, the wet heat whitening and heat-resistant peeling properties under high temperature and high humidity conditions are improved.

[0041] Examples of alkyl methacrylate monomers (a2) having alkyl groups with 4 to 8 carbon atoms include butyl methacrylate, 2-ethylhexyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, and octyl methacrylate. However, in this specification, alkyl methacrylate monomers having hydroxyl or carboxyl groups, even if they have alkyl groups with 4 to 8 carbon atoms, belong to (a1) or (a4), respectively.

[0042] The upper limit of the content of monomer (a2) is preferably 75% by mass, more preferably 70% by mass, and most preferably 65% ​​by mass. The lower limit of the content of monomer (a2) is preferably 25% by mass, more preferably 30% by mass. For example, it can be 25-70% by mass, 30-70% by mass, 25-65% by mass, or 30-65% by mass. By making the monomer (a2) in 100% by mass of the monomer mixture 25-75% by mass, the initial adhesion and gas release resistance are improved.

[0043] The monomer mixture also contains methyl acrylate (a3) ​​and may contain (meth)acrylate monomers with carboxyl groups (a4) and other monomers as needed.

[0044] In the monomer mixture, the content of methyl acrylate (a3) ​​in 100% by mass is preferably 25-60% by mass, more preferably 30-55% by mass. By making the content of methyl acrylate in 100% by mass of the monomer mixture 25-60% by mass, the adhesion and gas release resistance are improved.

[0045] As a (meth)acrylate monomer with a carboxyl group (a4), there are no restrictions on any monomer that has a carboxyl group within its molecule. Specifically, examples include (meth)acrylic acid, p-carboxybenzyl acrylate, and β-carboxyethyl acrylate. Among these, from the viewpoint of adhesion, (meth)acrylic acid is preferred, and acrylic acid is more preferred.

[0046] From the viewpoint of metal corrosion, monomer (a4) is preferably not included in the monomer mixture, but if monomer (a4) is included, the amount is preferably 0.3% by mass or less in 100% by mass of the monomer mixture. If it is 0.3% by mass or less, metal corrosion can be suppressed.

[0047] Other monomers are any monomers other than those listed in (a1) to (a4) above. Examples include alkyl methacrylate monomers with alicyclic structures, ethyl methacrylate and other methacrylate monomers with alkyl groups having 3 or fewer carbon atoms, lauryl methacrylate and other methacrylate monomers with alkyl groups having 9 or more carbon atoms, alkoxy methacrylate and other methacrylate monomers, nitrogen-containing monomers such as N-vinyl-2-pyrrolidone, etc.

[0048] (Manufacturing of acrylic polymer (A))

[0049] Acrylic polymers (A) can be manufactured by polymerizing the above-mentioned monomer mixture.

[0050] The polymerization method can be any known method such as solution polymerization, bulk polymerization, emulsion polymerization, or suspension polymerization, with solution polymerization being preferred. The solvent used in solution polymerization is preferably, for example, acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, or cyclohexanone. The polymerization temperature is preferably a boiling point reaction temperature of 60–120°C. Furthermore, the polymerization time is preferably approximately 3–8 hours.

[0051] The polymerization initiator used in polymerization is preferably a free radical polymerization initiator. Free radical polymerization initiators are typically azo compounds and peroxides.

[0052] Examples of azo compounds include: 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis(2-methylbutyronitrile), etc.

[0053] 2,2'-Azobis(4-methoxy-2,4-dimethylpentanonitrile), 2,2'-Azobis(2,4-dimethylpentanonitrile) and other 2,2'-azobispentanonitriles; 2,2'-Azobis(2-hydroxymethylpropionitrile) and other 2,2'-azobispropionitrile;

[0054] 1,1'-Azobis(cyclohexane-1-carboxynitrile), etc., 1,1'-Azobis-1-alkanenitrile, etc.

[0055] Examples of peroxides include: di-tert-butyl peroxide, dicumyl peroxide, tert-butyl cumyl peroxide, α,α'-bis(tert-butyl peroxide-m-isopropyl)benzene, 2,5-bis(tert-butyl peroxide)hexyne-3, and other dialkyl peroxides.

[0056] Peroxides such as tert-butyl peroxide, tert-butyl peracetate, and 2,5-dimethyl-2,5-di(benzoyl peroxide)hexane; and peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide.

[0057] 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)propane, 1,1-bis(tert-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, n-butyl 4,4-bis(tert-butylperoxy)valerate and other peroxide ketals;

[0058] Hydroperoxides such as cumene hydroperoxide, dicumyl hydroperoxide, and 2,5-dimethylcyclohexane-2,5-disperoxide;

[0059] Benzoyl peroxide, decanoyl peroxide, lauroyl peroxide, 2,4-dichlorobenzoyl peroxide and other diacyl peroxides;

[0060] Dicarbon peroxide, such as bis(tert-butylcyclohexyl) peroxide, etc.

[0061] The polymerization initiator is preferably 0.01 to 3 parts by mass relative to 100 parts by mass of the monomer mixture, and more preferably 0.04 to 1.5 parts by mass.

[0062] (weight-average molecular weight (Mw))

[0063] The weight-average molecular weight (Mw) of acrylic polymers (A) ranges from 400,000 to 1,200,000. When the weight-average molecular weight is below 400,000, the cohesive strength decreases and the heat resistance is insufficient. If the molecular weight exceeds 1,200,000, the workability and appearance after coating thick films greater than 100 μm are insufficient. It should be noted that the weight-average molecular weight is a value converted from polystyrene determined by gel permeation chromatography (GPC).

[0064] From the perspective of balancing thick film coating 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.

[0065] <Isocyanate-based curing agent (B)>

[0066] The curing agent (B) used in this disclosure has a weight-average molecular weight of 3,000 to 20,000 and an average number of functional groups of 1.8 to 2.5.

[0067] If the weight-average molecular weight of the curing agent (B) exceeds 20,000, the cohesiveness of the adhesive layer itself decreases, and the heat resistance decreases. If it is below 3,000, the mitigation ability decreases, and it cannot mitigate the stress caused by the thermal shrinkage of the substrate, resulting in the substrate lifting and reduced heat-resistant peeling.

[0068] By setting the average number of functional groups to 1.8 to 2.5, it is possible to impart flexibility to the heat-resistant and adhesive compositions, alleviate stress from the substrate and the adhered object, and improve heat-resistant peeling properties.

[0069] The weight-average molecular weight of the curing agent (B) is preferably 4,500 to 17,000, and most preferably 6,000 to 15,000. Furthermore, the average number of functional groups is more preferably 1.9 to 2.3.

[0070] By setting the weight-average molecular weight of the curing agent (B) to 4,500 to 17,000, heat resistance and heat-resistant peeling properties can be imparted. By setting the average number of functional groups to 1.9 to 2.3, stress from the substrate and the adhered material can be further mitigated, thereby improving heat-resistant peeling properties.

[0071] The average number of functional groups in the curing agent (B) was calculated using the number-average molecular weight determined by light scattering detection and the NCO value calculated based on the NCO content obtained by titration. Detailed calculation methods are shown in the examples.

[0072] Isocyanate-based curing agents refer to isocyanates or their end-capped forms having two or more isocyanate groups. Examples include biuret bodies, ureate esters, adducts, and ureocarbamate esters composed of aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic aliphatic polyisocyanates, as well as polyurethane polyisocyanates with terminal isocyanate groups that are reaction products of the aforementioned polyisocyanates with high molecular weight polyols. Considering good reactivity with the hydroxyl groups in the acrylic polymer (A) and its adhesion and heat resistance, polyurethane polyisocyanates with terminal isocyanate groups are preferred.

[0073] Examples of aromatic polyisocyanates include: 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, bianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4',4”-triphenylmethane triisocyanate, etc.

[0074] Examples of aliphatic polyisocyanates include: trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (also known as HMDI), pentamethylene diisocyanate, 1,2-propylidene diisocyanate, 2,3-butylidene diisocyanate, 1,3-butylidene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0075] Examples of aromatic aliphatic polyisocyanates include: ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylphenyldimethyl diisocyanate, 1,3-tetramethylphenyldimethyl diisocyanate, etc.

[0076] Examples of alicyclic polyisocyanates include: 3-isocyanate methyl-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'-methylene bis(cyclohexyl isocyanate), 1,4-bis(isocyanate methyl)cyclohexane, etc.

[0077] The aforementioned biuret is a self-condensing compound containing a biuret bond formed by the self-condensation of isocyanate monomers. Examples of biurets include the biuret of hexamethylene diisocyanate.

[0078] The aforementioned urea esters are trimers of isocyanate monomers. Examples include trimers of hexamethylene diisocyanate, isophorone diisocyanate, and toluene diisocyanate.

[0079] The aforementioned adducts are isocyanate compounds with two or more functions, formed by the reaction of isocyanate monomers with low-molecular-weight compounds having two or more active hydrogen groups within the molecule. The isocyanate monomers can be biuret bodies, urate bodies, adducts, and urethane bodies composed of the aforementioned aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic aliphatic polyisocyanates.

[0080] Examples of low-molecular-weight compounds with two or more active hydrogen groups include low-molecular-weight polyols and low-molecular-weight polyamines. It should be noted that low-molecular-weight compounds refer to monomers that do not possess polymerization units.

[0081] Examples of adducts include compounds formed by reacting trimethylolpropane with hexamethylene diisocyanate, compounds formed by reacting trimethylolpropane with toluene diisocyanate, compounds formed by reacting trimethylolpropane with phenylenediamine diisocyanate, compounds formed by reacting trimethylolpropane with isophorone diisocyanate, and compounds formed by reacting 1,6-hexanediol with hexamethylene diisocyanate.

[0082] The aforementioned urea-formate esters are difunctional or higher isocyanate compounds formed by reacting a monohydric alcohol with an excess of isocyanate in the presence of a urea-formate esterification catalyst. Examples of urea-formate esters include compounds formed by reacting monofunctional butanol with hexamethylene diisocyanate, compounds formed by reacting dodecyl alcohol with hexamethylene diisocyanate, and compounds formed by reacting polyoxypropylene with 2-ethylhexyl ether.

[0083] The aforementioned polyurethane polyisocyanates with terminal isocyanate groups are reaction products of one or more high molecular weight polyols and isocyanates.

[0084] Isocyanates can be biuret bodies, urate bodies, adducts, and urethane bodies composed of the above-mentioned aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic aliphatic polyisocyanates.

[0085] There are no restrictions on the type of polyol as long as it is a polymer compound with two or more hydroxyl groups. Examples include polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, and polyisoprene polyols. It should be noted that a polymer compound refers to a compound containing polymerization units.

[0086] Examples of polyurethane polyisocyanates having terminal isocyanate groups include: compounds formed by reacting polypropylene glycol with hexamethylene diisocyanate, compounds formed by reacting polyethylene glycol with hexamethylene diisocyanate, and compounds formed by reacting polyethylene glycol and polypropylene glycol (both polyols) with hexamethylene diisocyanate.

[0087] There are no particular limitations on the method for manufacturing polyurethane polyisocyanates with terminal isocyanate groups. Examples include methods that urethane-oxidize a polymeric polyol and an isocyanate in the presence of a urethane oxidizing catalyst. As a specific example, a method can be described by adding polypropylene glycol, hexamethylene diisocyanate, ethyl acetate, and dioctyltin as a urethane oxidizing catalyst to a reaction vessel and reacting at approximately 70°C for 6 hours under a nitrogen atmosphere to carry out urethane oxidization. The molar ratio (NCO / OH ratio) of the isocyanate group to the hydroxyl group of the polymeric polyol is preferably 1.10 to 1.65. With an NCO / OH ratio of 1.10 to 1.60, polyurethane polyisocyanates with terminal isocyanate groups can be stably manufactured, and unreacted isocyanate can be reduced, thus stabilizing the gel fraction of the cured adhesive layer.

[0088] In addition to the curing agent (B), the adhesive composition disclosed herein may use a known curing agent, such as an epoxy curing agent, an aziridine curing agent, or a carbodiimide curing agent.

[0089] From the viewpoint of adhesion and heat resistance, it is preferable to use isocyanate-based curing agents (B) alone.

[0090] <Silane Coupling Agent (C)>

[0091] The adhesive composition disclosed herein preferably further comprises a silane coupling agent (C). The inclusion of the silane coupling agent (C) improves adhesion, heat resistance, and resistance to damp heat whitening. The silane coupling agent (C) is preferably contained in an amount of 0.05 to 0.2 parts by weight relative to 100 parts by weight of the acrylic polymer (A). By setting it to 0.05 to 0.2 parts by weight, heat resistance and gas release resistance are easily balanced.

[0092] Examples of silane coupling agents (C) include alkoxysilane compounds having (meth)acryloyloxy groups, alkoxysilane compounds having vinyl groups, alkoxysilane compounds having amino groups, alkoxysilane compounds having mercapto groups, or alkoxysilane compounds having epoxy groups.

[0093] As commercially available products, examples include KBM-403 (3-epoxypropoxypropyltrimethoxysilane), KBE-403 (3-epoxypropoxypropyltriethoxysilane), and KBM-303 (2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane) (all manufactured by Shin-Etsu Chemical Industry Co., Ltd.).

[0094] The adhesive composition disclosed herein may also contain chlorinated polyolefins, plasticizers such as oils, pigments, dyes, antioxidants, ultraviolet absorbers, etc., as long as they are within the scope of solving the problem.

[0095] [Adhesive sheet]

[0096] The adhesive sheet disclosed herein refers to an adhesive sheet having an adhesive layer and a release film formed from the above-described adhesive composition. The adhesive layer is formed by curing the adhesive composition. The adhesive sheet of this disclosure may be configured to have a release film on both sides of the adhesive layer or to have a release film on only one side of the adhesive layer.

[0097] (Release film)

[0098] There are no particular restrictions on the type of release film used, but a plastic substrate is preferred. Examples of raw materials for the plastic substrate include polyester-based materials such as PET and acrylic-based materials such as PMMA.

[0099] The thickness of the plastic substrate is not particularly limited, but is preferably 10 to 5,000 μm, and more preferably 25 to 3,000 μm.

[0100] In the application of adhesive compositions, appropriate solvents can be added to adjust the viscosity. Examples include hydrocarbon solvents such as toluene, xylene, hexane, and heptane; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as acetone and methyl ethyl ketone; halogenated hydrocarbon solvents such as dichloromethane and chloroform; ether solvents such as diethyl ether, methoxytoluene, and dioxane; and other hydrocarbon solvents. However, water and alcohols may hinder the reaction between the hydroxyl groups in the acrylic polymer (A) and the isocyanate curing agent (B), so their use is best avoided.

[0101] There are no particular limitations on the coating method; various methods can be used, such as Mayer sticks, applicators, brushes, sprayers, rollers, gravure coaters, die coaters, lip coaters, corner roller coaters, doctor blade coaters, reverse coaters, and spin coaters. Furthermore, there are no particular limitations on the drying and curing method; methods utilizing hot air drying, infrared radiation, reduced pressure, or active energy rays can be used. From the viewpoint of resistance to gas release, heating with hot air or steam at 60–180°C is preferred.

[0102] The thickness of the adhesive layer is preferably 10 to 1,000 μm, more preferably 20 to 500 μm. It should be noted that the adhesive layer can be any of the following forms: a single layer or a stack of two or more layers.

[0103] The gel fraction of the 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. By making the gel fraction 40% by mass or more, heat resistance can be improved, and by making it 80% by mass or less, stress relief can be imparted to the adhesive layer, and heat-resistant peeling resistance can be improved.

[0104] It should be noted that the gel fraction of the adhesive layer was calculated using the following method.

[0105] An adhesive composition was coated onto a 75 μm thick release film (SP-PET-O3-B3: manufactured by Mitsui Chemicals Toccellulosic Co., Ltd.) with a thickness of 100 μm. After drying at 50°C for 3 minutes, it was dried at 100°C for 3 minutes. Following drying, a 38 μm thick release liner (SP-PET-O1-BU: manufactured by Mitsui Chemicals Toccellulosic Co., Ltd.) was laminated onto the adhesive layer as a release film. This liner was then cured at 40°C for 4 days in this state, yielding a peak (2270 cm⁻¹) from isocyanate groups that was not observable by FT-IR. -1 The adhesive tape formed by the cured material (near the isocyanate group peak disappears) is cut to a predetermined size, attached to an SUS 200 screen (mesh size: 0.077 mm, wire 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.

[0106] Gel fraction (mass%) = (G2 / G1) × 100

[0107] G1: Mass of the adhesive layer before extraction with ethyl acetate

[0108] G2: Quality of the adhesive layer after extraction with ethyl acetate and drying.

[0109] The adhesive sheet disclosed herein possesses excellent adhesion, resistance to damp heat whitening, resistance to gas release, and heat resistance, making it suitable for the formation and bonding of display components such as LCD, OLED, and input devices like touch panels. It is particularly suitable for fixing cover plates to optical display components. By using the adhesive disclosed herein to fix cover plates and optical display components, various durability requirements, such as heat resistance, resistance to damp heat whitening, resistance to gas release, and lightfastness, can be met.

[0110] (Cover plate)

[0111] Examples of cover materials include polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polycarbonate (PC), polyimide, polycyclic olefins, and glass.

[0112] [Layered Body]

[0113] The laminate disclosed herein comprises an adhesive layer formed from the above-described adhesive composition and a light-transmitting substrate. The method for manufacturing the laminate is not particularly limited; for example, a release film can be peeled off from one side of the adhesive sheet of this disclosure, and the adhesive layer can be attached to the light-transmitting substrate to form the laminate.

[0114] As a light-transmitting substrate, glass, transparent plastic substrates, etc., are used. Examples of transparent plastic substrates include polyethylene terephthalate (PET), polyethylene naphthalate, polymethyl methacrylate (PMMA), polycyclic olefins, polyimide, polycarbonate (PC), and other plastic materials. PET or PC are particularly preferred, and PC is preferred in terms of durability.

[0115] In addition, to improve the adhesion between the translucent substrate and the adhesive layer, appropriate surface treatments such as corona discharge treatment, plasma treatment, and chemical treatment such as primer treatment can be applied. Furthermore, the translucent substrate may also have a coating on the opposite side to the adhesive layer.

[0116] Example

[0117] The present disclosure is further illustrated below by way of examples, but the present disclosure is not limited to these examples. In the examples, unless otherwise specified, "parts" means "parts by mass", "%" means "% by mass", and "RH" means "relative humidity". Furthermore, the amounts in the table are parts by mass, and except for solvents, are converted values ​​for non-volatile components. Additionally, empty columns in the table indicate no mixing.

[0118] It should be noted that the methods for determining the weight-average molecular weight and average number of functional groups of acrylic polymer (A) and curing agent (B) are as follows.

[0119] <Determination of weight-average molecular weight (Mw)>

[0120] Weight-average molecular weight (Mw) was determined by gel permeation chromatography (GPC). The determination of acrylic polymers (A) was performed using the Shimadzu Corporation LC-GPC system "Prominence," with two TSKgel α-M columns connected in series. The determination of isocyanate curing agents (B) was performed using the Shimadzu Corporation LC-GPC system "Prominence," equipped with a Wyatte Technology DAWN HELEOS II multi-angle light scattering detector. Three SHODEXLF-804 columns were used, connected in series. N,N-dimethylformamide (DMF) was used as the eluent for each determination, and the measurement was performed at 40°C. Mw was determined by conversion using polystyrene, a standard with a known Mw, as a reference material.

[0121] <Average number of functional groups in curing agent (B)>

[0122] In the GPC determination described above, the number-average molecular weight (Mn) of the curing agent (B) was further calculated using the ASTRA analytical software from Wyatte Technology. Additionally, the NCO content (mass %) was determined using the method described in JISK 6806:2003, and the NCO value of the curing agent (B) was calculated using the following formula.

[0123] NCO value = (NCO content × 56100) ÷ (42 × 1000)

[0124] The average number of functional groups is calculated using the following formula from the obtained number-average molecular weight (Mn) and NCO value.

[0125] Average number of functional groups = (Mn × NCO value) ÷ 56100

[0126] <Examples of the manufacture of acrylic polymers>

[0127] (Acrylic polymer (A-1))

[0128] Using a reaction apparatus equipped with a stirrer, reflux condenser, nitrogen inlet pipe, thermometer, and dropper, 10 parts of 2-hydroxyethyl acrylate (HEA) as monomer (a1), 15 parts of butyl acrylate (BA) as monomer (a2), 25 parts of methyl acrylate (MA) as monomer (a3), 0.2 parts of azobisisobutyronitrile (AIB) as initiator, and 60 parts of ethyl acetate as solvent were added to a reaction vessel. The solution of 10 parts HEA, 15 parts BA, 25 parts MA, 60 parts ethyl acetate, and 0.2 parts AIB was added dropwise over approximately 2 hours via the dropper. Polymerization was carried out at approximately 80°C for 6 hours 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.

[0129] (Acrylic copolymers (A-2~A-23, A25~A-28, A'-1~A'-13))

[0130] The composition and proportions (parts by mass) were changed to those recorded in Tables 1 to 4, and the copolymers (A-2 to A-23, A25 to A-28, A'-1 to A'-13) were synthesized by the same method as the acrylic copolymer (A-1).

[0131] In addition, the weight-average molecular weights of the obtained acrylic copolymers are shown in Tables 1 to 4.

[0132] [Table 1]

[0133]

[0134] [Table 2]

[0135]

[0136] [Table 3]

[0137]

[0138] [Table 4]

[0139]

[0140] The following is a description of the abbreviations for the materials used in the manufacture of acrylic polymers.

[0141] [Single (a1)]

[0142] • HEA: 2-Hydroxyethyl acrylate

[0143] • HBA: 4-Hydroxybutyl acrylate

[0144] [Single (a2)]

[0145] • BA: Butyl acrylate (alkyl group has 4 carbon atoms)

[0146] • 2EHA: 2-Ethylhexyl butyl acrylate (alkyl group has 8 carbon atoms)

[0147] [Single (a3)]

[0148] • MA: Methyl acrylate

[0149] [Single (a4)]

[0150] • AA: Acrylic acid

[0151] [Other monomers]

[0152] • EA: Ethyl acrylate (alkyl group has 2 carbon atoms)

[0153] • DA: Dodecyl acrylate (alkyl group has 12 carbon atoms)

[0154] • MMA: Methyl methacrylate

[0155] • CHA: Cyclohexyl methacrylate

[0156] <Example of manufacturing isocyanate-based curing agents>

[0157] (Isocyanate-based curing agent (B-1))

[0158] Using a reaction apparatus equipped with a stirrer, reflux cooling pipe, nitrogen inlet pipe, thermometer, and dropper, 100 parts of PPG 1000 (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 Corporation, trade name "NEOSTANN U-810") as a carbamate catalyst were added to a reaction vessel. Under a nitrogen atmosphere, 20 parts of hexamethylene diisocyanate (HDI) and 80 parts of ethyl acetate were added dropwise over approximately 4 hours at about 70°C. After the addition was completed, the reaction was carried out 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 number of functional groups of 2.01.

[0159] (Isocyanate-based curing agents (B-2~B-20, B'-1~B'-3))

[0160] The compositions and proportions (parts by mass) of the isocyanate-based curing agents B-2 to B-20 and B'-1 to B'-3 were changed to those listed in Tables 5 and 6, and manufactured using the same method as that used for manufacturing the isocyanate-based curing agents (B-1). The weight-average molecular weights (Mw) of the resulting isocyanate-based curing agents are shown in Tables 5 and 6.

[0161] [Table 5]

[0162]

[0163] [Table 6]

[0164]

[0165] It should be noted that the abbreviations recorded in Tables 5 to 7 are as follows.

[0166] [Polyols]

[0167] • PPG 200: Polypropylene glycol (functional group number 2, number average molecular weight 200)

[0168] • PPG 400: Polypropylene glycol (functional group number 2, number average molecular weight 400)

[0169] • PPG 600: Polypropylene glycol (functional group number 2, number average molecular weight 600)

[0170] • PPG 1000: Polypropylene glycol (functional group number 2, number average molecular weight 1,000)

[0171] • PPG 2000: Polypropylene glycol (functional group number 2, number average molecular weight 2,000)

[0172] • PPG 5000: Polypropylene glycol (functional group number 2, number average molecular weight 5,000)

[0173] • PEG 200: Polyethylene glycol (functional group number 2, number average molecular weight 200)

[0174] • PEG 600: Polyethylene glycol (functional group number 2, number average molecular weight 600)

[0175] • P-510: Polyester polyol (functional groups 2, number average molecular weight 500, manufactured by Kuraray Co., Ltd., trade name "Kuraray Polyol P-510")

[0176] • P-1010: Polyester polyol (functional groups 2, number average molecular weight 1,000, manufactured by Kuraray Co., Ltd., trade name "Kuraray Polyol P-1010")

[0177] [Low molecular weight polyols]

[0178] • EG: Ethylene glycol (functional group number 2, number average molecular weight 62.07)

[0179] • TMP: Trimethylolpropane

[0180] [Isocyanate]

[0181] • HDI: Hexamethylene diisocyanate (functional group number 2, number average molecular weight 168.2)

[0182] • D-1: Urea carbamate-modified polyisocyanate (functional group number 2, number average molecular weight 620)

[0183] (Polyisocyanate compound (D-1))

[0184] Using a reaction apparatus equipped with a stirrer, reflux condenser, nitrogen inlet pipe, and thermometer, 100 parts of HDI and 8 parts of 2-ethylhexanol were added to the reaction vessel. The carbamate reaction was carried out at approximately 90°C for 2 hours under a nitrogen atmosphere. The temperature was then raised to 120°C, and 0.05 parts of a 20% mineral spirits solution (the solid component of zirconium 2-ethylhexanoate as a urea carbamate catalyst) were added. After 1.5 hours, 0.05 parts of pyrophosphate were added, and the reaction was stopped. The reaction solution was filtered and then distilled using a downflow thin-film distillation apparatus. Unreacted hexamethylene diisocyanate was removed in the first distillation at 160°C (27 Pa) and the second distillation at 150°C (13 Pa), thus purifying the polyisocyanate compound (D-1).

[0185] (Isocyanate-based curing agent (B-21))

[0186] 100 parts of the polyisocyanate compound (D-1) obtained above and 117 parts of PPG 1000 (polypropylene glycol (functional group number 2, number average molecular weight (Mn): 1,000)) were added to a reaction vessel and urethane-treated at about 120°C for 6 hours under a nitrogen atmosphere to produce an isocyanate-based curing agent (B-21) with a weight average molecular weight (Mw) of 8,900 and an average number of functional groups of 2.01.

[0187] (Isocyanate-based curing agent (B'-6))

[0188] In the same apparatus as isocyanate-based curing agent B-21, 7 parts of trimethylolpropane and 250 parts of HDI were added to a reaction vessel and urethane was urethane-treated at approximately 120°C for 4 hours under a nitrogen atmosphere. Then, unreacted hexamethylene diisocyanate was removed using the same procedure as 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.

[0189] (Isocyanate-based curing agents (B-22, 23, B'-4, B'-5))

[0190] The compositions and proportions (parts by mass) of the isocyanate-based curing agents B-22, B-23, B'-4, and B'-5 were changed to those listed in Table 7 and manufactured using the same method as that used for manufacturing the isocyanate-based curing agent (B-21). The weight-average molecular weight (Mw) of the resulting isocyanate-based curing agents is shown in Table 7.

[0191] [Table 7]

[0192]

[0193] <Example 1>

[0194] An adhesive composition was obtained by mixing 100 parts of acrylic polymer (A-1), 0.3 parts of curing agent (B-1), and 0.1 parts of KBE-403 (3-epoxypropoxypropyltriethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) as a silane coupling agent (C).

[0195] Using a corner-cutting wheel coater, the obtained adhesive composition was coated onto a 75 μm thick release liner (SP-PET-O3-B3: manufactured by Mitsui Chemicals Toccellulos) to achieve a dried thickness of 100 μm. The coating was dried at 50°C for 3 minutes, followed by drying at 100°C for 3 minutes. After drying, a 38 μm thick release liner (SP-PET-O1-BU: manufactured by Mitsui Chemicals Toccellulos) was laminated onto the adhesive layer as a release film. The film was then cured at 40°C for 4 days in this state to obtain the adhesive sheet.

[0196] <Examples 2-25, 27-53, Comparative Examples 1-19>

[0197] As shown in Tables 8 to 10, except for changing the types and amounts of acrylic polymers, curing agents, and silane coupling agents, the same procedures as in Example 1 were followed to obtain adhesive compositions and adhesive sheets, respectively.

[0198] <Physical Properties and Evaluation of Adhesive Compositions and Adhesive Sheets>

[0199] The thick film coating properties, initial adhesion of the adhesive composition of this disclosure, resistance to damp heat whitening, heat resistance, heat peeling resistance, and resistance to gas release were evaluated by the following methods. The results are shown in Tables 8 to 10.

[0200] Thick film coating properties

[0201] The obtained adhesive composition was coated onto a release liner (SP-PET-O3-B3: manufactured by Mitsui Chemicals Tosel Corporation) with a thickness of 75 μm as the release film, to a dried thickness of 100 μm. The coating was dried at 50°C for 3 minutes, followed by drying at 100°C for 3 minutes. The appearance of the dried coating was visually evaluated.

[0202] ◎: No foaming or wrinkles, excellent.

[0203] ○: Very few bubbles and / or wrinkles (if bubbles, there are more than 1 but less than 5; if wrinkles, the wrinkle area is less than 1% of the total area), good.

[0204] △: Slight foaming and / or wrinkling (if foaming, there are 5 or more but less than 10 wrinkles; if wrinkling, the wrinkles account for more than 1% but less than 3% of the total), slightly good.

[0205] ▲: It has foam and / or wrinkles (if foamed, there are more than 10 but less than 30 wrinkles; if wrinkled, the wrinkles are more than 3% but less than 10% of the whole), and it is practical.

[0206] ×: Contains many bubbles and / or wrinkles (more than 30 bubbles if bubbles are present, and more than 10% of the total area if wrinkles are present), making it unusable.

[0207] However, when both foaming and wrinkling occur simultaneously, the evaluation of the worse of the two evaluation criteria is adopted.

[0208] Initial adhesion

[0209] The 38μm release film of the obtained adhesive sheet was peeled off and laminated onto a 188μm thick PET film (A-4300: manufactured by Toyobo Co., Ltd.). Next, another 75μm release film of the adhesive sheet was peeled off and laminated onto a glass plate using a laminator in the same manner as above, and then pressed with rollers according to JIS Z-0237. After pressing, the peel strength was measured using a tensile testing machine (Tensilon: manufactured by Orientec Co., Ltd.) after 20 minutes and 24 hours (peel angle 180°, peel speed 300mm / min; unit N / 25mm width). The ratio P (%) of the peel strength after 20 minutes to the peel strength after 24 hours was calculated using the following formula.

[0210] P(%)=(X / Y)×100

[0211] X: Peel strength after 20 minutes (N / 25mm)

[0212] Y: Peel strength after 24 hours (N / 25mm)

[0213] [Evaluation Criteria]

[0214] ◎: P is above 85%, excellent.

[0215] ○: P is above 78% and below 85%, which is good.

[0216] △: P is above 70% and below 78%, which is slightly good.

[0217] ▲: P is above 60% and less than 70%, which is practical.

[0218] ×: P is less than 60%, not practical.

[0219] <Damp-Heat Albinism>

[0220] The 38μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was laminated to a glass plate using a laminator at 23°C and 50%RH. Next, another 75μm release liner of the adhesive sheet was peeled off and laminated to the glass plate using the same laminator. A pressure of 0.5MPa was applied at 50°C and held for 20 minutes to prepare a test piece stacked in the order of glass plate / adhesive layer / glass plate, which was then placed at 85°C and 85%RH for 1000 hours. After cooling at 23°C and 50%RH for 1 hour, the HAZE was measured. It should be noted that the HAZE was measured using a Turbidimeter NDH 5000W manufactured by Nippon Denshoku Kogyo Co., Ltd.

[0221] [Evaluation Criteria]

[0222] ◎: HAZE less than 1.0, excellent.

[0223] ○: HAZE is above 1.0 and less than 2.0, which is good.

[0224] △: HAZE is above 2.0 and below 3.5, which is slightly good.

[0225] ▲: A HAZE of 3.5 or higher but less than 5.0 is suitable for practical use.

[0226] ×: HAZE is 5.0 or higher, not usable.

[0227] <Heat resistance>

[0228] After preparing the adhesive sheet, cut it into test pieces measuring 25 mm wide and 100 mm long, the 38 μm release liner of the test piece was peeled off under an atmosphere of 23°C and 50%RH. On glass, a 2 kg hand roller was used to press the piece back and forth once, with the adhesion area being 25 mm wide × 40 mm long. After standing for 24 hours at 23°C and 50%RH, a 500 g load was applied, and the piece was left to stand at 80°C for 10 hours. The offset of the test piece after 10 hours was evaluated using a microscope.

[0229] ◎: The offset of the test piece is less than 0.1mm, which is excellent.

[0230] ○: The offset of the test piece is greater than 0.1mm and less than 0.3mm, which is good.

[0231] △: The offset of the test piece is greater than 0.3mm and less than 0.5mm, which is slightly good.

[0232] ▲: The offset of the test piece is greater than 0.5mm and less than 0.7mm, which is suitable for practical use.

[0233] ×: The offset of the test piece is greater than 0.7mm, and it is not practical.

[0234] <Heat peel resistance>

[0235] The 38μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was laminated onto a 0.5mm thick polycarbonate (PC) sheet (Iupilon NF2000: manufactured by Mitsubishi Gas Chemical Co., Ltd.) using a laminator under an atmosphere of 23°C and 50%RH. Next, another 75μm release liner of the adhesive sheet was peeled off and laminated onto a glass plate using the same method. A pressure of 0.5MPa was applied and held at 50°C for 20 minutes to create a test piece stacked in the order of PC sheet / adhesive layer / glass plate, which was then placed at 120°C for 1000 hours. After cooling at 23°C and 50%RH for 24 hours, the degree of peeling of the test piece was visually evaluated.

[0236] ◎: The peeled area is less than 5% of the whole, which is excellent.

[0237] ○: The area of ​​peeling is more than 5% and less than 15% of the whole, which is good.

[0238] △: The peeled area is more than 15% and less than 30% of the whole, which is slightly good.

[0239] ▲: If the area to be peeled off is more than 30% and less than 50% of the whole, it is practical.

[0240] ×: If the area to be peeled off exceeds 50% of the total area, it is not practical.

[0241] <Gas-releasing properties>

[0242] After preparing the test pieces following the same procedure as for evaluating resistance to damp heat whitening (PC composition), they were placed in environments of 85°C and 85%RH and 90°C and 85%RH for 72 hours respectively. Then, after placing them in an atmosphere of 23°C and 50%RH for 1 hour, the appearance of each test piece was visually observed.

[0243] [Evaluation Criteria]

[0244] ◎: No bubbles, floats, excellent.

[0245] ○: Very few air bubbles and / or adhesive layer floating (if air bubbles, there are more than 1 but less than 5; if floating, the area of ​​the floating is less than 3% of the whole), good.

[0246] △: Slight bubbles and / or loose adhesive layer (if bubbles, there are more than 5 but less than 15; if loose, the area of ​​loose adhesive layer is more than 3% but less than 5% of the total area), slightly good.

[0247] ▲: If there are air bubbles and / or adhesive layer floating (if there are air bubbles, there are more than 15 but less than 30; if there are floating areas, the floating area is more than 5% but less than 10% of the whole), it is usable.

[0248] ×: This product contains many air bubbles and / or has more than 30 air bubbles, or more than 10% of the total area of ​​the adhesive layer. It is not practical.

[0249] In cases where both bubbles and buoyancy occur simultaneously, the evaluation of the worse of the two evaluation criteria is adopted.

[0250] [Table 8]

[0251]

[0252] [Table 9]

[0253]

[0254] [Table 10]

[0255]

[0256] The present invention has been described with reference to the above-described embodiments, but the present invention is not limited to the above-described embodiments. Various modifications can be made to the structure and details of the present invention within the scope of the present invention.

[0257] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-188424 filed on November 2, 2023, and Japanese Patent Application No. 2024-165866 filed on September 25, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. An 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 comprising a hydroxyl group-containing monomer (al), an alkyl acrylate monomer (a2) having an alkyl group with a carbon atom number of 4 to 8, and methyl acrylate (a3), contains 5 to 50% by mass of the hydroxyl group-containing monomer (al), 20 to 80% by mass of the alkyl acrylate monomer (a2) having an alkyl group with a carbon atom number of 4 to 8, and 15 to 65% by mass of methyl acrylate (a3) in 100% by 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, the average number of functional groups of the isocyanate-based curing agent (B) is 1.8 to 2.

5.

2. The adhesive composition of claim 1, wherein, in the acrylic polymer (A), the content of the (meth)acrylate monomer (a4) having a carboxyl group in 100% by mass of the monomer mixture is 0.3% by mass or less.

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

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

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

6. A laminate provided with an adhesive layer formed of the adhesive composition according to any one of claims 1 to 3 and a light-transmissive substrate.

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