Optical adhesive, and adhesive sheet

Abstract

This invention provides an adhesive and adhesive sheet that simultaneously possess excellent adhesion, heat resistance, resistance to damp heat whitening, resistance to evaporation, and lightfastness. The problem of this invention is solved by the following optical adhesive: comprising an acrylic copolymer (A) and a hardener (B), wherein the acrylic copolymer (A) is a copolymer of monomers comprising, in 100% by mass, a monomer mixture containing 20% ​​to 60% by mass of an alkyl (meth)acrylate monomer (a1) having 1 to 2 carbon atoms, a monomer mixture containing 30% to 70% by mass of an alkyl (meth)acrylate monomer (a2) having 4 to 8 carbon atoms, and a monomer mixture containing 2.6% to 15% by mass of a hydroxyl-containing vinyl unsaturated monomer (a3), wherein the monomer mixture comprises at least two hydroxyl-containing vinyl unsaturated monomers (a3), and the ratio G'2 / G'1 of the storage elastic modulus G'1 at 175°C to the storage elastic modulus G'2 at 225°C is 0.4 to 1.4.

Description

Technical Field

[0001] This disclosure relates to an optical adhesive and an adhesive sheet. Prior Technology

[0002] Adhesive sheets with an adhesive layer formed by an adhesive are widely used in labeling and medical applications due to their ease of handling. Adhesives intended for long-term use, such as those used in marking films or window films, automotive components, and optical displays, require durability such as heat resistance, resistance to damp heat, weather resistance, and light resistance. In recent years, research has been actively focused on improving the durability of adhesives.

[0003] In addition, various optical displays, such as Liquid Crystal Displays (LCDs) and Organic Electroluminescence Displays (OLEDs), are widely used as display devices. Besides being used as display devices, optical displays are also used as input devices, such as touch panels. A cover panel is provided on the touch panel to protect its surface. Typically, the components constituting these optical displays are bonded together via adhesive layers.

[0004] As described above, adhesives intended for long-term use in optical displays require high durability, including resistance to peeling or flaking off the adhered material under high temperature / high humidity conditions (peel resistance), resistance to whitening of the adhesive layer itself (damp heat whitening resistance), and resistance to yellowing of the adhesive layer itself (yellowing resistance). Furthermore, adhesives used for fixing cover panels containing transparent plastic raw materials such as polycarbonate (PC) and polymethyl methacrylate (PMMA) require not only the aforementioned durability but also resistance to appearance defects caused by gases generated from the transparent plastic (gas escape resistance).

[0005] High durability is also required in optical displays, especially for automotive applications. In particular, due to the revolutionary advancements in information technologies such as 5G, the Internet of Things (IoT), and Artificial Intelligence (AI) in recent years, the electrification of automobiles and the development of vehicles with integrated external displays are underway. This has led to increasingly stringent performance requirements, such as heat resistance at temperatures as high as 120°C (previously around 85°C to 105°C). Therefore, developing adhesives that fully meet the requirements for heat resistance at higher temperatures, as well as the previously demanded resistance to damp heat whitening and evaporation, has become a major challenge.

[0006] To date, extensive research has been conducted to meet the durability requirements of adhesives used in optical displays. For example, in the adhesive described in Patent Document 1, an acrylic adhesive, copolymerized from hydroxyl-containing alkyl acrylates and nitrogen-containing acrylates, is used to impart resistance to damp heat whitening and gas escape. However, its heat resistance or lightfastness at 120°C is insufficient. Furthermore, in the adhesive described in Patent Document 2, an acrylic adhesive, copolymerized from alkyl acrylates with 4 to 8 carbon atoms and N-(2-hydroxyethyl)acrylamide, is used as the monomer to suppress uneven display. However, its heat resistance, resistance to damp heat whitening, gas escape, and adhesion at 120°C are insufficient. [Existing technical documents] [Patent Literature]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2017-106000 [Patent Document 2] Japanese Patent Application Publication No. 2007-264092 Summary of the Invention

[0008] The problem to be solved by this disclosure is to provide an adhesive and adhesive sheet that simultaneously possesses adhesion, heat resistance, resistance to damp heat whitening, resistance to evaporation, and light resistance.

[0009] The inventors have made repeated efforts to solve the aforementioned problem, resulting in this disclosure. Specifically, the embodiment of this disclosure is an optical adhesive comprising an acrylic copolymer (A) and an isocyanate-based curing agent (B). The acrylic copolymer (A) is a copolymer of monomers comprising, in 100% by mass, a monomer mixture containing 20% ​​to 60% by mass of an alkyl (meth)acrylate monomer (a1) having 1 to 2 carbon atoms, 30% to 70% by mass of an alkyl (meth)acrylate monomer (a2) having 4 to 8 carbon atoms, and 2.6% to 15% by mass of a hydroxyl-containing vinyl unsaturated monomer (a3). The monomer mixture contains at least two hydroxyl-containing vinyl unsaturated monomers (a3), and the ratio of the storage elastic modulus G'1 at 175°C to the storage elastic modulus G'2 at 225°C, G'2 / G'1, is 0.4 to 1.4.

[0010] Furthermore, the embodiment disclosed herein is the optical adhesive, wherein the hydroxyl-containing vinyl unsaturated monomer (a3) ​​comprises the hydroxyl-containing acetamine monomer (a3-1) represented by the following general formula (1) and the hydroxyl-containing (meth)acrylate alkyl ester monomer (a3-2) represented by the following general formula (2). CH₂=C(R₁)CONHR₂OH General formula (1) CH₂=C(R₃)COOR₄OH General formula (2) Here, R1 and R3 represent hydrogen atoms or methyl groups, and R2 and R4 represent alkyl groups with two or more carbon atoms.

[0011] Furthermore, the embodiment disclosed herein is the optical adhesive, wherein the isocyanate-based curing agent (B) comprises at least one of aliphatic isocyanate-based curing agents and alicyclic isocyanate-based curing agents.

[0012] Furthermore, the embodiment disclosed herein, which is the optical adhesive, further includes a silane coupling agent (C).

[0013] In addition, the embodiment disclosed herein is the optical adhesive used to bond the cover panel to the optical display component.

[0014] In addition, the disclosed embodiment is an adhesive sheet for fixing a cover panel, including an adhesive layer formed by the optical adhesive, and used to attach the cover panel to the optical display component.

[0015] The purpose of this disclosure is to provide an adhesive and adhesive sheet that simultaneously possess adhesion, heat resistance, resistance to damp heat whitening, resistance to evaporation, and light resistance. Simple Explanation of the Diagram

[0016] none Implementation

[0017] The following is a detailed explanation of the disclosure. Furthermore, in this specification, (meth)acrylates include acrylates and methacrylates. The term "monomer" refers to a monomer having an vinyl unsaturated group.

[0018] In addition, in this specification, "alkyl (meth)acrylate monomer (a1) having 1 to 2 carbon atoms" is sometimes referred to as "monomer (a1)", "alkyl (meth)acrylate monomer (a2) having 4 to 8 carbon atoms" is sometimes referred to as "monomer (a2)", "ethylene unsaturated monomer (a3) ​​having hydroxyl groups" is sometimes referred to as "monomer (a3)", "acetylamine monomer (a3-1) having hydroxyl groups represented by general formula (1)" is sometimes referred to as "monomer (a3-1)", "alkyl (meth)acrylate (a3-2) having hydroxyl groups represented by general formula (2)" is sometimes referred to as "monomer (a3-2)", and "isocyanate curing agent (B)" is sometimes referred to as "curing agent (B)".

[0019] Unless otherwise specified, each ingredient mentioned in this instruction manual may be used independently or in combination with two or more ingredients.

[0020] Optical adhesives The optical adhesive disclosed herein comprises an acrylic copolymer (A) and an isocyanate curing agent (B), and the ratio of the storage elastic modulus G'1 at 175°C to the storage elastic modulus G'2 at 225°C, G'2 / G'1, is 0.4 to 1.4.

[0021] Furthermore, the acrylic copolymer (A) is a copolymer of monomers in which, in 100% by mass, the content of alkyl (meth)acrylates having 1 to 2 carbon atoms (a1) is 20% to 60% by mass, the content of alkyl (meth)acrylates having 4 to 8 carbon atoms (a2) is 30% to 70% by mass, and the content of hydroxyl-containing vinyl unsaturated monomers (a3) ​​is 2.6% to 15% by mass, said monomer mixture comprising at least two hydroxyl-containing vinyl unsaturated monomers (a3).

[0022] This type of optical adhesive can simultaneously possess adhesion, heat resistance, resistance to damp heat whitening, resistance to evaporation, and light resistance.

[0023] [Storage elasticity coefficient] The storage elasticity coefficient of an adhesive is determined by viscoelasticity measurements at a frequency of 1 Hz. The storage elasticity coefficient corresponds to the portion of elastic energy stored as elastic energy during material deformation and is an indicator of the degree of hardness. That is, the higher the degree of crosslinking of the coating and the greater the hardness, the higher the storage elasticity coefficient; conversely, the lower the degree of crosslinking and the softer the coating, the lower the storage elasticity coefficient. Generally, monomers containing hydroxyl groups are known to undergo thermal crosslinking reactions at high temperatures. Therefore, acrylic copolymers obtained by copolymerizing a mixture of monomers containing a large amount of hydroxyl-containing vinyl unsaturated monomers undergo thermal crosslinking reactions at high temperatures, and the storage elasticity coefficient tends to increase in the high-temperature region above 150°C.

[0024] The optical adhesive disclosed herein has a storage elasticity coefficient G'1 at 175°C and a storage elasticity coefficient G'2 at 225°C, with a ratio G'2 / G'1 of 0.4 to 1.4, more preferably 0.5 to 1.2. The inventors have repeatedly conducted studies and found that the ratio G'2 / G'1 of the storage elasticity coefficient at 175°C and at 225°C is related to peel resistance under long-term high temperature / high humidity conditions. Specifically, in acrylic copolymers obtained by copolymerizing a monomer mixture containing more hydroxyl-containing vinyl unsaturated monomers (a-3) than the stated upper limit, excessive thermal crosslinking occurs, resulting in G'2 / G'1 exceeding 1.4, which in turn leads to a decrease in peel resistance under high temperature / high humidity conditions. On the other hand, in acrylic copolymers obtained by copolymerizing a monomer mixture containing less than the lower limit of (a-3), almost no thermal crosslinking reaction occurs, and G'2 / G'1 is less than 0.4. As a result, the coating film has insufficient cohesion, leading to a decrease in peel resistance under high temperature / high humidity conditions. In acrylic copolymers obtained by copolymerizing a monomer mixture containing (a-3) within the aforementioned range, the thermal crosslinking reaction of the hydroxyl-containing vinyl unsaturated monomers proceeds moderately, and G'2 / G'1 becomes 0.4 to 1.4. As a result, peel resistance under high temperature / high humidity conditions is improved by imparting moderate cohesion to the coating film.

[0025] <Acrylic copolymer (A)> Acrylic copolymer (A) is a copolymer comprising a monomer mixture (a1), a monomer (a2), and at least two monomers (a3), and the monomer mixture may also include monomers other than monomers (a1~a3) (a4) as needed.

[0026] Furthermore, in 100% by mass of the monomer mixture, the content of monomer (a1) is 20% to 60% by mass, the content of monomer (a2) is 30% to 70% by mass, and the content of monomer (a3) ​​is 2.6% to 15% by mass.

[0027] [Single (a1)] The monomer (a1) is an alkyl (meth)acrylate monomer having an alkyl group having 1 to 2 carbon atoms. The alkyl (meth)acrylate monomer (a1) having 1 to 2 carbon atoms is used in a quantity of 20 to 60 parts by mass of the total amount of (a2), (a3), and (a4) (hereinafter referred to as all monomers) in 100 parts by mass. The lower limit of the amount used is preferably 25 parts by mass, and more preferably 30 parts by mass. The upper limit is preferably 55 parts by mass, and more preferably 50 parts by mass. By using 20 to 60 parts by mass of (a1), the coating film can be given appropriate cohesion, improving peel resistance or gas escape resistance under high temperature / high humidity environments, thereby improving adhesion. Specific examples of (a1) are methyl (meth)acrylate and ethyl (meth)acrylate. Among these, methyl acrylate is preferred in terms of heat resistance, gas escape resistance, and adhesion. These can be used alone or in combination of two or more.

[0028] [Single (a2)] Monomer (a2) is an alkyl (meth)acrylate monomer having an alkyl group having 4 to 8 carbon atoms. The alkyl (meth)acrylate monomer (a2) having 4 to 8 carbon atoms can be used in a proportion of 30% to 70% by mass of the total amount of monomers (a1), (a3), and (a4) combined. The lower limit of the amount of monomer (a2) used in 100% by mass of all monomers is preferably 35% by mass, more preferably 40% by mass. The upper limit is preferably 65% ​​by mass, more preferably 60% by mass.

[0029] By using 30% to 70% by mass of monomer (a2), the coating film can be given appropriate cohesion, improving its peel resistance or gas escape resistance in high temperature / high humidity environments, thereby improving adhesion.

[0030] Specific examples of monomers (a2) include: butyl (meth)acrylate, amyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, cyclohexyl (meth)acrylate, and other cyclic alkyl (meth)acrylates. Among these alkyl (meth)acrylates (a2), butyl acrylate is particularly preferred due to its moderate adhesiveness and ease of adjustment of the weight-average molecular weight. These can be used alone or in combination of two or more.

[0031] [Single (a3)] Monomer (a3) ​​is an ethylene unsaturated monomer with hydroxyl groups, and the monomer mixture constituting the acrylic copolymer (A) disclosed herein contains at least two ethylene unsaturated monomers with hydroxyl groups.

[0032] The content of monomer (a3) ​​is in the form that, in 100% by mass of the monomer mixture, the total amount of at least two hydroxyl-containing vinyl unsaturated monomers is 2.6% by mass to 15% by mass. The lower limit is preferably 3.6% by mass, more preferably 5.1% by mass. The upper limit is preferably 12.6% by mass, more preferably 10.1% by mass.

[0033] If the content of monomer (a3) ​​exceeds 15% by mass, a thermal cross-linking reaction will occur under high temperature conditions, resulting in an excessive cross-linking state, which will cause the coating film to become brittle and reduce its peel resistance. If the content of monomer (a3) ​​is less than 2.6% by mass, a thermal cross-linking reaction will hardly occur under high temperature conditions, resulting in insufficient cohesion of the coating film and reduced peel resistance. By keeping the content of monomer (a3) ​​in the range of 2.6% to 15% by mass, peeling under high temperature / high humidity conditions can be suppressed.

[0034] Specific examples of monomers (a3) ​​include: amide monomers with hydroxyl groups such as monomers (a3-1) described later; alkyl methacrylate monomers with hydroxyl groups such as monomers (a3-2); and monomers with hydroxyl groups other than (a3-1) and (a3-2) such as polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, 1,4-cyclohexanediol mono(meth)acrylate, and caprolactone-modified (meth)acrylate (a3-3).

[0035] Among these, it is preferred to include at least one of a hydroxyl-containing alkyl methacrylate monomer (a3-1) and a hydroxyl-containing amide monomer (a3-2), more preferably to include at least two of a hydroxyl-containing alkyl methacrylate monomer (a3-1) and a hydroxyl-containing amide monomer (a3-2). From the viewpoint of adhesion or peel resistance, resistance to damp heat whitening, and resistance to evaporation, it is most preferably to include at least one hydroxyl-containing alkyl methacrylate monomer (a3-1) and at least one hydroxyl-containing amide monomer (a3-2).

[0036] Monomer (a3-1) has the effect of increasing hydrophilicity and resistance to damp heat whitening with as little as possible, while monomer (a3-2) has the effect of appropriately designing the cohesion of the coating film. By using monomer (a3-1) and monomer (a3-2) together, the effect of improving yellowing resistance can be achieved.

[0037] (Single (a3-1)) The monomer (a3-1) is a hydroxyl-containing acetamine monomer represented by the following general formula (1). CH₂=C(R₁)CONHR₂OH General formula (1) Here, R1 represents a hydrogen atom or a methyl group, and R2 represents an alkyl group with two or more carbon atoms.

[0038] R2 is an alkyl group having one or more carbon atoms, represented by -Cn'H2n'-, where n' is an integer of 1 or more. From the viewpoint of adhesion, resistance to damp heat whitening, and resistance to gas leakage, n' is preferably 4 or less, and more preferably 2 or less. Specifically, examples include: methylene, ethyl, propyl, and butyl.

[0039] The content of monomer (a3-1) is preferably 2.5% to 14.9% by mass of all monomers per 100% by mass. The lower limit is more preferably 3.5% by mass, and further preferably 5% by mass. The upper limit is more preferably 12.5% ​​by mass, and further preferably 10% by mass. Generally, to impart resistance to damp heat whitening, it is ideal to further copolymerize at least 15% by mass of alkyl methacrylate monomers with hydroxyl groups to hydrophilize the coating. However, as mentioned above, acrylic copolymers obtained by copolymerizing monomer mixtures containing a large amount of vinyl unsaturated monomers with hydroxyl groups sometimes become excessively crosslinked in heat resistance tests, leading to coating embrittlement and peeling. Since monomer (a3-1) has higher hydrophilicity than monomer (a3-2), resistance to damp heat whitening can be imparted with a smaller amount of vinyl unsaturated monomers with hydroxyl groups. As a result, designs that balance peel resistance and resistance to damp heat whitening under high temperature / high humidity conditions are possible. Furthermore, the highly polar amide bonds impart high cohesion to the coating film, improving its resistance to gas escape. By setting the amount of monomer (a3-1) within the aforementioned range, peel resistance, resistance to damp heat whitening, resistance to gas escape, and lightfastness are improved.

[0040] Examples of monomers (a3-1) include: N-hydroxymethylacrylamide, N-hydroxymethylacrylamide, N-(2-hydroxyethyl)acrylamide, N-(2-hydroxyethyl)acrylamide, N-(3-hydroxypropyl)acrylamide, N-(3-hydroxypropyl)acrylamide, N-(4-hydroxybutyl)acrylamide, and N-(4-hydroxybutyl)acrylamide. Among these, N-(2-hydroxyethyl)acrylamide is particularly preferred in terms of adhesion, resistance to damp heat whitening, and resistance to evaporation.

[0041] (Single (a3-2)) The monomer (a3-2) is an alkyl methacrylate monomer with hydroxyl groups. CH₂=C(R₃)COOR₄OH General formula (2) Here, R3 represents a hydrogen atom or a methyl group, and R4 represents an alkyl group with two or more carbon atoms.

[0042] R4 is an alkyl group having 2 or more carbon atoms, represented by -Cn''H2n''-, where n'' is an integer of 2 or more. From the viewpoint of adhesion, heat resistance, and gas escape resistance, n'' is preferably 6 or less, and more preferably 4 or less. Specifically, examples include: ethyl alkyl, propyl alkyl, butyl alkyl, pentyl alkyl, hexyl alkyl, etc.

[0043] The number of carbon atoms (n'') of the alkylene group in monomer (a3-2) is larger than the number of carbon atoms (n') of the alkylene group in monomer (a3-1) (n' < n''), and it is preferably a monomer containing at least one alkylene group with a long length. Thereby, when the acrylic copolymer (A) reacts with the isocyanate curing agent (B), the reactivity of monomer (a3-2) becomes higher than that of monomer (a3-1). As a result, the amide bond as the high-cohesion imparting site in monomer (a3-1) and the urethane bond as the high-cohesion imparting site generated by the reaction with the curing agent are appropriately dispersed in the coating film, improving the peel resistance, outgassing resistance, and light resistance in a high-temperature / high-humidity environment.

[0044] The content rate of monomer (a3-2) is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, based on 100% by mass of all monomers. The upper limit is preferably 5% by mass, more preferably 4% by mass. By setting the content rate of monomer (a3-2) to 0.1% by mass to 5% by mass, appropriate cohesion can be imparted to the coating film, improving the peel resistance, outgassing resistance, and light resistance.

[0045] Examples of monomer (a3-2) include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, etc. Among them, from the viewpoints of adhesion, heat resistance, and outgassing resistance, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred.

[0046] Furthermore, the ratio (a3-1) / (a3-2) of the contents of monomer (a3-1) and monomer (a3-2) is preferably (a3-1) / (a3-2) = 2 to 50, more preferably (a3-1) / (a3-2) = 4 to 30. By (a3-1) / (a3-2) = 2 to 50, the cohesion of the coating film after the heat resistance test, the degree of dispersion of the high-cohesion imparting site in the coating film, and the hydrophilicity of the coating film can be appropriately designed. As a result, the peel resistance, wet heat whitening resistance, outgassing resistance, and light resistance are further improved.

[0047] [Monomer (a4)] Monomer (a4) is a monomer other than monomers (a1 to a3). The monomer mixture constituting the acrylic copolymer (A) of the present disclosure may further contain monomer (a4) in addition to containing monomers (a-1 to a-3). Specific examples of monomer (a4) include nitrogen-containing (meth)acrylates such as acrylamide, alkoxy-based (meth)acrylates such as methoxyethyl acrylate, and vinyl-based monomers such as vinyl acetate.

[0048] The acrylic copolymer (A) can be free-radicalized using a free-radical polymerization initiator to polymerize all of the monomers. In the case of solution polymerization, the free-radical polymerization is preferably carried out in the presence of solvents such as ethyl acetate, toluene, xylene, anisole, acetone, methyl ethyl ketone, and cyclohexanone. The preferred free-radical polymerization temperature is in the range of 60°C to 120°C, and the preferred polymerization time is 3 hours to 10 hours.

[0049] As a free radical polymerization initiator, any known compound that can generate free radicals under the polymerization temperature conditions can be used without particular restrictions. Examples include: dialkyl peroxides, peroxide esters, peroxide ketones, peroxide ketals, diacyl peroxides, organic peroxides, azo compounds, etc.

[0050] As azo compounds, the following can be used: 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis(2-methylbutyronitrile), and other 2,2'-azobisbutyronitrile derivatives; 2,2'-azobis(4-methoxy-2,4-dimethylpentanitrile), 2,2'-azobis(2,4-dimethylpentanitrile), and other 2,2'-azobis(2-hydroxymethylpropionitrile), and 1,1'-azobis(cyclohexane-1-formonitrile), and other 1,1'-azobis-1-alkanenitrile derivatives. These can be used alone or in combination of two or more.

[0051] The amount of free radical polymerization initiator is preferably 0.001 to 5 parts, more preferably 0.01 to 2 parts, relative to 100 parts of ethylene unsaturated monomer.

[0052] In this disclosure, the acrylic copolymer (A) can be synthesized by solution polymerization, emulsion polymerization, suspension polymerization, etc. Among these polymerization methods, solution polymerization is preferred from the viewpoint of transparency or adhesion.

[0053] There are no particular limitations on the mass-average molecular weight of the acrylic copolymer (A), but it is preferably around 200,000 to 2,000,000. By setting the mass-average molecular weight within the aforementioned range, the peel resistance, gas escape resistance, and light resistance under high temperature / high humidity environments are further improved. Furthermore, the mass-average molecular weight is a value converted from polystyrene determined by gel permeation chromatography (GPC).

[0054] <Isocyanate-based hardener (B)> The optical adhesive disclosed herein includes an isocyanate-based curing agent (B) as a curing agent. Examples of curing agents include isocyanate-based curing agents (B), epoxy-based curing agents, aziridine-based curing agents, carbodiimide-based curing agents, and metal chelate-based curing agents. By simultaneously including an acrylic copolymer (A) and an isocyanate-based curing agent (B), an adhesive with excellent durability can be produced. Furthermore, other curing agents may be used in combination as needed, without compromising the effects of this disclosure.

[0055] Isocyanate-based curing agents (B) are isocyanates containing isocyanate groups. By reacting with the hydroxyl groups in the acrylic copolymer (A), they can improve the cohesiveness of the adhesive layer and enhance durability. Examples of isocyanate-based curing agents (B) include aromatic isocyanate-based curing agents, aliphatic isocyanate-based curing agents, aromatic aliphatic isocyanate-based curing agents, and alicyclic isocyanate-based curing agents. Among these, aliphatic isocyanate-based curing agents or alicyclic isocyanate-based curing agents are particularly preferred in terms of resistance to yellowing.

[0056] Examples of aromatic isocyanate-based curing agents include: 1,3-epenylphenyl diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-epenylphenyl 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, anisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, and 4,4',4''-triphenylmethane triisocyanate.

[0057] Examples of aliphatic isocyanate curing agents include: trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (also known as HMDI (hexamethylene diisocyanate)), pentamethylene diisocyanate, 1,2-epenylpropyl diisocyanate, 2,3-epenylbutyl diisocyanate, 1,3-epenylbutyl diisocyanate, dodecanethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0058] Examples of aromatic aliphatic isocyanate curing agents include: ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylbenzene dimethyl diisocyanate, and 1,3-tetramethylbenzene dimethyl diisocyanate.

[0059] Examples of alicyclic isocyanate curing agents include: 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI (isophorone diisocyanate), 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.

[0060] In addition, examples of the polyisocyanate include biuret, nurate, and adduct forms.

[0061] A biuret is a self-condensing compound containing biuret bonds, formed by the self-condensation of the isocyanate monomer. Examples include biurets of hexamethylene diisocyanate (Sumidur N-75, manufactured by Sumika Covestro Urethane; Duranate 24A-90CX, manufactured by Asahi Kasei Corporation; NP-1200, manufactured by Mitsui Chemicals Corporation), etc.

[0062] The term "urea ester" refers to the trimer of the isocyanate monomer. Examples include: trimers of hexamethylene diisocyanate (Sumidur N-3300, manufactured by Sumika Covestro Urethane; Coronate HX, manufactured by Tosoh; Duranate TPA100, manufactured by Asahi Kasei; D-172, manufactured by Mitsui Chemicals), trimers of isophorone diisocyanate (VESTANAT T-1890, manufactured by Evonik Degussa Japan; Desmodur Z-4370, manufactured by Sumika Covestro Urethane), and trimers of toluene diisocyanate (Coronate 2031, manufactured by Tosoh), etc.

[0063] The term "adductor compound" refers to an isocyanate compound having two or more isocyanate groups (difunctional or higher isocyanate compounds) obtained by reacting the isocyanate monomer with a low-molecular-weight compound containing active hydrogen. Examples of isocyanate compounds having three isocyanate groups (trifunctional isocyanate compounds) include: compounds obtained by reacting trimethylolpropane with hexamethylene diisocyanate (Coronate HL, manufactured by Tosoh; Sumidur HT, manufactured by Sumika Covestro Urethane; Takenate D-160N, manufactured by Mitsui Chemicals); and compounds obtained by reacting trimethylolpropane with toluene diisocyanate (Coronate L, manufactured by Tosoh; Sumidur L-75, manufactured by Sumika Covestro Urethane). Compounds produced by reacting trimethylolpropane with phenyl dimethyl diisocyanate (Takenate D-110N, manufactured by Mitsui Chemicals) and isophorone diisocyanate (Takenate D-140N, manufactured by Mitsui Chemicals) are examples of difunctional isocyanate compounds. Examples of difunctional isocyanate compounds include allophanate compounds produced by reacting 1,6-hexamethylene diisocyanate with a monohydric alcohol (Duranate D-201, manufactured by Asahi Kasei Corporation; Coronate 2770, manufactured by Tosoh Corporation; D-178NL, manufactured by Mitsui Chemicals).

[0064] Here, low-molecular-weight compounds containing active hydrogen can be listed as follows: aliphatic or alicyclic diols, trifunctional polyols, polyols with more than four functionalities, aromatic diols, aliphatic polyamines, aromatic polyamines, and polythiols. Specifically, examples include: 2-butyl-2-ethyl-1,3-propanediol (trimethylolpropane (TMP)), 1,1,1-trimethylolpropane, and ethylene dithiol.

[0065] In the isocyanate-based curing agent (B), a difunctional or higher isocyanate compound is preferred for the purpose of forming a sufficiently cross-linked structure. The isocyanate-based curing agent (B) can be used alone or in combination of two or more.

[0066] The content of isocyanate-based curing agent (B) is preferably 0.01 parts by weight or more, more preferably 0.1 parts by weight or more, relative to 100 parts by weight of acrylic copolymer (A). Furthermore, it is preferably 1 part by weight or less, more preferably 0.9 parts by weight or less. By setting it within the aforementioned range, adhesion, peel resistance, gas escape resistance, and lightfastness are improved.

[0067] <Silane Coupling Agent (C)> This disclosure may further include a silane coupling agent (C). When a silane coupling agent (C) is used in this disclosure, adhesion or resistance to damp heat whitening can be improved. As a silane coupling agent (C), specific examples include: γ-(meth)propenyloxymethyltrimethoxysilane, γ-(meth)propenyloxypropyltrimethoxysilane, γ-(meth)propenyloxypropyltriethoxysilane, γ-(meth)propenyloxypropyltributoxysilane, γ-(meth)propenyloxypropylmethyldimethoxysilane, γ-(meth)propenyloxypropylmethyldiethoxysilane, and other alkoxysilane compounds containing (meth)propenyloxy; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltributoxysilane, vinylmethyldimethoxysilane, and other vinyl alkoxysilane compounds containing vinyl groups; γ-amines Alkoxysilane compounds containing aminoalkyl groups, such as γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, and γ-aminopropylmethyldiethoxysilane; alkoxysilane compounds containing mercapto groups, such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyldiethoxysilane, β-mercaptomethylphenylethyltrimethoxysilane, mercaptomethyltrimethoxysilane, 6-mercaptohexyltrimethoxysilane, and 10-mercaptodecyltrimethoxysilane; methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, and dimethyldiethyl... Alkoxysilane compounds containing alkyl groups, such as oxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, hexyltrimethoxysilane, and decyltrimethoxysilane; alkoxysilane compounds containing phenyl groups, such as phenyltrimethoxysilane, phenyltriethoxysilane, phenyltripropoxysilane, and phenyltributoxysilane; alkoxysilane compounds without functional groups, such as tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, and tetrapropoxysilane; and compounds containing glycidyl groups, such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, and 3-glycidoxypropylmethyldimethoxysilane. Glyceryl alkoxysilane compounds; in addition, examples of alkoxysilane compounds include: 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-chloropropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, hexamethylsilazane, diphenyldimethoxysilane, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate, vinyltris(2-methoxyethoxy)silane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, etc.

[0068] The silane coupling agent (C) preferably exists in the adhesive layer in the form of a silane bond formed by the hydrolysis of alkoxy groups. This form facilitates hydrophilicity with water penetrating the adhesive layer or at the interface between the adhesive and the substrate, thus improving resistance to damp heat whitening. Furthermore, the silane coupling agent (C) is more preferably relatively free to move within the adhesive layer and is hydrophilic. Therefore, to further improve resistance to damp heat whitening, the silane coupling agent (C) preferably does not have reactive functional groups other than alkoxy groups, or has functional groups that are difficult to react with the functional groups present in the acrylic copolymer (A). For example, it is more preferably to have alicyclic epoxy groups in addition to alkoxy groups. Moreover, the above description does not preclude the silane coupling agent (C) from having reactive functional groups other than alicyclic epoxy groups.

[0069] Examples of silane coupling agents containing alicyclic epoxy groups include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane. Furthermore, silane coupling agents without reactive groups other than alkoxy groups include alkyl-containing alkoxysilane compounds, phenyl-containing alkoxysilane compounds, and alkoxysilane compounds without functional groups. More preferably, these are 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, methyltriethoxysilane, tetraethoxysilane, and phenyltriethoxysilane. Moreover, the silane coupling agent (C) can be used alone or in combination of two or more.

[0070] The amount of silane coupling agent (C) used relative to 100 parts by weight of acrylic copolymer (A) is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more. It is preferably 1 part by weight or less, more preferably 0.5 parts by weight or less. By using silane coupling agent (C) within the above range, adhesion and resistance to damp heat whitening can be further improved without compromising peel strength.

[0071] In addition to using acrylic copolymers (A) and hardeners (B), the adhesives disclosed herein can also be used with other resins, such as polyester resins, amino resins, epoxy resins, and polyurethane resins, as needed. Furthermore, depending on the application, additives such as blending agents, adhesive agents, fillers such as talc, calcium carbonate, and titanium dioxide, colorants, softeners, UV absorbers, antioxidants, defoamers, light stabilizers, weather stabilizers, curing accelerators, retarders, and phosphate esters can also be added.

[0072] Adhesive Film The adhesive sheet comprises an adhesive layer formed by the optical adhesive disclosed herein.

[0073] The adhesive sheet disclosed herein possesses excellent adhesion and durability, making it suitable as an adhesive for forming or bonding optical display components such as LCD or OLED display devices or touch panel-like input devices. It is particularly suitable for fixing cover panels to optical display components. By using the adhesive disclosed herein to fix the cover panel to the optical display component, various durability requirements can be met, including heat resistance, resistance to damp heat whitening, resistance to evaporation, and lightfastness.

[0074] The adhesive sheet disclosed herein has a structure in which release films are formed on both sides of the adhesive layer, and the adhesive layer formed between the release films is an adhesive layer formed by a mixture of an acrylic copolymer (A) and an isocyanate curing agent (B).

[0075] As raw materials for cover panels, glass and transparent plastics are generally included, with no particular limitations. However, the adhesive sheet disclosed herein is particularly suitable for cover panels containing transparent plastics. By using the adhesive sheet disclosed herein to fix cover panels containing transparent plastics, appearance defects caused by gas generation from the transparent plastic can be suppressed, and peeling will not occur in high temperature / high humidity environments, thus maintaining high transparency. Examples of raw materials for transparent plastics include, for example, acrylic resins such as polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA), polycarbonate, polycyclic olefins, and polyimide, with no particular limitations. PMMA or polycarbonate are preferred. Furthermore, plastic materials can be used alone or in combination of two or more.

[0076] <Resting Film> There are no particular limitations on the type of release film used, and transparent plastic substrates can be suitable. Examples of raw materials for transparent plastic substrates include: polyesters such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetin, polyurethane, polyarylates, polycyclic olefins, and other plastic materials. Furthermore, plastic materials can be used alone or in combination of two or more.

[0077] As a release film, among the transparent plastic substrates described above, a transparent plastic substrate with excellent heat resistance can be suitable, that is, a transparent plastic substrate that inhibits or prevents deformation under harsh conditions such as high temperature and high humidity. PET film or PET sheet is particularly suitable as a transparent plastic substrate.

[0078] There is no particular limitation on the thickness of the transparent plastic substrate, but it is preferably 10 μm to 200 μm, and more preferably 25 μm to 150 μm.

[0079] When applying adhesives, appropriate liquid media can be added to adjust the viscosity. Specifically, 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 or alcohols may hinder the reaction between the acrylic copolymer (A) and the isocyanate curing agent (B), therefore their use requires caution.

[0080] There are no particular limitations on the coating method; various methods can be listed, including Mayer bar, applicator, brush, sprayer, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, and spin coater. There are also no particular limitations on the drying method; methods using hot air, infrared radiation, or reduced pressure can be listed. As for drying conditions, hot air or steam heating at approximately 60℃ to 180℃ is typically used.

[0081] The thickness of the adhesive layer is preferably 2 μm to 1000 μm, and more preferably 5 μm to 500 μm. Furthermore, the adhesive layer can be a single layer or any of two or more layers in a laminated form.

[0082] The adhesive sheet disclosed herein possesses high durability, such as heat resistance and resistance to damp heat whitening, making it suitable for use as an adhesive in the formation of optical display components or for bonding such components together. It is particularly suitable for use in fixing cover panels that require high adhesion to optical display components. Furthermore, the adhesive sheet disclosed herein also possesses the required resistance to evaporation when the cover panel material is a transparent plastic, making it suitable for fixing cover panels made of transparent plastic materials. [Example]

[0083] The present disclosure will be 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" and "%" means "% by mass". Furthermore, the mixing amounts in the table are parts by mass, and values ​​other than solvents are converted values ​​for non-volatile components. Moreover, empty columns in the table indicate no mixing. Furthermore, the method for determining the mass average molecular weight of acrylic copolymers is as follows.

[0084] <Determination of weight-average molecular weight (Mw)> The weight-average molecular weight (Mw) was determined by gel permeation chromatography (GPC). The apparatus used was a Prominence Liquid Chromatography (LC)-GPC system manufactured by Shimadzu Corporation. For the columns, a Tosoh TSKgel α-M was used, with two columns connected in series. N,N-Dimethylformamide (DMF) was used as the washing buffer, and the determination was performed at 40°C. Mw was determined by conversion using polystyrene as a standard reference with a known Mw.

[0085] The materials used in the embodiments and comparative examples are described below. Hardening agent [Isocyanate-based hardener (B)] B-1: (NP-1200, manufactured by Mitsui Chemicals, a biuret form of hexamethylene diisocyanate) B-2: (“D-172N”, manufactured by Mitsui Chemicals, a ureate form of hexamethylene diisocyanate) B-3: (“D-160N”, manufactured by Mitsui Chemicals, a trimethylolpropane modified form of hexamethylene diisocyanate) B-4: ("Desmodur 2565", manufactured by Covestro, urea ester of isophorone diisocyanate) B-5: (Coronate L, manufactured by Tosoh Corporation, trimethylolpropane-modified toluene diisocyanate) [Other hardeners] D-1: Tetraacetone Zirconium: ("ORGATIX ZC-700", manufactured by Matsumoto Fine Chemical Co., Ltd.)

[0086] <Silane Coupling Agent (C)> KBM-303: (3-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, manufactured by Shin-Etsu Chemical Industry Co., Ltd.)

[0087] <Example of manufacturing acrylic copolymers> (Acrylic copolymer (A-1)) Using a reaction apparatus including a stirrer, reflux cooling pipe, nitrogen inlet pipe, thermometer, and dropper, a monomer mixture consisting of 40 parts of methyl acrylate (MA) as monomer (a1), 52 parts of butyl acrylate (BA) as monomer (a2), 7 parts of N-(2-Hydroxyethyl)acrylamide (HEAA) as monomer (a3-1), and 1 part of 4-hydroxybutyl acrylate (4-HBA) as monomer (a3-2), 0.2 parts of azobisisobutyronitrile as initiator, and 60 parts of ethyl acetate as solvent, was added dropwise over approximately 2 hours. The mixture of the remaining half of the monomer mixture and the 60 parts of ethyl acetate and 0.2 parts of azobisisobutyronitrile was then added dropwise through the dropper. Polymerization was carried out at approximately 80°C for 6 hours under nitrogen. After the reaction was completed, the solution was cooled and diluted with ethyl acetate to obtain an acrylic copolymer solution with 30% non-volatile components and a viscosity of 6000 mPa·s. Here, the obtained acrylic copolymer is designated as (A-1). Furthermore, the weight-average molecular weight (Mw) of the obtained acrylic copolymer is shown in Table 1.

[0088] (Acrylic copolymers (A-2~A-22, A'-1~A'-7)) The composition and blending amounts (parts by mass) were changed to those recorded in Tables 1 to 3. Otherwise, copolymers (A-2 to A-22, A'-1 to A'-7) were synthesized using the same method as that used for manufacturing acrylic copolymer (A-1). The average molecular weights of the obtained acrylic copolymers are shown in Tables 1 to 3.

[0089] [Table 1] Table 1 Acrylic copolymers (A), etc. copolymer (A-1) copolymer (A-2) copolymer (A-3) copolymer (A-4) copolymer (A-5) copolymer (A-6) copolymer (A-7) copolymer (A-8) copolymer (A-9) copolymer (A-10) copolymer (A-11) monomer (a1) MA 40 34 37 45 44.5 twenty four 10 10 58 58 40 EA 14 MMA 14 monomer (a2) BA 52 51 51 52 51 68 68 68 34 17 52 2EHA 17 monomer (a3) monomer (a3-1) HEAA(n'=2) 7 14 11 2.5 4 7 7 7 7 7 HBAA(n'=4) 7 monomer (a3-2) HEA(n''=2) 4HBA(n''=4) 1 1 1 0.5 0.5 1 1 1 1 1 6HBA(n''=6) 1 monomer (a3-3) AE-200 CA Monomer (a3) ​​content [%] 8 15 12 3 4.5 8 8 8 8 8 8 (a3-1) / (a3-2) 7.0 14.0 11.0 5.0 8.0 7.0 7.0 7.0 7.0 7.0 7.0 Mw 1.21 million 1.33 million 1.26 million 1.09 million 1.13 million 1.05 million 980,000 1.01 million 1.3 million 1.08 million 1.19 million

[0090] [Table 2] Table 2 Acrylic copolymers (A), etc. copolymer (A-12) copolymer (A-13) copolymer (A-14) copolymer (A-15) copolymer (A-16) copolymer (A-17) copolymer (A-18) copolymer (A-19) copolymer (A-20) copolymer (A-21) copolymer (A-22) monomer (a1) MA 40 36 40 40 40 40 40 25.5 37 37 37 EA MMA monomer (a2) BA 52 51 52 52.9 53 52.8 54 70 48 48 48 2EHA monomer (a3) monomer (a3-1) HEAA(n'=2) 7 7 3 7 4.5 4 8 HBAA(n'=4) 7 12 monomer (a3-2) HEA(n''=2) 1 12 4HBA(n''=4) 1 0.1 4 0.2 1.5 0.5 6HBA(n''=6) 1 monomer (a3-3) AE-200 12 CA 7 3 3 Monomer (a3) ​​content [%] 8 13 8 7.1 7 7.2 6 4.5 8 8 8 (a3-1) / (a3-2) 7.0 - - 70.0 0.8 35.0 3.0 8.0 - - - Mw 1.19 million 1.31 million 920,000 1.2 million 1.17 million 1.2 million 1.17 million 1.18 million 1.16 million 1.16 million 1.22 million

[0091] [Table 3] Table 3 Acrylic copolymers (A), etc. copolymer (A'-1) copolymer (A'-2) copolymer (A'-3) copolymer (A'-4) copolymer (A'-5) copolymer (A'-6) copolymer (A'-7) monomer (a1) MA 32 32 43 44 70 50 EA MMA monomer (a2) BA 47 47 55 53 92 twenty two 50 2EHA monomer (a3) monomer (a3-1) HEAA(n'=2) 20 1 3 7 7 HBAA(n'=4) monomer (a3-2) HEA(n''=2) 20 4HBA(n''=4) 1 1 1 1 1 6HBA(n''=6) monomer (a3-3) AE-200 CA Monomer (a3) ​​content [%] twenty one twenty one 2 3 8 8 0 (a3-1) / (a3-2) 20.0 - 1.0 - 7.0 7.0 - Mw 1.36 million 1.34 million 1.08 million 1.1 million 1.13 million 1.3 million 1.3 million

[0092] Furthermore, the abbreviation is as follows. MA: Methyl acrylate EA: Ethyl acrylate MMA: Methyl methacrylate BA: Butyl acrylate 2EHA: 2-Ethylhexyl acrylate HEAA: N-(2-hydroxyethyl)acrylamide (n'=2) HBAA: N-(4-hydroxybutyl)acrylamide (n'=4) 2HEA: 2-Hydroxyethyl acrylate (n''=2) 4HBA: 4-Hydroxybutyl acrylate (n''=4) 6HBA: 6-Hydroxyhexyl acrylate (n''=6) AE-200: Polyalkylene glycol monoacrylate (average 4.5 moles of ethylene oxide units; Blemmer AE-200 manufactured by Nichiyu Corporation) CA: Caprolactone acrylate

[0093] <Example 1> An adhesive for optical applications was obtained by mixing 0.2 parts of "NP-1200" (manufactured by Mitsui Chemicals, a biuret form of hexamethylene diisocyanate) as an isocyanate-based curing agent (B) and 0.1 parts of KBM-303 (3-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) as a silane coupling agent (C). Using a corner-cutting wheel coating machine, the obtained optical adhesive was applied to a 38 μm thick release liner (SP-PET-O1-BU: manufactured by Mitsui Chemicals Tohcello) to a dried thickness of 100 μm. After drying at 110°C for 3 minutes, a 75 μm thick release liner (SP-PET-O3-B3: manufactured by Mitsui Chemicals Tohcello) was attached to the adhesive layer. In this state, the adhesive was aged at 23°C for 7 days to obtain the adhesive sheet.

[0094] <Examples 2-29, Comparative Examples 1-8> As shown in Table 4, by changing the types and amounts of acrylic copolymers, hardeners, and silane coupling agents, optical adhesives and adhesive sheets were obtained in the same manner as in Example 1.

[0095] [Table 4] Table 4 acrylic copolymer (A) etc. Hardener (B) Silane coupling agent (C) G'2 / G'1 type Quantity (portions) type Quantity (portions) type Quantity (portions) Example 1 A-1 100 B-1 0.4 KBM-303 0.1 0.9 Example 2 A-1 100 B-1 0.7 KBM-303 0.1 1.1 Example 3 A-1 100 B-1 0.05 KBM-303 0.1 0.7 Example 4 A-1 100 B-2 0.4 KBM-303 0.1 0.9 Example 5 A-1 100 B-3 0.4 KBM-303 0.1 0.9 Example 6 A-1 100 B-4 0.4 KBM-303 0.1 0.9 Example 7 A-1 100 B-5 0.4 KBM-303 0.1 0.9 Example 8 A-2 100 B-1 0.4 KBM-303 0.1 1.3 Example 9 A-3 100 B-1 0.4 KBM-303 0.1 1.1 Example 10 A-4 100 B-1 0.4 KBM-303 0.1 0.4 Example 11 A-5 100 B-1 0.4 KBM-303 0.1 0.6 Example 12 A-6 100 B-1 0.4 KBM-303 0.1 0.6 Example 13 A-7 100 B-1 0.4 KBM-303 0.1 0.5 Example 14 A-8 100 B-1 0.4 KBM-303 0.1 0.8 Example 15 A-9 100 B-1 0.4 KBM-303 0.1 1.2 Example 16 A-10 100 B-1 0.4 KBM-303 0.1 1.1 Example 17 A-11 100 B-1 0.4 KBM-303 0.1 0.8 Example 18 A-12 100 B-1 0.4 KBM-303 0.1 0.9 Example 19 A-13 100 B-1 0.4 KBM-303 0.1 1 Example 20 A-14 100 B-1 0.4 KBM-303 0.1 0.6 Example 21 A-15 100 B-1 0.4 KBM-303 0.1 1 Example 22 A-16 100 B-1 0.4 KBM-303 0.1 0.9 Example 23 A-17 100 B-1 0.4 KBM-303 0.1 1 Example 24 A-18 100 B-1 0.4 KBM-303 0.1 0.9 Example 25 A-19 100 B-1 0.4 KBM-303 0.1 0.5 Example 26 A-19 100 B-1 0.4 - - 0.4 Example 27 A-20 100 B-1 0.4 KBM-303 0.1 0.4 Example 28 A-21 100 B-1 0.4 KBM-303 0.1 0.4 Example 29 A-22 100 B-1 0.4 KBM-303 0.1 0.4 Comparative Example 1 A'-1 100 B-1 0.4 KBM-303 0.1 1.9 Comparative Example 2 A'-2 100 B-1 0.4 KBM-303 0.1 1.5 Comparative Example 3 A'-3 100 B-1 0.4 KBM-303 0.1 0.3 Comparative Example 4 A'-4 100 B-1 0.4 KBM-303 0.1 0.5 Comparative Example 5 A'-5 100 B-1 0.4 KBM-303 0.1 0.5 Comparative Example 6 A'-6 100 B-1 0.4 KBM-303 0.1 1.3 Comparative Example 7 A'-7 100 B-1 0.4 KBM-303 0.1 <0.1 Comparative Example 8 A-1 100 D-1 0.4 KBM-303 0.1 2.3

[0096] Physical Properties and Evaluation of Optical Adhesives and Adhesive Sheets The physical properties, adhesion, heat resistance (peeling, yellowing), resistance to damp heat whitening, resistance to evaporation, and light resistance (peeling, yellowing) of the optical adhesives and adhesive sheets disclosed herein are evaluated by the following methods.

[0097] <Storage elasticity coefficient> Temperature dispersion measurements were performed using a Discovery HR-2 (DHR-2) instrument manufactured by TA Instruments-Waters LLC. The instrument employed a 1 Hz frequency, a temperature rise of 4 °C / min, and an 8.0 mm φ fixture under a normal load of 0.2 N. From the obtained measurement charts, the storage elasticity coefficients G'1 and G'2 at 175 °C and 225 °C were read, and their ratio G'2 / G'1 was calculated.

[0098] <Adhesion> The 38 μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was bonded to a PET film (manufactured by Toyobo Co., Ltd., Cosmoshine A-4360, 100 μm thick) as the substrate. The film was then cut into dimensions of 25 mm wide × 100 mm long to prepare a test adhesive sheet. Another 75 μm release liner of the test adhesive sheet was peeled off, and the adhesive layer was attached to a glass plate under conditions of 23°C and 50% relative humidity (RH). The film was then pressed using a roller according to Japanese Industrial Standards (JIS) Z-0237. After 24 hours of pressing, the peel strength was measured using a tensile testing machine (Tensilon: manufactured by Orientec Co., Ltd.) (peel angle 180°, peel speed 300 mm / min; unit N / 25 mm width). [Evaluation Criteria] A: Peel strength is above 25 N / 25 mm. Excellent. B: Peel strength is 20 N / 25 mm or higher but less than 25 N / 25 mm. Good. C: Peel strength is 15 N / 25 mm or higher but less than 20 N / 25 mm. Practical. D: Peel strength less than 15 N / 25 mm. Not suitable for practical use.

[0099] <Heat Resistance (Peeling)> The 38 μm release liner of the obtained adhesive sheet was peeled off and the adhesive layer was laminated onto a 0.5 mm thick polycarbonate (PC) sheet (Iupilon NF2000: manufactured by Mitsubishi Gas Chemical Co., Ltd.) using a laminator at 23°C–50%RH. Subsequently, another 75 μm release liner of the adhesive sheet was peeled off and laminated onto a glass plate using the same laminator. A test piece was prepared by applying a pressure of 0.5 MPa at 50°C for 20 minutes, thereby creating a PC sheet / adhesive layer / glass plate laminate in that order, and then placed at 120°C for 1000 hours. After cooling at 23°C–50%RH for 24 hours, the degree of peeling of the test piece was visually evaluated. [Evaluation Criteria] A: The stripped area is less than 5% of the total area. Excellent. B: The area of ​​stripping is more than 5% but less than 20% of the total area. Good. C: The area to be peeled off is more than 20% but less than 50% of the total area. Practical. D: The area to be peeled off is more than 50% of the total area. Not suitable for practical use.

[0100] <Heat resistance (yellowing)> The 38 μm release liner of the obtained adhesive sheet was peeled off and the adhesive layer was laminated onto a glass plate using a laminator at 23°C-50%RH. Then, another 75 μm release liner of the adhesive sheet was peeled off and laminated onto the glass plate using the same laminator. A test piece was prepared by applying a pressure of 0.5 MPa at 50°C for 20 minutes, thereby creating a glass plate / adhesive layer / glass plate stack in that order. This was then placed at 120°C for 1000 hours. After cooling at 23°C-50%RH for 1 hour, the b-value was measured, and the difference Δb from the b-value before the heat resistance test was calculated. Furthermore, the b-value was measured using a Nippon Denshoku Kogyo SE6000 spectrophotometer under D65 light source and a viewing angle of 2°. [Evaluation Criteria] A: Δb is less than 0.8. Excellent. B: Δb is 0.8 or higher but less than 1.5. Good. C: Δb is 1.5 or higher but less than 3.0. Practical. D: Δb is 3.0 or higher. Not practical.

[0101] <Resistance to damp heat whitening (glass structure)> The 38 μm release liner of the obtained adhesive sheet was peeled off and the adhesive layer was laminated onto a glass plate using a laminator at 23°C–50%RH. Then, another 75 μm release liner of the adhesive sheet was peeled off and laminated onto the glass plate using the same laminator. A test piece was prepared by applying a pressure of 0.5 MPa at 50°C for 20 minutes, thereby creating a glass plate / adhesive layer / glass plate stack in that order. This was then placed at 85°C–85%RH for 1000 hours. After cooling at 23°C–50%RH for 1 hour, the haze was measured. Furthermore, the haze was measured using a NDH5000W turbidimeter manufactured by Nippon Denshoku Kogyo Co., Ltd. [Evaluation Criteria] A: HAZE is below 1.0. Excellent. B: HAZE is 1.0 or higher but less than 3.0. Good. C:HAZE is 3.0 or higher but less than 5.0. It is usable. D:HAZE is 5.0 or higher. Not usable.

[0102] <Resistance to Moist Heat Whitening (PC Structure)> The 38 μm release liner of the obtained adhesive sheet was peeled off, and the adhesive layer was bonded to a PET film (Toyobo Co., Ltd., A-4300, 100 μm thick). The film was then cut into dimensions of 40 mm width × 60 mm length to create a test adhesive sheet. Next, another 75 μm release liner of the test adhesive sheet was peeled off and bonded to a 0.5 mm thick polycarbonate (PC) sheet (Iupilon NF2000: manufactured by Mitsubishi Gas Chemical Co., Ltd.). A test sheet was prepared by applying a pressure of 0.5 MPa at 50°C for 20 minutes, thereby creating a composite of PET film / adhesive layer / PC sheet. This sheet was then placed at 85°C-85%RH for 240 hours. After cooling at 23°C-50%RH for 1 hour, the HAZE was measured. Furthermore, the HAZE was measured using a NDH5000W turbidimeter manufactured by Nippon Denshoku Kogyo Co., Ltd. [Evaluation Criteria] A: HAZE is less than 1.5. Excellent. B: HAZE is 1.5 or higher but less than 3.5. Good. C:HAZE is 3.5 or higher but less than 5.5. Practical. D:HAZE is 5.5 or higher. Not practical.

[0103] <Resistance to gas> After preparing the test pieces according to the same procedure as for evaluating resistance to damp heat whitening (PC structure), they were placed in an environment of 85℃-85%RH for 72 hours. Then, after placing them in an environment of 23℃-50%RH for 1 hour, the appearance of the test pieces was visually observed. [Evaluation Criteria] A: No bubbles, floats. Excellent. B: A small number of air bubbles or adhesive layer floating (if air bubbles, there are more than one but less than five; if floating, the floating area is less than 5% of the whole). Good. C: A small number of air bubbles or adhesive layer floating (if air bubbles, there are five or more but less than twenty; if floating, the floating area is more than 5% but less than 10% of the total area). Practical. D: Numerous air bubbles or adhesive layer floating (more than twenty if air bubbles, and more than 10% of the total area if floating). Unusable.

[0104] <Lightfastness (peel resistance)> 100 parts of a surface protective coating (manufactured by Toyo Ink Co., Ltd., YL454UR, an acrylic varnish) were mixed with 10 parts of D-172N as a hardener to prepare a coating solution, which was then applied to the PC board using a bar coater. Afterward, the solution was aged at 40°C for 72 hours to produce a PC board with a surface protective layer. In addition to using the PC board with the surface protective layer, test pieces were prepared following the same procedure as for the heat resistance (peeling) evaluation. These pieces were then irradiated for 500 hours using a xenon weathering tester manufactured by Q-Lab Co., Ltd., at a black panel temperature of 83°C and an illuminance of 60 W / m². After cooling at 23°C-50%RH for 24 hours, the degree of peeling of the test pieces was evaluated visually. [Evaluation Criteria] A: The stripped area is less than 5% of the total area. Excellent. B: The area of ​​stripping is more than 5% but less than 20% of the total area. Good. C: The area to be peeled off is more than 20% but less than 50% of the total area. Practical. D: The area to be peeled off is more than 50% of the total area. Not suitable for practical use.

[0105] <Light resistance (yellowing)> After preparing the test pieces following the same procedure as for evaluating heat resistance (yellowing), they were irradiated for 1000 hours using a xenon weathering tester manufactured by Q-Lab, under conditions of a black panel temperature of 63°C and an illuminance of 85 W / m². After cooling for 1 hour at 23°C-50%RH, the b-value was measured, and the difference Δb between the b-value and the value before the lightfastness test was calculated. Furthermore, the b-value was measured using a spectrophotometer SE6000 manufactured by Nippon Denshoku Kogyo Co., Ltd., under conditions of a D65 light source and a viewing angle of 2°. [Evaluation Criteria] A: Δb is less than 1.0. Excellent. B: Δb is 1.0 or higher but less than 3.0. Good. C: Δb is 3.0 or higher but less than 5.0. Practical. D: Δb is 5.0 or higher. Not practical.

[0106] The results of the above evaluations are shown in Table 5.

[0107] [Table 5] Table 5 Adhesion Heat resistance Resistance to damp heat whitening Resistance to gas escape Lightfastness peeling Yellowing glass structure PC structure peeling Yellowing Example 1 A A A A A A A B Example 2 B B A A A B B B Example 3 A C A A A C B B Example 4 A A A A A B A B Example 5 A A A A A B A B Example 6 A A A A A C A B Example 7 A A C A A B A C Example 8 B C B A A C B C Example 9 A B B A A B B B Example 10 B C A B C C B A Example 11 B B A B B B A A Example 12 B B A A A B A B Example 13 B C A A A C A B Example 14 C B A A A B B B Example 15 B A A A A B A B Example 16 C A A A A B A B Example 17 B B A B C B A B Example 18 A C A A A C C B Example 19 B B A B C B A B Example 20 C C A C C C C A Example 21 A B A A A B A B Example 22 B B A B C C A B Example 23 A B A A A A A B Example 24 B B A B B C A B Example 25 B B A B B B B A Example 26 C B A C C B B A Example 27 B B A B C B A B Example 28 C C A C C C C A Example 29 C C B C C C C A Comparative Example 1 A D C A A D C C Comparative Example 2 B D B A A B B C Comparative Example 3 B D A D D D C A Comparative Example 4 B C A B C D C A Comparative Example 5 C D A B B D C B Comparative Example 6 D D A A A D C B Comparative Example 7 A D B D D D D A Comparative Example 8 A D C A A C D C

[0108] As shown in Table 5, the results demonstrate that the optical adhesive disclosed herein exhibits superior adhesion, heat resistance, resistance to damp heat whitening, resistance to evaporation, and lightfastness. In contrast, the optical adhesive of the comparative examples fails to meet all the requirements for adhesion, heat resistance, resistance to damp heat whitening, resistance to evaporation, and lightfastness. Based on these results, it can be stated that the optical adhesive disclosed herein is also suitable for fixing cover panels and optical display components.

[0109] This application claims priority based on Japanese Patent Application No. 2022-002688, filed on January 12, 2022, the entire contents of which are incorporated herein by reference.

[0110] none

Claims

1. An optical adhesive comprising an acrylic copolymer (A) and an isocyanate-based curing agent (B), wherein the acrylic copolymer (A) is a copolymer of monomers comprising, in 100% by mass, a (meth)acrylate alkyl monomer having 1 to 2 carbon atoms (a1) at a content of 20% to 60% by mass, a (meth)acrylate alkyl monomer having 4 to 8 carbon atoms (a2) at a content of 30% to 70% by mass, and a hydroxyl-containing vinyl unsaturated monomer (a3) ​​at a content of 2.6% to 15% by mass, wherein the monomer mixture comprises at least two hydroxyl-containing vinyl unsaturated monomers (a3), and the ratio G'2 / G'1 of the storage elastic modulus G'1 at 175°C to the storage elastic modulus G'2 at 225°C is 0.4 to 1.4, wherein, The hydroxyl-containing vinyl unsaturated monomer (a3) ​​comprises the hydroxyl-containing acetamine monomer (a3-1) represented by the following general formula (1) and the hydroxyl-containing (meth)acrylate alkyl ester monomer (a3-2) represented by the following general formula (2): CH2=C(R1)CONHR2OH General formula (1) CH2=C(R3)COOR4OH General formula (2) Here, R1 and R3 represent hydrogen atoms or methyl groups, R2 represents an alkyl group with 1 to 4 carbon atoms, and R4 represents an alkyl group with 2 to 6 carbon atoms.

2. The optical adhesive as described in claim 1, wherein, The isocyanate curing agent (B) includes at least one of aliphatic isocyanate curing agents and alicyclic isocyanate curing agents.

3. The optical adhesive as claimed in claim 1 further comprises a silane coupling agent (C).

4. The optical adhesive as described in claim 1, used to bond the cover panel to the optical display component.

5. An adhesive sheet for fixing a cover panel, comprising an adhesive layer formed of an optical adhesive as described in any one of claims 1 to 4, and for attaching the cover panel to an optical display component.