Adhesive composition, adhesive and adhesive sheet

Abstract

To provide an adhesive composition applicable for applications requiring transparency, which can obtain an adhesive having less coloration when exposed to high temperatures, excellent adhesive properties (adhesive force, holding power) during curing and low elasticity at low temperatures; and to provide an adhesive obtained by crosslinking the adhesive composition and an adhesive sheet having an adhesive layer composed of the adhesive.SOLUTION: There is provided an adhesive composition comprising an acrylic resin (A) wherein the acrylic resin (A) has a structural unit derived from an alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms, a structural unit derived from a phenolic hydroxyl group-containing ethylenically unsaturated monomer (a2) and the glass transition temperature (Tg) by dynamic viscoelasticity is -30°C or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, touch panels that combine a display and a position input device have become widely used in mobile devices such as televisions, PC monitors, laptops, mobile phones, smartphones, and tablet devices. Among these, capacitive touch panels are the most popular. A touch panel is typically composed of an organic electroluminescence (EL) or liquid crystal display, a transparent conductive film substrate (ITO substrate), and a protective film (protective glass). A transparent adhesive sheet is used to bond these components together.

[0003] Due to their characteristics, displays made of flexible devices such as organic electroluminescence (EL) devices can be used in a variety of shapes, including flat, curved, and even foldable and rollable displays. Foldable displays, in particular, are required to be able to withstand repeated bending without peeling or cracking. Transparent adhesive sheets used to bond foldable displays undergo large localized shape changes, generating strong stresses. Therefore, they are required to have both high peel strength to prevent peeling even under stress and high flexibility to accommodate large shape changes. Patent Documents 1 and 2 have been proposed to address these requirements.

[0004] Patent Document 1 discloses that a curable composition containing a monomer or polymer having a specific structure provides a curable composition, a cured product, and a copolymer that exhibit a low glass transition temperature of the cured product and an improved peel strength while maintaining high flexibility. Furthermore, Patent Document 2 discloses a method for producing a polymerizable compound for forming an adhesive / sticky layer, which comprises a step of obtaining a reaction product by reacting a compound having a specific structure with an isocyanate compound having a reactive double bond in the presence of an acid catalyst capable of generating active hydrogen. This production method is an efficient method for producing a polymerizable compound that can prepare an adhesive / sticky layer-forming composition or adhesive / sticky polymer that can impart or further enhance adhesiveness and adhesion, and form an adhesive layer or the like with excellent adhesiveness and adhesion on various substrates. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-165335 [Patent Document 2] Japanese Patent Application Publication No. 2023-152826 Summary of the Invention [Problem to be solved by the invention]

[0006] However, neither Patent Document 1 nor Patent Document 2 takes into consideration coloring, and there is a risk of coloring when exposed to high temperatures. Therefore, there is room for improvement in preventing coloring when exposed to high temperatures. Furthermore, although Patent Document 1 shows an improvement in peel strength, there is also room for improvement in that peel strength.

[0007] Therefore, an object of the present invention is to provide an adhesive composition that can be used in applications requiring transparency, that produces little discoloration when exposed to high temperatures, that has excellent adhesive properties (adhesive strength and holding power) when cured, and that produces an adhesive that has low elasticity at low temperatures; an adhesive obtained by crosslinking the adhesive composition; and an adhesive sheet having an adhesive layer made of the adhesive. [Means for solving the problem]

[0008] Means of Solving the Problems The present inventors have conducted extensive research to solve the above problems and have found that the above problems can be solved by using a pressure-sensitive adhesive composition containing an acrylic resin having a specific structure.

[0009] That is, the present invention has the following constituent features [1] to

[10] . [1] A pressure-sensitive adhesive composition comprising an acrylic resin (A), The pressure-sensitive adhesive composition has a structural unit derived from an alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms and a structural unit derived from an ethylenically unsaturated monomer containing a phenolic hydroxyl group (a2), and has a glass transition temperature (Tg) determined by dynamic viscoelasticity of -30°C or lower. [2] The pressure-sensitive adhesive composition according to [1], wherein the alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms has a glass transition temperature (Tg) of -100°C to -20°C when it forms a homopolymer. [3] The pressure-sensitive adhesive composition according to [1] or [2], wherein the content of the structural unit derived from the phenolic hydroxyl group-containing ethylenically unsaturated monomer (a2) is more than 0 to 10% by weight relative to the total weight (100% by weight) of the acrylic resin (A). [4] The pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the acrylic resin (A) has a weight average molecular weight of 100,000 to 2,000,000. [5] The pressure-sensitive adhesive composition according to any one of [1] to [4], further comprising a crosslinking agent (B). [6] The pressure-sensitive adhesive composition according to any one of [1] to [5], further comprising a photopolymerization initiator (C). [7] The pressure-sensitive adhesive composition according to any one of [1] to [6], wherein the content of volatile matter excluding the crosslinking agent (B) and the photopolymerization initiator (C) is 2% by weight or less based on the total weight of the pressure-sensitive adhesive composition. [8] [1] to [7] A pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition according to any one of the above items. [9] [8] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to [8].

[10] The pressure-sensitive adhesive sheet according to [8], wherein the pressure-sensitive adhesive layer is a multi-stage curing layer that cures in multiple stages. [Effects of the Invention]

[0010] According to the present invention, there are provided an adhesive composition that can be used in applications requiring transparency, which exhibits little coloration when exposed to high temperatures, has excellent adhesive properties when cured, and produces an adhesive that has low elasticity at low temperatures; an adhesive obtained by crosslinking the adhesive composition; and an adhesive sheet having an adhesive layer made of the adhesive.

[0011] In the present invention, it is presumed that the effects of the present invention are achieved by the interaction between the phenol group of the radical polymerizable compound and the surface of the adherend. Furthermore, when the surface of the adherend has a functional group containing an atom with high electronegativity, such as a hydroxyl group, a carboxyl group, a thiol group, an amino group, an amide group, or a fluorine-containing group, the functional group will undergo a non-covalent attractive interaction with the phenol group of the radical polymerizable compound, thereby achieving the effects of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below, but these are examples of preferred embodiments. In addition, the following terms used in this specification have the following meanings: "(Meth)acrylic" means acrylic or methacrylic. "(Meth)acryloyl" means acryloyl or methacryloyl. "(Meth)acrylate" means acrylate or methacrylate. The term "acrylic resin" refers to a resin obtained by polymerizing a monomer component containing at least one (meth)acrylic monomer. The term "sheet" conceptually encompasses sheets, films, and tapes. The symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0013] <Adhesive composition> The pressure-sensitive adhesive composition of the present invention may further contain a crosslinking agent (B), a photopolymerization initiator (C), a silane coupling agent (D), and other optional components in addition to the acrylic resin (A), as needed. Each component will be explained in turn below.

[0014] (Acrylic resin (A)) The acrylic resin (A) used in the present invention is an acrylic resin (A) having a structural unit derived from an alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms, a structural unit derived from a phenolic hydroxyl group-containing ethylenically unsaturated monomer (a2), a structural unit derived from a functional group-containing monomer (a3), and, as necessary, a structural unit derived from other copolymerizable ethylenically unsaturated monomers (a4). The copolymerization component is a general term for a monomer component having a polymerizable double bond, and does not include a polymerization initiator or a polymerization solvent.

[0015] The acrylic resin (A) of the present invention is obtained by copolymerizing an alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms, an ethylenically unsaturated monomer (a2) containing a phenolic hydroxyl group, a functional group-containing monomer (a3), and other copolymerization components used as needed. The content and composition of the structural moieties derived from each component of the acrylic resin (A) can be determined by NMR. Each copolymer component will be explained in turn below.

[0016] [Alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms] Examples of the alkyl(meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms used in the present invention include an alkyl(meth)acrylate (a1-1) containing a linear alkyl group and a branched alkyl(meth)acrylate (a1-2). Examples of alkyl (meth)acrylates (a1-1) containing a linear alkyl group include n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, lauryl (meth)acrylate, n-tridecyl (meth)acrylate, n-stearyl (meth)acrylate, and behenyl (meth)acrylate. Examples of the branched alkyl (meth)acrylate (a1-2) include alkyl group-containing (meth)acrylates such as isoamyl (meth)acrylate, 1-methylheptyl (meth)acrylate, 2-ethylhexyl acrylate (Tg = -70°C), 2-ethylhexyl methacrylate (Tg = -10°C), isononyl acrylate (Tg = -58°C), isononyl methacrylate, isodecyl acrylate (Tg = -62°C), isodecyl methacrylate (Tg = -41°C), isotridecyl (meth)acrylate, isomyristyl (meth)acrylate, and isostearyl (meth)acrylate. The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate (a1) having 5 or more carbon atoms is preferably 8 or more, and the upper limit is 24 or less, preferably 18 or less. The alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms may be used alone or in combination of two or more.

[0017] The presence of a structural unit derived from a branched alkyl (meth)acrylate (a1-2) is preferred in that it allows for efficient curing with active energy rays. Among these, 2-ethylhexyl (meth)acrylate is preferred because it has excellent active energy ray curability during curing. The number of carbon atoms in the alkyl group of the branched alkyl (meth)acrylate (a1-2) is 5 or more, preferably 8 or more, and the upper limit is 24 or less, preferably 18 or less.

[0018] The alkyl(meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms used in the present invention is preferably an alkyl(meth)acrylate having a glass transition temperature (Tg) when a homopolymer is formed, of −100° C. to −20° C., particularly preferably −80° C. to −30° C. By using an alkyl(meth)acrylate having a Tg in the above range, it is possible to improve the flex resistance at low temperatures when the adhesive is made into a pressure-sensitive adhesive.

[0019] [Phenolic Hydroxyl Group-Containing Ethylenically Unsaturated Monomer (a2)] The phenolic hydroxyl group-containing ethylenically unsaturated monomer (a2) used in the present invention contains one phenolic hydroxyl group and at least one ethylenically unsaturated group, and examples thereof include 4-hydroxyphenyl acrylate, 4-hydroxyphenyl methacrylate, 2-hydroxyphenyl (meth)acrylate, 4-hydroxyphenyl (meth)acrylamide, and 2-hydroxyphenyl (meth)acrylamide. Among these, 4-hydroxyphenyl acrylate and 4-hydroxyphenyl methacrylate are preferred because they have excellent compatibility with the alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms.

[0020] The hydroxyl groups (phenolic hydroxyl groups) directly bonded to the aromatic rings in the phenolic hydroxyl group-containing ethylenically unsaturated monomer are preferably one hydroxyl group bonded to each aromatic ring. When two or more hydroxyl groups are bonded, the polarity of the monomer becomes very high, which tends to make copolymerization with other monomers difficult during the polymerization process.

[0021] (Functional Group-Containing Monomer (a3)) Examples of the functional group-containing monomer (a3) ​​include hydroxyl group-containing monomers (a3-1) excluding (a2), carboxy group-containing monomers, functional group-containing monomers having a nitrogen atom, acetoacetyl group-containing monomers, isocyanate group-containing monomers, and glycidyl group-containing monomers. The functional group-containing monomer (a3) ​​may be used alone or in combination of two or more kinds. As the functional group-containing monomer (a3), a hydroxyl group-containing monomer (a3-1) is preferred in terms of imparting cohesive strength and crosslinking promoting action.

[0022] [Hydroxyl group-containing monomer (a3-1)] Examples of the hydroxyl group-containing monomer (a3-1) used in the present invention include hydroxy(meth)acrylates such as 2-hydroxyethyl acrylate (Tg=-15°C), 2-hydroxyethyl methacrylate (Tg=55°C), 4-hydroxybutyl acrylate (Tg=-32°C), 4-hydroxybutyl methacrylate, 5-hydroxypentyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate, and 8-hydroxyoctyl(meth)acrylate; Caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; Primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate; Secondary hydroxyl group-containing monomers such as 2-hydroxypropyl acrylate (Tg=-7°C), 2-hydroxypropyl methacrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate: Tertiary hydroxyl group-containing monomers such as 2,2-dimethyl-2-hydroxyethyl (meth)acrylate; and the like. These hydroxyl group-containing monomers (a3-1) may be used alone or in combination of two or more.

[0023] Among the hydroxyl group-containing monomers (a3-1), at least one selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate is preferred, and at least one selected from the group consisting of 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate is more preferred, in terms of the excellent balance between moist heat resistance and heat resistance reliability and the excellent flexibility at low temperatures.

[0024] In the hydroxyl group-containing monomer (a3-1), the content of di(meth)acrylate contained as an impurity is preferably as low as possible. For example, the content of di(meth)acrylate is preferably 0.5% by mass or less, more preferably 0.2% by mass or less, even more preferably 0.1% by mass or less, and particularly preferably 0% by mass.

[0025] Examples of carboxy group-containing monomers include (meth)acrylic acid, acrylic acid dimers such as β-carboxyethyl acrylate, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, N-glycolic acid, and cinnamic acid.

[0026] Examples of the amino group-containing monomer include: (meth)acrylates containing a primary amino group, such as aminomethyl (meth)acrylate and aminoethyl (meth)acrylate; (meth)acrylates containing a secondary amino group, such as t-butylaminoethyl (meth)acrylate and t-butylaminopropyl (meth)acrylate; tertiary amino group-containing (meth)acrylates such as ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, and dimethylaminopropyl acrylamide; etc.

[0027] Examples of the amide group-containing monomer include: (Meth)acrylamides; N-alkyl (meth)acrylamides such as N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, Nn-butyl (meth)acrylamide, diacetone (meth)acrylamide, and N,N'-methylenebis(meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-ethylmethylacrylamide, and N,N-diallyl(meth)acrylamide; alkoxyalkyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide and N-(n-butoxymethyl)(meth)acrylamide; Examples thereof include vinylpyrrolidone and acryloylmorpholine.

[0028] Examples of acetoacetyl group-containing monomers include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate. Examples of isocyanate group-containing monomers include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and alkylene oxide adducts of these monomers. Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0029] [Ethylenically unsaturated monomer (a4)] Other copolymerizable ethylenically unsaturated monomers (a4) include alkyl(meth)acrylates having an alkyl group having 1 to 4 carbon atoms, such as methyl acrylate (Tg=8°C), methyl methacrylate (Tg=105°C), ethyl acrylate (Tg=-22°C), ethyl methacrylate (Tg=65°C), n-butyl acrylate (Tg=-55°C), n-butyl methacrylate (Tg=20°C), isobutyl acrylate (Tg=-26°C), isobutyl methacrylate (Tg=48°C), t-butyl acrylate (Tg=14°C), and t-butyl methacrylate (Tg=107°C); Aromatic ring-containing monomers such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyl diethylene glycol (meth)acrylate, phenoxy polyethylene glycol (meth)acrylate, phenoxy polyethylene glycol-polypropylene glycol-(meth)acrylate, orthophenylphenoxyethyl (meth)acrylate, and nonylphenol ethylene oxide adduct (meth)acrylate; cyclohexyl acrylate (Tg=15°C), cyclohexyl Alicyclic monomers such as methacrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate (Tg=175°C), dicyclopentenyl (meth)acrylate, and cyclohexyloxyalkyl (meth)acrylate; 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-butoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, meth Ether chain-containing monomers such as oxytriethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, octoxypolyethylene glycol-polypropylene glycol mono(meth)acrylate, lauroxypolyethylene glycol mono(meth)acrylate, and stearoxypolyethylene glycol mono(meth)acrylate; benzophenone-containing monomers such as 4-(meth)acryloyloxybenzophenone; and other monomers such as acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, vinylpyridine, itaconic acid dialkyl esters, fumaric acid dialkyl esters, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone. The ethylenically unsaturated monomer (a4) may be used alone or in combination of two or more kinds.

[0030] Furthermore, ethylenically unsaturated monomers having two or more ethylenically unsaturated groups such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, and divinylbenzene can also be used in combination.

[0031] [Composition of acrylic resin (A)] The content of the structural unit derived from the alkyl (meth)acrylate (a1) having an alkyl group with 5 or more carbon atoms in the acrylic resin (A) is 50 to 99.5 wt %, preferably 75 to 99 wt %, and more preferably 90 to 98 wt %, based on the total weight of the acrylic resin (A) (100 wt %). If the content of the structural unit derived from the alkyl (meth)acrylate (a1) having an alkyl group with 5 or more carbon atoms is too low, the active energy ray curability and flexibility at low temperatures tend to decrease.

[0032] The content of the structural unit derived from the branched alkyl (meth)acrylate (a1-2) is Structural units derived from alkyl (meth)acrylate (a1) having an alkyl group with a prime number of 5 or more Of these, 50% by weight or more is preferable, 60% by weight or more is more preferable, and 70% by weight or more is particularly preferable. The content of structural units derived from branched alkyl (meth)acrylate (a1-2) is 50% by weight or more. By setting the content at this level, the adhesive will have excellent active energy ray curability. The upper limit is usually 99.5% by weight.

[0033] The content of the structural unit derived from the phenolic hydroxyl group-containing ethylenically unsaturated monomer (a2) in the acrylic resin (A) is preferably from more than 0 to 10 wt%, more preferably from 0.1 to 5 wt%, and even more preferably from 0.2 to 1 wt%, based on the total weight of the acrylic resin (A) (100 wt%). If the content is too low, the peel strength tends to decrease, while if the content is too high, the flexibility of the coating film after curing tends to decrease.

[0034] The content of the structural unit derived from the functional group-containing monomer (a3) ​​in the acrylic resin (A) is preferably from more than 0 to 15 wt%, more preferably from 0.1 to 10 wt%, even more preferably from 0.2 to 5 wt%, and particularly preferably from 0.5 to 3 wt%, based on the total weight of the acrylic resin (A) (100 wt%). If the content is too low, the peel strength tends to decrease, while if the content is too high, the flexibility of the coating film after curing tends to decrease.

[0035] When the acrylic resin (A) contains structural units derived from other copolymerizable ethylenically unsaturated monomers (a4), the content of the structural units derived from the ethylenically unsaturated monomers (a4) is preferably 50% by weight or less, more preferably 10% by weight or less, and even more preferably 5% by weight or less, based on the total weight of the acrylic resin (A) (100% by weight). If the content of other copolymerizable ethylenically unsaturated monomers (a4) is too high, the balance of the adhesive properties tends to deteriorate.

[0036] [Physical properties of acrylic resin (A)] The Tg based on dynamic viscoelasticity of the acrylic resin (A), i.e., the temperature at which the loss tangent of dynamic viscoelasticity is maximum (hereinafter referred to as Tg based on dynamic viscoelasticity), is -30°C or lower, more preferably -35°C or lower, even more preferably -38°C or lower, and particularly preferably -40°C or lower. If the Tg based on the dynamic viscoelasticity of the acrylic resin (A) is too high, when the pressure-sensitive adhesive layer is formed, the elastic modulus at temperatures below -20°C increases, and the bending performance tends to decrease.

[0037] The Tg based on dynamic viscoelasticity can be determined by the following measurement method. An appropriate organic solvent is added to prepare an acrylic resin solution containing only the acrylic resin (A) of the present invention and the organic solvent. After adjusting the concentration of the acrylic resin solution, it is coated onto a release sheet so that the thickness after drying is 50 μm. The organic solvent is then removed by drying, such as by heat treatment at 90 to 105°C for 5 to 10 minutes, and the resulting solution is then attached to a release sheet to prepare an acrylic resin sheet containing 99% by weight or more of the acrylic resin (A). Multiple acrylic resin sheets are then laminated to prepare an acrylic resin sheet with a thickness of approximately 800 μm. The dynamic viscoelasticity of the prepared sheet is measured under the following conditions, and the temperature at which the loss tangent (loss modulus G'' / storage modulus G'=tanδ) becomes maximum is read and taken as the glass transition temperature (Tg) of the acrylic resin (A) based on dynamic viscoelasticity.

[0038] (Dynamic viscoelasticity measurement conditions) Measuring equipment: Dynamic viscoelasticity measuring device (product name: DVA-225, manufactured by IT Measurement and Control Co., Ltd.) Deformation mode: Shear Distortion: 0.1% Measurement temperature: -100~60℃ Measurement frequency: 1Hz

[0039] In contrast, the calculated glass transition temperature (calculated Tg) is calculated by the following Fox formula: In the present invention, "Tg based on the dynamic viscoelasticity of the acrylic resin (A)" is different from the calculated Tg.

[0040]

number

[0041] Tg: Glass transition temperature of the copolymer (K) Tga: Glass transition temperature of the homopolymer of monomer A (K) Wa: Weight fraction of structural units derived from monomer A in the copolymer Tgb: Glass transition temperature of the homopolymer of monomer B (K) Wb: Weight fraction of structural units derived from monomer B in the copolymer Tgn: Glass transition temperature (K) of the homopolymer of monomer N Wn: weight fraction of structural units derived from monomer N in the copolymer (Wa+Wb+···+Wn=1)

[0042] The weight-average molecular weight (Mw) of the acrylic resin (A) is preferably 100,000 to 2,000,000, more preferably 150,000 to 1,500,000, and even more preferably 300,000 to 1,000,000. If the weight-average molecular weight of the acrylic resin (A) is too high, the viscosity tends to be too high, which can lead to poor coating properties and poor handling. If the weight-average molecular weight of the acrylic resin (A) is too low, the cohesive strength tends to decrease, which can lead to poor adhesive properties. The weight average molecular weight of the acrylic resin (A) is the weight average molecular weight at the time of completion of production. The weight average molecular weight is measured on the acrylic resin (A) that has not been heated or otherwise subjected to any treatment after production.

[0043] The weight-average molecular weight of the acrylic resin (A) is the weight-average molecular weight converted to the molecular weight of standard polystyrene. The weight-average molecular weight was measured using a high-performance liquid chromatograph (Waters Japan, "Waters 2695 (main unit)" and "Waters 2414 (detector)") with a Shodex GPC KF-806L column (exclusion limit molecular weight: 2 × 10 7 Separation range: 100 to 2 × 10 7 The measurement is performed using three columns in series (theoretical plate number: 10,000 / column, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm). The number average molecular weight can also be measured using a similar method. The dispersity can be determined from the weight average molecular weight and the number average molecular weight.

[0044] The dispersity (weight average molecular weight / number average molecular weight) of the acrylic resin (A) is preferably 15 or less, more preferably 10 or less, even more preferably 7 or less, and particularly preferably 5 or less. If the dispersity of the acrylic resin (A) is too high, the durability of the pressure-sensitive adhesive layer tends to decrease and foaming and the like tends to occur easily. If the dispersity of the acrylic resin (A) is too low, handleability tends to decrease. The lower limit of the dispersity is usually 1.1 in view of production limitations.

[0045] [Method for producing acrylic resin (A)] The acrylic resin (A) can be produced by polymerizing a polymerization component (a) containing various monomers (a1) to (a4).

[0046] Examples of the polymerization method for the acrylic resin (A) include conventionally known polymerization methods such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. Solution polymerization is preferred in terms of the safety and stability of the reaction and the ability to produce the acrylic resin (A) with any monomer composition. An example of a preferred method for producing the acrylic resin (A) will be described below.

[0047] First, the copolymerization component (a) and a polymerization initiator are mixed or dropped into an organic solvent to carry out solution polymerization. Examples of organic solvents used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as n-hexane; esters such as methyl acetate, ethyl acetate, and butyl acetate; aliphatic alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, and isopropyl alcohol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aliphatic ethers such as dimethyl ether and diethyl ether; halogenated aliphatic hydrocarbons such as methylene chloride and ethylene chloride; and cyclic ethers such as tetrahydrofuran. Among these organic solvents, esters and ketones are preferred, with ethyl acetate, acetone and methyl ethyl ketone being particularly preferred. The organic solvent may be used alone or in combination of two or more kinds.

[0048] As the polymerization initiator used in the polymerization reaction, azo-based polymerization initiators and peroxide-based polymerization initiators, which are common radical polymerization initiators, can be used. Examples of the azo polymerization initiator include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of peroxide polymerization initiators include benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, tert-butyl peroxypivalate, tert-hexyl peroxypivalate, tert-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, and diisobutyryl peroxide. Of these, azo-based polymerization initiators are preferred, and 2,2'-azobisisobutyronitrile and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) are more preferred. The polymerization initiator may be used alone or in combination of two or more kinds.

[0049] The amount of polymerization initiator used is usually 0.0001 to 10 parts by weight, preferably 0.0005 to 8 parts by weight, more preferably 0.001 to 6 parts by weight, particularly preferably 0.005 to 4 parts by weight, even more preferably 0.01 to 3 parts by weight, and most preferably 0.05 to 2 parts by weight, per 100 parts by weight of copolymerization component (a). If the amount of polymerization initiator used is too small, the polymerization rate of the acrylic resin (A) tends to decrease and the amount of residual monomer tends to increase. Also, the weight-average molecular weight of the acrylic resin (A) tends to increase. If the amount of polymerization initiator used is too large, the acrylic resin (A) tends to gel.

[0050] The polymerization conditions for solution polymerization are not particularly limited, and polymerization can be carried out according to conventionally known polymerization conditions. For example, polymerization can be carried out by mixing or dropping the copolymerization component (a) and a polymerization initiator into an organic solvent.

[0051] The polymerization temperature in the polymerization reaction is usually 40 to 120° C., but in the present invention, from the viewpoint of ensuring a stable reaction, it is preferably 50 to 90° C. If the polymerization temperature is too high, the acrylic resin (A) tends to gel easily, while if it is too low, the activity of the polymerization initiator decreases, which tends to reduce the polymerization rate and increase the amount of residual monomer. The polymerization time in the polymerization reaction is not particularly limited, but is preferably 0.5 hours or more, preferably 1 hour or more, more preferably 2 hours or more, and particularly preferably 5 hours or more from the final addition of the polymerization initiator. The polymerization reaction is preferably carried out while refluxing the solvent, since this facilitates heat removal.

[0052] (Crosslinking agent (B)) The pressure-sensitive adhesive composition of the present invention preferably further contains an acrylic resin (A) and a crosslinking agent (B). Examples of the crosslinking agent (B) include an active energy ray crosslinking agent (b1) and a thermal crosslinking agent (b2). The active energy ray crosslinking agent (b1) and the thermal crosslinking agent (b2) may be used alone or in combination of two or more.

[0053] When the crosslinking agent (B) contains only the active energy ray crosslinking agent (b1), multi-stage curing is possible simply by controlling the amount of active energy rays. When the crosslinking agent (B) contains both the active energy ray crosslinking agent (b1) and the thermal crosslinking agent (b2), multi-stage curing is also possible by using both thermal curing and active energy ray curing. By controlling the crosslinking reaction in this manner, the cohesive strength of the entire pressure-sensitive adhesive layer can be adjusted, and stable adhesive properties can be obtained after primary curing and final curing.

[0054] [Active energy ray crosslinking agent (b1)] Examples of the active energy ray crosslinking agent (b1) include polyfunctional crosslinking agents containing two or more ethylenically unsaturated groups in one molecule, such as polyfunctional (meth)acrylates, polyfunctional urethane (meth)acrylates, and polyfunctional epoxy (meth)acrylates. Examples of polyfunctional (meth)acrylates include hexanediol di(meth)acrylate, butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, (poly)ethylene glycol mono(meth)acrylate, (poly)butylene glycol mono(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, (poly)tetramethylene glycol di(meth)acrylate, (poly)pentamethylene glycol di(meth)acrylate, (poly) Examples of the acrylate include hexamethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, EO-modified glycerin tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, and ethylene oxide isocyanurate-modified tri(meth)acrylate. Among these, in terms of the balance of adhesive properties after curing, (meth)acrylates containing two ethylenically unsaturated groups are preferred, and (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, and (poly)tetramethylene glycol di(meth)acrylate are particularly preferred. The polyfunctional crosslinking agent may be used alone or in combination of two or more kinds.

[0055] [Thermal crosslinking agent (b2)] The thermal crosslinking agent (b2) exhibits excellent adhesive strength by reacting with functional groups derived from functional group-containing monomers, which are the constituent monomers of the acrylic resin (A). Examples of suitable crosslinking agents include isocyanate-based crosslinking agents (b2-1), epoxy-based crosslinking agents (b2-2), aziridine-based crosslinking agents (b2-3), melamine-based crosslinking agents (b2-4), aldehyde-based crosslinking agents (b2-5), amine-based crosslinking agents (b2-6), and metal chelate-based crosslinking agents (b2-7). Among these, isocyanate-based crosslinking agents (b2-1) are preferred for their improved adhesion to substrates and reactivity with the acrylic resin (A). The thermal crosslinking agent (b2) may be used alone or in combination of two or more.

[0056] Examples of the isocyanate crosslinking agent (b2-1) include tolylene diisocyanate compounds such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, xylylene diisocyanate compounds such as 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate and tetramethylxylylene diisocyanate, and aromatic isocyanate compounds such as 1,5-naphthalene diisocyanate and triphenylmethane triisocyanate; hexamethylene diisocyanate compounds such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate, and aliphatic isocyanate compounds such as lysine diisocyanate; alicyclic isocyanate compounds such as isophorone diisocyanate; and adducts of these isocyanate compounds with polyol compounds such as trimethylolpropane; and biuret and isocyanurate forms of these isocyanate compounds. Among the isocyanate-based crosslinking agents (b2-1), aromatic isocyanate-based compounds are preferred in terms of excellent reactivity, with tolylene diisocyanate-based compounds being particularly preferred, and aliphatic isocyanate-based compounds are preferred in terms of suppressing yellowing, with hexamethylene diisocyanate-based compounds being particularly preferred.

[0057] Examples of the epoxy crosslinking agent (b2-2) include bisphenol A-epichlorohydrin type epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, and diglycerol polyglycidyl ether.

[0058] Examples of the aziridine crosslinking agent (b2-3) include tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), and N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide).

[0059] Examples of the melamine-based crosslinking agent (b2-4) include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resins.

[0060] Examples of the aldehyde crosslinking agent (b2-5) include glyoxal, malondialdehyde, succindialdehyde, maleic dialdehyde, glutaric dialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

[0061] Examples of the amine-based crosslinking agent (b2-6) include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, and polyamides.

[0062] Examples of the metal chelate crosslinking agent (b2-7) include acetylacetone and acetoacetyl ester coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium.

[0063] (Photopolymerization initiator (C)) The pressure-sensitive adhesive composition of the present invention preferably contains a photopolymerization initiator (C) in addition to the acrylic resin (A). Examples of the photopolymerization initiator (C) include a hydrogen abstraction photopolymerization initiator (c1) and an intramolecular cleavage photopolymerization initiator (c2).

[0064] [Hydrogen Abstraction Photopolymerization Initiator (c1)] The hydrogen abstraction photopolymerization initiator (c1) has a structure capable of generating radicals by abstracting hydrogen from the photopolymerization initiator itself or from a compound other than the photopolymerization initiator itself, and specifically has a phenyl glyoxylate structure, a benzophenone structure, a thioxanthone structure, or the like. Examples of the hydrogen abstraction photopolymerization initiator (c1) include benzophenones such as methyl phenylglyoxylate, benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, 4-(meth)acryloyloxybenzophenone, 4-[2-((meth)acryloyloxy)ethoxy]benzophenone, 4-(meth)acryloyloxy-4'-methoxybenzophenone, carboxymethoxymethoxybenzophenone-polyethylene glycol 250 diester, methyl 2-benzoylbenzoate, and 4-(1,3-acryloyl-1,4,7,10,13-pentaoxotridecyl)benzophenone; and thioxanthones such as 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 2,4-diisopropylthioxanthone, and 1-chloro-4-propoxythioxanthone.

[0065] Among these, 4-(meth)acryloyloxybenzophenone, 4-[2-((meth)acryloyloxy)ethoxy]benzophenone, 4-(meth)acryloyloxy-4'-methoxybenzophenone, and carboxymethoxymethoxybenzophenone-polyethylene glycol 250 diester are preferred because they have multiple crosslinking points within the molecule and therefore have good crosslinking efficiency. Commercially available products include "Omnirad 754," "Omnirad BP," "Omnirad 4MBZ," "Esacure TZT," and "Omnipol BP," all manufactured by IGM RESINS BV. One type of hydrogen abstraction photopolymerization initiator (c1) may be used alone, or two or more types may be used in combination.

[0066] [Intramolecular cleavage-type photopolymerization initiator (c2)] The intramolecular cleavage type photopolymerization initiator (c2) has a structure that can generate radicals by cleavage of the photopolymerization initiator itself, and specifically, it is an acetophenone structure, a benzoin structure, an acylphosphonoxide structure, or the like. Examples of the intramolecular cleavage type photopolymerization initiator (c2) include oxyphenyl-acetic acid 2-[2-oxo-2-phenylacetoxyethoxy]ethyl ester; diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, 2-hydroxy- acetophenones such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether; and acylphosphine oxides such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. In addition, an example of a commercially available product is "Omnirad 184" manufactured by IGM RESINS BV. The molecular cleavage type photopolymerization initiator (c2) may be used alone or in combination of two or more kinds.

[0067] As an auxiliary agent for the photopolymerization initiator (C), it is also possible to use in combination triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, etc. The auxiliary for the photopolymerization initiator (C) may be used alone or in combination of two or more.

[0068] (Silane coupling agent (D)) The pressure-sensitive adhesive composition of the present invention preferably further contains a silane coupling agent (D) as a compound other than the acrylic resin (A), the crosslinking agent (B), and the photopolymerization initiator (C) in order to improve durability.

[0069] The silane coupling agent (D) is an organosilicon compound containing, in its structure, at least one reactive functional group and at least one alkoxy group bonded to a silicon atom. The silane coupling agent (D) may be of the monomeric or oligomeric type. Examples of the reactive functional group in the silane coupling agent (D) include an epoxy group, a (meth)acryloyl group, a mercapto group, a hydroxyl group, a carboxy group, an amino group, an amide group, an isocyanate group, etc. Among these, an epoxy group and a mercapto group are preferred from the viewpoint of excellent durability and reworkability.

[0070] The content of the reactive functional group in the silane coupling agent (D) is preferably 3,000 g / mol or less, more preferably 1,500 g / mol or less, and even more preferably 1,000 g / mol or less. When the reactive functional group is within the above numerical range, the balance between durability and reworkability is improved. The lower limit of the content of the reactive functional group in the silane coupling agent (D) is 200 g / mol.

[0071] The alkoxy group bonded to the silicon atom in the silane coupling agent (D) is preferably an alkoxy group having 1 to 8 carbon atoms from the viewpoint of durability and storage stability, with methoxy and ethoxy groups being more preferred. The silane coupling agent (D) may have an organic functional group other than a reactive functional group and an alkoxy group bonded to a silicon atom, such as an alkyl group or a phenyl group.

[0072] Examples of the silane coupling agent (D) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, methyltri(glycidyl)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, etc. Among these, γ-glycidoxypropyltrimethoxysilane is preferred from the viewpoint of heat resistance reliability. The silane coupling agent (D) may be used alone or in combination of two or more kinds.

[0073] (optional ingredient) The pressure-sensitive adhesive composition of the present invention may contain a pressure-sensitive adhesive as an optional component, if necessary. The pressure-sensitive adhesive composition of the present invention may contain conventionally known additives such as a carbodiimide, an antioxidant, an ultraviolet absorber, a crosslinking accelerator, an antistatic agent, a tackifier, and a functional dye.

[0074] (Composition of Pressure-Sensitive Adhesive Composition) The content of the acrylic resin (A) is preferably 80% by weight or more, more preferably 90 to 99.9% by weight, and even more preferably 92 to 99.9% by weight, based on the total weight of the adhesive composition. When the content of the acrylic resin (A) is within the above range, excellent adhesive properties are likely to be obtained after curing.

[0075] When the pressure-sensitive adhesive composition contains a crosslinking agent (B), the content of the crosslinking agent (B) is usually preferably 20 parts by weight or less, more preferably 0.001 to 10 parts by weight, and even more preferably 0.1 to 5.0 parts by weight, per 100 parts by weight of the acrylic resin (A). If the content of the crosslinking agent (B) is too high, the adhesive strength tends to decrease. If the content of the crosslinking agent (B) is too low, the durability tends to decrease.

[0076] When the pressure-sensitive adhesive composition contains an active energy ray crosslinking agent (b1), the content of the active energy ray crosslinking agent (b1) is usually preferably 0.01 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, and even more preferably 0.5 to 5.0 parts by weight, per 100 parts by weight of the acrylic resin (A). If the content of the active energy ray crosslinking agent (b1) is too low, the cohesive force will be insufficient and sufficient durability will tend to be insufficient, whereas if the content of the active energy ray crosslinking agent (b1) is too high, the adhesive properties after curing will tend to decrease.

[0077] When the pressure-sensitive adhesive composition contains a thermal crosslinking agent (b2), the content of the thermal crosslinking agent (b2) is usually preferably 0.001 to 5 parts by weight, more preferably 0.02 to 1 part by weight, and even more preferably 0.05 to 0.5 parts by weight, per 100 parts by weight of the acrylic resin (A). If the content of the thermal crosslinking agent (b2) is too low, the cohesive strength tends to be insufficient and the adhesive properties tend to be reduced, whereas if the content of the thermal crosslinking agent (b2) is too high, the peel strength after curing tends to be reduced.

[0078] The content of the photopolymerization initiator (C) is preferably 0.1 to 5.0 parts by weight, more preferably 0.5 to 3.0 parts by weight, and even more preferably 1.0 to 2.0 parts by weight, relative to 100 parts by weight of the acrylic resin (A). When the content of the photopolymerization initiator (C) is within the above range, sufficient curability can be obtained when curing is carried out.

[0079] When the pressure-sensitive adhesive composition contains a hydrogen abstraction photopolymerization initiator (c1), the content of the hydrogen abstraction photopolymerization initiator (c1) is preferably 0.1 to 3.0 parts by weight, more preferably 0.5 to 2.0 parts by weight, per 100 parts by weight of the acrylic resin (A). If the content of the hydrogen abstraction type photopolymerization initiator (c1) is too high, discoloration tends to occur after durability testing. If the content of the hydrogen abstraction type photopolymerization initiator (c1) is too low, the degree of crosslinking does not increase, and therefore the adhesive properties and durability tend to deteriorate.

[0080] The content of the intramolecular cleavage type photopolymerization initiator (c2) is preferably 0.1 to 5.0 parts by weight, more preferably 0.5 to 3.0 parts by weight, based on 100 parts by weight of the acrylic resin (A). If the content of the intramolecular cleavage type photopolymerization initiator (c2) is too high, the durability tends to deteriorate due to bleed-out, whereas if the content of the intramolecular cleavage type photopolymerization initiator (c2) is too low, the degree of crosslinking does not increase, and therefore the adhesive properties and durability tend to deteriorate.

[0081] When the pressure-sensitive adhesive composition contains a silane coupling agent (D), the content of the silane coupling agent (E) is preferably 0.001 to 3 parts by weight, more preferably 0.005 to 1 part by weight, even more preferably 0.01 to 0.5 parts by weight, and particularly preferably 0.015 to 0.3 parts by weight, per 100 parts by weight of the acrylic resin (A). If the content of the silane coupling agent (D) is too low, it tends to be difficult to obtain the effect of improving durability, whereas if the content of the silane coupling agent (D) is too high, the peel strength tends to decrease due to the effects of bleed-out, etc.

[0082] When the pressure-sensitive adhesive composition contains other pressure-sensitive adhesives or additives, the content of the other pressure-sensitive adhesives or additives is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, per 100 parts by weight of the acrylic resin (A).

[0083] (Preparation of Pressure-Sensitive Adhesive Composition) The pressure-sensitive adhesive composition of the present invention can be obtained by mixing an acrylic resin (A), and, if necessary, a crosslinking agent (B), a photopolymerization initiator (C), a silane coupling agent (D), and other optional components. The mixing method is not particularly limited, and various methods can be used, such as a method in which the components are mixed together, or a method in which optional components are mixed and then the remaining components are mixed together or sequentially.

[0084] (Application) The pressure-sensitive adhesive composition of the present invention has excellent adhesive strength and visibility when applied to a pressure-sensitive adhesive sheet, and also has excellent heat resistance reliability when applied to a pressure-sensitive adhesive sheet, and is therefore suitable for use in touch panels, image display devices, impact absorbing sheets, etc. For example, the pressure-sensitive adhesive composition of the present invention is preferably used as a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer obtained by crosslinking and curing the pressure-sensitive adhesive composition is provided on a base sheet, a double-sided pressure-sensitive adhesive sheet in which the pressure-sensitive adhesive layer is provided on a release sheet, or an optical component with a pressure-sensitive adhesive layer in which the pressure-sensitive adhesive layer is provided on an optical component.

[0085] <Adhesive> The pressure-sensitive adhesive of the present invention is obtained by crosslinking the pressure-sensitive adhesive composition of the present invention described above. When the pressure-sensitive adhesive composition of the present invention is crosslinked (cured), the acrylic resin (A) contained in the pressure-sensitive adhesive composition forms a crosslinked structure at least intramolecularly and / or intermolecularly. As a result, the pressure-sensitive adhesive composition of the present invention is crosslinked to become the pressure-sensitive adhesive according to the present invention. When the acrylic resin (A) has an active energy ray crosslinkable structural moiety, a crosslinked structure can be formed by irradiation with active energy rays.

[0086] The pressure-sensitive adhesive of the present invention exhibits multi-stage curing properties, allowing it to be cured in multiple stages. The pressure-sensitive adhesive of the present invention is in a low-crosslinked state through primary curing before final curing. Although the final curing and primary curing are not necessarily clearly distinguishable, they can be distinguished by differences in gel fraction and dynamic viscoelasticity.

[0087] The curing method for both the primary curing step and the final curing step is not particularly limited, and may be either heating or irradiation with active energy rays. The primary curing step may be carried out in multiple steps, or multi-stage curing may be carried out to achieve the final cured state.

[0088] It can also be said that the pressure-sensitive adhesive of the present invention contains at least a crosslinked product of the acrylic resin (A) of the present invention. The crosslinked product may be a partially crosslinked product in which at least a portion of the acrylic resin (A) is partially crosslinked, or a fully crosslinked product in which the entire acrylic resin (A) is entirely crosslinked. Furthermore, the pressure-sensitive adhesive of the present invention may contain both a partially crosslinked product and a fully crosslinked product of the acrylic resin (A).

[0089] <Adhesive sheet> The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive of the present invention. The pressure-sensitive adhesive sheet of the present invention can exhibit multi-stage curing properties in which the pressure-sensitive adhesive layer is cured in multiple stages. A pressure-sensitive adhesive sheet can be produced by providing a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive of the present invention on a substrate sheet. Alternatively, a double-sided pressure-sensitive adhesive sheet can be produced by providing the pressure-sensitive adhesive layer on a release sheet. Furthermore, a substrate-less double-sided pressure-sensitive adhesive sheet can be produced by forming the pressure-sensitive adhesive layer on a release sheet instead of a substrate sheet, and then laminating a release sheet to the opposite side of the pressure-sensitive adhesive layer. A thick pressure-sensitive adhesive layer can be further formed by forming another pressure-sensitive adhesive layer on the formed pressure-sensitive adhesive layer. When the obtained pressure-sensitive adhesive sheet or double-sided pressure-sensitive adhesive sheet is used, the release sheet is peeled off from the pressure-sensitive adhesive layer.

[0090] Examples of methods for producing the pressure-sensitive adhesive sheet include the following methods (i) and (ii). (i) A method in which the pressure-sensitive adhesive composition of the present invention is dissolved in a solvent and coated to form a pressure-sensitive adhesive sheet. (ii) A method in which the pressure-sensitive adhesive composition of the present invention is melted by heating to form a pressure-sensitive adhesive sheet.

[0091] Method (i) will now be explained. When the pressure-sensitive adhesive composition of the present invention is dissolved in a solvent and coated to form a pressure-sensitive adhesive sheet, the concentration of the coating solution containing the pressure-sensitive adhesive composition of the present invention is adjusted with an appropriate organic solvent and directly coated onto a substrate sheet. The coating is then dried, for example, by heat treatment at 80 to 105°C for 0.5 to 10 minutes, and then attached to a substrate sheet or a release sheet. The pressure-sensitive adhesive composition is then crosslinked (cured) by irradiation with active energy rays or aging, to produce a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive.

[0092] The organic solvent used to adjust the concentration may be any of the organic solvents used in the polymerization reaction of the acrylic resin (A). The concentration of the pressure-sensitive adhesive composition is usually 20 to 60% by weight, preferably 30 to 50% by weight, in terms of solid content.

[0093] Method (ii) will now be explained. When the pressure-sensitive adhesive composition of the present invention is melted by heating to form a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive layer having a desired thickness is formed on one or both sides of a substrate sheet by a method such as applying the molten composition to one or both sides of a substrate sheet and then cooling, or by extrusion laminating the composition onto the substrate sheet using a T-die, etc. Next, a release sheet can be attached to the surface of the pressure-sensitive adhesive layer as needed to produce a pressure-sensitive adhesive sheet. Furthermore, after forming a pressure-sensitive adhesive layer on a substrate sheet, if necessary, an active energy ray irradiation treatment is carried out, and further aging is carried out, whereby a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer in which the pressure-sensitive adhesive composition is cured (crosslinked) can be produced. Furthermore, a substrate-less double-sided PSA sheet can also be produced by forming a PSA layer on a release sheet and then laminating a release sheet to the opposite side of the PSA layer. When the obtained pressure-sensitive adhesive sheet or double-sided pressure-sensitive adhesive sheet is used, the release sheet is peeled off from the pressure-sensitive adhesive layer.

[0094] Examples of substrate sheets include polyester-based resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymer; polyolefin-based resins such as polyethylene, polypropylene, and polymethylpentene; polyethylene fluoride resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyethylene fluoride; polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; cellulose-based resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; polystyrene; polycarbonate; polyarylate; and synthetic resin sheets such as polyimide; metal foils such as aluminum, copper, and iron; paper such as fine paper and glassine paper; and woven and nonwoven fabrics made of glass fiber, natural fiber, synthetic fiber, etc. These substrate sheets can be used as a single layer or as a multi-layered body in which two or more types are laminated together. Among these, synthetic resin sheets are preferred from the viewpoint of weight reduction.

[0095] As the release sheet, for example, various synthetic resin sheets exemplified as the base material sheet, paper, woven fabric, nonwoven fabric, etc., which have been subjected to a release treatment can be used. As the release sheet, for example, a silicone-based release sheet is preferably used.

[0096] The method for applying the pressure-sensitive adhesive composition is not particularly limited, and examples thereof include roll coating, die coating, gravure coating, comma coating, slot coating, and screen printing.

[0097] Examples of active energy rays that can be used include light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, and infrared rays; electromagnetic waves such as X-rays and gamma rays; electron beams; proton beams; and neutron beams. Curing with ultraviolet rays is preferred in terms of curing speed, availability of irradiation equipment, cost, etc.

[0098] The gel fraction of the adhesive layer of the adhesive sheet before final curing is preferably 0.5 to 70% by weight, more preferably 20 to 65% by weight, because the adhesive sheet can be easily attached to the adherend regardless of its shape, and the adhesive layer can hold the adherend in place after attachment.

[0099] The gel fraction of the adhesive layer of the adhesive sheet after final curing is preferably 70 to 90% by weight, more preferably 72 to 87% by weight, and particularly preferably 75 to 85% by weight, from the viewpoints of durability and adhesive strength. If the gel fraction is too low, the cohesive strength tends to decrease, resulting in a decrease in durability. However, if the gel fraction is too high, the cohesive strength tends to increase, resulting in a decrease in adhesive strength.

[0100] The gel fraction can be adjusted appropriately, for example, by the following method. -Adjust the amount of active energy ray irradiation. Adjusting the content of active energy ray crosslinkable structural moieties in the acrylic resin (A). · Adjust the type and amount of crosslinking agent (B) and photopolymerization initiator (C).

[0101] The gel fraction is a measure of the degree of crosslinking (degree of cure) and is calculated, for example, by the following method. That is, an adhesive sheet (without a release sheet) consisting of an adhesive layer formed on a polymer sheet (e.g., polyethylene terephthalate (PET) film, etc.) serving as a substrate is wrapped in a 200-mesh SUS wire netting and immersed in toluene maintained at 23°C for 24 hours, and the weight percentage of the undissolved adhesive component remaining in the wire netting is taken as the gel fraction. However, the weight of the substrate is subtracted from the weight before and after dissolution in toluene to calculate the gel fraction.

[0102] The thickness of the adhesive layer of the adhesive sheet is usually preferably 10 to 3000 μm, more preferably 20 to 1000 μm, and particularly preferably 30 to 350 μm. If the adhesive layer is too thin, the impact absorption properties tend to decrease. If the adhesive layer is too thick, the overall thickness tends to increase when attached to, for example, an optical component, and the practicality tends to decrease.

[0103] The thickness of the adhesive layer in the present invention is a value obtained by subtracting the measured thickness of the constituent members other than the adhesive layer from the measured thickness of the entire adhesive layer-containing laminate using a Mitutoyo ID-C112B.

[0104] In the present invention, an optical member with a pressure-sensitive adhesive layer can be obtained by laminating a pressure-sensitive adhesive layer on an optical member. For example, an optical member with a pressure-sensitive adhesive layer can be obtained by attaching the pressure-sensitive adhesive layer side of the pressure-sensitive adhesive sheet of the present invention, in which a pressure-sensitive adhesive layer is formed on a release sheet, to an optical member and then peeling off the release sheet. In addition, optical members can also be attached to each other using the above-mentioned double-sided pressure-sensitive adhesive sheet.

[0105] Examples of optical components include components that constitute touch panels and image display devices, such as displays (organic EL, liquid crystal), transparent conductive film substrates (ITO substrates), protective films (glass), transparent antennas (films), and transparent wiring. [Example]

[0106] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following description. In the examples, "parts" and "%" are based on weight. The weight average molecular weight of the acrylic resin (A), the glass transition temperature based on dynamic viscoelasticity, the thickness of the pressure-sensitive adhesive layer, and the haze value (%) were measured according to the methods described in the above-mentioned embodiments.

[0107] <Abbreviations, raw materials> (Alkyl (meth)acrylate (a1) having an alkyl group with 5 or more carbon atoms) 2EHA: 2-Ethylhexyl acrylate

[0108] (Phenolic Hydroxyl Group-Containing Ethylenically Unsaturated Monomer (a2)) PHOH: 4-hydroxyphenyl methacrylate (Blenmer PHOH, manufactured by NOF Corporation)

[0109] (Functional Group-Containing Monomer (a3)) 4HBA: 4-hydroxybutyl acrylate (Osaka Organic Chemical Industry Co., Ltd.) NVP: Vinylpyrrolidone (Nippon Shokubai Co., Ltd.)

[0110] (Radical polymerization initiator) ADVN: 2,2'-azobis(2,4-dimethylvaleronitrile) (10-hour half-life temperature 52°C)

[0111] (Crosslinking agent (B)) [Active energy ray crosslinking agent (b1): multifunctional acrylate] Polypropylene glycol #400 diacrylate (NK Ester APG400, manufactured by Shin-Nakamura Chemical Co., Ltd.)

[0112] (Photopolymerization initiator (C)) [Hydrogen Abstraction Photopolymerization Initiator (c1)] Esacure TZT: A blend of 2-4-6 trimethylbenzophenone and 4-methylbenzophenone (manufactured by IGM Resins BV)

[0113] (Silane coupling agent (D)) KBM403: 3-glycidoxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.)

[0114] <Production Example 1: Production of acrylic resin (A-1)> A 2 L flask equipped with a condenser was charged with 24 parts of ethyl acetate (boiling point 77°C) and 16 parts of acetone (boiling point 56°C) as a polymerization solvent, 0.01 parts of ADVN as a polymerization initiator, and 24.4 parts of 2EHA and 0.5 parts of 4HBA as monomers, and the mixture was heated to reflux in the flask. A mixture of 10 parts acetone, 0.09 parts ADVN, 73.1 parts 2EHA, 1.5 parts 4HBA, and 0.5 parts PHOH was added dropwise over 3 hours. After 50 minutes, a mixture of 12 parts ethyl acetate and 0.13 parts ADVN was added dropwise over 1 hour. After another 30 minutes, a mixture of 4 parts ethyl acetate and 0.06 parts ADVN was added and allowed to react, yielding a solution of acrylic resin (A-1). The weight-average molecular weight (Mw), polydispersity, and glass transition temperature (Tg) based on dynamic viscoelasticity of the acrylic resin (A-1) are shown in Table 1.

[0115] <Production Example 2: Production of acrylic resin (A'-1)> A 2 L flask equipped with a condenser was charged with 20 parts of ethyl acetate (boiling point 77°C), 20 parts of acetone (boiling point 56°C) as a polymerization solvent, 0.01 parts of ADVN as a polymerization initiator, and 24.5 parts of 2EHA and 0.5 parts of 4HBA as monomers, and the mixture was heated to reflux in the flask. A mixture of 10 parts ethyl acetate, 0.09 parts ADVN, 73.5 parts 2EHA, and 1.5 parts 4HBA was added dropwise over 3 hours. After 50 minutes, a mixture of 12 parts ethyl acetate and 0.13 parts ADVN was added dropwise over 1 hour. After another 30 minutes, a mixture of 4 parts ethyl acetate and 0.06 parts ADVN was added and allowed to react, yielding a solution of acrylic resin (A-2). The weight-average molecular weight (Mw), polydispersity, and glass transition temperature (based on dynamic viscoelasticity) of acrylic resin (A-2) were measured and the results are shown in Table 1.

[0116] <Production Example 3: Production of acrylic resin (A'-2)> A 2 L flask equipped with a condenser was charged with 24 parts of ethyl acetate (boiling point 77°C), 16 parts of acetone (boiling point 56°C) as a polymerization solvent, 0.01 parts of ADVN as a polymerization initiator, and 24 parts of 2EHA and 0.75 parts of 4HBA as monomers, and the mixture was heated to reflux in the flask. A mixture of 10 parts ethyl acetate, 0.09 parts ADVN, 72 parts 2EHA, 2.25 parts 4HBA, and 1 part NVP was added dropwise over 3 hours. After 50 minutes of addition, a mixture of 12 parts ethyl acetate and 0.13 parts ADVN was added dropwise over 1 hour, and after another 30 minutes, a mixture of 4 parts ethyl acetate and 0.06 parts ADVN was added and allowed to react, yielding a solution of acrylic resin (A-3). The weight-average molecular weight (Mw), polydispersity, and glass transition temperature (based on dynamic viscoelasticity) of acrylic resin (A-3) were measured and the results are shown in Table 1.

[0117] [Table 1]

[0118] Example 1 A pressure-sensitive adhesive composition was obtained by mixing 100 parts (solid content) of the acrylic resin (A-1) solution with 1.5 parts (solid content), 2.0 parts (solid content) of Esacure TZT, and 0.1 parts (solid content) of KBM403. The resulting pressure-sensitive adhesive composition was adjusted to a solid content of 40% with toluene, applied to a polyester release sheet so that the thickness after drying was approximately 50 μm, and dried at 100 ° C. for 5 minutes to form a pressure-sensitive adhesive composition layer. The polyester release sheet was then pressed against the adhesive composition layer to obtain a pressure-sensitive adhesive composition sheet in which both sides of the pressure-sensitive adhesive composition layer were sandwiched between polyester release sheets.

[0119] The pressure-sensitive adhesive composition layer sheet thus obtained was subjected to a high-pressure mercury UV irradiation device with a peak irradiance of 150 mW / cm 2 , cumulative exposure: 1000mJ / cm 2 1 pass) to form a pressure-sensitive adhesive layer (primary curing), and a substrate-less double-sided pressure-sensitive adhesive sheet with a pressure-sensitive adhesive layer thickness of 50 μm was obtained. Next, the release sheet on one side was peeled off from the adhesive layer of the obtained substrateless double-sided adhesive sheet, and the exposed adhesive layer side was pressed against an easy-adhesion treated polyethylene terephthalate (PET) sheet (thickness 125 μm) to obtain a PET sheet with an adhesive layer having a thickness of 50 μm.

[0120] <Comparative Examples 1 and 2> Except for changing the acrylic resin (A-1) as shown in the table, the pressure-sensitive adhesive composition of each example was prepared in the same manner as in Example 1. Next, a substrate-less double-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer thickness of 50 μm and a PET sheet with a pressure-sensitive adhesive layer were successively produced in the same manner as in Example 1. The composition of the pressure-sensitive adhesive composition of each example is shown in Table 2.

[0121] <Measurement and evaluation methods> The measurement and evaluation methods for the pressure-sensitive adhesive compositions of the Examples and Comparative Examples are shown below.

[0122] (Gel fraction: before secondary curing (after primary curing)) The substrate-less double-sided PSA sheet of each example was cut to 40 mm x 40 mm and left to stand for 30 minutes under conditions of 23 °C x 50% RH. One release sheet was then peeled off, and the exposed PSA layer was attached to a 50 mm x 100 mm SUS mesh sheet (200 mesh). The remaining release sheet was peeled off, and the PSA layer was wrapped in the SUS mesh sheet by folding back the center longitudinally. This was immersed in a sealed container containing 250 g of toluene kept at 23 °C for 24 hours, and the gel fraction (%) was calculated from the change in weight.

[0123] [Table 2]

[0124] (Gel fraction: after secondary curing) The substrate-less double-sided adhesive sheet in each example was subjected to high-pressure mercury UV irradiation with a peak irradiance of 150 mW / cm 2 , cumulative exposure: 1000mJ / cm 2 (1000mJ / cm 2After irradiating the sample with ultraviolet light (×1 pass), it was cut into a 40 mm × 40 mm piece and left to stand for 30 minutes under conditions of 23°C × 50% RH. One of the release sheets was then peeled off, and the exposed pressure-sensitive adhesive layer side was attached to a 50 mm × 100 mm SUS mesh sheet (200 mesh). The remaining release sheet was peeled off, and the SUS mesh sheet was folded back from the center in the longitudinal direction to encase the pressure-sensitive adhesive layer in the SUS mesh sheet. This was immersed for 24 hours in a sealed container containing 250 g of toluene kept at 23°C, and the gel fraction (%) was calculated from the change in weight.

[0125] (Adhesive strength: 180° peel strength (glass) tested at 23°C, after secondary curing) The PET sheet with the adhesive layer of each example was cut to a size of 25 mm wide x 100 mm long, and the release sheet was peeled off. The exposed adhesive layer was attached to a corona-treated non-alkali glass sheet (Corning Eagle XG, 1.1 mm thick) by pressing it twice with a 2 kg rubber roller under an atmosphere of 23°C and 50% RH. The sheet was then autoclaved (0.5 MPa, 50°C, 20 minutes) and allowed to stand for 30 minutes under an atmosphere of 23°C and 50% RH. The 180° peel strength (N / 25 mm) was then measured at room temperature (23°C) at a peel rate of 300 mm / min. The evaluation criteria were as follows: ○ Peel strength (N / 25mm) is 1.5N or more. × Peel strength (N / 25mm) is less than 1.5N.

[0126] (Adhesive strength: 180° peel strength (PET) 23℃ test, after secondary curing) The PET sheet with the adhesive layer of each example was cut to a size of 25 mm wide x 100 mm long, and the release sheet was peeled off. The exposed adhesive layer side was attached to a corona-treated PET sheet (Toray Industries, Inc.'s "Lumirror T60," 100 μm thick) by pressing it twice with a 2 kg rubber roller under an atmosphere of 23°C and 50% RH. The sheet was then autoclaved (0.5 MPa, 50°C, 20 minutes) and left to stand under an atmosphere of 23°C and 50% RH. The 180° peel strength (N / 25 mm) was then measured at room temperature (23°C) at a peel rate of 300 mm / min. The evaluation criteria were as follows: ○ Peel strength (N / 25mm) is 5N or more. × Peel strength (N / 25mm) is less than 5N.

[0127] (Adhesive strength: 180° peel strength (glass) 60℃ test, after secondary curing) The PET sheet with the adhesive layer of each example was cut to a size of 25 mm wide x 100 mm long, and the release sheet was peeled off. The exposed adhesive layer side was attached to alkali-free glass (Corning Eagle XG, 1.1 mm thick) under an atmosphere of 23°C and 50% RH by pressing with a 2 kg rubber roller twice. The sheet was then autoclaved (50°C, 0.5 MPa, 20 minutes) and left to stand in an atmosphere of 23°C and 50% RH. After standing for 60 minutes in a dry atmosphere at 60°C, the 180° peel strength (N / 25 mm) was measured at 60°C and a peel rate of 300 mm / min. The evaluation criteria are as follows: ○ Peel strength (N / 25mm) is 0.5N or more. × Peel strength (N / 25mm) is less than 0.5N.

[0128] (Holding power: after secondary curing) The PET sheet with adhesive layer of each example was cut into a size of 25 mm x 50 mm and With a pressure mercury UV irradiation device, peak irradiance: 150mW / cm 2 , cumulative exposure: 1000mJ / cm 2 (1000mJ / cm 2After UV irradiation (×1 pass), the release sheet was peeled off. A stainless steel plate (SUS304) was placed on the exposed adhesive layer side, and a 2 kg roller was pressed back and forth to adhere (adhesion area 25 mm × 25 mm). The adhesion was measured using a creep tester (Tester Sangyo Co., Ltd., constant humidity chamber equipped adhesion tester BE-501) with a load of 1 kg applied in an 80°C atmosphere for 24 hours. The evaluation criteria are as follows: ◎ No misalignment (NC). ○ The deviation is less than 0.1 mm. × The deviation is 0.1 mm or more, or the PET sheet has fallen.

[0129] [Table 3]

[0130] (Elasticity evaluation: low temperature mechanical properties, after secondary curing) 16 substrate-less double-sided adhesive sheets were exposed to a high-pressure mercury UV irradiation device with a peak irradiance of 150 mW / cm 2 , cumulative exposure: 1000mJ / cm 2 (1000mJ / cm 2 The adhesive was then repeatedly laminated together, with one release sheet being peeled off, to produce a substrate-less double-sided adhesive sheet approximately 800 μm thick. After peeling off all of the release sheets from the laminated substrate-less double-sided PSA sheets, the dynamic viscoelasticity was measured under the following conditions, and the storage modulus G' [kPa] at -30°C was evaluated according to the following criteria. Measuring equipment: DVA-225 (manufactured by IT Instrumentation and Control Co., Ltd.) Deformation mode: Shear Distortion: 0.1% ·Measurement temperature: -80~80℃ ·Measurement frequency: 1Hz (evaluation) ◯: The storage modulus G' at -30°C is less than 300 kPa. ×: The storage modulus G' at -30°C is 300 kPa or more.

[0131] (Coloring evaluation) The substrate-less double-sided adhesive sheet in each example was subjected to high-pressure mercury UV irradiation with a peak irradiance of 150 mW / cm 2 , cumulative exposure: 1000mJ / cm 2 (1000mJ / cm 2 After irradiating the sample with ultraviolet light (1 pass x 1), one of the release sheets was peeled off and the exposed adhesive layer side was attached to alkali-free glass (Corning Eagle XG, thickness 1.1 mm). The sample was then autoclaved (50°C, 0.5 MPa, 20 minutes) and left to stand for 30 minutes in an atmosphere of 23°C and 50% RH to prepare a test piece with a layer structure of alkali-free glass / adhesive layer / release sheet.

[0132] The release sheet was peeled off from the obtained test piece, and the color difference b* value was measured using the test piece having a layer structure of alkali-free glass / adhesive layer. [Color difference] The color difference b* was measured in accordance with JIS K7105, and the measurement was carried out under transmission conditions using a spectrocolorimeter (SE6000: manufactured by Nippon Denshoku Industries Co., Ltd.). In the present invention, the color difference b* value is measured by attaching only the adhesive layer to alkali-free glass (b* value=0.16).

[0133] The obtained test piece was left standing in an atmosphere of 110°C for 7 days and in an atmosphere of 130°C for 7 days. After that, the release sheet was peeled off to obtain an alkali-free glass / adhesive layer configuration, and the b* value was measured. The b* value was measured in the same manner as in the measurement of the optical properties of the adhesive layer described above. The evaluation criteria for the heat resistance reliability test are as follows: (evaluation) ○ b* value is less than 0.5 after leaving it for 7 days × b* value is 0.5 or more after leaving it for 7 days

[0134] (Transparency Assessment) The substrate-less double-sided adhesive sheet in each example was subjected to high-pressure mercury UV irradiation with a peak irradiance of 150 mW / cm 2 , cumulative exposure: 1000mJ / cm 2 (1000mJ / cm2 After irradiating the specimen with ultraviolet light (1 pass x 1), one of the release sheets was peeled off and the exposed adhesive layer side was attached to alkali-free glass (Corning Eagle XG, thickness 1.1 mm). The specimen was then autoclaved (50°C, 0.5 MPa, 20 minutes) and left to stand in an atmosphere of 23°C and 50% RH for 30 minutes, after which the remaining release sheet was peeled off to produce a test specimen with an "alkali-free glass / adhesive layer" layer structure.

[0135] The haze value was measured using the obtained test piece. [Haze value] The haze value was calculated by measuring the diffuse transmittance and total luminous transmittance using a HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.) and substituting the obtained diffuse transmittance (DT) and total luminous transmittance (TT) values ​​into the following formula 1. This machine complies with JIS K7361-1. Haze value (%) = (DT / TT) × 100 [Equation 1]

[0136] [Table 4]

[0137] In Example 1, in which the adhesive composition of the present invention was used, an adhesive having excellent heat resistance reliability, flexibility at low temperatures (viscoelastic behavior), and peel strength against various adherends, and an adhesive sheet having an adhesive layer made of the adhesive were obtained. On the other hand, Comparative Example 1, which does not contain a structural unit derived from the specific phenolic hydroxyl group-containing ethylenically unsaturated monomer (a2) used in the present invention, exhibited poor peel strength on various adherends, and Comparative Example 2 exhibited poor viscoelastic behavior at low temperatures and poor heat resistance reliability. [Industrial Applicability]

[0138] The pressure-sensitive adhesive composition of the present invention provides excellent adhesive properties in terms of heat resistance reliability and high-temperature peel strength. The pressure-sensitive adhesive composition of the present invention is particularly useful as a pressure-sensitive adhesive for use in bonding optical components constituting touch panels and image display devices, sealing organic EL displays, etc.

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic resin (A), The pressure-sensitive adhesive composition has a structural unit derived from an alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms and a structural unit derived from an ethylenically unsaturated monomer containing a phenolic hydroxyl group (a2), and a glass transition temperature (Tg) determined by dynamic viscoelasticity of −30° C. or lower.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the alkyl (meth)acrylate (a1) having an alkyl group having 5 or more carbon atoms has a glass transition temperature (Tg) of −100° C. to −20° C. when it forms a homopolymer.

3. The pressure-sensitive adhesive composition according to claim 1, wherein the content of the structural unit derived from the phenolic hydroxyl group-containing ethylenically unsaturated monomer (a2) is more than 0 to 10 wt % relative to the total acrylic resin (A) (100 wt %).

4. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic resin (A) has a weight average molecular weight of 100,000 to 2,000,000.

5. The pressure-sensitive adhesive composition according to claim 1 , further comprising a crosslinking agent (B).

6. The pressure-sensitive adhesive composition according to claim 1 , further comprising a photopolymerization initiator (C).

7. The pressure-sensitive adhesive composition according to claim 5, wherein the content of volatile components excluding the crosslinking agent (B) is 2% by weight or less based on the total weight of the pressure-sensitive adhesive composition.

8. The pressure-sensitive adhesive composition according to claim 6, wherein the content of volatile components excluding the photopolymerization initiator (C) is 2% by weight or less based on the total weight of the pressure-sensitive adhesive composition.

9. A pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition according to any one of claims 1 to 8.

10. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to claim 9.

11. The pressure-sensitive adhesive sheet according to claim 9 , wherein the pressure-sensitive adhesive layer is a multi-stage curing layer that is cured in multiple stages.

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