Adhesive composition, adhesive, and adhesive sheet

Abstract

To provide an adhesive composition usable even in applications demanding colorlessness and transparency, the composition allowing formation of an adhesive with little discoloration in high-temperature exposure and superior adhesion characteristics upon curing; an adhesive obtained by crosslinking the adhesive composition; and an adhesive sheet including an adhesive layer made of the adhesive.SOLUTION: An adhesive composition comprises an acrylic resin (A) and a radically polymerizable compound (B), wherein the acrylic resin (A) has a glass transition temperature of -35°C or lower as determined by dynamic viscoelasticity, and the radically polymerizable compound (B) includes a radically polymerizable compound (b1) having one phenolic hydroxyl group and at least one radical polymerizable reactive group.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 a curable composition, a cured product, and a copolymer that contain a monomer or polymer having a specific structure, and that exhibits improved peel strength while maintaining a low glass transition temperature and high flexibility in the cured product. 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 colorlessness and transparency, that produces an adhesive that undergoes little coloration when exposed to high temperatures and has excellent adhesive properties when cured; 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] As a result of intensive research conducted by the present inventors to solve the above-mentioned problems, it was found that the above-mentioned problems can be solved by using a pressure-sensitive adhesive composition containing a radically polymerizable compound having a specific structure and an acrylic resin.

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

[15] . [1] A pressure-sensitive adhesive composition containing an acrylic resin (A) and a radically polymerizable compound (B), the acrylic resin (A) has a glass transition temperature determined by dynamic viscoelasticity of −35° C. or lower; The pressure-sensitive adhesive composition, wherein the radically polymerizable compound (B) contains a radically polymerizable compound (b1) having one phenolic hydroxyl group and at least one radically polymerizable reactive group. [2] The pressure-sensitive adhesive composition according to [1], wherein the acrylic resin (A) contains a structural unit derived from a copolymerizable monomer (a1) having an alkyl group with a branched structure. [3] The pressure-sensitive adhesive composition according to [1] or [2], wherein the content of structural units derived from the copolymerizable monomer (a1) having an alkyl group with a branched structure is 50% by weight or more relative to the total structural units of the acrylic resin (A). [4] The pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the copolymerizable monomer (a1) having an alkyl group with a branched structure is 2-ethylhexyl acrylate (a1-1). [5] The pressure-sensitive adhesive composition according to any one of [1] to [4], wherein the acrylic resin (A) contains a structural unit derived from a functional group-containing monomer (a2). [6] The pressure-sensitive adhesive composition according to [5], wherein the content of structural units derived from the functional group-containing monomer (a2) is more than 0 to 15 wt % relative to all structural units of the acrylic resin (A). [7] The pressure-sensitive adhesive composition according to [5] or [6], wherein the functional group-containing monomer (a2) is a hydroxyl group-containing monomer (a2-1). [8] The pressure-sensitive adhesive composition according to any one of [1] to [7], wherein the content of the radically polymerizable compound (B) is 0.01 to 10 parts by weight per 100 parts by weight of the acrylic resin (A). [9] The pressure-sensitive adhesive composition according to any one of [1] to [8], further comprising a crosslinking agent (C).

[10] The pressure-sensitive adhesive composition according to [9], wherein the crosslinking agent (C) contains an active energy ray crosslinking agent (c1).

[11] The pressure-sensitive adhesive composition according to

[10] , wherein the active energy ray crosslinking agent (c1) contains a polyfunctional (meth)acrylate.

[12] The pressure-sensitive adhesive composition according to any one of [1] to

[11] , further comprising a photopolymerization initiator (D).

[13] A pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition according to any one of [1] to

[12] .

[14] The pressure-sensitive adhesive according to

[13] , wherein the crosslinking is carried out by irradiation with active energy rays.

[15] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to

[13] or

[14] . [Effects of the Invention]

[0010] According to the present invention, there are provided an adhesive composition that can be used in applications where colorlessness and transparency are required, which adhesive composition produces an adhesive that undergoes little coloration when exposed to high temperatures and has excellent adhesive properties when cured; 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 contains an acrylic resin (A) and a radically polymerizable compound (B). The pressure-sensitive adhesive composition of the present invention may further contain, in addition to the acrylic resin (A) and the radically polymerizable compound (B), a crosslinking agent (C), a photopolymerization initiator (D), a silane coupling agent (E), and other optional components, as necessary. Each component will be explained in turn below.

[0014] (Acrylic resin (A)) The acrylic resin (A) used in the present invention has structural units derived from at least one (meth)acrylic monomer, and, if necessary, structural units derived from a copolymerizable monomer (a1) having a branched alkyl group, structural units derived from a functional group-containing monomer (a2), and structural units derived from other ethylenically unsaturated monomers (a3). The acrylic resin (A) of the present invention is a resin obtained by polymerizing a copolymerization component (a), which contains at least one (meth)acrylic monomer. The copolymerization component (a) can also be obtained by copolymerizing a copolymerization component (a) containing a copolymerizable monomer (a1) having a branched alkyl group, a functional group-containing monomer (a2), and another ethylenically unsaturated monomer (a3), as needed. The copolymerization component is a general term for monomer components having a polymerizable double bond. The copolymerization component does not include a polymerization initiator or a polymerization solvent. The content and composition of structural moieties derived from each component of the acrylic resin (A) can be determined by NMR. The content of each monomer relative to the total copolymerization component (a) can be considered as the content of structural units derived from that monomer in the acrylic resin (A) which is a copolymer. Each copolymer component will be explained in turn below.

[0015] [Copolymerizable monomer (a1) having an alkyl group with a branched structure] Examples of the copolymerizable monomer (a1) having an alkyl group with a branched structure used in the present invention include 2-ethylhexyl acrylate (Tg = -70°C), 2-ethylhexyl methacrylate (Tg = -10°C), isobutyl acrylate (Tg = -26°C), isobutyl methacrylate (Tg = 48°C), t-butyl acrylate (Tg = 14°C), t-butyl methacrylate (Tg = 107°C), isoamyl (meth)acrylate, 1-methylheptyl (meth)acrylate, 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 copolymerizable monomer (a1) having an alkyl group with a branched structure may be used alone or in combination of two or more kinds.

[0016] The copolymerizable monomer (a1) having an alkyl group with a branched structure used in the present invention is preferably an alkyl(meth)acrylate having a glass transition temperature (Tg) of −80° C. to 0° C. when forming a homopolymer, and particularly preferably −75° C. to −20° C. By using an alkyl(meth)acrylate having a Tg in the above range, it is possible to improve the active energy ray curability and the adhesive properties after curing.

[0017] [Functional group-containing nomer (a2)] The acrylic resin (A) used in the present invention may further contain a structural unit derived from a functional group-containing monomer (a2) as required. Examples of the functional group-containing monomer (a2) include a hydroxyl group-containing monomer (a2-1), a carboxy group-containing monomer, a functional group-containing monomer having a nitrogen atom, an acetoacetyl group-containing monomer, an isocyanate group-containing monomer, and a glycidyl group-containing monomer. The functional group-containing monomer (a2) may be used alone or in combination of two or more kinds. As the functional group-containing monomer (a2), a hydroxyl group-containing monomer (a2-1) is preferred in terms of imparting cohesive strength and crosslinking promoting action.

[0018] [Hydroxyl group-containing monomer (a2-1)] Examples of the hydroxyl group-containing monomer (a2-1) used in the present invention include hydroxy(meth)acrylates such as 2-hydroxyethyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate, 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 (meth)acrylate, 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 (a2-1) may be used alone or in combination of two or more.

[0019] Among the hydroxyl group-containing monomers (a2-1), at least one selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate is preferred, as it has an excellent balance between moist heat resistance and heat resistance, and at least one selected from the group consisting of 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate is more preferred.

[0020] In the hydroxyl group-containing monomer (a2-1), 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.

[0021] 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.

[0022] 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.

[0023] 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; hydroxyalkyl(meth)acrylamides such as N-hydroxymethyl(meth)acrylamide and N-hydroxyethyl(meth)acrylamide; alkoxyalkyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide and N-(n-butoxymethyl)(meth)acrylamide; vinylpyrrolidone; and the like.

[0024] 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.

[0025] [Ethylenically unsaturated monomer (a3)] Other copolymerizable ethylenically unsaturated monomers (a3) ​​include, for example, 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), n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, and lauryl (meth)acrylate. Acrylate, n-tridecyl (meth)acrylate, n-stearyl (meth)acrylate, behenyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol-polypropylene glycol-(meth)acrylate, orthophenylphenoxyethyl (meth)acrylate, nonyl phenoxy Aromatic ring-containing monomers such as ethylene oxide adduct (meth)acrylate; alicyclic ring-containing monomers such as cyclohexyloxyalkyl (meth)acrylate; ether chain-containing monomers such as 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, methoxytriethylene 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;Other examples include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, itaconic acid dialkyl ester, fumaric acid dialkyl ester, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone. The ethylenically unsaturated monomer (a3) ​​may be used alone or in combination of two or more kinds.

[0026] 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.

[0027] [Composition of acrylic resin (A)] The content of structural units derived from copolymerizable monomer (a1) having an alkyl group with a branched structure in the acrylic resin (A) is preferably 25 to 99 wt %, more preferably 40 to 98.5 wt %, and even more preferably 50 to 98 wt %, based on the total weight of the acrylic resin (A) (100 wt %). When the content of structural units derived from copolymerizable monomer (a1) having an alkyl group with a branched structure is within the above range, the active energy ray curability and adhesive properties after curing are excellent.

[0028] The content of the structural unit derived from the functional group-containing monomer (a2) in the acrylic resin (A) is preferably from more than 0 to 15 wt%, more preferably from 0.1 to 12.5 wt%, and even more preferably from 1 to 10 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.

[0029] When the acrylic resin (A) contains structural units derived from other ethylenically unsaturated monomers (a3), the content of the structural units derived from the ethylenically unsaturated monomers (a3) ​​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 the ethylenically unsaturated monomers (a3) ​​is too high, the balance of the adhesive properties tends to deteriorate.

[0030] [Physical properties of acrylic resin (A)] The glass transition temperature based on dynamic viscoelasticity of the acrylic resin (A), i.e., the temperature at which the loss tangent of dynamic viscoelasticity becomes maximum (hereinafter referred to as Tg based on dynamic viscoelasticity), is −35° C. or lower, more preferably −36° 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, the peel strength tends to decrease as the step-following ability and adhesion of the pressure-sensitive adhesive layer decrease.

[0031] 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.

[0032] (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

[0033] 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.

[0034]

number

[0035] 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)

[0036] 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.

[0037] 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.

[0038] 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.

[0039] [Method for producing acrylic resin (A)] The acrylic resin (A) can be produced by polymerizing various monomers (a1) to (a3).

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] (Radical polymerizable compound (B)) The radical polymerizable compound (B) used in the present invention contains a radical polymerizable compound (b1) having one phenol group (phenolic hydroxyl group) and at least one radical polymerization reactive group. Examples of the radical polymerizable compound (b1) having one phenol group and at least one radical reactive group include 4-hydroxyphenyl acrylate, 4-hydroxyphenyl methacrylate, etc. Among these, 4-hydroxyphenyl methacrylate is preferred because it is easier to achieve the effects of the present invention.

[0047] Other examples of the radically polymerizable compound (B) include 2-hydroxyphenyl(meth)acrylate, 4-hydroxyphenyl(meth)acrylamide, and 2-hydroxyphenyl(meth)acrylamide.

[0048] (Crosslinking agent (C)) The pressure-sensitive adhesive composition of the present invention preferably further contains a crosslinking agent (C) in addition to the acrylic resin (A) and the radically polymerizable compound (B). Examples of the crosslinking agent (C) include an active energy ray crosslinking agent (c1) and a thermal crosslinking agent (c2). The active energy ray crosslinking agent (c1) and the thermal crosslinking agent (c2) may be used alone or in combination of two or more.

[0049] When the crosslinking agent (C) contains only the active energy ray crosslinking agent (c1), multi-stage curing is possible simply by controlling the amount of active energy rays. When the crosslinking agent (C) contains both the active energy ray crosslinking agent (c1) and the thermal crosslinking agent (c2), 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.

[0050] [Active energy ray crosslinking agent (c1)] Examples of the active energy ray crosslinking agent (c1) 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, (meth)acrylates containing three or more ethylenically unsaturated groups are preferred in terms of the balance of adhesive properties after curing, and trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and dipentaerythritol hexa(meth)acrylate are particularly preferred. The polyfunctional crosslinking agent may be used alone or in combination of two or more kinds.

[0051] [Thermal crosslinking agent (c2)] The thermal crosslinking agent (c2) 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 (c2-1), epoxy-based crosslinking agents (c2-2), aziridine-based crosslinking agents (c2-3), melamine-based crosslinking agents (c2-4), aldehyde-based crosslinking agents (c2-5), amine-based crosslinking agents (c2-6), and metal chelate-based crosslinking agents (c2-7). Among these, isocyanate-based crosslinking agents (c2-1) are preferred for their improved adhesion to substrates and reactivity with the acrylic resin (A). The thermal crosslinking agent (c2) may be used alone or in combination of two or more kinds.

[0052] Examples of the isocyanate crosslinking agent (c2-1) 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 (c2-1), 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.

[0053] Examples of epoxy crosslinking agents (c2-2) 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.

[0054] Examples of the aziridine crosslinking agent (c2-3) 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).

[0055] Examples of the melamine-based crosslinking agent (c2-4) include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resins.

[0056] Examples of the aldehyde crosslinking agent (c2-5) include glyoxal, malondialdehyde, succindialdehyde, maleic dialdehyde, glutaric dialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

[0057] Examples of the amine-based crosslinking agent (c2-6) include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, and polyamides.

[0058] Examples of the metal chelate crosslinking agent (c2-7) 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.

[0059] (Photopolymerization initiator (D)) The pressure-sensitive adhesive composition of the present invention preferably contains a photopolymerization initiator (D) in addition to the acrylic resin (A). Examples of the photopolymerization initiator (D) include a hydrogen abstraction photopolymerization initiator (d1) and an intramolecular cleavage photopolymerization initiator (d2).

[0060] [Hydrogen Abstraction Photopolymerization Initiator (d1)] The hydrogen abstraction photopolymerization initiator (d1) 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 (d1) 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.

[0061] Among these, 4-(meth)acryloyloxybenzophenone, 4-[2-((meth)acryloyloxy)ethoxy]benzophenone, 4-(meth)acryloyloxy-4'-methoxybenzophenone, and carboxymethoxymethoxybenzophenone-polyethylene glycol 250 diester, which have multiple crosslinking points within the molecule, are preferred because they allow for high crosslinking. 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 (d1) may be used alone, or two or more types may be used in combination.

[0062] [Intramolecular cleavage-type photopolymerization initiator (d2)] The intramolecular cleavage type photopolymerization initiator (d2) 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 (d2) 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 (d2) may be used alone or in combination of two or more kinds.

[0063] As an auxiliary agent for the photopolymerization initiator (D), 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 (D) may be used alone or in combination of two or more.

[0064] (Silane coupling agent (E)) The pressure-sensitive adhesive composition of the present invention preferably further contains a silane coupling agent (E) as a compound other than the acrylic resin (A), the radically polymerizable compound (B), the crosslinking agent (C), and the photopolymerization initiator (D), in order to improve durability.

[0065] The silane coupling agent (E) 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 (E) may be of the monomer type or oligomer type. Examples of the reactive functional group in the silane coupling agent (E) 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.

[0066] The content of the reactive functional group in the silane coupling agent (E) 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 (E) is 200 g / mol.

[0067] The alkoxy group bonded to the silicon atom in the silane coupling agent (E) 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 (E) 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.

[0068] Examples of the silane coupling agent (E) 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. The silane coupling agent (E) may be used alone or in combination of two or more kinds.

[0069] (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.

[0070] (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.

[0071] The content of the radical polymerizable compound (B) is 0.01 to 10 parts by weight, preferably 0.05 to 5.0 parts by weight, more preferably 0.1 to 4.0 parts by weight, and even more preferably 0.5 to 3.0 parts by weight, relative to 100 parts by weight of the acrylic resin (A). When the content of the radical polymerizable compound (B) is within the above range, excellent peel strength is likely to be obtained.

[0072] The content of the radical polymerizable compound (b1) having one phenolic hydroxyl group and at least one radical polymerization reactive group is 0.01 to 10 parts by weight, preferably 0.05 to 5.0 parts by weight, more preferably 0.1 to 4.0 parts by weight, and even more preferably 0.5 to 3.0 parts by weight, per 100 parts by weight of the acrylic resin (A). When the content of the radical polymerizable compound (B) is within the above range, excellent peel strength is likely to be obtained.

[0073] When the pressure-sensitive adhesive composition contains a crosslinking agent (C), the content of the crosslinking agent (C) 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 7.5 parts by weight, per 100 parts by weight of the acrylic resin (A). If the content of the crosslinking agent (C) is too high, the adhesive strength tends to decrease. If the content of the crosslinking agent (C) is too low, the durability tends to decrease.

[0074] When the pressure-sensitive adhesive composition contains an active energy ray crosslinking agent (c1), the content of the active energy ray crosslinking agent (c1) 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 7.5 parts by weight, per 100 parts by weight of the acrylic resin (A). If the content of the active energy ray crosslinking agent (c1) 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 (c1) is too high, the adhesive properties after curing will tend to decrease.

[0075] When the pressure-sensitive adhesive composition contains a thermal crosslinking agent (c2), the content of the thermal crosslinking agent (c2) 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 (c2) 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 (c2) is too high, the peel strength after curing tends to be reduced.

[0076] The content of the photopolymerization initiator (D) is preferably 0.1 to 5.0 parts by weight, more preferably 0.5 to 4.0 parts by weight, and even more preferably 1.0 to 3.0 parts by weight, relative to 100 parts by weight of the acrylic resin (A). When the content of the photopolymerization initiator (D) is within the above range, sufficient curability can be obtained when curing is carried out.

[0077] When the pressure-sensitive adhesive composition contains a hydrogen abstraction photopolymerization initiator (d1), the content of the hydrogen abstraction photopolymerization initiator (d1) 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 photopolymerization initiator (d1) is too high, discoloration tends to occur after durability testing. If the content of the hydrogen abstraction photopolymerization initiator (d1) is too low, the degree of crosslinking does not increase, and therefore the adhesive properties and durability tend to deteriorate.

[0078] The content of the intramolecular cleavage type photopolymerization initiator (d2) is preferably 0.1 to 3.0 parts by weight, more preferably 0.5 to 2.0 parts by weight, based on 100 parts by weight of the acrylic resin (A). If the content of the cleavage-type photopolymerization initiator (d2) is too high, the durability tends to deteriorate due to bleed-out, whereas if the content of the cleavage-type photopolymerization initiator (d2) is too low, the degree of crosslinking does not increase, and therefore the adhesive properties and durability tend to deteriorate.

[0079] When the pressure-sensitive adhesive composition contains a silane coupling agent (E), 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 (E) is too low, it tends to be difficult to obtain the effect of improving durability, whereas if the content of the silane coupling agent (E) is too high, the peel strength tends to decrease due to the effects of bleed-out, etc.

[0080] 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).

[0081] (Preparation of Pressure-Sensitive Adhesive Composition) The pressure-sensitive adhesive composition of the present invention can be obtained by mixing an acrylic resin (A), a radically polymerizable compound (B), and, if necessary, a crosslinking agent (C), a photopolymerization initiator (D), a silane coupling agent (E), 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.

[0082] (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 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.

[0083] <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.

[0084] 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.

[0085] 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.

[0086] 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).

[0087] <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.

[0088] 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.

[0089] 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.

[0090] The organic solvent used to adjust the concentration may be any of the organic solvents listed as being usable 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] The gel fraction of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet before final curing when cured in multiple stages is preferably 0.5 to 70% by weight, more preferably 20 to 65% by weight, because the sheet can be easily bonded to the adherend regardless of its shape, and the pressure-sensitive adhesive layer can hold the adherend in place after bonding.

[0097] The final gel fraction of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet after curing is preferably 60 to 90% by weight, more preferably 62 to 87% by weight, and particularly preferably 65 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.

[0098] 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 (C) and photopolymerization initiator (D).

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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]

[0104] 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.

[0105] <Abbreviations, raw materials> (Copolymerizable monomer (a1) having an alkyl group with a branched structure) 2EHA: 2-ethylhexyl acrylate (Tg of homopolymer = -70°C)

[0106] (Hydroxyl group-containing monomer (a2-1)) 4HBA: 4-hydroxybutyl acrylate (homopolymer Tg = -32°C)

[0107] (Radical polymerizable compound (B)) [Radical polymerizable compound (b1) having a phenolic hydroxyl group and a polymerizable functional group] Blenmer PHOH: 4-hydroxyphenyl methacrylate, manufactured by NOF Corporation [Other radically polymerizable compounds] Dopamine Aam: Dopamine acrylamide, manufactured by Osaka Organic Chemical Industry Co., Ltd.

[0108] (Radical polymerization initiator) AIBN: 2,2'-azobis(isobutyronitrile) (10-hour half-life temperature 65°C)

[0109] (Crosslinking agent (C)) [Active energy ray crosslinking agent (c1): multifunctional acrylate] TMPTA (Aronix M-309, manufactured by Toagosei Co., Ltd.)

[0110] (Photopolymerization initiator (D)) [Hydrogen Abstraction Photopolymerization Initiator (d1)] Omnirad 754: Manufactured by IGM Resins BV [Intramolecular cleavage-type photopolymerization initiator (d2)] Omnirad 184: Manufactured by IGM Resins BV

[0111] <Production Example 1: Production of acrylic resin (A-1)> A 2L flask equipped with a condenser was charged with 54 parts ethyl acetate (boiling point 77°C), 30 parts acetone (boiling point 56°C) as the polymerization solvent, 0.02 parts AIBN as the polymerization initiator, and 95 parts 2EHA and 5 parts 4HBA as the monomers. The mixture was heated to reflux in the flask and allowed to react for 1 hour. Then, 20 parts ethyl acetate (boiling point 77°C) and 0.04 parts AIBN were added dropwise over 1 hour. The mixture was then heated to reflux for 3.5 hours to allow the reaction to proceed, 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.

[0112] <Production Example 2: Production of acrylic resin (A-2)> A 2L flask equipped with a condenser was charged with 54 parts ethyl acetate (boiling point 77°C), 30 parts acetone (boiling point 56°C) as the polymerization solvent, 0.02 parts AIBN as the polymerization initiator, and 98 parts 2EHA and 2 parts 4HBA as the monomers. The mixture was heated to reflux in the flask and allowed to react for 1 hour. Then, 20 parts ethyl acetate (boiling point 77°C) and 0.04 parts AIBN were added dropwise over 1 hour. The mixture was then heated to reflux for 3.5 hours to allow the reaction to proceed, yielding a solution of acrylic resin (A-2). The weight-average molecular weight (Mw), polydispersity, and glass transition temperature (Tg) based on dynamic viscoelasticity of the acrylic resin (A-2) are shown in Table 1.

[0113] [Table 1]

[0114] Example 1 A pressure-sensitive adhesive composition was obtained by mixing 100 parts (solids content) of the acrylic resin (A-1) solution with 0.5 parts (solids content) of a radically polymerizable compound (b1) Blemmer PHOH having one phenolic hydroxyl group and a radical polymerization reactive group, 1.0 parts (solids content) of Omnirad 754, 1.0 parts (solids content) of Omnirad 184, and 3.0 parts (solids content) of TMPTA. The resulting pressure-sensitive adhesive composition was adjusted to a solids concentration of 35% 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 pressure-sensitive 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.

[0115] The release sheet on one side of the adhesive composition layer sheet thus obtained was peeled off, and the sheet was pressed against an easy-adhesion polyethylene terephthalate (PET) sheet (thickness 125 μm) that had been subjected to corona discharge treatment to obtain a PET sheet with an adhesive composition layer. Next, the obtained PET sheet with the pressure-sensitive adhesive composition layer was irradiated with a high-pressure mercury UV irradiation device at a peak irradiance of 150 mW / cm 2 , cumulative exposure: 1000mJ / cm 2 An adhesive layer was formed by irradiating the sheet with ultraviolet light (×1 pass), and a PET sheet with an adhesive layer having a thickness of 50 μm was obtained.

[0116] <Examples 2 to 4, Comparative Examples 1 to 4> As shown in the table, the adhesive composition of each example was prepared in the same manner as in Example 1, except that the acrylic resin (A-1) and the phenolic hydroxyl group compound (b-1) were changed as shown in Table 2.

[0117] [Table 2]

[0118] <Measurement and evaluation methods> The measurement and evaluation methods for the pressure-sensitive adhesive compositions of the Examples and Comparative Examples are shown below.

[0119] (gel fraction) The pressure-sensitive adhesive composition sheet of each example was irradiated with a high-pressure mercury UV irradiation device at a peak irradiance of 150 mW / cm 2 , cumulative exposure dose: 1000mJ / cm2 (1000mJ / cm 2 A pressure-sensitive adhesive layer was formed by irradiating the sheet with ultraviolet light (×1 pass), and a substrate-less double-sided pressure-sensitive adhesive sheet was obtained. The resulting substrate-less double-sided PSA sheet was then cut to 40 mm x 40 mm and left to stand for 30 minutes at 23°C and 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. The sheet was then immersed in a sealed container containing 250 g of toluene at 23°C for 24 hours, and the gel fraction (%) was calculated from the change in weight.

[0120] (180° peel strength (room temperature adhesive strength): 23℃ test) The PET sheet with the adhesive layer for 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) using pressure applied twice with a 2 kg rubber roller in 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 in an atmosphere of 23°C and 50% RH. The 180° peel strength (N / 25 mm) was then measured and evaluated at room temperature (23°C) at a peel rate of 300 mm / min. The results are shown in Table 3. The evaluation criteria are as follows: ◎ Peel strength is 10.0N / 25mm or more. ○ Peel strength is 6.0N / 25mm or more and less than 10.0N / 25mm. × Peel strength is less than 6.0 N / 25 mm.

[0121] (180° peel strength (high temperature adhesive strength): 60℃ test) The PET sheet with the adhesive layer for 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) using pressure applied twice with a 2 kg rubber roller in an atmosphere of 23°C and 50% RH. The sheet was then autoclaved (50°C, 0.5 MPa, 20 minutes) and left to stand for 60 minutes in a dry atmosphere at 60°C. The 180° peel strength (N / 25 mm) was then measured at 60°C at a peel rate of 300 mm / min, and the evaluation results are shown in Table 3. The evaluation criteria are as follows: ◎ Peel strength is 10.0N / 25mm or more. ○ Peel strength is 6.0N / 25mm or more and less than 10.0N / 25mm. × Peel strength is less than 6.0 N / 25 mm.

[0122] (optical measurement) The pressure-sensitive adhesive composition sheet of each example was irradiated with a high-pressure mercury UV irradiation device at a peak irradiance of 150 mW / cm 2 , cumulative exposure: 1000mJ / cm 2 (1000mJ / cm 2 The adhesive layer was formed by irradiating the sheet with ultraviolet light (×1 pass) to obtain a substrateless double-sided adhesive sheet. One of the release sheets was then peeled off, and the exposed adhesive layer side was attached to alkali-free glass (Corning Eagle XG, 1.1 mm thick). The sheet was then autoclaved (50°C, 0.5 MPa, 20 minutes), left to stand in an atmosphere of 23°C and 50% RH for 30 minutes, and the remaining release sheet was peeled off to produce a test specimen with an alkali-free glass / adhesive layer structure.

[0123] Using the obtained test piece, the color difference b * The measured values ​​are shown in Table 3. [Color difference] 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 *The value was measured by separating only the adhesive layer from the non-alkali glass (b * The value was measured by attaching the tape to a surface (value = 0.16).

[0124] Using the obtained test piece, a heat resistance test was carried out in an atmosphere of 130°C for 50 hours. After that, the remaining release sheet was peeled off, and the b * The value of b after the heat resistance test was measured. * From the value, b before the heat resistance test * By subtracting the value, △b * The values ​​were calculated and evaluated according to the following criteria. The results are shown in Table 3. * The values ​​were measured in the same manner as in the measurement of the optical properties of the pressure-sensitive adhesive layer described above. (evaluation) 〇···△b * Value less than 0.5 × △b * Value is 0.5 or more

[0125] [Table 3]

[0126] In Examples 1 to 4, which used the adhesive composition of the present invention, adhesives that provide excellent heat resistance and excellent peel strength at high temperatures, and adhesive sheets having an adhesive layer made of the adhesive, were obtained. On the other hand, Comparative Examples 1 and 2, which did not use the specific radically polymerizable compound (b1) used in the present invention, were inferior in peel strength at high temperatures, and Comparative Examples 3 and 4 were inferior in heat resistance. [Industrial Applicability]

[0127] The pressure-sensitive adhesive composition of the present invention provides excellent adhesive properties in terms of heat resistance 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 containing an acrylic resin (A) and a radically polymerizable compound (B), The acrylic resin (A) has a glass transition temperature determined by dynamic viscoelasticity of −35° C. or lower, The pressure-sensitive adhesive composition, wherein the radically polymerizable compound (B) contains a radically polymerizable compound (b1) having one phenolic hydroxyl group and at least one radically polymerizable reactive group.

2. The pressure-sensitive adhesive composition according to claim 1 , wherein the acrylic resin (A) contains a structural unit derived from a copolymerizable monomer (a1) having an alkyl group with a branched structure.

3. The pressure-sensitive adhesive composition according to claim 2, wherein the content of the structural units derived from the copolymerizable monomer (a1) having an alkyl group with a branched structure is 50% by weight or more based on all structural units of the acrylic resin (A).

4. 3. The pressure-sensitive adhesive composition according to claim 2, wherein the copolymerizable monomer (a1) having an alkyl group with a branched structure is 2-ethylhexyl acrylate (a1-1).

5. The pressure-sensitive adhesive composition according to claim 1 , wherein the acrylic resin (A) contains a structural unit derived from a functional group-containing monomer (a2).

6. The pressure-sensitive adhesive composition according to claim 5, wherein the content of structural units derived from the functional group-containing monomer (a2) is more than 0 to 15 wt% relative to all structural units of the acrylic resin (A).

7. 6. The pressure-sensitive adhesive composition according to claim 5, wherein the functional group-containing monomer (a2) is a hydroxyl group-containing monomer (a2-1).

8. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the content of the radically polymerizable compound (B) is 0.01 to 10 parts by weight per 100 parts by weight of the acrylic resin (A).

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

10. The pressure-sensitive adhesive composition according to claim 9, wherein the crosslinking agent (C) contains an active energy ray crosslinking agent (c1).

11. The pressure-sensitive adhesive composition according to claim 10 , wherein the active energy ray crosslinking agent (c1) contains a polyfunctional (meth)acrylate.

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

13. A pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition according to any one of claims 1 to 12.

14. The pressure-sensitive adhesive according to claim 13, wherein the crosslinking is carried out by irradiation with active energy rays.

15. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to claim 13.

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