Adhesive composition, adhesive, and adhesive sheet

Abstract

To provide an adhesive composition capable of obtaining excellent adhesive properties in a low crosslinked state after primary curing and obtaining excellent adhesive properties and reliability even after complete curing.SOLUTION: There is provided an adhesive composition comprising an acrylic resin (A) which has a structural unit derived from a hydroxyl group-containing monomer (a1) which has a glass transition temperature of 0°C or more when forming a homopolymer and a structural unit derived from an alkyl(meth)acrylate (a2) having a branched alkyl group which contains two or more tertiary carbon atoms. The glass transition temperature of the acrylic resin (A) based on dynamic viscoelasticity is -10°C or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to adhesive compositions, adhesives, and adhesive sheets. [Background technology]

[0002] In recent years, touch panels, which combine a display and a position input device, have been widely used in televisions, computer monitors, laptops, mobile phones, smartphones, tablet devices, and other mobile devices. Among these, capacitive touch panels are the most common. A touch panel typically consists of a display made of organic EL or liquid crystal, a transparent conductive film substrate (ITO substrate), and a protective film (protective glass). A transparent adhesive sheet is used to bond these touch panel components together.

[0003] Displays made of flexible devices such as organic EL can be used in a variety of shapes, including flat, curved, foldable, and rollable displays, due to their characteristics. In transparent adhesive sheets used to bond laminates composed of displays with complex shapes such as curved surfaces, it is necessary to bond components of various shapes, so the adhesive for transparent adhesive sheets is bonded in a low-crosslinking state before complete curing. Therefore, sufficient adhesive properties are required during the process of completely curing the low-crosslinking adhesive layer. For example, when bonding to components with complex shapes, bonding defects are likely to occur due to the transparent adhesive sheet sticking to areas other than the intended location. Therefore, there is a demand for transparent adhesive sheets with low tackiness. Furthermore, in order to fix complexly shaped components together, it is necessary to suppress the peeling of the transparent adhesive sheet from the components under stress. Therefore, there is a demand for transparent adhesive sheets that have high holding power even in a low-crosslinking state.

[0004] In addition, the adhesive layer after complete curing requires not only excellent adhesive properties such as normal tackiness, but also superior reliability when bonding various materials such as polarizing plates and glass. For example, to obtain excellent durability after complete curing, a low degree of crosslinking is required until bonding to the substrate, and the degree of crosslinking must be efficiently increased during complete curing.

[0005] Therefore, it is expected that sufficient adhesion to the substrate will be possible by bonding the adhesive sheet to the substrate in a low-crosslinking state. Furthermore, it is expected that the adhesive sheet will become highly crosslinked when fully cured while bonded to the substrate in a low-crosslinking state, thereby improving durability. Generally, primary curing occurs through thermal crosslinking or irradiation with active energy rays, while complete curing occurs through crosslinking with irradiation with active energy rays. Examples of adhesive sheets using such multi-stage curing adhesives include the adhesive sheets described in Patent Documents 1 to 3.

[0006] Patent Document 1 discloses that by further using an organic solvent that is easily volatile under general drying conditions, and by incorporating a specific proportion of ethylenically unsaturated monomers that are not easily volatile, in a solvent-based adhesive made of acrylic resin, thick coating is possible, and an adhesive layer with a beautiful coating surface can be obtained. Furthermore, Patent Document 2 discloses that, in order to form a three-dimensional network structure of a solvent-type acrylic ester adhesive without using a crosslinking agent, a hydrogen pulping type photopolymerization initiator is used, and the aging process is omitted by irradiating with light after the coating and drying process. Furthermore, Patent Document 3 discloses that by using an acrylic resin with a high glass transition temperature, an adhesive with high step-following ability and blister resistance can be obtained. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2012-111939 [Patent Document 2] Japanese Patent Publication No. 2017-210542 [Patent Document 3] International Publication No. 2017 / 022770 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, none of the patent documents 1 to 3 consider the tackiness in the low-crosslinking state during primary curing. Therefore, the tackiness in the low-crosslinking state during primary curing may be insufficient, and there is room for improvement. The present invention aims to provide an adhesive composition that can be used for multi-stage curing, which provides excellent adhesive properties in a low-crosslinking state after primary curing, and also provides excellent adhesive properties and reliability after complete curing; 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]

[0009] To solve the above problems, the inventors conducted diligent research and found that by using an adhesive composition containing an acrylic resin obtained using copolymer components of a specific composition and a photopolymerization initiator, it is possible to achieve excellent adhesive properties such as low tackiness and high holding power even in a low-crosslinking state after primary curing, and also to achieve excellent adhesive properties and reliability after complete curing.

[0010] In other words, the present invention relates to an adhesive composition comprising an acrylic resin (A) containing structural units derived from a hydroxyl group-containing monomer (a1) having a glass transition temperature of 0°C or higher when a homopolymer is formed, and structural units derived from an alkyl (meth)acrylate (a2) having a branched alkyl group containing two or more tertiary carbons, wherein the glass transition temperature of the acrylic resin (A) based on its dynamic viscoelasticity is -10°C or higher. [Effects of the Invention]

[0011] According to the present invention, there is provided an adhesive composition that can be used for multi-stage curing, which exhibits excellent adhesive physical properties in a low cross-linked state after primary curing and also exhibits excellent adhesive physical properties and reliability even after complete curing; an adhesive obtained by cross-linking the adhesive composition; and an adhesive sheet having an adhesive layer made of the adhesive.

Mode for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail, but these are examples of desirable embodiments. In addition, the meanings of the following terms in this specification are shown below. “(meth)acrylic” means acrylic or methacrylic. “(meth)acryloyl” means acryloyl or methacryloyl. “(meth)acrylate” means acrylate or methacrylate. “Acrylic resin” is a resin obtained by polymerizing a monomer component containing at least one (meth)acrylic monomer. “Sheet” is a term conceptually encompassing sheets, films, and tapes. “~” indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value.

[0013] <Adhesive Composition> The adhesive composition of the present invention contains an acrylic resin (A). In addition to the acrylic resin (A), the adhesive composition of the present invention may further contain a photoinitiator (B), a cross-linking agent (C), a silane coupling agent (D), a carbodiimide-based compound (E), and other optional components as needed. Hereinafter, each component will be described in order.

[0014] (Acrylic Resin (A)) The acrylic resin (A) used in the present invention contains structural units derived from a hydroxyl group-containing monomer (a1) whose glass transition temperature when a homopolymer is formed is 0°C or higher, and structural units derived from an alkyl (meth)acrylate (a2) having a branched alkyl group containing two or more tertiary carbons, and may optionally contain structural units derived from other copolymer components. Furthermore, the acrylic resin (A) used in the present invention is a polymerization product of a hydroxyl group-containing monomer (a1) having a glass transition temperature of 0°C or higher when a homopolymer is formed, an alkyl (meth)acrylate (a2) having a branched alkyl group containing two or more tertiary carbons, and other copolymer components used as needed. Copolymer components are a general term for monomer components that have polymerizable double bonds. Copolymer components do not include polymerization initiators or polymerization solvents.

[0015] [Hydroxyl group-containing monomers (a1) with a glass transition temperature of 0°C or higher when forming homopolymers] The hydroxyl group-containing monomer (a1) used in the present invention, which has a glass transition temperature of 0°C or higher when forming a homopolymer, contains one or more hydroxyl groups and an ethylenically unsaturated group. Examples of hydroxyl group-containing monomers (a1) include hydroxyl group-containing monomers such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate, N-methylol(meth)acrylamide, and N-2-hydroxyethyl(meth)acrylamide. In particular, 2-hydroxyethyl methacrylate is preferred in terms of its adhesive properties.

[0016] [Alkyl (meth)acrylate (a2) having a branched alkyl group containing two or more tertiary carbons] Alkyl (meth)acrylate (a2) does not have a hydroxyl group. Examples of branched alkyl (meth)acrylates (a2) used in the present invention that have a branched alkyl group containing two or more tertiary carbons include isodecyl (meth)acrylate, isomiristyl (meth)acrylate, isotridecyl (meth)acrylate, isostearyl (meth)acrylate, and other branched alkyl (meth)acrylates. Among these, isodecyl (meth)acrylate is preferred due to its excellent active energy ray curability upon complete curing. You may use one of these types alone, or you may use two or more types in combination.

[0017] [High Tg alkyl (meth)acrylate (a3) ​​with a glass transition temperature of 0°C or higher when forming a homopolymer] High Tg alkyl (meth)acrylate (a3) ​​does not contain a hydroxyl group or a branched alkyl group containing two or more tertiary carbon atoms. Examples of high-Tg alkyl monomers used in the present invention that have a glass transition temperature of 0°C or higher when forming homopolymers include linear alkyl(meth)acrylates such as methyl(meth)acrylate, ethyl methacrylate, n-butyl methacrylate, and hexyl methacrylate; branched alkyl(meth)acrylates such as isobutyl methacrylate and tert-butyl(meth)acrylate; and cycloalkyl(meth)acrylates such as cyclohexyl(meth)acrylate, dicyclopentanyl(meth)acrylate, and isobornyl(meth)acrylate. In particular, methyl (meth)acrylate, ethyl methacrylate, and isobutyl methacrylate are preferred in terms of adhesive properties.

[0018] [Ethylene-unsaturated monomer (a4)] The acrylic resin (A) used in the present invention may further contain, if necessary, structural units derived from hydroxyl group-containing monomers (a1) and alkyl (meth)acrylates (a2) and other copolymerizable ethylenically unsaturated monomers (a4) other than high-Tg alkyl (meth)acrylates (a3). Examples of ethylenically unsaturated monomers (a4) include linear alkyl (meth)acrylates such as ethyl acrylate, n-butyl acrylate, hexyl acrylate, octyl (meth)acrylate, and lauryl acrylate; branched alkyl acrylates such as isobutyl acrylate, isoamyl acrylate, 2-ethylhexyl (meth)acrylate, and isononyl acrylate / phenyl (meth)acrylate; hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate, which have a glass transition temperature of less than 0°C when forming homopolymers; aromatic ring-containing monomers such as benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol-polypropylene glycol-(meth)acrylate, orthophenylphenoxyethyl (meth)acrylate, and nonylphenol ethylene oxide adduct (meth)acrylate; and 2-methyl Ether chain-containing monomers such as toxyethyl (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, stearoxypolyethylene glycol mono(meth)acrylate; acrylate dimers such as (meth)acrylic acid and β-carboxyethyl acrylate; carboxyl group-containing monomers such as crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, N-glycolic acid, and cinnamic acid;Examples include amide group-containing monomers such as (meth)acrylamide, N-(n-butoxyalkyl)(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, and N,N-dimethylaminoalkyl(meth)acrylamide; benzophenone-containing monomers such as 4-(meth)acryloyloxybenzophenone; and others such as acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyltoluene, vinylpyridine, vinylpyrrolidone, dialkyl itaconicate, dialkyl fumarate, acrylic chloride, methyl vinyl ketone, N-acrylamide methyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone. The ethylenically unsaturated monomer (a4) may be used alone or in combination of two or more types.

[0019] Furthermore, 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, divinylbenzene, etc., can also be used in combination as ethylenically unsaturated monomers having two or more ethylenically unsaturated groups.

[0020] [Composition of acrylic resin (A)] The content of structural units derived from the hydroxyl group-containing monomer (a1) in the acrylic resin (A) is preferably 5 to 30% by weight, particularly preferably 7 to 25% by weight, and more preferably 9 to 20% by weight, relative to the total acrylic resin (A) (100% by weight). If the content of structural units derived from the hydroxyl group-containing monomer (a1) is too low, the heat resistance to moisture and high temperatures after complete curing tend to decrease. If the content of structural units derived from the hydroxyl group-containing monomer (a1) is too high, the viscosity tends to increase due to the strengthening of hydrogen bonds, and the workability tends to decrease.

[0021] The content of alkyl (meth)acrylate (a2)-derived structural units in the acrylic resin (A) is preferably 5 to 30% by weight, particularly preferably 7 to 25% by weight, and more preferably 9 to 20% by weight, relative to the total acrylic resin (A) (100% by weight). If the content of alkyl (meth)acrylate (a2)-derived structural units is too low, the reliability during primary curing tends to decrease. If the content of alkyl (meth)acrylate (a2)-derived structural units is too high, the durability after complete curing tends to decrease.

[0022] The content of structural units derived from high-Tg alkyl (meth)acrylate (a3) ​​in the acrylic resin (A) is preferably 5 to 30% by weight, particularly preferably 7 to 25% by weight, and more preferably 9 to 20% by weight, relative to the total acrylic resin (A) (100% by weight). If the content of structural units derived from alkyl (meth)acrylate (a3) ​​is too low, the reliability during primary curing tends to decrease. If the content of structural units derived from high-Tg alkyl (meth)acrylate (a3) ​​is too high, the tackiness after complete curing tends to deteriorate.

[0023] When the acrylic resin (A) contains structural units derived from ethylenically unsaturated monomers (a4), the content of structural units derived from ethylenically unsaturated monomers (a4) is usually 80% by weight or less, preferably 70% by weight or less, and more preferably 60% by weight or less, relative to the total acrylic resin (A) (100% by weight). If the content of structural units derived from ethylenically unsaturated monomers (a4) is too high, the balance of adhesive properties tends to deteriorate.

[0024] [Physical properties of acrylic resin (A)] The temperature at which the Tg of the acrylic resin (A), based on its dynamic viscoelasticity, i.e., the loss tangent of its dynamic viscoelasticity, is maximized is -10°C or higher, preferably -5 to 20°C, more preferably 0 to 15°C, and particularly preferably 2 to 13°C. If the temperature at which the loss tangent of the dynamic viscoelasticity of the acrylic resin (A) is maximized is too high, the adhesive strength tends to decrease due to a decrease in the step-following ability and adhesion of the adhesive layer. If the temperature at which the loss tangent of the dynamic viscoelasticity of the acrylic resin (A) is maximized is too low, the adhesive properties tend to decrease in the low-crosslinking state during primary curing.

[0025] The Tg based on dynamic viscoelasticity is determined by the following measurement method. An acrylic resin solution containing only the acrylic resin (A) of the present invention and the organic solvent is prepared by adding a suitable 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. Then, the organic solvent is removed by drying by heat treatment at 90~105°C for 5~10 minutes, etc., and this is attached to the release sheet to create an acrylic resin sheet containing 99% by weight or more of the acrylic resin (A). Then, multiple acrylic resin sheets are laminated to create an acrylic resin sheet with a thickness of approximately 800 μm. The dynamic viscoelasticity of the fabricated sheet is measured under the following conditions, and the temperature at which the loss tangent (loss modulus G'' / storage modulus G'=tanδ) is maximized is read and defined as the glass transition temperature of the acrylic resin (A) based on dynamic viscoelasticity.

[0026] (Measurement conditions for dynamic viscoelasticity) Measuring instrument: Dynamic viscoelasticity measuring device (Product name: DVA-225, manufactured by IT Measurement & Control Co., Ltd.) Deformation mode: Shear Distortion: 0.1% Measurement temperature: -100~60℃ Measurement frequency: 1Hz

[0027] In contrast, the calculated glass transition temperature (calculated Tg) is calculated using Fox's formula shown below. The "Tg based on the dynamic viscoelasticity of the acrylic resin (A)" in this invention is different from the calculated Tg.

[0028]

number

[0029] Tg: Glass transition temperature (K) of the copolymer Tga: Glass transition temperature (K) of the homopolymer of monomer A Wa: Weight fraction of constituent units derived from monomer A in the copolymer Tgb: Glass transition temperature (K) of monomer B homopolymer Wb: Weight fraction of constituent units derived from monomer B in the copolymer Tgn: Glass transition temperature (K) of monomer N homopolymer Wn: Weight fraction of constituent units derived from monomer N in the copolymer (Wa + Wb + ... + Wn = 1)

[0030] The weight-average molecular weight (Mw) of the acrylic resin (A) is preferably 50,000 to 500,000, more preferably 100,000 to 400,000, and even more preferably 150,000 to 350,000. If the weight-average molecular weight of the acrylic resin (A) is too high, the viscosity tends to become too high, reducing the coating properties and handling. If the weight-average molecular weight of the acrylic resin (A) is too low, the cohesive force decreases, which tends to reduce the adhesive properties and the durability after complete curing. The weight-average molecular weight of acrylic resin (A) is the weight-average molecular weight at the time of completion of manufacturing. The weight-average molecular weight is measured for acrylic resin (A) that has not been heated or otherwise subjected to processing after manufacturing.

[0031] The weight-average molecular weight of acrylic resin (A) is the weight-average molecular weight converted to the standard polystyrene molecular weight. The weight-average molecular weight was measured using a high-performance liquid chromatograph (Waters Corporation Japan, "Waters2695 (main unit)" and "Waters2414 (detector)") with a Shodex GPC KF-806L column (exclusion limit molecular weight: 2 × 10⁶). 7 Separation range: 100~2×10 7 The measurement is performed by using three tubes in series (theoretical plate count: 10,000 stages / tube, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm). The number-average molecular weight can be measured using a similar method. Furthermore, the degree of dispersion can be determined from the weight-average molecular weight and the number-average molecular weight.

[0032] The degree of dispersion (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 degree of dispersion of the acrylic resin (A) is too high, the durability of the adhesive layer decreases and foaming tends to occur more easily. If the degree of dispersion of the acrylic resin (A) is too low, handling tends to decrease. The lower limit of the degree of dispersion is usually 1.1 from the standpoint of manufacturing limitations.

[0033] [Method for producing acrylic resin (A)] Acrylic resin (A) can be produced by polymerizing the hydroxyl group-containing monomer (a1), alkyl (meth)acrylate (a2), high Tg alkyl (meth)acrylate (a3), and ethylenically unsaturated monomer (a4) used as needed (hereinafter, these are collectively referred to as copolymer component (a)).

[0034] Examples of polymerization methods for acrylic resin (A) include conventionally known polymerization methods such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. Solution polymerization is preferred in terms of reaction safety and stability, and the ability to produce acrylic resin (A) with any monomer composition. The following is an example of a preferred manufacturing method for acrylic resin (A).

[0035] First, the copolymer component (a) and polymerization initiator are mixed or added dropwise to an organic solvent, and solution polymerization is carried out. Examples of organic solvents used in polymerization reactions 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; aliphatic halogenated hydrocarbons such as methylene chloride and ethylene chloride; and cyclic ethers such as tetrahydrofuran. Among these organic solvents, esters and ketones are preferred, and ethyl acetate, acetone, and methyl ethyl ketone are particularly preferred. Organic solvents may be used individually or in combination of two or more.

[0036] As polymerization initiators used in polymerization reactions, conventional radical polymerization initiators such as azo polymerization initiators and peroxide polymerization initiators can be used. Examples of azo polymerization initiators 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-based 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. Among these, azo polymerization initiators are preferred, and more preferably 2,2'-azobisisobutyronitrile and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Polymerization initiators may be used individually or in combination of two or more.

[0037] The amount of polymerization initiator used is usually 0.001 to 10 parts by weight per 100 parts by weight of copolymer component (a), preferably 0.1 to 8 parts by weight, more preferably 0.5 to 6 parts by weight, particularly preferably 1 to 4 parts by weight, even more preferably 1.5 to 3 parts by weight, and most preferably 2 to 2.5 parts by weight. If the amount of polymerization initiator used is too little, 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 much, the acrylic resin (A) tends to gel.

[0038] 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 copolymer component (a) and polymerization initiator into an organic solvent.

[0039] The polymerization temperature in polymerization reactions is usually 40 to 120°C, but in the present invention, 50 to 90°C is preferred for stable reaction. If the polymerization temperature is too high, the acrylic resin (A) tends to gel easily, and 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. There are no particular restrictions on the polymerization time in the polymerization reaction, but it is preferably 0.5 hours or more, more preferably 1 hour or more, more preferably 2 hours or more, and most preferably 5 hours or more, from the addition of the last polymerization initiator. Polymerization reactions are preferably carried out under reflux of the solvent because it facilitates heat removal.

[0040] (Photopolymerization initiator (B)) The adhesive composition of the present invention preferably contains a photopolymerization initiator (B) in addition to an acrylic resin (A). The photopolymerization initiator (B) preferably contains an intramolecular hydrogen abstraction type photopolymerization initiator (b1) and an intermolecular hydrogen abstraction type photopolymerization initiator (b2). The photopolymerization initiator (B) may further contain other photopolymerization initiators (b3) other than the intramolecular hydrogen abstraction type photopolymerization initiator (b1) and the intermolecular hydrogen abstraction type photopolymerization initiator (b2), as long as the effects of the invention are not impaired.

[0041] [Intramolecular hydrogen abstraction type photopolymerization initiator (b1)] Intramolecular hydrogen abstraction type photopolymerization initiators (b1) have a structure that can generate radicals by abstracting hydrogen from the photopolymerization initiator itself, specifically such as a phenylglyoxylate structure. Examples of intramolecular hydrogen abstraction type photopolymerization initiators (b1) include oxyphenyl-acetic acid 2-[2-oxo-2-phenylacetoxy-ethoxy]ethyl ester and methyl phenylglyoxylate. Among these, oxyphenyl-acetic acid 2-[2-oxo-2-phenylacetoxy-ethoxy]-ethyl ester, which has multiple crosslinking sites within the molecule, is preferred in terms of crosslinking efficiency upon complete curing. Other commercially available options include the "Omnirad MBF" and "Omnirad 754" from IGM Resins BV. The intramolecular hydrogen abstraction type photopolymerization initiator (b1) may be used alone or in combination of two or more types.

[0042] [Intermolecular hydrogen abstraction type photopolymerization initiator (b2)] Intermolecular hydrogen abstraction type photopolymerization initiators (b2) have a structure that can generate radicals by abstracting hydrogen from something other than the photopolymerization initiator itself, specifically such as a benzophenone structure. Examples include 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, 2-benzoylmethyl benzoate, and 4-(1,3-acryloyl-1,4,7,10,13-pentaoxotridecyl)benzophenone.

[0043] Among these, 2,4,6-trimethylbenzophenone is preferred because it is a low-viscosity liquid and easy to handle. Furthermore, 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 sites within the molecule and are highly crosslinkable. Other commercially available products include Shinryo's "MBP," and IGM Resins BV's "OmniradBP," "Omnirad 4MBZ," "Esacure TZT," and "Omnipol BP." The intermolecular hydrogen abstraction type photopolymerization initiator (b2) may be used alone or in combination of two or more types.

[0044] [Other photopolymerization initiators (b3)] Other photopolymerization initiators (b3) include, for example, diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethylketal, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexylphenyl ketone, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, and 2-hydroxy-2-methyl-1-[4-(1-methylvinyl Examples include acetophenones such as phenyl]propanone oligomers; benzoins such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether; and acyl phosphonates such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Other photopolymerization initiators (b3) may be used individually or in combination of two or more.

[0045] It is also possible to use triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, 4-dimethylaminobenzoate ethyl, 4-dimethylaminobenzoate (n-butoxy)ethyl, 4-dimethylaminobenzoate isoamyl, 4-dimethylaminobenzoate 2-ethylhexyl, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, etc., in combination as auxiliary agents for the photopolymerization initiator (B). The photopolymerization initiator (B) may be used alone or in combination of two or more auxiliary agents.

[0046] (Crosslinking agent (C)) The adhesive composition of the present invention preferably further contains a crosslinking agent (C) in addition to an acrylic resin (A) and a photopolymerization initiator (B). Examples of crosslinking agents (C) include active energy ray crosslinking agents (c1) and thermal crosslinking agents (c2). The active energy ray crosslinking agent (c1) and thermal crosslinking agents (c2) may be used individually or in combination of two or more.

[0047] When only an active energy ray crosslinking agent (c1) is included as the crosslinking agent (C), multi-stage curing is possible simply by controlling the active energy dose. Furthermore, when both an active energy ray crosslinking agent (c1) and a thermal crosslinking agent (c2) are included as the crosslinking agent (C), multi-stage curing is also possible by using thermal curing and active energy ray curing in combination. By controlling the crosslinking reaction in this way, the cohesive force of the entire adhesive layer can be adjusted, and stable adhesive properties can be obtained after primary curing and complete curing.

[0048] [Activated energy ray crosslinking agent (c1)] Examples of active energy ray crosslinking agents (c1) include polyfunctional crosslinking agents containing two or more ethylenically unsaturated groups in one molecule. For example, 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)hexamethylene glycol di(meth)acrylate Examples include 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, ethylene oxide isocyanurate-modified tri(meth)acrylate, and polyfunctional urethane (meth)acrylate. In particular, (meth)acrylates containing two ethylenically unsaturated groups are preferred in terms of the balance of adhesive properties after curing, and (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, and (poly)tetramethylene glycol di(meth)acrylate are especially preferred. The polyfunctional crosslinking agent may be used alone or in combination of two or more types.

[0049] [Thermal crosslinking agent (c2)] The thermal crosslinking agent (c2) can exhibit excellent tackiness by reacting primarily with functional groups derived from functional group-containing monomers that are constituent monomers of the acrylic resin (A). Examples 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, the isocyanate-based crosslinking agent (c2-1) is preferably used in terms of improving adhesion to the substrate and its reactivity with the acrylic resin (A). The thermal crosslinking agent (c2) may be used alone or in combination of two or more types.

[0050] Examples of isocyanate crosslinking agents (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; 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 burettes and isocyanurates of these isocyanate compounds. Among isocyanate crosslinking agents (c2-1), aromatic isocyanate compounds are preferred due to their excellent reactivity, and tolylene diisocyanate compounds are particularly preferred. Furthermore, aliphatic isocyanate compounds are preferred due to their ability to suppress yellowing, and hexamethylene diisocyanate compounds are particularly preferred.

[0051] 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.

[0052] Examples of aziridine-based crosslinking agents (c2-3) include tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinylcarboxamide), and N,N'-hexamethylene-1,6-bis(1-aziridinylcarboxamide).

[0053] Examples of melamine-based crosslinking agents (c2-4) include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexapoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resins.

[0054] Examples of aldehyde-based crosslinking agents (c2-5) include glyoxal, malondialdehyde, succinidaldehyde, maleidaldehyde, glutardialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

[0055] Examples of amine-based crosslinking agents (c2-6) include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, and polyamides.

[0056] Examples of metal chelating crosslinking agents (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.

[0057] (Silane coupling agent (D)) The adhesive composition of the present invention preferably further contains a silane coupling agent (D) as a compound other than the acrylic resin (A), photopolymerization initiator (B), and crosslinking agent (C) in order to improve durability.

[0058] Silane coupling agents (D) are organosilicon compounds that contain one or more reactive functional groups and one or more alkoxy groups bonded to silicon atoms in their structure. Examples of silane coupling agents (D) include monomeric and oligomeric types. Examples of reactive functional groups in the silane coupling agent (D) include epoxy groups, (meth)acryloyl groups, mercapto groups, hydroxyl groups, carboxyl groups, amino groups, amide groups, and isocyanate groups. Among these, epoxy groups and mercapto groups are preferred due to their excellent durability and reworkability.

[0059] The content of reactive functional groups 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 groups are within the above numerical range, the balance between durability and reworkability is improved. The lower limit of the content of reactive functional groups in the silane coupling agent (D) is 200 g / mol.

[0060] As for the alkoxy group bonded to the silicon atom in the silane coupling agent (D), a C1-C8 alkoxy group is preferred from the viewpoint of durability and storage stability. Among these, a methoxy group and an ethoxy group are more preferred. The silane coupling agent (D) may have organic functional groups other than reactive functional groups and alkoxy groups bonded to silicon atoms, such as alkyl groups, phenyl groups, etc.

[0061] Examples of silane coupling agents (D) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, methyltri(glycidyl)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. Among these, γ-glycidoxypropyltrimethoxysilane is preferred from the viewpoint of heat resistance. The silane coupling agent (D) may be used alone or in combination of two or more types.

[0062] (Carbodiimide compound (E)) The adhesive composition of the present invention preferably further contains a carbodiimide compound (E) as a compound other than the acrylic resin (A), photopolymerization initiator (B), crosslinking agent (C), and silane coupling agent (D) from the viewpoint of heat resistance. Examples of carbodiimide compounds (E) include monocarbodiimides such as bis(2,6-diisopropylphenyl)carbodiimide, dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, di-t-butylcarbodiimide, and didodecylcarbodiimide, as well as polycarbodiimides containing multiple carbodiimides and cyclic carbodiimides. Among these, monocarbodiimide compounds are preferred from the viewpoint of heat resistance, and bis(2,6-diisopropylphenyl)carbodiimide is more preferred. Carbodiimide compound (E) may be used alone or in combination of two or more.

[0063] (optional ingredient) The adhesive composition of the present invention may optionally contain other adhesive components. The adhesive composition of the present invention may also contain conventionally known additives such as crosslinking accelerators, antistatic agents, tackifiers, and functional dyes.

[0064] (Composition of adhesive composition) The content of acrylic resin (A) is preferably 80% by weight or more, more preferably 90-99.9% by weight, and even more preferably 92-99.9% by weight, relative to the total adhesive composition. When the content of acrylic resin (A) is within the above numerical range, excellent adhesive properties are easily obtained in the low-crosslinking state after primary curing.

[0065] The content of the photopolymerization initiator (B) 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, per 100 parts by weight of the acrylic resin (A). When the content of the photopolymerization initiator (B) is within the above numerical range, sufficient curability can be obtained when complete curing is performed.

[0066] The content of the intramolecular hydrogen abstraction type photopolymerization initiator (b1) is preferably 0.1 to 5.0 parts by weight, and more preferably 0.5 to 3.0 parts by weight, per 100 parts by weight of the acrylic resin (A). If the content of intramolecular hydrogen abstraction type photopolymerization initiator (b1) is too high, discoloration tends to occur after humid heat endurance. If the content of intramolecular hydrogen abstraction type photopolymerization initiator (b1) is too low, the degree of crosslinking does not increase, which tends to worsen the tackiness during primary curing and the durability after complete curing.

[0067] The content of the intermolecular hydrogen abstraction type photopolymerization initiator (b2) is preferably 0.1 to 3.0 parts by weight, and 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 intermolecular hydrogen abstraction type photopolymerization initiator (b2) is too high, durability tends to deteriorate due to bleed-out. If the content of the intermolecular hydrogen abstraction type photopolymerization initiator (b2) is too low, the degree of crosslinking does not increase, which tends to deteriorate the tackiness during primary curing and the durability after complete curing.

[0068] If the photopolymerization initiator (B) contains another photopolymerization initiator (b3), the content of the photopolymerization initiator (b3) is preferably 2.0 parts by weight or less, and more preferably 1.0 part by weight or less, per 100 parts by weight of the acrylic resin (A).

[0069] When the adhesive composition contains a crosslinking agent (C), the amount of 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 amount of crosslinking agent (C) is too high, the adhesive strength tends to decrease. If the amount of crosslinking agent (C) is too low, the durability tends to decrease.

[0070] When the 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 not be obtained. If the content of the active energy ray crosslinking agent (C1) is too high, the tackiness during primary curing will tend to decrease.

[0071] When the 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 amount of thermal crosslinking agent (C2) is too low, the cohesive force will be insufficient, and the adhesive properties will tend to decrease during primary curing. If the amount of thermal crosslinking agent (C2) is too high, the adhesive strength will tend to decrease during complete curing.

[0072] If the adhesive composition contains a silane coupling agent (D), the content of the silane coupling agent (D) 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 silane coupling agent (D) content is too low, it tends to be difficult to achieve the desired effect of improving durability. If the silane coupling agent (D) content is too high, it tends to reduce adhesive strength due to effects such as bleed-out.

[0073] When the adhesive composition contains a carbodiimide compound (E), the content of the carbodiimide compound (E) is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, even more preferably 0.2 to 2 parts by weight, and particularly preferably 0.3 to 1 part by weight, per 100 parts by weight of the acrylic resin (A). If the content of carbodiimide compound (E) is too low, the thermal stability of the acrylic resin (A) tends to decrease. If the content of carbodiimide compound (E) is too high, the durability tends to decrease due to effects such as bleed-out.

[0074] If the adhesive composition contains other adhesives or additives, the content of the other adhesives or additives is preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, per 100 parts by weight of acrylic resin (A).

[0075] (Preparation of adhesive composition) The adhesive composition of the present invention can be obtained by mixing an acrylic resin (A), and optionally a photopolymerization initiator (B), a crosslinking agent (C), a silane coupling agent (D), a carbodiimide compound (E), and other optional components. The mixing method is not particularly limited, and various methods can be employed, such as mixing each component all at once, or mixing optional components first and then mixing the remaining components all at once or sequentially.

[0076] (Application) The adhesive composition of the present invention can be suitably used as an adhesive for multi-stage curing adhesive sheets that cure in multiple stages. Excellent adhesive properties are obtained even in the low-crosslinking state after primary curing, and furthermore, after complete curing, not only are the adhesive properties such as normal adhesive strength exhibited, but excellent durability is also shown when bonding various types and shapes of materials such as polarizing plates and glass. The adhesive composition of the present invention exhibits excellent adhesive properties, such as low tackiness and high holding power even in a low-crosslinking state after primary curing, thereby improving workability and reliability. Therefore, it is particularly suitable for use as an adhesive or adhesive sheet in touch panels, image display devices, and the like.

[0077] <Adhesive> The adhesive of the present invention is obtained by crosslinking the adhesive composition of the present invention described above. When the adhesive composition of the present invention is crosslinked (cured), the acrylic resin (A) contained in the adhesive composition forms a crosslinked structure at least on an intramolecular and intermolecular basis. As a result, the adhesive composition of the present invention is crosslinked to become the adhesive according to the present invention. If the acrylic resin (A) has an active energy ray crosslinkable structural region, the crosslinked structure can be formed by irradiation with active energy rays.

[0078] The adhesive of the present invention exhibits multi-stage curing properties, allowing it to be cured in multiple stages. The adhesive of the present invention reaches a low-crosslinking state through primary curing before complete curing. While complete curing and primary curing are not always clearly distinguishable, they can be distinguished by differences in gel fraction and dynamic viscoelasticity.

[0079] The curing method is not particularly limited in either the primary curing step or the complete curing step, and may be either heating or irradiation with active energy rays. Furthermore, the primary curing step may be performed in multiple stages, and multi-stage curing may be performed to achieve a complete cured state. Because the adhesive of the present invention exhibits excellent adhesive properties after primary curing, it is suitable for bonding optical components that constitute touch panels, image display devices, and the like.

[0080] The adhesive of the present invention can also be said to contain at least a crosslinked acrylic resin (A) of the present invention. The crosslinked material may be a partially crosslinked material in which at least a part of the acrylic resin (A) is partially crosslinked, or it may be a fully crosslinked material in which all of the acrylic resin (A) is crosslinked. Furthermore, the adhesive of the present invention may contain both a partially crosslinked material and a fully crosslinked material of the acrylic resin (A).

[0081] <Adhesive sheet> The adhesive sheet of the present invention has an adhesive layer made of the adhesive of the present invention. The adhesive sheet of the present invention may exhibit multi-stage curing properties in which the adhesive layer hardens in multiple stages. An adhesive sheet can be formed by providing an adhesive layer made of the adhesive of the present invention on a base sheet. Alternatively, a double-sided adhesive sheet can be formed by providing the adhesive layer on a release sheet. Furthermore, a base-less double-sided adhesive sheet can be produced by forming the adhesive layer on a release sheet instead of a base sheet, and then bonding the release sheet to the opposite side of the adhesive layer. A further adhesive layer may be formed on the formed adhesive layer to create a thicker adhesive layer. The resulting adhesive sheets and double-sided adhesive sheets are used after peeling off the release sheet from the adhesive layer.

[0082] Examples of methods for producing adhesive sheets include the following methods (i) and (ii). (i) A method of forming an adhesive sheet by dissolving the adhesive composition of the present invention in a solvent and coating it. (ii) A method for melting the adhesive composition of the present invention by heating to form an adhesive sheet.

[0083] Method (i) will be explained. When the adhesive composition of the present invention is dissolved in a solvent and applied to form an adhesive sheet, the concentration of the coating solution containing the adhesive composition of the present invention is adjusted with a suitable organic solvent and applied directly to a base sheet. Then, it is dried by, for example, heat treatment at 80 to 105°C for 0.5 to 10 minutes, and this is attached to a base sheet or release sheet. Subsequently, the adhesive composition is crosslinked (cured) by irradiation with active energy rays or aging, and an adhesive sheet having an adhesive layer made of adhesive can be produced.

[0084] As the organic solvent used for adjusting the concentration, those listed as organic solvents used in the polymerization reaction of acrylic resin (A) can be used. The concentration of the adhesive composition is usually 20 to 60% by weight as solid content, preferably 30 to 50% by weight.

[0085] Method (ii) will be explained. When the adhesive composition of the present invention is melted by heating to form an adhesive sheet, an adhesive layer of a desired thickness is formed on one or both sides of the base sheet by methods such as coating the molten material onto one or both sides of the base sheet and then cooling it, or by extruding and laminating it onto the base sheet using a T-die or the like. Then, if necessary, a release sheet is attached to the surface of the adhesive layer to produce the adhesive sheet. Furthermore, after forming an adhesive layer on a base sheet, an adhesive sheet having an adhesive layer formed by curing (crosslinking) the adhesive composition by performing an active energy ray irradiation treatment as needed and then aging can be produced. Furthermore, by forming an adhesive layer on a release sheet and attaching the release sheet to the adhesive layer on the opposite side, a substrate-less double-sided adhesive sheet can also be produced. The resulting adhesive sheets and double-sided adhesive sheets are used after peeling off the release sheet from the adhesive layer.

[0086] Examples of base sheets include polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymers; polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; polyfluoroethylene resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyfluoroethylene; 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 resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; synthetic resin sheets such as polystyrene, polycarbonate, polyarylate, and polyimide; metal foils such as aluminum, copper, and iron; paper such as fine paper and glassine paper; and woven or nonwoven fabrics made of glass fibers, natural fibers, and synthetic fibers. These base sheets can be used as single layers or as multi-layered structures made by laminating two or more types. Among these, synthetic resin sheets are preferred from the viewpoint of weight reduction and other factors.

[0087] As the release sheet, for example, various synthetic resin sheets as exemplified in the base sheet, paper, textiles, nonwoven fabrics, etc., that have been treated with a release agent can be used. As the release sheet, for example, it is preferable to use a silicone-based release sheet.

[0088] The method of coating the adhesive composition is not particularly limited. Examples include roll coating, die coating, gravure coating, comma coating, slot coating, and screen printing.

[0089] As active energy rays, light rays such as far ultraviolet, ultraviolet, near ultraviolet, and infrared rays; electromagnetic waves such as X-rays and gamma rays; electron beams; proton beams; and neutron beams can be used. Curing by ultraviolet light is preferred due to its curing speed, availability of irradiation equipment, and cost.

[0090] The gel fraction of the adhesive layer of the adhesive sheet before complete curing is preferably 0.1 to 60% by weight, more preferably 1 to 50% by weight, and particularly preferably 5 to 45% by weight, in order to allow for easy bonding regardless of the shape of the adherend and for the adhesive layer to hold the adherend after bonding.

[0091] Regarding the gel fraction of the adhesive layer of the adhesive sheet after complete curing, it is preferably 60-90% by weight, more preferably 62-87% by weight, and particularly preferably 65-85% by weight, from the viewpoint of durability and adhesive strength. If the gel fraction is too low, the cohesive force decreases, which tends to reduce durability. Conversely, if the gel fraction is too high, the cohesive force increases, which tends to reduce adhesive strength.

[0092] The gel fraction can be adjusted as needed using, for example, the following method. • Adjust the amount of activated energy radiation. • Adjust the content of the active energy ray crosslinkable structural moiety in the acrylic resin (A). • Adjust the type and amount of photopolymerization initiator (B) and crosslinking agent (C).

[0093] The gel fraction is an indicator of the degree of crosslinking (degree of hardening) and can be calculated, for example, by the following method: An adhesive sheet (without a release sheet) consisting of a polymer sheet (e.g., polyethylene terephthalate (PET) film) as the base material is wrapped in a 200-mesh stainless steel wire mesh and immersed in toluene maintained at 23°C for 24 hours. The weight percentage of the insoluble adhesive component remaining in the wire mesh is taken as the gel fraction. However, the weight of the base material is subtracted from the weight before and after toluene dissolution.

[0094] The thickness of the adhesive layer of the adhesive sheet is usually preferably 50 to 3000 μm, more preferably 75 to 1000 μm, and particularly preferably 100 to 350 μm. If the adhesive layer is too thin, the shock absorption tends to decrease. If the adhesive layer is too thick, the overall thickness increases when it is attached to, for example, an optical component, which tends to reduce its practicality.

[0095] In this invention, the thickness of the adhesive layer is determined by subtracting the measured thickness of the components other than the adhesive layer from the measured thickness of the entire adhesive layer-containing laminate, using the "ID-C112B" manufactured by Mitutoyo Corporation.

[0096] The adhesive layer of the adhesive sheet of the present invention preferably has a haze value of 2% or less when the thickness of the adhesive layer is 100 μm, more preferably 0 to 1.5%, and particularly preferably 0 to 1%. If the haze value is too high, the adhesive layer tends to whiten and its transparency decreases. The haze value is calculated by measuring the diffuse transmittance and total light transmittance using a HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.), and substituting the obtained values ​​of diffuse transmittance (DT) and total light transmittance (TT) into the following formula [Equation 1]. This instrument conforms to JIS K7361-1. Haze value (%) = (DT / TT) × 100 ... [Equation 1]

[0097] In the present invention, an optical member with an adhesive layer can be obtained by laminating an adhesive layer onto an optical member. For example, an optical member with an adhesive layer can be obtained by attaching the adhesive layer surface of the adhesive sheet of the present invention, in which an adhesive layer is formed on a release sheet, to an optical member, and then peeling off the release sheet. Alternatively, optical members can be bonded together using the above-mentioned double-sided adhesive sheet.

[0098] Optical components include those that make up touch panels and image display devices. Examples include displays (organic EL, liquid crystal), transparent conductive film substrates (ITO substrates), protective films (glass), transparent antennas (film), and transparent wiring. [Examples]

[0099] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description. In the examples, "parts" and "%" mean by weight basis. Furthermore, the weight-average molecular weight of the acrylic resin (A), the glass transition temperature based on dynamic viscoelasticity, the thickness of the adhesive layer, and the haze value (%) were measured according to the methods described in the embodiments above.

[0100] <Abbreviations, raw materials> (A hydroxyl group-containing monomer (a1) with a glass transition temperature of 0°C or higher when forming a homopolymer) • HEMA: 2-hydroxyethyl methacrylate (homopolymer Tg: 55℃)

[0101] (Alkyl (meth)acrylate (a2) containing two or more tertiary carbon atoms) • IDMA: Isodecyl methacrylate (Tg of homopolymer: -41℃) • IDA: Isodecyl acrylate (Tg of homopolymer: -62℃)

[0102] [High Tg alkyl (meth)acrylate (a3) ​​with a glass transition temperature of 0°C or higher when forming a homopolymer] • MMA: Methyl methacrylate (homopolymer Tg: 105℃) MAE: Methyl acrylate (homopolymer Tg: 8℃) • EMA: Ethyl methacrylate (homopolymer Tg: 65℃) • IBMA: Isobutyl methacrylate (homopolymer Tg: 48℃)

[0103] (Ethylene-unsaturated monomer (a4)) • 2EHA: 2-Ethylhexyl acrylate (homopolymer Tg: -70°C) • HEA: 2-hydroxyethyl acrylate • 4HBA: 4-hydroxybutyl acrylate

[0104] ADVN: 2,2'-Azobis(2,4-dimethylvaleronitrile) (half-life at 10 hours, temperature 52°C)

[0105] (Photopolymerization initiator (B)) [Intramolecular hydrogen abstraction type photopolymerization initiator (b1)] • Omnirad 754: A product manufactured by IGM Resins BV. [Intermolecular hydrogen abstraction type photopolymerization initiator (b2)] • Esacure TZT: A product manufactured by IGM Resins BV. • MBP: A product manufactured by Shinryo Co., Ltd.

[0106] (Crosslinking agent (C)) • Polypropylene glycol #400 diacrylate (NK ester APG400, a product manufactured by Shin Nakamura Chemical Industry Co., Ltd.)

[0107] (Silane coupling agent (D)) • KBM403 (a product manufactured by Shin-Etsu Chemical Co., Ltd.)

[0108] <Manufacturing Example 1: Manufacturing of Acrylic Resin (A-1)> In a 2L flask equipped with a condenser, 40 parts ethyl acetate (boiling point 77°C) was added as the polymerization solvent, 0.08 parts ADVN as the polymerization initiator, and 5.0 parts 2EHA, 0.5 parts MAE, 1.5 parts EMA, and 1.5 parts IDMA as monomers. The mixture was heated under reflux in the flask, and then 8.33 parts ethyl acetate (boiling point 77°C), 0.09 parts ADVN, 45.0 parts 2EHA, 4.5 parts MAE, 13.5 parts EMA, 13.5 parts HEMA, and 13.5 parts IDMA were added dropwise over 3 hours. After 15 minutes, a mixture of 1.66 parts ethyl acetate and 1.5 parts HEMA was added, and 15 minutes later, a mixture of 10 parts ethyl acetate and 0.13 parts ADVN was added dropwise over 1 hour to obtain a solution of acrylic resin (A-1). Table 1 shows the measurement results for the weight-average molecular weight (Mw), degree of dispersion (Mw / Mn), and glass transition temperature based on dynamic viscoelasticity of the acrylic resin (A-1).

[0109] <Manufacturing Example 2: Manufacturing of Acrylic Resin (A-2)> In a 2L flask equipped with a condenser, 40 parts ethyl acetate (boiling point 77°C) was added as the polymerization solvent, 0.08 parts ADVN as the polymerization initiator, and 5 parts 2EHA, 1.0 part IBMA, 1.0 part MMA, and 1.5 parts IDA as monomers. The mixture was heated under reflux in the flask, and then 8.33 parts ethyl acetate (boiling point 77°C), 0.09 parts ADVN, 45.0 parts 2EHA, 9.0 parts IBMA, 9.0 parts MMA, 13.5 parts HEMA, and 13.5 parts IDA were added dropwise over 3 hours. After 15 minutes, a mixture of 1.66 parts ethyl acetate and 1.5 parts HEMA was added, and 15 minutes later, a mixture of 10 parts ethyl acetate and 0.13 parts ADVN was added dropwise over 1 hour to obtain a solution of acrylic resin (A-2). Table 1 shows the measurement results for the weight-average molecular weight (Mw), dispersion (Mw / Mn), and glass transition temperature based on dynamic viscoelasticity of the acrylic resin (A-2).

[0110] <Manufacturing Example 3: Manufacturing of Acrylic Resin (A-3)> In a 2L flask equipped with a condenser, 40 parts of ethyl acetate (boiling point 77°C) were added as the polymerization solvent, 0.08 parts of ADVN as the polymerization initiator, and 5.5 parts of 2EHA, 1.0 part of IBMA, 1.0 part of EMA, and 1.0 part of IDMA as monomers. After heating under reflux in the flask, 8.33 parts of ethyl acetate (boiling point 77°C), 0.09 parts of ADVN, 49.5 parts of 2EHA, 9.0 parts of IBMA, 9.0 parts of EMA, 13.5 parts of HEMA, and 9.0 parts of IDMA were added dropwise over 3 hours. Furthermore, 15 minutes after the initial dropwise addition, a mixture of 1.66 parts ethyl acetate and 1.5 parts HEMA was added, and 15 minutes later, a mixture of 10 parts ethyl acetate and 0.13 parts ADVN was added dropwise over 1 hour to allow the reaction to proceed. The weight-average molecular weight (Mw), dispersion (Mw / Mn), and glass transition temperature based on dynamic viscoelasticity of the acrylic resin (A-3) were measured and are shown in Table 1.

[0111] <Manufacturing Example 4: Manufacturing of Acrylic Resin (A-4)> In a 2L flask equipped with a condenser, 40 parts ethyl acetate (boiling point 77°C) was added as the polymerization solvent, 0.08 parts ADVN as the polymerization initiator, 5.0 parts 2EHA, 0.5 parts IBMA, 1.5 parts EMA, 1.5 parts IDMA as monomers, and 0.5 parts HEA. The mixture was heated under reflux in the flask, and then 8.33 parts ethyl acetate (boiling point 77°C), 0.09 parts ADVN, 45.0 parts 2EHA, 4.5 parts IBMA, 13.5 parts EMA, 4.5 parts HEA, 9.0 parts HEMA, and 13.5 parts IDMA were added dropwise over 3 hours. Furthermore, 15 minutes after the initial dropwise addition, a mixture of 1.66 parts ethyl acetate and 1.0 part HEMA was added, and 15 minutes later, a mixture of 10 parts ethyl acetate and 0.13 parts ADVN was added dropwise over 1 hour to obtain a solution of acrylic resin (A-4). Table 1 shows the weight-average molecular weight (Mw), dispersion (Mw / Mn), and glass transition temperature based on dynamic viscoelasticity of the acrylic resin (A-4).

[0112] <Comparative Manufacturing Example 1: Manufacturing of Acrylic Resin (A'-1)> In a 2L flask equipped with a condenser, 40 parts ethyl acetate (boiling point 77°C) was added as the polymerization solvent, 0.08 parts ADVN as the polymerization initiator, and 6.0 parts 2EHA, 1.25 parts IBMA, and 1.25 parts EMA as monomers. The mixture was heated under reflux in the flask, and then 8.33 parts ethyl acetate (boiling point 77°C), 0.09 parts ADVN, 54.0 parts 2EHA, 11.25 parts IBMA, 11.25 parts EMA, and 13.5 parts HEMA were added dropwise over 3 hours. After 15 minutes, a mixture of 1.66 parts ethyl acetate and 1.5 parts HEMA was added, and 15 minutes later, a mixture of 10 parts ethyl acetate and 0.13 parts ADVN was added dropwise over 1 hour to obtain a solution of acrylic resin (A'-1). Table 1 shows the measurement results for the weight-average molecular weight (Mw), degree of dispersion (Mw / Mn), and glass transition temperature based on dynamic viscoelasticity of the acrylic resin (A'-1).

[0113] <Comparative Manufacturing Example 2: Manufacturing of Acrylic Resin (A'-2)> A monomer solution was prepared by mixing 55 parts IDMA, 30 parts IBMA, and 15 parts 4HBA. In a 2 L flask equipped with a condenser, 16.67 parts ethyl acetate (boiling point 77°C), 16.67 parts methyl ethyl ketone (boiling point 80°C) as polymerization solvents, 0.01 part ADVN as a polymerization initiator, and 10% of the 100 parts of the pre-prepared monomer solution were added. After heating under reflux in the flask, 10 parts ethyl acetate and a mixed solution of 90% of the remaining monomer solution were added dropwise over 3 hours. Furthermore, 30 minutes after the dropwise addition, a mixture of 10 parts ethyl acetate and 0.15 parts ADVN was added dropwise over 1 hour to allow the reaction to proceed and obtain a solution of acrylic resin (A'-2). The weight-average molecular weight (Mw), dispersion (Mw / Mn), and glass transition temperature based on dynamic viscoelasticity of the acrylic resin (A'-2) are shown in Table 1.

[0114] [Table 1]

[0115] <Example 1> To 100 parts (solids content) of a solution of acrylic resin (A-1), 2.0 parts (solids content) of Omnirad 754, 1.0 part (solids content) of Esacure TZT, 3.0 parts (solids content) of polypropylene glycol #400 diacrylate, and 0.1 parts (solids content) of KBM403 were mixed to obtain an adhesive composition. The obtained adhesive composition was adjusted to a solids content of 45% with toluene, applied to a polyester release sheet to a thickness of approximately 50 μm after drying, and dried at 100°C for 5 minutes to form an adhesive composition layer.

[0116] Two polyester release sheets, each with an adhesive composition layer formed in this manner, were prepared and laminated with the two adhesive composition layers facing each other. With the laminated adhesive composition layers sandwiched between the polyester release sheets, they were subjected to high-pressure mercury UV irradiation with a peak illuminance of 150 mW / cm². 2 Total exposure: 1000 mJ / cm² 2 (1000 mJ / cm 2By irradiating with ultraviolet light in a single pass, an adhesive layer was formed (primary curing), and a substrate-less double-sided adhesive sheet with an adhesive layer thickness of 100 μm was obtained. Next, the release sheet was peeled off one side of the adhesive layer of the obtained substrate-less double-sided adhesive sheet, and the exposed adhesive layer side was pressed onto an easily-adhered polyethylene terephthalate (PET) sheet (thickness 125 μm) to obtain a PET sheet with an adhesive layer thickness of 100 μm.

[0117] <Examples 3-5, Comparative Examples 1 and 2> As shown in Table 2, adhesive compositions for each example were prepared in the same manner as in Example 1, except that the acrylic resin (A-1) was changed. Next, substrate-less double-sided adhesive sheets and PET sheets with adhesive layers were sequentially manufactured in the same manner as in Example 1, with an adhesive layer thickness of 100 μm. The composition of the adhesive compositions for each example is shown in Table 2.

[0118] <Example 2> As shown in Table 2, the adhesive compositions for each example were prepared in the same manner as in Example 1, except that the intermolecular hydrogen abstraction type photopolymerization initiator (b2) was changed. Next, substrate-less double-sided adhesive sheets and PET sheets with adhesive layers were sequentially prepared in the same manner as in Example 1, with an adhesive layer thickness of 100 μm. The compositions of the adhesive compositions for each example are shown in Table 2.

[0119] [Table 2]

[0120] <Measurement methods, evaluation methods> The measurement and evaluation methods for the adhesive compositions of the examples and comparative examples are shown below. The results are shown in Tables 3 to 5.

[0121] (Gel fraction: Before complete curing (after primary curing)) Each example of the substrate-less double-sided adhesive sheet was cut to 40mm x 40mm and left to stand for 30 minutes under conditions of 23°C x 50%RH. Then, one release sheet was peeled off, and the exposed adhesive layer was bonded to a 50mm x 100mm SUS mesh sheet (200 mesh). The remaining release sheet was peeled off, and the adhesive layer was wrapped in the SUS mesh sheet by folding it back from the center along the longitudinal direction of the SUS mesh sheet. The gel fraction (%) was calculated from the weight change when this was immersed for 24 hours in a sealed container containing 250g of toluene maintained at 23°C.

[0122] (Probe tack: Before complete curing (after primary curing)) For each example of PET sheet with an adhesive layer, the sheet was cut to a size of 12 mm wide x 12 mm long, the release sheet was peeled off, and the probe tack (unit: N) was measured using a probe tack tester (Tester Sangyo Co., Ltd., Probe Tack Tester TE-6001) under the following conditions: pressurization time 1 second, bonding pressure 500 gf, indentation speed 120 mm / min, lifting speed 600 mm / min, probe diameter 5.1 mm (diameter). The evaluation criteria are as follows. ◎...Probe tack (unit: N) is less than 5. ○...The probe tack (unit: N) is 5 or greater and less than 7.5. △···The probe tack (unit: N) is 7.5 or greater and less than 10. ×...The probe tack (unit: N) is 10 or greater.

[0123] (Holding force (40℃): Before complete curing (after primary curing)) For each example, the PET sheet with adhesive layer was cut to a size of 25 mm x 50 mm, and the release sheet was peeled off. A stainless steel plate (SUS304) was placed on the side with the exposed adhesive layer, and a 2 kg roller was used to pressurize and attach it (attachment area 25 mm x 25 mm). The holding force was measured using a creep tester (BE-501, a holding force tester with a constant humidity chamber, manufactured by Tester Sangyo Co., Ltd.) under a 40°C atmosphere with a load of 1 kg applied for 24 hours. The evaluation criteria are as follows. ○...The holding time is 100 minutes or more. ×···The holding time is less than 100 minutes.

[0124] (Gel fraction: after complete curing) For the double-sided adhesive sheet with a substrate release layer in each example, using a high-pressure mercury UV irradiation device, peak illuminance: 150 mW / cm 2 , integrated exposure dose: 4000 mJ / cm 2 (1000 mJ / cm 2 ×4 passes), after performing ultraviolet irradiation, it was cut into 40 mm × 40 mm and left standing for 30 minutes under the conditions of 23°C × 50% RH. Then, one release sheet was peeled off, and the exposed adhesive layer side was bonded to a 50 mm × 100 mm SUS mesh sheet (200 mesh). The remaining release sheet was peeled off, and it was folded back from the center in the longitudinal direction of the SUS mesh sheet to wrap the adhesive layer with the SUS mesh sheet. The gel fraction (%) was calculated from the weight change when this was immersed in a sealed container containing 250 g of toluene maintained at 23°C for 24 hours.

[0125] (180-degree peel strength (adhesive force): after complete curing) For the PET sheet with an adhesive layer in each example, it was cut into a size of 25 mm in width × 100 mm in length, and using a high-pressure mercury UV irradiation device, peak illuminance: 150 mW / cm 2 , integrated exposure dose: 4000 mJ / cm 2 (1000 mJ / cm 2 ×4 passes), after performing ultraviolet irradiation, the release sheet was peeled off. The exposed adhesive layer side was pressed and adhered to non-alkali glass (Corning's "Eagle XG", thickness 1.1 mm) with a 2 kg rubber roller reciprocating twice in an atmosphere of 23°C and 50% RH, and left standing for 30 minutes in the same atmosphere. After that, at room temperature (23°C), the 180-degree peel strength (N / 25 mm) was measured at a peel rate of 300 mm / min.

[0126] (Retention force (80°C): after complete curing) For the PET sheet with an adhesive layer in each example, it was cut into a size of 25 mm × 50 mm, and using a high-pressure mercury UV irradiation device, peak illuminance: 150 mW / cm 2 , integrated exposure dose: 4000 mJ / cm 2 (1000 mJ / cm2 After UV irradiation (4 passes), the release sheet was peeled off. A stainless steel plate (SUS304) was placed on the exposed adhesive layer side, and a 2kg roller was used to pressurize and attach it (attachment area 25mm x 25mm). The holding force was measured using a creep tester (BE-501, constant humidity chamber holding force tester, manufactured by Tester Sangyo Co., Ltd.) with a load of 1kg applied for 24 hours in an 80°C atmosphere. The evaluation criteria are as follows. ◎...No misalignment (NC). ○...The misalignment is less than 0.5 mm. ×...The displacement is 0.5mm or more, or the PET sheet has fallen.

[0127] (Heat and humidity resistance test: after complete curing) Each example of the PET sheet with adhesive layer was cut to a size of 30mm x 50mm and irradiated using a high-pressure mercury UV irradiation device with a peak irradiance of 150mW / cm². 2 Total exposure: 4000 mJ / cm² 2 (1000 mJ / cm 2 After UV irradiation (4 passes), the release sheet was peeled off. The exposed adhesive layer was bonded to alkali-free glass (Corning Eagle XG, 1.1 mm thick). Subsequently, it was autoclaved at 50°C, 0.5 MPa for 20 minutes, and then left to stand for 30 minutes in an atmosphere of 23°C and 50% RH to produce a test specimen with a layer structure of "alkali-free glass / adhesive layer / PET". The obtained test specimens were subjected to a humid and heat resistance test for 7 days (168 hours) under an atmosphere of 85°C and 85% RH, and the haze values ​​were measured before and after the humid and heat resistance test. The haze value after the humidity and heat resistance test was measured after leaving the test in an atmosphere of 23°C and 50% RH for 2 hours.

[0128] The haze value was calculated by measuring the diffuse transmittance and total light transmittance using a HAZE MATER NDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.), and substituting the obtained values ​​of diffuse transmittance (DT) and total light transmittance (TT) into Equation 1 below. Furthermore, the percentage increase in the haze value was calculated from Equation 2 below. This machine conforms to JIS K7361-1. Haze value (%) = (DT / TT) × 100 ... [Equation 1] Haze value difference (%) = Haze value after humidity and heat resistance test - Haze value before humidity and heat resistance test ·[Formula 2]

[0129] The evaluation criteria for the humidity and heat resistance test are as follows: ○...The haze value difference is less than 2.0%. ×...The haze value difference is 2.0% or more.

[0130] (Probe tack: after complete curing) For each example, the PET sheet with adhesive layer was cut to a size of 12 mm wide x 12 mm long and treated with a high-pressure mercury UV irradiation device at a peak irradiance of 150 mW / cm². 2 Total exposure: 4000 mJ / cm² 2 (1000 mJ / cm 2 After UV irradiation (4 passes), the release sheet was peeled off, and the probe tack (unit: N) was measured using a probe tack tester (TE-6001, manufactured by Tester Sangyo Co., Ltd.) under the following conditions: pressurization time 5 seconds, bonding pressure 1000 gf, indentation speed 120 mm / min, lifting speed 600 mm / min, and probe diameter 5.1 mm (diameter).

[0131] (Curved surface durability: after complete curing) For each example, the PET sheet with the adhesive layer was cut to a size of 40 mm x 120 mm, and the release sheet was peeled off. The exposed adhesive layer side was pressure-bonded to one of the TAC film surface polarizers of a polarizer plate in which TAC film was laminated on both sides of the polarizer, to obtain a laminate with a layer structure of "PET sheet / adhesive layer / polarizer plate". Subsequently, the laminate was attached to an aluminum plate (70 mm wide, 150 mm long, 0.3 mm thick) with tape, ensuring the PET surface was facing outwards, to create an aluminum plate-fixed sample. The prepared sample was bent to a diameter of 5 mm using a mandrel testing machine, fixed in that position, and then autoclaved (0.5 MPa × 50°C × 20 minutes). Finally, it was subjected to high-pressure mercury UV irradiation with a peak irradiance of 150 mW / cm².2 Total exposure: 4000 mJ / cm² 2 (1000 mJ / cm 2 A sample was prepared for curved surface durability evaluation by irradiating a sample that had been bent using a 4-pass UV irradiation. The curved surface durability evaluation sample has a layered structure from the outside in, consisting of PET / adhesive layer / polarizing plate / aluminum plate. The aluminum plate is on the innermost layer. The obtained samples for evaluating curved surface durability were exposed to conditions of 80°C, Dry, for 7 days, and 60°C, 90%RH, for 7 days, respectively. The bent portion and the edge of the polarizing plate excluding the bent portion were then observed and evaluated according to the following criteria.

[0132] (Evaluation criteria: Bending section) A... No lifting, foaming, or excess glue is observed. B... Lifting, foaming, or excess glue is visible.

[0133] (Evaluation criteria: polarizer edge) A...Floats at the edges, and no air bubbles are visible. B...A small gap of less than 0.5 mm or a very small amount of air bubbles can be seen at the edges. C...A lift of 0.5 mm or more is observed at the edges, or air bubbles are present throughout, or both.

[0134] (Evaluation criteria: Overall evaluation) ◎...The evaluation of the bent section is A, and the evaluation of the polarizing plate edge is also A. ○...The evaluation of the bent section is A, and the evaluation of the polarizing plate edge is B. ×...The evaluation of the bent portion is A and the evaluation of the polarizer edge is C, or the evaluation of the bent portion is B and the evaluation of the polarizer edge is A to C.

[0135] (Polarizing plate durability: after complete curing) For each example, the substrate-less double-sided adhesive sheet was cut to a size of 60 mm x 100 mm, and one release sheet was peeled off. The exposed adhesive layer was pressure-bonded to one of the TAC film surface polarizers of a polarizer plate in which TAC film was laminated on both sides of the polarizer. Next, the other release sheet was peeled off, and the exposed adhesive layer was bonded to alkali-free glass (Corning Eagle XG, 1.1 mm thick), and autoclaved (50°C, 0.5 MPa, 20 minutes). After that, a high-pressure mercury UV irradiation device was used to irradiate the alkali-free glass side with a peak irradiance of 150 mW / cm². 2 Total exposure: 4000 mJ / cm² 2 (1000 mJ / cm 2 Samples for evaluating the durability of polarizing plates were prepared by irradiating them with ultraviolet light (4 passes). Samples for evaluating the durability of polarizing plates were left standing for one day in an atmosphere of 23°C and 50%RH. Then, durability tests were conducted for 7 days (168 hours) each in an atmosphere of 80°C and 60°C and 90%RH, and evaluated according to the following criteria. ○...No lifting is observed in the polarizing plate. △···The lift at the edge of the polarizing plate is less than 0.5 mm. ×...The edge of the polarizing plate is lifted by 0.5 mm or more.

[0136] [Table 3]

[0137] [Table 4]

[0138] [Table 5]

[0139] The adhesive sheets produced using the adhesive compositions of the examples exhibited excellent adhesive properties, such as high holding power and low tackiness, even in the low-crosslinking state before complete curing (after primary curing). Furthermore, they also showed excellent adhesive properties and durability after complete curing. On the other hand, in Comparative Example 1, where the acrylic resin (A) did not contain structural units derived from alkyl (meth)acrylate (a2) containing two or more tertiary carbon atoms, the adhesive properties in the low-crosslinking state after primary curing and after complete curing were inferior. Furthermore, in Comparative Example 2, which did not contain structural units derived from hydroxyl group-containing monomers (a1) with a glass transition temperature of 0°C or higher when homopolymer was formed in the acrylic resin (A), the durability after complete curing was inferior. [Industrial applicability]

[0140] The adhesive composition of the present invention provides excellent tackiness in a low-crosslinked state after primary curing. The adhesive composition of the present invention is particularly useful as an adhesive for bonding optical components constituting touch panels and image display devices, and for encapsulating organic EL displays.

Claims

1. An adhesive composition comprising an acrylic resin (A) containing 5 to 30% by weight of structural units derived from a hydroxyl group-containing monomer (a1) having a glass transition temperature of 0°C or higher when forming a homopolymer, 5 to 30% by weight of structural units derived from an alkyl (meth)acrylate (a2) having a branched alkyl group containing two or more tertiary carbons, 5 to 30% by mass of structural units derived from a high Tg alkyl (meth)acrylate (a3) ​​having a glass transition temperature of 0°C or higher when forming a homopolymer, and 10 to 80% by weight of structural units derived from an ethylenically unsaturated monomer (a4), wherein the glass transition temperature of the acrylic resin (A) based on its dynamic viscoelasticity is -10°C or higher.

2. The adhesive composition according to claim 1, further comprising a photopolymerization initiator (B).

3. The adhesive composition according to claim 2, wherein the photopolymerization initiator (B) contains a hydrogen abstraction type photopolymerization initiator.

4. The adhesive composition according to claim 3, wherein the photopolymerization initiator (B) contains an intramolecular hydrogen abstraction type photopolymerization initiator (b1) and an intermolecular hydrogen abstraction type polymerization initiator (b2).

5. The adhesive composition according to claim 1, further containing a crosslinking agent (C).

6. An adhesive comprising a crosslinked adhesive composition according to any one of claims 1 to 5.

7. The adhesive according to claim 6, wherein crosslinking is performed by irradiation with active energy rays.

8. An adhesive sheet having an adhesive layer made of the adhesive described in claim 6.

9. An adhesive sheet having an adhesive layer made of the adhesive described in claim 7.

10. The adhesive sheet according to claim 8, wherein the adhesive layer has multi-stage curing properties, curing in multiple stages.

11. The adhesive sheet according to claim 9, wherein the adhesive layer has multi-stage curing properties, curing in multiple stages.

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