Adhesive sheet, adhesive sheet for surface protective film of flexible image display device, and laminate for surface protective film of flexible image display device

Abstract

To provide an adhesive sheet having good flexibility and excellent oil resistance.SOLUTION: The adhesive sheet is formed from a photocurable adhesive composition [I] containing a (meth)acrylic copolymer (A) and a photopolymerization initiator (B). The ratio (O / C) of the number of oxygen atoms to the number of carbon atoms in the adhesive sheet measured by X-ray photoelectron spectroscopy is 0.25-0.5%. The (meth)acrylic copolymer (A) is a (meth)acrylic copolymer containing a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an adhesive sheet, an adhesive sheet for a surface protective film of a flexible image display device, and a laminate for a surface protective film of a flexible image display device, and more specifically to an adhesive sheet, an adhesive sheet for a surface protective film of a flexible image display device, and a laminate for a surface protective film of a flexible image display device, which have sufficient adhesiveness and flexibility, as well as excellent oil resistance. [Background technology]

[0002] In recent years, flexible image display devices using organic light-emitting diodes (OLEDs) and quantum dots (QDs) have been developed and are becoming widely commercialized. Flexible image display devices include bendable devices with a curved image display surface, foldable devices that can be repeatedly bent, rollable devices that can be rolled up, and stretchable devices that can be stretched and contracted. Such flexible image display devices require not only optical properties but also flexibility, particularly high durability against bending.

[0003] For example, Patent Document 1 discloses a laminated film with an adhesive layer that is free from the risk of causing distortion of the image displayed at the folded portion after repeated folding. Furthermore, Patent Document 2 discloses a laminate comprising a double-sided pressure-sensitive adhesive sheet having a glass transition temperature and storage modulus within a predetermined range, and a flexible member for an image display device, which does not break or peel even in a bending test approximating an actual use environment.

[0004] Incidentally, the cover window member for the display screen used in the flexible image display device as described above is expensive, and in some cases a surface protection film is further laminated on the surface of the cover window to prevent scratches or the like. The surface protection film for the display screen is required to have not only surface protection properties but also high durability against bending.

[0005] Furthermore, in recent years, when using laptops, tablets, or smartphones, there are many opportunities for people's fingers and the like to come into contact with the housing or image display screen, and in addition to sweat, oily components such as sebum and cosmetics are present on the surface of the skin. Therefore, over long periods of use, oily components and the like gradually penetrate, for example, from the edge of the joint between the protective panel and the housing, and penetrate into the adhesive layer of the adhesive sheet, causing problems such as the adhesive of the adhesive sheet spilling over the edge of the adherend or a decrease in adhesive strength causing peeling, and therefore there is a growing demand for improved oil resistance.

[0006] For example, Patent Document 3 describes an adhesive containing a hydroxyl group-containing (meth)acrylic resin and an isocyanate curing agent, in which the use of an acrylic resin with a specific structure and an isocyanate curing agent with a specific structure in combination has been used to improve bending suitability, sebum resistance, etc. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-196255 [Patent Document 2] International Publication No. 2018 / 173896 [Patent Document 3] Japanese Patent Publication No. 2020-45443 Summary of the Invention [Problem to be solved by the invention]

[0008] However, although the techniques disclosed in Patent Documents 1 and 2 take durability when folded into consideration, they do not take oil resistance into consideration. Furthermore, although Patent Document 3 examines oil resistance, the adhesive contains methyl acrylate (Tg: 8°C) and methyl methacrylate (Tg: 105°C), which increase cohesive strength, as well as an isocyanate crosslinking agent, and therefore has a high glass transition temperature. This means that the adhesive is still insufficient in terms of flexibility, particularly flexibility at low temperatures, which is required in recent years, and further improvements are required to achieve both flexibility and oil resistance.

[0009] Therefore, against this background, the present invention aims to provide an adhesive sheet, an adhesive sheet for a surface protective film of a flexible image display device, and a laminate for a surface protective film of a flexible image display device, which have good flexibility and excellent oil resistance. [Means for solving the problem]

[0010] However, in view of these circumstances, the present inventors have conducted extensive research into an excellent adhesive sheet that combines flexibility and oil resistance, in particular an adhesive sheet for a surface protection film used in a flexible image display device. As a result, they have found that in a photocurable adhesive composition [I] containing a (meth)acrylic copolymer (A) and a photopolymerization initiator (B), a (meth)acrylic copolymer containing a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a1) is used, and that an adhesive sheet formed from the photocurable adhesive composition [I] has a ratio of the number of oxygen atoms to the number of carbon atoms (O / C) within a predetermined range, thereby achieving good flexibility and excellent oil resistance, and have completed the present invention.

[0011] That is, the present invention has the following aspects. [1] A pressure-sensitive adhesive sheet formed from a photocurable pressure-sensitive adhesive composition [I] containing a (meth)acrylic copolymer (A) and a photopolymerization initiator (B), The ratio of the number of oxygen atoms to the number of carbon atoms (O / C) of the pressure-sensitive adhesive sheet measured by X-ray photoelectron spectroscopy is 0.25 to 0.5; The pressure-sensitive adhesive sheet, wherein the (meth)acrylic copolymer (A) is a (meth)acrylic copolymer containing a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a1). [2] The pressure-sensitive adhesive sheet according to [1], wherein the (meth)acrylic copolymer (A) is a (meth)acrylic copolymer containing a structural moiety derived from the hydroxyl group-containing (meth)acrylate (a1) and a structural moiety derived from an alkyl (meth)acrylate (a2) containing an alkyl group having 1 to 10 carbon atoms. [3] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the hydroxyl group-containing (meth)acrylate (a1) is a (meth)acrylate containing a hydroxyalkyl group having 3 to 10 carbon atoms. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3], wherein the (meth)acrylic copolymer (A) has a weight average molecular weight of 600,000 to 1,500,000. [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4], wherein the photocurable pressure-sensitive adhesive composition [I] further contains a crosslinking agent (C). [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5], wherein the pressure-sensitive adhesive sheet has a storage shear modulus (G') at -20°C of 500 kPa or less. [7] The pressure-sensitive adhesive sheet according to any one of [1] to [6], wherein the pressure-sensitive adhesive sheet has a gel fraction of 30 to 95% by weight. [8] The pressure-sensitive adhesive sheet according to any one of [1] to [7], wherein the pressure-sensitive adhesive sheet has a swelling degree with oleic acid of 25% by weight or less. [9] The pressure-sensitive adhesive sheet according to any one of [1] to [8], which is used as a surface protection film for a flexible image display device.

[10]

[0023] A pressure-sensitive adhesive sheet for a surface protective film of a flexible image display device, comprising the pressure-sensitive adhesive sheet according to any one of [1] to [9].

[11] A laminate for a surface protective film of a flexible image display device, comprising the pressure-sensitive adhesive sheet according to any one of [1] to [9] and a surface protective film laminated thereon, A laminate for a surface protection film for a flexible image display device, wherein the surface protection film has a surface hardness of 400 MPa or more at a contact depth of 200 to 400 nm as measured by a nanoindenter, and the appearance does not change when a bending test is carried out 200,000 times at -20°C under the condition of a radius of curvature (R) of 1.5 mm.

[12] The laminate for a surface protective film of a flexible image display device according to

[11] , wherein the surface protective film comprises any member selected from a polyethylene terephthalate film, a polyimide film, an aramid film, and a glass plate. [Effects of the Invention]

[0012] The adhesive sheet according to one embodiment of the present invention has surface protection function and flexibility while being used, for example, by being attached to a flexible image display device, and also serves as an adhesive sheet for surface protection films that has excellent oil resistance. DETAILED DESCRIPTION OF THE INVENTION

[0013] An example of an embodiment of the present invention will be described in detail below, but the present invention is not limited to the embodiment described below. In the present invention, the term "film" conceptually encompasses sheets, films, and tapes. Furthermore, when the term "panel" is used, such as an image display panel or a protective panel, it encompasses a plate, a sheet, and a film.

[0014] In the present invention, when it is stated that "X to Y" (X and Y are any numbers), unless otherwise specified, it means "X or more and Y or less", and also means "preferably larger than X" or "preferably smaller than Y". Furthermore, when it is stated that the amount is "X or more" (X is any number), it also means that the amount is "preferably greater than X" unless otherwise specified, and when it is stated that the amount is "Y or less" (Y is any number), it also means that the amount is "preferably smaller than Y" unless otherwise specified. Furthermore, "X and / or Y (X and Y are any configuration)" means at least one of X and Y, and can mean three possibilities: X only, Y only, or X and Y.

[0015] In the present invention, the term "main component" refers to a component that has a significant effect on the properties of the target object, and the content of the component is usually 30% by weight or more, preferably 35% by weight or more, and more preferably 50% by weight or more of the target object. In addition, in the present invention, "(meth)acrylic" is a comprehensive term that includes acrylic and methacrylic, "(meth)acrylate" is a comprehensive term that includes acrylate and methacrylate, and "(meth)acryloyl" is a comprehensive term that includes acryloyl and methacryloyl. In the present invention, "X and / or Y (X and Y are any configurations)" means at least one of X and Y, and means three possibilities: X only, Y only, and X and Y.

[0016] The pressure-sensitive adhesive sheet according to one embodiment of the present invention is formed from a photocurable pressure-sensitive adhesive composition [I] containing a (meth)acrylic copolymer (A) and a photopolymerization initiator (B).

[0017] <Photocurable adhesive composition [I]> The photocurable pressure-sensitive adhesive composition [I] used in the present invention will now be described. The photocurable pressure-sensitive adhesive composition (hereinafter sometimes abbreviated as "pressure-sensitive adhesive composition") [I] contains a (meth)acrylic copolymer (A) and a photopolymerization initiator (B).

[0018] The pressure-sensitive adhesive composition [I] is preferably cured by active energy rays, since this makes it easier to adjust the crosslink density and the degree of cure, and also causes less damage to the substrate and the like. The pressure-sensitive adhesive composition [I] may be one that can be cured in multiple stages, as described below.

[0019] [(Meth)acrylic copolymer (A)] The (meth)acrylic copolymer (A) is a (meth)acrylic copolymer containing a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a1), and it is particularly preferred that the (meth)acrylic copolymer (A) contains a hydroxyl group-containing (meth)acrylate (a1) as a copolymerization component. Furthermore, the (meth)acrylic copolymer (A) preferably contains a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a1) and a structural moiety derived from an alkyl (meth)acrylate (a2) containing an alkyl group having 1 to 10 carbon atoms, and particularly preferably contains a hydroxyl group-containing (meth)acrylate (a1) and an alkyl (meth)acrylate (a2) containing an alkyl group having 1 to 10 carbon atoms as copolymerization components.

[0020] In addition to the hydroxyl group-containing (meth)acrylate (a1) and the alkyl (meth)acrylate (a2) containing an alkyl group having 1 to 10 carbon atoms, an ethylenically unsaturated monomer (a3) ​​copolymerizable therewith may be contained as a copolymerization component.

[0021] Examples of the hydroxyl group-containing (meth)acrylate (a1) 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 hydroxy(meth)acrylates such as caprolactone-modified 2-hydroxyethyl(meth)acrylate; diethylene glycol(meth)acrylate; polyethylene glycol (meth)acrylate; Examples of such hydroxyl group-containing (meth)acrylates include oxyalkylene-modified (meth)acrylates such as ethylene glycol (meth)acrylate, primary hydroxyl group-containing (meth)acrylates such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate, secondary hydroxyl group-containing (meth)acrylates such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate, and tertiary hydroxyl group-containing (meth)acrylates such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate, etc. These may be used alone or in combination of two or more.

[0022] Among the hydroxyl group-containing (meth)acrylates (a1), in terms of reducing the storage shear modulus (G') at low temperatures, primary hydroxyl group-containing (meth)acrylates such as 2-hydroxy(meth)acrylate, 4-hydroxy(meth)acrylate, and 2-hydroxypropyl(meth)acrylate are preferred, and particularly preferred are hydroxy(meth)acrylates having 3 to 10 carbon atoms such as 4-hydroxybutyl(meth)acrylate and 2-hydroxypropyl(meth)acrylate, with 4-hydroxybutyl(meth)acrylate being particularly preferred.

[0023] From the viewpoint of adhesive strength, the lower limit of the content of the hydroxyl group-containing (meth)acrylate (a1) is usually 3% by weight or more, preferably 5% by weight or more, more preferably 8% by weight or more, even more preferably 10% by weight or more, and particularly preferably 12% by weight or more, based on the total copolymerization components of the (meth)acrylic copolymer (A). On the other hand, the upper limit of the content of the hydroxyl group-containing (meth)acrylate (a1) is usually 60% by weight or less, preferably 45% by weight or less, more preferably 35% by weight or less, even more preferably 30% by weight or less, and particularly preferably 25% by weight or less, from the viewpoint of suppressing an increase in the storage shear modulus (G') at low temperatures.

[0024] Examples of the alkyl (meth)acrylate (a2) containing an alkyl group having 1 to 10 carbon atoms (excluding the component (a1)) include linear alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, and n-decyl (meth)acrylate; isopropyl (meth)acrylate; Examples of the acrylate include branched alkyl (meth)acrylates such as butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate; and alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate and t-butylcyclohexyl (meth)acrylate. These may be used alone or in combination of two or more.

[0025] Among these, linear alkyl (meth)acrylates are preferred from the viewpoint of adhesion and recovery, and linear alkyl (meth)acrylates having 4 to 8 carbon atoms, and more preferably 4 to 6 carbon atoms, such as n-butyl (meth)acrylate, n-pentyl (meth)acrylate, and n-hexyl (meth)acrylate, are particularly preferred from the viewpoint of oil resistance, and n-butyl (meth)acrylate is particularly preferred.

[0026] Furthermore, from the viewpoint of improving the cohesive strength of the adhesive, it is preferable to use alkyl(meth)acrylates having 1 to 3 carbon atoms, such as methyl(meth)acrylate and ethyl(meth)acrylate.

[0027] Acrylate is particularly preferred from the viewpoint of suppressing an increase in storage shear modulus (G') at low temperatures.

[0028] In the present invention, examples of the ethylenically unsaturated monomer (a3) ​​copolymerizable with the hydroxyl group-containing (meth)acrylate (a1) and / or the alkyl (meth)acrylate (a2) containing an alkyl group having 1 to 10 carbon atoms (excluding the components (a1) and (a2)) include, for example, an ethylenically unsaturated group monomer having a functional group other than a hydroxyl group, a (meth)acrylate containing an alkyl group having 11 to 20 carbon atoms, other copolymerizable monomers, etc. These may be used alone or in combination of two or more kinds.

[0029] Examples of the ethylenically unsaturated group monomer having a functional group other than a hydroxyl group (hereinafter, sometimes referred to as a "functional group-containing ethylenically unsaturated monomer") include a functional group-containing monomer having a nitrogen atom, a carboxy group-containing monomer, an acetoacetyl group-containing monomer, and a glycidyl group-containing monomer. Among these, functional group-containing monomers having a nitrogen atom are preferred in terms of imparting cohesive strength and crosslinking-promoting action, more preferably amino group-containing monomers, amide group-containing monomers, and isocyanate group-containing monomers, and even more preferably amino group-containing monomers.

[0030] Examples of the amino group-containing monomer as the functional group-containing monomer having a nitrogen atom include primary amino group-containing (meth)acrylates such as aminomethyl (meth)acrylate and aminoethyl (meth)acrylate; secondary amino group-containing (meth)acrylates such as t-butylaminoethyl (meth)acrylate and t-butylaminopropyl (meth)acrylate; and tertiary amino group-containing (meth)acrylates such as ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, and dimethylaminopropylacrylamide.

[0031] Examples of the amide group-containing monomer include (meth)acrylamide; 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; and alkoxyalkyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide and N-(n-butoxymethyl)(meth)acrylamide.

[0032] Examples of the isocyanate group-containing monomer include 2-(meth)acryloyloxyethyl isocyanate and alkylene oxide adducts thereof, etc. The isocyanate group may be protected with a blocking agent such as methyl ethyl ketone oxime, 3,5-dimethylpyrazole, 1,2,4-triazole, or diethyl malonate.

[0033] Examples of the carboxy group-containing monomer include (meth)acrylic acid, carboxyethyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxypropyl phthalic acid, 2-(meth)acryloyloxyethyl maleic acid, 2-(meth)acryloyloxypropyl maleic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxypropyl succinic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, monomethyl maleate, and monomethyl itaconate.

[0034] Examples of the acetoacetyl group-containing monomer include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.

[0035] Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0036] These functional group-containing ethylenically unsaturated monomers may be used alone or in combination of two or more. The upper limit of the content of the functional group-containing ethylenically unsaturated monomer is preferably 30% by weight or less, more preferably 20% by weight or less, even more preferably 10% by weight or less, and particularly preferably 5% by weight or less, based on the total copolymerization components of the (meth)acrylic copolymer (A), from the viewpoint of reducing the possibility of a decrease in tackiness and oil resistance due to bleed-out. The lower limit is usually 0% by weight.

[0037] Examples of the (meth)acrylate containing an alkyl group having 11 to 20 carbon atoms include linear alkyl (meth)acrylates such as undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, cetyl (meth)acrylate, and stearyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Examples of the alicyclic (meth)acrylate include branched alkyl (meth)acrylates such as butyl (meth)acrylate, isooctyl (meth)acrylate, and isostearyl (meth)acrylate, and alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, 3,5,5-trimethylcyclohexane (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and isobornyl (meth)acrylate. These may be used alone or in combination of two or more.

[0038] Furthermore, in order to maintain oil resistance, the upper limit of the content of the (meth)acrylate containing an alkyl group having 11 to 20 carbon atoms is preferably 40% by weight or less, more preferably 30% by weight or less, and even more preferably 20% by weight or less, based on the total copolymerization components of the (meth)acrylic copolymer (A). The lower limit is usually 0% by weight.

[0039] Examples of the other copolymerizable monomers include aromatic (meth)acrylates such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyl diethylene glycol (meth)acrylate, phenoxy polyethylene glycol (meth)acrylate, phenoxy polyethylene glycol-polypropylene glycol-(meth)acrylate, and nonylphenol ethylene oxide adduct (meth)acrylate; 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, 4-acryloyloxyethoxy-4'-bromobenzophenone, 4-methacryloyloxybenzophenone, and 4-methacryloyloxyethoxybenzophenone. Examples of suitable vinyl monomers include (meth)acrylates having a benzophenone structure, such as benzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone, and mixtures thereof, acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl stearate, vinyl propionate, vinyl acetate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, vinylpyridine, vinylpyrrolidone, dialkyl itaconate esters, dialkyl fumarate esters, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone. These may be used alone or in combination of two or more.

[0040] The (meth)acrylic copolymer (A) may have a photoactive moiety, such as a polymerizable carbon-carbon double bond group, introduced into its side chain, which can enhance the crosslinking efficiency of the pressure-sensitive adhesive composition [I] and can crosslink the pressure-sensitive adhesive composition [I] upon irradiation with active energy rays for a shorter period of time, thereby increasing productivity.

[0041] Examples of a method for introducing a polymerizable carbon double bond group into the side chain of the (meth)acrylic copolymer (A) include a method in which a copolymer containing the above-mentioned hydroxyl group-containing (meth)acrylate (a1) or a functional group-containing ethylenically unsaturated monomer is prepared, and then a compound having a polymerizable carbon double bond group and a functional group reactive with the functional group is subjected to a condensation or addition reaction while maintaining the activity of the polymerizable carbon double bond group.

[0042] Examples of combinations of these functional groups include an epoxy group (glycidyl group) and a carboxy group, an amino group and a carboxy group, an amino group and an isocyanate group, an epoxy group (glycidyl group) and an amino group, a hydroxyl group and an epoxy group, and a hydroxyl group and an isocyanate group. Among these combinations of functional groups, a combination of a hydroxyl group and an isocyanate group is preferred because of the ease of reaction control. Of these, a combination in which the copolymer has a hydroxyl group and the compound has an isocyanate group is preferred. Examples of the isocyanate compound having a polymerizable carbon-carbon double bond group include the above-mentioned 2-(meth)acryloyloxyethyl isocyanate and alkylene oxide adducts thereof.

[0043] The content of the compound having a functional group reactive with the functional group and a polymerizable carbon-carbon double bond group is preferably 10 parts by weight or less, more preferably 8 parts by weight or less, even more preferably 5 parts by weight or less, and particularly preferably 3 parts by weight or less, per 100 parts by weight of the (meth)acrylic copolymer (A) from the viewpoint of improving adhesiveness and stress relaxation. From the viewpoint of reaction efficiency, it is preferably 1 part by weight or more.

[0044] The glass transition temperature (Tg) of the (meth)acrylic copolymer (A) is preferably −20° C. or lower, more preferably −23° C. or lower, even more preferably −25° C. or lower, and particularly preferably −30° C. or lower, in order to suppress an increase in the storage shear modulus (G′) at low temperatures. The lower limit of the glass transition temperature (Tg) is usually −50° C.

[0045] In the present invention, the glass transition temperature (Tg) of the (meth)acrylic copolymer (A) can be determined by reading the temperature at which the loss tangent (loss modulus G" / storage modulus G'=tanδ) becomes maximum when the dynamic viscoelasticity is measured in a shear mode at a frequency of 1 Hz using a dynamic viscoelasticity measuring device. For example, the (meth)acrylic copolymer (A) is molded into a cylindrical body with a diameter of 8 mm (height of 1.0 mm), and the loss tangent (tanδ) of this can be measured using a viscoelasticity measuring device (manufactured by TA Instruments, product name "DHR 2") under the following measurement conditions.

[0046] (Measurement conditions) Measurement jig: Φ8mm parallel plate Distortion: 0.1% Frequency: 1Hz ·Measurement temperature: -60~100℃ Heating rate: 5℃ / min

[0047] The weight average molecular weight (Mw) of the (meth)acrylic copolymer (A) is preferably 600,000 or more, more preferably 700,000 or more, and even more preferably 800,000 or more, from the viewpoint of obtaining a pressure-sensitive adhesive composition [I] with high cohesive strength. In addition, the upper limit of the weight average molecular weight (Mw) of the (meth)acrylic copolymer (A) is preferably 1.5 million or less, more preferably 1.2 million or less, and even more preferably 1.1 million or less, from the viewpoints of handleability and uniform stirring.

[0048] In the present invention, the weight average molecular weight (Mw) can be determined, for example, as follows. (Method for measuring weight-average molecular weight) 4 mg of the (meth)acrylic copolymer (A) is dissolved in 12 mL of tetrahydrofuran (THF) to prepare a measurement sample. The molecular weight distribution curve is measured under the following conditions using a gel permeation chromatography (GPC) analyzer (HLC-8320GPC, manufactured by Tosoh Corporation), whereby the weight average molecular weight (Mw) can be determined. Guard column: TSKguardcolumnHXL Separation column: TSKgel GMHXL (4 columns) ·Temperature: 40℃ ·Injection volume: 100μL Polystyrene equivalent Solvent: THF ·Flow rate: 1.0mL / min

[0049] [Photopolymerization initiator (B)] The photopolymerization initiator (B) may be any compound that generates radicals when exposed to active energy rays. Photopolymerization initiators (B) are broadly classified into two types based on the radical generation mechanism: cleavage-type photopolymerization initiators that can generate radicals by cleaving and decomposing the single bond of the initiator itself, and hydrogen abstraction-type photopolymerization initiators that form an exciplex between the excited initiator and a hydrogen donor in the system and can transfer hydrogen from the hydrogen donor.

[0050] The photopolymerization initiator (B) may be either a cleavage-type photopolymerization initiator or a hydrogen-abstraction-type photopolymerization initiator, and may be used either alone or in combination with one or more of these.

[0051] In the present invention, it is preferable to use a hydrogen abstraction photopolymerization initiator, since the (meth)acrylic copolymer (A) itself does not require a functional group such as a carbon-carbon double bond and crosslinking can be efficiently achieved.

[0052] Examples of the cleavage-type photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-(4-(2-hydroxyethoxy)phenyl)-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-[4-{4-(2-hydroxy-2-methyl-propionyl)benzyl}phenyl]-2-methyl-propan-1-one, oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone), methyl phenylglyoxylate, 2-benzyl-2-dimethylamino- Examples of such compounds include 1-(4-morpholinophenyl)butan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide, and derivatives thereof.

[0053] Examples of the hydrogen abstraction photopolymerization initiator include benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, 4-(meth)acryloyloxybenzophenone, methyl 2-benzoylbenzoate, methyl benzoylformate, bis(2-phenyl-2-oxoacetate)oxybisethylene, 4-(1,3-acryloyl-1,4,7,10,13-pentaoxotridecyl)benzophenone, thioxanthone, 2-chlorothioxanthone, 3-methylthioxanthone, 2,4-dimethylthioxanthone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-t-butylanthraquinone, 2-aminoanthraquinone, and derivatives thereof. Among these, 4-methylbenzophenone and 2,4,6-trimethylbenzophenone are preferred.

[0054] The content of the photopolymerization initiator (B) is usually 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, and more preferably 1 to 3 parts by weight, per 100 parts by weight of the (meth)acrylic copolymer (A). When the content is equal to or greater than the lower limit, poor curing tends to be prevented, while when the content is equal to or less than the upper limit, a decrease in solution stability such as precipitation from the pressure-sensitive adhesive composition [I] tends to be suppressed, and problems such as embrittlement and coloration tend to be suppressed.

[0055] [Crosslinker (C)] The pressure-sensitive adhesive composition [I] preferably contains a crosslinking agent (C) in addition to the (meth)acrylic copolymer (A) and the photopolymerization initiator (B).

[0056] By including the crosslinking agent (C) in the pressure-sensitive adhesive composition [I], the pressure-sensitive adhesive composition [I] forms a crosslinked structure, which can impart cohesive strength and appropriate toughness to the pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet). The appropriate toughness of the pressure-sensitive adhesive layer can prevent the surface of the image display device component from undulating and the pressure-sensitive adhesive layer from deforming and cracking when cut.

[0057] The crosslinking agent (C) is a compound and / or composition that forms a crosslinked structure in the pressure-sensitive adhesive composition [I], and examples thereof include (meth)acrylic monomers and (meth)acrylic oligomers having two or more functional groups, which can be used alone or in combination of two or more.

[0058] Examples of the (meth)acrylic monomer having two or more functional groups include 1,4-butanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin glycidyl ether di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tricyclodecane dimethacrylate, tricyclodecane dimethanol di(meth)acrylate, bisphenol A polyethoxy di(meth)acrylate, bisphenol A polyethoxy di(meth)acrylate, bisphenol B polyethoxy di(meth)acrylate, bisphenol C ... Nol A polypropoxy di(meth)acrylate, bisphenol F polyethoxy di(meth)acrylate, ethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane trioxyethyl (meth)acrylate, ε-caprolactone-modified tris(2-hydroxyethyl) isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propoxylated pentaerythritol tri(meth)acrylate, ethoxylated pentaerythritol tri(meth)acrylate ) acrylate, pentaerythritol tetra(meth)acrylate, propoxylated pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, tris(acryloxyethyl) isocyanurate, dipentaerythritol hexa(meth)acrylate, dipenta Examples of the acrylate include erythritol penta(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol penta(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, di(meth)acrylate of an ε-caprolactone adduct of neopentyl glycol hydroxypivalate, trimethylolpropane tri(meth)acrylate, trimethylolpropane polyethoxytri(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate. Among these, (meth)acrylic monomers are preferred from the viewpoint of imparting appropriate toughness to the cured product, and among these, polyfunctional (meth)acrylic monomers having an alkylene glycol skeleton such as polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate, and particularly bifunctional (meth)acrylic monomers are more preferred.

[0059] The weight-average molecular weight of the (meth)acrylic monomer having two or more functional groups is preferably 100 or more, more preferably 200 or more, and even more preferably 250 or more, from the viewpoint of imparting appropriate flexibility to the cured product. The upper limit is usually 1,000.

[0060] Furthermore, when the pressure-sensitive adhesive composition [I] is cured with visible light, a cured product with high toughness can be obtained. In other words, from the viewpoint of obtaining a cured product with appropriate flexibility, the crosslinking agent (C) is preferably a (meth)acrylic oligomer having two or more functional groups, and preferably has a weight-average molecular weight of 3,000 or more, more preferably 5,000 or more, even more preferably 8,000 or more, and particularly preferably 10,000 or more. The upper limit of the weight-average molecular weight is usually 100,000. The weight average molecular weight is measured, if necessary, by applying the method for measuring the weight average molecular weight of the (meth)acrylic copolymer (A).

[0061] Examples of the (meth)acrylic oligomer having two or more functional groups include polyfunctional (meth)acrylic oligomers such as polyester (meth)acrylate, epoxy (meth)acrylate, urethane (meth)acrylate, and polyether (meth)acrylate. Among these, urethane (meth)acrylate oligomers are preferred from the viewpoint of imparting appropriate toughness to the cured product.

[0062] The content of the crosslinking agent (C) is preferably 1 part by weight or more, more preferably 2 parts by weight or more, even more preferably 4 parts by weight or more, and particularly preferably 10 parts by weight or more, per 100 parts by weight of the (meth)acrylic copolymer (A), from the viewpoint of imparting shape stability to the pressure-sensitive adhesive sheet and durability when formed into a laminate. The upper limit of the content of the crosslinking agent (C) is preferably 100 parts by weight or less, more preferably 60 parts by weight or less, even more preferably 40 parts by weight or less, and particularly preferably 30 parts by weight or less, per 100 parts by weight of the (meth)acrylic copolymer (A), from the viewpoint of ensuring adhesiveness.

[0063] In addition to the crosslinking agent (C), a thermal crosslinking agent (C') can also be used in combination in order to further increase the crosslink density and improve long-term reliability. Examples of such a thermal crosslinking agent (C') include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, aldehyde-based crosslinking agents, amine-based crosslinking agents, metal chelate-based crosslinking agents, etc. Among these, it is preferable to use an isocyanate-based crosslinking agent because of its excellent reactivity with the (meth)acrylic copolymer (A).

[0064] <Other ingredients> The pressure-sensitive adhesive composition [I] may contain, as "other components", as needed, various additives such as plasticizers, silane coupling agents, ultraviolet absorbers, rust inhibitors, tackifying resins, antioxidants, light stabilizers, metal deactivators, antioxidants, moisture absorbers, rust inhibitors, and inorganic particles, to the extent that the effects of the present invention are not impaired. If necessary, a reaction catalyst such as a tertiary amine compound, a quaternary ammonium compound, or a tin laurate compound may be appropriately contained. These may be used alone or in combination of two or more.

[0065] (plasticizer) A plasticizer is a material that improves processability and flexibility by softening a resin with a high elastic modulus. Examples of the plasticizer include monofunctional (meth)acrylic oligomers such as polyester (meth)acrylate, urethane (meth)acrylate, and polyether (meth)acrylate. Among them, urethane (meth)acrylate oligomers are preferred from the viewpoint of imparting appropriate toughness to the cured product.

[0066] (Silane coupling agent) Silane coupling agents are organosilicon compounds containing, in their structure, at least one reactive functional group and at least one alkoxy group bonded to a silicon atom. Examples of the reactive functional group include epoxy groups, (meth)acryloyl groups, mercapto groups, hydroxyl groups, carboxy groups, amino groups, amide groups, and isocyanate groups. Among these, epoxy groups and mercapto groups are preferred in terms of balance of durability.

[0067] The alkoxy group bonded to the silicon atom preferably contains an alkoxy group having 1 to 8 carbon atoms from the viewpoint of durability and storage stability, and is particularly preferably a methoxy group or an ethoxy group. The silane coupling agent may have an organic substituent other than the reactive functional group and the alkoxy group bonded to the silicon atom, such as an alkyl group or a phenyl group.

[0068] Examples of the silane coupling agent used in the present invention include monomeric epoxy group-containing silane coupling agents, which are silane compounds such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; and oligomeric epoxy group-containing silane coupling agents, which are silane compounds obtained by hydrolysis and condensation polymerization of a portion of the silane compounds, or by co-condensation of the silane compounds with alkyl group-containing silane compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane; Monomeric mercapto group-containing silane coupling agents, which are silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, γ-mercaptopropyldimethoxymethylsilane, and 3-mercaptopropylmethyldimethoxysilane; and oligomeric mercapto group-containing silane coupling agents, which are silane compounds obtained by hydrolysis and condensation polymerization of a portion of the silane compounds, or by co-condensation of the silane compounds with alkyl group-containing silane compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane; (meth)acryloyl group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane; amino group-containing silane coupling agents such as N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane; isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane; Examples include vinyl group-containing silane coupling agents such as vinyltrimethoxysilane and vinyltriethoxysilane. These may be used alone or in combination of two or more.

[0069] Among these, epoxy group-containing silane coupling agents and mercapto group-containing silane coupling agents are preferably used because of their excellent durability, and epoxy group-containing silane coupling agents are particularly preferred.

[0070] The content of the silane coupling agent is preferably 0.005 to 10 parts by weight, particularly preferably 0.01 to 5 parts by weight, and even more preferably 0.05 to 1 part by weight, relative to 100 parts by weight of the (meth)acrylic copolymer (A). When the content is equal to or greater than the lower limit, durability tends to be improved, and when the content is equal to or less than the upper limit, durability tends to be improved.

[0071] (ultraviolet absorber) Examples of the ultraviolet absorber include benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, benzoxazine-based ultraviolet absorbers, etc. These ultraviolet absorbers can be used alone or in combination of two or more.

[0072] The content of the ultraviolet absorber is preferably 0.01 to 20 parts by weight, particularly preferably 0.1 to 15 parts by weight, and even more preferably 0.5 to 10 parts by weight, relative to 100 parts by weight of the (meth)acrylic copolymer (A). When the content is equal to or greater than the lower limit, lightfastness reliability tends to improve, and when the content is equal to or less than the upper limit, yellowing resistance tends to improve.

[0073] (rust inhibitor) As the rust inhibitor, for example, triazoles, benzotriazoles, etc. are preferable, and they can prevent corrosion of optical members. The content of the rust inhibitor is preferably 0.01 to 5 parts by weight, and more preferably 0.1 to 3 parts by weight, per 100 parts by weight of the (meth)acrylic copolymer (A).

[0074] The content of the other components is preferably 5 parts by weight or less, particularly preferably 1 part by weight or less, and even more preferably 0.5 parts by weight or less, per 100 parts by weight of the (meth)acrylic copolymer (A), with the lower limit usually being 0 part by weight. If the content is too high, compatibility with the (meth)acrylic copolymer (A) decreases, and durability tends to decrease.

[0075] The pressure-sensitive adhesive composition [I] is prepared by mixing predetermined amounts of the (meth)acrylic copolymer (A) and the photopolymerization initiator (B), and, if necessary, the crosslinking agent (C), the silane coupling agent, the ultraviolet absorber, the rust inhibitor, and other components. The pressure-sensitive adhesive composition [I] thus obtained can be used for pressure-sensitive adhesive sheets, particularly pressure-sensitive adhesive sheets for surface protective films of flexible image display devices.

[0076] <This adhesive sheet> The pressure-sensitive adhesive sheet and pressure-sensitive adhesive sheet for a surface protective film of a flexible image display device according to one embodiment of the present invention (hereinafter sometimes collectively referred to as "the pressure-sensitive adhesive sheet") can be produced, for example, as follows.

[0077] In producing the present adhesive sheet, an adhesive composition [I] for forming the present adhesive sheet is prepared, which contains a (meth)acrylic copolymer (A), a photopolymerization initiator (B), and, if necessary, other components, and the like; the adhesive composition [I] is formed into a sheet, crosslinked, i.e., polymerized, to harden it, and then processed appropriately as necessary to produce the present adhesive sheet.

[0078] Alternatively, the pressure-sensitive adhesive composition [I] may be prepared, coated onto a substrate sheet or a flexible substrate, and cured to form a laminate containing the pressure-sensitive adhesive sheet. However, the method is not limited to this.

[0079] When preparing the pressure-sensitive adhesive composition [I] for forming the pressure-sensitive adhesive sheet, the raw materials may be kneaded using a temperature-controllable kneader (e.g., a single-screw extruder, a twin-screw extruder, a planetary mixer, a twin-screw mixer, a pressure kneader, etc.). When mixing various raw materials, various additives such as silane coupling agents and antioxidants may be blended with the resin in advance and then supplied to the kneader, or all materials may be melt-mixed in advance and then supplied, or a master batch in which only the additives are concentrated in the resin may be prepared and then supplied.

[0080] The pressure-sensitive adhesive composition [I] can be formed into a sheet by any known method, such as wet lamination, dry lamination, extrusion casting using a T-die, extrusion lamination, calendaring, inflation, injection molding, and liquid injection curing. Among these, when producing a sheet, wet lamination, extrusion casting, and extrusion lamination are preferred.

[0081] The pressure-sensitive adhesive composition [I] can be cured by irradiating it with active energy rays to produce a cured product. In addition to irradiating it with active energy rays, it can also be further cured by heating. In particular, the pressure-sensitive adhesive sheet can be produced by irradiating a molded product, for example, a sheet, of the pressure-sensitive adhesive composition [I] with active energy rays. In addition to the irradiation with active energy rays, the composition can also be further cured by heating.

[0082] Furthermore, the irradiation energy, irradiation time, irradiation method, etc. of the active energy rays are not particularly limited as long as they can activate the photopolymerization initiator (B) and polymerize the monomer components. When a hydrogen abstraction type photopolymerization initiator is used as the photopolymerization initiator (B), a hydrogen abstraction reaction also occurs from the (meth)acrylic copolymer (A), and the (meth)acrylic copolymer (A) is incorporated into the crosslinked structure, thereby forming a crosslinked structure with many crosslinking points. Therefore, the present pressure-sensitive adhesive sheet is preferably one that is cured using a hydrogen abstraction type photopolymerization initiator.

[0083] In another embodiment of the method for producing the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive composition [I] can be dissolved in an appropriate solvent and then coated using various coating techniques. When a coating method is used, the present pressure-sensitive adhesive sheet can be obtained by heat curing in addition to the above-mentioned curing by irradiation with active energy rays. In the case of coating, the thickness of the present pressure-sensitive adhesive sheet can be adjusted by the coating thickness and the solids concentration of the coating liquid.

[0084] For example, the pressure-sensitive adhesive composition [I] can be dissolved in a solvent, coated on a release film, dried, and cured by active energy ray irradiation to form the present pressure-sensitive adhesive sheet. Furthermore, a release film may be laminated, if necessary. In this case, the pressure-sensitive adhesive composition [I] may be coated on a release film, dried, cured by active energy ray irradiation, and a release film may be laminated thereon. Alternatively, the pressure-sensitive adhesive sheet may be formed by coating on a release film, drying, laminating a release film, and then curing by active energy ray irradiation.

[0085] The solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition [I], and examples thereof include ester solvents such as methyl acetate, ethyl acetate, methyl acetoacetate, and ethyl acetoacetate; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic solvents such as toluene and xylene; and alcohol solvents such as methanol, ethanol, and propyl alcohol. These can be used alone or in combination of two or more. Among them, ethyl acetate, acetone, methyl ethyl ketone, and toluene are more preferred in terms of solubility, drying properties, cost, etc., and ethyl acetate is particularly preferred.

[0086] In terms of drying property, the content of the solvent is preferably 600 parts by weight or less, more preferably 500 parts by weight or less, even more preferably 400 parts by weight or less, and particularly preferably 350 parts by weight or less, relative to 100 parts by weight of the (meth)acrylic copolymer (A), while it is preferably 1 part by weight or more, more preferably 50 parts by weight or more, even more preferably 100 parts by weight or more, and particularly preferably 150 parts by weight or more. The coating method may be any conventional method such as roll coating, die coating, gravure coating, comma coating, screen printing, or bar coating.

[0087] Furthermore, the pressure-sensitive adhesive composition [I] is preferably applied so that the thickness after drying is 1 to 200 μm, more preferably 5 to 100 μm, and even more preferably 10 to 50 μm, so that the effects of the present invention can be effectively exhibited.

[0088] During the drying, the solvent content in the pressure-sensitive adhesive composition [I] is preferably 1% by weight or less, more preferably 0.5% by weight or less, particularly preferably 0.1% by weight or less, and most preferably 0% by weight.

[0089] The drying temperature is usually 40 to 150° C., more preferably 45 to 140° C., even more preferably 50 to 130° C., and particularly preferably 55 to 120° C. Within this temperature range, the solvent can be removed efficiently and relatively safely while suppressing thermal deformation of the release film.

[0090] The drying time is usually 1 to 30 minutes, more preferably 3 to 25 minutes, and even more preferably 5 to 20 minutes. When the drying time is within this range, the solvent can be removed efficiently and sufficiently.

[0091] Drying methods include, for example, drying with a dryer, drying with a heated roll, drying by blowing hot air onto the film, etc. Among these, using a dryer is preferred because it allows for uniform and easy drying. These methods can be used alone or in combination of two or more.

[0092] Examples of the active energy rays in the active energy ray irradiation include light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, infrared rays, and visible light rays, and ionizing radiation such as X-rays, α-rays, β-rays, γ-rays, electron beams, proton beams, and neutron beams. Among these, ultraviolet rays are preferred from the viewpoints of suppressing damage to optical device components and controlling reactions. Furthermore, curing by ultraviolet irradiation is advantageous in terms of curing speed, availability of irradiation equipment, cost, and the like.

[0093] Examples of light sources for ultraviolet irradiation include high-pressure mercury lamps, ultra-high-pressure mercury lamps, carbon arc lamps, metal halide lamps, xenon lamps, chemical lamps, electrodeless discharge lamps, and LEDs that emit light in the wavelength range of 150 to 450 nm. Of these, it is preferable to use a high-pressure mercury lamp.

[0094] The amount of active energy ray irradiation (cumulative light amount) is 30 to 3000 mJ / cm from the viewpoint of curing. 2 is preferred, and more preferably 100 to 2000 mJ / cm 2 , and more preferably 300 to 1500 mJ / cm 2 This is carried out under the following conditions. After irradiation with active energy rays, the degree of cure can be increased by heating, if necessary.

[0095] The pressure-sensitive adhesive composition [I] is cured by irradiation with active energy rays to form the pressure-sensitive adhesive sheet. The thickness of the pressure-sensitive adhesive sheet formed is preferably 1 to 200 μm, particularly preferably 5 to 100 μm, and even more preferably 10 to 50 μm. If the thickness is equal to or greater than the lower limit, the adhesive properties tend to be stable, while if the thickness is equal to or less than the upper limit, efficient drying is facilitated, and concerns about adhesive overflow when rolled can be reduced.

[0096] A release film may be provided on at least one surface of the pressure-sensitive adhesive sheet obtained above to prevent blocking and adhesion of foreign matter.

[0097] As such a release film, any known release film can be used appropriately. As the material for the release film, for example, a film such as a polyester film, a polyolefin film, a polycarbonate film, a polystyrene film, an acrylic film, a triacetyl cellulose film, or a fluororesin film that has been coated with a silicone resin to provide a release treatment, or release paper, etc. can be appropriately selected and used.

[0098] The thickness of the release film is not particularly limited, but from the viewpoint of processability and handling, it is preferably 10 to 250 μm, more preferably 25 to 200 μm, and even more preferably 35 to 190 μm.

[0099] If necessary, embossing or various unevenness (conical, pyramidal, hemispherical, etc.) may be performed. Furthermore, for the purpose of improving adhesion to various member sheets, the surface may be subjected to various surface treatments such as corona treatment, plasma treatment, and primer treatment.

[0100] The gel fraction of the pressure-sensitive adhesive sheet is preferably 30 to 95% by weight, more preferably 35 to 90% by weight, and even more preferably 40 to 85% by weight. A gel fraction of at least the lower limit mentioned above is preferred because it tends to reduce the risk of adhesive overflow over time. The gel fraction is a measure of the degree of crosslinking (degree of hardening) and can be measured under the measurement conditions described in the examples below.

[0101] The ratio of oxygen atoms to carbon atoms (O / C) of this pressure-sensitive adhesive sheet can be measured by X-ray photoelectron spectroscopy (XPS), and it is important that it be 0.25 to 0.5, as this provides a good balance between adhesive strength and oil resistance. The preferred range for this ratio (O / C) is 0.25 to 0.4, more preferably 0.26 to 0.35, particularly preferably 0.27 to 0.34, and especially preferably 0.28 to 0.32. If the ratio is too small, oil resistance will decrease; if it is too large, the storage shear modulus (G') at low temperatures will increase too much, resulting in decreased flexibility (particularly dynamic bending properties).

[0102] The ratio (O / C) can be adjusted to fall within the above range by, for example, (1) increasing the amount of copolymerization of the hydroxyl group-containing (meth)acrylate, (2) using a monomer component with a relatively short carbon chain as the main monomer component in the copolymerization components, (3) introducing an oxyalkylene chain into the (meth)acrylic copolymer (A), or (4) appropriately combining the methods (1) to (3), among others. In particular, it is preferable to include the method (2) in terms of oil resistance.

[0103] The ratio (O / C) can be measured under the measurement conditions described in the Examples below.

[0104] The adhesive strength of the pressure-sensitive adhesive sheet to a transparent polyimide film (peel angle: 180°, peel speed: 300 mm / min) is preferably 4 to 30 N / cm, more preferably 4.5 to 20 N / cm, and even more preferably 5 to 15 N / cm. Within this range, sufficient adhesiveness is obtained, and the pressure-sensitive adhesive sheet tends to be suitable for use as a surface protection film for flexible image display devices. The adhesive strength can be measured under the measurement conditions described in the Examples below.

[0105] The lower the swelling rate of this pressure-sensitive adhesive sheet with respect to oleic acid, the better the oil resistance, and it is preferably 25% by weight or less, more preferably 15% by weight or less, even more preferably 10% by weight or less, and most preferably 0% by weight. The swelling ratio can be measured under the measurement conditions described in the Examples below.

[0106] The glass transition temperature (Tg) of the pressure-sensitive adhesive sheet is preferably −20° C. or lower, more preferably −23° C. or lower, even more preferably −25° C. or lower, and particularly preferably −30° C. or lower, in order to suppress an increase in the storage shear modulus (G') at low temperatures. The lower limit of the glass transition temperature (Tg) is usually −50° C. The glass transition temperature (Tg) can be measured under the measurement conditions described in the Examples below.

[0107] The storage shear modulus (G') of the pressure-sensitive adhesive sheet at -20°C is preferably 500 kPa or less, more preferably 400 kPa or less, from the viewpoint of preventing delamination during folding, particularly at high speeds or low temperatures. The lower limit is preferably 50 kPa from the viewpoints of preventing adhesive extrusion and maintaining the shape of the pressure-sensitive adhesive sheet. The storage shear modulus (G') at -20°C can be measured under the measurement conditions described in the Examples below.

[0108] The storage shear modulus (G') of the pressure-sensitive adhesive sheet at 60°C is preferably 200 kPa or less, more preferably 100 kPa or less, and even more preferably 50 kPa or less, from the viewpoint of maintaining high adhesiveness. The lower limit is preferably 1 kPa from the viewpoints of preventing adhesive extrusion and maintaining the shape of the pressure-sensitive adhesive sheet. The storage shear modulus (G') at 60°C can be measured under the measurement conditions described in the Examples below.

[0109] The recovery of the pressure-sensitive adhesive sheet is preferably 30% or more, more preferably 35% or more, and even more preferably 40% or more. Since a higher recovery is preferable, the upper limit is 100%. The restorability can be measured under the measurement conditions described in the Examples below.

[0110] The pressure-sensitive adhesive sheet thus obtained can be laminated with, for example, a surface protection film made of various materials to form a laminate for a surface protection film of a flexible image display device.

[0111] The surface protection film preferably has a surface hardness of 400 MPa or more, more preferably 450 MPa or more, and particularly preferably 500 MPa or more, at a contact depth of 200 to 400 nm as measured with a nanoindenter. The upper limit is usually 9 GPa. Within this range, sufficient scratch resistance and impact resistance can be obtained when the film is formed into a laminate for a surface protection film for a flexible image display device. Furthermore, it is preferable that the surface protection film is a component that does not change in appearance when subjected to a 200,000-cycle bending test at -20°C with a curvature radius (R) of 1.5 mm. In this case, when it is made into a laminate for a surface protection film for a flexible image display device, it is preferable because creases and delamination are less likely to occur at the bent portions.

[0112] In the present invention, the surface hardness of the surface protection film was evaluated by nanoindentation. Generally, the nanoindentation method involves pressing the indenter of a nanoindenter into a sample to a predetermined depth (contact depth) with a constant load (load), then lifting the indenter up until it separates from the sample (unloading), and analyzing the mechanical properties of the sample surface from the relationship between displacement and load at that time (load-displacement curve). The surface hardness in the present invention was calculated using the following formula under the following measurement conditions. H IT =F MAX / A p (H IT :Surface hardness, F MAX : Maximum test load, A p :Contact projected area)

[0113] (Measurement conditions) Measurement equipment: Bruker TI980 Maximum load: 1000uN Indenter material: Diamond Indenter shape: Berkovich Applied load: 1mN Contact depth: 300nm

[0114] Examples of the surface protective film include polyethylene terephthalate film, polyimide film, aramid film, glass plate, etc. Among these, polyethylene terephthalate film is preferred from the viewpoint of versatility, polyimide film from the viewpoint of enabling a small bending angle, and glass plate from the viewpoint of obtaining high surface strength, and polyimide film and glass plate are particularly effective from the viewpoint of high surface hardness.

[0115] The member may have a coating layer provided on the surface. The coating layer is not particularly limited, and examples thereof include an easy-adhesion coating layer, a release layer, a hard coating layer, an antistatic coating layer, and an anti-fingerprint layer.

[0116] In the present invention, examples of the layer structure include the following structures, but the present invention is not limited to these. (Viewing side) Hard coat / Polyimide film / Adhesive sheet (OLED side) (Surface hardness: 906 MPa) (Viewing side) Hard coat / PET film / Adhesive sheet (OLED side) (Surface hardness: 418 MPa) (Viewing side) Hard coat / PET film / Adhesive sheet / Glass (OLED side) (Surface hardness: 376 MPa) (Viewing side) Hard coat / PET film / Adhesive sheet (OLED side) (Surface hardness: 484 MPa)

[0117] In the present invention, as a dynamic bending reliability test for the flexible image display device surface protection film, a U-shaped bending cycle evaluation is performed under settings of a radius of curvature R=1.5 mm, 60 rpm (1 Hz), and -20°C, and the number of bending cycles at which defects (delamination, breakage, buckling, flow) at the bent portion do not occur is preferably 100,000 or more, and more preferably 200,000 or more.

[0118] Furthermore, as a dynamic bending reliability test for the flexible image display device surface protection film, in a U-shaped bending cycle evaluation under the settings of a curvature radius R=1.5 mm, 60 rpm (1 Hz), 85°C, and 85% RH, it is preferable that the number of bending cycles without any defects (delamination, breakage, buckling, flow) occurring in the bent portion is 100,000 or more, and more preferably 200,000 or more.

[0119] Furthermore, as a static bending reliability test for the flexible image display device surface protection film, the film is maintained in a bent state at a curvature radius R of 1.5 mm, 85°C, and 85% RH, and the storage time during which no defects (delamination, breakage, buckling, or flow) occur in the bent portion is preferably 24 hours or more, and more preferably 120 hours or more.

[0120] <Flexible image display device> The laminate for a surface protection film obtained from the pressure-sensitive adhesive sheet according to one embodiment of the present invention is attached to the surface of a flexible image display device. An example of a flexible image display device is an image display device having a structure in which the laminate for a surface protection film and components of an image display device are combined and laminated.

[0121] The flexible image display device preferably has a structure in which the constituent members of the image display device and the laminate for a surface protection film are directly laminated together. In this case, examples of "image display device components" include a reflective sheet, a light guide plate and a light source, a diffusion film, a prism sheet, a liquid crystal panel, a retardation plate, a glass substrate, a polarizing plate, an organic EL panel, an electrode, an anti-reflection film, a color filter, a touch sensor, a cover glass, a cover plastic, or a composite integrated combination of two or more of these components. In addition to the above-mentioned members, other layers may be interposed as necessary, such as an antistatic layer, a hard coat layer, an anchor layer, a release layer, an easy-adhesion layer, a protective layer, a bleeding prevention layer, and a flattening layer.

[0122] Examples of such flexible image display devices include bendable devices with a curved image display surface, foldable devices that can be repeatedly bent, rollable devices that can be rolled up, and stretchable devices that can be stretched and contracted. Examples of such image display devices include liquid crystal displays, organic EL displays, inorganic EL displays, electronic paper, plasma displays, and microelectromechanical system (MEMS) displays. [Example]

[0123] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts" and "%" are by weight.

[0124] <(Meth)acrylic copolymer> Acrylic copolymers (A-1) to (A-4) and (A'-1) to (A'-2) were prepared with the copolymerization component compositions shown in Table 1, and the glass transition temperatures (Tg) and weight average molecular weights (Mw) of these acrylic copolymers are also shown in Table 1.

[0125] [Table 1]

[0126] [Examples 1 to 4, Comparative Examples 1 and 2] 100 parts of the acrylic copolymer were homogeneously mixed with 3 parts of a mixture of 4-methylbenzophenone and 2,4,6-trimethylbenzophenone (Esacure TZT, hydrogen abstraction type, manufactured by IGM) as a photopolymerization initiator (B) and 200 parts of ethyl acetate as a solvent to obtain a pressure-sensitive adhesive composition solution (solid concentration 33%).

[0127] The pressure-sensitive adhesive composition solution was coated onto a release film (a silicone release-treated polyester film manufactured by Mitsubishi Chemical Corporation, thickness 100 μm) so that the thickness after drying would be 50 μm. After coating, the film was placed in a dryer heated to 90° C. and held for 7 minutes to volatilize and dry the solvent contained in the pressure-sensitive adhesive composition. Furthermore, a release film (a silicone release-treated polyester film manufactured by Mitsubishi Chemical Corporation, thickness 75 μm) was laminated on the surface of the pressure-sensitive adhesive composition from which the solvent had been dried to form a laminate, and the pressure-sensitive adhesive composition was irradiated with ultraviolet light through the release film using a high-pressure mercury lamp to obtain the integrated light amount shown in Table 1, thereby obtaining pressure-sensitive adhesive sheet laminates (pressure-sensitive adhesive sheets with release film) (1) to (6). The resulting pressure-sensitive adhesive sheet laminates (1) to (6) were evaluated as follows.

[0128] <Gel fraction> The release film was removed from each pressure-sensitive adhesive sheet laminate produced in the Examples and Comparative Examples, and multiple pressure-sensitive adhesive sheets were laminated to a thickness of 1 mm. An 8 mm diameter cylinder was then punched out, and this was used as a sample. This was wrapped in a 200-mesh SUS wire mesh and immersed in ethyl acetate adjusted to 23°C for 72 hours. The sample was then dried at 75°C for 4.5 hours, and the weights of the pressure-sensitive adhesive before and after immersion in ethyl acetate were measured, and the difference between the two weights was taken as the weight of the undissolved pressure-sensitive adhesive remaining in the wire mesh. The weight percentage of the undissolved pressure-sensitive adhesive remaining in the wire mesh relative to the weight of the pressure-sensitive adhesive before immersion in ethyl acetate was calculated as the gel fraction.

[0129] <Ratio of oxygen atoms to carbon atoms (O / C)> The release film was removed from each of the adhesive sheet laminates produced in the Examples and Comparative Examples to obtain a sample adhesive sheet, and the ratio of the number of oxygen atoms to the number of carbon atoms (O / C) was measured as follows. Measurement equipment: XPS K-Alpha (Thermo Fisher Scientific) X-ray: Monochromated Al Kα ·Analysis area: 400μmΦ Angle between sample surface and detector: 90° Etching: None

[0130] <Adhesive strength> One release film was removed from each of the pressure-sensitive adhesive sheet laminates produced in the Examples and Comparative Examples, and a polyethylene terephthalate film (Diafoil "S100", manufactured by Mitsubishi Chemical Corporation, thickness 50 μm) was roll-laminated using a hand roller to the adhesive surface of the pressure-sensitive adhesive sheet laminate. This was then cut into 10 mm wide x 150 mm long strips, and the remaining release film was peeled off to expose the adhesive surface, which was then roll-laminated using a hand roller to a transparent polyimide film (main component: transparent polyimide, "C_50" manufactured by KOLON Corporation, hereinafter referred to as "CPI film") that had been previously laminated to a stainless steel plate, to produce a laminate consisting of CPI film / pressure-sensitive adhesive sheet / backing film. This laminate was then left to stand overnight at room temperature (23°C) to cure, and a sample for adhesive strength measurement was prepared. The surface hardness of the transparent polyimide film measured with a nanoindenter at a contact depth of 200 to 400 nm was 542 MPa. Furthermore, when a bending test was carried out 200,000 times at -20°C with a curvature radius (R) of 1.5 mm, no change in appearance was observed.

[0131] The backing film was peeled off at an angle of 180° to the CPI film at a peeling speed of 300 mm / min, and the tensile strength was measured using a load cell to determine the 180° peel strength (N / 10 mm) of the adhesive sheet against the CPI film, which was taken as the adhesive strength (23°C).

[0132] <Oil resistance> To evaluate oil resistance, the swelling ratio in oleic acid was measured according to the following measurement method.

[0133] [Swelling rate] The release film was removed from each adhesive sheet laminate produced in the Examples and Comparative Examples, and multiple adhesive sheets were laminated to a thickness of 1 mm. The laminate was then cut into a 1 cm square and its weight was measured (weight A [g]). The sample was immersed in oleic acid that had been left standing in an 85°C / 85% RH environment for 1 hour. After immersion, the pressure-sensitive adhesive sheet was washed with ethanol and dried with a dryer, after which the weight was measured (weight B [g]). The swelling ratio was calculated using the following formula. Swelling rate [%] = (Weight B [g] - Weight A [g]) / Weight A [g] × 100 The smaller the swelling ratio, the better the oil resistance.

[0134] <Flexibility> To evaluate flexibility, the dynamic viscoelasticity of the adhesive sheet was measured, and the maximum temperature of the loss tangent (tan δ) (dynamic glass transition temperature: Tg) and the storage shear modulus (G') at -20°C or 60°C were read from the results. The restorability was also evaluated as follows.

[0135] [Loss tangent (tanδ), storage shear modulus (G')] The release film was removed from each of the pressure-sensitive adhesive sheet laminates produced in the Examples and Comparative Examples, and a plurality of pressure-sensitive adhesive sheets were laminated to form a laminate having a thickness of 1.0 mm. A cylindrical body with a diameter of 8 mm (height of 1.0 mm) was punched out from the obtained laminate of pressure-sensitive adhesive sheets, and this was used as a sample. The temperature dispersion of dynamic viscoelasticity of the sample was measured using a viscoelasticity measuring device (manufactured by TA Instruments, product name "DHR 2") under the following measurement conditions. From the obtained temperature dispersion data of dynamic viscoelasticity, the peak temperature of the loss tangent (tan δ) (glass transition temperature (Tg)) and the storage shear modulus G' at -20°C or 60°C were read.

[0136] (Measurement conditions) Measurement jig: Φ8mm parallel plate Distortion: 0.1% Frequency: 1Hz ·Measurement temperature: -60~100℃ Heating rate: 5℃ / min

[0137] [Resilience] The release film was removed from each of the pressure-sensitive adhesive sheet laminates produced in the Examples and Comparative Examples, and a plurality of pressure-sensitive adhesive sheets were laminated to form a laminate having a thickness of 1.0 mm. A cylindrical body with a diameter of 8 mm (height of 1.0 mm) was punched out from the obtained laminate of pressure-sensitive adhesive sheets, and this was used as a sample. The recovery properties of the samples were measured using a viscoelasticity measuring device (manufactured by TA Instruments, product name "DHR 2") under the following measurement conditions. That is, a shear strain equivalent to 7 times the thickness was applied at 25° C. and maintained for 10 minutes, and then the residual strain value was read 10 minutes after the stress was removed to measure the recovery. The resilience is calculated using the following formula: Restorability (%) = [(700 - residual strain value) / 700] x 100

[0138] <Bending durability> The release film was removed from each adhesive sheet laminate produced in the Examples and Comparative Examples, and a CPI film (main component: transparent polyimide, "C_50" manufactured by KOLON) was attached to both sides of the adhesive sheet using a hand roll to obtain a laminate sheet (sample) for bending durability. The laminated sheets (samples) prepared as described above were evaluated as follows.

[0139] [Dynamic bending durability] The laminated sheet (sample) was subjected to a U-bending cycle evaluation using a thermo-hygrostat durability system and a sheet-shaped no-load U-bending tester (manufactured by Yuasa System Co., Ltd.) at a temperature of -20°C or 85°C and 85% RH, with a curvature radius of R = 1.5 mm and a speed of 60 rpm (1 Hz). The number of cycles was 200,000. Evaluation was based on the following criteria. ◯: No delamination, breakage, buckling or flow occurred at the bent portion. ×: Delamination, breakage, buckling or flow occurred at the bent portion.

[0140] [Static bending durability] The laminated sheet (sample) was bent with a curvature radius R of 1.5 mm with the CPI film side facing inward, and stored at 85°C and 85% RH for 24 hours. After opening the jig, the static bending durability was evaluated based on the restored inner angle after 1 hour at room temperature (23°C). The restored inner angle was confirmed and evaluated according to the following criteria. Similarly, the restored inner angle of the component sheet (CPI film) alone was confirmed, and the inner angle of the film was 60°. ○: The internal angle of the bent part was restored to 60° or more. ×: The inner angle of the bent portion was restored to less than 60°.

[0141] The results obtained by the above measurements and evaluations are shown in Table 2.

[0142] [Table 2]

[0143] From the above evaluation results, the adhesive sheet for the surface protection film of a flexible image display device obtained in the example was a hydroxyl group-containing acrylic copolymer with an O / C within the specified range, and therefore had good adhesive strength and flexibility, as well as excellent oil resistance. Furthermore, it also had excellent static bending durability and dynamic bending durability. On the other hand, the surface protection adhesive sheet obtained in the comparative example was an acrylic copolymer containing hydroxyl groups, but the O / C was outside the specified range, so it did not provide a balanced and satisfactory combination of flexibility and oil resistance. In addition, Example 1, which used 2-hydroxyethyl acrylate as the hydroxyl group-containing (meth)acrylate (a1), provided higher adhesiveness and oil resistance. On the other hand, Examples 2 and 3, which used 4-hydroxybutyl acrylate as the hydroxyl group-containing (meth)acrylate (a1), provided good flexibility because they were able to reduce the storage shear modulus (G') at -20°C, and both were very useful as pressure-sensitive adhesive sheets for surface protection films for flexible image display devices. Therefore, it is clear that a flexible image display device using the present pressure-sensitive adhesive sheet has excellent flexibility and reliability in terms of oil resistance. [Industrial Applicability]

[0144] The pressure-sensitive adhesive sheet of the present invention, particularly the pressure-sensitive adhesive sheet for a surface protective film for a flexible image display device, has a surface protective function and flexibility such as reliability against bending (bending durability) while being attached to an image display device and in use, and furthermore, a laminate for a surface protective film having excellent oil resistance can be obtained. Therefore, the obtained laminate for a surface protective film is useful as a laminate for a surface protective film for various flexible image display devices such as bendable, foldable, rollable, and stretchable, and is particularly suitable as a laminate for a surface protective film for a foldable image display device that is repeatedly bent.

Claims

1. A pressure-sensitive adhesive sheet formed from a photocurable pressure-sensitive adhesive composition [I] containing a (meth)acrylic copolymer (A) and a photopolymerization initiator (B), the (meth)acrylic copolymer (A) is a (meth)acrylic copolymer containing a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a1), the ratio of the number of oxygen atoms to the number of carbon atoms (O / C) of the pressure-sensitive adhesive sheet measured by X-ray photoelectron spectroscopy is 0.25 to 0.5; the pressure-sensitive adhesive sheet has a storage shear modulus (G') of 500 kPa or less at -20°C; the pressure-sensitive adhesive sheet has a gel fraction of 30 to 95% by weight, the adhesive strength of the pressure-sensitive adhesive sheet to the transparent polyimide film (peel angle: 180°, peel rate: 300 mm / min) is 4.5 to 30 N / cm; Adhesive sheet.

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the (meth)acrylic copolymer (A) is a (meth)acrylic copolymer containing a structural moiety derived from the hydroxyl group-containing (meth)acrylate (a1) and a structural moiety derived from an alkyl (meth)acrylate (a2) containing an alkyl group having 1 to 10 carbon atoms.

3. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the hydroxyl group-containing (meth)acrylate (a1) is a (meth)acrylate containing a hydroxyalkyl group having 3 to 10 carbon atoms.

4. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the (meth)acrylic copolymer (A) has a weight average molecular weight of 600,000 to 1,500,000.

5. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the photocurable pressure-sensitive adhesive composition [I] further contains a crosslinking agent (C).

6. The pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein the pressure-sensitive adhesive sheet has a swelling degree with oleic acid of 25% by weight or less.

7. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, which is used as a surface protection film for a flexible image display device.

8. A pressure-sensitive adhesive sheet for a surface protective film of a flexible image display device, comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 7.

9. A laminate for a surface protective film of a flexible image display device, comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 7 and a surface protective film laminated thereon, The surface protective film has a surface hardness of 400 MPa or more at a contact depth of 200 to 400 nm as measured by a nanoindenter, and does not change in appearance when subjected to a bending test of 200,000 times at −20° C. under the condition of a radius of curvature (R) of 1.5 mm.

10. 10. The laminate for a surface protective film of a flexible image display device according to claim 9, wherein the surface protective film comprises any member selected from the group consisting of a polyethylene terephthalate film, a polyimide film, an aramid film, and a glass plate.

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