Adhesive sheet, adhesive sheet with mold release film, and adhesive sheet for flexible image display device constituent members

Abstract

The present invention provides, as an adhesive sheet having excellent flexibility and excellent oil resistance, an adhesive sheet which is provided with an adhesive layer that is formed of an adhesive composition that contains a (meth)acrylic copolymer (A), a photocurable compound (B) and a photopolymerization initiator (C), wherein: the (meth)acrylic copolymer (A) contains a constituent unit derived from an alkyl (meth)acrylate (a1) that has a linear and / or branched alkyl group having 3 to 6 carbon atoms and a constituent unit derived from a (meth)acrylate (a2) that has a lower glass transition temperature than the alkyl (meth)acrylate (a1); the ratio of the constituent unit derived from an alkyl (meth)acrylate (a1) is 20% by mass to 60% by mass; the content mass ratio (W(a2) / W(a1)) of the constituent unit derived from a (meth)acrylate (a2) to the constituent unit derived from an alkyl (meth)acrylate (a1) is 0.3 to 3.0; and the shear storage elastic modulus (G') at -20°C is 800 kPa or less.

Description

Adhesive sheet, adhesive sheet with release film, and adhesive sheet for flexible image display device components

[0001] The present invention relates to an adhesive sheet, an adhesive sheet with a release film, and an adhesive sheet for a component of a flexible image display device, and more particularly to an adhesive sheet, an adhesive sheet with a release film, and an adhesive sheet for a component of a flexible image display device, which have sufficient adhesiveness and flexibility as well as excellent oil resistance.

[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 curved image display surfaces, 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 image distortion at the folded portion after repeated folding. Patent Document 2 discloses a laminate that includes a double-sided 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 that approximates an actual usage environment.

[0004] Incidentally, the cover window member of 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, etc. 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, and smartphones, there are more opportunities for the skin of people's fingers or the like to come into contact with the housing or image display screen. Normally, in addition to sweat, oily components such as sebum and cosmetics are present on the surface of the skin. Therefore, over a long period of use, these oily components may gradually penetrate, for example, from the edge of the joint between the protective panel and the housing, and may even penetrate into the adhesive layer of the adhesive sheet. When oily components or the like penetrate into the adhesive layer, problems such as the adhesive of the adhesive sheet spilling over the edge of the adherend or a decrease in the adhesive strength of the surface protection film causing peeling can occur, and therefore there is a growing demand for improved oil resistance.

[0006] For example, Patent Document 3 describes that in a pressure-sensitive adhesive containing a hydroxy group-containing (meth)acrylic resin and an isocyanate curing agent, the use of an acrylic resin with a specific structure and an isocyanate curing agent with a specific structure in combination has resulted in improvements in bending suitability, sebum resistance, and the like.

[0007] JP 2020-196255 A International Publication No. 2018 / 173896 JP 2020-45443 A

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

[0009] Under such circumstances, the present invention provides a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive sheet with a release film, and a pressure-sensitive adhesive sheet for flexible image displays, which have good flexibility and excellent oil resistance.

[0010] In view of these circumstances, the present inventors have found that by setting the storage shear modulus at -20°C within a specific range for a pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition containing: a (meth)acrylic copolymer that contains structural units derived from an alkyl (meth)acrylate having a specific alkyl group and structural units derived from a (meth)acrylate having a glass transition temperature lower than that of the alkyl (meth)acrylate, and in which the proportion of the structural units derived from the alkyl (meth)acrylate and the mass ratio of the structural units derived from the (meth)acrylate having a glass transition temperature lower than that of the alkyl (meth)acrylate to the structural units derived from the alkyl (meth)acrylate are within specific ranges; a photocurable compound; and a photopolymerization initiator, the flexibility and oil resistance can be improved.

[0011] That is, the present invention has the following aspects. [1] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition comprising a (meth)acrylic copolymer (A), a photocurable compound (B), and a photopolymerization initiator (C), wherein the (meth)acrylic copolymer (A) comprises structural units derived from an alkyl (meth)acrylate (a1) having a linear and / or branched alkyl group having 3 to 6 carbon atoms, and structural units derived from a (meth)acrylate (a2) having a lower glass transition temperature when formed into a homopolymer than that of the alkyl (meth)acrylate (a1), the proportion of the structural units derived from the alkyl (meth)acrylate (a1) relative to 100% by mass of all structural units constituting the (meth)acrylic copolymer (A) is 20% by mass or more and 60% by mass or less, the mass ratio of the structural units derived from the (meth)acrylate (a2) to the structural units derived from the alkyl (meth)acrylate (a1), (W(a2) / W(a1)), is 0.3 to 3.0, The pressure-sensitive adhesive sheet has a storage shear modulus (G') at -20°C of 800 kPa or less. [2] The pressure-sensitive adhesive sheet according to [1], wherein the (meth)acrylic copolymer (A) further contains a structural unit derived from a polar group-containing monomer (a3). [3] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the (meth)acrylic copolymer (A) has a weight-average molecular weight of 600,000 to 1,500,000. [4] The pressure-sensitive adhesive sheet according to any of [1] to [3], wherein the photocurable compound (B) is a (meth)acrylate having a polyalkylene oxide skeleton. [5] The pressure-sensitive adhesive sheet according to any of [1] to [4], wherein the pressure-sensitive adhesive composition further contains a silane coupling agent (D). [6] The pressure-sensitive adhesive sheet according to any 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 of [1] to [6], wherein the pressure-sensitive adhesive sheet has a gel fraction of 30 to 95 mass%. [8] The pressure-sensitive adhesive sheet according to any one of [1] to [7], wherein the oil-resistant adhesion rate (X) calculated by the following formula is 84% ​​or more.X (%) = (B / A) x 100. A: The adhesive strength to the surface of a polyimide film when a pressure-sensitive adhesive sheet is cut to a width of 10 mm and a length of 150 mm and laminated to a polyimide film, and then peeled at 23°C, 50% RH, a peel angle of 180°, and a peel rate of 300 mm / min. B: The adhesive strength to the surface of a polyimide film when a pressure-sensitive adhesive sheet is cut to a width of 10 mm and a length of 150 mm and laminated to a polyimide film, and a 1:1 mixture of oleic acid and squalene (artificial sebum liquid) is dropped onto both ends of the pressure-sensitive adhesive sheet in the longitudinal direction at 1 μL / cm. After storage at 23°C and 50% RH for 5 days, the adhesive strength to the surface of the polyimide film is measured. [9] The pressure-sensitive adhesive sheet according to any one of [1] to [8] is transparent.

[10] The pressure-sensitive adhesive sheet according to any one of [1] to [9] has a total light transmittance of 80% or more and a haze of 5% or less.

[11] The pressure-sensitive adhesive sheet according to any one of [1] to

[10] , which is used as a component of a flexible image display device.

[12] A pressure-sensitive adhesive sheet with a release film, having a configuration in which the pressure-sensitive adhesive sheet according to any one of [1] to

[11] and a release film are laminated together.

[13] A pressure-sensitive adhesive sheet for a component of a flexible image display device, comprising the pressure-sensitive adhesive sheet according to any one of [1] to

[11] or the pressure-sensitive adhesive sheet with a release film according to

[12] .

[14] The pressure-sensitive adhesive sheet for a component of a flexible image display device according to

[13] , wherein the component of a flexible image display device includes any member selected from a polyethylene terephthalate film, a polyimide film, an aramid film, and a glass plate.

[0012] The adhesive sheet according to one embodiment of the present invention, when used by being attached to, for example, a flexible image display device, serves as an adhesive sheet for a surface protection film that has surface protection function and flexibility such as bendability, flexibility, and recovery, and also has excellent oil resistance.

[0013] An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the embodiment described below. In the present invention, the term "film" conceptually includes a sheet, a film, and a tape. Furthermore, when the term "panel" is used, such as an image display panel or a protective panel, it includes 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), it means "x or more and y or less" unless otherwise specified, and also means "preferably greater than x" or "preferably smaller than y". Furthermore, when it is stated that "x or more" (x is any number), it means "preferably greater than x" unless otherwise specified, and when it is stated that "y or less" (y is any number), it also means "preferably smaller than y" unless otherwise specified. Furthermore, "x and / or y (x and y are any configurations)" 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 mass or more, preferably 35% by mass or more, and more preferably 50% by mass or more, of the target object. Furthermore, in the present invention, "(meth)acrylic" refers to a comprehensive definition of acrylic and methacrylic, "(meth)acrylate" refers to a comprehensive definition of acrylate and methacrylate, and "(meth)acryloyl" refers to a comprehensive definition of acryloyl and methacryloyl.

[0016] <Adhesive Composition> A pressure-sensitive adhesive sheet according to one embodiment of the present invention (hereinafter referred to as "the sheet") is formed from a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer (A) as a main component, and further containing a photocurable compound (B), and a photocurable compound (B).

[0017] The pressure-sensitive adhesive composition is preferably cured by active energy rays, since the crosslink density and the degree of cure can be easily adjusted and damage to the substrate and the like is minimized. In addition, the pressure-sensitive adhesive composition may be cured in multiple stages, as described below. Each component contained in the pressure-sensitive adhesive composition will be described below.

[0018] [(Meth)acrylic Copolymer (A)] The (meth)acrylic copolymer (A) contains a structural unit derived from an alkyl (meth)acrylate (a1) having a linear and / or branched alkyl group having 3 to 6 carbon atoms, and a structural unit derived from a (meth)acrylate (a2) having a lower glass transition temperature when made into a homopolymer than the alkyl (meth)acrylate (a1).

[0019] [Alkyl (meth)acrylate (a1)] When the alkyl (meth)acrylate (a1) having a linear and / or branched alkyl group having 3 to 6 carbon atoms is made into a homopolymer, the glass transition temperature is usually −10 to −80°C, preferably −15 to −70°C, and particularly preferably −40 to −60°C. By setting the glass transition temperature of the alkyl (meth)acrylate (a1) within the above range, the oil resistance tends to be excellent. Note that, for example, the value described in the Polymer Handbook can be used as the glass transition temperature when the homopolymer is made.

[0020] Specific examples of the alkyl (meth)acrylate (a1) having an alkyl group include linear alkyl (meth)acrylates such as n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, and n-hexyl (meth)acrylate; branched alkyl (meth)acrylates such as s-butyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, and neopentyl (meth)acrylate; and alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate. These may be contained alone or in combination of two or more as structural units in the (meth)acrylic copolymer (A). Of these, linear alkyl (meth)acrylates are preferred from the viewpoint of oil resistance, and n-butyl (meth)acrylate is particularly preferred.

[0021] The proportion of the structural units derived from the alkyl (meth)acrylate (a1) relative to 100% by mass of all structural units constituting the (meth)acrylic copolymer (A) is 20 to 60% by mass, preferably 24 to 56% by mass, and particularly preferably 28 to 52% by mass. By setting the proportion of the structural units derived from the alkyl (meth)acrylate (a1) within this range, excellent oil resistance is achieved.

[0022] [(Meth)acrylate (a2)] The (meth)acrylate (a2) having a lower glass transition temperature than the alkyl (meth)acrylate (a1) when made into a homopolymer is not particularly limited, and examples thereof include alkyl (meth)acrylates (excluding the alkyl (meth)acrylate (a1)), hydroxyl group-containing (meth)acrylates, amino group-containing (meth)acrylates, isocyanate group-containing (meth)acrylates, carboxy group-containing (meth)acrylates, acetoacetyl group-containing (meth)acrylates, and glycidyl group-containing (meth)acrylates. In the present invention, among these, it is sufficient to use a (meth)acrylate having a glass transition temperature lower than the alkyl (meth)acrylate (a1). The (meth)acrylate (a2) may be contained alone or in combination of two or more as a structural unit in the (meth)acrylic copolymer (A).

[0023] Furthermore, when the (meth)acrylic copolymer (A) contains two or more types of structural units derived from alkyl (meth)acrylates (a1), it is necessary to use a (meth)acrylate (a2) having a glass transition temperature lower than that of all of the alkyl (meth)acrylates (a1) contained therein.

[0024] Examples of the alkyl (meth)acrylate include linear alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, cetyl (meth)acrylate, and stearyl (meth)acrylate; 2-ethylhexyl (meth)acrylate; branched alkyl (meth)acrylates such as t-butylcyclohexyl (meth)acrylate, 3,5,5-trimethylcyclohexane (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, and the like; and alicyclic (meth)acrylates such as t-butylcyclohexyl (meth)acrylate, 3,5,5-trimethylcyclohexane (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, isobornyl (meth)acrylate.

[0025] Examples of the hydroxyl group-containing (meth)acrylate 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 the hydroxyl group-containing (meth)acrylate 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, and the like.

[0026] Examples of the amino group-containing (meth)acrylate 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.

[0027] Examples of the isocyanate group-containing (meth)acrylate 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.

[0028] Examples of the carboxy group-containing (meth)acrylate 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, and 2-(meth)acryloyloxypropyl succinic acid.

[0029] Examples of the acetoacetyl group-containing (meth)acrylate include 2-(acetoacetoxy)ethyl (meth)acrylate.

[0030] Examples of the glycidyl group-containing (meth)acrylate include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0031] When the (meth)acrylate (a2) is a homopolymer, the glass transition temperature is usually −20 to −90° C., preferably −40 to −85° C., and particularly preferably −60 to −80° C. By setting the glass transition temperature of the (meth)acrylate (a2) within the above range, flexibility tends to be excellent.

[0032] The difference in glass transition temperature between the alkyl (meth)acrylate (a1) and the (meth)acrylate (a2) is usually 1 to 40° C., preferably 5 to 30° C., and particularly preferably 10 to 20° C. When a plurality of alkyl (meth)acrylates (a1) and (meth)acrylates (a2) are contained, it is sufficient that the difference between the alkyl (meth)acrylate (a1) having the lowest glass transition temperature and the (meth)acrylate (a2) having the highest glass transition temperature is within the above range.

[0033] Among these, the (meth)acrylate (a2) is preferably an alkyl(meth)acrylate from the viewpoint of flexibility, and more preferably a branched alkyl(meth)acrylate. A preferred specific example of the (meth)acrylic copolymer (A) is one in which the alkyl(meth)acrylate (a1) is n-butyl(meth)acrylate and the (meth)acrylate (a2) is 2-ethylhexyl(meth)acrylate.

[0034] The proportion of the structural units derived from the (meth)acrylate (a2) relative to 100% by mass of all structural units constituting the (meth)acrylic copolymer (A) is usually 10 to 60% by mass, preferably 14 to 50% by mass, and particularly preferably 18 to 45% by mass. By setting the proportion of the structural units derived from the (meth)acrylate (a2) within this range, flexibility tends to be excellent.

[0035] The mass ratio of the structural units derived from the (meth)acrylate (a2) to the structural units derived from the alkyl (meth)acrylate (a1) [W(a2) / W(a1)] is 0.3 to 3.0, and preferably 0.4 to 1.5. By setting the mass ratio of the alkyl (meth)acrylate (a1) to the (meth)acrylate (a2) in the above range, excellent flexibility and oil resistance are achieved.

[0036] In the present invention, the (meth)acrylic copolymer (A) can obtain high oil resistance by containing structural units derived from the alkyl (meth)acrylate (a1), and excellent flexibility by containing structural units derived from the (meth)acrylate (a2). The (meth)acrylate (a1) and the (meth)acrylate (a2) have different alkyl chain carbon numbers and functional group structures, so they tend to be insufficiently compatible, which can lead to a phase separation structure during polymerization, resulting in the polymer becoming cloudy. However, when the mass ratio [W(a2) / W(a1)] of the structural units derived from the (meth)acrylate (a2) to the structural units derived from the alkyl (meth)acrylate (a1) is set within a predetermined range, it is possible to obtain an optically homogeneous transparent adhesive sheet that combines good oil resistance and flexibility.

[0037] The (meth)acrylic copolymer (A) preferably further contains a structural unit derived from a polar group-containing monomer (a3), which tends to impart cohesive strength and crosslinking-accelerating properties.

[0038] Examples of the polar group-containing monomer (a3) ​​include hydroxyl group-containing monomers, carboxyl group-containing monomers, and nitrogen atom-containing monomers. These may be contained alone or in combination of two or more as structural units in the (meth)acrylic copolymer (A). Among these, hydroxyl group-containing monomers and carboxyl group-containing monomers are more preferred, and hydroxyl group-containing monomers are even more preferred, in terms of excellent reactivity with the photocurable compound (B) described below.

[0039] Examples of the hydroxyl group-containing monomer include the monomers described above for the hydroxyl group-containing (meth)acrylate.

[0040] Examples of the carboxy group-containing monomer include the monomers described above for the carboxy group-containing (meth)acrylate, as well as crotonic acid, fumaric acid, maleic acid, itaconic acid, monomethyl maleate, and monomethyl itaconate.

[0041] Examples of the nitrogen atom-containing monomer include an amino group-containing monomer, an amide group-containing monomer, and an isocyanate group-containing monomer.

[0042] Examples of the amino group-containing monomer include the monomers described above in connection with the amino group-containing (meth)acrylate.

[0043] 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, N-n-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.

[0044] Examples of the isocyanate group-containing monomer include the monomers described above for the isocyanate group-containing (meth)acrylate.

[0045] From the viewpoint of cohesive strength, the (meth)acrylic copolymer (A) preferably contains a structural unit derived from a hydroxyl group-containing monomer, among the structural units derived from the polar group-containing monomer (a3), more preferably contains a structural unit derived from a primary hydroxyl group-containing (meth)acrylate, and particularly preferably contains a structural unit derived from 2-hydroxyethyl (meth)acrylate and / or 4-hydroxybutyl acrylate.

[0046] The proportion of the structural units derived from the polar group monomer (a3) ​​relative to 100% by mass of all structural units constituting the (meth)acrylic copolymer (A) is usually 45% by mass or less, preferably 1 to 40% by mass, more preferably 5 to 37% by mass, and particularly preferably 15 to 35% by mass.

[0047] In addition, when the polar group-containing monomer (a3) ​​also corresponds to the (meth)acrylate (a2), the polar group-containing monomer (a3) ​​is excluded from the (meth)acrylate (a2). However, when the only structural unit derived from the (meth)acrylate (a2) contained in the (meth)acrylic copolymer (A) is a structural unit derived from the polar group-containing monomer (a3), the polar group-containing monomer (a3) ​​is considered to be the (meth)acrylate (a2).

[0048] The (meth)acrylic copolymer (A) may contain a structural unit derived from a monomer that does not fall under the category of the (meth)acrylate (a2) among the monomers described above for the (meth)acrylate (a2) or other copolymerizable monomers (hereinafter collectively referred to as "other monomers"). These may be contained alone or in combination of two or more as structural units in the (meth)acrylic copolymer (A).

[0049] Examples of the other copolymerizable monomers include aromatic (meth)acrylates such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene 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, 4-methacryloyloxyethoxybenzophenone, 4-methacryloyloxybenzophenone, 4-methacryloyloxyethoxybenzophenone, and 4-acryloyloxyethoxybenzophenone. (meth)acrylates having a benzophenone structure such as 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, itaconic acid dialkyl esters, fumaric acid dialkyl esters, allyl acetoacetate, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyl trimethylammonium chloride, and vinyl group-containing monomers such as dimethyl allyl vinyl ketone.

[0050] The proportion of structural units derived from other monomers relative to 100% by mass of all structural units constituting the (meth)acrylic copolymer (A) is usually 30% by mass or less, preferably 25% by mass or less, and more preferably 20% by mass or less, with the lower limit usually being 0% by mass.

[0051] The (meth)acrylate copolymer (A) can be obtained by copolymerizing the alkyl (meth)acrylate (a1), (meth)acrylate (a2), preferably the polar group-containing monomer (a3), and if necessary, other monomers, so as to achieve the ratio of the structural units described above.As the polymerization method, for example, a conventionally known polymerization method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used, but the solution polymerization method is preferred in that it can safely and stably produce the (meth)acrylic copolymer (A) with the ratio of any structural units.

[0052] The (meth)acrylic copolymer (A) may have a photoactive moiety, such as a polymerizable carbon-carbon double bond group, introduced into its side chain, thereby improving the crosslinking efficiency of the pressure-sensitive adhesive composition, allowing the pressure-sensitive adhesive composition to be crosslinked by irradiation with active energy rays for a shorter period of time, thereby increasing productivity.

[0053] Examples of a method for introducing a polymerizable carbon-carbon double bond group into a side chain of the (meth)acrylic copolymer (A) include a method in which a (meth)acrylic copolymer (A) having a structural unit derived from the above-mentioned polar group-containing monomer (a3) ​​or a glycidyl group-containing (meth)acrylate is produced, and then a compound having a polymerizable carbon-carbon double bond group and a functional group reactive with these functional groups is subjected to a condensation or addition reaction while maintaining the activity of the polymerizable carbon-carbon double bond group.

[0054] 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 ease of reaction control. Of these, a combination in which the (meth)acrylic copolymer (A) has a hydroxy group and the compound has an isocyanate group is particularly suitable. Examples of isocyanate compounds having a polymerizable carbon double bond group include the above-mentioned 2-(meth)acryloyloxyethyl isocyanate and alkylene oxide adducts thereof.

[0055] 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 mass or less, more preferably 8 parts by mass or less, even more preferably 5 parts by mass or less, and particularly preferably 3 parts by mass or less, per 100 parts by mass of the (meth)acrylic copolymer (A) from the viewpoint of improving adhesiveness and stress relaxation property. From the viewpoint of reaction efficiency, it is preferably 1 part by mass or more.

[0056] From the viewpoint of obtaining a pressure-sensitive adhesive composition with high cohesive strength, the weight-average molecular weight (Mw) of the (meth)acrylic copolymer (A) is preferably 600,000 to 1,500,000, more preferably 700,000 to 1,200,000, and even more preferably 800,000 to 1,100,000. When the weight-average molecular weight of the (meth)acrylic copolymer (A) is within the above range, a pressure-sensitive adhesive composition with high cohesive strength tends to be obtained, and the pressure-sensitive adhesive composition also tends to have excellent handleability and uniform stirring properties.

[0057] 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, and the weight average molecular weight (Mw) can be determined by measuring a molecular weight distribution curve under the following conditions using a gel permeation chromatography (GPC) analyzer (HLC-8320GPC, manufactured by Tosoh Corporation). Guard column: TSKguardcolumnHXL Separation column: TSKgelGMHXL (4 columns) Temperature: 40°C Injection volume: 100 μL Polystyrene equivalent Solvent: THF Flow rate: 1.0 mL / min

[0058] 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.

[0059] 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'=tan δ) becomes maximum when dynamic viscoelasticity is measured using a dynamic viscoelasticity measuring device in a shear mode at a frequency of 1 Hz. For example, the (meth)acrylic copolymer (A) can be molded into a cylindrical body with a diameter of 8 mm (height of 1.0 mm), and the loss tangent (tan δ) can be measured using a viscoelasticity measuring device (DHR 2, manufactured by T.A. Instruments) under the following measurement conditions. (Measurement Conditions) Measuring jig: Φ8 mm parallel plate Strain: 0.1% Frequency: 1 Hz Measurement temperature: -60 to 100°C Heating rate: 5°C / min

[0060] [Photocurable Compound (B)] The photocurable compound (B) is a compound that has the property of being cured by light irradiation. When the photocurable compound (B) is contained in the pressure-sensitive adhesive composition, the rheological properties of the pressure-sensitive adhesive composition and the adhesion to an adherend can be adjusted.

[0061] Examples of the photocurable compound (B) include (meth)acrylic monomers and (meth)acrylic oligomers, and the use of these is preferred because it makes it easier to adjust the storage shear modulus (G') and glass transition temperature (Tg) of the pressure-sensitive adhesive composition.

[0062] For example, when a monofunctional (meth)acrylic monomer or a monofunctional (meth)acrylic oligomer having a glass transition temperature (Tg) lower than that of the (meth)acrylic copolymer (A) when made into a homopolymer is added, the glass transition temperature (Tg) of the pressure-sensitive adhesive composition can be lowered, and flexibility at low temperatures (e.g., −20°C) can be increased, tending to provide excellent flexural durability at that temperature. Furthermore, when a polyfunctional (meth)acrylic monomer or a polyfunctional (meth)acrylic oligomer having two or more functional groups is used, a crosslinked structure tends to be formed, which can impart cohesive strength and moderate toughness to the pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet). Furthermore, the pressure-sensitive adhesive layer having moderate toughness not only prevents the pressure-sensitive adhesive layer from deforming and collapsing when cut, but also tends to prevent the surface of the image display device component from undulating even when stress is applied after lamination, resulting in excellent resilience. The photocurable compound (B) can be used alone or in combination of two or more types. Among these, (meth)acrylic oligomers are preferred, and it is more preferred to contain a monofunctional (meth)acrylic oligomer as the main component.

[0063] As the monofunctional (meth)acrylic monomer, the compounds exemplified as the (meth)acrylate monomer used as a constituent unit of the (meth)acrylic copolymer (A) can be used as appropriate. Among them, from the viewpoint of imparting flexibility to the PSA sheet, (meth)acrylate monomers having a glass transition temperature (Tg) of −20° C. or lower, preferably −30° C. or lower, more preferably −40° C. or lower when made into a homopolymer are preferred. The lower limit of the glass transition temperature (Tg) is not particularly limited, but is, for example, −100° C. Furthermore, from the viewpoint of imparting adhesion to an adherend, (meth)acrylic monomers containing a polar group and / or an alkylene oxide skeleton are preferred.

[0064] Examples of the monofunctional (meth)acrylic oligomer include monofunctional polyester (meth)acrylate oligomers, monofunctional epoxy (meth)acrylate oligomers, monofunctional urethane (meth)acrylate oligomers, monofunctional polyether (meth)acrylate oligomers, etc. Among these, monofunctional urethane (meth)acrylate oligomers are preferred from the viewpoints of providing a cured product with appropriate toughness and flexibility and excellent adhesion to an adherend.

[0065] The monofunctional urethane (meth)acrylate oligomer can be obtained, for example, by reacting a polyol, a polyisocyanate, and a hydroxyl group-containing mono(meth)acrylate or an isocyanate group-containing mono(meth)acrylate.

[0066] The polyol may be a polyol generally used in urethane (meth)acrylate oligomers, such as polyether polyols (e.g., polyethylene glycol, polypropylene glycol, polytetramethylene glycol); condensation polymers of polycarboxylic acids (e.g., phthalic acid, adipic acid, maleic acid) with polyhydric alcohols (e.g., ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, trimethylolpropane, pentaerythritol); polyester polyols (e.g., ring-opening polymers of cyclic esters (lactones)); and polycarbonate polyols (e.g., 1,6-hexanediol carbonate polyol). These may be used alone or in combination of two or more. Of these, polyether polyols are preferred, and polypropylene glycol is particularly preferred.

[0067] Examples of the polyisocyanate include aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysine diisocyanate, and lysine triisocyanate; alicyclic polyisocyanates such as hydrogenated xylylene diisocyanate, hydrogenated diphenylmethane diisocyanate, isophorone diisocyanate, and norbornene diisocyanate; aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, polyphenylmethane polyisocyanate, modified diphenylmethane diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate; and trimer compounds of the polyisocyanates and polymer compounds of the polyisocyanates. Further, examples of the polyisocyanate include allophanate type polyisocyanates, biuret type polyisocyanates, etc. These may be used alone or in combination of two or more kinds.

[0068] Examples of the hydroxyl group-containing mono(meth)acrylate 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 suitable 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. These may be used alone or in combination of two or more. Among these, primary hydroxyl group-containing (meth)acrylates are preferred in terms of reactivity, and 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are particularly preferred in terms of durability and low-temperature flexibility.

[0069] Examples of isocyanate group-containing mono(meth)acrylates include 2-isocyanatoethyl(meth)acrylate, 1,1-bis(acryloyloxymethyl)ethyl isocyanate, 2-(0-[1'methylpropylideneamino]carboxyamino)ethyl methacrylate, etc. Among these, 2-isocyanatoethyl(meth)acrylate is preferred.

[0070] The monofunctional (meth)acrylic oligomer typically has a weight-average molecular weight (Mw) of 5,000 or more, more preferably 7,000 or more, and even more preferably 9,000 or more. The upper limit is not particularly limited, but is, for example, 100,000. If the monofunctional (meth)acrylic oligomer is a compound having such a weight-average molecular weight, it tends to be possible to suppress changes over time, such as bleed-out, while maintaining compatibility with the (meth)acrylic copolymer (A). The weight-average molecular weight of the photocurable compound (B) can be measured, if necessary, using the same method for measuring the weight-average molecular weight of the (meth)acrylic copolymer (A).

[0071] The monofunctional (meth)acrylic oligomer may be used in combination with a polyfunctional (meth)acrylic oligomer, as described below. In this case, the average number of (meth)acryloyl groups in the (meth)acrylic oligomer component is not particularly limited, but is typically about 1.1 to 4, preferably about 1.2 to 3. By having the average number of (meth)acryloyl groups in this range, it is possible to form an appropriate crosslinked structure in the pressure-sensitive adhesive while maintaining flexibility and adhesion to the substrate. The average number of (meth)acryloyl groups refers to the average number of (meth)acryloyl groups present in one molecule of the (meth)acrylic oligomer.

[0072] The monofunctional (meth)acrylic oligomer has a glass transition temperature (Tg) after photocuring of usually −20° C. or lower, preferably −30° C. or lower, and more preferably −40° C. or lower. The lower limit of the glass transition temperature (Tg) is not particularly limited, but is, for example, −100° C. When the monofunctional (meth)acrylic oligomer has a glass transition temperature (Tg) within this range, it is possible to obtain a pressure-sensitive adhesive sheet that is imparted with flexibility that can withstand buckling during bending deformation and also has restoring properties.

[0073] The glass transition temperature (Tg) of the monofunctional (meth)acrylic oligomer after photocuring can be determined by adding 3 parts by mass of a photopolymerization initiator to 100 parts by mass of the monofunctional (meth)acrylic oligomer to form a resin composition, and applying an integrated light intensity of 1000 mJ / cm at a wavelength of 365 nm. 2The glass transition temperature (Tg) after curing by irradiation with ultraviolet light is defined as follows:

[0074] In the present invention, the term "photocurable" refers to reactivity (curability) to radiation in general. Specifically, it refers to the property of being cured by light in the wavelength range of 200 nm to 780 nm, and is preferably used to mean reactivity (curability) to ultraviolet light in particular.

[0075] Examples of the polyfunctional (meth)acrylic monomer 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 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, dipentaerythritol Examples of the di(meth)acrylate include trimethylolpropane tri(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 polyethoxy tri(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate.Among these, polyfunctional (meth)acrylic monomers having a polyalkylene oxide skeleton, such as polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate, are preferred from the viewpoint of imparting appropriate toughness to the cured product.

[0076] The weight average molecular weight of the polyfunctional (meth)acrylic monomer is usually 100 or more, preferably 200 or more, and more preferably 250 or more, from the viewpoint of imparting appropriate flexibility to the cured product. The upper limit is usually 1,000.

[0077] Furthermore, when the pressure-sensitive adhesive composition is cured with visible light, a cured product with high toughness can be obtained, in other words, a cured product with appropriate flexibility can be obtained. Therefore, a polyfunctional (meth)acrylic oligomer is preferred as the photocurable compound (B).

[0078] Examples of the polyfunctional (meth)acrylic oligomer include polyfunctional polyester (meth)acrylate oligomers, polyfunctional epoxy (meth)acrylate oligomers, polyfunctional urethane (meth)acrylate oligomers, polyfunctional polyether (meth)acrylate oligomers, etc. Among these, polyfunctional urethane (meth)acrylate oligomers are preferred from the viewpoint of imparting appropriate toughness to the cured product.

[0079] The polyfunctional urethane (meth)acrylate oligomer can be obtained, for example, by reacting a compound containing isocyanate groups at both ends, which is obtained by reacting a polyol with a polyisocyanate, with a hydroxyl group-containing (meth)acrylate.

[0080] Examples of the polyol include the polyols described above. These may be used alone or in combination of two or more. Among these, polyether polyols are preferred, and polypropylene glycol is particularly preferred.

[0081] Examples of the polyisocyanate include the polyisocyanates described above. These may be used alone or in combination of two or more kinds.

[0082] Examples of the hydroxyl group-containing (meth)acrylate include the hydroxyl group-containing (meth)acrylates described above in connection with the (meth)acrylic copolymer (A). These may be used alone or in combination of two or more. Among these, primary hydroxyl group-containing (meth)acrylates are preferred, and 2-hydroxyethyl (meth)acrylate is more preferred.

[0083] The polyfunctional urethane (meth)acrylate oligomer is preferably a polyfunctional urethane (meth)acrylate oligomer having a polyalkylene oxide skeleton, and particularly preferably a polyfunctional urethane (meth)acrylate oligomer having a propylene glycol skeleton.

[0084] The weight average molecular weight of the polyfunctional (meth)acrylic oligomer is usually 3000 or more, preferably 5000 or more, more preferably 8000 or more, and particularly preferably 10000 or more. The upper limit of the weight average molecular weight is usually 100,000.

[0085] The content of the photocurable compound (B) is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 4 parts by mass or more, and particularly preferably 10 parts by mass or more, relative to 100 parts by mass 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. With regard to the upper limit of the content of the photocurable compound (B), from the viewpoint of ensuring adhesiveness, it is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less, relative to 100 parts by mass of the (meth)acrylic copolymer (A).

[0086] In addition to the photocurable compound (B), a thermal crosslinking agent can be used in combination to further improve crosslink density and long-term reliability. Examples of such thermal crosslinking agents 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, and metal chelate-based crosslinking agents. Among these, it is preferable to use an isocyanate-based crosslinking agent because of its excellent reactivity with the (meth)acrylic copolymer (A).

[0087] [Photopolymerization initiator (C)] The photopolymerization initiator (C) may be any compound that generates radicals when exposed to active energy rays. The photopolymerization initiator (C) is broadly classified into two types based on the radical generation mechanism: a cleavage-type photopolymerization initiator that can generate radicals by cleaving and decomposing the single bond of the initiator itself, and a hydrogen abstraction-type photopolymerization initiator that can transfer hydrogen from the hydrogen donor by forming an exciplex between the excited initiator and a hydrogen donor in the system.

[0088] The photopolymerization initiator (C) may be either a cleavage-type photopolymerization initiator or a hydrogen-abstraction-type photopolymerization initiator, and either one may be used alone or a mixture of the two may be used. Furthermore, one or more types of each may be used in combination.

[0089] In the present invention, it is preferable to use a hydrogen abstraction type 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 carried out.

[0090] 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.

[0091] 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.

[0092] The content of the photopolymerization initiator (C) is usually 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass, and more preferably 1 to 3 parts by mass, relative to 100 parts by mass 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, deterioration in solution stability, such as precipitation from the pressure-sensitive adhesive composition, tends to be easily suppressed, and problems such as embrittlement and coloration tend to be easily suppressed.

[0093] The pressure-sensitive adhesive composition contains a (meth)acrylic copolymer (A), a photocurable compound (B), and a photopolymerization initiator (C), and preferably further contains a silane coupling agent (D). The pressure-sensitive adhesive composition may also contain other components described below.

[0094] [Silane coupling agent (D)] Silane coupling agent (D) is the organosilicon compound, which contains reactive functional group and alkoxy group bonded with silicon atom in its structure.As the reactive functional group, for example, epoxy group, (meth)acryloyl group, mercapto group, hydroxyl group, carboxyl group, amino group, amide group, isocyanate group can be listed, among these, epoxy group and mercapto group are preferred from the viewpoint of balance of durability.

[0095] The alkoxy group bonded to the silicon atom preferably contains an alkoxy group having 1 to 8 carbon atoms, particularly preferably a methoxy group or an ethoxy group, from the viewpoints of durability and storage stability. The silane coupling agent (D) 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.

[0096] Examples of the silane coupling agent (D) 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 of suitable silane coupling agents include vinyl group-containing silane coupling agents such as vinyltrimethoxysilane and vinyltriethoxysilane. These may be used alone or in combination of two or more.

[0097] Among these, epoxy group-containing silane coupling agents and mercapto group-containing silane coupling agents are preferably used because of their excellent durability, and among these, epoxy group-containing silane coupling agents are preferred, with 3-glycidoxypropyltrimethoxysilane being particularly preferred.

[0098] The content of the silane coupling agent (D) is preferably 0.005 to 10 parts by mass, particularly preferably 0.01 to 5 parts by mass, and even more preferably 0.05 to 1 part by mass, relative to 100 parts by mass of the (meth)acrylic copolymer (A). When the content is equal to or greater than the lower limit, durability tends to be improved, whereas when the content is equal to or less than the upper limit, durability tends to be improved.

[0099] [Other Components] The pressure-sensitive adhesive composition may contain various additives such as plasticizers, UV absorbers, rust inhibitors, tackifier resins, antioxidants, light stabilizers, metal deactivators, anti-aging agents, moisture absorbers, rust inhibitors, and inorganic particles as "other components" as needed, to the extent that the effects of the present invention are not impaired. Furthermore, the pressure-sensitive adhesive composition may contain reaction catalysts such as tertiary amine compounds, quaternary ammonium compounds, and tin laurate compounds as needed. These may be used alone or in combination of two or more.

[0100] (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 these, urethane (meth)acrylate oligomers are preferred from the viewpoint of imparting appropriate toughness to the cured product.

[0101] (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 may be used alone or in combination of two or more.

[0102] The content of the ultraviolet absorber is preferably 0.01 to 20 parts by mass, particularly preferably 0.1 to 15 parts by mass, and even more preferably 0.5 to 10 parts by mass, relative to 100 parts by mass of the (meth)acrylic copolymer (A). When the content is equal to or greater than the lower limit, lightfastness reliability tends to improve, while when the content is equal to or less than the upper limit, yellowing resistance tends to improve.

[0103] (Rust inhibitor) As the rust inhibitor, for example, triazoles, benzotriazoles, etc. are preferred, which can prevent corrosion of optical components. The content of the rust inhibitor is preferably 0.01 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (A).

[0104] The content of the other components is preferably 5 parts by mass or less, particularly preferably 1 part by mass or less, and even more preferably 0.5 parts by mass or less, per 100 parts by mass of the (meth)acrylic copolymer (A), and the lower limit is usually 0 part by mass. If the content is too high, the compatibility with the (meth)acrylic copolymer (A) decreases, and transparency and durability tend to decrease.

[0105] The pressure-sensitive adhesive composition is prepared by mixing predetermined amounts of the (meth)acrylic copolymer (A), the photocurable compound (B), and the photopolymerization initiator (C), preferably the silane coupling agent (D), and other components as needed. The pressure-sensitive adhesive composition thus obtained can be used for pressure-sensitive adhesive sheets, particularly pressure-sensitive adhesive sheets for components of flexible image display devices.

[0106] <Adhesive Sheet> The adhesive sheet and adhesive sheet for a component of a flexible image display device according to one embodiment of the present invention (hereinafter sometimes collectively referred to as "the adhesive sheet") can be produced, for example, as follows, although the method is not limited to this.

[0107] In producing the present pressure-sensitive adhesive sheet, a pressure-sensitive adhesive composition containing the (meth)acrylic copolymer (A), the photocurable compound (B), the photopolymerization initiator (C), preferably the silane coupling agent (D), and other components as necessary is prepared, the pressure-sensitive adhesive composition is formed into a sheet, crosslinked, i.e., polymerized, to harden the composition, and then processed appropriately as necessary to produce the present pressure-sensitive adhesive sheet.

[0108] When preparing the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive sheet, the raw materials may be kneaded using a temperature-controllable kneader (for example, a single-screw extruder, a twin-screw extruder, a planetary mixer, a twin-screw mixer, a pressure kneader, etc.). When mixing the various raw materials, various additives such as the silane coupling agent (D) and the antioxidant may be blended together with the resin in advance and then fed to the kneader, or all of the materials may be melt-mixed in advance and then fed, or a masterbatch in which only the additives are concentrated in the resin may be prepared and then fed.

[0109] Next, the obtained adhesive composition is dissolved in an appropriate solvent, and the adhesive composition is formed into a sheet using various coating methods.

[0110] The solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition, 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 these, ethyl acetate, acetone, methyl ethyl ketone, and toluene are more preferred in terms of solubility, drying properties, cost, and the like, and ethyl acetate is particularly preferred.

[0111] In terms of drying property, the content of the solvent is preferably 600 parts by mass or less, more preferably 500 parts by mass or less, even more preferably 400 parts by mass or less, and particularly preferably 350 parts by mass or less, relative to 100 parts by mass of the (meth)acrylic copolymer (A), while it is preferably 1 part by mass or more, more preferably 50 parts by mass or more, even more preferably 100 parts by mass or more, and particularly preferably 150 parts by mass or more.

[0112] The present pressure-sensitive adhesive sheet can be formed by dissolving the pressure-sensitive adhesive composition in a solvent, coating the composition on a release film, drying, and curing by irradiation with active energy rays. That is, the present pressure-sensitive adhesive sheet is preferably a pressure-sensitive adhesive sheet with a release film having a configuration in which the present pressure-sensitive adhesive sheet and a release film are laminated together.

[0113] As the release film, any known release film can be used as appropriate. Examples of the material for the release film include a polyester film, a polyolefin film, a polycarbonate film, a polystyrene film, an acrylic film, a triacetyl cellulose film, a fluororesin film, or the like, which has been subjected to a release treatment by coating with a silicone resin, and release paper, etc.

[0114] The thickness of the release film is not particularly limited. Among them, from the viewpoint of processability and handling, for example, it is preferably 10 to 250 μm, more preferably 25 to 200 μm, and even more preferably 35 to 190 μm.

[0115] Furthermore, the release film may be embossed or processed to have various irregularities (such as a conical, pyramidal, or hemispherical shape) as needed. Furthermore, the release film may be subjected to various surface treatments such as corona treatment, plasma treatment, and primer treatment in order to improve adhesion to various component sheets.

[0116] The coating method may be a conventional method such as roll coating, die coating, gravure coating, comma coating, screen printing, or bar coating.

[0117] Furthermore, the coating is preferably carried out so that the thickness of the pressure-sensitive adhesive composition after drying is 1 to 200 μm, more preferably 5 to 100 μm, and even more preferably 10 to 50 μm, in order to effectively exert the effects of the present invention.

[0118] 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.

[0119] 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. When the temperature is within this range, the solvent can be removed efficiently and relatively safely while suppressing thermal deformation of the release film.

[0120] 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.

[0121] In the drying, the solvent content after drying is preferably 1% by mass or less, more preferably 0.5% by mass or less, particularly preferably 0.1% by mass or less, and most preferably 0% by mass.

[0122] The irradiation energy, irradiation time, irradiation method, etc. of the active energy ray irradiation are not particularly limited as long as they can activate the photopolymerization initiator (C) and polymerize the monomer components. When a hydrogen abstraction photopolymerization initiator is used as the photopolymerization initiator (C), a hydrogen abstraction reaction also occurs from the (meth)acrylic copolymer (A), and the (meth)acrylic copolymer (A) is incorporated into the crosslinked structure, forming a crosslinked structure with many crosslinking points. Therefore, it is preferable that the pressure-sensitive adhesive sheet is cured using a hydrogen abstraction photopolymerization initiator.

[0123] 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, as well as 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 from the viewpoints of curing speed, ease of availability of an irradiation device, cost, and the like.

[0124] 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, all of which emit light in the wavelength range of 150 to 450 nm. Of these, it is preferable to use a high-pressure mercury lamp.

[0125] 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 , more preferably 300 to 1500 mJ / cm 2 After the irradiation of the active energy rays, the degree of cure can be increased by heating, if necessary.

[0126] The pressure-sensitive adhesive composition 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. The thickness of the pressure-sensitive adhesive sheet can be adjusted by the coating thickness and the solids concentration of the coating liquid.

[0127] The obtained pressure-sensitive adhesive sheet may be pre-cured by crosslinking with active energy rays so as to have latent active energy ray reactivity, in other words, so as to retain active energy ray reactivity. When pre-curing, each layer may be crosslinked with active energy rays by irradiating with active energy rays through the release film. In this case, the degree of active energy ray crosslinking (gel fraction) can be adjusted by controlling the amount of active energy ray irradiation, but as mentioned above, it is also possible to adjust the degree of active energy ray crosslinking (gel fraction) by irradiating with ultraviolet rays through the release film so as to partially block the active energy rays.

[0128] The present pressure-sensitive adhesive sheet may further be laminated with a release film, if necessary. In this case, the pressure-sensitive adhesive composition may be coated onto a release film, dried, and then cured by irradiation with active energy rays, and a release film may be laminated thereon. Alternatively, the present pressure-sensitive adhesive sheet may be formed by coating the pressure-sensitive adhesive composition onto a release film, drying it, laminating a release film, and then curing it by irradiation with active energy rays.

[0129] When the present pressure-sensitive adhesive sheet is produced using the above-mentioned coating method, the present pressure-sensitive adhesive sheet can also be obtained by heat curing in addition to the above-mentioned curing by irradiation with active energy rays.

[0130] In another embodiment of the present invention, the pressure-sensitive adhesive sheet can be produced by forming the pressure-sensitive adhesive composition into a sheet, using known methods such as wet lamination, dry lamination, extrusion casting using a T-die, extrusion lamination, calendaring, inflation, injection molding, and liquid injection curing. Of these, when producing a sheet, wet lamination, extrusion casting, and extrusion lamination are preferred.

[0131] Furthermore, the pressure-sensitive adhesive sheet may be formed by preparing the pressure-sensitive adhesive composition, coating it onto a surface protection film or a component of an image display device, which will be described later, and then curing the pressure-sensitive adhesive composition.

[0132] The gel fraction of the pressure-sensitive adhesive sheet is preferably 30 to 95% by mass, more preferably 35 to 90% by mass, and even more preferably 40 to 85% by mass. A gel fraction equal to or greater than the lower limit mentioned above tends to reduce the risk of adhesive overflow over time, which is preferable. The gel fraction is an indicator of the degree of crosslinking (degree of cure) and can be measured under the measurement conditions described in the Examples below.

[0133] The adhesive strength (A) of this pressure-sensitive adhesive sheet to a polyimide film surface [23°C, 50% RH, peel angle: 180°, peel rate: 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 (A) can be measured under the measurement conditions described in the Examples below.

[0134] Furthermore, when a 1:1 mixture of oleic acid and squalene (artificial sebum liquid) is dropped onto the pressure-sensitive adhesive sheet and the sheet is stored at 23°C and 50% RH for 5 days, the adhesive strength (B) to a polyimide film surface [23°C, 50% RH, peel angle: 180°, peel rate: 300 mm / min] is preferably 3 to 20 N / cm, more preferably 4 to 15 N / cm, and even more preferably 4.5 to 10 N / cm. Within this range, the sheet has sufficient resistance to oil, making it suitable for use as a pressure-sensitive adhesive sheet for components of flexible image display devices. The adhesive strength (B) can be measured under the measurement conditions described in the Examples below.

[0135] The oil-resistant adhesion ratio (X) of the pressure-sensitive adhesive sheet is preferably 84% or more, and more preferably 85% or more. The oil-resistant adhesion ratio (X) can be calculated using the following formula: Oil-resistant adhesion ratio (X) = [Adhesive strength (B) / Adhesive strength (A)] x 100

[0136] 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 typically −50°C. By including the (meth)acrylic copolymer (A) containing a predetermined amount of structural units derived from the alkyl (meth)acrylate (a1), the pressure-sensitive adhesive sheet tends to have excellent oil resistance but insufficient flexibility. However, in the present invention, by setting the glass transition temperature of the pressure-sensitive adhesive sheet within the above range, excellent flexibility can be obtained while maintaining oil resistance. The glass transition temperature (Tg) can be measured under the measurement conditions described in the Examples below.

[0137] The pressure-sensitive adhesive sheet has a storage shear modulus (G') at -20°C of 800 kPa or less. Having a storage shear modulus (G') at -20°C of 800 kPa or less allows for flex resistance at low temperatures (e.g., -20°C). From this perspective, it is preferably 700 kPa, and more preferably 600 kPa or less. Furthermore, the storage shear modulus (G') at -20°C of the pressure-sensitive adhesive sheet is preferably 500 kPa or less, and 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 or more, from the viewpoint 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. By containing the (meth)acrylic copolymer (A) containing a predetermined amount of structural units derived from the alkyl (meth)acrylate (a1), the pressure-sensitive adhesive sheet has excellent oil resistance, but tends to have insufficient flexibility. However, in the present invention, by setting the storage shear modulus (G') at -20°C of the pressure-sensitive adhesive sheet within the above range, it is possible to obtain excellent flexibility while maintaining oil resistance.

[0138] The storage shear modulus (G') of this pressure-sensitive adhesive sheet at 25°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 adhesion. The lower limit is preferably 1 kPa or more, from the viewpoint 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.

[0139] 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 recovery can be measured under the measurement conditions described in the Examples below.

[0140] The pressure-sensitive adhesive sheet is preferably transparent. Being transparent allows for an excellent appearance to be obtained without impairing the visibility of the image display surface. The pressure-sensitive adhesive sheet being transparent means that the pressure-sensitive adhesive sheet has a total light transmittance of 50% or more as measured in accordance with JIS K7361-1 (ISO-13468-1) and a haze value of 10% or less as measured in accordance with JIS K7136 (ISO-14782).

[0141] The total light transmittance of the pressure-sensitive adhesive sheet measured in accordance with JIS K7361-1 (ISO-13468-1) is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more, from the viewpoint of usefulness in applications requiring transparency, such as image display devices. The upper limit is preferably as high as possible, and is not particularly limited.

[0142] The haze of the pressure-sensitive adhesive sheet, measured in accordance with JIS K7136 (ISO-14782), is preferably 5% or less, more preferably 3% or less, even more preferably 2% or less, and particularly preferably 1% or less, from the viewpoint of usefulness in applications requiring transparency, such as image display devices. The lower the lower limit, the better, and there are no particular limitations.

[0143] Methods for adjusting the total light transmittance and haze include, for example, adjusting the composition of the (meth)acrylic copolymer (A) and the photocurable compound (B), using a colorless photopolymerization initiator (C), or eliminating the inclusion of colorants, particles, etc. Furthermore, coloring due to heating or deterioration over time may be suppressed by using an antioxidant. However, the methods are not limited to these.

[0144] The pressure-sensitive adhesive sheet thus obtained can be laminated with components of an image display device to form a laminate for a flexible image display device (hereinafter also referred to as "the laminate"). In this case, "image display device components" include, for example, 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 with two or more of these components, or a surface protective film. In addition to the above components, other layers may be interposed as needed, 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 planarizing layer.

[0145] 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 typically 9 GPa. Within this range, sufficient scratch resistance and impact resistance can be obtained when the surface protection film is formed into a laminate for a flexible image display device component. Furthermore, the surface protection film is preferably a member 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. This is preferable because, when the surface protection film is formed into a laminate for a flexible image display device component, creases and delamination are less likely to occur at the bent portions.

[0146] In the present invention, the surface hardness of the surface protection film is evaluated by nanoindentation. Generally, the nanoindentation method is a technique in which the indenter of a nanoindenter is pressed into a sample to a predetermined depth (contact depth) with a constant load (load), and then the indenter is pulled up until it separates from the sample (unload), and the mechanical properties of the sample surface are analyzed from the relationship between the displacement and load at this time (load-displacement curve). The surface hardness in the present invention is 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) (Measurement conditions) Measuring device: TI980 manufactured by Bruker Maximum load: 1000 uN Indenter material: Diamond Indenter shape: Berkovich Applied load: 1 mN Contact depth: 300 nm

[0147] 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.

[0148] The member may have a coating layer on its 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.

[0149] Examples of the layer structure of the laminate of the surface protection film and the pressure-sensitive adhesive sheet include, but are not limited to, the following structures: (Viewing side) hard coat / polyimide film / adhesive sheet (organic EL side) (surface hardness: 906 MPa) (Viewing side) hard coat / PET film / adhesive sheet (organic EL side) (surface hardness: 418 MPa) (Viewing side) hard coat / PET film / adhesive sheet / glass (organic EL side) (surface hardness: 376 MPa) (Viewing side) hard coat / PET film / adhesive sheet (organic EL side) (surface hardness: 484 MPa)

[0150] When the laminate for flexible image display device components is subjected to a dynamic bending reliability test in which 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, it is preferable that the laminate can be bent 40,000 times or more without causing defects (delamination, breakage, buckling, flow) at the bent portion, and more preferably the laminate can be bent 100,000 times or more.

[0151] Furthermore, when the laminate for flexible image display device components is subjected to a dynamic bending reliability test in which 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., it is preferable that the number of bending cycles at which defects (delamination, breakage, buckling, flow) at the bent portion do not occur is 40,000 or more, and more preferably 100,000 or more.

[0152] Furthermore, as a reliability test for static bending of a laminate for a flexible image display device component, the laminate 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.

[0153] <Flexible image display device> Examples of flexible image display devices include a configuration in which the present laminate is incorporated into the housing of a flexible image display device, and an image display device having a structure in which the present laminate, which is composed of a laminated structure of the present pressure-sensitive adhesive sheet and the surface protection film, is laminated on the viewing side surface of the image display device.

[0154] 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.

[0155] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.

[0156] Example 1 A (meth)acrylic copolymer (A-1) was obtained by random copolymerization of 40 parts by mass of n-butyl acrylate (homopolymer Tg: −55° C.) as the alkyl (meth)acrylate (a1), 40 parts by mass of 2-ethylhexyl acrylate (homopolymer Tg: −70° C.) as the (meth)acrylate (a2) having a lower glass transition temperature when made into a homopolymer than the alkyl (meth)acrylate (a1), 17.5 parts by mass of hydroxyethyl acrylate (Tg: −15° C.) as the polar group-containing monomer (a3), and 2.5 parts by mass of methyl acrylate (Tg: 10° C.). A solution of a pressure-sensitive adhesive composition was prepared by uniformly mixing 100 parts by mass of the obtained (meth)acrylate copolymer (A-1), 25 parts by mass of a urethane acrylate oligomer (LD301, manufactured by AGC, weight average molecular weight: approximately 10,000, Tg: -63°C) mainly composed of a monofunctional urethane acrylate having a propylene glycol skeleton as the photocurable compound (B), 3 parts by mass of a mixture of 4-methylbenzophenone and 2,4,6-trimethylbenzophenone (ESACURE TZT, manufactured by IGM) as the photopolymerization initiator (C), 0.3 parts by mass of a silane coupling agent (D) (KBM403, manufactured by Shin-Etsu Silicones Co., Ltd.), and 200 parts by mass of ethyl acetate as the solvent.

[0157] The solution of the pressure-sensitive adhesive composition 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 25 μm. After coating, the film was placed in a dryer heated to 90°C and held for 10 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. A high-pressure mercury lamp was used to irradiate the laminate with an integrated light intensity of 500 mJ / cm at a wavelength of 365 nm. 2 The adhesive sheet was irradiated with ultraviolet light through the release film so that the adhesive sheet was adhered to the release film.

[0158] Examples 2 to 4, Comparative Examples 1 and 2 Pressure-sensitive adhesive sheets were produced in the same manner as in Example 1, except that (meth)acrylic copolymers (A-2) to (A-6) having structural units as shown in Table 1 below were used instead of the (meth)acrylic copolymer (A-1).

[0159] Comparative Example 3 A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that a (meth)acrylic copolymer (A-7) having a structural unit as shown in Table 1 below was used and the amount of the photocurable compound (B) was 10 parts by mass.

[0160] [Evaluation of Pressure-Sensitive Adhesive Sheets] The pressure-sensitive adhesive sheets obtained in the examples and comparative examples were measured and evaluated as follows. The results are shown in Table 1 below, together with the formulations of the pressure-sensitive adhesive compositions used in Examples 1 to 4 and Comparative Examples 1 to 3.

[0161] [Gel Fraction] The release film was removed from each pressure-sensitive adhesive sheet produced in the Examples and Comparative Examples, and multiple pressure-sensitive adhesive sheets were laminated to a thickness of 1 mm. A cylindrical object with a diameter of 8 mm was then punched out. This was used as a sample, wrapped in a 200-mesh SUS wire mesh, and immersed in ethyl acetate adjusted to 23°C for 72 hours. After drying at 75°C for 4.5 hours, the mass of the pressure-sensitive adhesive before and after immersion in ethyl acetate was measured, and the difference between the two masses was taken as the mass of the insoluble pressure-sensitive adhesive remaining in the wire mesh. The mass percentage of the insoluble pressure-sensitive adhesive remaining in the wire mesh relative to the mass of the pressure-sensitive adhesive before immersion in ethyl acetate was calculated as the gel fraction.

[0162] [Glass Transition Temperature (Tg), Storage Modulus (G')] The release film was removed from each pressure-sensitive adhesive sheet produced in the Examples and Comparative Examples, and multiple layers of pressure-sensitive adhesive sheets were laminated to form a 1.0 mm thick laminate. From the resulting pressure-sensitive adhesive sheet laminate, a cylindrical object with a diameter of 8 mm (height of 1.0 mm) was punched out, and this was used as a sample. For this sample, the temperature dispersion of dynamic viscoelasticity was measured under the following measurement conditions using a viscoelasticity measuring device (DHR 2, manufactured by T.A. Instruments). From the obtained temperature dispersion data of dynamic viscoelasticity, the peak temperature of the loss tangent (tan δ) was read as the glass transition temperature (Tg). In addition, the storage shear modulus (G') at -20°C and 25°C was read. (Measurement Conditions) - Measurement jig: Φ8 mm parallel plate - Strain: 0.1% - Frequency: 1 Hz - Measurement temperature: -60 to 100°C - Heating rate: 5°C / min

[0163] [Adhesive Strength] One release film was removed from each of the pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples, and a polyethylene terephthalate film (Mitsubishi Chemical Corporation, S100, thickness 50 μm) was roll-laminated as a backing film to the adhesive surface of the pressure-sensitive adhesive sheet using a hand roller. This was cut into 10 mm wide x 150 mm long strips, and the remaining release film was peeled off, and the exposed adhesive surface was roll-laminated using a hand roller to a transparent polyimide film (main component: transparent polyimide, KOLON Corporation, C50, hereinafter referred to as "CPI film") that had been previously laminated to a glass plate, to produce a laminate consisting of CPI film / pressure-sensitive adhesive sheet / backing film.

[0164] The laminate was left to stand for 5 days at room temperature (23°C, 50% RH) to cure, and then the backing film was peeled off at an angle of 180° to the CPI film at a peeling rate of 300 mm / min, and the tensile strength was measured with a load cell to determine the 180° peel strength (N / cm) of the adhesive sheet against the CPI film, which was defined as the adhesive strength (A).

[0165] A laminate consisting of a CPI film / adhesive sheet / backing film was prepared using the same procedure as for preparing the adhesive strength measurement sample. A 1:1 oleic acid:squalene mixture (referred to as "artificial sebum liquid") was dropped onto both longitudinal ends of the adhesive sheet of the laminate at 1 μL / cm, and the laminate was left to stand at room temperature (23°C, 50% RH) for 5 days to age. The backing film was then peeled off at an angle of 180° to the CPI film at a peeling rate of 300 mm / min, and the tensile strength was measured using a load cell. The 180° peel strength (N / cm) of the adhesive sheet relative to the CPI film was measured and recorded as adhesive strength (B).

[0166] [Oil-resistant Adhesion Ratio] Using the values ​​of adhesive strength (A) and adhesive strength (B) measured in the adhesive strength test, the oil-resistant adhesion ratio (X) was calculated according to the following formula: Oil-resistant adhesion ratio (X) [%] = (B / A) x 100

[0167] [Restoration Rate (Constant Stress)] The release film was removed from each of the pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples, and multiple layers of pressure-sensitive adhesive sheets were laminated to form a 1.0 mm thick laminate. A cylindrical object with a diameter of 8 mm (height of 1.0 mm) was punched out from the resulting pressure-sensitive adhesive sheet laminate to serve as a sample. The maximum strain value (ε ) of this sample after applying a stress of 20 kPa at 25°C for 10 minutes was measured using a viscoelasticity measuring device (DHR 2, manufactured by T.A. Instruments). max The recovery rate was measured by reading the residual strain value 10 minutes after the stress was removed from the test piece. The recovery rate was calculated using the following formula: Recovery rate (%) = [(ε max -residual strain value) / ε max ]×100

[0168] [Flexural durability] The release film was removed from each of the pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples, and a polyethylene terephthalate film (manufactured by Mitsubishi Chemical Corporation, S100, thickness 50 μm) and a CPI film (main component: transparent polyimide, manufactured by KOLON Corporation, C50, thickness 50 μm) were bonded to the surface of the pressure-sensitive adhesive sheet using a hand roll to obtain a laminated sheet (sample) for flexural durability.

[0169] The laminated sheet (sample) was subjected to a U-bending cycle evaluation under conditions of 25°C or -20°C using a thermo-hygrostat durability system and a sheet-shaped no-load U-bending tester (manufactured by Yuasa System Co., Ltd.) with a curvature radius R of 3 mm and 60 rpm (1 Hz). The number of cycles evaluated was 40,000. The evaluation was based on the following evaluation criteria: ○ (Very good): No delamination, breakage, buckling, or flow occurred at the bent portion. × (Poor): Any of delamination, breakage, buckling, or flow occurred at the bent portion.

[0170]

[0171] As can be seen from Table 1, the pressure-sensitive adhesive sheets of Examples 1 to 4 were excellent in flexibility and oil resistance. On the other hand, the pressure-sensitive adhesive sheet of Comparative Example 1, which did not contain alkyl(meth)acrylate (a1), and the pressure-sensitive adhesive sheet of Comparative Example 2, which contained too much structural units derived from alkyl(meth)acrylate (a1), were excellent in flexibility but poor in oil resistance. The pressure-sensitive adhesive sheet of Comparative Example 3 was excellent in oil resistance, but had a high storage shear modulus (G') at -20°C and poor in flexural durability at low temperatures.

[0172] Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are all intended to fall within the scope of the present invention.

[0173] The pressure-sensitive adhesive sheet of the present invention, particularly the pressure-sensitive adhesive sheet for flexible image displays, has surface protection function and flexibility such as reliability against bending (bending durability) while being attached to an image display device and in use, and furthermore, it is possible to obtain a laminate for a surface protection film that is excellent in oil resistance. Therefore, the obtained laminate for a surface protection film is useful as a laminate for a surface protection film for various flexible image displays such as bendable, foldable, rollable, and stretchable, and is particularly suitable as a laminate for a surface protection film for a foldable image display device that is repeatedly bent.

Claims

1. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition including a (meth)acrylic copolymer (A), a photocurable compound (B), and a photopolymerization initiator (C), the (meth)acrylic copolymer (A) comprises a structural unit derived from an alkyl (meth)acrylate (a1) having a linear and / or branched alkyl group having 3 to 6 carbon atoms, and a structural unit derived from a (meth)acrylate (a2) having a lower glass transition temperature when formed into a homopolymer than the alkyl (meth)acrylate (a1); the proportion of the structural units derived from the alkyl (meth)acrylate (a1) relative to 100% by mass of all structural units constituting the (meth)acrylic copolymer (A) is 20% by mass or more and 60% by mass or less; the mass ratio (W(a2) / W(a1)) of the content of the structural units derived from the (meth)acrylate (a2) to the structural units derived from the alkyl (meth)acrylate (a1) is 0.3 to 3.0; The pressure-sensitive adhesive sheet has a storage shear modulus (G') at -20°C of 800 kPa or less.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the (meth)acrylic copolymer (A) further contains a structural unit derived from a polar group-containing monomer (a3).

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

4. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the photocurable compound (B) is a (meth)acrylate having a polyalkylene oxide skeleton.

5. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive composition further comprises a silane coupling agent (D).

6. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive sheet has a storage shear modulus (G') at -20°C of 500 kPa or less.

7. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive sheet has a gel fraction of 30 to 95% by mass.

8. 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the oil-resistant adhesion rate (X) calculated by the following formula is 84% ​​or more. X (%) = (B / A) x 100 A: The adhesive sheet was cut to a width of 10 mm and a length of 150 mm, and the cut piece was attached to a polyimide film. The adhesive strength to the surface of the polyimide film was measured at 23°C, 50% RH, at a peel angle of 180°, and at a peel rate of 300 mm / min. B: An adhesive sheet was cut to a width of 10 mm and a length of 150 mm and attached to a polyimide film. A mixed liquid (artificial sebum liquid) of oleic acid:squalene = 1:1 was dropped onto both longitudinal ends of the adhesive sheet at 1 μL / cm, and the sheet was stored at 23°C and 50% RH for 5 days. The adhesive strength to the surface of the polyimide film was measured when the sheet was peeled off at a peel angle of 180° and a peel rate of 300 mm / min.

9. The pressure-sensitive adhesive sheet according to claim 1 or 2, which is transparent.

10. 3. The pressure-sensitive adhesive sheet according to claim 1, which has a total light transmittance of 80% or more and a haze of 5% or less.

11. 3. The pressure-sensitive adhesive sheet according to claim 1, which is used as a component of a flexible image display device.

12. 3. A pressure-sensitive adhesive sheet with a release film, comprising the pressure-sensitive adhesive sheet according to claim 1 or 2 laminated with a release film.

13. 3. A pressure-sensitive adhesive sheet for use as a component of a flexible image display device, comprising the pressure-sensitive adhesive sheet according to claim 1 or 2.

14. 14. The pressure-sensitive adhesive sheet for a component of a flexible image display device according to claim 13, wherein the component of the flexible image display device comprises any member selected from the group consisting of a polyethylene terephthalate film, a polyimide film, an aramid film, and a glass plate.

15. An adhesive sheet for a component of a flexible image display device, comprising the adhesive sheet with release film according to claim 12.

16. An adhesive sheet for flexible image display device components as described in Claim 15, wherein the flexible image display device components include any one of polyethylene terephthalate film, polyimide film, aramid film, and glass plate.