Pressure-sensitive adhesive sheet, pressure-sensitive adhesive sheet equipped with release film, laminate for image display device, flexible image display device, and pressure-sensitive adhesive sheet for constituent member of flexible image display device

Abstract

Provided is a pressure-sensitive adhesive sheet having excellent adherability to a flexible member, especially a polyimide, and also having excellent flexibility.　Specifically provided is a pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive agent composition containing an acrylic polymer (A), a radical polymerizable compound (B), and a photopolymerization initiation agent (C), wherein the photopolymerization initiation agent (C) includes a hydrogen abstraction-type photopolymerization initiation agent (C1) and an α-aminoalkylphenone cleavage-type photopolymerization initiation agent (C2).

Description

Adhesive sheet, adhesive sheet with release film, laminate for image display device, flexible image display device, and adhesive sheet for flexible image display device constituent member

[0001] The present invention relates to an adhesive sheet, an adhesive sheet with a release film, a laminate for an image display device, a flexible image display device, 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.

[0002] In recent years, flexible image display devices using organic light-emitting diodes (OLEDs) and quantum dots (QDs) have been developed and are becoming widely commercialized. Flexible image display devices include bendable devices with a curved image display surface, foldable devices that can be repeatedly bent, rollable devices that can be rolled up, and stretchable devices that can be stretched and contracted. Such image display devices have a laminated structure in which multiple component sheets, such as a surface protection film, a cover lens, a circular polarizing plate, a touch film sensor, and a light-emitting element, are bonded together with a transparent adhesive sheet, and each of these laminated structures can be considered as a laminated sheet in which the component sheet and the adhesive sheet are stacked together.

[0003] Bendable flexible display devices have various issues due to interlayer stress when folded. For example, there is a need for a laminate sheet that quickly restores to a flat state when the screen is unfolded without any residual effects from being in a bent state. Furthermore, repeated folding operations can cause the adhesive sheet to peel off, or stress can be applied to the adherend, causing cracks and eventually fractures. Therefore, there is a need for a laminate sheet that is durable under repeated folding operations, particularly under harsh conditions such as low temperatures. The adhesive sheet in such flexible image display devices must have not only good optical properties but also flexibility, particularly high durability against bending.

[0004] 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.

[0005] JP 2020-196255 A International Publication No. 2018 / 173896

[0006] Flexible components for image display devices other than adhesive sheets are not only made of a wide variety of materials, but may also be surface-treated to prevent bending or breaking. Adhesive sheets for integrating such component sheets must have stable adhesive strength across a wide range of materials. However, the technologies disclosed in Patent Documents 1 and 2 do not take into consideration adhesive strength for flexible components.

[0007] Therefore, against this background, the present invention provides an adhesive sheet, an adhesive sheet with a release film, a flexible image display device, a laminate for an image display device, and an adhesive sheet for a flexible image display device, which have excellent adhesion to flexible materials, particularly polyimide, and also have excellent flexibility.

[0008] In view of these circumstances, the present inventors have found that a pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition containing a photopolymerization initiator comprising an acrylic polymer, a radically polymerizable compound, a hydrogen abstraction photopolymerization initiator, and an α-aminoalkylphenone cleavage photopolymerization initiator can be obtained, which has excellent adhesive strength to flexible members and also excellent flexibility.

[0009] That is, the present invention has the following aspects. [1] A pressure-sensitive adhesive sheet formed from a pressure-sensitive adhesive composition containing an acrylic polymer (A), a radically polymerizable compound (B), and a photopolymerization initiator (C), wherein the photopolymerization initiator (C) comprises a hydrogen abstraction photopolymerization initiator (C1) and an α-aminoalkylphenone cleavage-type photopolymerization initiator (C2). [2] The pressure-sensitive adhesive sheet according to [1], wherein the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) has a weight-average molecular weight of 800 or less. [3] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) contains a sulfur element. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3], wherein the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) has a maximum absorption wavelength in the 270 to 315 nm region of the light absorption spectrum. [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4], wherein the content of the photopolymerization initiator (C) is 0.1 to 10 parts by mass relative to 100 parts by mass of the acrylic polymer (A), and the content ratio (C1 / C2) of the hydrogen abstraction photopolymerization initiator (C1) to the α-aminoalkylphenone cleavage photopolymerization initiator (C2) is 0.5 to 10, in mass ratio. [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5], wherein the radical polymerizable compound (B) has an alkylene glycol skeleton. [7] The pressure-sensitive adhesive sheet according to any one of [1] to [6], wherein the radical polymerizable compound (B) has a urethane bond. [8] The pressure-sensitive adhesive sheet according to any one of [1] to [7], wherein the acrylic polymer (A) is an acrylic polymer having a structural moiety derived from a (meth)acrylate (a1) having an alkyl group with 3 or more carbon atoms in the alkyl group, and a structural moiety (a2) derived from a hydroxyl group-containing (meth)acrylate. [9] The pressure-sensitive adhesive sheet according to any one of [1] to [8], wherein the pressure-sensitive adhesive composition further comprises a polyfunctional epoxy compound (D).

[10] The pressure-sensitive adhesive sheet according to any one of [1] to [9], wherein the pressure-sensitive adhesive composition has a shear storage modulus (G'(25°C)) at 25°C of 60 kPa or less, as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz.

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

[10] , which has a shear storage modulus (G'(-30°C)) at -30°C of 1200 kPa or less, as obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz.

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

[11] , which has a glass transition temperature (Tg) defined as the maximum value of Tan δ of -20°C or less, as obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz.

[13] The pressure-sensitive adhesive sheet has a thickness of 0.5 to 1.2 mm, and has a strain (γ) after applying a 400% strain at 25°C for 600 seconds. max ) and the strain (γ min The pressure-sensitive adhesive sheet according to any one of [1] to

[12] , wherein the recovery rate calculated from the following formula using the pressure-sensitive adhesive sheet is 60% or more: Recovery rate (%) = [(γ max -γ min ) / γ max ] x 100

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

[13] , wherein the pressure-sensitive adhesive sheet has a gel fraction of 30 to 95 mass %.

[15] A pressure-sensitive adhesive sheet with a release film, comprising the pressure-sensitive adhesive sheet according to any one of [1] to

[14] and a release film laminated on the pressure-sensitive adhesive sheet.

[16] A laminate for an image display device, comprising two components of an image display device and the pressure-sensitive adhesive sheet according to any one of [1] to

[14] interposed between the two components of the image display device.

[17] A flexible image display device, comprising the laminate for an image display device according to

[16] .

[18] 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

[14] .

[0010] The pressure-sensitive adhesive sheet of the present invention has excellent adhesive strength to flexible materials, particularly polyimide, and also has excellent flexibility. In particular, the pressure-sensitive adhesive sheet has good adhesive strength not only at room temperature (23°C) but also at high temperatures (e.g., 40 to 80°C, particularly 50 to 70°C), and the change in adhesive strength between room temperature and high temperatures is small. Therefore, the pressure-sensitive adhesive sheet of the present invention can be suitably used as a pressure-sensitive adhesive sheet for flexible image display devices.

[0011] 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 this specification, 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.

[0012] In this specification, 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 includes the meaning of "preferably greater than x" or "preferably smaller than y." Furthermore, when it is stated that "x or more" (x is any number), it also includes the meaning of "preferably greater than x" unless otherwise specified, and when it is stated that "y or less" (y is any number), it also includes the meaning of "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. In this specification, "(meth)acrylic" means a comprehensive definition of acrylic and / or methacrylic, "(meth)acrylate" means a comprehensive definition of acrylate and / or methacrylate, and "(meth)acryloyl" means a comprehensive definition of acryloyl and / or methacryloyl. In addition, in this specification, 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 typically 40% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, particularly preferably 70% by mass or more, and may even be 100% by mass. Regarding the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range can also be replaced with the values ​​shown in the examples.

[0013] A pressure-sensitive adhesive sheet according to an embodiment of the present invention (hereinafter referred to as "the pressure-sensitive adhesive sheet") is formed from a pressure-sensitive adhesive composition containing an acrylic polymer (A), a radically polymerizable compound (B), and a photopolymerization initiator (C), wherein the photopolymerization initiator (C) contains a hydrogen abstraction photopolymerization initiator (C1) and an α-aminoalkylphenone cleavage photopolymerization initiator (C2). The pressure-sensitive adhesive sheet will be described below.

[0014] [Acrylic Polymer (A)] The acrylic polymer (A) is the main component of the pressure-sensitive adhesive composition and typically contains a structural moiety derived from a (meth)acrylate (a1) having an alkyl group with 3 or more carbon atoms (hereinafter sometimes referred to as "alkyl(meth)acrylate (a1)"). In particular, the acrylic polymer (A) used in the pressure-sensitive adhesive sheet preferably contains a structural moiety derived from an alkyl(meth)acrylate (a1) and a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a2). Such an acrylic polymer (A) is typically obtained by polymerizing copolymerization components containing an alkyl(meth)acrylate (a1) and a hydroxyl group-containing (meth)acrylate (a2).

[0015] In addition to the structural moieties derived from the alkyl (meth)acrylate (a1) and the hydroxyl group-containing (meth)acrylate (a2), the acrylic polymer (A) may also contain structural moieties derived from at least one copolymerizable monomer (a3) ​​selected from the group consisting of (meth)acrylates having an alkyl group with 1 or 2 carbon atoms and vinyl ester monomers (hereinafter referred to as "copolymerizable monomer (a3)"). A structural moiety derived from a functional group-containing ethylenically unsaturated monomer (a4), or a structural moiety derived from another copolymerizable monomer (a5). That is, the copolymerization components may contain components other than the alkyl (meth)acrylate (a1) and the hydroxyl group-containing (meth)acrylate (a2), such as the copolymerizable monomer (a3), the functional group-containing ethylenically unsaturated monomer (a4), or another copolymerizable monomer (a5). In terms of adhesive properties, the acrylic polymer (A) preferably does not contain a structural moiety derived from a carboxyl group-containing (meth)acrylate.

[0016] [Alkyl (meth)acrylate (a1)] Examples of the alkyl (meth)acrylate (a1) include linear alkyl (meth)acrylates such as n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, lauryl (meth)acrylate, n-tridecyl (meth)acrylate, stearyl (meth)acrylate, icosyl (meth)acrylate, henicosyl (meth)acrylate, and behenyl (meth)acrylate; isopropyl (meth)acrylate, isobutyl (meth)acrylate, and sec-butyl (meth)acrylate. Examples of suitable alicyclic (meth)acrylates include branched alkyl (meth)acrylates such as butyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, isostearyl (meth)acrylate, and isoicosyl (meth)acrylate; and alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, and adamantyl (meth)acrylate. These may be used alone or in combination of two or more.

[0017] Among these, linear alkyl (meth)acrylates are preferred from the viewpoints of adhesion and recovery, more preferably linear alkyl (meth)acrylates having an alkyl group with 3 to 8 carbon atoms, and particularly preferably n-butyl (meth)acrylate and n-octyl (meth)acrylate. Furthermore, from the viewpoint of balancing adhesion and flexibility at low temperatures, linear and branched alkyl (meth)acrylates having an alkyl group with 3 to 18 carbon atoms, even more preferably 3 to 16 carbon atoms, particularly 3 to 12 carbon atoms, and especially 3 to 8 carbon atoms are preferred. Specific examples include n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, decyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Among these, n-butyl(meth)acrylate, n-octyl(meth)acrylate, and 2-ethylhexyl(meth)acrylate are preferred, and 2-ethylhexyl(meth)acrylate is particularly preferred. Furthermore, the alkyl(meth)acrylate (a1) is particularly preferably an acrylate, from the viewpoint of suppressing an increase in the shear storage modulus (G') at low temperatures and improving flexibility.

[0018] The content of the structural moiety derived from alkyl (meth)acrylate (a1) relative to the acrylic polymer (A) is typically 40 to 95 mass %, preferably 45 to 90 mass %, and particularly preferably 50 to 85 mass % of the acrylic polymer (A) in order to suppress an increase in the shear storage modulus (G') at low temperatures. When the content of the structural moiety derived from alkyl (meth)acrylate (a1) is equal to or greater than the lower limit, an increase in the shear storage modulus (G') at low temperatures can be suppressed, and when it is equal to or less than the upper limit, it is preferable in terms of achieving compatibility with other physical properties such as adhesion.

[0019] [Hydroxyl Group-Containing (Meth)acrylate (a2)] Examples of the hydroxyl group-containing (meth)acrylate (a2) include hydroxyalkyl (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; and polypropylene glycol (meth)acrylate polytetrafluoroethylene. Examples of such acrylates include (meth)acrylates having an oxyalkylene glycol structure, such as lamethylene glycol (meth)acrylate and polyoxyethylene polyoxypropylene 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.

[0020] Among the hydroxyl group-containing (meth)acrylates (a2), from the viewpoint of reducing the shear storage modulus (G') at low temperatures, hydroxyl group-containing (meth)acrylates having a hydroxyalkyl group having 1 to 10 carbon atoms, further 1 to 6 carbon atoms, and particularly 2 to 4 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate, are preferred, and primary hydroxyl group-containing (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate, are particularly preferred, with 4-hydroxyethyl (meth)acrylate being particularly preferred from the viewpoint of reducing the shear storage modulus (G') at low temperatures.

[0021] Furthermore, when 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are used as the hydroxyl group-containing (meth)acrylate (a2), the ratio thereof [2-hydroxyethyl (meth)acrylate / 4-hydroxybutyl (meth)acrylate] is preferably 95 / 5 to 30 / 70 by mass, more preferably 90 / 10 to 40 / 60, particularly preferably 85 / 15 to 45 / 65, and especially preferably 80 / 20 to 50 / 50. If the amount of 2-hydroxyethyl (meth)acrylate is too small, the adhesive strength when used as an adhesive tends to decrease, whereas if the amount is too large, the bending durability when used as an adhesive tends to decrease.

[0022] The hydroxyl group-containing (meth)acrylate (a2) preferably contains as little di(meth)acrylate as an impurity in the hydroxyl group-containing monomer (a2) as possible. Specifically, it is preferable to use one having a content of 0.5% by mass or less, particularly preferably 0.2% by mass or less, and even more preferably 0.1% by mass or less.

[0023] The content of the structural moiety derived from the hydroxyl group-containing (meth)acrylate (a2) relative to the acrylic polymer (A) is usually 5 to 60% by mass, preferably 8 to 45% by mass, particularly preferably 10 to 35% by mass, even more preferably 11 to 30% by mass, and especially preferably 12 to 25% by mass. When the content is within the above range, the adhesive tends to have good moist heat resistance when used as a pressure-sensitive adhesive, which is preferable.

[0024] [Copolymerizable Monomer (a3)] The acrylic polymer (A) preferably further has a structural moiety derived from a copolymerizable monomer (a3) ​​from the viewpoint of improving cohesive strength and further improving adhesive strength when used as a pressure-sensitive adhesive.

[0025] Examples of the copolymerizable monomer (a3) ​​include methyl (meth)acrylate, ethyl (meth)acrylate, and vinyl acetate. These copolymerizable monomers (a3) ​​may be used alone or in combination of two or more. Among them, from the viewpoint of improving cohesive strength when used as a pressure-sensitive adhesive, methyl (meth)acrylate and ethyl (meth)acrylate are preferred, and ethyl (meth)acrylate is particularly preferred.

[0026] When the acrylic polymer (A) contains a structural moiety derived from the copolymerizable monomer (a3), the content thereof is usually 1 to 70 mass %, preferably 3 to 60 mass %, and more preferably 5 to 45 mass %, of the acrylic polymer (A). When the content of the copolymerizable monomer (a3) ​​is equal to or greater than the lower limit, the adhesive strength when used as a pressure-sensitive adhesive tends to be good, while when it is equal to or less than the upper limit, the durability when used as a pressure-sensitive adhesive tends to be less likely to decrease.

[0027] Furthermore, when methyl (meth)acrylate and / or ethyl (meth)acrylate is used as the copolymerizable monomer (a3), the content of the structural moieties derived from methyl (meth)acrylate and / or ethyl (meth)acrylate relative to the acrylic polymer (A) is usually 5 to 40 mass%, preferably 7 to 30 mass%, and more preferably 10 to 25 mass% of the acrylic polymer (A). When the content of the structural moieties derived from methyl (meth)acrylate and / or ethyl (meth)acrylate is equal to or less than the upper limit, deterioration in handleability during processing due to an increase in viscosity tends to be suppressed, while when it is equal to or more than the lower limit, adhesive strength tends to be good when used as a pressure-sensitive adhesive.

[0028] [Functional Group-Containing Ethylenically Unsaturated Monomer (a4)] The acrylic polymer (A) may, if necessary, have a structural moiety derived from a functional group-containing ethylenically unsaturated monomer (a4) (excluding the hydroxyl group-containing monomer (a2)).

[0029] Examples of the functional group-containing ethylenically unsaturated monomer (a4) include functional group-containing monomers having a nitrogen atom, acetoacetyl group-containing monomers, isocyanate group-containing monomers, glycidyl group-containing monomers, etc. Among these, from the viewpoint of imparting cohesive strength and crosslinking promoting action, functional group-containing monomers having a nitrogen atom are preferred, amino group-containing monomers and amide group-containing monomers are more preferred, and amino group-containing monomers are particularly preferred.

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

[0031] Examples of the amide group-containing monomer include (meth)acrylamide; N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, 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.

[0032] Examples of the acetoacetyl group-containing monomer include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.

[0033] Examples of the isocyanate group-containing monomer include 2-(meth)acryloyloxyethyl isocyanate and alkylene oxide adducts thereof.

[0034] Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0035] These functional group-containing ethylenically unsaturated monomers (a4) may be used alone or in combination of two or more.

[0036] When the acrylic polymer (A) has a structural portion derived from a functional group-containing ethylenically unsaturated monomer (a4), its content is usually 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less of the acrylic polymer (A). When the content of the structural portion derived from a functional group-containing ethylenically unsaturated monomer (a4) is equal to or less than the upper limit, the deterioration of the heat resistance of the acrylic polymer (A) tends to be suppressed. The lower limit is usually 0.1% by mass, preferably 1% by mass.

[0037] [Other Copolymerizable Monomers (a5)] The acrylic polymer (A) may also have a structural moiety derived from other copolymerizable monomers (a5), if necessary.

[0038] Examples of the other copolymerizable monomer (a5) include (meth)acrylates having an alkoxyalkylene glycol skeleton, such as methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, butoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, butoxypolypropylene glycol (meth)acrylate, methoxypolytetramethylene glycol (meth)acrylate, butoxypolytetramethylene glycol (meth)acrylate, methoxypolyoxyethylene polyoxypropylene glycol (meth)acrylate, and butoxypolyoxyethylene polyoxypropylene glycol (meth)acrylate; phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate; phenyl di (meth)acrylate; Examples of suitable monomers include aromatic (meth)acrylic acid ester monomers such as ethylene glycol (meth)acrylate, phenoxy polyethylene glycol (meth)acrylate, phenoxy polyethylene glycol-polypropylene glycol-(meth)acrylate, and nonylphenol ethylene oxide adduct (meth)acrylate, as well as monomers such as acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, dialkyl itaconate ester, dialkyl fumarate ester, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone. These may be used alone or in combination of two or more.

[0039] Furthermore, when the purpose is to increase the molecular weight of the acrylic polymer (A), a small amount of a compound having two or more ethylenically unsaturated groups, such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, or divinylbenzene, can also be used in combination. In this case, these compounds having two or more ethylenically unsaturated groups are highly reactive and do not usually remain unreacted when used as a polymerization component of the acrylic polymer (A). However, if the amount used is too large, these compounds having two or more ethylenically unsaturated groups will remain unreacted, and the acrylic polymer (A) will tend to gel.

[0040] When the acrylic polymer (A) contains a structural portion derived from another copolymerizable monomer (a5), its content is usually 50% by mass or less, preferably 40% by mass or less, and more preferably 20% by mass or less of the acrylic polymer (A). If the content of the other copolymerizable monomer (a5) is below the upper limit, the heat resistance and adhesive strength tend to be reduced. The lower limit is usually 0.1% by mass, preferably 1% by mass.

[0041] The acrylic polymer (A) used in the present pressure-sensitive adhesive sheet can be obtained by appropriately selecting and polymerizing the above-mentioned copolymerization components.

[0042] Examples of the method for polymerizing the acrylic polymer (A) include conventionally known methods such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. Among these, solution polymerization is preferred in that it can safely and stably produce the acrylic polymer (A) with any monomer composition. Hereinafter, an example of a preferred method for producing the acrylic polymer (A) used in the present invention will be shown.

[0043] First, the copolymerization components and polymerization initiator are mixed or dropped into an organic solvent, followed by solution polymerization to obtain an acrylic polymer solution.

[0044] [Organic Solvent] Examples of organic solvents used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane, esters such as ethyl acetate and butyl acetate, aliphatic alcohols such as n-propyl alcohol and isopropyl alcohol, and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. These solvents can be used alone or in combination of two or more. Among these solvents, ethyl acetate is preferred.

[0045] [Polymerization initiator] The polymerization initiator used in the polymerization reaction can be a typical radical polymerization initiator, such as an azo polymerization initiator or a peroxide polymerization initiator. Examples of the azo polymerization initiator include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of the peroxide polymerization initiator include benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, t-butyl peroxypivalate, t-hexyl peroxypivalate, t-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, and diisobutyryl peroxide. These polymerization initiators can be used alone or in combination of two or more. Among these, azo polymerization initiators are preferred, and 2,2'-azobis(2,4-dimethylvaleronitrile) is particularly preferred.

[0046] The amount of the polymerization initiator used is usually 0.001 to 10 parts by mass, preferably 0.1 to 8 parts by mass, particularly preferably 0.5 to 6 parts by mass, even more preferably 1 to 4 parts by mass, particularly preferably 1.5 to 3 parts by mass, and most preferably 2 to 2.5 parts by mass, relative to 100 parts by mass of the copolymerization components. When the amount of the polymerization initiator used is equal to or greater than the lower limit, a decrease in the polymerization rate of the acrylic polymer (A) and an increase in the amount of residual monomers, as well as an increase in the weight-average molecular weight of the acrylic polymer (A), tend to be suppressed. When the amount used is equal to or less than the upper limit, gelation during polymerization tends to be suppressed.

[0047] [Polymerization Conditions, etc.] The solution polymerization may be carried out under conventionally known polymerization conditions. For example, polymerization components and a polymerization initiator may be mixed or dropped into a solvent and polymerized under predetermined polymerization conditions.

[0048] The polymerization temperature in the polymerization reaction is usually 40 to 120° C., but in the present invention, from the viewpoint of ensuring a stable reaction, it is preferably 50 to 90° C., particularly preferably 55 to 75° C., and further preferably 60 to 70° C. If the polymerization temperature is too high, the acrylic polymer (A) tends to be easily gelled, whereas if the polymerization temperature is too low, the activity of the polymerization initiator decreases, which tends to reduce the polymerization rate and increase the amount of residual monomer.

[0049] The polymerization time in the polymerization reaction (the time until the start of the follow-up heating when follow-up heating described below is performed) is not particularly limited, but is preferably 0.5 hours or more from the addition of the final polymerization initiator, particularly preferably 1 hour or more, further preferably 2 hours or more, and particularly preferably 5 hours or more. The upper limit of the polymerization time is usually 72 hours. The polymerization reaction is preferably carried out while refluxing the solvent, as this facilitates heat removal.

[0050] In the production of the acrylic polymer (A), in order to reduce the amount of residual polymerization initiator, it is preferable to thermally decompose the polymerization initiator by follow-up heating.

[0051] The drive-in heating temperature is preferably higher than the 10-hour half-life temperature of the polymerization initiator, and specifically is usually 40 to 150°C, and from the viewpoint of suppressing gelation, it is preferably 55 to 130°C, and particularly preferably 75 to 95°C. If the drive-in heating temperature is too high, the acrylic polymer (A) tends to turn yellow, while if it is too low, the polymerization components and polymerization initiator tend to remain, and the stability over time and thermal stability of the acrylic polymer (A) tend to decrease. In this way, the acrylic polymer (A) can be obtained.

[0052] The acrylic polymer (A) may have a photoactive moiety, such as an ethylenically unsaturated group, introduced into a side chain thereof, thereby increasing the crosslinking efficiency of the pressure-sensitive adhesive composition, enabling the pressure-sensitive adhesive composition to be crosslinked in a shorter time, and improving productivity.

[0053] Examples of a method for introducing an ethylenically unsaturated group into a side chain of the acrylic polymer (A) include a method in which an acrylic polymer (A) having a structural moiety derived from the above-mentioned hydroxyl group-containing (meth)acrylate (a2) or functional group-containing ethylenically unsaturated monomer (a4) is prepared, and then a compound having an ethylenically unsaturated group and a functional group reactive with the functional group is subjected to a condensation or addition reaction while maintaining the activity of the ethylenically unsaturated 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. Among these, a combination in which the acrylic polymer (A) has a hydroxyl group and the compound has an isocyanate group is preferred.

[0055] Examples of the isocyanate compound having an ethylenically unsaturated group include the above-mentioned 2-(meth)acryloyloxyethyl isocyanate and alkylene oxide adducts thereof.

[0056] From the viewpoint of improving adhesiveness and stress relaxation properties, the content of the compound having a functional group reactive with the functional group and an ethylenically unsaturated group is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 1 part by mass or less, and particularly preferably 0.1 parts by mass or less, relative to 100 parts by mass of the acrylic polymer (A). The lower limit is usually 0 part by mass.

[0057] The hydroxyl value of the acrylic polymer (A) is preferably 30 mgKOH / g or more, more preferably 50 mgKOH / g or more, and particularly preferably 70 mgKOH / g or more. The upper limit of the hydroxyl value is usually 150 mgKOH / g, preferably 120 mgKOH / g. The hydroxyl value can be determined by determining the amount of free hydroxyl groups contained in 1 g of the acrylic polymer (A) from the composition ratio of the monomers used in the polymerization, and then calculating the amount of potassium hydroxide (unit: mg) required to neutralize the acetic acid required to acetylate the free hydroxyl groups.

[0058] The glass transition temperature (Tg) of the acrylic polymer (A) is preferably −5° C. or lower, more preferably −10° C. or lower, even more preferably −15° C. or lower, and particularly preferably −20° C. or lower, in order to suppress an increase in the shear storage modulus (G′) at low temperatures. Note that the lower limit of the glass transition temperature (Tg) is usually −50° C. due to concerns about adhesive extrusion due to a decrease in the shear storage modulus at high temperatures.

[0059] In the present invention, the glass transition temperature (Tg) can be determined by reading the temperature (maximum value) at which the loss tangent (tan δ) is maximized when dynamic viscoelasticity is measured in a shear mode at a frequency of 1 Hz using a dynamic viscoelasticity measuring device. For example, the acrylic polymer (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 (manufactured by T.A. Instruments, "DHR 2") under the following measurement conditions. (Measurement Conditions) Measuring jig: Φ8 mm parallel plate; Strain: 0.1%; Frequency: 1 Hz; Measurement temperature: -50 to 80°C; Heating rate: 5°C / min

[0060] The weight average molecular weight (Mw) of the acrylic polymer (A) is preferably 400,000 or more, more preferably 500,000 or more, and even more preferably 550,000 or more, from the viewpoint of obtaining a pressure-sensitive adhesive composition with high cohesive strength. The upper limit of the weight average molecular weight (Mw) of the acrylic polymer (A) is preferably 1,500,000 or less, more preferably 1,200,000 or less, even more preferably 1,100,000 or less, particularly preferably 1,000,000 or less, and especially preferably 900,000 or less, from the viewpoint of handleability and uniform stirability.

[0061] 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 acrylic polymer (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

[0062] The content of the acrylic polymer (A) in the pressure-sensitive adhesive composition is usually 10 to 75% by mass, preferably 12 to 73% by mass, more preferably 20 to 71% by mass, and particularly preferably 30 to 69% by mass.

[0063] [Radical Polymerizable Compound (B)] The pressure-sensitive adhesive composition contains a radically polymerizable compound (B) because the pressure-sensitive adhesive composition has excellent adhesive strength to flexible members.

[0064] The radical polymerizable compound (B) preferably has an alkylene glycol skeleton from the viewpoint of flexibility, and also preferably has a urethane bond from the viewpoint of flexibility.

[0065] As the alkylene glycol skeleton, from the viewpoint of decreasing the shear storage modulus (G') at low temperatures, an alkylene glycol skeleton having an alkylene chain having 2 to 10 carbon atoms, further 2 to 8 carbon atoms, particularly 2 to 6 carbon atoms, and especially 2 to 4 carbon atoms is preferred, and an ethylene glycol skeleton, a propylene glycol skeleton, a butylene glycol skeleton, or a combination thereof is particularly preferred, and a propylene glycol skeleton is more preferred.

[0066] The radical polymerizable compound having an alkylene glycol skeleton includes, for example, a monofunctional (meth)acrylic oligomer represented by the following general formula (1): CH═CR—COO—R—Y—(RO) k -R4 (1) In the formula, R1 represents hydrogen or a methyl group. R2 represents an alkylene group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms, which may have an ether bond or a cyclic structure in the chain. R4 represents an alkyl group having 1 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms, which may have an ether bond or a cyclic structure in the chain. Y represents a linking group selected from a urethane bond, an ester bond, an ether bond, a carbonate bond, an amide bond, and a urea bond. R3 represents an alkylene group which is an ethylene group or a propylene group. k represents the repeating unit (C2H4O) r and (C3H6O) s represents the total number of repeating units r+s and is an integer of 1 to 500. When an oxyethylene structure and an oxypropylene structure coexist, they may be of a random type or a block type.

[0067] The positive number "k" in the general formula (1) is preferably 10 to 500, more preferably 100 to 450, and even more preferably 200 to 400, from the viewpoint of reducing the shear storage modulus at low temperatures while maintaining high recovery upon bending.

[0068] Among these, the radical polymerizable compound having an alkylene glycol skeleton is preferably a monofunctional urethane (meth)acrylate having a urethane bond, because it has excellent flexibility.

[0069] The monofunctional urethane (meth)acrylate is particularly effective because it has high polarity and a long chain length, and therefore tends to provide high recovery due to entanglement of the polymer chains, and also tends to provide a low shear storage modulus due to the presence of an oxypropylene structure with high molecular rotation.

[0070] From the viewpoint of reducing the shear storage modulus at low temperatures while maintaining high recovery upon bending, the radical polymerizable compound (B) preferably has a glass transition temperature of −40° C. or lower, more preferably −45° C. or lower, and even more preferably −50° C. or lower when homopolymerized, i.e., when only the radical polymerizable compound (B) is polymerized to form a polymer. In view of concerns about adhesive extrusion due to a decrease in shear storage modulus at high temperatures, the radical polymerizable compound (B) preferably has a glass transition temperature of −80° C. or higher, more preferably −75° C. or higher, and even more preferably −70° C. or higher when homopolymerized.

[0071] The weight average molecular weight (Mw) of the radical polymerizable compound (B) is preferably 30,000 or less, more preferably 28,000 or less, and even more preferably 25,000 or less, from the viewpoint of maintaining high recovery upon bending while reducing the shear storage modulus at low temperatures. The lower limit of the weight average molecular weight (Mw) of the radical polymerizable compound having an alkylene glycol skeleton is preferably 3,000 or more, more preferably 4,000 or more, and even more preferably 5,000 or more, from the viewpoint of maintaining high recovery upon bending while preventing a decrease in adhesiveness due to bleed-out. The weight average molecular weight (Mw) of the radical polymerizable compound (B) can be determined in accordance with the "Method for measuring weight average molecular weight" described for the acrylic polymer (A).

[0072] The radical polymerizable compound (B) preferably comprises the radical polymerizable compound having the alkylene glycol skeleton as a main component.In addition, as the radical polymerizable compound (B), in addition to the radical polymerizable compound having the alkylene glycol skeleton, for example, monofunctional (meth)acrylic monomers, polyfunctional (meth)acrylic monomers, polyfunctional (meth)acrylic oligomers, etc. can also be used.These can be used alone or in combination of two or more.

[0073] [Monofunctional (meth)acrylic monomer] The monofunctional (meth)acrylic monomer is one other than the radical polymerizable compound having an alkylene glycol skeleton, and examples thereof include linear or branched alkyl (meth)acrylates. Specific examples thereof include n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, and t-butylcyclohexyl (meth). ) acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, isobornyl (meth)acrylate, 3,5,5-trimethylcyclohexane (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate.

[0074] [Polyfunctional (meth)acrylic monomer] The polyfunctional (meth)acrylic monomer is one other than the radical polymerizable compound having an alkylene glycol skeleton, and examples thereof include 1,4-butanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin glycidyl ether di(meth)acrylate, tricyclodecane dimethacrylate, tricyclodecane dimethanol di(meth)acrylate, bisphenol A polyethoxy di(meth)acrylate, bisphenol A polypropoxy Di(meth)acrylate, bisphenol F polyethoxydi(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 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 acrylate include erythritol penta(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol penta(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, di(meth)acrylate of an ε-caprolactone adduct of neopentyl glycol hydroxypivalate, trimethylolpropane tri(meth)acrylate, trimethylolpropane polyethoxy tri(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate.

[0075] [Polyfunctional (meth)acrylic oligomer] The polyfunctional (meth)acrylic oligomer is one other than the radical polymerizable compound having an alkylene glycol skeleton, and examples thereof include polyfunctional (meth)acrylic oligomers such as polyfunctional polyester (meth)acrylate oligomers, polyfunctional epoxy (meth)acrylate oligomers, polyfunctional urethane (meth)acrylate oligomers, and polyfunctional polyether (meth)acrylate oligomers.

[0076] The content of the radical polymerizable compound (B) is usually 10 to 100 parts by mass, preferably 20 to 90 parts by mass, and particularly preferably 40 to 80 parts by mass, relative to 100 parts by mass of the acrylic polymer (A). By setting the content of the radical polymerizable compound (B) within this range, a pressure-sensitive adhesive sheet with excellent flexibility tends to be obtained.

[0077] [Photopolymerization Initiator (C)] The pressure-sensitive adhesive composition contains a photopolymerization initiator (C). The photopolymerization initiators (C) are broadly classified into two types based on the radical generation mechanism: hydrogen abstraction photopolymerization initiators (C1), in which an excited initiator and a hydrogen donor in the system form an exciplex, thereby transferring hydrogen from the hydrogen donor; and cleavage photopolymerization initiators, in which a single bond of the initiator itself is cleaved and decomposed to generate radicals. The present invention uses a photopolymerization initiator (C) containing a hydrogen abstraction photopolymerization initiator (C1) and an α-aminoalkylphenone cleavage photopolymerization initiator (C2), which is a type of cleavage photopolymerization initiator. When the hydrogen abstraction photopolymerization initiator (C1) is used as the photopolymerization initiator (C), a hydrogen abstraction reaction also occurs from the acrylic polymer (A), and the acrylic polymer (A) is incorporated into the crosslinked structure, forming a crosslinked structure with many crosslinking points. However, when only a hydrogen abstraction photopolymerization initiator (C1) is used as the photopolymerization initiator (C), unreacted radical polymerizable compound (B) tends to remain, resulting in a decrease in adhesive strength. Therefore, in the present invention, by using a hydrogen abstraction photopolymerization initiator (C1) in combination with an α-aminoalkylphenone cleavage photopolymerization initiator (C2), the radical polymerizable compound (B) can be incorporated into a crosslinked structure, thereby achieving sufficient adhesive strength. Furthermore, a PSA sheet can be obtained that has good adhesive strength not only at room temperature but also at high temperatures, with little change in adhesive strength between room temperature and high temperatures.

[0078] Examples of the hydrogen abstraction photopolymerization initiator (C1) 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. These may be used alone or in combination of two or more. Of these, 4-methylbenzophenone and 2,4,6-trimethylbenzophenone are preferred.

[0079] In addition, from the viewpoint of adhesive strength, the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) preferably has a weight-average molecular weight of 800 or less, more preferably 500 or less, and particularly preferably 300 or less. The lower limit of the weight-average molecular weight is usually 100, and preferably 150.

[0080] Furthermore, the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) preferably contains sulfur element from the viewpoint of yellowing resistance.

[0081] In addition, it is preferable from the viewpoint of yellowing resistance that the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) has a maximum absorption wavelength in the region of 270 to 315 nm in the light absorption spectrum.

[0082] Specific examples of the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) include 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, 2-(dimethylamino)-2-(4-methylbenzyl)-1-(4-morpholinophenyl)butan-1-one, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, and polyethylene glycol (200) di(β-4[4-(2-dimethylamino-2-benzyl)butanoylphenyl]piperazine)propionate. These may be used alone or in combination of two or more. Of these, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one is preferred.

[0083] The photopolymerization initiator (C) may contain a cleavage-type photopolymerization initiator other than the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2). However, from the viewpoint of the effects of the present invention, it is preferable that the photopolymerization initiator (C) consists solely of the hydrogen abstraction-type photopolymerization initiator (C1) and the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2). In the present invention, the hydrogen abstraction-type photopolymerization initiator (C1) is used in combination with the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) as the cleavage-type photopolymerization initiator. This allows for efficient elongation of the radical polymerizable compound (B) and crosslinking with the acrylic polymer (A), contributing to improved adhesive strength. On the other hand, cleavage-type photopolymerization initiators other than the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) tend not to contribute as much to adhesive strength.

[0084] Examples of the cleavage-type photopolymerization initiator other than the α-aminoalkylphenone-based cleavage-type photopolymerization initiator (C2) include α-hydroxyacetophenone-based initiators such as 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, and 2-hydroxy-1-[4-{4-(2-hydroxy-2-methyl-propionyl)benzyl}phenyl]-2-methyl-propan-1-one. Examples of cleavage-type photopolymerization initiators include acylphosphine oxide cleavage-type photopolymerization initiators such as bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide; oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone); methyl phenylglyoxylate; and derivatives thereof. These may be used alone or in combination of two or more.

[0085] The content of the photopolymerization initiator (C) is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 6 parts by mass, and particularly preferably 1 to 4 parts by mass, relative to 100 parts by mass of the acrylic polymer (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.

[0086] The content ratio (C1 / C2) of the hydrogen abstraction photopolymerization initiator (C1) to the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) is preferably 0.5 to 10 by mass, more preferably 0.7 to 7, particularly preferably 0.9 to 6, and especially preferably 1 to 5. When the content ratio of the hydrogen abstraction photopolymerization initiator (C1) to the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) is within the above range, the adhesiveness to flexible materials, particularly to polyimide, tends to be excellent.

[0087] [Multifunctional Epoxy Compound (D)] The pressure-sensitive adhesive composition preferably further contains a multifunctional epoxy compound (D) from the viewpoint of excellent adhesiveness to flexible materials, particularly polyimide. The multifunctional epoxy compound (D) is not particularly limited as long as it has two or more epoxy groups in one molecule, and may be solid or liquid.

[0088] Silane coupling agents are generally used as additives (adhesive aids) to improve the adhesiveness of pressure-sensitive adhesive sheets. However, although silane coupling agents are effective in improving adhesiveness to glass materials, they are insufficient as adhesive aids for flexible materials. However, by using the polyfunctional epoxy compound (D), adhesiveness to flexible materials, particularly polyimides, tends to be excellent.

[0089] The effect of improving adhesive strength to flexible materials by using the multifunctional epoxy compound (D) is thought to be manifested by the following mechanism. The epoxy groups of the multifunctional epoxy compound (D) can form interactions such as hydrogen bonds or covalent bonds with functional groups such as hydroxyl groups of the acrylic polymer (A) or the crosslinking agent. Furthermore, the epoxy groups can also form interactions with functional groups on the flexible material (e.g., maleimide groups or amide groups in the case of polyimide, or ester groups in the case of polyester) through non-reversible covalent bonds or hydrogen bonds. Thus, the multifunctional epoxy compound (D) acts not only with the components of the pressure-sensitive adhesive composition but also at the interface with the flexible material, thereby improving adhesive strength to flexible materials, particularly polyimides. Furthermore, the multifunctional epoxy compound (D) has adequate compatibility with the pressure-sensitive adhesive composition, so that some of the epoxy groups segregate to the surface of the pressure-sensitive adhesive sheet and form bonds or interactions with functional groups on the flexible material.

[0090] Examples of the polyfunctional epoxy compound (D) include aromatic epoxy compounds such as bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, naphthalene type epoxy compounds, biphenyl type epoxy compounds, resorcinol type epoxy compounds, phenol novolac type epoxy compounds, and cresol novolac type epoxy compounds, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, butanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, trimethylolpropane diglycidyl ether, and the like. Examples of epoxy compounds include aliphatic epoxy compounds such as dipropane triglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, cyclohexane diglycidyl ether, dicyclopentadiene diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hexahydrophthalic acid diglycidyl ester, vinyl(3,4-cyclohexene) dioxide, 2-(3,4-epoxycyclohexyl)-5,1-spiro-(3,4-epoxycyclohexyl)-m-dioxane, and epoxidized polybutadiene; as well as heterocyclic epoxy compounds such as triglycidyl isocyanurate, halogenated epoxy compounds, glycidylamine epoxy compounds, epoxy group-containing rubber compounds, epoxy group-containing polyurethane compounds, and epoxy group-containing acrylic compounds.

[0091] Among these, bifunctional epoxy compounds are preferred from the viewpoint of increasing adhesive strength to the adherend. Furthermore, aliphatic epoxy compounds are preferred from the viewpoint of maintaining adequate compatibility with the pressure-sensitive adhesive composition and flexibility of the pressure-sensitive adhesive sheet. Among these, polyalkylene glycol diglycidyl ethers are preferred, and polyethylene glycol diglycidyl ether is particularly preferred from the viewpoint of having adequate compatibility.

[0092] When the pressure-sensitive adhesive composition contains a polyfunctional epoxy compound (D), the content thereof is usually 0.01 to 10 parts by mass, preferably 0.03 to 5 parts by mass, and particularly preferably 0.05 to 3 parts by mass, relative to 100 parts by mass of the acrylic polymer (A). When the content is equal to or greater than the lower limit, the adhesive strength to the adherend tends to be improved, whereas when the content is equal to or less than the upper limit, the flexibility of the pressure-sensitive adhesive sheet tends to be easily maintained, and a pressure-sensitive adhesive sheet with excellent flexibility tends to be obtained.

[0093] [Thermal Crosslinking Agent] The pressure-sensitive adhesive composition may contain a thermal crosslinking agent to further improve crosslink density and long-term reliability. Examples of such thermal crosslinking agents include isocyanate-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 acrylic polymers.

[0094] The content of the thermal crosslinking agent is usually 0.1 to 30 parts by mass, preferably 0.5 to 10 parts by mass, based on 100 parts by mass of the acrylic polymer (A).

[0095] When the polyfunctional (meth)acrylic monomer or polyfunctional (meth)acrylic oligomer described above as the radical polymerizable compound (B) is used, it also acts as a crosslinking agent.

[0096] When the polyfunctional (meth)acrylic monomer or polyfunctional (meth)acrylic oligomer is used as the crosslinking agent, the content thereof is usually 10 to 100 parts by mass, preferably 20 to 90 parts by mass, and particularly preferably 40 to 80 parts by mass, relative to 100 parts by mass of the acrylic polymer (A). By setting the content of the other radically polymerizable compound within the above range, a pressure-sensitive adhesive sheet with excellent flexibility tends to be obtained.

[0097] [Other Components] The pressure-sensitive adhesive composition may contain various additives such as ultraviolet absorbers, rust inhibitors, silane coupling agents, tackifier resins, antioxidants, light stabilizers, metal deactivators, antiaging agents, moisture absorbents, 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.

[0098] (Ultraviolet Absorber) Examples of the ultraviolet absorber include benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, benzoxazine-based ultraviolet absorbers, etc. These ultraviolet absorbers can be used alone or in combination of two or more.

[0099] When an ultraviolet absorber is used, the content thereof 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 acrylic polymer (A). When the content is equal to or greater than the lower limit, lightfastness reliability tends to improve, and when the content is equal to or less than the upper limit, yellowing resistance tends to improve.

[0100] (Rust inhibitor) As the rust inhibitor, for example, triazoles, benzotriazoles, etc. are preferred, and they can prevent corrosion of optical components. These may be used alone or in combination of two or more. When a rust inhibitor is used, the content thereof 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 acrylic polymer (A).

[0101] (Silane coupling agent) Silane coupling agent is the organosilicon compound that contains reactive functional group and one or more 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.

[0102] The alkoxy group bonded to the silicon atom preferably contains an alkoxy group having 1 to 8 carbon atoms, from the viewpoint of durability and storage stability, and is particularly preferably a methoxy group or an ethoxy group. The silane coupling agent may also contain 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.

[0103] Examples of the silane coupling agent 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 silane coupling agents in which a part of the silane compound is hydrolyzed and condensed, or in which the silane compound is polymerized with methyltriethoxysilane, ethyltriethoxysilane, and the like. oligomeric epoxy group-containing silane coupling agents which are silane compounds obtained by co-condensation of alkyl group-containing silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, γ-mercaptopropyldimethoxymethylsilane, 3-mercaptopropylmethyldimethoxysilane, and the like; monomeric mercapto group-containing silane coupling agents which are silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, γ-mercaptopropyldimethoxymethylsilane, 3-mercaptopropylmethyldimethoxysilane, and the like; and mercapto group-containing silane coupling agents which are silane compounds obtained by hydrolysis and condensation polymerization of a part of the silane compounds or by condensation polymerization of the silane compounds with methyl groups. oligomeric mercapto group-containing silane coupling agents which are silane compounds obtained by co-condensation of alkyl group-containing silane compounds such as 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane; (meth)acryloyl group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane; coupling agents: 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.

[0104] Among these, epoxy group-containing silane coupling agents and mercapto group-containing silane coupling agents are preferably used because of their excellent durability, and epoxy group-containing silane coupling agents are particularly preferred.

[0105] The content of the silane coupling agent 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 acrylic polymer (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.

[0106] 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 acrylic polymer (A). If the content is too high, the compatibility with the acrylic polymer decreases, and durability tends to decrease.

[0107] The pressure-sensitive adhesive composition is prepared by mixing predetermined amounts of the acrylic polymer (A), the radically polymerizable compound (B), and the photopolymerization initiator (C), preferably the polyfunctional epoxy compound (D), and, if necessary, further a thermal crosslinking agent and other components.

[0108] <Method for producing the present pressure-sensitive adhesive sheet> Next, a method for producing the present pressure-sensitive adhesive sheet will be described. However, the following description is an example of a method for producing the present pressure-sensitive adhesive sheet, and the present pressure-sensitive adhesive sheet is not limited to sheets produced by this method.

[0109] In producing the present pressure-sensitive adhesive sheet, a pressure-sensitive adhesive composition for forming the present pressure-sensitive adhesive sheet is prepared, which contains an acrylic polymer (A), a radically polymerizable compound (B), and a photopolymerization initiator (C), preferably a polyfunctional epoxy compound (D), and, if necessary, a thermal crosslinking agent and other components, and the pressure-sensitive adhesive composition is formed into a sheet, crosslinked, i.e., polymerized, to harden the sheet, and then processed appropriately as necessary to produce the present pressure-sensitive adhesive sheet.

[0110] In addition, in producing the present pressure-sensitive adhesive sheet, the present pressure-sensitive adhesive sheet may be formed by preparing a pressure-sensitive adhesive composition for forming the present pressure-sensitive adhesive sheet in the same manner as described above, coating this onto a component sheet or a component of a flexible image display device, and curing the pressure-sensitive adhesive composition, although the method is not limited to this.

[0111] 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 kneading the various raw materials, various additives such as antioxidants 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.

[0112] The method for forming the pressure-sensitive adhesive composition into a sheet can be a known method, such as a wet lamination method, a dry lamination method, an extrusion casting method using a T-die, an extrusion lamination method, a calendar method, an inflation method, injection molding, a liquid injection curing method, etc. Among these, when producing a sheet, the wet lamination method, the extrusion casting method, and the extrusion lamination method are preferred.

[0113] The pressure-sensitive adhesive composition can be cured by irradiating it with active energy rays, and the pressure-sensitive adhesive sheet can be produced by irradiating a molded product of the pressure-sensitive adhesive composition, for example, a sheet, with active energy rays. In addition to irradiating it with active energy rays, further curing can be achieved by heating.

[0114] The irradiation energy, irradiation time, irradiation method, etc. of the active energy rays are not particularly limited as long as they can activate the photopolymerization initiator (C) and polymerize the monomer components.

[0115] 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.

[0116] Examples of light sources for ultraviolet irradiation include high-pressure mercury lamps, ultra-high-pressure mercury lamps, low-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.

[0117] The amount of active energy ray irradiation (cumulative light amount) is 0.03 to 3 J / cm from the viewpoint of curing. 2 is preferred, and more preferably 0.1 to 2 J / cm 2 , more preferably 0.3 to 1.5 J / cm 2 This is carried out under the following conditions.

[0118] In another embodiment of the method for producing the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive composition can be dissolved in an appropriate solvent and coated using various coating methods. When using a coating method, the pressure-sensitive adhesive sheet can be obtained by curing with heat, in addition to curing by irradiation with active energy rays. In the case of coating, the thickness of the pressure-sensitive adhesive sheet can be adjusted by the coating thickness and the solids concentration of the coating solution.

[0119] For example, the pressure-sensitive adhesive composition can be dissolved in a solvent, coated on a release film, dried, and cured by active energy ray irradiation to form the pressure-sensitive adhesive sheet. Furthermore, a release film may be laminated, if necessary. In this case, the pressure-sensitive adhesive composition may be coated on a release film, dried, cured by active energy ray irradiation, and a release film may be laminated thereon. Alternatively, the pressure-sensitive adhesive sheet may be formed by coating on a release film, drying, laminating a release film, and then curing by active energy ray irradiation.

[0120] 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, butyl 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 solvents can be used alone or in combination of two or more. Among them, ethyl acetate, acetone, methyl ethyl ketone, and toluene are preferred in terms of solubility, drying properties, cost, and the like, and ethyl acetate is particularly preferred.

[0121] 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 300 parts by mass or less, relative to 100 parts by mass of the acrylic polymer (A) in terms of drying property. On the other hand, 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. The coating method can be, for example, a conventional method such as roll coating, die coating, gravure coating, comma coating, screen printing, or bar coating.

[0122] The solvent content in the pressure-sensitive adhesive composition 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] (Thickness) The thickness of the present pressure-sensitive adhesive sheet is not particularly limited, and if the thickness is 10 μm or more, it is easy to handle, and if the thickness is 1000 μm or less, it can contribute to making the present pressure-sensitive adhesive sheet thinner.Therefore, the thickness of the present pressure-sensitive adhesive sheet is preferably 10 μm or more, more preferably 15 μm or more, particularly preferably 20 μm or more, and even more preferably 25 μm or more.On the other hand, the upper limit is preferably 1000 μm or less, more preferably 500 μm or less, particularly preferably 250 μm or less, even more preferably 100 μm or less, and even more preferably 75 μm or less.

[0127] A release film may be provided on at least one surface of the pressure-sensitive adhesive sheet obtained as described above from the viewpoint of preventing blocking and adhesion of foreign matter. That is, the present pressure-sensitive adhesive sheet may also be provided as a pressure-sensitive adhesive sheet with a release film (pressure-sensitive adhesive sheet laminate) having a configuration in which a release film is laminated on one or both surfaces of a pressure-sensitive adhesive layer (the present pressure-sensitive adhesive sheet) made of a pressure-sensitive adhesive composition.

[0128] When release films are provided on both sides of the present pressure-sensitive adhesive sheet, it is preferable to use a laminate configuration in which a light-release film with a relatively low release strength and a heavy-release film with a relatively high release strength are laminated together. When using a pressure-sensitive adhesive sheet with release films provided on both sides, first, one release film (light-release film) is peeled off to expose one side of the pressure-sensitive adhesive sheet, and then the pressure-sensitive adhesive sheet is bonded to a component sheet or a flexible image display device component (referred to as the first component), and the other release film (heavy-release film) is peeled off to expose the other side of the pressure-sensitive adhesive sheet, and then the component sheet or the flexible image display device component (referred to as the second component) is bonded to the other side of the pressure-sensitive adhesive sheet.

[0129] As such a release film, a known release film can be appropriately used. Examples of the material for the release film include films such as polyester films, polyolefin films, polycarbonate films, polystyrene films, acrylic films, triacetyl cellulose films, and fluororesin films that have been subjected to a release treatment by coating with a release agent such as silicone resin, and release paper, etc., and these can be appropriately selected and used. Among these, polyester films, and even more so polyethylene terephthalate (PET) films, particularly biaxially oriented PET films, are preferred because of their excellent transparency, mechanical strength, heat resistance, flexibility, etc. A release film can be used in which a release layer formed by curing a curable silicone-based release agent containing silicone resin as the main component is provided on the substrate.

[0130] Generally, when a pressure-sensitive adhesive sheet having excellent flexibility is used as a pressure-sensitive adhesive sheet with a release film, if the release force of the release film is high, the pressure-sensitive adhesive sheet is flexible, and when the release film is peeled off, the pressure-sensitive adhesive sheet tends to deform and leave peeling marks. For this reason, the release film used for a pressure-sensitive adhesive sheet having excellent flexibility, particularly a light-release film, is preferably a release film that can be peeled off with even less force than the light-release type release films that have been commonly used in the past.

[0131] However, if the thickness of the release agent layer is increased in order to make the release film easier to release, depending on the type of release agent used, components derived from the release agent layer may migrate to the surface of the pressure-sensitive adhesive sheet, thereby impairing the reliability of the pressure-sensitive adhesive sheet. For this reason, it is preferable that the release film has good releasability from the pressure-sensitive adhesive sheet and little migration of the release agent to the pressure-sensitive adhesive sheet.

[0132] The peel strength between the pressure-sensitive adhesive sheet and the release film is preferably 0.05 to 1.5 N / cm, more preferably 0.06 to 1.2 N / cm, and even more preferably 0.07 to 1.0 N / cm. The peel strength between the release film and the pressure-sensitive adhesive sheet is measured in a 180° peel test at a test speed of 300 mm / min. If the peel strength is within this range, it is possible to prevent peel marks when the release film is peeled from the pressure-sensitive adhesive sheet.

[0133] Furthermore, the peak intensity of silicon atoms measured using an X-ray fluorescence analyzer on the adhesive surface exposed by peeling off the release film from this pressure-sensitive adhesive sheet is preferably 100 cps or less. If the peak intensity is 100 cps or less, it is preferable that the release agent migrated to the pressure-sensitive adhesive sheet surface does not impair the reliability when the pressure-sensitive adhesive sheet is used as a laminate for constituting an image display device. From this perspective, the peak intensity is more preferably 90 cps or less, even more preferably 80 cps or less, and particularly preferably 70 cps or less. The lower limit is usually 0 cps.

[0134] The thickness of the release film is not particularly limited. In terms of processability and handleability, the thickness is preferably 10 to 250 μm, more preferably 25 to 200 μm, and even more preferably 35 to 190 μm.

[0135] If necessary, the sheet may be embossed or may have various irregularities (such as a cone, pyramid, or hemisphere).In addition, the sheet 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.

[0136] The present pressure-sensitive adhesive sheet may be a single-layer sheet consisting of only an acrylic pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition, or a multi-layer sheet in which multiple acrylic pressure-sensitive adhesive layers and / or other pressure-sensitive adhesive layers are laminated.

[0137] <Physical Properties of the Present Pressure-Sensitive Adhesive Sheet> The present pressure-sensitive adhesive sheet can have the following physical properties.

[0138] (Shear storage modulus (G')) The pressure-sensitive adhesive sheet preferably has a shear storage modulus at -30°C (G'(-30°C)), obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of 1200 kPa or less, more preferably 1000 kPa or less, even more preferably 800 kPa or less, particularly preferably 700 kPa or less, and especially preferably 500 kPa or less. The lower limit of the shear storage modulus (G'(-30°C)) of the pressure-sensitive adhesive sheet is preferably 100 kPa or more, in view of the balance with the shear storage modulus at high temperatures.

[0139] The pressure-sensitive adhesive sheet has a shear storage modulus at -20°C (G'(-20°C)), obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of typically 1000 kPa or less, preferably 400 kPa or less, particularly preferably 300 kPa or less, and especially preferably 250 kPa or less. The lower limit of the shear storage modulus (G'(-20°C)) of the pressure-sensitive adhesive sheet is preferably 50 kPa or more, in view of the balance with the shear storage modulus at high temperatures.

[0140] The shear storage modulus (G'(25°C)) of the pressure-sensitive adhesive sheet at 25°C, as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, is preferably 60 kPa or less, more preferably 55 kPa or less, particularly preferably 50 kPa or less, and most preferably 45 kPa or less. The lower limit of the shear storage modulus (G'(25°C)) of the pressure-sensitive adhesive sheet is preferably 5 kPa or more, from the viewpoints of preventing adhesive extrusion and maintaining the shape of the pressure-sensitive adhesive sheet.

[0141] The shear storage modulus (G'(60°C)) of this pressure-sensitive adhesive sheet at 60°C, as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, is typically 50 kPa or less, preferably 40 kPa or less, particularly preferably 35 kPa or less, and especially preferably 30 kPa or less. The lower limit of the shear storage modulus (G'(60°C)) of this pressure-sensitive adhesive sheet is preferably 1 kPa or more, from the viewpoints of preventing adhesive extrusion and maintaining the shape of the pressure-sensitive adhesive sheet.

[0142] The shear storage modulus (G'(80°C)) of this pressure-sensitive adhesive sheet at 80°C, as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, is typically 30 kPa or less, preferably 25 kPa or less, particularly preferably 20 kPa or less, and especially preferably 15 kPa or less. The lower limit of the shear storage modulus (G'(80°C)) of this pressure-sensitive adhesive sheet is preferably 1 kPa or more, from the viewpoints of preventing adhesive extrusion and maintaining the shape of the pressure-sensitive adhesive sheet.

[0143] When the shear storage modulus (G') of the present adhesive sheet is within the above range, for example, when the present adhesive sheet is adhered to a component sheet to form a laminate or a laminate for an image display device, the interlayer stress when the laminate or the laminate for an image display device is bent can be reduced, particularly at low to high temperatures, and peeling or cracking of the component sheet or flexible image display device component can be suppressed.

[0144] Furthermore, the ratio of the shear storage modulus at -20°C (G'(-20°C)) to the shear storage modulus at 60°C (G'(60°C)) [G'(-20°C) / G'(60°C)] is typically 3 to 30, preferably 5 to 20, and particularly preferably 7 to 15. By setting G'(-20°C) / G'(60°C) within the above range, for example, when the pressure-sensitive adhesive sheet is attached to a component sheet to form a laminate or a laminate for an image display device, the interlayer stress when the laminate or the laminate for an image display device is folded can be reduced, and peeling or cracking of the component sheet or the component of a flexible image display device can be suppressed.

[0145] (Loss tangent (tan δ)) The pressure-sensitive adhesive sheet preferably has a loss tangent (tan δ) at 25 to 60°C, as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of 0.18 or more, more preferably 0.20 or more, and particularly preferably 0.25 or more. The upper limit is usually 1. When the loss tangent (tan δ) at 25 to 60°C is equal to or greater than the above-mentioned value, the sheet tends to have excellent flexibility.

[0146] (Maximum point of loss tangent (tan δ) and glass transition temperature (Tg)) For the present pressure-sensitive adhesive sheet, the maximum point of the loss tangent (tan δ) obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is preferably −20°C or lower, more preferably −25°C or lower, particularly preferably −30°C or lower, and even more preferably −35°C or lower. The lower limit is typically −80°C. The maximum point of the loss tangent (tan δ) can be interpreted as the glass transition temperature (Tg), and having a glass transition temperature (Tg) in the above range tends to make it easier to adjust the shear storage modulus (G'(−20°C)) of the present pressure-sensitive adhesive sheet to 1000 kPa or lower.

[0147] When only one inflection point is observed in the loss tangent (tan δ) obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, in other words, when the tan δ curve exhibits a single peak, it can be considered that the glass transition temperature (Tg) is single.

[0148] The "maximum point" of the loss tangent (tan δ) means the point having the maximum value in a predetermined range or the entire range among the peak values ​​in the tan δ curve, that is, the inflection points where the tan δ curve changes from positive (+) to negative (-) when differentiated.

[0149] The shear storage modulus (G') and loss tangent (tan δ) at various temperatures can be measured using a rheometer.

[0150] The shear storage modulus (G') and loss tangent (tan δ) can be adjusted to the above ranges by adjusting the types and weight average molecular weights of the components (e.g., the acrylic polymer (A) and the radically polymerizable compound (B)) contained in the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive sheet, and by adjusting the gel fraction of the pressure-sensitive adhesive sheet, etc. However, this method is not limited to this.

[0151] (Resilience) The pressure-sensitive adhesive sheet has a thickness of 0.5 to 1.2 mm, and is subjected to a strain of 400% at 25°C for 600 seconds, after which the strain (γ max ) and the strain (γ min The restoration rate calculated from [γ ] by the following formula is preferably 60% or more, and more preferably 65% ​​or more. max -γ min ) / γ max ]×100

[0152] If the pressure-sensitive adhesive sheet has such resilience, it can be made into a pressure-sensitive adhesive sheet with excellent flexibility that does not leave fold marks due to being placed in a bent state, even when the pressure-sensitive adhesive sheet is attached to a component sheet and subjected to a folding operation at low or high temperatures. Note that, since a higher resilience is preferable, the upper limit of the resilience is 100%.

[0153] In this pressure-sensitive adhesive sheet, a radically polymerizable compound (B) is used to improve flexibility. The radically polymerizable compound (B) is preferably a polymerizable compound containing an oxyalkylene structure having an alkylene group having a length within the aforementioned certain range. By using such a polymerizable compound having an alkylene glycol skeleton, it becomes easier to bond with the acrylic polymer (A), and the entanglement of the polymer chains becomes stronger. Therefore, the entropy difference before and after elongation increases, and the entropy elasticity can improve recovery. Furthermore, in this pressure-sensitive adhesive sheet, in order to improve flexibility, it is preferable that the acrylic polymer (A) has a structural moiety derived from an alkyl (meth)acrylate (a1) and a structural moiety derived from a hydroxyl group-containing (meth)acrylate (a2). However, the method for adjusting recovery (flexibility) is not limited to these methods.

[0154] (Gel Fraction) The gel fraction of the present pressure-sensitive adhesive sheet is 95% or less, preferably 90% or less, and more preferably 85% or less. By having the gel fraction of the present pressure-sensitive adhesive sheet be equal to or less than the above-mentioned value, the adhesive strength to flexible members can be increased. The lower limit is usually 30% or more, preferably 40% or more, and particularly preferably 50% or more. By having a gel fraction equal to or greater than the above-mentioned lower limit, the shape tends to be sufficiently maintained. The gel fraction is an indicator of the degree of crosslinking (degree of curing) and can be measured under the measurement conditions described in the Examples below.

[0155] (Adhesive Strength) The present pressure-sensitive adhesive sheet has excellent adhesive strength at room temperature and also good adhesive strength at high temperatures. The adhesive strength to polyimide at 23°C (P(23°C)) is preferably 3.0 N / cm or more, and the adhesive strength to polyimide at 60°C (P(60°C)) is preferably 2.0 N / cm or more. A pressure-sensitive adhesive sheet satisfying the above-mentioned requirements has excellent adhesive strength over a wide temperature range, and is less likely to peel even when a laminate attached to an adherend such as a component of an image display device is bent, resulting in excellent durability. From this perspective, the adhesive strength to polyimide at 23°C (P(23°C)) is preferably 3.5 N / cm or more, more preferably 3.6 N / cm or more, even more preferably 3.8 N / cm or more, particularly preferably 4.0 N / cm or more, and especially preferably 4.5 N / cm or more. From the same viewpoint, the adhesive strength to polyimide at 60°C (P(60°C)) is more preferably 2.1 N / cm or more, even more preferably 2.5 N / cm or more, particularly preferably 3.0 N / cm or more, and particularly preferably 3.5 N / cm or more. Specifically, the adhesive strength can be measured by the method described in the examples below.

[0156] Furthermore, the ratio of the adhesive strength to polyimide at 23°C to the adhesive strength to polyimide at 60°C (P(23°C) / P(60°C)) of the present pressure-sensitive adhesive sheet is typically 0.3 to 2.6, preferably 0.4 to 2.5, more preferably 0.5 to 2.4, even more preferably 0.6 to 2.3, particularly preferably 0.7 to 2.2, and especially preferably 0.8 to 2.0. Pressure-sensitive adhesive sheets that satisfy the above-mentioned criteria have little temperature dependency of adhesive strength and excellent adhesiveness over a wide temperature range, and therefore tend to be less susceptible to peeling even when a laminate bonded to an adherend such as a component of an image display device is bent, and therefore have excellent durability. Furthermore, from the viewpoint of stronger adhesion at room temperature, the adhesive strength ratio is preferably 1.0 or more, more preferably 1.1 or more, even more preferably 1.2 or more, and particularly preferably 1.3 or more.

[0157] (Transparency, Haze) The pressure-sensitive adhesive sheet has transparency when visually observed, and transparency indicates that the components are uniformly dissolved in each other.

[0158] Furthermore, the pressure-sensitive adhesive sheet preferably has a total light transmittance of 80% or more, more preferably 85% or more, and particularly preferably 90% or more. When the pressure-sensitive adhesive sheet has a total light transmittance of this value or more, it tends to be suitable for use in image display devices.

[0159] Furthermore, the pressure-sensitive adhesive sheet preferably has a haze of 5% or less, more preferably 4% or less, and particularly preferably 1% or less. When the pressure-sensitive adhesive sheet has a haze of the above-mentioned value or less, it tends to be suitable for use in image display devices.

[0160] In order to set the total light transmittance and haze of the pressure-sensitive adhesive sheet within the above ranges, it is preferable that the pressure-sensitive adhesive sheet does not contain particles such as organic particles.

[0161] <Preferred uses of the present pressure-sensitive adhesive sheet> The present pressure-sensitive adhesive sheet is suitably used for bonding components of image display devices. Specifically, it is suitably used for bonding components that constitute display members (also referred to as "display members"), in particular, components of flexible image display devices used in producing displays, and is used as a pressure-sensitive adhesive sheet for components of flexible image display devices. Note that the same components of flexible image display devices as those described below can be used.

[0162] <<Laminate for Image Display Device>> A laminate for an image display device according to one example of an embodiment of the present invention (hereinafter sometimes referred to as "the present laminate for an image display device") is a laminate for an image display device having a configuration in which two components of the image display device are laminated with the present pressure-sensitive adhesive sheet interposed therebetween. Furthermore, the present laminate for an image display device is preferably a laminate for a flexible image display device having a configuration in which two components of a flexible image display device are laminated with the present pressure-sensitive adhesive sheet interposed therebetween.

[0163] Of the components of the present laminate for an image display device, the present pressure-sensitive adhesive sheet has been described above, and the components other than the pressure-sensitive adhesive sheet will be described below.

[0164] (Image Display Device Components) Examples of image display device components constituting the present image display device laminate include flexible image display device components. Examples of the flexible image display device components include flexible displays such as organic electroluminescence (EL) displays, cover lenses (cover films), polarizing plates, polarizers, retardation films, barrier films, viewing angle compensation films, brightness enhancement films, contrast enhancement films, diffusion films, semi-transmissive reflective films, electrode films, transparent conductive films, metal mesh films, and touch sensor films. Any one of these may be used alone or in combination of two of two types. Examples include a combination of a flexible display with another flexible image display device component, or a combination of a cover lens with another flexible image display device component.

[0165] The term "flexible image display device component" refers to a bendable component, particularly a component that can be repeatedly bent. In particular, it is preferable that the component be a component that can be fixed into a curved shape with a curvature radius of 25 mm or more, and particularly a component that can withstand repeated bending at a curvature radius of less than 25 mm, more preferably less than 3 mm.

[0166] In the above-described configuration, the main component of the flexible image display device component may be a resin sheet or glass. Examples of materials for such a resin sheet include polyester resin, cycloolefin resin, triacetyl cellulose resin, polymethyl methacrylate resin, polyurethane, epoxy resin, polyimide resin, and aramid resin. These may be one type of resin or two or more types of resin. Among these, a resin sheet containing at least one resin selected from the group consisting of polyester resin, cycloolefin resin, triacetyl cellulose resin, polymethyl methacrylate resin, epoxy resin, polyimide resin, aramid resin, and polyurethane resin as its main component is preferred. Here, the term "main component" refers to the component that occupies the largest mass ratio among the components constituting the flexible image display device component. Specifically, the main component is a component that occupies 50% by mass or more, preferably 55% by mass or more, and particularly preferably 60% by mass or more, of the resin composition (resin sheet) forming the flexible image display device component. The flexible image display device component may also be made of thin-film glass.

[0167] In the above-described configuration, it is preferable that one of the two flexible image display device constituent members, i.e., the first flexible image display device constituent member, has a tensile strength at 25°C measured in accordance with ASTM D882 of 10 to 900 MPa, more preferably 15 to 800 MPa, and particularly preferably 20 to 700 MPa. If the 25°C tensile strength (ASTM D882) of one of the flexible image display device constituent members is within the above range, it is preferable because it is less likely to crack when bent.

[0168] Furthermore, the other flexible image display device component, i.e., the second flexible image display device component, preferably has a tensile strength at 25°C measured in accordance with ASTM D882 of 10 to 900 MPa, more preferably 15 to 800 MPa, and particularly preferably 20 to 700 MPa. If the 25°C tensile strength (ASTM D882) of the other flexible image display device component falls within the above range, it is preferable because it is less likely to crack when bent.

[0169] Examples of flexible image display device components with high tensile strength include polyimide films, polyester films, aramid films, etc., which generally have a tensile strength of 900 MPa or less. On the other hand, examples of flexible image display device components with somewhat low tensile strength include triacetyl cellulose (TAC) films, cycloolefin polymer (COP) films, etc., which generally have a tensile strength of 10 MPa or more. Even if the present laminate for flexible image display devices includes flexible image display device components made of such materials with somewhat low tensile strength, defects such as cracking can be suppressed by the action of the present pressure-sensitive adhesive sheet.

[0170] <Method for manufacturing the present laminate for an image display device> The method for manufacturing the present laminate for an image display device is not particularly limited, and as described above, for example, the adhesive composition may be applied onto a component of an image display device, preferably onto a component of a flexible image display device, to form an adhesive sheet, or an adhesive sheet may be formed in advance and then laminated to a component of an image display device, preferably a component of a flexible image display device.

[0171] <<Flexible Image Display Device>> A flexible image display device according to one embodiment of the present invention (hereinafter may be referred to as "the flexible image display device") is an image display device incorporating a laminate for a flexible image display device, having a configuration in which two flexible image display device components are bonded together via the present pressure-sensitive adhesive sheet. For example, the flexible image display device including the laminate can be formed by laminating a laminate for a flexible image display device, having a configuration in which two flexible image display device components are bonded together via the present pressure-sensitive adhesive sheet, onto another image display device component.

[0172] In the present invention, the term "flexible image display device" refers to an image display device that leaves no trace of bending even when repeatedly bent, can quickly restore to its original state when released from bending, and can display images without distortion even when bent. More specifically, an example of such an image display device is an image display device made of a member that can be curved and fixed to a curvature radius of 25 mm or more, particularly a member that can withstand repeated bending with a curvature radius of less than 25 mm, more preferably less than 3 mm.

[0173] One of the features of this image display device body is that it can prevent peeling or cracking of the laminate even when folded in a high-temperature environment, and it has good recovery properties, making it possible to manufacture flexible image display devices with excellent flexibility.

[0174] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples. In the examples, "parts" refers to parts by mass.

[0175] <Raw Materials> First, the acrylic polymer (A) and the pressure-sensitive adhesive composition prepared in the examples and comparative examples will be described in detail.

[0176] <Acrylic polymer (A)> Acrylic polymer (A-1): a random copolymer of 60 parts of 2-ethylhexyl acrylate, 15 parts of butyl acrylate, 5 parts of ethyl methacrylate, and 20 parts of 2-hydroxyethyl acrylate (hydroxyl value: 96 mg KOH / g, weight average molecular weight: 940,000, glass transition temperature: -23°C) Acrylic polymer (A-2): a random copolymer of 67 parts of 2-ethylhexyl acrylate, 5 parts of methyl acrylate, 10 parts of ethyl acrylate, 14 parts of 2-hydroxyethyl acrylate, and 4 parts of 4-hydroxybutyl acrylate (hydroxyl value: 83 mg KOH / g, weight average molecular weight: 700,000, glass transition temperature: -23°C) Acrylic polymer (A-3): a random copolymer of 80 parts of n-octyl acrylate and 20 parts of 4-hydroxybutyl acrylate (hydroxyl value: 27 mg KOH / g, weight average molecular weight: 770,000, glass transition temperature: -59°C) Acrylic polymer (A-4): a random copolymer of 81 parts of n-butyl acrylate and 19 parts of 4-hydroxybutyl acrylate (hydroxyl value: 23 mg KOH / g, weight average molecular weight: 840,000, glass transition temperature: −52° C.)

[0177] <Radical polymerizable compound (B)> Radical polymerizable compound (B-1): Monofunctional urethane acrylate having a polypropylene glycol skeleton (but containing a small amount of bifunctionality) ("PEM-X264" manufactured by AGC) Radical polymerizable compound (B-2): Monofunctional urethane acrylate having a polypropylene glycol skeleton (but containing a small amount of bifunctionality) ("PEM-X435" manufactured by AGC)

[0178] <Photopolymerization initiator (C)> [Hydrogen abstraction photopolymerization initiator (C1)] Photopolymerization initiator (C1-1): a mixture of 4-methylbenzophenone and 2,4,6-trimethylbenzophenone (Ezacure TZT manufactured by IGM) [α-Aminoalkylphenone cleavage photopolymerization initiator (C2)] Photopolymerization initiator (C2-1): 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one (Omnirad 369 manufactured by IGM, weight average molecular weight: 367, maximum absorption wavelength: 323 nm) Photopolymerization initiator (C2-2): 2-(dimethylamino)-2-(4-methylbenzyl)-1-(4-morpholinophenyl)butan-1-one (Omnirad 369 manufactured by IGM, weight average molecular weight: 367, maximum absorption wavelength: 323 nm) 379", weight average molecular weight: 381, maximum absorption wavelength: 320 nm) Photopolymerization initiator (C2-3): 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one (IGM "Omnirad 907", weight average molecular weight: 279, maximum absorption wavelength: 303 nm) [Other cleavage-type photopolymerization initiators] Photopolymerization initiator (C-1): 2-hydroxy-1-[4-{4-(2-hydroxy-2-methyl-propionyl)benzyl}phenyl]-2-methyl-propan-1-one (IGM "Omnirad 127") Photopolymerization initiator (C-2): 2,2-dimethoxy-1,2-diphenylethan-1-one (IGM "Omnirad 651") Photopolymerization initiator (C-3): 2,4,6-trimethylbenzoyldiphenylphosphine oxide ("Omnirad TPO H" manufactured by IGM)

[0179] <Multifunctional Epoxy Compounds (D)> Multifunctional epoxy compound (D-1): polyethylene glycol #400 diglycidyl ether ("Epolight 400E" manufactured by Kyoeisha Chemical Co., Ltd.) Multifunctional epoxy compound (D-2): polyethylene glycol diglycidyl ether ("Denacol EX-841" manufactured by Nagase ChemteX Corporation)

[0180] [Examples 1 to 13, Comparative Examples 1 to 8] The raw materials of the pressure-sensitive adhesive compositions and ethyl acetate as a solvent were uniformly mixed according to the formulations shown in Tables 1 and 2 below to obtain pressure-sensitive adhesive composition solutions (solid content concentration: 40% by mass).

[0181] The pressure-sensitive adhesive composition solution was coated onto a release film (manufactured by Mitsubishi Chemical Corporation, silicone release-treated polyester film, thickness 100 μm) to a dry thickness of 50 μm. After coating, the coating was placed in a dryer heated to 90°C for 7 minutes to evaporate and dry the solvent contained in the pressure-sensitive adhesive composition. Furthermore, a release film (manufactured by Mitsubishi Chemical Corporation, silicone release-treated polyester film, 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. The pressure-sensitive adhesive composition was irradiated with ultraviolet light through the release film using a high-pressure mercury lamp (wavelength 365 nm) (see Tables 1 and 2 for the cumulative light dose), thereby obtaining a pressure-sensitive adhesive sheet with a release film. The resulting pressure-sensitive adhesive sheet was evaluated as follows. The results are shown in Tables 1 and 2 below.

[0182] <Shear storage modulus (G'), loss tangent (Tan δ), glass transition temperature (Tg)> The release film on one side of the pressure-sensitive adhesive sheet with release film prepared in the examples and comparative examples was removed, and the sheet was repeatedly laminated with a hand roller to a thickness of approximately 0.8 mm. A circle with a diameter of 8 mm was punched out to prepare a sample. The obtained sample was placed in a viscoelasticity measuring device ("DHR2" manufactured by T.A. Instruments) and subjected to dynamic viscoelasticity measurement under the conditions of measurement jig: 8 mm diameter parallel plate, frequency: 1 Hz, measurement temperature: -50 to 80 ° C, and heating rate: 5 ° C / min. The shear storage modulus (G') value at -30 to 80 ° C and the loss tangent (Tan δ) value at 25 to 60 ° C were read. In addition, from the temperature dispersion data of the obtained dynamic viscoelasticity, the temperature at the maximum point of the loss tangent (tan δ) was read as the glass transition temperature (Tg).

[0183] <Resilience> The release film on one side was removed from the pressure-sensitive adhesive sheets with release film prepared in the Examples and Comparative Examples, and the sheets were repeatedly laminated with a hand roller to a thickness of approximately 0.8 mm, and then punched into circles with a diameter of 8 mm to prepare samples. The samples were measured using a viscoelasticity measuring device ("DHR2" manufactured by T.A. Instruments) to determine the maximum strain value (γmax) after applying a 400% strain at 25°C for 600 seconds, and the residual strain value (γmin ) was read.

[0184] The maximum strain value (γ max ) and residual strain value (γ min ) was substituted into the following formula to determine the restoration rate: max -γ min ) / γ max ]×100

[0185] <Gel fraction> The release film was removed from the pressure-sensitive adhesive sheets with release film prepared in the Examples and Comparative Examples, and this was used as a sample. This sample was wrapped in a 150-mesh SUS wire mesh and immersed in ethyl acetate for 24 hours. After that, it was dried at 70°C for 4.5 hours, and the mass of the pressure-sensitive adhesive sheet was measured before and after immersion in ethyl acetate, and the difference between the two masses was taken as the mass of the insoluble pressure-sensitive adhesive sheet remaining in the wire mesh. The mass percentage of the insoluble pressure-sensitive adhesive sheet remaining in the wire mesh relative to the mass of the pressure-sensitive adhesive sheet before immersion in ethyl acetate was calculated as the gel fraction (%).

[0186] <Adhesion to polyimide (CPI)> The release film on one side was removed from the pressure-sensitive adhesive sheets with release film prepared in the Examples and Comparative Examples, and a PET film (Diafilm S-100, manufactured by Mitsubishi Chemical Corporation, thickness 50 μm) was attached as a backing film using a hand roller. This was cut into strips 10 mm wide x 150 mm long, and the remaining release film was peeled off, and the exposed adhesive surface was attached with a hand roller to a transparent polyimide (CPI) film ("C_50" manufactured by KOLON Corporation) that had been previously attached to a SUS plate, to prepare an adhesion measurement sample. The obtained adhesive strength measurement sample was pulled at an angle of 180° at a peeling rate of 300 mm / min at 23°C and 60°C, and the adhesive sheet was peeled off from the CPI film together with the backing film. The tensile strength (N / cm) was measured with a load cell, and the adhesive strength to polyimide at 23°C (P(23°C)) and the adhesive strength to polyimide at 60°C (P(60°C)) were determined.

[0187] From the adhesive strength to polyimide measured above, the ratio of the adhesive strength to polyimide at 23°C to the adhesive strength to polyimide at 60°C (P(23°C) / P(60°C)) was calculated.

[0188]

[0189]

[0190] The PSA sheets of Examples 1 to 13 were formed from PSA compositions containing an acrylic polymer (A), a radically polymerizable compound (B), and a photopolymerization initiator (C) containing a hydrogen abstraction photopolymerization initiator (C1) and an α-aminoalkylphenone cleavage photopolymerization initiator (C2). Therefore, they exhibited excellent adhesion to flexible materials and excellent flexibility. In particular, the adhesive strength was excellent both at 23°C and 60°C. While the reasons for these characteristics are unclear, the following may be considered: The combined use of the hydrogen abstraction photopolymerization initiator (C1) and the α-aminoalkylphenone cleavage photopolymerization initiator (C2) improved the reactivity of the radically polymerizable compound (B), reducing the amount of low-molecular-weight components migrating to the polyimide interface, which is the adherend. This likely resulted in improved adhesive strength compared to the hydrogen abstraction photopolymerization initiator (C1) alone. Furthermore, by using the hydrogen abstraction photopolymerization initiator (C1) in combination with the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2), the shear storage modulus (G') decreased, the pressure-sensitive adhesive composition became softer, and its wettability to the polyimide surface improved, which is thought to have resulted in improved adhesive strength. On the other hand, the pressure-sensitive adhesive sheets of Comparative Examples 1 to 5, which did not contain the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2), and the pressure-sensitive adhesive sheets of Comparative Examples 6 to 8, which used the hydrogen abstraction photopolymerization initiator (C1) and other cleavage-type photopolymerization initiators as the photopolymerization initiator (C), did not satisfy both 23°C and 60°C in terms of adhesiveness to flexible materials, and were inferior in at least one of these.

[0191] 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.

[0192] The adhesive sheet of the present invention has excellent adhesive strength to flexible materials and is flexible, and is therefore useful as an adhesive sheet for obtaining various flexible image display devices such as bendable, foldable, rollable, and stretchable, and is particularly suitable as an adhesive sheet for foldable image display devices that are subject to repeated bending.

Claims

1. An adhesive sheet formed from an adhesive composition containing an acrylic polymer (A), a radically polymerizable compound (B), and a photopolymerization initiator (C), wherein the photopolymerization initiator (C) contains a hydrogen abstraction type photopolymerization initiator (C1) and an α-aminoalkylphenone cleavage type photopolymerization initiator (C2).

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the weight-average molecular weight of the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) is 800 or less.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) contains elemental sulfur.

4. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the α-aminoalkylphenone cleavage-type photopolymerization initiator (C2) has a maximum absorption wavelength in the region of 270 to 315 nm in the light absorption spectrum.

5. The adhesive sheet according to claim 1 or 2, wherein the content of the photopolymerization initiator (C) is 0.1 to 10 parts by mass per 100 parts by mass of the acrylic polymer (A), and the content ratio (C1 / C2) of the hydrogen abstraction type photopolymerization initiator (C1) to the α-aminoalkylphenone cleavage type photopolymerization initiator (C2) is 0.5 to 10 by mass.

6. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the radically polymerizable compound (B) has an alkylene glycol skeleton.

7. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the radically polymerizable compound (B) has a urethane bond.

8. The adhesive sheet according to claim 1 or 2, wherein the acrylic polymer (A) is an acrylic polymer having a structural portion derived from a (meth)acrylate (a1) having an alkyl group with 3 or more carbon atoms, and a structural portion derived from a hydroxyl group-containing (meth)acrylate (a2).

9. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive composition further contains a multifunctional epoxy compound (D).

10. The pressure-sensitive adhesive sheet according to claim 1 or 2, which has a shear storage modulus (G'(25°C)) at 25°C, as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of 60 kPa or less.

11. The pressure-sensitive adhesive sheet according to claim 1 or 2, which has a shear storage modulus (G'(-30°C)) at -30°C, as determined by dynamic viscoelastic measurement in a shear mode at a frequency of 1 Hz, of 1,200 kPa or less.

12. The pressure-sensitive adhesive sheet according to claim 1 or 2, which has a glass transition temperature (Tg) defined as the maximum value of Tan δ obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz, of -20°C or lower.

13. The thickness is 0.5 to 1.2 mm, and the strain (γ max ) and the strain after 600 seconds of unloading (γ min 3. The pressure-sensitive adhesive sheet according to claim 1, wherein the recovery rate calculated from the following formula is 60% or more. max -γ min ) / γ max 〕×100 14. The adhesive sheet according to claim 1 or 2, wherein the gel fraction of the adhesive sheet is 30 to 95 mass %.

15. An adhesive sheet with a release film, comprising the adhesive sheet according to claim 1 or 2 and a release film laminated on the adhesive sheet.

16. A laminate for an image display device, comprising two components of the image display device and the adhesive sheet according to claim 1 or 2 interposed between the two components of the image display device.

17. A flexible image display device comprising the laminate for an image display device according to claim 16.

18. An adhesive sheet for use as a component of a flexible image display device, comprising the adhesive sheet according to claim 1 or 2.

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