JP2024079653A - Pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet, pressure-sensitive adhesive sheet with release film, laminate for image display device, image display device, and pressure-sensitive adhesive sheet for organic EL display device - Google Patents

Abstract

[Problem] To provide a pressure-sensitive adhesive composition that has ultraviolet absorbing properties, can be cured by active energy rays, and produces few photodecomposition products. [Solution] A pressure-sensitive adhesive composition comprising a (meth)acrylic polymer (A), a photoinitiator (B), and an ultraviolet absorber (C), wherein the photoinitiator (B) contains a photoinitiator (b1) having a glyoxylate structure represented by *-CO-COOR1 (wherein R1 is substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C3-C20 cycloalkyl, or substituted or unsubstituted C2-C20 heterocycloalkyl; * represents a bond), and having a molar absorption coefficient at a wavelength of 405 nm of 30 (L/mol cm) or more. [Selected Figure] None

Description

The present invention relates to an adhesive composition, and an adhesive sheet using the same, an adhesive sheet with a release film, a laminate for an image display device, an image display device, and an adhesive sheet for an organic electroluminescence display device.

In recent years, in order to improve the visibility of image display devices, the gap between an image display panel such as a liquid crystal display (LCD), plasma display (PDP) or electroluminescence display (ELD) and an optical component such as a protective panel or touch panel component arranged on the front side (viewing side) of the image display panel has been filled with a resin such as an adhesive or bonding agent to suppress reflection of incident light and outgoing light from the displayed image at the air layer interface.

For example, Patent Document 1 discloses a method for manufacturing a laminated component for an image display device, which has a configuration in which an image display device component is laminated on at least one side of a transparent double-sided adhesive sheet, in which an adhesive sheet that has been primarily crosslinked with ultraviolet light is attached to the image display device component, and then the adhesive sheet is irradiated with ultraviolet light through the image display device component for secondary curing.

Patent Document 2 also discloses a pressure-sensitive adhesive sheet containing a (meth)acrylic copolymer having an ultraviolet crosslinkable site, as an adhesive sheet useful for displays and touch panels.

Patent No. 4971529 Japanese Patent No. 6062740

In recent years, with the need for power saving, weight reduction, and thinning of image display devices, organic electroluminescence (EL) panels are becoming more and more popular as image display panels, replacing conventional liquid crystal panels. In image display devices such as organic EL display devices, components within the image display device may be deteriorated by incident ultraviolet light, and there is an increasing need for adhesive sheets containing an ultraviolet absorber to suppress deterioration caused by the ultraviolet light.
Many adhesive sheets that form a crosslinked structure by UV irradiation contain a photoinitiator that generates radicals when irradiated with UV light. However, when the adhesive sheet contains a UV absorber, the UV light is blocked, which can cause the curing reaction to not proceed sufficiently.

For this reason, photocurable adhesive sheets using photoinitiators that have absorption in the longer wavelength ultraviolet or visible light regions, such as α-aminoacetophenone-based or acylphosphine oxide-based photoinitiators, have been developed. However, these cleavage-type photoinitiators are not considered to be preferable photoinitiators because they generate outgassing products such as benzaldehyde as photodecomposition products.
On the other hand, hydrogen abstraction photoinitiators such as thioxanthone and anthraquinone, which do not produce photodecomposition products during reaction, have absorption in the ultraviolet and visible light regions of the long wavelength range, but they have a problem of coloring, especially yellowing, caused by the photoinitiator in the cured product. Therefore, in applications where colorlessness or transparency is required, there is a limit to the amount that can be added, and sufficient curing sensitivity cannot be obtained.

The present invention has been made in consideration of the above problems, and a first object of the present invention is to provide a pressure-sensitive adhesive composition that has ultraviolet absorbing properties, can be cured by active energy rays, and produces few photodecomposition products.
A second object of the present invention is to provide an adhesive sheet that has ultraviolet absorbing properties while also being curable with active energy rays, and an adhesive sheet with a release film, a laminate for an image display device, an image display device, and an adhesive sheet for an organic EL display device using the same.

An embodiment of the present invention includes the following configuration.
[1] A composition comprising a (meth)acrylic polymer (A), a photoinitiator (B), and an ultraviolet absorber (C),
The pressure-sensitive adhesive composition, wherein the photoinitiator (B) comprises a photoinitiator (b1) having a glyoxylate structure represented by the following formula 1 and having a molar absorption coefficient of light having a wavelength of 405 nm of 30 (L/mol cm) or more.

(In the above formula 1, R ¹ is a substituted or unsubstituted C ₁ -C ₂₀ alkyl, a substituted or unsubstituted C ₃ -C ₂₀ cycloalkyl, or a substituted or unsubstituted C ₂ -C ₂₀ heterocycloalkyl. * indicates a bond.)
[2] The pressure-sensitive adhesive composition according to [1], wherein the photoinitiator (b1) is a compound containing a biphenyl structure to which the bond * in the formula 1 is bonded.
[3] The pressure-sensitive adhesive composition according to [1], wherein the photoinitiator (b1) is a compound containing a sulfurized biphenyl structure to which the bond * in the formula 1 is bonded.
[4] The pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the photoinitiator (b1) is a compound having two or more radical generating groups in a molecule.
[5] The pressure-sensitive adhesive composition according to any one of [1] to [4], further comprising a polyfunctional (meth)acrylate (D).
[6] The pressure-sensitive adhesive composition according to [5], wherein the content of the polyfunctional (meth)acrylate (D) is 0.1 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the (meth)acrylic polymer (A).
[7] The pressure-sensitive adhesive composition according to [1], wherein the (meth)acrylic polymer (A) comprises a structural unit derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 3 to 30 carbon atoms in the alkyl group, and a structural unit derived from a hydroxyl group-containing monomer and/or a structural unit derived from a nitrogen-containing monomer.
[8] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of [1] to [7].
[9] The pressure-sensitive adhesive sheet according to [8], having a light transmittance of 10% or less at a wavelength of 380 nm.
[10] The pressure-sensitive adhesive sheet according to [8] or [9], having a light transmittance of 30% or less at a wavelength of 400 nm.
[11] The pressure-sensitive adhesive sheet according to any one of [8] to [10], having a total light transmittance of 80% or more.
[12] The pressure-sensitive adhesive sheet according to any one of [8] to [11], having a gel fraction (X0) of 20% or more.
[13] The pressure-sensitive adhesive sheet according to [12], wherein the pressure-sensitive adhesive sheet has active energy ray curability, and the gel fraction (X1) is 30% or more when the pressure-sensitive adhesive sheet is irradiated with active energy rays having a wavelength of 405 nm so that the integrated light amount is 2000 to 4000 mJ/ ^cm2 .
[14] The pressure-sensitive adhesive sheet according to [13], wherein the difference (X1-X0) between the gel fraction (X1) and the gel fraction (X0) is 10% or more.
[15] The pressure-sensitive adhesive sheet according to any one of [8] to [14], wherein the pressure-sensitive adhesive sheet has active energy ray curability, and when the pressure-sensitive adhesive sheet is irradiated with active energy rays having a wavelength of 405 nm so that the integrated light amount is 2000 to 4000 mJ/ ^cm2 , the chromaticity (b*1) is 2.5 or less, and the difference (b*1-b*0) from the chromaticity (b*0) before irradiation with the active energy rays is 1.0 or less.
[16] The pressure-sensitive adhesive sheet according to any one of [8] to [15], which is used for bonding optical members.
[17] A pressure-sensitive adhesive sheet with a release film, comprising the pressure-sensitive adhesive sheet according to any one of [8] to [16] and a release film laminated thereon.
[18] A laminate for an image display device, comprising two optical members laminated together via the pressure-sensitive adhesive sheet according to any one of [8] to [16].
[19] An image display device comprising the laminate for an image display device according to [18].
[20] An adhesive sheet for an organic electroluminescence display device, comprising the adhesive sheet according to any one of [8] to [16].
[21] A pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition containing a (meth)acrylic polymer (A), a photoinitiator (B) and an ultraviolet absorber (C),
The pressure-sensitive adhesive sheet, wherein the photoinitiator (B) comprises a compound represented by the following formula 2:

(In the above formula 2, A is O, S, NR ⁴ , or a linear or branched alkylene or cycloalkylene having 1 to 6 carbon atoms.
R ¹ is a substituted or unsubstituted C ₁ -C ₂₀ alkyl, a substituted or unsubstituted C ₃ -C ₂₀ cycloalkyl, or a substituted or unsubstituted C ₂ -C ₂₀ heterocycloalkyl.
^R2 is a hydrogen atom, a substituted or unsubstituted _C1 - _C20 alkyl, a substituted or unsubstituted _C3 - _C20 cycloalkyl, a substituted or unsubstituted _C2 - _C20 heterocycloalkyl, a substituted or unsubstituted _C6 - _C20 aryl, a substituted or unsubstituted _C1 - _C20 heteroaryl, ^SR5 , ^OR6 , ^{NR7R8 ,} C(O) ^R9 , or C(O) ^OR13 .
R ⁴ is a group selected from the group consisting of a hydrogen atom, a C ₁ -C ₁₈ alkyl, a C ₂ -C ₁₈ alkanoyl, a C ₆ -C ₁₀ aryl, and a C ₇ -C ₁₁ aroyl.
R ⁵ and R ⁶ are each independently a group selected from the group consisting of a hydrogen atom, a C ₁ -C ₂₀ alkyl, a C ₂ -C ₂₀ alkanoyl, a C ₆ -C ₁₀ aryl, and a C ₇ -C ₁₁ aroyl.
R ⁷ and R ⁸ are each independently a group selected from the group consisting of a hydrogen atom, a C ₁ -C ₂₀ alkyl, a C ₂ -C ₂₀ alkanoyl, a C ₇ -C ₁₁ aroyl, and a C ₆ -C ₁₀ aryl.
R ⁹ is a group selected from the group consisting of a hydrogen atom, a C ₁ -C ₂₀ alkyl, and a C ₆ -C ₂₀ aryl.
^R13 has the same meaning as ^R1 .

According to the present invention, there is provided a pressure-sensitive adhesive composition which has ultraviolet absorbing properties, is curable by active energy rays, and produces few photodecomposition products.
The adhesive sheet of the present invention has ultraviolet absorption properties, can be cured by active energy rays, and produces few photodecomposition products, and therefore can be suitably used as an adhesive sheet used for bonding optical components, in particular as an adhesive sheet for organic EL display devices.

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

In the present invention, when it is described as "x to y" (x and y are arbitrary numbers), unless otherwise specified, it includes the meaning of "x or more and y or less", as well as the meaning of "preferably larger than x" or "preferably smaller than y".
In addition, when it is stated that the amount is "x or more" (where x is any number), it also means that the amount is "preferably greater than x" unless otherwise specified, and when it is stated that the amount is "y or less" (where y is any number), it also means that the amount is "preferably smaller than y" unless otherwise specified.
Furthermore, "x and/or y (x and y are optional configurations)" means at least one of x and y, and means three possibilities: x only, y only, and x and y.
In the present invention, "(meth)acrylic" refers to a comprehensive definition of acrylic and methacrylic, "(meth)acrylate" refers to a comprehensive definition of acrylate and methacrylate, and "(meth)acryloyl" refers to a comprehensive definition of acryloyl and methacryloyl.
The term "(meth)acrylic polymer" refers to a polymer having a structural unit derived from a (meth)acrylic monomer. The (meth)acrylic polymer may further have a structural unit derived from a monomer other than the (meth)acrylic monomer (e.g., styrene, etc.).

<<Adhesive composition>>
The pressure-sensitive adhesive composition according to the present invention (hereinafter referred to as "the pressure-sensitive adhesive composition") is a pressure-sensitive adhesive composition containing a (meth)acrylic polymer (A), and by containing the (meth)acrylic polymer (A), the obtained pressure-sensitive adhesive sheet can be flexible and have good adhesive strength. The pressure-sensitive adhesive composition contains the (meth)acrylic polymer (A), a photoinitiator (B) and an ultraviolet absorber (C), and is characterized in that the photoinitiator (B) contains a photoinitiator (b1) having a glyoxylate structure and a molar absorption coefficient of light with a wavelength of 405 nm of 30 (L/mol cm) or more.
The pressure-sensitive adhesive composition can be suitably used for bonding optical members.
Each component contained in the pressure-sensitive adhesive composition will be described in detail below.

<(Meth)acrylic polymer (A)>
Examples of the (meth)acrylic polymer (A) contained in the present pressure-sensitive adhesive composition include homopolymers of alkyl (meth)acrylates, as well as copolymers obtained by polymerizing a monomer component copolymerizable therewith.
Among these, it is preferable that the (meth)acrylic polymer contains two or more copolymerization components, and at least one of the copolymerization components is an alkyl (meth)acrylate having an alkyl group with 3 to 30 carbon atoms.

More specifically, the (meth)acrylic polymer (A) may be a copolymer of monomer components including an alkyl (meth)acrylate having an alkyl group with 3 to 30 carbon atoms and one or more monomers selected from (a1) a carboxyl group-containing monomer, (a2) a hydroxyl group-containing monomer, (a3) a nitrogen-containing monomer, (a4) an epoxy group-containing monomer, (a5) a vinyl monomer, (a6) an alkyl (meth)acrylate monomer having an alkyl group with 1 or 2 carbon atoms, (a7) an alicyclic monomer, and (a8) other copolymerizable monomers that are copolymerizable therewith, other than the alkyl (meth)acrylate.

(1) Among the above copolymerizable monomers (a1) to (a8), the copolymerizable monomers (a1), (a2) and (a3) are particularly preferred.
(2) It is particularly preferred that the composition does not contain the copolymerizable monomer (a1) but contains either the copolymerizable monomer (a2) or (a3). By containing either the copolymerizable monomer (a2) or (a3), it is possible to provide both corrosion resistance, adhesion, and wet heat whitening resistance when the adherend contains a corrosive component such as metal. It is particularly preferred that the composition contains both the copolymerizable monomers (a2) and (a3) in order to enhance cohesion.
(3) Furthermore, among the copolymerizable monomers (a3), those having a tertiary nitrogen atom are preferred because they have a sensitizing effect on the hydrogen abstraction reaction described below, and as a result, can efficiently form crosslinks.
(4) Among the above alkyl (meth)acrylates, alkyl (meth)acrylates containing a tertiary carbon atom in the alkyl group are preferred. By using such alkyl (meth)acrylates, a hydrogen abstraction reaction is likely to occur upon light irradiation, and as a result, crosslinking is likely to be efficiently formed.

The alkyl (meth)acrylate is a linear or branched alkyl (meth)acrylate having an alkyl group with 3 to 30 carbon atoms, and is represented by the following formula (m1).
CH ₂ ═C(R ¹⁴ )—COO(R ¹⁵ ) Formula (m1)
(In formula m1, R ¹⁴ represents a hydrogen atom or a methyl group, and R ¹⁵ represents a linear or branched alkyl group having 3 to 30 carbon atoms.)

Examples of the alkyl (meth)acrylate represented by formula (m1) include linear alkyl (meth)acrylates such as n-propyl (meth)acrylate, i-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, undecyl (meth)acrylate, lauryl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, icosyl (meth)acrylate, henicosyl (meth)acrylate, and behenyl (meth)acrylate; sec-butyl Examples of branched alkyl (meth)acrylates include (meth)acrylate, isobutyl (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, isoicosyl (meth)acrylate, butyloctyl (meth)acrylate, isomyristyl (meth)acrylate, isocetyl (meth)acrylate, hexyldecyl (meth)acrylate, isostearyl (meth)acrylate, octyldecyl (meth)acrylate, octyldodecyl (meth)acrylate, and isobehenyl (meth)acrylate. These may be used alone or in combination of two or more.

Among these, linear alkyl (meth)acrylates are preferred from the viewpoint of obtaining flexibility. Furthermore, from the viewpoint of balancing adhesion and flexibility, alkyl (meth)acrylates having an alkyl group with 3 to 20 carbon atoms, further 5 to 18, particularly 6 to 16, and especially 7 to 14 carbon atoms are preferred, such as n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, decyl (meth)acrylate, and lauryl (meth)acrylate.

Among these, it is preferable to use branched alkyl (meth)acrylates, because the hydrogen abstraction reaction described below is likely to occur upon irradiation with light, and as a result, crosslinked structures can be efficiently formed. Among these, branched alkyl (meth)acrylates having an alkyl group with 3 to 20 carbon atoms, more preferably 5 to 18, particularly 6 to 16, and especially 7 to 14 carbon atoms are preferred, and examples of preferred are sec-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate.

The ratio of the alkyl (meth)acrylate-derived structural unit to all structural units constituting the (meth)acrylic polymer (A) is preferably 5% by mass or more and 95% by mass or less, more preferably 10% by mass or more and 90% by mass or less, even more preferably 15% by mass or more and 85% by mass or less, and particularly preferably 20% by mass or more and 80% by mass or less. If the ratio of the alkyl (meth)acrylate-derived structural unit is above the lower limit, the flexibility tends to be excellent, and the conformability to unevenness tends to be excellent when the adherend has unevenness. If it is below the upper limit, the effect of the copolymerizable monomer described later is easily obtained, and the adhesive strength and cohesive strength tend to be excellent.
The lower limit and the upper limit of the content of the structural unit derived from the alkyl (meth)acrylate can be combined in any desired manner.

Examples of the carboxyl group-containing monomer (a1) include (meth)acrylic acid, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethylphthalic acid, 2-(meth)acryloyloxypropylphthalic acid, 2-(meth)acryloyloxyethylmaleic acid, 2-(meth)acryloyloxypropylmaleic acid, 2-(meth)acryloyloxyethylsuccinic acid, 2-(meth)acryloyloxypropylsuccinic acid, crotonic acid, fumaric acid, maleic acid, and itaconic acid. These may be used alone or in combination of two or more.

Examples of the hydroxyl group-containing monomer (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, polypropylene glycol (meth)acrylate, polytetramethylene glycol (meth)acrylate, and polyoxyethylene poly(meth)acrylate. Examples of the hydroxyl group-containing (meth)acrylate include (meth)acrylates having an oxyalkylene structure such as oxypropylene 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, 3-chloro-2-hydroxypropyl (meth)acrylate, tertiary hydroxyl group-containing (meth)acrylates such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate, and vinyl ethers such as 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, and 4-hydroxybutyl vinyl ether. These can be used alone or in combination of two or more.
The hydroxyl group-containing monomer (a2) improves the adhesive strength of the pressure-sensitive adhesive sheet and suppresses whitening under moist heat. When the pressure-sensitive adhesive composition contains a thermal crosslinking agent described below, the hydroxyl group-containing monomer (a2) serves as a crosslinking reaction site.

Among the hydroxyl group-containing monomers (a2), hydroxyl group-containing monomers having a hydroxyalkyl group with 1 to 10 carbon atoms, further 1 to 6, and especially 2 to 4 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, and 4-hydroxybutyl vinyl ether, are preferred, and primary hydroxyl group-containing (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate, are particularly preferred.

The content of the structural units derived from the hydroxyl group-containing monomer (a2) in the (meth)acrylic polymer (A) is preferably 3 to 30% by mass, more preferably 5 to 25% by mass, and particularly preferably 7 to 20% by mass, based on the total structural units of the (meth)acrylic polymer (A), from the viewpoint of imparting adhesive strength and resistance to wet heat whitening.

Examples of the nitrogen-containing monomer (a3) include amino group-containing monomers, amide group-containing monomers, isocyanate group-containing monomers, and (meth)acrylonitrile. The nitrogen-containing monomer (a3) improves the cohesive strength of the pressure-sensitive adhesive sheet and can suppress whitening under moist heat. These monomers may be used alone or in combination of two or more. The nitrogen-containing monomer (a3) also has the effect of promoting the hydrogen abstraction reaction described below.

Examples of the amino group-containing monomer as the nitrogen-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; 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; and monomers such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinylacetamides, and N-vinylcaprolactam.

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'-methylene bis (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-ethylmethyl acrylamide, and N,N-diallyl (meth)acrylamide; hydroxyalkyl (meth)acrylamides such as N-hydroxymethyl (meth)acrylamide and N-hydroxyethyl (meth)acrylamide; alkoxyalkyl (meth)acrylamides such as N-methoxymethyl (meth)acrylamide and N-(n-butoxymethyl) (meth)acrylamide; maleimide or a derivative thereof.

The isocyanate group-containing monomer may, for example, be 2-(meth)acryloyloxyethyl isocyanate or an alkylene oxide adduct thereof. The isocyanate group may be protected with a blocking agent such as methyl ethyl ketone oxime, 3,5-dimethylpyrazole, 1,2,4-triazole, or diethyl malonate.

Among these, those having a tertiary nitrogen atom are preferred because they have a sensitizing effect on the hydrogen abstraction reaction described below, and as a result, can efficiently form a crosslinked structure. For example, tertiary amino group-containing (meth)acrylates, N,N-dialkyl (meth)acrylamides, N-vinylpyrrolidone, acryloylmorpholine, etc. are particularly preferred.

The content of the constituent units derived from the nitrogen-containing monomer (a3) in the (meth)acrylic polymer (A) is preferably 0.1 to 15% by mass, more preferably 0.5 to 13% by mass, particularly preferably 1 to 10% by mass, and especially preferably 2 to 7% by mass, based on the total constituent units of the (meth)acrylic polymer (A), from the viewpoint of imparting cohesive strength and resistance to wet heat whitening.

Examples of the epoxy group-containing monomer (a4) include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate glycidyl ether. These may be used alone or in combination of two or more.

The vinyl monomer (a5) may be a compound having a vinyl group in the molecule. Examples of such compounds include vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl laurate, and vinyl stearate, as well as aromatic vinyl monomers such as styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, and other substituted styrenes. These may be used alone or in combination of two or more.

Examples of the alkyl (meth)acrylate monomer (a6) having an alkyl group with 1 or 2 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, etc. These may be used alone or in combination of two or more.
From the viewpoint of imparting cohesive strength to the pressure-sensitive adhesive sheet, the content of the structural units derived from the copolymerizable monomer (a6) in the (meth)acrylic polymer (A) is preferably 0.1 to 15 mass%, more preferably 0.5 to 13 mass%, particularly preferably 1 to 10 mass%, and especially preferably 2 to 7 mass%, based on all structural units of the (meth)acrylic polymer (A).

Examples of the alicyclic monomer (a7) include cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, adamantyl (meth)acrylate, etc. These may be used alone or in combination of two or more.
From the viewpoint of imparting cohesive strength to the pressure-sensitive adhesive sheet, the content of the structural units derived from the copolymerizable monomer (a7) in the (meth)acrylic polymer (A) is preferably 0.1 to 15 mass%, more preferably 0.5 to 13 mass%, particularly preferably 1 to 10 mass%, and especially preferably 2 to 7 mass%, based on all structural units of the (meth)acrylic polymer (A).

Examples of the other copolymerizable monomers (a8) 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, butoxypolyoxyethylene polyoxypropylene glycol (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol-polypropylene glycol-(meth)acrylate, aromatic (meth)acrylates such as acrylates and nonylphenol ethylene oxide adduct (meth)acrylates, 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, 4-acryloyloxyethoxy-4'-bromobenzophenone, 4-methacryloyloxybenzophenone, 4- Examples of the benzophenone structure-containing (meth)acrylates include methacryloyloxyethoxybenzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone, and mixtures thereof; heterocyclic ring-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate; and macromonomers. These can be used alone or in combination of two or more.

The content of the structural unit derived from the copolymerizable monomer (a8) in the (meth)acrylic polymer (A) is preferably 1% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less, based on all the structural units constituting the (meth)acrylic polymer (A). The lower limit and upper limit of the content can be arbitrarily combined.

The (meth)acrylic polymer (A) may have a photoactive site, such as a polymerizable carbon-carbon double bond group, introduced into the side chain. This can increase the crosslinking efficiency of the pressure-sensitive adhesive composition, and the pressure-sensitive adhesive composition can be crosslinked in a shorter time, thereby increasing productivity.

As a method for introducing a polymerizable carbon-carbon double bond group into the side chain of the (meth)acrylic polymer (A), for example, a method can be mentioned in which a copolymer containing the above-mentioned hydroxyl group-containing monomer (a2) or a functional group-containing ethylenically unsaturated monomer is prepared, and then a compound having a functional group that can react with these functional groups and a polymerizable carbon-carbon double bond group is subjected to a condensation or addition reaction while maintaining the activity of the polymerizable carbon-carbon double bond group.

Examples of combinations of these functional groups include epoxy groups (glycidyl groups) and carboxy groups, amino groups and carboxy groups, amino groups and isocyanate groups, epoxy groups (glycidyl groups) and amino groups, hydroxyl groups and epoxy groups, and hydroxyl groups and isocyanate groups. Among these combinations of functional groups, the combination of hydroxyl groups and isocyanate groups is preferred because of the ease of reaction control. Of these, a combination in which the copolymer has a hydroxyl group and the compound has an isocyanate group is preferred.

Examples of isocyanate compounds having a polymerizable carbon-carbon double bond group include the above-mentioned 2-(meth)acryloyloxyethyl isocyanate and its alkylene oxide adducts.

The content of the compound having a functional group capable of reacting with the functional group and a polymerizable carbon-carbon double bond 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, per 100 parts by mass of the (meth)acrylic polymer (A), from the viewpoint of improving adhesion and stress relaxation properties. The lower limit is usually 0 parts by mass.

From the viewpoint of obtaining a pressure-sensitive adhesive composition having high cohesive strength, the weight average molecular weight (Mw) of the (meth)acrylic polymer (A) is preferably 200,000 or more, more preferably 300,000 or more, and even more preferably 400,000 or more.
In addition, the upper limit of the weight average molecular weight (Mw) of the (meth)acrylic polymer (A) is preferably 1.5 million or less, more preferably 1.2 million or less, even more preferably 1.1 million or less, and particularly preferably 1 million or less, from the viewpoints of handleability and uniform stirrability.
The lower limit and the upper limit of the weight average molecular weight of the (meth)acrylic polymer (A) can be combined in any desired manner.
The weight average molecular weight of the (meth)acrylic polymer (A) is a value calculated in terms of standard polystyrene as measured by gel permeation chromatography (GPC).

The method for producing the (meth)acrylic polymer (A) is not particularly limited, and any known method can be used. For example, a method can be used in which a monomer mixture containing an alkyl (meth)acrylate having an alkyl group with 3 to 30 carbon atoms and one or more copolymerizable monomers selected from the copolymerizable monomers (a1) to (a8) used as necessary is polymerized.

<Photoinitiator (B)>
The pressure-sensitive adhesive composition contains, as the photoinitiator (B), a photoinitiator (b1) having a glyoxylate structure and a molar absorption coefficient at a wavelength of 405 nm of 30 (L/mol·cm) or more.

A photoinitiator is a compound that generates radicals when exposed to active energy rays.
Photoinitiators are roughly classified into two types according to the radical generation mechanism: cleavage-type photoinitiators that can generate radicals by cleaving and decomposing the single bond of the initiator itself, and hydrogen abstraction-type photoinitiators that can generate radicals by an excited initiator abstracting hydrogen from a hydrogen donor in the system.

Since the cleavage-type photoinitiator itself becomes a radical and undergoes an addition reaction with a polymerizable carbon-carbon double bond group in the system, it is necessary for the (meth)acrylic polymer (A) to have a polymerizable carbon-carbon double bond group, or for a certain amount or more of the polymerizable carbon-carbon double bond group of the polyfunctional (meth)acrylate (D) to obtain sufficient active energy ray curability. When a certain amount or more of the polyfunctional (meth)acrylate (D) is added, the reaction of the polyfunctional (meth)acrylate proceeds quickly due to light irradiation during the production of the pressure-sensitive adhesive sheet, which causes problems such as difficulty in controlling the state in which there is room left for curing by active energy rays and a decrease in adhesive strength.
On the other hand, a hydrogen abstraction type photoinitiator abstracts hydrogen from a hydrogen donor such as the (meth)acrylic polymer (A) in the system to generate radicals in the (meth)acrylic polymer (A). Therefore, even if there is no polymerizable carbon-carbon double bond group in the system, the (meth)acrylic polymer (A) itself can be bonded by a radical addition reaction, and sufficient active energy ray curability can be obtained, and therefore the photoinitiator is preferably used.

In addition, as photoinitiators having high photosensitivity to light in the long wavelength region, α-aminoacetophenone-based and acylphosphine oxide-based photoinitiators have been mainly used. However, since these are cleavage-type photoinitiators, they generate outgassing products such as benzaldehyde as photodecomposition products, and therefore improvements thereon have been strongly desired.
In addition, hydrogen abstraction photoinitiators such as thioxanthone and anthraquinone, which have been conventionally known as photoinitiators sensitive to light in the long wavelength region, do not generate photodecomposition products, but have the problem of yellowing, which limits their use.

Under these circumstances, the present inventors conducted extensive research and obtained the following findings.
It was thought that the curing reaction would not proceed with glyoxylate-type hydrogen abstraction photoinitiators because the efficiency of abstracting hydrogen from hydrogen donors is low when exposed to light in the long wavelength region. However, it was unexpectedly discovered that the use of a glyoxylate-type hydrogen abstraction photoinitiator having a molar absorption coefficient of 30 (L/mol cm) or more at a wavelength of 405 nm allows the composition to be cured by energy rays on the long wavelength side, for example, energy rays with a wavelength of 405 nm, without problems such as insufficient curing or yellowing, and this led to the present invention.
The glyoxylate-type photoinitiator is preferably a compound having an absorption wavelength in the range of 380 to 430 nm.

The photoinitiator (b1) has a molar absorption coefficient of 30 (L/mol·cm) or more at 405 nm, and therefore has excellent sensitivity to active energy rays of long wavelengths. Therefore, the photoinitiator (b1) can provide the present pressure-sensitive adhesive composition that can be cured by active energy rays of relatively long wavelengths (for example, active energy rays of 405 nm, which are longer than 380 nm). From this viewpoint, the molar absorption coefficient is preferably 40 (L/mol·cm) or more, more preferably 50 (L/mol·cm) or more, even more preferably 60 (L/mol·cm) or more, and particularly preferably 70 (L/mol·cm) or more.
In terms of internal (or deep) curing properties, the upper limit of the molar absorption coefficient is preferably 1.0 x 10 ⁶ (L/mol·cm) or less, more preferably 5.0 x 10 ⁵ (L/mol·cm) or less, even more preferably 1.0 x 10 ⁵ (L/mol·cm) or less, and particularly preferably 5.0 x 10 ⁴ (L/mol·cm) or less.
The lower limit and the upper limit of the molar extinction coefficient can be combined in any desired manner.
The molar absorption coefficient of the photoinitiator (b1) at 405 nm is calculated from the absorbance obtained by dissolving a predetermined concentration of the photoinitiator (b1) in chloroform or the like and measuring the absorbance at 405 nm using an ultraviolet-visible spectrophotometer according to the following formula.
A = εLc
(A is absorbance, ε is molar absorption coefficient (L/mol cm), c is molar concentration of photoinitiator (b1) (mol/L), and L is optical path length (cm).)

The photoinitiator (b1) has a glyoxylate structure represented by the following formula 1.

In the above formula 1, R ¹ is a substituted or unsubstituted C ₁ -C ₂₀ alkyl, a substituted or unsubstituted C ₃ -C ₂₀ cycloalkyl, or a substituted or unsubstituted C ₂ -C ₂₀ heterocycloalkyl. * indicates a bond.
In addition, "C ₁ -C ₂₀ alkyl" means an alkyl group having 1 to 20 carbon atoms. The same applies to C ₃ -C ₂₀ cycloalkyl, C ₂ -C ₂₀ heterocycloalkyl, and the like.

In the formula 1, when R ¹ is a C ₁ to C ₂₀ alkyl, the C ₁ to C ₂₀ alkyl may be interrupted by one or more identical or different groups selected from the group consisting of O, S, N(R ³ ), C(O), C(O)O and OC(O), and may have one or more identical or different groups R ^1a .
wherein each R ^1a is independently selected from the group consisting of F, Cl, Br, I, CN, NO ₂ , SR ⁵ , OR ⁶ , NR ⁷ R ⁸ , C(O)R ⁹ , C(O)OR ¹⁰ , C(O)NR ¹¹ R ¹² , C ₃ -C ₂₀ cycloalkyl optionally interrupted by one or more C(O) groups, C ₆ -C ₁₀ aryl, and (meth)acryloyloxy groups;
C ₃ -C ₂₀ cycloalkyl and C ₆ -C ₁₀ aryl in R ^1a may carry one or more identical or different groups R ^1aa ;
R ^1aa are each independently selected from the group consisting of C ₁ -C ₁₂ alkyl, C ₂ -C ₁₂ alkenyl, F, Cl, Br, I, NO ₂ , SR ⁵ , OR ⁶ , and NR ⁷ R ⁸ ;
The C ₁ -C ₁₂ alkyl in R ^1aa may be interrupted by one or more groups selected from the group consisting of O, S, N(R ³ ), C(O), C(O)O, and OC(O), and may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, NO ₂ , SR ⁵ , OR ⁶ , NR ⁷ R ⁸ , C(O)R ⁹ , C(O)OR ¹⁰ , and C(O)NR ¹¹ R ¹² .

In the above formula 1, when R ¹ is a C ₃ -C ₂₀ cycloalkyl or a C ₂ -C ₂₀ heterocycloalkyl, the C ₃ -C ₂₀ cycloalkyl or the C ₂ -C ₂₀ heterocycloalkyl may be interrupted by one or more C(O) groups and may have one or more identical or different groups R ^1b .
wherein each R ^1b is independently selected from the group consisting of C ₁ -C ₁₂ alkyl, C ₂ -C ₁₂ alkenyl, F, Cl, Br, I, CN, NO ₂ , SR ⁵ , OR ⁶ and NR ⁷ R ⁸ ;
The C ₁ -C ₁₂ alkyl in R ^1b may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, NO ₂ , SR ⁵ , OR ⁶ , NR ⁷ R ⁸ , C(O)R ⁹ , C(O)OR ¹⁰ , and C(O)NR ¹¹ R ¹² .

R ³ is selected from the group consisting of a hydrogen atom, a C ₁ -C ₁₈ alkyl, a C ₂ -C ₁₈ alkanoyl, a C ₆ -C ₁₀ aryl and a C ₇ -C ₁₁ aroyl;
The C ₁ -C ₁₈ alkyl in R ³ may be interrupted by one or more groups selected from the group consisting of O, S, N(C ₁ -C ₁₂ alkyl), C(O), C(O)O, and OC(O), and may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, C ₃ -C ₁₀ cycloalkyl, C ₂ -C ₁₀ heterocycloalkyl, C ₆ -C ₁₀ aryl, OH, and SH;
The C ₂ -C ₂₀ alkanoyl in R ³ may be interrupted by one or more groups selected from the group consisting of O, S, CO, C(O)O, and OC(O), and may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, C ₃ -C ₁₀ cycloalkyl, C ₂ -C ₁₀ heterocycloalkyl, and C ₆ -C ₁₀ aryl;
The C ₆ -C ₁₀ aryl in R ³ may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkoxy, and C ₂ -C ₁₁ acyloxy;
The C ₇ -C ₁₁ aroyl in R ³ may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkoxy, and C ₂ -C ₁₁ acyloxy.

R ⁵ and R ⁶ are each independently selected from the group consisting of a hydrogen atom, a C ₁ -C ₂₀ alkyl, a C ₂ -C ₂₀ alkanoyl, a C ₆ -C ₁₀ aryl, and a C ₇ -C ₁₁ aroyl;
The C ₁ -C ₂₀ alkyl in R ⁵ and R ⁶ may be interrupted by one or more groups selected from the group consisting of O, S, N(C ₁ -C ₁₂ alkyl), C(O), C(O)O, and OC(O), and may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, C ₃ -C ₁₀ cycloalkyl, C ₂ -C ₁₀ heterocycloalkyl, C ₆ -C ₁₀ aryl, OH, and SH;
The _C2 - _C20 alkanoyl in ^R5 and ^R6 may be interrupted by one or more groups selected from the group consisting of O, S, C(O), C(O)O, and OC(O), and may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, _C3 - _C10 cycloalkyl, _C2 - _C10 heterocycloalkyl, and _C6 - _C10 aryl;
The C ₆ -C ₁₀ aryl in R ⁵ and R ⁶ may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, C ₁ -C ₆ alkyl, C ₁ -C ₁₀ alkoxy, and C ₂ -C ₁₁ acyloxy;
The C ₇ -C ₁₁ aroyl in R ⁵ and R ⁶ may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkoxy, and C ₂ -C ₁₁ acyloxy.

R ⁷ and R ⁸ are each independently selected from the group consisting of a hydrogen atom, a C ₁ -C ₂₀ alkyl, a C ₂ -C ₂₀ alkanoyl, a C ₇ -C ₁₁ aroyl, and a C ₆ -C ₁₀ aryl;
The C ₁ -C ₂₀ alkyl in R ⁷ and R ⁸ may be interrupted by one or more groups selected from the group consisting of O, S, N(C ₁ -C ₁₂ alkyl), C(O), C(O)O, and OC(O), and may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, NO ₂ , C ₃ -C ₁₀ cycloalkyl, heterocycloalkyl, phenyl, OH, SH, and CN;
The C ₂ -C ₂₀ alkanoyl in R ⁷ and R ⁸ may be interrupted by one or more groups selected from the group consisting of O and S, and may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, OH and C ₁ -C ₆ alkoxy;
The C ₇ -C ₁₁ aroyl in R ⁷ and R ⁸ may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, C ₁ -C ₆ alkyl, -OH and C ₁ -C ₆ alkoxy;
The C ₆ -C ₁₀ aryl in R ⁷ and R ⁸ may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, C ₁ -C ₆ alkyl, -OH, and C ₁ -C ₆ alkoxy;
^R7 and ^R8 together with the nitrogen atom to which they are attached may form a saturated 5-, 6- or 7-membered nitrogen heterocycle, which may have as ring members groups selected from the group consisting of O, S, N( _C1 - _C12 alkyl), C(O), and C(O)O, and which may have one or more _C1 - _C4 alkyls.

R ⁹ is selected from the group consisting of a hydrogen atom, a C ₁ -C ₂₀ alkyl, and a C ₆ -C ₂₀ aryl;
The C ₁ -C ₂₀ alkyl in R ⁹ may be interrupted by one or more groups selected from the group consisting of O, S and C(O), and may have one or more identical or different R ^9a ;
R ^9a is independently selected from the group consisting of F, Cl, Br, I, C ₃ -C ₁₀ cycloalkyl, heterocycloalkyl, phenyl, OH, and SH;
The C ₆ -C ₂₀ aryl in R ⁹ may have one or more identical or different groups selected from the group consisting of F, Cl, Br, I, SR ⁵ , OR ⁶ , NR ⁷ R ⁸ , C ₁ -C ₁₂ alkyl, and C ₂ -C ₁₂ acyloxy.
R ¹⁰ has the same meaning as R ⁶ ; R ¹¹ and R ¹² have the same meaning as R ⁷ and R ⁸ .

By having a glyoxylate structure, the photoinitiator (b1) functions as a hydrogen abstraction type photoinitiator.
The hydrogen abstraction type photoinitiator is preferred because it does not generate photodecomposition products as in the case of the cleavage type photoinitiator, and is also preferred because it easily forms a crosslinked structure having many crosslinking points since it also causes a hydrogen abstraction reaction from the (meth)acrylic polymer (A) and the (meth)acrylic polymer (A) is incorporated into the crosslinked structure.

Hydrogen abstraction photoinitiators are roughly classified into intermolecular hydrogen abstraction photoinitiators that abstract hydrogen from other molecules, and intramolecular hydrogen abstraction photoinitiators that also cause a hydrogen abstraction reaction within the same molecule. By having the glyoxylate structure, the photoinitiator (b1) functions as an intramolecular hydrogen abstraction photoinitiator.
An intramolecular hydrogen abstraction type photoinitiator is preferred in that it can act not only as a hydrogen donor in the system but also as a starting point for radical generation.

In terms of solubility, R ¹ is preferably a linear or branched alkyl group or a cycloalkyl group, more preferably a linear or branched alkyl group.
In terms of photocurability, the alkyl group of R ¹ preferably has 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, further preferably 1 to 8 carbon atoms, and particularly preferably 1 or 2 carbon atoms.
In terms of photocurability, the cycloalkyl group of R ¹ preferably has 3 to 20 carbon atoms, and more preferably has 3 to 10 carbon atoms.

The photoinitiator (b1) is preferably a compound having two or more radical generating groups in the molecule (provided that at least one of the radical generating groups has a glyoxylate structure). Here, the "radical generating group" means a group that generates a radical that initiates a polymerization reaction under excitation by active energy rays.
The "radical generating group" is preferably a group having a structure that is excited by irradiation with active energy rays and generates a radical by causing a hydrogen abstraction reaction.
Since the photoinitiator (b1) has two or more radical generating groups, the pressure-sensitive adhesive composition can form crosslinks with high efficiency.

Radical generating groups other than the glyoxylate structure include, for example, a benzophenone structure, a benzyl structure, a thioxanthone structure, a 3-ketocoumarin structure, an anthraquinone structure, and a camphorquinone structure.

From the viewpoint of increasing the sensitivity to active energy rays of long wavelengths and the molar absorption coefficient at a wavelength of 405 nm, the photoinitiator (b1) is preferably a compound containing a biphenyl structure to which the bonds of the glyoxylate structure represented by formula 1 are bonded, and in particular, a compound containing a sulfide biphenyl structure to which the bonds of the glyoxylate structure represented by formula 1 are bonded is preferred.

Examples of the photoinitiator (b1) include the compound represented by the following formula 2.

In the above formula 2, A is O, S, NR ⁴ , or a linear or branched alkylene or cycloalkylene having 1 to 6 carbon atoms.
Here, ^R4 has the same meaning as ^R3 . ^R1 has the same meaning as in formula 1.
^R2 is a hydrogen atom, a substituted or unsubstituted _C1 - _C20 alkyl, a substituted or unsubstituted _C3 - _C20 cycloalkyl, a substituted or unsubstituted _C2 - _C20 heterocycloalkyl, a substituted or unsubstituted _C6 - _C20 aryl, a substituted or unsubstituted _C1 - _C20 heteroaryl, ^SR5 , ^OR6 , ^{NR7R8 ,} C(O) ^R9 , or C(O) ^OR13 , where ^R13 has the same meaning as ^R1 .

In the formula 2, when R ² is a C ₁ to C ₂₀ alkyl, the C ₁ to C ₂₀ alkyl may be interrupted by one or more of the same or different groups selected from the group consisting of O, S, N(R ³ ), C(O), C(O)O, and OC(O), and may have one or more of the same or different groups R ^2a .
Here, R ^2a has the same meaning as R ^1a .

In the formula 2, when R ² is a C ₃ -C ₂₀ cycloalkyl or a C ₂ -C ₂₀ heterocycloalkyl, the C ₃ -C ₂₀ cycloalkyl or the C ₂ -C ₂₀ heterocycloalkyl may be interrupted by one or more C(O) groups and may have one or more identical or different groups R ^2b , where R ^2b has the same meaning as R ^1b .

In the formula 2, when R ² is C ₆ -C ₂₀ aryl or C ₁ -C ₂₀ heteroaryl, the C ₆ -C ₂₀ aryl or C ₁ -C ₂₀ heteroaryl may have one or more identical or different groups R ^2c ;
R ^2c is independently selected from the group consisting of C ₁ -C ₁₂ alkyl, C ₂ -C ₁₂ alkenyl, F, Cl, Br, I, CN, NO ₂ , SR ⁵ , OR ⁶ , NR ⁷ R ⁸ , C(O)R ⁹ , C(O)OR ¹⁰ , C(O)NR ¹¹ R ¹² , C ₆ -C ₁₀ aryl, C ₁ -C ₂₀ heteroaryl, C ₃ -C ₁₀ cycloalkyl, and C ₂ -C ₁₀ heterocycloalkyl;
The C ₁ -C ₁₂ alkyl in R ^2c may have one or more identical or different groups selected from F, Cl, Br, I, NO ₂ , SR ⁵ , OR ⁶ , NR ⁷ R ⁸ , C(O)R ⁹ , C(O)OR ¹⁰ , and C(O)NR ¹¹ R ¹² ;
C ₁ -C ₁₂ alkyl, C ₃ -C ₁₀ cycloalkyl and C ₂ -C ₁₀ heterocycloalkyl in R ^2c may be interrupted by one or more C(O) groups;
The C ₆ -C ₁₀ aryl, C ₁ -C ₂₀ heteroaryl, C ₃ -C ₁₀ cycloalkyl and C ₂ -C ₁₀ heterocycloalkyl in R ^2c may have one or more identical or different groups R ^1ca , where R ^1ca has the same meaning as R ^1aa above.

Among the compounds represented by formula 2, diphenyl sulfide derivatives in which A in the formula is a sulfur atom are preferred from the viewpoint of photoreactivity.
Among these, from the viewpoint of photoreactivity, ^R2 is preferably a substituted or unsubstituted aromatic group having 6 to 20 carbon atoms or C(O) ^OR13 . ^R13 has the same meaning as ^R1 .

As the photoinitiator (b1), one or more compounds selected from the compounds represented by the following formulas 3 to 5 are more preferred.

ここで、ｎは０～５の整数である。

Here, n is an integer from 0 to 5.

ここで、ｏは０～３の整数であり、ｐは０～４の整数である。

Here, o is an integer from 0 to 3, and p is an integer from 0 to 4.

Among these, from the viewpoint of photoreactivity, the photoinitiator (b1) preferably contains a compound represented by the above formulas 3 to 5 in which R ¹ and R ¹³ are linear or branched alkyl having 1 to 8 carbon atoms, and n, o, and p are 0, and it is particularly preferable that the photoinitiator (b1) contains either one or both of a compound represented by the following formula 3-1 and a compound represented by the following formula 4-1.

The photoinitiator (b1) can be used alone or in combination of two or more kinds.
The content of the photoinitiator (b1) in the pressure-sensitive adhesive composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, relative to 100 parts by mass of the (meth)acrylic polymer (A). The upper limit is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 5 parts by mass or less, and particularly preferably 3 parts by mass or less. If the content of the photoinitiator (b1) is equal to or more than the lower limit, there is a tendency to prevent poor curing, and if it is equal to or less than the upper limit, there is a tendency to suppress bleeding out of the photoinitiator (b1) and to easily suppress problems such as embrittlement and coloring. The lower limit and upper limit of the content of the photoinitiator (b1) can be arbitrarily combined.

As long as the effect of the present invention is not impaired, the pressure-sensitive adhesive composition may contain a photoinitiator (b2) other than the photoinitiator (b1) as the photoinitiator (B). The photoinitiator (b2) may be either a hydrogen abstraction type photoinitiator or a cleavage type photoinitiator, and may be used alone or in combination of the two.

The terms used in the photoinitiator (b1) above are defined as follows:

The term "alkyl" in photoinitiator (b1) generally refers to a saturated linear or branched hydrocarbon group having 1 to 20, preferably 1 to 12, more preferably 1 to 10 carbon atoms. Examples of alkyl groups are e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl, neo-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, and n-eicosyl.
The alkyl may be interrupted by one or more identical or different groups selected from O, S, N(R ³ ), C(O), C(O)O, and OC(O). When multiple O, S, N(R ³ ), C(O), C(O)O, and OC(O) are present, they are usually separated from each other by at least one methylene group. R ³ is as defined above. Examples of alkyl interrupted by one or more O atoms are, for example, -CH ₂ -O-CH ₃ , -CH ₂ CH ₂ -O-CH ₂ CH ₃ , -[CH ₂ CH ₂ O] _y -CH ₃ (y is 1 to 9), -(CH ₂ CH ₂ O) _y CH ₂ CH ₃ (y is 1 to 9), -CH ₂ -CH(CH ₃ )-O-CH ₂ -CH ₂ CH ₃ , -CH ₂ -CH ₂ CH(CH ₃ )-O-CH ₂ -CH ₂ CH ₃ , -CH ₂ -CH ₂ CH(CH ₃ )-O-CH ₂ CH ₃ , -CH ₂ -CH ₂ CH(CH ₃ )-O-CH ₃ and -CH ₂ CH(CH ₃ )-O-CH ₂ CH. The answer is ₃ .

The term "cycloalkyl" in photoinitiator (b1) refers to a monocyclic or polycyclic aliphatic group typically having 3 to 20, preferably 3 to 16, more preferably 3 to 12 carbon atoms.
Examples of the monocyclic aliphatic group include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl, and cyclopentyl and cyclohexyl are particularly preferred.
Examples of polycyclic rings include perhydroanthracyl, perhydronaphthyl, perhydrofluorenyl, perhydrochrysenyl, perhydropicenyl, adamantyl, bicyclo[1.1.1]pentyl, bicyclo[2.2.1]heptyl, bicyclo[4.2.2]decyl, bicyclo[2.2.2]octyl, bicyclo[3.3.0]octyl, bicyclo[3.3.2]decyl, bicyclo[4.4.0]decyl, bicyclo[4.3.2]undecyl, bicyclo[4.3.3]dodecyl, bicyclo[3.3.3]undecyl, bicyclo[4.3.1]decyl, bicyclo[4.2.1]nonyl, bicyclo[3.3.1]nonyl, and bicyclo[3.2.1]octyl.
Cycloalkyl may be interrupted by one or more C(O) groups. An example of a cycloalkyl interrupted by one C(O) is 3-oxobicyclo[2.2.1]heptyl.

The term "heterocycloalkyl" in the photoinitiator (b1) generally refers to 3-8 membered, especially 5-, 6-, 7- or 8-membered, monocyclic and bicyclic heterocyclic non-aromatic groups. The monocyclic and bicyclic non-aromatic groups may be saturated or unsaturated. The monocyclic and bicyclic heterocyclic non-aromatic groups also usually contain 1, 2, 3 or 4 heteroatoms selected from N, O and S, especially 1 or 2 heteroatoms, as ring members, where the S atom as ring member may be present as S, SO or _SO2 . The heterocycloalkyl may be interrupted by one or more C(O) groups, usually by 1 or 2 groups.
Examples of the saturated or unsaturated 3- to 8-membered non-aromatic heterocyclic group include oxiranyl, oxetanyl, thietanyl, thietanyl-S-oxide (S-oxothietanyl), thietanyl-S-dioxide (S-dioxothietanyl), pyrrolidinyl, pyrazolinyl, imidazolinyl, pyrrolinyl, pyrazolinyl, imidazolinyl, tetrahydrofuranyl, dihydrofuranyl, 1,3-dioxolanyl, dioxolenyl, thiolanyl, S-oxothiolanyl, S-dioxothiolanyl, dihydrothienyl, S-oxodihydrothienyl, S-dioxodihydrothienyl, oxazolidinyl, isoxazolidinyl, oxazolinyl, and isoxazo. Examples of such compounds include pyranyl, thiazolinyl, isothiazolinyl, thiazolidinyl, isothiazolidinyl, oxathiolanyl, piperidinyl, piperazinyl, pyranyl, dihydropyranyl, tetrahydropyranyl, 1,3- and 1,4-dioxanyl, thiopyranyl, S-oxothiopyranyl, S-dioxothiopyranyl, dihydrothiopyranyl, S-oxodihydrothiopyranyl, S-dioxodihydrothiopyranyl, tetrahydrothiopyranyl, S-oxotetrahydrothiopyranyl, S-dioxotetrahydrothiopyranyl, morpholinyl, thiomorpholinyl, S-oxothiomorpholinyl, S-dioxothiomorpholinyl, and thiazinyl.
Heterocyclic rings which also contain one or two carbonyl groups as ring members include, for example, pyrrolidin-2-onyl, pyrrolidine-2,5-dioneyl, imidazolidin-2-onyl, oxazolidin-2-onyl, thiazolidin-2-onyl.

The term "aryl" in the photoinitiator (b1) refers to monovalent monocyclic aromatic groups having ring carbon atoms as well as polycyclic aromatic groups. Monocyclic aromatic groups include, for example, phenyl. Polycyclic aromatic groups include, for example, bicyclic, tricyclic or tetracyclic aromatic groups such as naphthyl, phenanthrenyl, anthracenyl or pyrenyl. Preferred examples of aryl are phenyl and naphthyl. Substituted phenyl is substituted by 1, 2, 3, 4 or 5 substituents. Naphthyl is usually substituted by 1, 2, 3, 4, 5, 6 or 7 substituents, preferably by 1, 2, 3 or 4 substituents. Substituted phenyl is, for example, pentafluorophenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2-ethylphenyl, 3-ethylphenyl, 4-ethylphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 2-ethoxyphenyl, 3-ethoxyphenyl, 4-ethoxyphenyl, 3-nitrophenyl, 4-nitrophenyl, 2-chlorophenyl, 3-chlorophenyl, 4-chlorophenyl, 3-vinylphenyl, 4-vinylphenyl, 4-trifluoromethylphenyl, 3,5-diethoxycarbonylphenyl.

The term "heteroaryl" in photoinitiator (b1) generally refers to unsaturated monocyclic and polycyclic heterocyclic groups that are aromatic. Heteroaryls usually contain, in addition to one or more carbon atoms as ring members, one, two, three or four heteroatoms selected from N, O and S as ring members. Examples of monocyclic heteroaromatic groups include 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 1-pyrrolyl, 2-pyrrolyl, 3-pyrrolyl, 1-pyrazolyl, 3-pyrazolyl, 4-pyrazolyl, 5-pyrazolyl, 2-oxazolyl, 4-oxazolyl, 5-oxazolyl, 2-thiazolyl, 4-thiazolyl, 5-thiazolyl, 3-isoxazolyl, 4-isoxazolyl or 5-isoxazolyl, 3-isothiazolyl, 4-isothiazolyl or 5-isothiazolyl, 1-imidazolyl, 2-imidazolyl, 4-imidazolyl, 2- or 5-[1,3,4]oxadiazolyl, 4- or 5-(1,2,3-oxadiazol)yl, 3- or 5-(1,2,4- Examples of the aryl group include 1H-, 2H-, or 3H-1,2,3-triazol-4-yl, 1,3,4-triazol-2-yl, 2H-triazol-3-yl, 1H-, 2-, or 4H-1,2,4-triazolyl, 1H- or 2H-tetrazolyl, 2-pyridinyl, 3-pyridinyl, 4-pyridinyl, 3-pyridazinyl, 4-pyridazinyl, 2-pyrimidinyl, 4-pyrimidinyl, 5-pyrimidinyl, and 2-pyrazinyl. Examples of polycyclic heterocyclic groups include benzofuranyl, benzothienyl, indolyl, indazolyl, benzimidazolyl, benzoxathiazolyl, benzoxadiazolyl, benzothiadiazolyl, benzoxazinyl, quinolinyl, isoquinolinyl, purinyl, 1,8-naphthyridyl, pteridyl, pyrido[3,2-d]pyrimidyl, pyridoimidazolyl, carbazoyl, and acridinyl.

The term "alkanoyl" in photoinitiator (b1) refers to alkyl-C(O), a saturated linear or branched alkyl group as defined above, usually having 3 to 20 carbon atoms, bonded at any position in the alkyl group through the carbon atom of a carbonyl group, e.g., acetyl, propanoyl, 2-methyl-propanoyl, butanoyl, pentanoyl, hexanoyl.

The term "aroyl" in photoinitiator (b1) refers to aryl-C(O) groups bonded at any position in the aryl group defined above through the carbon atom of a carbonyl group, e.g., benzoyl and naphthoyl.

The term "heteroaroyl" in photoinitiator (b1) is heteroaryl-C(O) and refers to a group bonded at any position in a heteroaryl group as defined above through the carbon atom of a carbonyl group.

The term "alkylene" in the photoinitiator (b1) refers in each case to an alkyl group having carbon atoms as defined above, in which one hydrogen atom at any position of the alkyl group is replaced by one further bonding site to form a divalent group. Thus, C ₁ -C ₆ alkylene includes divalent branched or unbranched saturated aliphatic chains having 1 to 6 carbon atoms, such as, for example, —CH ₂ —, —CH ₂ CH 2 —, —CH(CH ₃ )—, —CH 2 CH ₂ CH _{2 —} , —CH(CH 3 ₎ CH ₂ —, —C(CH ₃ ) ₂ —, —CH ₂ CH ₂ CH ₂ CH ₂ —, —CH ₂ CH(CH ₃ )CH ₂ —, —CH(CH ₃ )CH( _{CH 3 )} —, —CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ —, —CH ₂ CH ₂ CH ₂ CH(CH ₃ )—, —CH ₂ C(CH ₃ ) ₂ CH ₂ —, —CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH _2- is one of them.

The term "cycloalkylene" in photoinitiator (b1) refers to a cycloalkyl group as defined above, in which one hydrogen atom at any position of the cycloalkyl is replaced by one additional bonding site to form a divalent group. In the case of polycyclic cycloalkylenes, the bonding points are located either in the same ring or in different rings. Monocyclic rings include, for example, cyclopropylene, cyclobutylene, cyclopentylene, cyclohexylene or cycloheptylene, especially cyclohexylene. Examples of polycyclic rings include perhydroanthracylene, perhydronaphthylene, perhydrofluorenylene, perhydrochrysenylene, perhydropicenylene, adamantylene, bicyclo[1.1.1]pentylene, bicyclo[2.2.1]heptylene, bicyclo[4.2.2]decylene, bicyclo[2.2.2]octylene, bicyclo[3.3.2]decylene, bicyclo[4.3.2]undecylene, bicyclo[4.3.3]dodecylene, bicyclo[3.3.3]undecylene, bicyclo[4.3.1]decylene, bicyclo[4.2.1]nonylene, bicyclo[3.3.1]nonylene, and bicyclo[3.2.1]octylene.

Examples of the hydrogen abstraction type photoinitiator as the photoinitiator (b2) include benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, 2-benzoyl methyl benzoate, 4-[(4-methylphenyl)thio]benzophenone, 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, and 4-acryloyloxyethoxy-4'-bromobenzophenone. intermolecular hydrogen abstraction type photoinitiators such as benzoylphenone, 4-methacryloyloxybenzophenone, 4-methacryloyloxyethoxybenzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, and 4-methacryloyloxyethoxy-4'-bromobenzophenone; and intramolecular hydrogen abstraction type photoinitiators such as methyl benzoylformate, oxyphenylacetic acid-2-(2-oxo-2-phenyl-acetoxy-ethoxy)ethyl ester, and oxyphenylacetic acid-2-(2-hydroxy-ethoxy)ethyl ester.
Among these, 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, etc., which have a radically polymerizable functional group having a carbon-carbon double bond in the molecule, are preferred in that they are incorporated into the polymerization structure after the photoreaction, thereby suppressing bleed-out of the photoinitiator and improving the cohesive strength of the pressure-sensitive adhesive sheet.
Furthermore, intramolecular hydrogen abstraction type photoinitiators are preferred in that they not only function as hydrogen donors in the system but also themselves can serve as the origin of radical generation.

In addition, a cleavage-type photoinitiator may be used as the photoinitiator (b2) to the extent that photodecomposition products do not affect the quality. The cleavage-type photoinitiator is preferred because it has high photosensitivity.
Examples of the cleavage-type photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)benzyl]phenyl}-2-methyl-propan-1-one, oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone), 2-benzyl-2-dimethylamino-1-(4-morpholino-1-methylamino)propanone, and 2-benzyl-2-dimethylamino-1-(4-morpholino-1-methylamino)propanone. Examples of suitable phosphine oxides include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide, and derivatives thereof.

The content of the photoinitiator (b2) in the pressure-sensitive adhesive composition is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, even more preferably 3 parts by mass or less, and particularly preferably 2 parts by mass or less, per 100 parts by mass of the (meth)acrylic polymer (A). The lower limit is usually 0 parts by mass.

<Ultraviolet absorber (C)>
The present pressure-sensitive adhesive composition contains an ultraviolet absorber (C). Image display components are usually susceptible to ultraviolet degradation, but by using a pressure-sensitive adhesive sheet formed from the present pressure-sensitive adhesive composition containing an ultraviolet absorber (C), it becomes easy to prevent the image display components from deteriorating due to light.
Since the pressure-sensitive adhesive composition contains an ultraviolet absorber (C), when photocuring is performed, it is preferable to cure the composition by using active energy rays having a wavelength other than the absorption wavelength of the ultraviolet absorber (C).

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

Examples of the benzophenone-based ultraviolet absorbers include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-benzyloxybenzophenone, 2-hydroxy-4-methoxy-5-sulfoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfoxytrihydridolate benzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxy-5-sodium sulfoxybenzophenone, bis(5-benzoyl-4-hydroxy-2-methoxyphenyl)methane, 2-hydroxy-4-n-dodecyloxybenzophenone, and 2-hydroxy-4-methoxy-2'-carboxybenzophenone.

Examples of the benzotriazole-based ultraviolet absorbers include 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole, 2-(2-hydroxy-3,5-dicumylphenyl)phenylbenzotriazole, 2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole, 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], 2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-4-octoxyphenyl)benzotriazole, 2,2'-methylenebis(4-cumyl-6-benzotriazolephenyl), 2,2'-p-phenylenebis(1,3-benzoxazin-4-one, 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimidomethyl)-5-methylphenyl]benzotriazole, etc. can be mentioned.

Examples of the triazine-based ultraviolet absorbers include 2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-ethoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-propoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-butoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-hexyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, and 2-(2-hydroxy-4-octyloxyphenyl)-4,6-diphenyl-1,3,5-triazine. phenyl-1,3,5-triazine, 2-(2-hydroxy-4-dodecyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-benzyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2,4-bis(2-hydroxy-4-butoxyphenyl)-6-(2,4-dibutoxyphenyl)-1,3-5-triazine, 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine, 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5- triazine, 2-[4-[(2-hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-(2'-ethyl)hexyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3 -octyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-nonyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-decyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine, 2-(2-hydroxy-4-acryloyloxyethoxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, etc. can be mentioned.

Examples of the salicylic acid-based ultraviolet absorbers include phenyl salicylate, p-tert-butylphenyl salicylate, and p-octylphenyl salicylate.

Examples of the cyanoacrylate-based ultraviolet absorber include 2-ethylhexyl-2-cyano-3,3'-diphenylacrylate, ethyl-2-cyano-3,3'-diphenylacrylate, etc.

Among these, from the viewpoint of effectively suppressing light reaching the components of the image display device, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, and triazine-based ultraviolet absorbers are preferred. Among these, from the viewpoint of excellent yellowing resistance, benzophenone-based ultraviolet absorbers and triazine-based ultraviolet absorbers are more preferred. Furthermore, from the viewpoint of being able to block light rays up to the long wavelength region, ultraviolet absorbers having absorption in the wavelength region longer than 400 nm are preferred.
Examples of commercially available ultraviolet absorbents include "CHINOSORB S" manufactured by BASF Japan Ltd., "KEMISORB111" manufactured by Chemipro Kasei Co., Ltd., and "CONFOGUARD UV002" manufactured by Fuji Film Corporation.

The lower limit of the content of the ultraviolet absorber (C) in the pressure-sensitive adhesive composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.5 parts by mass or more, particularly preferably 1 part by mass or more, and especially preferably 1.5 parts by mass or more, relative to 100 parts by mass of the (meth)acrylic polymer (A), from the viewpoint of improving light resistance reliability. On the other hand, the upper limit of the content of the ultraviolet absorber (C) is preferably 15 parts by mass or less, more preferably 12 parts by mass or less, even more preferably 10 parts by mass or less, particularly preferably 8 parts by mass or less, especially preferably 5 parts by mass or less, and most preferably 3 parts by mass or less, relative to 100 parts by mass of the (meth)acrylic polymer (A), from the viewpoint of suppressing bleed-out and suppressing coloration.

<Polyfunctional (meth)acrylate (D)>
From the viewpoint of promoting the crosslinking reaction, the present adhesive composition preferably contains a multifunctional (meth)acrylate (D). This allows the present adhesive composition to quickly form a crosslinked structure even with the same light irradiation amount, for example. In addition, when a crosslinked structure is formed in an adhesive sheet using the present adhesive composition, it is possible to prevent the adhesive from overflowing during storage or when wound into a roll, and to obtain good adhesion and cohesion.
However, in the case where the acrylic polymer (A) undergoes a hydrogen abstraction reaction due to the action of the photoinitiator (B) or the like and a sufficient crosslinked structure can be formed within the acrylic polymer (A) and/or between the acrylic polymers (A), it is not necessarily necessary to contain the polyfunctional (meth)acrylate (D).

Examples of polyfunctional (meth)acrylates (D) include (meth)acrylic monomers and (meth)acrylic oligomers having two or more functional groups. These can be used alone or in combination of two or more types.

Examples of (meth)acrylic monomers having two or more functional groups include pentanediol di(meth)acrylate, hexadiol di(meth)acrylate, heptanediol di(meth)acrylate, octanediol di(meth)acrylate, nonanediol di(meth)acrylate, decanediol di(meth)acrylate, undecanediol di(meth)acrylate, dodecanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin glycidyl ether di(meth)acrylate, (meth)acrylate, tricyclodecane dimethacrylate, tricyclodecane dimethanol di(meth)acrylate, bisphenol A polyethoxy di(meth)acrylate, bisphenol A polypropoxy di(meth)acrylate, bisphenol F polyethoxy di(meth)acrylate, ethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane trioxyethyl (meth)acrylate, ε-caprolactone modified tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate 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, dipe Examples of such compounds include pentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol penta(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, di(meth)acrylate of hydroxypivalic acid neopentyl glycol ε-caprolactone adduct, trimethylolpropane tri(meth)acrylate, trimethylolpropane polyethoxy tri(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate.

Examples of the polyfunctional (meth)acrylic oligomer include polyester (meth)acrylate oligomers, epoxy (meth)acrylate oligomers, urethane (meth)acrylate oligomers, and polyether (meth)acrylate oligomers.
Among these, (meth)acrylate monomers and oligomers having a glycol structure are preferred from the viewpoint of imparting appropriate flexibility to the cured product.

The content of the polyfunctional (meth)acrylate (D) in the present pressure-sensitive adhesive composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, relative to 100 parts by mass of the (meth)acrylic polymer (A), from the viewpoint of imparting shape stability to the pressure-sensitive adhesive sheet and durability when made into a laminate for an image display device. The upper limit is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, particularly preferably 10 parts by mass or less, and especially preferably 5 parts by mass or less, from the viewpoint of maintaining the flexibility of the pressure-sensitive adhesive sheet.
The lower limit and the upper limit of the content of the polyfunctional (meth)acrylate (D) can be combined in any desired manner.

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

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

[Silane coupling agent]
Silane coupling agent is an organic silicon compound that contains one or more reactive functional groups and one or more alkoxy groups bonded to silicon atoms in its structure.The reactive functional groups include, for example, epoxy groups, (meth)acryloyl groups, mercapto groups, hydroxyl groups, carboxy groups, amino groups, amide groups, and isocyanate groups, and among these, epoxy groups and mercapto groups are preferred from the viewpoint of durability balance.

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 have an organic substituent other than the reactive functional group and the alkoxy group bonded to the silicon atom, such as an alkyl group or a phenyl group.

Examples of the silane coupling agent used in the present invention include monomeric epoxy group-containing silane coupling agents which are silane compounds such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and silane coupling agents which are partially hydrolyzed and condensed with the silane compounds or which are combined with methyltriethoxysilane, ethyltriethoxysilane, methyltrimethy ... oligomer-type 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 monomer-type mercapto group-containing silane compounds such as silane compounds obtained by hydrolysis and condensation polymerization of a part of the silane compounds, or silane compounds obtained by hydrolysis and condensation polymerization of a part of the silane compounds with methyltriethoxysilane, ethyltriethoxysilane, etc. oligomeric mercapto group-containing silane coupling agents which are silane compounds obtained by co-condensation of alkyl group-containing silane compounds such as methyltrimethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane; (meth)acryloyl group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane; N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane; Examples of the silane include amino group-containing silane coupling agents such as silane, 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; and vinyl group-containing silane coupling agents such as vinyltrimethoxysilane and vinyltriethoxysilane.
These may be used alone or in combination of two or more kinds.

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

The content of the silane coupling agent in the pressure-sensitive adhesive composition is preferably 0.005 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, and particularly preferably 0.05 to 1 part by mass, per 100 parts by mass of the (meth)acrylic polymer (A). If the content is equal to or greater than the lower limit, durability tends to improve, and if the content is equal to or less than the upper limit, durability tends to improve.

[Plasticizer]
The present pressure-sensitive adhesive composition may contain a plasticizer in order to impart flexibility to the pressure-sensitive adhesive sheet.

Examples of plasticizers include, but are not limited to, those selected from the group consisting of polyisobutylene, polyisoprene, polybutadiene, amorphous polyolefins and their copolymers, silicones, polyacrylates, oligomeric polyurethanes, ethylene propylene copolymers, and any combination or mixture thereof.
Among these, the plasticizer is preferably polyisobutylene. Examples of polyisobutylene plasticizers that can be used herein include those commercially available from BASF under the trade name OPPANOL, particularly those selected from the OPPANOLB series.

From the viewpoint of environmental protection, the smaller the volatile organic compound (VOC) value of the plasticizer used, the better. When measured by thermogravimetric analysis, it is preferably less than 1000 ppm, more preferably less than 800 ppm, even more preferably less than 600 ppm, and most preferably less than 400 ppm.

The content of the plasticizer in the pressure-sensitive adhesive composition is not particularly limited, but is preferably 0.1 to 20 parts by mass, and more preferably 0.5 to 15 parts by mass, per 100 parts by mass of the (meth)acrylic polymer (A).

[Tackifier]
The present pressure-sensitive adhesive composition may contain a tackifier to improve the adhesive strength to the pressure-sensitive adhesive sheet.
Examples of tackifiers include terpene resins such as polyterpene (e.g., α-pinene resins, β-pinene resins, and limonene resins) and aromatic modified polyterpene resins (e.g., phenol modified polyterpene resins); coumaran-indene resins; petroleum resins such as C5 hydrocarbon resins, C9 hydrocarbon resins, C5/C9 hydrocarbon resins, and dicyclopentadiene resins; and rosins such as modified rosin, hydrogenated rosin, polymerized rosin, and rosin esters.

The content of the tackifier in the adhesive composition is not particularly limited, but is preferably 0.1 to 20 parts by mass, and more preferably 0.5 to 15 parts by mass, per 100 parts by mass of the (meth)acrylic polymer (A).

[anti-rust]
The present pressure-sensitive adhesive composition may contain a rust inhibitor to prevent corrosion when the adherend contains a corrosive portion such as metal wiring.
Examples of the rust inhibitor include triazoles and benzotriazoles.
The content of the rust inhibitor in the present pressure-sensitive adhesive composition is preferably 0.01 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the (meth)acrylic polymer (A).

The method for preparing the pressure-sensitive adhesive composition is not particularly limited. For example, the pressure-sensitive adhesive composition is prepared by mixing the (meth)acrylic polymer (A), the photoinitiator (b1), and the ultraviolet absorber (C) with other components such as the photoinitiator (b2), the polyfunctional (meth)acrylate (D), and the silane coupling agent in predetermined amounts, as required.
The pressure-sensitive adhesive composition thus obtained is suitably used for pressure-sensitive adhesive sheets, particularly pressure-sensitive adhesive sheets used for bonding optical members.

The pressure-sensitive adhesive composition may be in a syrup form. The syrup component in this case may be composed of an acrylic polymer and a monomer component. In one example, such a syrup component may be formed by so-called partial polymerization, and may be prepared by adding a monomer to a polymer in which the monomer constituting the (meth)acrylic polymer (A) is completely polymerized or partially polymerized. That is, when a specific monomer composition is partially polymerized, some of the monomers are polymerized to form an oligomer or polymer, and some of the monomers remain, thereby forming a syrup component. In another example, the syrup can be formed by adding a monomer component to a partially or completely polymerized polymer.
Therefore, in this specification, the constituent unit derived from a monomer constituting the (meth)acrylic polymer (A) may mean a monomer present in a state in which an oligomer or polymer is formed in the component of the acrylic polymer, or a monomer contained in a syrup component before polymerization.

<<Adhesive sheet>>
The pressure-sensitive adhesive sheet of the present invention (hereinafter also referred to as "the pressure-sensitive adhesive sheet") is a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition. The pressure-sensitive adhesive sheet is particularly useful as a pressure-sensitive adhesive sheet for organic EL display devices.
The present adhesive sheet may be a single-layer sheet consisting only of an adhesive layer (hereinafter also referred to as "the present adhesive layer") formed from the present adhesive composition, or a multilayer sheet in which multiple layers of the present adhesive are laminated.

<Physical properties of this adhesive sheet>
The pressure-sensitive adhesive sheet can have the following physical properties.

[Gel fraction (X0)]
The gel fraction (X0) of the pressure-sensitive adhesive sheet is preferably 20% or more. If the gel fraction of the pressure-sensitive adhesive sheet is equal to or greater than the lower limit, the pressure-sensitive adhesive sheet is likely to retain its shape sufficiently. From this viewpoint, the gel fraction (X0) is more preferably 25% or more, even more preferably 30% or more, and particularly preferably 35% or more.
Furthermore, from the viewpoint of obtaining flexibility, the gel fraction (X0) of the present pressure-sensitive adhesive sheet is preferably 90% or less, more preferably 80% or less, even more preferably 70% or less, even more preferably 60% or less, even more preferably 55% or less, and particularly preferably 50% or less.
The lower limit and the upper limit of the gel fraction (X0) can be combined in any desired manner.
The gel fraction (X0) is an indicator of the degree of crosslinking (degree of curing), and can be measured under the measurement conditions described in the Examples below.

It is preferable that the adhesive sheet has active energy ray curing properties. However, "the adhesive sheet has active energy ray curing properties" means that the adhesive sheet has the property of being cured by active energy rays, in other words, that the adhesive sheet has room to be cured by active energy rays.

The pressure-sensitive adhesive sheet may be one in which the pressure-sensitive adhesive composition has been cured to a state in which there is still room for the pressure-sensitive adhesive composition to be cured by active energy rays (hereinafter also referred to as "primary curing"), or the pressure-sensitive adhesive composition may be crosslinked (primary curing) by a thermal crosslinking agent and cured by active energy rays. The pressure-sensitive adhesive sheet in the primarily cured state can be cured (hereinafter also referred to as "secondary curing") by irradiating the pressure-sensitive adhesive sheet with active energy rays before or after being attached to an adherend.
When the pressure-sensitive adhesive sheet is active energy ray-curable, the "gel fraction X0" refers to the gel fraction of the pressure-sensitive adhesive sheet in a primarily cured state.

When the pressure-sensitive adhesive sheet is primarily cured, it may be primarily cured by heat or by active energy rays, but from the viewpoint of easily controlling the gel fraction (X0) within a predetermined range, it is preferable that the pressure-sensitive adhesive sheet is primarily cured by irradiation with active energy rays.

The active energy rays used in the primary curing are preferably active energy rays having a wavelength longer than 380 nm, and more preferably active energy rays having a wavelength longer than 400 nm.
When the pressure-sensitive adhesive sheet is primarily cured by active energy rays, for example, it is preferable to perform the primary curing by irradiating active energy rays with an integrated irradiation amount at 405 nm of 10 to 4000 mJ/cm ^2. In such active energy ray irradiation, the preferred irradiation amount is 50 mJ/cm ² or more and 3500 mJ/cm ² or less, more preferably 100 mJ/cm ² or more and 3000 mJ/cm ² or less, particularly preferably 200 mJ/cm ² or more and 2500 mJ/cm ² or less, and even more preferably 300 mJ/cm ² or more and 2000 mJ/cm ² or less. If the irradiation amount is within the above range, it is preferable because there is a tendency that the degree of curing can be adjusted while leaving room for curing.
The amount of active energy ray irradiation is the sum of the integrated energy on one side and the integrated energy on the other side when active energy ray is irradiated from both sides.

[Gel fraction (X1)]
When the pressure-sensitive adhesive sheet has active energy ray curability, the gel fraction ( ^X1 ) after the pressure-sensitive adhesive sheet is irradiated with active energy rays having a wavelength of 405 nm so that the integrated light amount is 2000 to 4000 mJ/cm2 (after secondary curing) is preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, and particularly preferably 60% or more.
By having a gel fraction (X1) after secondary curing of 30% or more, a laminate for an image display device using the pressure-sensitive adhesive sheet will have excellent durability.

Furthermore, the difference (X1-X0) between the gel fraction (X1) after the secondary curing and the gel fraction (X0) before the irradiation with active energy rays (before the secondary curing), i.e., in the primary cured state, is preferably 2% or more, more preferably 5% or more, even more preferably 10% or more, even more preferably 15% or more, and particularly preferably 20% or more. By having the difference (X1-X0) be equal to or greater than the lower limit, it is possible to achieve a higher level of both adhesion to a component of an image display device when the pressure-sensitive adhesive sheet is laminated to the component, and durability of the laminate for an image display device after lamination.
The gel fraction (X1) can be measured by the method described in the Examples below.

[Adhesive force]
The adhesive sheet preferably has an adhesive strength of 3.0 N/cm or more, more preferably 4.0 N/cm or more, and even more preferably 5.0 N/cm or more against soda lime glass at a peel angle of 180° and a peel speed of 60 mm/min.

[Adhesive strength after curing]
When the pressure-sensitive adhesive sheet has active energy ray curing properties, it is preferable that the adhesive strength (post-curing adhesive strength) to soda-lime glass at a peel angle of 180° and a peel speed of 60 mm/ ^min when the pressure-sensitive adhesive sheet is laminated to soda-lime glass and then irradiated with active energy rays having a wavelength of 405 nm so that the integrated light amount is 2000 to 4000 mJ/cm2 is higher than the aforementioned adhesive strength.
Specifically, the adhesive strength after curing is preferably 5.0 N/cm or more, more preferably 6.0 N/cm or more, and even more preferably 7.0 N/cm or more. When the adhesive strength after curing is 5.0 N/cm or more, the laminate for an image display device using the pressure-sensitive adhesive sheet has excellent durability.

[Chromaticity]
When the pressure-sensitive adhesive sheet is irradiated with active energy rays having a wavelength of 405 nm so that the accumulated light amount is 2000 to 4000 mJ/ ^cm2 , the chromaticity (b*1) is preferably 2.5 or less, more preferably 2.0 or less, even more preferably 1.5 or less, and most preferably 1.0 or less.
In this pressure-sensitive adhesive sheet, the difference (b*1-b*0) between the chromaticity (b*1) after irradiation with the active energy rays and the chromaticity (b*0) before irradiation with the active energy rays is preferably 1.0 or less, more preferably 0.5 or less, even more preferably 0.1 or less, and particularly preferably 0 or less.
When the (b*1) and (b*1-b*0) satisfy the above ranges, a pressure-sensitive adhesive sheet in which yellowing due to irradiation with active energy rays is suppressed can be obtained.
The chromaticity (b*1) and chromaticity (b*0) can be measured by the method described in the Examples below.

Photoinitiators that are highly sensitive to light in the long wavelength region generally have the problem of being easily discolored, but acylphosphine oxide photoinitiators have a photobleaching effect and have been widely used in applications where discoloration is a concern. However, this effect is due to the decomposition of cleavage-type photoinitiators after photoreaction, and it was thought that hydrogen abstraction-type photoinitiators, which do not undergo photodecomposition, do not have a photobleaching effect.
However, it was surprisingly found that the photoinitiator (b1) not only does not yellow after irradiation with light, but also has a photobleaching effect, even though it is a hydrogen abstraction type photoinitiator. The pressure sensitive adhesive sheet not only does not produce photodecomposition products, but also has excellent active energy ray curing properties and color resistance while having ultraviolet absorption properties, so it can be suitably used for image display devices.

[Light transmittance]
The light transmittance of the pressure-sensitive adhesive sheet at a wavelength of 380 nm is preferably 10% or less. By having such optical properties, it becomes easy to protect the components of the image display device from deterioration caused by ultraviolet rays. From this viewpoint, the light transmittance is more preferably 7% or less, even more preferably 5% or less, and particularly preferably 3% or less.

The light transmittance of the pressure-sensitive adhesive sheet at a wavelength of 400 nm is preferably 30% or less. By having such optical properties, even image display device components that are easily deteriorated by light can be firmly protected from incident light. From this viewpoint, the light transmittance is more preferably 20% or less, even more preferably 10% or less, and particularly preferably 5% or less.
The light transmittance can be measured by the method described in the Examples below.

[Total light transmittance, haze]
The total light transmittance of the present pressure-sensitive adhesive sheet is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.
The total light transmittance can be measured by the method described in the Examples below.

The haze of the pressure-sensitive adhesive sheet is preferably 1.0% or less, more preferably 0.8% or less, and even more preferably 0.5% or less. Since the pressure-sensitive adhesive sheet has a haze of 1.0% or less, it can be used as a pressure-sensitive adhesive sheet for an image display device that requires transparency.
The haze can be measured with a haze meter.
In order to set the haze of the present pressure-sensitive adhesive sheet within the above range, it is preferable that the present pressure-sensitive adhesive sheet does not contain particles such as organic particles.

<Thickness>
The thickness of the pressure-sensitive adhesive sheet is not particularly limited, but if it is 10 μm or more, the handling property is good, and if it is 1000 μm or less, it can contribute to making the pressure-sensitive adhesive sheet thinner. From this viewpoint, the thickness of the pressure-sensitive adhesive sheet is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, and particularly preferably 25 μm or more. On the other hand, the upper limit is preferably 1000 μm or less, more preferably 500 μm or less, even more preferably 400 μm or less, particularly preferably 300 μm or less, and especially preferably 250 μm or less.

<Method of manufacturing 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 merely one 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 production method.

The adhesive sheet may be produced, for example, by preparing the adhesive composition, forming the adhesive composition into a sheet, curing it by crosslinking, i.e., polymerization, and then processing it appropriately as necessary. Alternatively, the adhesive sheet may be formed by preparing the adhesive composition, coating it on a component for an image display device, and curing the adhesive composition.

When preparing the present pressure-sensitive adhesive composition, the above-mentioned raw materials may be mixed using a propeller stirrer or a kneader (for example, a single-screw extruder, a twin-screw extruder, a planetary mixer, a twin-screw mixer, a pressure kneader, etc.).
When mixing various raw materials, various additives such as silane coupling agents and antioxidants may be blended together with the resin in advance and then supplied to a mixer or kneader, or all of the materials may be melt-mixed in advance and then supplied, or a master batch in which only the additives are concentrated in the resin may be prepared and then supplied.

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

The adhesive composition can be cured by irradiating it with active energy rays, and the adhesive sheet can be produced by irradiating a molded product of the adhesive composition, for example a sheet, with active energy rays. In addition to irradiating it with active energy rays, the adhesive composition can also be heated to further cure it.

There are no particular limitations on the irradiation energy, irradiation time, irradiation method, etc. of the active energy rays, as long as the photopolymerization initiator can be activated to crosslink the pressure-sensitive adhesive composition.

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 or visible light rays are preferred from the viewpoints of suppressing damage to components of the image display device and ease of reaction control. Furthermore, curing by irradiation with ultraviolet rays or visible light is advantageous from the viewpoints of curing speed, ease of availability of irradiation equipment, price, and the like. Among these, curing by visible light rays, for example, active energy rays of 405 nm, is preferred from the viewpoint of preventing curing inhibition by ultraviolet absorbers.

Light sources for active energy ray 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, LEDs, etc. that emit light in the 150 to 450 nm wavelength range.

The amount of active energy ray irradiation (accumulated light amount) is preferably from 10 to 6000 mJ/ ^cm2 , more preferably from 50 mJ/ ^cm2 to 5500 mJ/ ^cm2 , still more preferably from 100 mJ/ ^cm2 to 5000 mJ/ ^cm2 , particularly preferably from 200 mJ/ ^cm2 to 4000 mJ/ ^cm2, and particularly preferably from 300 mJ/ ^cm2 to 3000 mJ/ ^cm2 , from the viewpoint of curing.

In another embodiment of the method for producing the pressure-sensitive adhesive sheet, the pressure-sensitive adhesive composition may be dissolved in a suitable solvent and various coating methods may be used. When the pressure-sensitive adhesive composition is in a syrup form, it is also possible to coat the composition without using a solvent.
When a coating method is used, the present pressure-sensitive adhesive sheet can be obtained by heat curing in addition to the above-mentioned curing by irradiation with active energy rays. In the case of coating, the thickness of the present pressure-sensitive adhesive sheet can be adjusted by the coating thickness and the solids concentration of the coating liquid.

For example, the adhesive composition can be dissolved in a solvent, coated on a release film, dried, and cured by active energy ray irradiation to form the present adhesive sheet. Furthermore, a release film may be laminated as necessary. In this case, the adhesive composition may be coated on a release film, dried, cured by active energy ray irradiation, and a release film may be laminated on top of the coating, or the adhesive composition may be coated on a release film, dried, and a release film may be laminated on top of the coating, and then cured by active energy ray irradiation to form the present adhesive sheet.

Such a solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition, and examples thereof include ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, methyl acetoacetate, and ethyl acetoacetate; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic solvents such as toluene and xylene; and alcohol-based solvents such as methanol, ethanol, and propyl alcohol. These can be used alone or in combination of two or more. Among them, ethyl acetate, acetone, methyl ethyl ketone, and toluene are preferred from the standpoints of solubility, drying property, and cost, and ethyl acetate is particularly preferred.

The amount of the solvent used 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 (meth)acrylic polymer (A), in terms of drying property, while it is preferably 1 part by mass or more, more preferably 50 parts by mass or more, even more preferably 100 parts by mass or more, and particularly preferably 150 parts by mass or more.
The coating method can be a commonly used method such as roll coating, die coating, gravure coating, comma coating, screen printing, bar coating, etc.

After drying, the solvent content in the adhesive composition 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.

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

The drying time is usually 1 to 30 minutes, more preferably 3 to 25 minutes, and even more preferably 5 to 20 minutes. This time range allows the solvent to be removed efficiently and sufficiently.

Drying methods include, for example, drying with a dryer, drying with a heated roll, and drying by blowing hot air onto the film. Among these, the use of 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.

<<Adhesive sheet with release film>>
The present pressure-sensitive adhesive sheet can also be provided as a pressure-sensitive adhesive sheet with a release film (pressure-sensitive adhesive sheet laminate) by laminating a release film on one or both sides of the pressure-sensitive adhesive layer (the present pressure-sensitive adhesive sheet) made of the present pressure-sensitive adhesive composition.
When the release film is provided on both sides of the present pressure-sensitive adhesive sheet, it is preferable to use a laminate structure in which a light release film with a relatively low release force and a heavy release film with a relatively high release force are laminated. When using a pressure-sensitive adhesive sheet with a release film 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 the image display device component (first component) is bonded to the other side of the pressure-sensitive adhesive sheet exposed by peeling off the other release film (heavy release film), and another image display device component (second component) is bonded to the other side of the pressure-sensitive adhesive sheet.

As such a release film, any known release film can be appropriately used.
As the material of the release film, for example, a polyester film, a polyolefin film, a polycarbonate film, a polystyrene film, an acrylic film, a triacetyl cellulose film, a fluororesin film, etc., which is subjected to a release treatment by applying a release agent such as a silicone resin, or a release paper, etc. can be appropriately selected and used. Among them, polyester film, and more particularly, polyethylene terephthalate (PET) film, particularly biaxially stretched PET film, are preferred in terms of excellent transparency, mechanical strength, heat resistance, flexibility, etc. A release film in which a release layer formed by curing a curable silicone-based release agent mainly composed of a silicone resin is provided on the above-mentioned substrate can be used.

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

<Preferred uses of the pressure-sensitive adhesive sheet>
The pressure-sensitive adhesive sheet is preferably used for bonding optical members. Specifically, the pressure-sensitive adhesive sheet is preferably used for bonding members constituting a display, particularly members used for manufacturing a display, and is used as a pressure-sensitive adhesive sheet for bonding an image display panel and image display device components such as a protective panel or touch panel disposed on the front side (viewing side) of the image display panel, or components constituting the image display device components.
Incidentally, the image display device components may be the same as those described below.

<<Laminate for image display device>>
A laminate for an image display device according to an embodiment of the present invention (hereinafter, sometimes referred to as "the laminate for the 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 via the present pressure-sensitive adhesive sheet. The laminate for the image display device is preferably a laminate for an image display device having a configuration in which two components of the image display device are laminated via the present pressure-sensitive adhesive sheet.

Of the components of this laminate for an image display device, the adhesive sheet is as described above, and the components other than the adhesive sheet are described below.

<Image display device components>
Examples of image display device components constituting the present laminate for image display devices include flat panel image display device components and flexible image display device components. Examples of such image display device components include flexible displays such as liquid crystal displays and organic electroluminescence (EL) displays, cover lenses (cover films), polarizing plates, polarizers, retardation films, barrier films, viewing angle compensation films, brightness improvement films, contrast improvement films, diffusion films, semi-transmissive reflective films, electrode films, transparent conductive films, metal mesh films, and touch sensor films. Any one of these or two of them may be used in combination. For example, a combination of a flexible display and other image display device components, or a combination of a cover lens and other image display device components may be used.

Note that flexible image display device components are bendable components, meaning components used in image display devices with curved shapes and components that can be repeatedly bent. In particular, components that can be fixed into a curved shape with a radius of curvature of 25 mm or more, and particularly components that can withstand bending with a radius of curvature of less than 25 mm, and more preferably less than 3 mm, are preferred.

In the above-mentioned configuration, examples of the members constituting the image display device include a resin sheet, glass, and the like.
Examples of the material of such a resin sheet include polyester resin, cycloolefin resin, triacetyl cellulose resin, polymethyl methacrylate resin, polyurethane, epoxy resin, polyimide resin, and aramid resin, which may be one type of resin or two or more types of resin. Among them, a resin sheet containing at least one type of 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 a main component is preferable.
Here, the term "main component" refers to a component that occupies the largest weight ratio among the components that make up the image display device constituent member, and specifically, it is a component that occupies 50 mass % or more of the resin composition (resin sheet) that forms the image display device constituent member, and preferably 55 mass % or more, and particularly preferably 60 mass % or more.

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

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

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.

First, we will explain the details of the raw materials used in the adhesive compositions prepared in the examples.

<(Meth)acrylic polymer (A)>
(Meth)acrylic polymer (A-1): an acrylic copolymer obtained by random copolymerization of 46.4 parts by mass of 2-ethylhexyl acrylate, 45.1 parts by mass of methyl acrylate, and 8.5 parts by mass of N-vinyl-2-pyrrolidone (weight average molecular weight: about 230,000)
(Meth)acrylic polymer (A-2): an acrylic copolymer obtained by random copolymerization of 64.0 parts by mass of 2-ethylhexyl acrylate, 19.0 parts by mass of methyl acrylate, and 17.0 parts by mass of hydroxyethyl acrylate (weight average molecular weight: about 460,000)

<Photoinitiator (B)>
Photoinitiator (b1-1): a photoinitiator having a glyoxylate structure represented by the following formula 3-1 (molar absorption coefficient at a wavelength of 405 nm: 3.3×10 ² L/mol·cm)

Photoinitiator (b2-1): Methylbenzoylformate ("Omnirad MBF" manufactured by IGM, molar absorption coefficient at a wavelength of 405 nm: 6.5 L/mol cm)
Photoinitiator (b2-2): 2,4-diethylthioxanthone ("Omnirad DETX" manufactured by IGM, molar absorption coefficient at a wavelength of 405 nm: 3.3×10 ³ L/mol·cm)
Photoinitiator (b2-3): Ethyl (2,4,6-trimethylbenzoyl)-phenylphosphinate (IGM "Omnirad TPO-L", molar absorption coefficient at a wavelength of 405 nm: 81 L/mol cm)

<Ultraviolet absorber (C)>
Ultraviolet absorber (C-1): bisethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S, manufactured by BASF Japan Ltd.)

<Polyfunctional (meth)acrylate (D)>
Multifunctional (meth)acrylate (D-1): Polypropylene glycol #400 diacrylate (NK Ester APG-400, manufactured by Shin-Nakamura Chemical Co., Ltd.)
Multifunctional (meth)acrylate (D-2): Propylene oxide modified pentaerythritol tri(tetra)acrylate (NK Ester ATM-4PL, manufactured by Shin-Nakamura Chemical Co., Ltd.)
Multifunctional (meth)acrylate (D-3): Pentaerythritol tri(tetra)acrylate (NK Ester ATMM3L, manufactured by Shin-Nakamura Chemical Co., Ltd.)

[Example 1]
A pressure-sensitive adhesive composition was prepared by uniformly mixing 100 parts by mass of a (meth)acrylic polymer (A-1), 1.5 parts by mass of a photoinitiator (b1-1), 1.4 parts by mass of an ultraviolet absorber (C-1), and 1.5 parts by mass of a polyfunctional (meth)acrylate (D-1).
The pressure-sensitive adhesive composition was spread in the form of a sheet having a thickness of 100 μm on a silicone release-treated release film (a PET film manufactured by Mitsubishi Chemical Corporation).

Next, a silicone release-treated release film (PET film manufactured by Mitsubishi Chemical Corporation) having a thickness of 75 μm was laminated on top of the sheet-like pressure-sensitive adhesive composition to form a laminate, thereby obtaining a pressure-sensitive adhesive sheet with a release film consisting of release film/pressure-sensitive adhesive sheet/release film.
Next, using a 405 nm LED light source (FireJet FJ200 405 nm), both surfaces of the pressure-sensitive adhesive sheet with release film were irradiated with light having a peak wavelength of 405 nm through the release film so that each surface was 1000 mJ/cm ² (accumulated light amount 2000 mJ/cm ² ), thereby semi-curing the pressure-sensitive adhesive sheet. The accumulated light amount was measured using an ultraviolet integrating light meter "UIT-250" (manufactured by Ushio Inc.) and a light receiver "UVD-C405" (manufactured by Ushio Inc.) (hereinafter the same).
The obtained pressure-sensitive adhesive sheet with a release film had an active energy ray-curable pressure-sensitive adhesive sheet.

[Example 2]
A pressure-sensitive adhesive sheet with a release film was prepared in the same manner as in Example 1, except that the pressure-sensitive adhesive composition was changed to the formulation shown in Table 1.

[Example 3]
A pressure-sensitive adhesive composition was prepared by uniformly mixing 100 parts by mass of a (meth)acrylic polymer (A-1), 1.5 parts by mass of a photoinitiator (b1-1), 1.2 parts by mass of an ultraviolet absorber (C-1), and 1.5 parts by mass of a polyfunctional (meth)acrylate (D-1).
The pressure-sensitive adhesive composition was spread in the form of a sheet having a thickness of 100 μm on a silicone release-treated release film (a PET film manufactured by Mitsubishi Chemical Corporation).

Next, a silicone release-treated release film (PET film manufactured by Mitsubishi Chemical Corporation) having a thickness of 75 μm was laminated on top of the sheet-like pressure-sensitive adhesive composition to form a laminate, thereby obtaining a pressure-sensitive adhesive sheet with a release film consisting of release film/pressure-sensitive adhesive sheet/release film.
Next, using a metal halide lamp, light was irradiated from one side of the adhesive sheet with the release film through the release film so that the integrated light amount at a wavelength of 405 nm was 2000 mJ/ ^cm2 , thereby semi-curing the adhesive sheet.
The obtained pressure-sensitive adhesive sheet with a release film had an active energy ray-curable pressure-sensitive adhesive sheet.

[Examples 4 and 5]
A pressure-sensitive adhesive sheet with a release film was prepared in the same manner as in Example 3, except that the formulation of the pressure-sensitive adhesive composition and the light irradiation conditions were changed as shown in Table 1.

[Comparative Examples 1 to 3]
A pressure-sensitive adhesive sheet with a release film was prepared in the same manner as in Example 1, except that the pressure-sensitive adhesive composition was changed to the formulation shown in Table 1.

[Physical property measurement and evaluation]
The pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples were subjected to the following various measurements and evaluations. The evaluation results are summarized in Table 1.

<Gel Fraction>
For the adhesive sheets with release film prepared in the examples and comparative examples, about 0.1 g of adhesive sheet pieces were taken from the adhesive sheets from which the release film was peeled off. The collected adhesive sheet pieces were wrapped in a SUS mesh (#150) with a mass X (g) that had been previously made into a bag shape, and the mouth of the bag was closed to obtain a sample, and the mass Y (g) of the sample was measured. The sample was immersed in ethyl acetate and stored in a dark place at 23°C for 24 hours, and then the sample was taken out and heated at 70°C for 4.5 hours to evaporate the ethyl acetate, and the mass Z (g) of the dried sample was measured. From each measured mass, the gel fraction (X0) after primary curing was calculated according to the following formula.
Gel fraction (%)=[(Z−X)/(Y−X)]×100

In addition, the adhesive sheets with release films prepared in the examples and comparative examples were irradiated with light having a peak wavelength of 405 nm through the release film using a 405 nm LED light source (FireJet FJ200 405 nm) so that the accumulated light amount was 3000 mJ/cm ² , thereby curing the adhesive sheets. Using the cured adhesive sheets, the gel fraction (X1) after secondary curing was calculated in the same manner as the gel fraction (X0).

<Chromaticity>
The release film was peeled off from the pressure-sensitive adhesive sheet with release film prepared in the examples and comparative examples, and the exposed adhesive surfaces on both sides were sandwiched between two sheets of soda lime glass (thickness 0.55 mm) to prepare a laminated sample. The chromaticity (b*0) after primary curing was measured for the laminated sample using a spectrophotometer (Suga Test Instruments Co., Ltd.) "SC-T" with a D65 light source and a 10° field of view according to a method based on JIS K7103.

In addition, the adhesive sheets with release films prepared in the examples and comparative examples were irradiated with light having a peak wavelength of 405 nm through the release film using a 405 nm LED light source (FireJet FJ200 405 nm) so that the cumulative light amount was 3000 mJ/cm ² , and the adhesive sheets were cured. Using the cured adhesive sheets, the chromaticity (b*1) after secondary curing was measured in the same manner as the chromaticity (b*0).
When the chromaticity (b*1) after the secondary curing was 2.5 or less, it was determined that there was no problem in practical use.

<Light transmittance>
One release film of the pressure-sensitive adhesive sheet with release film prepared in the Examples and Comparative Examples was peeled off, and the exposed adhesive surface was roll-pressed to a soda lime glass (82 mm x 53 mm x 0.5 mm thick). Next, the remaining release film was peeled off, and the exposed adhesive surface was roll-pressed to another soda lime glass (82 mm x 53 mm x 0.5 mm thick). Thereafter, autoclave treatment (60 ° C, gauge pressure 0.2 MPa, 20 minutes) was performed to finish adhesion, and the pressure-sensitive adhesive sheet was cured by irradiating light with a peak wavelength of 405 nm using a 405 nm LED light source (FireJet FJ200 405 nm) so that the accumulated light amount was 3000 mJ / cm ² , and an evaluation laminate was prepared.
The spectral transmittance (%) of the evaluation laminate at wavelengths of 300 nm to 800 nm was measured using a spectrophotometer (UV2000 manufactured by Shimadzu Corporation) to determine the light transmittance at wavelengths of 380 nm and 400 nm.

<Adhesive strength>
One of the release films from the pressure-sensitive adhesive sheets with release films prepared in the Examples and Comparative Examples was peeled off, and a 100 μm thick polyethylene terephthalate film ("Cosmoshine A4300" manufactured by Toyobo Co., Ltd.) was attached as a backing film to prepare a laminate.
The laminate was cut to a length of 150 mm and a width of 10 mm, the remaining release film was peeled off, and the exposed adhesive surface was brought into contact with soda lime glass and rolled back and forth once to roll-press the adhesive sheet. The resulting laminate was aged at 60°C for 30 minutes for finish-pasting, and then irradiated with light through the backing film using a 405 nm LED light source (FireJet FJ200 405 nm) so that the accumulated light amount was 3000 mJ/ ^cm2 to cure the adhesive sheet, and then aged at 23°C for 15 hours to obtain a sample for measuring adhesive strength.
The adhesive strength measurement sample was peeled off from glass at a peel angle of 180° and a peel speed of 60 mm/min in an environment of 23°C and 40% RH, and the peel strength (N/cm) to glass was measured to determine the adhesive strength (P1) after secondary curing.

The pressure-sensitive adhesive sheets of Examples 1 to 5 had sufficient curability with respect to a 405 nm LED light source, and the chromaticity (b*) was within the standard range, which was a favorable result.
On the other hand, the adhesive sheets of Comparative Examples 1 and 2 had poor curability with respect to a 405 nm LED light source. This is believed to be due to the low molar absorption coefficient of the photoinitiator used at a wavelength of 405 nm.
The pressure-sensitive adhesive composition of Comparative Example 3 used a cleavage-type photoinitiator, and therefore produced photodecomposition products when irradiated with active energy rays.
In addition, since the pressure-sensitive adhesive sheet of Comparative Example B3 contains 10.010 parts by mass of the polyfunctional (meth)acrylate (D), the reaction of the polyfunctional (meth)acrylate (D) proceeds quickly due to the light irradiation during the production of the pressure-sensitive adhesive sheet, resulting in a large gel fraction (X0). Also, the difference in gel fraction (X1-X0) is small, and the margin for curing by active energy rays is reduced.

Claims (21)

The composition comprises a (meth)acrylic polymer (A), a photoinitiator (B), and an ultraviolet absorber (C),
The pressure-sensitive adhesive composition, wherein the photoinitiator (B) comprises a photoinitiator (b1) having a glyoxylate structure represented by the following formula 1 and having a molar absorption coefficient at a wavelength of 405 nm of 30 (L/mol cm) or more:

(In the above formula 1, R ¹ is a substituted or unsubstituted C ₁ -C ₂₀ alkyl, a substituted or unsubstituted C ₃ -C ₂₀ cycloalkyl, or a substituted or unsubstituted C ₂ -C ₂₀ heterocycloalkyl. * indicates a bond.) The pressure-sensitive adhesive composition according to claim 1, wherein the photoinitiator (b1) is a compound containing a biphenyl structure to which the bond * in formula 1 is bonded. The pressure-sensitive adhesive composition according to claim 1, wherein the photoinitiator (b1) is a compound containing a sulfide biphenyl structure to which the bond * in formula 1 is bonded. The pressure-sensitive adhesive composition according to claim 1, wherein the photoinitiator (b1) is a compound having two or more radical generating groups in the molecule. The pressure-sensitive adhesive composition according to claim 1, further comprising a multifunctional (meth)acrylate (D). The pressure-sensitive adhesive composition according to claim 5, wherein the content of the polyfunctional (meth)acrylate (D) is 0.1 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the (meth)acrylic polymer (A). The pressure-sensitive adhesive composition according to claim 1, wherein the (meth)acrylic polymer (A) contains a structural unit derived from an alkyl (meth)acrylate having a linear or branched alkyl group with 3 to 30 carbon atoms in the alkyl group, and a structural unit derived from a hydroxyl group-containing monomer and/or a structural unit derived from a nitrogen-containing monomer. An adhesive sheet having an adhesive layer formed from the adhesive composition according to any one of claims 1 to 7. The adhesive sheet according to claim 8, which has a light transmittance of 10% or less at a wavelength of 380 nm. The adhesive sheet according to claim 8, which has a light transmittance of 30% or less at a wavelength of 400 nm. The adhesive sheet according to claim 8, having a total light transmittance of 80% or more. The adhesive sheet according to claim 8, wherein the gel fraction (X0) is 20% or more. The pressure-sensitive adhesive sheet according to claim 12, wherein the pressure-sensitive adhesive sheet has active energy ray curability, and when the pressure-sensitive adhesive sheet is irradiated with active energy rays having a wavelength of 405 nm so that the integrated light amount is 2000 to 4000 mJ/ ^cm2 , the gel fraction (X1) is 30% or more. The pressure-sensitive adhesive sheet according to claim 13, wherein the difference (X1-X0) between the gel fraction (X1) and the gel fraction (X0) is 2% or more. The pressure-sensitive adhesive sheet according to claim 8, wherein the pressure-sensitive adhesive sheet has active energy ray curability, and when the pressure-sensitive adhesive sheet is irradiated with active energy rays having a wavelength of 405 nm so that the integrated light amount is 2000 to 4000 mJ/ ^cm2 , the chromaticity (b*1) is 2.5 or less, and the difference (b*1-b*0) from the chromaticity (b*0) before irradiation with the active energy rays is 1.0 or less. The pressure-sensitive adhesive sheet according to claim 8, which is used for bonding optical components. An adhesive sheet with a release film having a configuration in which the adhesive sheet according to claim 8 and a release film are laminated together. A laminate for an image display device having a configuration in which two optical members are laminated via the adhesive sheet described in claim 8. An image display device comprising the laminate for an image display device according to claim 18. An adhesive sheet for an organic EL display device comprising the adhesive sheet according to claim 8. a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition containing a (meth)acrylic polymer (A), a photoinitiator (B) and an ultraviolet absorber (C);
The pressure-sensitive adhesive sheet, wherein the photoinitiator (B) comprises a compound represented by the following formula 2:

(In the above formula 2, A is O, S, NR ⁴ , or a linear or branched alkylene or cycloalkylene having 1 to 6 carbon atoms.
R ¹ is a substituted or unsubstituted C ₁ -C ₂₀ alkyl, a substituted or unsubstituted C ₃ -C ₂₀ cycloalkyl, or a substituted or unsubstituted C ₂ -C ₂₀ heterocycloalkyl.
^R2 is a hydrogen atom, a substituted or unsubstituted _C1 - _C20 alkyl, a substituted or unsubstituted _C3 - _C20 cycloalkyl, a substituted or unsubstituted _C2 - _C20 heterocycloalkyl, a substituted or unsubstituted _C6 - _C20 aryl, a substituted or unsubstituted _C1 - _C20 heteroaryl, ^SR5 , ^OR6 , ^{NR7R8 ,} C(O) ^R9 , or C(O) ^OR13 .
R ⁴ is a group selected from the group consisting of a hydrogen atom, a C ₁ -C ₁₈ alkyl, a C ₂ -C ₁₈ alkanoyl, a C ₆ -C ₁₀ aryl, and a C ₇ -C ₁₁ aroyl.
R ⁵ and R ⁶ are each independently a group selected from the group consisting of a hydrogen atom, a C ₁ -C ₂₀ alkyl, a C ₂ -C ₂₀ alkanoyl, a C ₆ -C ₁₀ aryl, and a C ₇ -C ₁₁ aroyl.
R ⁷ and R ⁸ are each independently a group selected from the group consisting of a hydrogen atom, a C ₁ -C ₂₀ alkyl, a C ₂ -C ₂₀ alkanoyl, a C ₇ -C ₁₁ aroyl, and a C ₆ -C ₁₀ aryl.
R ⁹ is a group selected from the group consisting of a hydrogen atom, a C ₁ -C ₂₀ alkyl, and a C ₆ -C ₂₀ aryl.
^R13 has the same meaning as ^R1 .