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

Abstract

The purpose of the present invention is to provide: a transparent adhesive sheet which has high sensitivity to active energy rays and can be efficiently cured; a transparent adhesive sheet with a release film using the transparent adhesive sheet; a transparent adhesive sheet for a flexible image display device constituent member; a laminate for an image display device; the transparent pressure-sensitive adhesive sheet is formed from a pressure-sensitive adhesive composition (I) that contains a precursor. The precursor contains a (meth) acrylic polymer (A), a compound (B) having a radical-polymerizable functional group having a carbon-carbon double bond and a radical-generating structure in the molecule, and a photopolymerization initiator (C) comprising a compound other than the compound (B). The transparent adhesive sheet has a shear storage modulus (G '(-20 DEG C)) of 10 kPa to 1000 kPa (inclusive) at-20 DEG C as determined by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz.

Description

Technical Field

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

[0002] This application claims priority based on Japanese Patent Application No. 2022-186460 filed in Japan on November 22, 2022, and incorporates its content herein. Background Art

[0003] In recent years, image display devices including curved portions using organic light-emitting diodes (OLEDs) and quantum dots (QDs), and flexible image display devices that can be bent and wound have been developed and are being widely commercialized.

[0004] In such display devices, a plurality of sheet members such as a cover glass lens, a circular polarizing plate, a touch film sensor, a color filter, and a light-emitting element are formed into a laminated structure bonded by a transparent adhesive sheet. When focusing on a certain adhesive sheet, it can be regarded as a laminate formed by laminating the member and the adhesive sheet.

[0005] In Patent Document 1, regarding a foldable flexible image display device, an adhesive and an adhesive sheet that can be applied to a device for repeated bending, and a bent laminate member and a device for repeated bending are disclosed by setting the product value of the creep compliance change value and the relaxation modulus change value within an appropriate range.

[0006] In Patent Document 2, as an adhesive that can form a hot-meltable adhesive layer excellent in holding power and adhesive force, an adhesive containing a (meth)acrylic polymer having a weight-average molecular weight of 50,000 to 1,000,000 obtained by polymerizing a monomer mixture containing a macromonomer having a number-average molecular weight of 500 or more and less than 6000 and a vinyl monomer is disclosed.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Laid-Open No. 2019-123826

[0010] Patent Document 2: International Publication No. 2015 / 080244 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] However, in the conventional adhesive sheets such as those in Patent Documents 1 and 2, the sensitivity during curing with active energy rays is insufficient, so it is difficult to perform high-efficiency curing.

[0013] An object of the present invention is to provide a transparent adhesive sheet having high sensitivity to active energy rays and capable of being cured efficiently, a transparent adhesive sheet with a release film using the aforementioned transparent adhesive sheet, a transparent adhesive sheet for a flexible image display device component, a laminate for an image display device, and a flexible image display device.

[0014] Means for Solving the Problems

[0015] One embodiment of the present invention includes the following aspects.

[0016] [1] A transparent adhesive sheet formed from an adhesive composition (I), wherein the adhesive composition (I) contains a precursor, and the precursor contains a (meth)acrylic polymer (A), a compound (B) having a radically polymerizable functional group with a carbon-carbon double bond and a structure that generates free radicals in the molecule, and a photopolymerization initiator (C) formed from a compound other than the aforementioned compound (B).

[0017] The shear storage modulus (G'(-20°C)) at -20°C of the transparent adhesive sheet obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 10 kPa or more and 1000 kPa or less.

[0018] [2] The transparent adhesive sheet according to [1], wherein the ratio (G'(-20°C) / G'(60°C)) of the shear storage modulus G'(-20°C) at -20°C to the shear storage modulus G'(60°C) at 60°C of the transparent adhesive sheet obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 20 or less.

[0019] [3] The transparent adhesive sheet according to [1] or [2], wherein the shear storage modulus (G'(30°C)) at 30°C of the transparent adhesive sheet obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 100 kPa or less.

[0020] [4] The transparent adhesive sheet according to any one of [1] to [3], wherein the aforementioned compound (B) is an alkenyl unsaturated group-containing benzophenone compound.

[0021] [5] The transparent adhesive sheet according to any one of [1] to [4], wherein the aforementioned compound (B) is a compound having at least one structure selected from a benzophenone structure, a benzil structure, an o-benzoylbenzoate structure, a thioxanthone structure, a 3-coumarinone structure, a 2-ethylanthraquinone structure, and a camphorquinone structure.

[0022] [6] The transparent adhesive sheet according to any one of [1] to [5], wherein the aforementioned photopolymerization initiator (C) contains a hydrogen abstraction type photopolymerization initiator (C1).

[0023] [7] The transparent adhesive sheet according to any one of [1] to [6], wherein the photopolymerization initiator (C) includes a cleavage-type photopolymerization initiator (C2).

[0024] [8] The transparent adhesive sheet according to any one of [1] to [7], wherein the glass transition temperature (Tg) defined by the maximum value of Tanδ obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is -20°C or lower.

[0025] [9] The transparent adhesive sheet according to any one of [1] to [8], wherein the content of the compound (B) is 0.01 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic polymer (A).

[0026]

[10] The transparent adhesive sheet according to any one of [1] to [9], wherein the mass ratio (B / C) of the content of the compound (B) to the content of the photopolymerization initiator (C) is 0.2 to 10.

[0027]

[11] The transparent adhesive sheet according to any one of [1] to

[10] , wherein the adhesive composition (I) includes a photocurable compound (D).

[0028]

[12] The transparent adhesive sheet according to any one of [1] to

[11] , wherein the content of monofunctional urethane (meth)acrylate in the adhesive composition (I) is 10% by mass or less.

[0029]

[13] The transparent adhesive sheet according to any one of [1] to

[12] , wherein the adhesive composition (I) includes a silane coupling agent (E).

[0030]

[14] The transparent adhesive sheet according to any one of [1] to

[13] , wherein the (meth)acrylic polymer (A) is a block copolymer or a graft copolymer having a segment containing a structural unit derived from a (meth)acrylic acid alkyl ester having an alkyl group with 9 or more and 30 or less carbon atoms.

[0031]

[15] The transparent adhesive sheet according to any one of [1] to

[14] , wherein when the thickness of the transparent adhesive sheet is 0.7 to 1.0 mm, the strain (γ max ) when a pressure of 2 kPa is applied at 60°C for 600 seconds and the strain (γ min ) after removing the stress and after 600 seconds are calculated by the following formula, and the recovery rate is 75% or more.

[0032] Recovery rate (%) = [(γ max - γ min ) / γmax 〕 × 100

[0033]

[16] The transparent adhesive sheet according to any one of [1] to

[15] has a gel fraction of 45% or more.

[0034]

[17] A transparent adhesive sheet with a release film, which has a structure formed by laminating the transparent adhesive sheet according to any one of [1] to

[16] and a release film.

[0035]

[18] A transparent adhesive sheet for a flexible image display device component, which contains the transparent adhesive sheet according to any one of [1] to

[16] .

[0036]

[19] A laminate for an image display device, wherein two image display device components are laminated with the transparent adhesive sheet according to any one of [1] to

[16] interposed therebetween, and at least one of the aforementioned image display device components has a step with a height difference of 2 μm or more on the contact surface with the aforementioned transparent adhesive sheet.

[0037]

[20] A flexible image display device, which has the laminate for an image display device described in

[19] .

[0038] Effects of the Invention

[0039] According to the present invention, it is possible to provide a transparent adhesive sheet that is highly sensitive to actinic energy rays and can be cured efficiently, and a transparent adhesive sheet with a release film, a transparent adhesive sheet for a flexible image display device component, a laminate for an image display device, and a flexible image display device that use the above-mentioned transparent adhesive sheet. Detailed Embodiments

[0040] The definitions of the following terms apply to this specification and the claims.

[0041] "Structure that generates free radicals" refers to a structure that can generate free radicals that initiate a polymerization reaction under the excitation of actinic energy rays. Hereinafter, the "structure that generates free radicals" will also be referred to as "free radical generating structure".

[0042] "Actinic energy rays" refer to energy rays that can decompose a compound that generates active species to generate active species. Examples of such actinic energy rays include visible light, ultraviolet rays, infrared rays, X-rays, α-rays, β-rays, γ-rays, and electron beams, etc. Ultraviolet rays and electron beams are preferred, and ultraviolet rays are particularly preferred.

[0043] "(Meth)acrylate" is a general term for acrylate and methacrylate. The same applies to "(meth)acryloyl", "(meth)acrylic acid", "(meth)acrylonitrile", and "(meth)acrylamide".

[0044] “(Meth)acrylic polymer” means a polymer having a structural unit derived from a (meth)acrylic monomer. The (meth)acrylic polymer may also have a structural unit derived from a monomer other than the (meth)acrylic monomer (such as styrene, etc.).

[0045] “(Meth)acrylic monomer” means a monomer having a (meth)acryloyl group.

[0046] “Vinyl monomer” means a compound having an ethylenically unsaturated bond (polymerizable carbon-carbon double bond).

[0047] The “~” indicating a numerical range means that the numerical values described before and after it are included as the lower limit value and the upper limit value.

[0048] [Transparent adhesive sheet]

[0049] One embodiment of the present invention relates to a transparent adhesive sheet.

[0050] The transparent adhesive sheet of the embodiment is a transparent adhesive sheet formed from an adhesive composition (I).

[0051] The adhesive composition (I) contains a precursor, and the precursor contains a (meth)acrylic polymer (A), a compound (B) having a radical polymerizable functional group with a carbon-carbon double bond and a radical generating structure in the molecule (hereinafter also simply referred to as “compound (B)”), and a photopolymerization initiator (C) formed from a compound other than the aforementioned compound (B).

[0052] It is considered that the compound (B) contained in the adhesive composition (I) polymerizes with each other through the reaction of the radical polymerizable functional group, thereby becoming a compound having a plurality of radical generating structures in one molecule. Therefore, through the action of radical generation and radical recombination, etc., a crosslinked structure is formed in the (meth)acrylic polymer (A) and can function as a crosslinking point. Moreover, the compound (B) can also function as a polymerization initiator through the action of the radical generating structure. The function of the compound (B) alone as a polymerization initiator is insufficient, or its function is significantly lower, but by using it in combination with the photopolymerization initiator (C), it can fully function as a polymerization initiator.

[0053] In the “precursor” of the adhesive composition (I), in addition to the state where the compounds (B) do not polymerize with each other and all the compounds (B) are contained in an unreacted state, it may also contain a state where a part or all of the compounds (B) polymerize with each other and are polymerized to a high molecular weight. In addition, it may contain a partially polymerized state where the (meth)acrylic polymer (A) is partially polymerized to a high molecular weight.

[0054] [(Meth)acrylic polymer (A)]

[0055] As the aforementioned (meth)acrylic polymer, for example, in addition to the homopolymer of (meth)acrylic acid alkyl ester, a copolymer obtained by polymerizing (meth)acrylic acid alkyl ester and a monomer component copolymerizable therewith can also be mentioned.

[0056] Among them, as the (meth)acrylic polymer (A), a copolymer preferably containing two or more copolymer components and at least one copolymer component being a (meth)acrylic acid alkyl ester having 4 to 30 carbon atoms in the alkyl group is preferred. The (meth)acrylic polymer (A) can also be made into a block copolymer or a graft copolymer having a segment, and the segment contains a structural unit derived from a (meth)acrylic acid alkyl ester having an alkyl group with 9 to 30 carbon atoms.

[0057] More specifically, as the (meth)acrylic polymer (A), a copolymer containing a (meth)acrylic acid alkyl ester having 4 to 30 carbon atoms in the alkyl group and one or more monomer components selected from the following monomers copolymerizable therewith, which are other than the aforementioned (meth)acrylic acid alkyl esters: (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) a (meth)acrylic acid alkyl ester monomer having 1 to 3 carbon atoms in the alkyl group, (a7) an alicyclic monomer, (a8) a macromonomer, (a9) other copolymerizable monomers, can be mentioned.

[0058] (1) Among the aforementioned copolymerizable monomers (a1) to (a9), the following copolymerizable monomers (a1), (a2), or (a3) are particularly preferred.

[0059] (2) In addition, the monomer component for obtaining the (meth)acrylic polymer (A) particularly preferably does not contain the aforementioned copolymerizable monomer (a1) and contains either of the copolymerizable monomers (a2) or (a3). By containing either of the copolymerizable monomers (a2) or (a3), it is possible to have corrosion resistance characteristics, adhesiveness, and moisture and heat resistance whitening characteristics when the adherend contains corrosive components such as metal.

[0060] (3) Furthermore, among the copolymerizable monomers (a3), from the aspect of having a hydrogen abstraction reaction sensitization effect described later and being able to effectively form crosslinks as a result, a copolymerizable monomer having a tertiary nitrogen atom is preferred.

[0061] (4) Among the aforementioned (meth)acrylic acid alkyl esters, a (meth)acrylic acid alkyl ester in which the alkyl group contains a tertiary carbon atom is preferred. By using such a (meth)acrylic acid alkyl ester, a hydrogen abstraction reaction easily occurs during light irradiation, and as a result, crosslinks are easily and effectively formed.

[0062] The aforementioned (meth)acrylic acid alkyl ester is a linear or branched alkyl (meth)acrylate in which the alkyl group has 4 to 30 carbon atoms and is represented by the following formula (1).

[0063] CH2=CH(R 1 )-COO(R 2 )···(1)

[0064] (In the formula, R 1 represents a hydrogen atom or a methyl group, and R 2 represents a linear or branched alkyl group having 4 to 30 carbon atoms.)

[0065] Examples of the (meth)acrylic acid alkyl ester represented by the formula (1) include linear (meth)acrylic acid alkyl esters such as 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, eicosyl (meth)acrylate, heneicosyl (meth)acrylate, docosyl (meth)acrylate, etc.; secondary butyl (meth)acrylate, isobutyl (meth)acrylate; tert-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, isoeicosyl (meth)acrylate, butyloctyl (meth)acrylate, isotetradecyl (meth)acrylate, isohexadecyl (meth)acrylate, hexyl decyl (meth)acrylate, isostearyl (meth)acrylate, octyl decyl (meth)acrylate, octyldodecyl (meth)acrylate, isodocosyl (meth)acrylate, etc. These may be used alone or in combination of two or more kinds.

[0066] Among them, from the viewpoint of obtaining flexibility, linear (meth)acrylic acid alkyl esters are preferred. In addition, from the viewpoint of achieving a balance between adhesiveness and flexibility, (meth)acrylic acid alkyl esters having 4 to 20 carbon atoms in the alkyl group, more preferably 5 to 18 carbon atoms, particularly preferably 6 to 16 carbon atoms, and especially preferably 7 to 14 carbon atoms are preferred. For example, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate are preferred.

[0067] In addition, from the viewpoint that the following hydrogen abstraction reaction is likely to occur upon light irradiation and as a result, a crosslinking reaction can be effectively formed, it is preferable to use a (meth)acrylic acid branched alkyl ester. Among them, it is preferable that the number of carbon atoms of the alkyl group is 4 to 20, more preferably 5 to 18, particularly preferably 6 to 16, and especially preferably 7 to 14 for the (meth)acrylic acid branched alkyl ester. For example, sec-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate are preferred.

[0068] Relative to all the structural units (100% by mass) constituting the (meth)acrylic polymer (A), the content of the structural units derived from the aforementioned (meth)acrylic acid alkyl ester 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, further 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 proportion of the structural units derived from the (meth)acrylic acid alkyl ester is at least the aforementioned lower limit value, there is a tendency for excellent flexibility and excellent unevenness followability when there are unevenness on the adherend. If it is at most the aforementioned upper limit value, there is a tendency to easily obtain the effects of the following copolymerizable monomers, and excellent adhesiveness and cohesion.

[0069] The lower limit and the upper limit of the content of the structural units derived from the aforementioned (meth)acrylic acid alkyl ester can be arbitrarily combined.

[0070] Examples of the carboxyl group-containing monomer (a1) include (meth)acrylic acid, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl hexahydrophthalate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxypropyl phthalate, 2-(meth)acryloyloxyethyl maleate, 2-(meth)acryloyloxypropyl maleate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxypropyl succinate, crotonic acid, fumaric acid, maleic acid, and itaconic acid. They can be used alone or in combination of two or more.

[0071] Examples of the hydroxyl group-containing monomer (a2) include (meth)acrylic acid hydroxyalkyl esters 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 (meth)acrylic acid hydroxyalkyl esters such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified (meth)acrylic acid esters such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; (meth)acrylic acid esters having a primary hydroxyl group such as 2-acryloyloxyethyl 2-hydroxyethyl phthalate; (meth)acrylic acid esters having a secondary hydroxyl group such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate; (meth)acrylic acid esters having a tertiary hydroxyl group such as 2,2-dimethyl-2-hydroxyethyl (meth)acrylate; and vinyl ethers such as 2-hydroxyethyl vinyl ether, diethylene glycol mono vinyl ether, and 4-hydroxybutyl vinyl ether. They may be used alone or in combination of two or more kinds.

[0072] By using the hydroxyl group-containing monomer (a2), the adhesive strength of the adhesive sheet can be improved, and the wet heat whitening can be suppressed.

[0073] Among the hydroxyl group-containing monomers (a2), hydroxyl group-containing monomers having a hydroxyalkyl group having 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, particularly preferably 2 to 4 carbon atoms are preferred. Examples thereof include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxyethyl vinyl ether, diethylene glycol mono vinyl ether, and 4-hydroxybutyl vinyl ether. (Meth)acrylic acid esters having a primary hydroxyl group are particularly preferred, such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate.

[0074] From the viewpoints of imparting adhesive strength and resistance to wet heat whitening, the content of the structural unit 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, particularly preferably 7 to 20% by mass, based on all the structural units of the (meth)acrylic polymer (A).

[0075] Examples of the nitrogen-containing monomer (a3) include amino group-containing monomers, amide group-containing monomers, isocyanate group-containing monomers, and (meth)acrylonitrile. By using the nitrogen-containing monomer (a3), the cohesion of the adhesive sheet is improved, and the wet heat whitening can be suppressed. They may be one kind or a combination of two or more kinds. In addition, the nitrogen-containing monomer (a3) has an effect of promoting the dehydrogenation reaction described below.

[0076] Examples of the aforementioned amino group-containing monomers include: (meth)acrylate esters containing a primary amino group such as amino methyl (meth)acrylate and amino ethyl (meth)acrylate; (meth)acrylate esters containing a secondary amino group such as tert-butylaminoethyl (meth)acrylate and tert-butylaminopropyl (meth)acrylate; (meth)acrylate esters containing a tertiary amino group such as ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, and dimethylaminopropyl acrylamide; N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinylacetamide monomers, and N-vinylcaprolactam.

[0077] Examples of the aforementioned amide group-containing monomers include: (meth)acrylamide; N-alkyl (meth)acrylamides such as N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, N-n-butyl (meth)acrylamide, diacetone (meth)acrylamide, and N,N'-methylenebis(meth)acrylamide; N,N-dialkyl (meth)acrylamides such as N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-ethylmethylacrylamide, and N,N-diallyl (meth)acrylamide; hydroxyalkyl (meth)acrylamides such as N-hydroxymethyl (meth)acrylamide and N-hydroxyethyl (meth)acrylamide; alkoxyalkyl (meth)acrylamides such as N-methoxymethyl (meth)acrylamide and N-(n-butoxymethyl)(meth)acrylamide; maleimide or its derivatives.

[0078] Examples of the aforementioned isocyanate group-containing monomers include 2-(meth)acryloyloxyethyl isocyanate and their alkylene oxide adducts. The isocyanate group can be protected by a blocking agent such as methyl ethyl ketoxime, 3,5-dimethylpyrazole, 1,2,4-triazole, and diethyl malonate.

[0079] Among them, from the viewpoint of having a sensitizing effect of hydrogen abstraction reaction described later and being able to effectively form crosslinks as a result, substances having a tertiary nitrogen atom are preferred, and particularly preferred are, for example, (meth)acrylate esters containing a tertiary amino group, N,N-dialkyl (meth)acrylamides, N-vinylpyrrolidone, and acryloylmorpholine.

[0080] From the viewpoints of imparting cohesiveness and resistance to wet heat whitening, the content of the structural unit 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 particularly preferably 2 to 7% by mass, based on all the structural units of the (meth)acrylic polymer (A).

[0081] Examples of the epoxy group-containing monomer (a4) include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, and glycidyl 4-hydroxybutyl (meth)acrylate. They may be used alone or in combination of two or more.

[0082] Examples of the vinyl monomer (a5) include compounds 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, and aromatic vinyl monomers such as styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, and other substituted styrenes. They may be used alone or in combination of two or more.

[0083] They may be used alone or in combination of two or more.

[0084] Examples of the (meth)acrylic acid alkyl ester monomer (a6) having 1 to 3 carbon atoms in the alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate. They may be used alone or in combination of two or more.

[0085] From the viewpoint of imparting cohesiveness to the adhesive sheet, the content of the structural unit derived from the copolymerizable monomer (a6) 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 particularly preferably 2 to 7% by mass, based on all the structural units of the (meth)acrylic polymer (A).

[0086] Examples of the alicyclic monomer (a7) include cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentyl (meth)acrylate, dicyclopentenoxyethyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, and adamantyl (meth)acrylate. They may be used alone or in combination of two or more.

[0087] From the viewpoint of imparting cohesiveness to the adhesive sheet, the content of the structural unit derived from the alicyclic monomer (a7) 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 particularly preferably 2 to 7% by mass, based on all the structural units of the (meth)acrylic polymer (A).

[0088] The macromonomer (a8) is a monomer that can easily extend the number of carbon atoms in the side chain when polymerized into a (meth)acrylic (co)polymer, for example, a monomer having 20 or more carbon atoms. By using the macromonomer (a8), the (meth)acrylic (co)polymer can be made into a graft copolymer having a segment containing a structural unit derived from the macromonomer (a8).

[0089] Therefore, by selecting the macromonomer (a8) and other monomers and their compounding ratios, the properties of the main chain and side chain of the graft copolymer can be changed.

[0090] As the macromonomer (a8), it is preferred that the backbone component is composed of an acrylic polymer or a vinyl polymer. Examples of the backbone component of the macromonomer include those exemplified in the (meth)acrylic linear or branched alkyl esters having 4 to 30 carbon atoms in the aforementioned alkyl group, the aforementioned copolymerizable monomers (a5), (a6), and (a7), etc.

[0091] Among them, from the aspect of being able to produce an adhesive sheet with excellent cohesiveness, it is preferred to use (meth)acrylic alkyl esters having 1 to 8 carbon atoms in the alkyl group, alicyclic monomers, aromatic monomers such as styrene.

[0092] On the other hand, from the aspect of being able to produce an adhesive sheet with excellent flexibility, it is preferred to use (meth)acrylic alkyl esters having 9 to 30 carbon atoms.

[0093] They can be used alone or in combination of two or more.

[0094] The macromonomer has a radically polymerizable functional group, or a functional group such as a hydroxyl group, isocyanate group, epoxy group, carboxyl group, amino group, amide group, or thiol group. As the macromonomer, a macromonomer having a radically polymerizable functional group capable of copolymerizing with other monomers is preferred. The radically polymerizable functional group may contain one or two or more, and particularly preferably one. When the macromonomer has a functional group, the functional group may contain one or two or more, and particularly preferably one.

[0095] In addition, it may contain either a radically polymerizable functional group or a functional group, or both.

[0096] The weight-average molecular weight of the macromonomer (a8) is preferably 1,000 or more and 40,000 or less, more preferably 1,500 or more and 20,000 or less, and still more preferably 2,000 or more and 15,000 or less.

[0097] As the macromonomer, a commonly produced macromonomer (for example, the macromonomer manufactured by Toagosei Co., Ltd.) can be appropriately used.

[0098] With respect to all the structural units of the (meth)acrylic polymer (A), the content of the structural units derived from the macromonomer (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 still more preferably 5% by mass or more and 15% by mass or less. When the above content is not less than the above lower limit value, the force of phase separation between the segment containing the structural units derived from the macromonomer (a8) and the segment formed by other structural units becomes stronger, and the shape retention force when the adhesive sheet is not adhered is more excellent. If the above content is not more than the above upper limit value, the phase separation structure is easily destroyed during adhesion, and the unevenness followability is more excellent. The lower limit and the upper limit of the above content can be arbitrarily combined.

[0099] As other copolymerizable monomers (a9), for example, 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 and other (meth)acrylates having an alkoxyalkylene glycol skeleton, phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol-polypropylene glycol-(meth)acrylate, nonylphenol ethylene oxide adduct (meth)acrylate and other aromatic (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-methacryloyloxyethoxybenzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone and their mixtures and other (meth)acrylates having a benzophenone structure; (meth)acrylates containing a heterocycle such as tetrahydrofurfuryl (meth)acrylate, etc.

[0100] In addition, a photocurable compound (D) having two or more functional groups described later can also be used as a comonomer. They can be used alone or in combination of two or more.

[0101] The weight average molecular weight (Mw) of the (meth)acrylic polymer (A) is preferably 50,000 or more and 2,000,000 or less, more preferably 100,000 or more and 1,500,000 or less, and further preferably 300,000 or more and 1,000,000 or less. When the weight average molecular weight of the (meth)acrylic polymer (A) is at least the above lower limit value, the durability after lamination of the transparent adhesive sheet tends to be good. When the weight average molecular weight of the (meth)acrylic polymer (A) is at most the above upper limit value, the moldability during the production of the transparent adhesive sheet tends to be good. The lower limit and the upper limit of the weight average molecular weight of the (meth)acrylic polymer (A) can be arbitrarily combined.

[0102] In the present invention, the weight average molecular weight (Mw) can be determined as follows, for example.

[0103] (Method for measuring weight-average molecular weight)

[0104] Using a 0.27 mass% tetrahydrofuran solution of the (meth)acrylic acid-based polymer as a measurement sample, the weight-average molecular weight (Mw) based on standard polystyrene conversion can be determined under the following conditions.

[0105] · GPC device: "HLC-8320" manufactured by Tosoh Corporation

[0106] · Columns: Two columns of "TSKgel SuperHZM-H" (6.0 mm ID × 15 cm L) manufactured by Tosoh Corporation are connected in series for use. A guard column of "TSKguardcolumn SuperHZ-H" (4.6 mm ID × 3.5 cm L) manufactured by Tosoh Corporation is used.

[0107] · Injection volume: 10 μL

[0108] · Eluent: Tetrahydrofuran (stabilizer BHT)

[0109] · Flow rate: 0.5 mL / minute

[0110] · Column temperature: 40 °C

[0111] The melt viscosity of the (meth)acrylic acid-based polymer (A) at 130 °C is preferably 20 Pa·s or more and 800 Pa·s or less, more preferably 20 Pa·s or more and 600 Pa·s or less, further preferably 50 Pa·s or more and 600 Pa·s or less, and particularly preferably 100 Pa·s or more and 500 Pa·s or less. If the melt viscosity of the (meth)acrylic acid-based polymer (A) at 130 °C is within the aforementioned range, coating can be performed by a hot melt method in which the resin composition (I) is directly heated. The lower limit and upper limit of the melt viscosity of the (meth)acrylic acid-based polymer (A) at 130 °C can be combined arbitrarily.

[0112] The melt viscosity can be measured, for example, using a viscoelasticity measuring device Rheosol-G5000 manufactured by UBM Corporation.

[0113] From the aspect of obtaining a flexible and transparent adhesive sheet, the glass transition temperature (Tg) of the (meth)acrylic acid-based polymer (A) is preferably -10 °C or lower, more preferably -20 °C or lower, and further preferably -30 °C or lower. On the other hand, the lower limit of the glass transition temperature (Tg) of the (meth)acrylic acid-based polymer (A) is usually -80 °C.

[0114] In the present invention, the glass transition temperature (Tg) is determined by reading the temperature at which the loss tangent (tanδ) reaches its maximum when measuring the dynamic viscoelasticity in a shear mode at a frequency of 1 Hz using a dynamic viscoelasticity measuring device.

[0115] For example, a (meth)acrylic polymer can be molded into a cylinder with a diameter of 8 mm (height 1.0 mm). For this molded body, the loss tangent (tanδ) is measured using a viscoelasticity measuring device (manufactured by T.A. Instruments, "DHR 2") under the following measurement conditions.

[0116] (Measurement conditions)

[0117] · Measurement fixture: Φ8 mm parallel plates

[0118] · Strain: 0.1%

[0119] · Frequency: 1 Hz

[0120] · Measurement temperature: -60°C to 100°C

[0121] · Heating rate: 5°C / minute

[0122] The (meth)acrylic polymer (A) preferably has a relative dielectric constant of 3.5 or less. If the relative dielectric constant is 3.5 or less, it becomes possible to thin the adhesive layer when the transparent adhesive sheet is mounted on the touch panel, and the responsiveness of the touch panel also becomes good.

[0123] The method for producing the (meth)acrylic polymer (A) is not particularly limited. For example, in the case where the macromonomer (a8) has a radically polymerizable functional group, a method of polymerizing a monomer mixture containing the macromonomer (a8) and a (meth)acrylic acid alkyl ester having 4 to 30 carbon atoms in the alkyl group can be used. The monomer mixture may further contain copolymerizable monomers (a1) to (a7) and (a9).

[0124] As the polymerization method, it can be produced by a known polymerization method such as solution polymerization, suspension polymerization, and emulsion polymerization. For use as a transparent adhesive sheet, solution polymerization is preferred.

[0125] In the case where the macromonomer (a8) has an addition-reactive functional group and at least a part of the copolymerizable monomers (a1) to (a7) and (a9) has a functional group capable of reacting with the functional group of the macromonomer (a8), a method of reacting (adding) the (meth)acrylic polymer (A) with the macromonomer (a8) can be used.

[0126] (Compound (B))

[0127] Compound (B) has a radically polymerizable functional group having a carbon-carbon double bond and a radical-generating structure within the molecule. Compound (B) can polymerize with each other, and can form a crosslinked structure between the molecules of the (meth)acrylic polymer (A).

[0128] Examples of the "radically polymerizable functional group having a carbon-carbon double bond" include functional groups having an unsaturated double bond (olefinically unsaturated group) such as (meth)acryloyl group and vinyl group.

[0129] The number of radically polymerizable functional groups possessed by compound (B) can be 1 or 2 or more, preferably 1.

[0130] As the radical-generating structure, from the viewpoint of easily forming a crosslinked structure between the molecules of the (meth)acrylic polymer (A), a structure that generates radicals by undergoing a hydrogen abstraction reaction when excited by irradiation with active energy rays is preferred. For example, examples include benzophenone structure, benzil structure, o-benzoylbenzoate structure, thioxanthone structure, 3-coumarinone structure, 2-ethylanthraquinone structure, and camphorquinone structure.

[0131] The number of radical-generating structures possessed by compound (B) can be 1 or 2 or more, preferably 1.

[0132] Examples of compound (B) include compounds having an olefinically unsaturated group such as (meth)acryloyl group and having one or more selected from benzophenone structure, benzil structure, o-benzoylbenzoate structure, thioxanthone structure, 3-coumarinone structure, 2-ethylanthraquinone structure, and camphorquinone structure. Among them, as compound (B), a benzophenone-based compound containing an olefinically unsaturated group is preferred. Specifically, a compound having a (meth)acryloyl group and a benzophenone structure is preferred.

[0133] Examples of compound (B) having a (meth)acryloyl group and a benzophenone structure include 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, 4-acryloyloxyethoxy-4'-bromobenzophenone, 4-methacryloyloxybenzophenone, 4-methacryloyloxyethoxybenzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone.

[0134] Compound (B) can be used alone or in combination of two or more.

[0135] In the present invention, from the viewpoint of being able to be sufficiently cured with a relatively small irradiation amount of active energy rays, the content of the aforementioned compound (B) in the adhesive composition (I) is preferably 0.01 part by mass or more and 10 parts by mass or less, particularly preferably 0.2 part by mass or more and 5 parts by mass or less, and still more preferably 0.5 part by mass or more and 2 parts by mass or less, based on 100 parts by mass of the aforementioned (meth)acrylic polymer (A).

[0136] (Photoinitiator (C))

[0137] The photoinitiator (C) is a photoinitiator formed from a compound other than the compound (B).

[0138] As the photoinitiator (C), a compound that generates active radical species by irradiating light such as ultraviolet rays and visible light, more specifically light with a wavelength of 200 nm to 780 nm, can be used, and examples thereof include hydrogen abstraction type photoinitiators (C1) and cleavage type photoinitiators (C2). Among them, the cleavage type photoinitiator decomposes into other compounds when generating free radicals by light irradiation and no longer has the function of an initiator once excited. Therefore, it does not remain as an active species in the adhesive after the crosslinking reaction and does not cause unexpected photo-degradation or the like to the adhesive, and is thus preferred.

[0139] On the other hand, the hydrogen abstraction type photoinitiator does not generate decomposition products such as those of the cleavage type photoinitiator during the free radical generation reaction based on irradiation with active energy rays such as ultraviolet rays, and thus is not easily a volatile component after the reaction and can reduce damage to the adherend, and is useful in this regard.

[0140] In the present invention, from the aspect of being able to form crosslinking points between (meth)acrylic polymers (A) by generating free radical reaction points in the (meth)acrylic polymer (A), as the photoinitiator (C), a hydrogen abstraction type photoinitiator (C1) is preferably included.

[0141] Examples of the hydrogen abstraction type photoinitiator (C1) include: benzophenone, 4-methyl-benzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, 4-(meth)acryloyloxybenzophenone, methyl 2-benzoylbenzoate, methyl benzoylformate, bis(2-phenyl-2-oxoacetic acid)oxy divinyl ester, 4-(1,3-acryloyl-1,4,7,10,13-pentaoxatridecyl)benzophenone, thioxanthone, 2-chlorothioxanthone, 3-methylthioxanthone, 2,4-dimethylthioxanthone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone or derivatives thereof.

[0142] As the cleavage-type photoinitiator (C2), for example, the following can be exemplified: 2,2-dimethoxy-1,2-diphenylethane-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-methylethenyl)phenyl)acetone), methyl phenylglyoxylate, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide, and their derivatives.

[0143] As the photoinitiator (C) for photopolymerization, one kind can be used alone, or two or more kinds can be used.

[0144] In the present invention, from the viewpoint of being able to be sufficiently cured with a smaller irradiation amount of active energy rays, with respect to 100 parts by mass of the aforementioned (meth)acrylic polymer (A), the content of the aforementioned photoinitiator (C) in the adhesive composition (I) is preferably 0.01 part by mass or more and 10 parts by mass or less, particularly preferably 0.2 part by mass or more and 5 parts by mass or less, and further preferably 0.5 part by mass or more and 2 parts by mass or less.

[0145] (Photocurable compound (D))

[0146] The adhesive composition (I) preferably further contains a photocurable compound (D).

[0147] The photopolymerizable compound (D) is a compound having one or more radically polymerizable functional groups (wherein, the compound (B) is excluded). As the radically polymerizable functional group, a (meth)acryloyl group is preferred.

[0148] As the photocurable compound (D), for example, monofunctional (meth)acrylic monomers, polyfunctional (meth)acrylic monomers, and (meth)acrylic oligomers can be exemplified, and polyfunctional (meth)acrylic monomers, (meth)acrylic oligomers, etc. are preferred.

[0149] The monofunctional (meth)acrylic monomer has one (meth)acryloyl group.

[0150] Examples of the monofunctional (meth)acrylic monomer include the monomers exemplified as the monomers for forming the (meth)acrylic polymer (A).

[0151] The polyfunctional (meth)acrylic monomer has two or more (meth)acryloyl groups.

[0152] Examples of the polyfunctional (meth)acrylic monomer include: 1,4-butanediol di(meth)acrylate, glycerol di(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol glycidyl ether di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tricyclodecane dimethacrylate, tricyclodecane dimethanol di(meth)acrylate, bisphenol A polyethoxy di(meth)acrylate, bisphenol A polypropoxy di(meth)acrylate, bisphenol F polyethoxy di(meth)acrylate, ethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane trioxyethyl (meth)acrylate, ε-caprolactone-modified tris(2-hydroxyethyl) isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propoxylated pentaerythritol tri(meth)acrylate, ethoxylated pentaerythritol tri(meth)acrylate, 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(acryloyloxyethyl) isocyanurate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, tripentaerythritol hexa(meth)acrylate, tripentaerythritol penta(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, bis(meth)acrylate of ε-caprolactone adduct of hydroxypivalic acid neopentyl glycol, trimethylolpropane tri(meth)acrylate, trimethylolpropane polyethoxy tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate.

[0153] Among them, from the viewpoint of imparting moderate toughness to the cured product, polyfunctional (meth)acrylic monomers having an alkylene glycol skeleton such as polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate are more preferable.

[0154] From the viewpoint of imparting appropriate flexibility to the cured product, the molecular weight of the polyfunctional (meth)acrylic monomer is preferably 200 or more, more preferably 300 or more, still more preferably 400 or more, and particularly preferably 500 or more. The upper limit of the molecular weight of the polyfunctional (meth)acrylic monomer is usually 3000 or less, preferably 2000 or less.

[0155] Examples of the (meth)acrylic oligomer include polyester (meth)acrylate, epoxy (meth)acrylate, urethane (meth)acrylate, polyether (meth)acrylate, and the like.

[0156] Among them, from the viewpoint of imparting appropriate toughness to the cured product, urethane (meth)acrylate oligomers are preferred.

[0157] However, from the viewpoint of curability, the content of the monofunctional urethane (meth)acrylate in the adhesive composition (I) is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less, and particularly preferably 1% by mass or less relative to the total mass of the adhesive composition (I). When the content is too large, there is a tendency for the curability to decrease.

[0158] From the aspect that a cured product having high toughness, in other words, a cured product having appropriate flexibility can be obtained when the transparent adhesive sheet of the embodiment is cured, the molecular weight of the (meth)acrylic oligomer is preferably 3000 or more, more preferably 5000 or more, still more preferably 8000 or more, and particularly preferably 10000 or more. It should be noted that the upper limit of the molecular weight is usually 100000 or less, preferably 50000 or less.

[0159] The photocurable compound (D) can be used alone or in combination of two or more.

[0160] (Silane coupling agent (E))

[0161] The adhesive composition (I) preferably further contains a silane coupling agent (E).

[0162] The silane coupling agent (E) is not particularly limited, and a silane coupling agent containing a glycidyl group and a silane coupling agent having a (meth)acryloyl group or a vinyl group are particularly preferred. By containing them, the adhesion to the component sheet is improved when the transparent adhesive sheet is made into a laminate, and the foaming phenomenon in a humid and hot environment can be suppressed.

[0163] For example, the following can be exemplified: silane compounds such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, etc., which are monomeric epoxy group-containing silane coupling agents; silane compounds formed by hydrolysis and polycondensation of a part of the foregoing silane compounds, or co-condensation of the foregoing silane compounds with alkyl group-containing silane compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, etc., which are oligomeric epoxy group-containing silane coupling agents; silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, γ-mercaptopropyl dimethoxymethylsilane, 3-mercaptopropylmethyldimethoxysilane, etc., which are monomeric mercapto group-containing silane coupling agents, hydrolysis and polycondensation of a part of the foregoing silane compounds, or silane compounds formed by co-condensation of the foregoing silane compounds with alkyl group-containing silane compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, etc., which are oligomeric mercapto group-containing silane coupling agents; (meth)acryloyl group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, etc.; amino group-containing silane coupling agents such as N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, etc.; isocyanate group-containing silane coupling agents such as 3-isocyanatopropyltriethoxysilane, etc.; vinyl group-containing silane coupling agents such as vinyltrimethoxysilane, vinyltriethoxysilane, etc.

[0164] The silane coupling agent (E) can be used alone in one kind, or two or more kinds can be used in combination.

[0165] (Other components)

[0166] Various additives such as tackifying resins, plasticizers, antioxidants, light stabilizers, metal deactivators, anti-aging agents, moisture absorbents, polymerization inhibitors, ultraviolet absorbers, rust inhibitors, inorganic particles, sensitizers, pigments, etc. can be added to the adhesive composition (I) as needed. The amounts of these additives are typically preferably set in such a way as not to have an adverse effect on the curing of the transparent adhesive sheet or not to have an adverse effect on the physical properties of the transparent adhesive sheet.

[0167] (Composition of the adhesive composition (I))

[0168] With respect to the total mass of the adhesive composition (I), the content of the (meth)acrylic polymer (A) in the adhesive composition (I) is preferably 50% by mass or more, more preferably 75% by mass or more, and still more preferably 90% by mass or more. With respect to the total mass of the adhesive composition (I), the content of the (meth)acrylic polymer (A) is preferably 99.5% by mass or less, more preferably 99% by mass or less, and still more preferably 98% by mass or less. The lower limit and the upper limit of the content of the aforementioned (meth)acrylic polymer (A) can be arbitrarily combined.

[0169] From the aspect of being able to be sufficiently cured with a smaller amount of active energy ray irradiation, with respect to the total mass of the adhesive composition (I), the content of the compound (B) in the adhesive composition (I) is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more, particularly preferably 0.3% by mass or more, and most preferably 0.5% by mass or more. From the aspect of being able to suppress the decrease in adhesive strength due to over-curing, with respect to the total mass of the adhesive composition (I), the content of the compound (B) is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 2% by mass or less, particularly preferably 1.5% by mass or less. The lower limit and the upper limit of the content of the aforementioned compound (B) can be arbitrarily combined.

[0170] From the aspect of being able to be sufficiently cured with a smaller amount of active energy ray irradiation, with respect to the total mass of the adhesive composition (I), the content of the photoinitiator (C) in the adhesive composition (I) is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more, and particularly preferably 0.3% by mass or more. From the aspect of being able to suppress the decrease in adhesive strength due to over-curing, with respect to the total mass of the adhesive composition (I), the content of the photoinitiator (C) is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 2% by mass or less, and particularly preferably 1.5% by mass or less. The lower limit and the upper limit of the content of the aforementioned photoinitiator (C) can be arbitrarily combined.

[0171] From the viewpoint of effectively generating crosslinking points with the generated free radicals, the mass ratio (B / C) of the content of the compound (B) to the content of the photoinitiator (C) in the adhesive composition (I) is preferably 0.2 or more, more preferably 0.5 or more, and still more preferably 0.7 or more. From the aspect of improving the free radical generation efficiency, the mass ratio (B / C) is preferably 10 or less, more preferably 5 or less, and still more preferably 2 or less. The lower limit and the upper limit of the content of the aforementioned mass ratio (B / C) can be arbitrarily combined.

[0172] From the viewpoint of sufficient curing with a small amount of active energy ray irradiation dose, the total content of the compound (B) and the photopolymerization initiator (C) is preferably 0.02 parts by mass or more, more preferably 0.2 parts by mass or more, still more preferably 0.3 parts by mass or more, and particularly preferably 0.5 parts by mass or more with respect to 100 parts by mass of the (meth)acrylic polymer (A). From the viewpoint of suppressing the decrease in adhesion caused by excessive crosslinking points, the total content of the compound (B) and the photopolymerization initiator (C) is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, still more preferably 3 parts by mass or less, and particularly preferably 2 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic polymer (A). The lower limit and the upper limit of the total content of the aforementioned compound (B) and photopolymerization initiator (C) can be arbitrarily combined.

[0173] From the viewpoint of easily imparting excellent durability when forming a laminate of the transparent adhesive sheet, the content of the photocurable compound (D) in the adhesive composition (I) is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, still more preferably 1.2 parts by mass or more, and particularly preferably 1.5 parts by mass or more with respect to 100 parts by mass of the (meth)acrylic polymer (A). From the viewpoints of ensuring the shape retention and adhesiveness of the transparent adhesive sheet, the content of the photocurable compound (D) is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, still more preferably 3 parts by mass or less, and particularly preferably 2 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic polymer (A). The lower limit and the upper limit of the content of the aforementioned photocurable compound (D) can be arbitrarily combined.

[0174] From the viewpoint of ensuring durability in a reliability test when assembled to an image display device, the content of the silane coupling agent (E) in the adhesive composition (I) is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, still more preferably 0.2 parts by mass or more with respect to 100 parts by mass of the (meth)acrylic polymer (A). From the viewpoint of suppressing the decrease in adhesion caused by side reactions, the content of the silane coupling agent (E) is preferably 1 part by mass or less, more preferably 0.7 parts by mass or less, still more preferably 0.5 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic polymer (A). The lower limit and the upper limit of the content of the aforementioned silane coupling agent (E) can be arbitrarily combined.

[0175] (Physical properties of the transparent adhesive sheet)

[0176] Hereinafter, the physical properties of the transparent adhesive sheet of an example of the embodiment will be described. Each of the physical properties of the transparent adhesive sheet described below is the physical property of the transparent adhesive sheet formed from the adhesive composition (I), and preferably the physical property of the cured transparent adhesive sheet. For example, the cumulative light amount at a wavelength of 365 nm is 500 to 5000 mJ / cm2 The physical properties of the transparent adhesive sheet cured by irradiating ultraviolet rays in any irradiation dose mode.

[0177] The transparent adhesive sheet of an example of the embodiment satisfies the following requirement (1). In addition, the transparent adhesive sheet of an example of the embodiment preferably satisfies either or both of the following requirements (2) and (3).

[0178] (1) The shear storage modulus (G’(-20°C)) at -20°C obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz is 10 kPa or more and 1000 kPa or less.

[0179] (2) The ratio ((G’(-20°C) / G’(60°C))) of the shear storage modulus G’(-20°C) at -20°C to the shear storage modulus G’(60°C) at 60°C obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz is 20 or less.

[0180] (3) The shear storage modulus (G’(30°C)) at 30°C obtained by dynamic viscoelasticity measurement in a shear mode with a frequency of 1 Hz is 100 kPa or less.

[0181] The transparent adhesive sheet that satisfies requirement (1) is soft even at low temperatures and has excellent flexibility. For example, even when the folding operation is repeatedly performed at a low temperature of -20°C, the member that is the adherend of the transparent adhesive sheet is not likely to crack or break.

[0182] From the viewpoints of the shape retention force of the transparent adhesive sheet when not adhered and the durability after adhesion, G’(-20°C) of requirement (1) is more preferably 30 kPa or more, further preferably 50 kPa or more, and particularly preferably 100 kPa or more. From the viewpoint of the flexibility of the transparent adhesive sheet in a low-temperature environment, G’(-20°C) of requirement (1) is more preferably 500 kPa or less, further preferably 300 kPa or less, particularly preferably 250 kPa or less, and most preferably 200 kPa or less. The lower limit and the upper limit of G’(-20°C) of the aforementioned requirement (1) can be arbitrarily combined.

[0183] As a method for adjusting G’(-20°C) of requirement (1) of the transparent adhesive sheet to the above range, for example, methods of adjusting the composition, molecular weight of the (meth)acrylic polymer (A), the type, and the addition amount of the photocurable compound (D) can be exemplified. However, it is not limited to these methods.

[0184] The transparent adhesive sheet that satisfies requirement (2) has an excellent balance between flexibility at low temperatures and high-temperature adhesiveness.

[0185] From the viewpoint of improving flexibility at low temperatures, G’(-20°C) / G’(60°C) of requirement (2) is preferably 20 or less, more preferably 15 or less, and still more preferably 10 or less. From the viewpoint of improving high-temperature adhesiveness, G’(-20°C) / G’(60°C) of requirement (2) is preferably 3 or more, more preferably 5 or more, and still more preferably 7 or more. The upper and lower limits of G’(-20°C) / G’(60°C) of the aforementioned requirement (2) can be arbitrarily combined.

[0186] As a method for adjusting G’(-20°C) / G’(60°C) of requirement (2) in the transparent adhesive sheet to the aforementioned range, for example, in addition to methods for adjusting the composition, molecular weight, type, and addition amount of the (meth)acrylic polymer (A), a method for adjusting the active energy ray irradiation amount can also be exemplified. However, the methods are not limited to these.

[0187] The adhesive sheet satisfying requirement (3) has excellent flexibility.

[0188] From the viewpoint of excellent flexibility, G’(30°C) of requirement (3) is more preferably 80 kPa or less, still more preferably 60 kPa or less, and particularly preferably 50 kPa or less. From the aspect of having shape retention, G’(30°C) of requirement (3) is preferably 5 kPa or more, more preferably 10 kPa or more, and still more preferably 15 kPa or more. The lower and upper limits of G’(30°C) of requirement (3) can be arbitrarily combined.

[0189] As a method for adjusting G’(30°C) of requirement (3) in the transparent adhesive sheet to the above range, for example, methods for adjusting the composition, molecular weight, type, and addition amount of the (meth)acrylic polymer (A) and the photocurable compound (D) can be exemplified. However, the methods are not limited to these.

[0190] In order to accurately measure the shear storage modulus G’, it is necessary to avoid the situation where the measurement results vary due to the influence of the measurement jig caused by insufficient thickness of the transparent adhesive sheet. The shear storage modulus G’ in requirements (1) to (3) is a value measured after adjusting the thickness to the range of 0.7 to 1.0 mm, whereby the shear storage modulus G’ can be accurately measured without being affected by the measurement jig.

[0191] It should be noted that the aforementioned “thickness of 0.7 to 1.0 mm” means that when the thickness of the transparent adhesive sheet as the measurement sample is less than this range, the thickness of the measurement sample is adjusted to this range by overlapping several sheets, etc. The same applies to the case of specifying the thickness of the measurement sample in other tests.

[0192] The measurements of G’(-20 °C), G’(60 °C), and G’(30 °C) in requirements (1) to (3) are carried out as follows, for example.

[0193] After repeatedly laminating the transparent adhesive sheet to adjust the thickness to 0.7 to 1.0 mm, a circular sample with a diameter of 8 mm is punched out. For the obtained sample, using a rheometer, dynamic viscoelasticity measurement is carried out under the conditions of a measurement jig: a parallel plate with a diameter of 8 mm, a frequency: 1 Hz, a measurement temperature: -50 °C to 150 °C, and a heating rate: 5 °C / minute, and the values of the shear storage modulus (G’) at -20 °C, 30 °C, and 60 °C are read.

[0194] The transparent adhesive sheet of an example of the embodiment preferably satisfies the following requirement (4).

[0195] (4) The thickness is 0.7 to 1.0 mm, and the strain (creep strain) when a pressure of 2 kPa is applied at a temperature of 60 °C for 600 seconds is 3% or more and 1000% or less.

[0196] The transparent adhesive sheet that satisfies requirement (4) is likely to deform at high temperatures and has excellent uneven following properties during bonding. Therefore, even when the component of the image display device that is the adherend has unevenness on the surface, it tends to have excellent following properties for steps. In addition, the following properties during bending of the laminated sheet or the flexible image display device component at high temperatures are excellent, and delamination and cracking of the component sheet or the flexible component can be suppressed.

[0197] From this viewpoint, the creep strain of requirement (4) is more preferably 5% or more, further preferably 6% or more, and particularly preferably 7% or more. On the other hand, from the viewpoint of the shape retention of the transparent adhesive sheet at temperatures below room temperature, the creep strain of requirement (4) is more preferably 800% or less, further preferably 500% or less, and particularly preferably 200% or less. The lower limit and the upper limit of the creep strain of the aforementioned requirement (4) can be arbitrarily combined.

[0198] The measurement of the creep strain of requirement (4) is carried out as follows, for example.

[0199] After repeatedly laminating the transparent adhesive sheet to adjust the thickness to 0.7 to 1.0 mm (for example, 0.8 mm), a circular sample with a diameter of 8 mm is punched out. For the obtained sample, using a rheometer, the strain (creep strain) (%) after 600 seconds is measured under the conditions of a measurement jig: a parallel plate with a diameter of 8 mm, a temperature: 60 °C, and a pressure: 2 kPa.

[0200] As a method for adjusting the creep strain of the essential element (4) to the above range, for example, methods such as adjusting the composition, molecular weight of the (meth)acrylic polymer (A), the type and addition amount of the photocurable compound (D), and adjusting the irradiation amount of the active energy ray can be exemplified. However, it is not limited to these methods.

[0201] The transparent adhesive sheet of an example of the embodiment preferably satisfies the following essential element (5).

[0202] (5) In the holding force measurement according to JIS-Z-0237 (ISO29863), when bonded to a SUS plate with an area of 20 mm × 20 mm and a load of 500 gf is applied in an atmosphere of 70 °C, the offset amount after 30 minutes is 5 mm or less.

[0203] The transparent adhesive sheet that satisfies the essential element (5) has high shape retention force, and the transparent adhesive sheet does not protrude from between the release films during storage before bonding, and a transparent adhesive sheet with excellent storage stability and excellent durability can be produced.

[0204] From this viewpoint, the offset amount of the essential element (5) is preferably 3 mm or less, more preferably 2 mm or less, further preferably 1 mm or less, particularly preferably 0.5 mm or less, and most preferably 0.2 mm or less. In addition, the lower limit of the offset amount is usually 0 mm.

[0205] The measurement of the holding force of the essential element (5) is carried out as follows, for example.

[0206] A polyester film for backing a substrate is adhered to one side of the transparent adhesive sheet, and it is cut into a strip shape with a width of 20 mm × a length of 100 mm to make a test piece. One end of the above test piece is bonded to a SUS plate with a bonding area of 20 mm × 20 mm. After curing in an atmosphere of 70 °C for 15 minutes, a 500 gf (4.9 N) heavy object is installed at the other end of the test piece. The SUS plate is leaned vertically with the heavy object side facing down and left standing still. After applying the load of the heavy object to the above test piece and standing still for 30 minutes, the distance (offset amount) by which the above test piece is offset is measured.

[0207] As a method for adjusting the holding force of the essential element (5) to the above range, for example, methods such as adjusting the composition, molecular weight of the (meth)acrylic polymer (A), the type and addition amount of the photocurable compound (D) can be exemplified. However, it is not limited to these methods.

[0208] The transparent adhesive sheet of an example of the embodiment preferably satisfies the following essential element (6).

[0209] (6) The glass transition temperature (Tg) defined by the maximum value of Tanδ obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is -20 °C or lower.

[0210] The flexible transparency adhesive sheet satisfying the requirement (6) is excellent in flexibility.

[0211] From the viewpoint of obtaining excellent flexibility, the Tg of the requirement (6) is preferably -25 °C or lower, more preferably -30 °C or lower, and still more preferably -35 °C or lower. On the other hand, the lower limit is usually -80 °C.

[0212] As a method for adjusting the Tg of the requirement (6) to the above range, for example, in addition to the methods of adjusting the composition, molecular weight, type, and addition amount of the photocurable compound of the (meth)acrylic polymer (A), a method of adjusting the irradiation amount of the active energy ray can also be exemplified. However, it is not limited to these methods.

[0213] The transparency adhesive sheet of an example of the embodiment preferably satisfies the following requirement (7).

[0214] (7) The transparency adhesive sheet has a thickness of 0.7 to 1.0 mm, and the recovery rate calculated by the following formula from the strain (γ max ) when a pressure of 2 kPa is applied at 60 °C for 600 seconds and the strain (γ min ) after removing the stress and passing 600 seconds is 75% or more.

[0215] Recovery rate (%) = [(γ max - γ min ) / γ max × 100

[0216] The transparency adhesive sheet satisfying the requirement (7) is excellent in the recovery property during bending.

[0217] From the viewpoint of obtaining a transparency adhesive sheet excellent in the recovery property during bending, the recovery rate of the requirement (7) is preferably 80% or more, more preferably 90% or more, and still more preferably 95% or more. From the viewpoint of improving the adhesive force, the recovery rate of the requirement (7) is preferably 99% or less, more preferably 98% or less, and still more preferably 97% or less. The lower limit and the upper limit of the recovery rate of the aforementioned requirement (7) can be arbitrarily combined.

[0218] The measurement of the recovery rate of the requirement (7) is carried out as follows, for example.

[0219] After repeatedly laminating the transparency adhesive sheet to adjust the thickness to 0.7 to 1.0 mm, a circular sample with a diameter of 8 mm is punched out. For the obtained sample, using a rheometer, the strain (γ max ) after applying a pressure of 2 kPa at 60 °C for 600 seconds and the strain (γ min ) after removing the stress and passing 600 seconds are measured. The obtained values are substituted into the following formula to calculate the recovery rate.

[0220] Recovery rate (%) = [(γ max - γ min ) / γ max × 100

[0221] As a method for adjusting the recovery rate of the requirement (7) to the above range, for example, methods for adjusting the composition, molecular weight, type, and addition amount of the photopolymerizable compound of the (meth)acrylic polymer (A), and methods for adjusting the amount of active energy ray irradiation can be exemplified. However, it is not limited to these methods.

[0222] The transparent adhesive sheet of an example of the embodiment preferably satisfies the following requirement (8).

[0223] (8) The gel fraction of the transparent adhesive sheet is 45% or more.

[0224] The active energy ray curability of the adhesive sheet that satisfies the requirement (8) is excellent.

[0225] From the viewpoint of active energy ray curability, the gel fraction of the requirement (8) is preferably 50% or more, more preferably 60% or more, still more preferably 70% or more, and particularly preferably 75% or more. On the other hand, from the viewpoint of obtaining adhesiveness, the gel fraction of the requirement (8) is preferably 90% or less, more preferably 87% or less, still more preferably 85% or less. The lower limit and upper limit of the gel fraction of the aforementioned requirement (8) can be arbitrarily combined.

[0226] The measurement of the gel fraction of the requirement (8) is carried out as follows, for example.

[0227] The pre-weighed transparent adhesive sheet is wrapped with a 150-mesh SUS metal mesh and immersed in ethyl acetate for 24 hours. Then, it is dried at 70 °C for 4.5 hours, and the masses of the adhesive before and after the ethyl acetate immersion are measured respectively. The difference between the two masses is taken as the mass of the undissolved adhesive remaining in the metal mesh (post-immersion mass). The percentage of the mass of the undissolved adhesive remaining in the metal mesh (post-immersion mass) relative to the mass of the adhesive before the ethyl acetate immersion (pre-immersion mass) is calculated as the gel fraction (%) in the fully cured state.

[0228] As a method for adjusting the gel fraction of the requirement (8) to the above range, for example, methods for adjusting the composition, molecular weight, type, and addition amount of the (meth)acrylic polymer (A), and methods for adjusting the amount of active energy ray irradiation can be exemplified. However, it is not limited to these methods.

[0229] The transparent adhesive sheet of the embodiment may be composed of a single layer or multiple layers. In the case of a multi-layer structure, each layer is formed of an adhesive composition containing the (meth)acrylic polymer (A).

[0230] From the aspect of good operability and easy attainment of excellent concavo-convex followability, the thickness of the transparent adhesive sheet of the embodiment is preferably 5 μm or more, more preferably 10 μm or more, still more preferably 15 μm or more, and particularly preferably 20 μm or more. From the aspect of easily relieving stress during bending and making the flexible image display device using the transparent adhesive sheet thinner, the thickness of the transparent adhesive sheet of the embodiment is preferably 100 μm or less, more preferably 80 μm or less, still more preferably 70 μm or less, and particularly preferably 60 μm or less. The lower limit and the upper limit of the thickness of the aforementioned transparent adhesive sheet can be arbitrarily combined.

[0231] The total light transmittance of the transparent adhesive sheet of the embodiment is preferably 85% or more, more preferably 88% or more, and still more preferably 90% or more.

[0232] The total light transmittance can be measured, for example, in accordance with JIS-K-7361-1 (ISO13468-1).

[0233] The haze of the transparent adhesive sheet of the embodiment is preferably 1.0% or less, more preferably 0.8% or less, and still more preferably 0.5% or less.

[0234] The haze value can be measured, for example, in accordance with JIS-K-7136 (ISO14782).

[0235] (Method for manufacturing a transparent adhesive sheet)

[0236] The method for manufacturing the transparent adhesive sheet of the embodiment is not particularly limited. For example, an adhesive composition (I) is prepared by mixing a (meth)acrylic polymer (A), a compound (B), and a photopolymerization initiator (C) with a photocurable compound (D), a silane coupling agent (E), additives, etc. used as needed, each in a specified amount, and the adhesive composition (I) is formed into a sheet shape, whereby the transparent adhesive sheet of the embodiment can be obtained. If necessary, the formed transparent adhesive sheet can be temporarily cured.

[0237] As a method for mixing the respective components, for example, methods using a single-screw extruder, a twin-screw extruder, a planetary mixer, a twin-screw mixer, a pressure kneader, etc. can be exemplified.

[0238] As a method for forming the adhesive composition (I) into a sheet shape, for example, a wet lamination method, a dry lamination method, an extrusion casting method using a T die, an extrusion lamination method, a calendering method, a blow molding method, an injection molding method, and a liquid injection curing method can be exemplified.

[0239] The transparent adhesive sheet of the embodiment can be formed by dissolving the adhesive composition in an appropriate solvent and applying it using various coating methods.

[0240] The transparent adhesive sheet of the embodiment described above has high sensitivity to actinic energy rays and can be cured efficiently.

[0241] The transparent adhesive sheet of the embodiment can be suitably used for a flexible image display device. That is, the transparent adhesive sheet of the embodiment can be suitably used as a transparent adhesive sheet for a constituent member of a flexible image display device.

[0242] [Transparent Adhesive Sheet with Release Film]

[0243] Another embodiment of the present invention relates to a transparent adhesive sheet with a release film.

[0244] Preferably, a release film is laminated on at least one surface of the transparent adhesive sheet of the embodiment before bonding, and more preferably, release films are laminated on both surfaces. It may also be in a form in which a plurality of transparent adhesive sheets are laminated with a release film interposed therebetween.

[0245] Examples of the release film include a polyester film, a polyolefin film, a polycarbonate film, a polystyrene film, an acrylic film, a triacetyl cellulose film, and a fluororesin film. Among them, a polyester film and a polyolefin film are preferred, and a polyester film is more preferred.

[0246] In addition, from the aspect of being easily peeled from the transparent adhesive sheet after irradiation with actinic energy rays, the release film preferably has a peel force of 0.1 N / cm or less when measured under the conditions of a peel angle of 180° and a peel speed of 300 mm / minute with respect to the transparent adhesive sheet irradiated with actinic energy rays having an irradiation wavelength of 365 nm and a cumulative light quantity of 500 to 5000 mJ / cm 2

[0247] From the viewpoints of processability and operability, the thickness of the release film is preferably 25 μm or more and 500 μm or less, more preferably 38 μm or more and 250 μm or less, and further preferably 50 μm or more and 200 μm or less. The lower limit and the upper limit of the thickness of the aforementioned release film can be arbitrarily combined.

[0248] [Laminate for Image Display Device]

[0249] Another embodiment of the present invention relates to a laminate for an image display device.

[0250] In the laminate for an image display device of the embodiment, two constituent members of the image display device are laminated with the transparent adhesive sheet of the present invention interposed therebetween, and at least one of the aforementioned constituent members of the image display device has a step with a height difference of 2 μm or more on the contact surface with the above transparent adhesive sheet.

[0251] ​Due to excellent uneven following properties, the transparent adhesive sheet of the present invention can deform following the steps on the surface of the member for an image display device, absorb the steps, and bond two members for an image display device.

[0252] The member for an image display device is not particularly limited. For example, it may include a cover lens, a polarizing plate, a retardation film, a barrier film, a touch sensor film, a light-emitting element, a PSA, a color filter, a flexible printed circuit board, a metal substrate, a rigid board, etc.

[0253] The material of the member for an image display device is not particularly limited. For example, it may include a resin sheet, a thin film glass, a metal, etc., mainly composed of a resin such as a urethane resin, a cycloolefin resin, a triacetyl cellulose resin, a (meth)acrylate resin, an epoxy resin, a polyimide resin, etc. Here, the "main component" means the component with the largest mass ratio among the components constituting the member for an image display device, preferably 50% by mass or more, more preferably 55% by mass or more, and further preferably 60% by mass or more.

[0254] The steps on the contact surface of the member for an image display device with the transparent adhesive sheet are not particularly limited, and various unevennesses based on wiring, printing, pattern development, surface treatment, embossing, etc. can be cited.

[0255] The height difference of the steps of the member for an image display device is preferably 2 μm or more, more preferably 3 μm or more, and further preferably 4 μm or more. On the other hand, it is preferably 10 μm or less, more preferably 8 μm or less, further preferably 7 μm or less, and particularly preferably 6 μm or less. The lower limit and the upper limit of the height difference of the aforementioned steps can be arbitrarily combined.

[0256] The steps on the contact surface of the member for an image display device with the transparent adhesive sheet can be, for example, unevennesses provided at intervals of 2 to 10 μm in height difference and 10 mm or less.

[0257] From the aspect of good operability, the thickness of the laminate for an image display device according to the embodiment is preferably 0.02 mm or more, more preferably 0.03 mm or more, and further preferably 0.05 mm or more. From the aspect of enabling the laminate to be thinned, the thickness of the laminate for an image display device according to the embodiment is preferably 1.0 mm or less, more preferably 0.7 mm or less, and further preferably 0.5 mm or less. The lower limit and the upper limit of the thickness of the aforementioned laminate for an image display device can be arbitrarily combined.

[0258] The manufacturing method of the laminate for an image display device according to the embodiment is not particularly limited.

[0259] For example, the following method can be cited: a transparent adhesive sheet is attached to a surface having a step of a component of an image display device, the transparent adhesive sheet of the present invention is irradiated with active energy rays, another component of an image display device is attached to the other surface of the transparent adhesive sheet, and a heating treatment is performed as required to heat-melt the transparent adhesive sheet. The transparent adhesive sheet of the present invention can be heat-melted even after being cured by active energy rays, and can be attached in a manner that follows the step and absorbs the step.

[0260] When using a transparent adhesive sheet with release films laminated on both sides of the transparent adhesive sheet, the adhesive sheet with one release film peeled off is attached to the surface with a step of a component of the image display device, and the transparent adhesive sheet is irradiated with active energy rays through the other release film. Then, the other release film is peeled off, another component of the image display device is attached to the other surface of the transparent adhesive sheet, and a heating treatment is performed as needed to heat-melt the transparent adhesive sheet.

[0261] In addition, after irradiating the transparent adhesive sheet with active energy rays to cure it, the transparent adhesive sheet may be bonded to each of the two image display device constituent members.

[0262] When at least one of the two image display device components transmits light, the following method can be adopted: after laminating two image display device components having at least one bonding surface with a step via the transparent adhesive sheet of the present invention, the transparent adhesive sheet is irradiated with active energy rays through the image display device component that transmits light.

[0263] Examples of the active energy rays used for irradiation include ionizing radiation such as α rays, β rays, γ rays, neutron rays, and electron beams, ultraviolet rays, and visible rays. Among them, ultraviolet rays are preferred from the viewpoint of suppressing damage to components of the image display device and controlling reactions.

[0264] Examples of the light source for irradiating the active energy ray include a high-pressure mercury lamp, a low-pressure mercury lamp, a metal halide lamp, a xenon lamp, a halogen lamp, an LED lamp, and a fluorescent lamp.

[0265] From the viewpoint of efficiently curing the transparent adhesive sheet, the irradiation amount of the active energy ray is preferably 5000 mJ / cm 2 Below, more preferably 4500mJ / cm 2 Below, more preferably 4200mJ / cm 2 From the viewpoint of sufficient curing, the irradiation amount of active energy rays is preferably 500 mJ / cm 2 More preferably, 1000 mJ / cm 2 More preferably, 1300 mJ / cm2 Above, particularly preferably 1500 mJ / cm 2 Above, particularly preferably 2000 mJ / cm 2 Above. The lower limit and the upper limit of the irradiation dose of the active energy ray can be arbitrarily combined.

[0266] The method of bonding the transparent adhesive sheet to the stepped surface of the component constituting the image display device is not particularly limited. For example, known methods such as roll bonding, pressure bonding using parallel flat plates, and diaphragm bonding can be used. As the bonding environment, it can be either an air bonding method in which bonding is performed under normal pressure or a vacuum bonding method in which bonding is performed under reduced pressure.

[0267] In addition, a heat treatment can also be performed when bonding the component constituting the image display device and the transparent adhesive sheet. The heating temperature during the heat treatment is preferably 40°C or higher and 100°C or lower, more preferably 50°C or higher and 90°C or lower, and still more preferably 55°C or higher and 85°C or lower.

[0268] A pressing pressure can also be applied to the laminate together with the heat treatment. In addition, a heat treatment can also be performed together with an autoclave treatment.

[0269] [Flexible Image Display Device]

[0270] Another embodiment of the present invention relates to a flexible image display device.

[0271] "Flexible image display device" refers to an image display device that does not leave bending marks even when bending, flexing, and winding operations are repeatedly performed, and can quickly return to the state before the operation and display an image without deformation when the bent state, flexed state, and wound state are released.

[0272] The flexible image display device of the embodiment includes the laminate for an image display device of the present invention. In the flexible image display device of the embodiment, for example, the laminate for an image display device is disposed on the side opposite to the viewing side of the image display panel, that is, the light source side.

[0273] In the flexible image display device of the embodiment, other components can be further laminated between the image display panel and the laminate for an image display device of the present invention, and on the side opposite to the image display panel of the laminate for an image display device of the present invention. As the other components, components similar to the components constituting the image display device exemplified in the description of the laminate for an image display device of the embodiment can be exemplified.

[0274] In the flexible image display device according to the embodiment, even if there is a step with a height difference of 2 μm or more on the contact surface between the component of the image display device and the adhesive sheet, the adhesive sheet follows the step and absorbs the step, suppressing the generation of bubbles. In addition, even when bending, flexing, or winding operations are performed in a low-temperature environment, delamination and cracking are suppressed.

[0275] It should be noted that the present invention is not limited to the above-described embodiments. Within the scope not departing from the gist of the present invention, the constituent elements in the above-described embodiments can be appropriately replaced with known constituent elements, and in addition, the above-described modification examples can be appropriately combined.

[0276] Examples

[0277] Hereinafter, the present invention will be further described in detail by way of examples and comparative examples. However, the present invention is not limited by any of these examples. In addition, "parts" in the examples refer to "parts by mass".

[0278] The measurements and evaluations in the examples were carried out by the methods shown below.

[0279] (Molecular weight of macromonomer)

[0280] A 0.2 mass% tetrahydrofuran solution of the macromonomer was prepared, and the weight-average molecular weight (Mw) based on standard polystyrene conversion was determined under the following conditions.

[0281] · GPC device: "HLC-8320" manufactured by Tosoh Corporation

[0282] · Columns: The following columns manufactured by Tosoh Corporation were connected in series and used. As the guard column, "TSKguardcolumn SuperHZ-L" (4.6 mm ID × 2.0 cm L) manufactured by Tosoh Corporation was used.

[0283] "TSKgel SuperHZM-M" (4.6 mm ID × 15 cm L) × 2 columns

[0284] "TSKgel SuperHZ2000" (4.6 mm ID × 15 cm L) × 1 column

[0285] · Injection volume: 10 μL

[0286] · Eluent: Tetrahydrofuran (stabilizer BHT)

[0287] · Flow rate: 0.35 mL / minute

[0288] · Column temperature: 40 °C

[0289] (Molecular weight of (meth)acrylic polymer)

[0290] Prepare a 0.27 mass% tetrahydrofuran solution of the (meth)acrylic acid copolymer, and determine the weight-average molecular weight (Mw) based on standard polystyrene conversion under the following conditions.

[0291] · GPC device: "HLC-8320" manufactured by Tosoh Corporation

[0292] · Columns: Two columns of "TSKgel SuperHZM-H" (6.0 mm ID × 15 cm L) manufactured by Tosoh Corporation are connected in series. A guard column of "TSKguardcolumn SuperHZ-H" (4.6 mm ID × 3.5 cm L) manufactured by Tosoh Corporation is used.

[0293] · Injection volume: 10 μL

[0294] · Eluent: Tetrahydrofuran (stabilizer BHT)

[0295] · Flow rate: 0.5 mL / minute

[0296] · Column temperature: 40 °C

[0297] (Non-volatile component)

[0298] Place about 1 g of the sample on an aluminum dish, dry it in an oven with a blower at 105 °C for 2 hours, measure the mass before and after drying with an electronic balance, and calculate the non-volatile component concentration using the following formula.

[0299] Non-volatile component concentration (%) = (mass of the dried sample (g) / mass of the sample before drying (g)) × 100

[0300] (Glass transition temperature)

[0301] Remove the release film on one side from the transparent adhesive sheet with a release film, laminate it repeatedly with a manual roller, adjust the thickness to about 0.8 mm, punch it into a circular shape with a diameter of 8 mm, and use it as a sample. Place the obtained sample on a rheometer ("DHR-2" manufactured by T.A. Instruments), and perform dynamic viscoelasticity measurement under the conditions of measurement jig: 8 mm diameter parallel plate, frequency: 1 Hz, measurement temperature: -50 °C to 150 °C, heating rate: 5 °C / minute. Then, calculate the glass transition temperature (Tg) defined by the maximum value of Tanδ obtained from the dynamic viscoelasticity measurement in the shear mode at a frequency of 1 Hz.

[0302] (Shear storage modulus G’)

[0303] The release film on one side was removed from the transparent adhesive sheets with release films prepared in each example, and they were repeatedly laminated with a manual roller to adjust the thickness to approximately 0.8 mm. They were punched into circular shapes with a diameter of 8 mm and used as samples. The obtained samples were set in a rheometer ("DHR-2" manufactured by T.A. Instruments), and dynamic viscoelasticity measurements were carried out under the conditions of a measuring jig: parallel plates with a diameter of 8 mm, a frequency of 1 Hz, a measuring temperature of -50°C to 150°C, and a heating rate of 5°C / minute. The values of the shear storage modulus G' at -20°C, 25°C, 30°C, 60°C, and 80°C were read.

[0304] (Creep strain)

[0305] The release film on one side was removed from the transparent adhesive sheets with release films prepared in each example, and they were repeatedly laminated with a manual roller to adjust the thickness to 0.8 mm. They were punched into circular shapes with a diameter of 8 mm and used as samples. The obtained samples were set in a rheometer ("DHR-2" manufactured by T.A. Instruments), and the strain after applying a pressure of 2 kPa for 600 seconds at 60°C was read as the creep strain.

[0306] (Recovery rate)

[0307] The release film on one side was removed from the transparent adhesive sheets with release films prepared in each example, and they were repeatedly laminated with a manual roller to adjust the thickness to 0.8 mm. They were punched into circular shapes with a diameter of 8 mm and used as samples. The obtained samples were set in a rheometer ("DHR-2" manufactured by T.A. Instruments), and the recovery rate was measured under the following measurement conditions.

[0308] That is, based on the creep strain (γ max ) after applying a pressure of 2 kPa for 600 seconds at 60°C and the residual strain (γ min ) after removing the stress and passing 600 seconds later, the recovery rate was calculated by the following formula.

[0309] Recovery rate (%) = [(γ max - γ min ) / γ max × 100

[0310] (Gel fraction)

[0311] The release film was removed from the laminate of the transparent adhesive sheets with release films prepared in each example, and it was used as a sample.

[0312] Wrap the sample with a 150-mesh SUS metal mesh and immerse it in ethyl acetate for 24 hours. Then, dry it at 70 °C for 4.5 hours, measure the mass of the adhesive before and after the ethyl acetate immersion respectively, and take the difference between the two masses as the mass of the insoluble adhesive remaining in the metal mesh. Calculate the percentage of the mass of the insoluble adhesive remaining in the metal mesh (mass after immersion) relative to the mass of the adhesive before the ethyl acetate immersion (mass before immersion) as the gel fraction (%) in the fully cured state.

[0313] (Retention force)

[0314] For the polyester film used for single-sided backing of the transparent adhesive sheet prepared in each example, cut it into strips with a width of 20 mm × a length of 100 mm to make test pieces. Attach one end of the aforementioned test piece to a SUS plate with a bonding area of 20 mm × 20 mm. After curing in an atmosphere of 70 °C for 15 minutes, attach a 500 gf (4.9 N) heavy object to the other end of the above test piece. Stand the SUS plate upright in the vertical direction with the heavy object side facing down and let it stand still. After applying the load generated by the heavy object to the aforementioned test piece and letting it stand still for 30 minutes, measure the distance (offset amount) (mm) by which the aforementioned test piece is displaced. It should be noted that the case where the test piece falls within 30 minutes is recorded as "falls" in the table.

[0315] (Materials used)

[0316] SLMA: A mixture of an alkyl methacrylate with 12 carbon atoms in the alkyl group and an alkyl methacrylate with 13 carbon atoms in the alkyl group, manufactured by Mitsubishi Chemical Corporation, trade name: ACRIESTER SL.

[0317] nBA: n-Butyl acrylate (manufactured by Mitsubishi Chemical Corporation)

[0318] AMBN: 2,2'-Azobis(2-methylbutyronitrile) (manufactured by Otsuka Chemical Co., Ltd.)

[0319] <Compound (B)>

[0320] B-1: 4-Acryloyloxybenzophenone

[0321] B-2: 4-Methacryloyloxybenzophenone

[0322] <Photoinitiator (C)>

[0323] C-1: A mixture of 4-methoxybenzophenone and 2,4,6-trimethylbenzophenone (manufactured by IGM, Esacure TZT)

[0324] C-2: 2,2-Dimethoxy-2-phenylacetophenone (manufactured by IGM, Omnirad 651)

[0325] <Photocurable compound (D)>

[0326] D-1: Violet light UV-3700B (manufactured by Mitsubishi Chemical Corporation)

[0327] (Production Example 1: Production of macromonomer)

[0328] 100 parts of SLMA, 0.00075 part of bis[(difluoroboryl)diphenylglyoxime]cobalt(II) as a chain transfer agent, and 58 parts of ethyl acetate were placed in a four-necked flask equipped with a stirring device, a thermometer, a cooling tube, and a nitrogen inlet, and oxygen was displaced by nitrogen bubbling. Then, 0.4 part of AMBN as a polymerization initiator and 2 parts of ethyl acetate were added. Then, the external temperature was raised to 90 °C with a water bath, and the reaction was carried out for 2 hours under reflux. Then, 0.2 part of AMBN and 20 parts of ethyl acetate were added dropwise over 1 hour, and then the mixture was further kept under reflux for 2 hours. Then, the reaction solution was cooled to 40 °C to obtain a solution containing the macromonomer (SLMA-MM). The concentration of the non-volatile component was adjusted to 50 mass% by adding ethyl acetate to this solution.

[0329] The weight-average molecular weight of the macromonomer (SLMA-MM) was 9420.

[0330] (Example 1)

[0331] <Production of polymer>

[0332] 25 parts of ethyl acetate, 2 parts of isopropyl alcohol (IPA), and 15 parts of a solution of the macromonomer (SLMA-MM) (concentration 50 mass%) were placed in a four-necked flask equipped with a stirring device, a thermometer, a cooling tube, and a nitrogen inlet, and the external temperature was raised to 85 °C with a water bath under nitrogen flow. After the reflux state was stabilized, a mixture of 20 parts of ethyl acetate, 85 parts of nBA, and 0.13 part of NYPER BK40 MT (manufactured by NOF Corporation) was added dropwise over 4 hours. After the addition was completed and kept for 1 hour, a mixture of 0.3 part of PEROCTA O (manufactured by NOF Corporation) and 15 parts of ethyl acetate was added over 1 hour. Then, after keeping for 2 hours, 0.5 part of "IRGANOX 1010" (trade name of BASF Corporation) as an antioxidant and 23 parts of ethyl acetate were added, and the mixture was cooled to room temperature to obtain a (meth)acrylic polymer (A-1) (SLMA-MM / nBA (mass ratio) = 15 / 85, weight-average molecular weight: 460,000, Tg: -38 °C).

[0333] <Production of transparent adhesive sheet>

[0334] Mix 100 parts (solid content) of the above-mentioned (meth)acrylic polymer (A-1), 0.3 part of compound (B-1), 1.2 parts of photoinitiator (C-1), 1.5 parts of photocurable compound (D-1), and 154.5 parts of ethyl acetate to prepare a solvent-containing adhesive composition. On a silicone-released release film with a thickness of 100 μm (PET film manufactured by Mitsubishi Chemical Corporation), the above adhesive composition was spread into a sheet so that the dried thickness was 50 μm.

[0335] Next, the sheet-shaped adhesive composition and the release film were placed in a dryer heated to 90 °C and kept for 10 minutes to volatilize the solvent contained in the adhesive composition. Further, a silicone-released release film with a thickness of 75 μm (PET film manufactured by Mitsubishi Chemical Corporation) was laminated on the sheet-shaped adhesive composition after drying the solvent, and using a high-pressure mercury lamp, the adhesive composition was irradiated with ultraviolet light through the above-mentioned release film so that the cumulative light amount at a wavelength of 365 nm became 4000 mJ / cm 2 to cure it, and a transparent adhesive sheet with release films laminated on both the front and back sides of a transparent adhesive sheet with a thickness of 50 μm was obtained.

[0336] (Examples 2 to 10, Comparative Examples 1 to 2)

[0337] Except for changing the mixing amounts as shown in Table 1, a transparent adhesive sheet with release films was produced in the same manner as in Example 1.

[0338] (Example 11)

[0339] (Production of Transparent Adhesive Sheet)

[0340] Mix 100 parts (solid content) of a (meth)acrylic polymer (A-2) (random copolymer with a mass ratio of 2EHA / BA / EMA / HEA = 60 / 15 / 5 / 20, weight average molecular weight: 770,000, Tg: -23 °C), 0.75 part of compound (B-1), 0.75 part of photoinitiator (C-1), and 152.3 parts of ethyl acetate to prepare a solvent-containing adhesive composition. On a silicone-released release film with a thickness of 100 μm (PET film manufactured by Mitsubishi Chemical Corporation), the above adhesive composition was spread into a sheet so that the dried thickness was 50 μm.

[0341] Next, the sheet-like adhesive composition is placed together with a release film in a dryer heated to 90°C and maintained for 10 minutes to volatilize the solvent contained in the adhesive composition. Further, a release film (PET film manufactured by Mitsubishi Chemical Corporation) with a thickness of 75 μm after silicone release treatment is laminated on the sheet-like adhesive composition after the solvent is dried, and using a high-pressure mercury lamp, the adhesive composition is irradiated with ultraviolet rays through the aforementioned release film in such a way that the cumulative light amount at a wavelength of 365 nm becomes 1000 mJ / cm 2 and cured to obtain a transparent adhesive sheet with release films laminated on both the front and back sides of a transparent adhesive sheet with a thickness of 50 μm.

[0342] (Example 12)

[0343] A transparent adhesive sheet with a release film was produced in the same manner as in Example 11 except that the compounding amounts were changed as shown in Table 1.

[0344] The measurement and evaluation results of the transparent adhesive sheets of each example are shown in Table 1.

[0345] [Table 1]

[0346]

[0347] As shown in Table 1, compared with the transparent adhesive sheets of Comparative Example 1 and Comparative Example 2 that used only one of the compound (B) and the photopolymerization initiator (C), the transparent adhesive sheets of Examples 1 to 12 that used the compound (B) and the photopolymerization initiator (C) in combination had a higher gel fraction and the curing reaction proceeded efficiently.

Claims

1. A transparent adhesive sheet formed from an adhesive composition (I), the adhesive composition (I) comprising a precursor, the precursor comprising a (meth)acrylic polymer (A), a compound (B) having a radical polymerizable functional group with a carbon-carbon double bond and a structure for generating radicals in the molecule, and a photoinitiator (C) formed from a compound other than the compound (B). The shear storage modulus (G'(-20°C)) at -20°C of the transparent adhesive sheet obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 10 kPa or more and 1000 kPa or less.

2. The transparent adhesive sheet according to claim 1, wherein the ratio (G'(-20°C) / G'(60°C)) of the shear storage modulus G'(-20°C) at -20°C to the shear storage modulus G'(60°C) at 60°C of the transparent adhesive sheet obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 20 or less.

3. The transparent adhesive sheet according to claim 1 or 2, wherein the shear storage modulus (G'(30°C)) at 30°C of the transparent adhesive sheet obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is 100 kPa or less.

4. The transparent adhesive sheet according to claim 1 or 2, wherein, The compound (B) is a benzophenone compound containing an ethylenically unsaturated group.

5. The transparent adhesive sheet according to claim 1 or 2, wherein The compound (B) is a compound having at least one structure selected from a benzophenone structure, a benzil structure, a benzoylbenzoate structure, a thioxanthone structure, a 3-coumarone structure, a 2-ethylanthraquinone structure, and a camphorquinone structure.

6. The transparent adhesive sheet according to claim 1 or 2, wherein The photoinitiator (C) contains a hydrogen abstraction type photoinitiator (C1).

7. The transparent adhesive sheet according to claim 1 or 2, wherein The photoinitiator (C) contains a cleavage type photoinitiator (C2).

8. The transparent adhesive sheet according to claim 1 or 2, wherein the glass transition temperature (Tg) defined by the maximum value of Tanδ of the transparent adhesive sheet obtained by dynamic viscoelasticity measurement in a shear mode at a frequency of 1 Hz is -20°C or less.

9. The transparent adhesive sheet according to claim 1 or 2, wherein The content of the compound (B) is 0.01 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the (meth)acrylic polymer (A).

10. The transparent adhesive sheet according to claim 1 or 2, wherein, The mass ratio (B / C) of the content of the compound (B) to the content of the photoinitiator (C) is 0.2 to 10.

11. The transparent adhesive sheet according to claim 1 or 2, wherein, The adhesive composition (I) contains a photocurable compound (D).

12. The transparent adhesive sheet according to claim 1 or 2, wherein, In the adhesive composition (I), the content of monofunctional urethane (meth)acrylate is 10% by mass or less.

13. The transparent adhesive sheet according to claim 1 or 2, wherein, The adhesive composition (I) contains a silane coupling agent (E).

14. The transparent adhesive sheet according to claim 1 or 2, wherein, The (meth)acrylic polymer (A) is a block copolymer or a graft copolymer having a segment, the segment containing a structural unit derived from a (meth)acrylic acid alkyl ester having an alkyl group with 9 or more and 30 or less carbon atoms.

15. The transparent adhesive sheet according to claim 1 or 2, wherein The transparent adhesive sheet has a thickness of 0.7 to 1.0 mm, and the recovery rate calculated by the following formula from the strain (γ max ) when a pressure of 2 kPa is applied at 60 °C for 600 seconds and the strain (γ min ) after the stress is removed and 600 seconds have passed is 75% or more. Recovery rate (%) = [(γ max - γ min ) / γ max × 100 16. The transparent adhesive sheet according to claim 1 or 2, having a gel fraction of 45% or more.

17. A transparent adhesive sheet with a release film, having a structure in which the transparent adhesive sheet according to claim 1 or 2 is laminated with a release film.

18. A transparent adhesive sheet for a flexible image display device component, which comprises the transparent adhesive sheet according to claim 1 or 2.

19. A laminate for an image display device, wherein, Two flexible image display device components are laminated with the transparent adhesive sheet according to claim 1 or 2 therebetween, and at least one of the flexible image display device components has a step with a height difference of 2 μm or more on the contact surface with the transparent adhesive sheet.

20. A flexible image display device, which includes the laminate for a flexible image display device according to claim 19.

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