Curable composition and adhesive

Abstract

Provided are: a curable composition from which an adhesive having a small residual strain, excellent impact resistance, and excellent low-temperature bending durability is obtained; and an adhesive. This curable composition comprises a (meth)acrylic resin and a first urethane (meth)acrylate, wherein the first urethane (meth)acrylate is a reaction product of a polyol and a monoisocyanate having a (meth)acryloyloxy group, and has a polyoxypropylene group, and at least two (meth)acryloyloxy groups in each molecule thereof.

Description

Curable composition and adhesive

[0001] The present invention relates to a pressure-sensitive adhesive that can be suitably applied to flexible members.

[0002] In addition to rigid displays, flexible displays are also being developed as display panels. Flexible displays, such as organic electroluminescence (EL) displays, include a laminate in which flexible members such as optical films and surface protection films are bonded to a flexible display panel body with an adhesive layer.

[0003] As mobile devices become more functional and their designs more diverse, there is a demand for display panels that are curved, foldable, etc. Accordingly, adhesives used in flexible displays are also required to have properties such as small residual strain, bending durability that prevents cracks or fractures even when repeatedly bent, and high impact resistance.

[0004] In response to this, for example, Patent Document 1 discloses that a pressure-sensitive adhesive obtained by crosslinking a composition containing an acrylic resin and a specific urethane (meth)acrylate has excellent bending durability.

[0005] Japanese Patent Application Laid-Open No. 2023-82703

[0006] However, although the pressure-sensitive adhesive described in Patent Document 1 has good bending durability at room temperature (23°C), it cannot be said that the bending durability is sufficient in lower temperature environments, for example, below freezing point.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a curable composition and a pressure-sensitive adhesive that can provide a pressure-sensitive adhesive having small residual strain, excellent impact resistance, and excellent low-temperature bending durability.

[0008] The present invention is based on the discovery that a pressure-sensitive adhesive having excellent low-temperature bending durability can be obtained from a curable composition that combines a (meth)acrylic resin and a specified polyfunctional urethane (meth)acrylate.

[0009] The present invention provides the following means. [1] A curable composition comprising a (meth)acrylic resin and a first urethane (meth)acrylate, wherein the first urethane (meth)acrylate is a urethane reaction product of a polyether polyol and a monoisocyanate having a (meth)acryloyloxy group, and has a polyoxypropylene group and two or more (meth)acryloyloxy groups per molecule. [2] The curable composition of [1], wherein the content of the first urethane (meth)acrylate is 10 to 100 parts by mass per 100 parts by mass of the (meth)acrylic resin. [3] The curable composition of [1] or [2], wherein the weight-average molecular weight of the first urethane (meth)acrylate is 5,000 to 200,000. [4] The curable composition of any of [1] to [3], further comprising a second urethane (meth)acrylate having one (meth)acryloyloxy group per molecule. [5] The curable composition of [4], wherein the weight average molecular weight of the second urethane (meth)acrylate is 5,000 to 200,000. [6] The curable composition of any of [1] to [5], wherein the weight average molecular weight of the (meth)acrylic resin is 100,000 to 3,000,000.

[0010] [7] A pressure-sensitive adhesive which is a cured product of the curable composition of any one of [1] to [6]. [8] The pressure-sensitive adhesive of [7], wherein the cured product has a glass transition temperature of -35°C or lower. [9] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive of [7] or [8].

[10] A laminate having a flexible member and a pressure-sensitive adhesive layer present on the flexible member, the pressure-sensitive adhesive layer being made of the pressure-sensitive adhesive of [7] or [8].

[11] The laminate of

[10] , wherein the flexible member is at least one selected from the group consisting of a surface protection panel, an optical film, a touch panel, and a display panel main body.

[12] A flexible display comprising the laminate of

[10] or

[11] .

[0011] By using the curable composition of the present invention, it is possible to provide a pressure-sensitive adhesive having small residual strain, excellent impact resistance, and excellent low-temperature bending durability, as well as a pressure-sensitive adhesive sheet, a laminate, and a flexible display using the pressure-sensitive adhesive.

[0012] The definitions and meanings of terms and notations used in this specification are as follows. "(Meth)acrylic" is a general term for acrylic and methacrylic. Similarly, "(meth)acrylate" is a general term for acrylate and methacrylate, and "(meth)acryloyloxy" is a general term for acryloyloxy and methacryloyloxy. A numerical range expressed using "to" means that the numbers before and after "to" are the lower and upper limits. For numerical ranges (e.g., ranges of content, etc.), the lower and upper limits described in stages may be independently combined. The lower and upper limits of the numerical ranges may be replaced with values ​​described in the Examples. The weight-average molecular weight (Mw) and number-average molecular weight (Mn) are polystyrene-equivalent molecular weights determined by gel permeation chromatography (GPC) based on a calibration curve prepared using a standard polystyrene sample. Specifically, they are determined by the method described in the Examples. The glass transition temperature (Tg) is the maximum peak temperature of the loss tangent tanδ in dynamic viscoelasticity measurement of a polymer or cured product reacted with a polymerization initiator. Specifically, it is determined by the method described in the Examples. The viscosity is a value measured at 25°C using an E-type viscometer. Specifically, it is determined by the method described in the Examples. The term "sheet" includes films and tapes, and no particular distinction is made between them. The "isocyanate index" is a value expressed as a percentage of the number of moles of isocyanate groups of an isocyanate compound per mole of hydroxyl groups of a polyol.

[0013] [Curable Composition] The curable composition of an embodiment of the present invention (hereinafter referred to as the present embodiment) comprises a (meth)acrylic resin and a first urethane (meth)acrylate, the first urethane (meth)acrylate being a reaction product of a polyol and a monoisocyanate having a (meth)acryloyloxy group, and having a polyoxypropylene group and two or more (meth)acryloyloxy groups per molecule. A curable composition comprising such components can provide a pressure-sensitive adhesive having small residual strain, excellent impact resistance, and excellent low-temperature bending durability.

[0014] ((Meth)acrylic Resin) From the viewpoint of good curability of the curable composition, the (meth)acrylic resin, which is a component of the curable composition of the present embodiment, preferably contains a structural unit based on a hydroxyl group-containing (meth)acrylate monomer. One type of (meth)acrylic resin may be used alone, or two or more types may be used in combination.

[0015] Examples of hydroxyl group-containing (meth)acrylate monomers include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, caprolactone-modified 2-hydroxyethyl (meth)acrylate, diethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, 2-acryloyloxyethyl-2-hydroxyethyl phthalate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 2,2-dimethyl-2-hydroxyethyl (meth)acrylate, etc. One type of hydroxyl group-containing (meth)acrylate monomer may be used alone, or two or more types may be used in combination. Of these, from the viewpoints of good curability of the curable composition and low-temperature bending durability of the pressure-sensitive adhesive, 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate are preferred, and 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are more preferred.

[0016] From the viewpoint of good adhesiveness of the pressure-sensitive adhesive, it is preferable that the monomer constituting the (meth)acrylic resin further contains another monomer other than the hydroxyl group-containing (meth)acrylate monomer. Examples of the other monomer include alkyl (meth)acrylate monomers, as well as ethylenically unsaturated monomers copolymerizable with the hydroxyl group-containing (meth)acrylate monomer, such as carboxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, acetoacetyl group-containing monomers, glycidyl group-containing monomers, aromatic (meth)acrylate monomers, and other vinyl monomers. These may be used alone or in combination of two or more. Of these, alkyl (meth)acrylate monomers are preferably used from the viewpoint of good adhesiveness of the pressure-sensitive adhesive, ease of handling, and availability.

[0017] The alkyl (meth)acrylate monomer is preferably one in which an alkyl group having 1 to 14 carbon atoms is bonded to a (meth)acryloyloxy group. From the viewpoint of lowering the glass transition temperature of the (meth)acrylic resin and obtaining a pressure-sensitive adhesive having excellent low-temperature bending durability, the alkyl (meth)acrylate monomer preferably contains an alkyl (meth)acrylate monomer in which the alkyl group has 5 to 14 carbon atoms, more preferably 6 to 8 carbon atoms, specific examples of which include hexyl acrylate, n-octyl acrylate, and 2-ethylhexyl acrylate. From the viewpoint of good adhesive properties of the pressure-sensitive adhesive, the alkyl (meth)acrylate monomer also preferably contains an alkyl (meth)acrylate monomer in which the alkyl group has 1 to 4 carbon atoms, specific examples of which include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, isobutyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate.

[0018] Examples of carboxy group-containing monomers include (meth)acrylic acid, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxypropyl phthalic acid, 2-(meth)acryloyloxyethyl maleic acid, 2-(meth)acryloyloxypropyl maleic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxypropyl succinic acid, crotonic acid, fumaric acid, maleic acid, and itaconic acid.

[0019] Examples of amino group-containing monomers include aminomethyl (meth)acrylate, aminoethyl (meth)acrylate, tert-butylaminoethyl (meth)acrylate, tert-butylaminopropyl (meth)acrylate, ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and diethylaminopropyl (meth)acrylate.

[0020] Examples of amide group-containing monomers include (meth)acrylamide; N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-n-butyl(meth)acrylamide, diacetone(meth)acrylamide, N,N'-methylenebis(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-ethylmethylacrylamide, N,N-diallyl(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-(n-butoxymethyl)(meth)acrylamide, and vinylpyrrolidone.

[0021] Examples of acetoacetyl group-containing monomers include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.

[0022] Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0023] Examples of aromatic (meth)acrylate monomers include phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol-polypropylene glycol-(meth)acrylate, and nonylphenol ethylene oxide adduct (meth)acrylate.

[0024] Examples of other vinyl monomers include (meth)acrylonitrile, styrene, α-methylstyrene, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, vinylpyridine, itaconic acid dialkyl esters, fumaric acid dialkyl esters, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone.

[0025] When the (meth)acrylic resin contains a hydroxyl group-containing (meth)acrylate monomer, the content of the hydroxyl group-containing (meth)acrylate monomer in the total amount of constituent monomers of the (meth)acrylic resin is preferably 5 to 60 mass %, more preferably 10 to 40 mass %, and even more preferably 15 to 20 mass %, from the viewpoints of good adhesiveness and low-temperature bending durability of the pressure-sensitive adhesive, and compatibility between the (meth)acrylic resin and the first urethane (meth)acrylate.

[0026] Among the other monomers constituting the (meth)acrylic resin, the content of alkyl (meth)acrylate in which an alkyl group having 5 to 14 carbon atoms is bonded to a (meth)acryloyloxy group is preferably 30 to 80 mass%, more preferably 40 to 70 mass%, and even more preferably 50 to 60 mass%, of the total amount of constituent monomers, from the viewpoint of good adhesive properties and low-temperature bending durability of the adhesive. The content of alkyl (meth)acrylate in which an alkyl group having 1 to 4 carbon atoms is bonded to a (meth)acryloyloxy group is preferably 5 to 40 mass%, more preferably 10 to 35 mass%, and even more preferably 15 to 30 mass%, of the total amount of constituent monomers, from the viewpoint of good adhesive properties of the adhesive.

[0027] The content of monomers other than alkyl (meth)acrylates among the other constituent monomers of the (meth)acrylic resin is preferably 20 mass% or less, more preferably 10 mass% or less, and even more preferably 5 mass% or less, of the total amount of constituent monomers, from the viewpoint of good adhesiveness and ease of handling of the adhesive, and may be 0 mass%.

[0028] A preferred embodiment of the constituent monomer composition of the (meth)acrylic resin is, for example, such that, based on the total amount of constituent monomers, the content of hydroxyl group-containing (meth)acrylate monomer is 10 to 30 mass %, the content of alkyl (meth)acrylate in which an alkyl group having 5 to 14 carbon atoms is bonded to a (meth)acryloyloxy group is 40 to 70 mass %, and the content of alkyl (meth)acrylate in which an alkyl group having 1 to 4 carbon atoms is bonded to a (meth)acryloyloxy group is 10 to 40 mass %.

[0029] The weight average molecular weight of the (meth)acrylic resin is preferably 100,000 to 3,000,000, more preferably 500,000 to 2,000,000, and even more preferably 700,000 to 1,000,000, from the viewpoint of good adhesive properties and ease of handling of the adhesive.

[0030] From the viewpoint of good adhesiveness and low-temperature bending durability of the pressure-sensitive adhesive, the glass transition temperature of the (meth)acrylic resin is preferably −50 to −20° C., more preferably −40 to −21° C., and even more preferably −30 to −22° C. When two or more (meth)acrylic resins are contained in the curable composition, it is preferable that each of the (meth)acrylic resins has a weight average molecular weight and a glass transition temperature within the above-mentioned numerical ranges.

[0031] The synthesis method of the (meth)acrylic resin is not particularly limited, and the resin can be synthesized by, for example, solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. Among these, solution polymerization is preferred from the viewpoints of ease of adjusting the monomer composition, stable reactivity, safety, etc.

[0032] For example, in solution polymerization, a solution of a (meth)acrylic resin is obtained by polymerizing constituent monomers of the (meth)acrylic resin in an organic solvent in the presence of a polymerization initiator.

[0033] Examples of organic solvents include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane; esters such as ethyl acetate and butyl acetate; aliphatic alcohols such as n-propyl alcohol and isopropyl alcohol; and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. One organic solvent may be used alone, or two or more organic solvents may be used in combination. Of these, ethyl acetate, acetone, methyl ethyl ketone, and methyl acetate are preferred, with ethyl acetate and acetone being more preferred, depending on the type of constituent monomer of the (meth)acrylic resin.

[0034] Examples of the polymerization initiator include azo-based polymerization initiators and peroxide-based polymerization initiators. One type of polymerization initiator may be used alone, or two or more types may be used in combination. Examples of the azo-based polymerization initiator include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of peroxide polymerization initiators include benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, tert-butyl peroxypivalate, tert-hexyl peroxypivalate, tert-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, and diisobutyryl peroxide.

[0035] From the viewpoint of controlling the reaction rate and degree of polymerization appropriately, the amount of the polymerization initiator used is usually preferably 0.001 to 10 parts by mass, more preferably 0.005 to 5 parts by mass, and even more preferably 0.01 to 3 parts by mass, relative to the total amount (100 parts by mass) of the constituent monomers of the (meth)acrylic resin. The polymerization initiator may be added all at once or incrementally as the reaction progresses.

[0036] The reaction temperature of the polymerization reaction is preferably 40 to 120°C, more preferably 50 to 100°C, and even more preferably 60 to 90°C, from the viewpoint of controlling the reaction rate and degree of polymerization appropriately. The reaction may be carried out by heating under reflux. The reaction time is preferably 0.5 to 72 hours, more preferably 1 to 48 hours, and more preferably 2 to 24 hours.

[0037] The content of the (meth)acrylic resin in the curable composition is preferably 30% by mass or more, more preferably 50 to 90% by mass, and even more preferably 60 to 85% by mass, based on the total mass of the curable composition, from the viewpoints of good adhesiveness of the pressure-sensitive adhesive and low-temperature bending durability.

[0038] (First Urethane (Meth)acrylate) The first urethane (meth)acrylate, a component of the curable composition of the present embodiment, is a urethane reaction product of a polyether polyol and a monoisocyanate having a (meth)acryloyloxy group, and has a polyoxypropylene group and two or more (meth)acryloyloxy groups in one molecule. The first urethane (meth)acrylate may be used alone or in combination of two or more.

[0039] <Polyether polyol> Polyether polyol preferably has two or more hydroxyl groups in one molecule and has a polyoxyalkylene group (including a polyoxypropylene group).Polyether polyol can be obtained by ring-opening polymerization of a compound having a cyclic ether structure with an initiator having two or more active hydrogens in one molecule.In addition, commercially available products can also be used. Commercially available polyether polyols include, for example, "Preminol (registered trademark; hereinafter, abbreviated) S 4013F," "Preminol S 4318F," "Preminol S 3011," "Preminol 5001F," "Preminol 7001K," "Preminol 7012," "Preminol S 4011," "Preminol S 4015," "Preminol S 3025," and "Preminol S 6420" (all manufactured by AGC Inc.); "ACCLAIM (registered trademark; hereinafter, abbreviated) 4200," "ACCLAIM 8200," "ACCLAIM 2220N," "ACCLAIM 3300N," "ACCLAIM 4220N," "ACCLAIM 6300," "Acclaim 2200," and "ACCLAIM 6320N" (both manufactured by Covestro).

[0040] The polyoxyalkylene group includes a polyoxypropylene group. The polyoxyalkylene group may further include a linear or branched oxyalkylene group having 1 to 14 carbon atoms. The number of carbon atoms in the oxyalkylene group is more preferably 2 to 4. The oxyalkylene group may be a single type, or two or more types may be included. The oxyalkylene group other than the polyoxypropylene group is preferably an oxyethylene group. From the viewpoint of good impact resistance of the PSA, the content of the polyoxypropylene group among the polyoxyalkylene groups is preferably 50% by mass or more, more preferably 60 to 100% by mass, even more preferably 80 to 100% by mass, and even more preferably 100% by mass. Note that in the present embodiment, the content of the polyoxypropylene group among the polyoxyalkylene groups is a value based on the blend amount of the raw material compound constituting the polyoxyalkylene group among the raw materials for synthesizing the polyether polyol.

[0041] Examples of compounds having a cyclic ether structure include ethylene oxide, propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, methyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, lauryl glycidyl ether, hexyl glycidyl ether, tetrahydrofuran, etc. Propylene oxide can constitute a polyoxypropylene group.

[0042] Examples of the group having an active hydrogen in the initiator include a hydroxyl group, a carboxyl group, an amino group having a hydrogen atom bonded to a nitrogen atom, etc. Among these, a hydroxyl group is preferred, and an alcoholic hydroxyl group is more preferred. Examples of initiators having two or more active hydrogen atoms in one molecule include polyols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, butylene glycol, 1,4-butanediol, 1,6-hexanediol, triethylene glycol, tripropylene glycol, polyoxyalkylene diols (e.g., polyethylene glycol, polypropylene glycol, etc.), glycerin, trimethylolethane, trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol, diglycerin, dipentaerythritol, sorbitol, sucrose, polyoxyalkylene polyols (e.g., polyoxyethylene polyol, polyoxypropylene polyol, etc.), and triethanolamine; bisphenols such as bisphenol A, bisphenol F, and bisphenol AD; dihydroxybenzenes such as catechol, resorcinol, and hydroquinone; and amines such as methylamine, ethylamine, propylamine, butylamine, ethylenediamine, and diethylenetriamine. Of these, polyols are preferred.

[0043] The ring-opening polymerization can be carried out by a method using a known catalyst, such as an alkali catalyst such as potassium hydroxide, a transition metal compound-porphyrin complex catalyst such as a complex obtained by reacting an organoaluminum compound with porphyrin, a composite metal cyanide complex catalyst (for example, a zinc hexacyanocobaltate complex having tert-butanol as a ligand), or a catalyst made of a phosphazene compound.

[0044] <Monoisocyanate> The monoisocyanate to be reacted with the polyether polyol for urethane formation is a monoisocyanate having a (meth)acryloyloxy group, that is, a compound having a (meth)acryloyloxy group and one isocyanate group per molecule.

[0045] The monoisocyanate is preferably a compound in which a (meth)acryloyloxy group is bonded to a hydrocarbon skeleton having one isocyanate group. The hydrocarbon skeleton is preferably an aliphatic hydrocarbon group, which may contain an etheric oxygen atom. The aliphatic hydrocarbon group preferably has 8 or less carbon atoms, more preferably 2 to 6, and even more preferably 2 to 4 carbon atoms. The number of (meth)acryloyloxy groups in one molecule of the monoisocyanate may be one or two or more, and is preferably one or two.

[0046] Examples of monoisocyanates having a (meth)acryloyloxy group include compounds having one (meth)acryloyloxy group in one molecule, such as isocyanate methyl (meth)acrylate, 2-isocyanate ethyl (meth)acrylate, and 1,1-(bisacryloyloxymethyl)ethyl isocyanate; and compounds having two (meth)acryloyloxy groups in one molecule, such as 1,1-(bis(meth)acryloyloxymethyl)ethyl isocyanate and 1,1-(bis(meth)acryloyloxymethyl)propyl isocyanate. Commercially available products include Karenz (registered trademark; hereafter abbreviated) AOI (2-isocyanate ethyl acrylate), Karenz MOI (2-isocyanate ethyl methacrylate), Karenz BEI (1,1-(bisacryloyloxymethyl)ethyl isocyanate), and Karenz MOI-EG (1,1-(bisacryloyloxymethyl)ethyl isocyanate) (all manufactured by Resonac Corporation).

[0047] The first urethane (meth)acrylate is obtained by subjecting the polyether polyol and the monoisocyanate to a urethanization reaction. The urethanization reaction can be carried out by a known method, typically by mixing the polyether polyol and the monoisocyanate and carrying out the reaction using a urethanization catalyst under a nitrogen gas or inert gas atmosphere. Examples of the urethanization catalyst include organotin compounds such as dibutyltin(IV) dilaurate, dioctyltin(IV) dilaurate, dibutyltin(IV) dioctoate, and tin(II) 2-ethylhexanoate; iron compounds such as iron(III) acetylacetonate and iron(III) chloride; lead compounds such as lead(II) 2-ethylhexanoate; bismuth compounds such as bismuth(III) 2-ethylhexanoate; and tertiary amines such as triethylamine and triethylenediamine. Among these, organotin compounds, lead(II) 2-ethylhexanoate, and bismuth(III) 2-ethylhexanoate are preferred. The urethanization catalyst may be used alone or in combination of two or more.

[0048] The amount of the urethanization catalyst used is preferably 0.001 to 1 part by mass, more preferably 0.002 to 0.5 parts by mass, and even more preferably 0.005 to 0.1 part by mass, relative to 100 parts by mass of the polyether polyol reactant. The reaction temperature for the urethanization reaction is preferably 20 to 100°C, more preferably 30 to 90°C, and even more preferably 40 to 80°C.

[0049] From the viewpoint of preventing oxidation, an antioxidant such as hydroquinones, for example, 2,5-di-tert-butylhydroquinone, may be added to the first urethane (meth)acrylate obtained by the urethanization reaction within a range that does not affect the physical properties and effects of the curable composition (for example, an added amount of 0.1 ppm by mass or less relative to 100 parts by mass of polyether polyol).

[0050] The weight average molecular weight of the first urethane (meth)acrylate is preferably 5,000 to 200,000, more preferably 7,000 to 100,000, and even more preferably 10,000 to 50,000, from the viewpoint of good adhesiveness and ease of handling of the adhesive.

[0051] The glass transition temperature of the first urethane (meth)acrylate is preferably −85 to −55° C., more preferably −80 to −57° C., and even more preferably −75 to −60° C., from the viewpoint of good adhesive properties and low-temperature bending durability of the adhesive.

[0052] The viscosity (25°C) of the first urethane (meth)acrylate is preferably 1.0 to 40.0 Pa·s, more preferably 2.0 to 35.0 Pa·s, and even more preferably 3.0 to 30.0 Pa·s, from the viewpoint of ease of handling of the curable composition and the pressure-sensitive adhesive.

[0053] When two or more types of first urethane (meth)acrylates are contained in the curable composition, it is preferable that each of the first urethane (meth)acrylates has a weight average molecular weight, a glass transition temperature, and a viscosity within the above-described numerical ranges.

[0054] The first urethane (meth)acrylate, which is the urethane reaction product as described above, has a polyoxypropylene group and two or more (meth)acryloyloxy groups per molecule. Because the first urethane (meth)acrylate has such a structure, the cured product of the curable composition is likely to form a uniform crosslinked network, and a pressure-sensitive adhesive having small residual strain and excellent low-temperature bending durability and impact resistance can be obtained.

[0055] In contrast, the urethane (meth)acrylate obtained by reacting a polyether polyol, a polyisocyanate, and a hydroxyl group-containing (meth)acrylate tends to have a higher urethane bond content (mass ratio) than the first urethane (meth)acrylate of this embodiment. The higher the urethane bond content, the higher the glass transition temperature tends to be. Consequently, the pressure-sensitive adhesive cannot achieve sufficient low-temperature bending durability.

[0056] From the viewpoint of good adhesiveness of the pressure-sensitive adhesive and low-temperature bending durability, the content of the first urethane (meth)acrylate in the curable composition is preferably 10 to 100 parts by mass, more preferably 15 to 80 parts by mass, and even more preferably 20 to 50 parts by mass, relative to 100 parts by mass of the (meth)acrylic resin.

[0057] (Second Urethane (Meth)acrylate) In this embodiment, in addition to the (meth)acrylic resin and the first urethane (meth)acrylate, the curable composition preferably further contains a second urethane (meth)acrylate having one (meth)acryloyloxy group per molecule. The second urethane (meth)acrylate tends to have a lower glass transition temperature and a lower elastic modulus than the (meth)acrylic resin and the first urethane (meth)acrylate, thereby contributing to improving the low-temperature bending durability of the pressure-sensitive adhesive. In addition, since there is one (meth)acryloyloxy group per molecule, the curable composition has good stability and also has the effect of making it less likely for bleeding to occur in the cured product obtained by curing the curable composition.

[0058] From the viewpoint of accelerating the curing rate, the second urethane (meth)acrylate is preferably a urethane acrylate having one acryloyloxy group in one molecule.

[0059] The second urethane (meth)acrylate is preferably a urethane reaction product of a polyether monool and a monoisocyanate having a (meth)acryloyloxy group.

[0060] The polyether monool is preferably a polyol having one hydroxyl group per molecule and a polyoxyalkylene group (including a polyoxypropylene group). The polyether monool can be obtained by ring-opening polymerization of a compound having a cyclic ether structure with an initiator having one active hydrogen per molecule. Commercially available products can also be used. Examples of commercially available polyether monools include "Preminol S 1011" and "Preminol S 1004F" (both manufactured by AGC Inc.).

[0061] The polyoxyalkylene group preferably contains a polyoxypropylene group. The polyoxyalkylene group may further contain a linear or branched oxyalkylene group having 1 to 14 carbon atoms. The number of carbon atoms in the oxyalkylene group is more preferably 2 to 4. The oxyalkylene group may be a single type, or two or more types may be contained. The oxyalkylene group other than the (poly)oxypropylene group is preferably an oxyethylene group. From the viewpoint of good impact resistance of the PSA, the content of the polyoxypropylene group among the polyoxyalkylene groups is preferably 50% by mass or more, more preferably 60 to 100% by mass, even more preferably 80 to 100% by mass, and even more preferably 100% by mass. Note that in the present embodiment, the content of the polyoxypropylene group among the polyoxyalkylene groups is a value based on the blend amount of the raw material compound constituting the polyoxyalkylene group among the synthetic raw materials for the polyether monool.

[0062] The compound having a cyclic ether structure, the group having active hydrogen in the initiator, and the catalyst for ring-opening polymerization are the same as those in the polyether polyol in the first urethane (meth)acrylate described above.

[0063] Examples of initiators having one active hydrogen per molecule include monohydric alcohols, monohydric phenols, monocarboxylic acids, and secondary amines. Of these, monohydric aliphatic alcohols and monohydric aliphatic carboxylic acids are preferred. The number of carbon atoms in the monohydric aliphatic alcohol is preferably 1 to 20, more preferably 2 to 8. The number of carbon atoms in the monohydric aliphatic carboxylic acid is preferably 2 to 20, more preferably 2 to 8. Polyoxyalkylene monools (e.g., polyethylene glycol, polypropylene glycol, etc.) can also be used as initiators.

[0064] The monoisocyanate to be reacted with the polyether monool for urethane formation and the method of the urethane formation may be the same as those for the polyether polyol in the first urethane (meth)acrylate described above. The preferred weight average molecular weight, glass transition temperature, and viscosity of the second urethane (meth)acrylate are the same as those of the first urethane (meth)acrylate described above.

[0065] When the curable composition contains a second urethane (meth)acrylate, its content is preferably 40 parts by mass or less, more preferably 1 to 35 parts by mass, and even more preferably 5 to 30 parts by mass, per 100 parts by mass of the (meth)acrylic resin, from the viewpoint of good adhesive properties and low-temperature bending durability of the adhesive. The content of the second urethane (meth)acrylate in the curable composition is preferably equal to or less than the content of the first urethane (meth)acrylate, from the viewpoint of good adhesive properties and low-temperature bending durability of the adhesive. From the same viewpoint, the total content of the first urethane (meth)acrylate and the second urethane (meth)acrylate in the curable composition is preferably 10 to 60 parts by mass, more preferably 15 to 55 parts by mass, and even more preferably 20 to 50 parts by mass, per 100 parts by mass of the (meth)acrylic resin.

[0066] (Other Components) The curable composition may contain other components in addition to the (meth)acrylic resin, the first urethane (meth)acrylate, and the second urethane (meth)acrylate, depending on the ease of handling and its intended use. Examples of other components include polymerization initiators, other monomer components (e.g., active energy ray-curable monomers) other than the first urethane (meth)acrylate and the second urethane (meth)acrylate, colorants such as pigments and dyes, silane coupling agents, tackifier resins, antioxidants, light stabilizers, metal deactivators, rust inhibitors, antiaging agents, moisture absorbers, hydrolysis inhibitors, antifoaming agents, and fillers. An organic solvent may also be contained.

[0067] The total content of the (meth)acrylic resin, the first urethane (meth)acrylate, and the second urethane (meth)acrylate in the curable composition (excluding the organic solvent) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and still more preferably 99% by mass or more.

[0068] The content of the organic solvent in the curable composition is within a range that does not impair the effects of the present invention, and from the viewpoints of uniform mixing and coatability of the curable composition, is preferably 50 parts by mass or less, more preferably 10 to 50 parts by mass, and even more preferably 10 to 40 parts by mass. When the curable composition contains an organic solvent, the organic solvent is preferably removed by volatilization during or after curing.

[0069] <Polymerization initiator> The polymerization initiator is preferably a radical polymerization initiator, and may be a photopolymerization initiator or a thermal polymerization initiator, and known initiators can be used. The polymerization initiator may be added as a component separate from the curable composition when producing the pressure-sensitive adhesive. From the viewpoint of ease of control of the polymerization reaction, the photopolymerization initiator is preferably one that can be used by irradiation with ultraviolet light having a wavelength of 380 nm or less, and the thermal polymerization initiator is preferably one that can be used by heating within a range of 50 to 120°C.

[0070] Examples of the photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2-(2-oxo-2-phenylacetoxyethoxy)ethyl oxyphenylacetate, 2-(2-hydroxyethoxy)ethyl oxyphenylacetate, 2-hydroxy-2-methylpropiophenone, diethoxyacetophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropanone, 1-(4-dodecylphenyl)-2-hydroxy-2-methylpropanone, 4-(2-hydroxyethoxy)-phenyl(2-hydroxy-2-propyl)ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone, benzoin, benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether. Examples of the photopolymerization initiator include propyl ether, benzoin-n-butyl ether, benzoin phenyl ether, benzil dimethyl ketal, benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate, 4-phenylbenzophenone-4-methoxybenzophenone, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropyl thioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, methylphenyl glyoxylate, benzil, and camphorquinone. One type of photopolymerization initiator may be used alone, or two or more types may be used in combination.

[0071] Examples of the thermal polymerization initiator include azo compounds; and organic peroxides such as hydroperoxides, dialkyl peroxides, peroxyesters, diacyl peroxides, peroxydicarbonates, peroxyketals, and ketone peroxides. Specific examples include azobisisobutyronitrile, benzoyl peroxide, tert-butylperoxy-2-ethylhexanoate, 2,5-dimethyl-2,5-di(2-ethylhexanoyl)peroxyhexane, tert-butylperoxybenzoate, te Examples of the thermal polymerization initiator include rt-butyl peroxide, cumene hydroperoxide, dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-dibutylperoxyhexane, 2,4-dichlorobenzoyl peroxide, 1,4-di(2-t-butylperoxyisopropyl)benzene, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, methyl ethyl ketone peroxide, and 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate. One type of thermal polymerization initiator may be used alone, or two or more types may be used in combination.

[0072] The components in the curable composition are preferably mixed uniformly, and the order of mixing is not limited. Heat treatment may be performed after mixing the components. The components may be mixed in advance or immediately before curing. For example, the polymerization initiator may be added to a premix in which components other than the polymerization initiator are mixed in advance, immediately before curing.

[0073] From the viewpoint of an appropriate polymerization rate, the content of the polymerization initiator in the curable composition is preferably 0.001 to 20 parts by mass, more preferably 0.01 to 10 parts by mass, and even more preferably 0.1 to 7 parts by mass, relative to 100 parts by mass of the (meth)acrylic resin.

[0074] [Adhesive] The adhesive of this embodiment is a cured product of the curable composition of this embodiment described above. The adhesive of this embodiment has small residual strain when subjected to dynamic shear strain. In addition, the adhesive of this embodiment has high impact absorption ability and excellent impact resistance.

[0075] In order to provide the pressure-sensitive adhesive of the present embodiment with excellent bending durability at low temperatures below the freezing point (e.g., −20° C.), the glass transition temperature is preferably −35° C. or lower, more preferably −80 to −36° C., and even more preferably −60 to −37° C.

[0076] The curable composition can be cured by known methods such as irradiation with active energy rays (for example, light such as ultraviolet rays, or electron beams) or heating.

[0077] When a pressure-sensitive adhesive is obtained by irradiating a curable composition with light, the light source can be appropriately selected depending on the light absorption ability of the photopolymerization initiator and active energy ray-curable monomer used. For example, ultraviolet light-emitting diodes (LEDs), low-pressure mercury lamps, high-pressure mercury lamps, mercury-xenon lamps, metal halide lamps, tungsten lamps, arc lamps, excimer lamps, excimer lasers, semiconductor lasers, YAG lasers, laser systems combining lasers with nonlinear optical crystals, and high-frequency induced ultraviolet generators can be used as light sources. The integrated light amount is, for example, 0.01 to 50 J / cm. ２ In the case of ultraviolet irradiation, the dose is usually 0.01 to 10 J / cm ２ , preferably 0.1 to 5 J / cm ２ From the viewpoint of further stabilizing the physical properties of the pressure-sensitive adhesive, a heat treatment may be further carried out after light irradiation. When the heat treatment is carried out, the heating temperature is preferably 40 to 200°C, and the heating time is preferably 1 minute to 15 hours. The physical properties of the pressure-sensitive adhesive can also be stabilized by leaving the pressure-sensitive adhesive at room temperature (15 to 25°C) for 1 to 48 hours.

[0078] When a pressure-sensitive adhesive is obtained by heating a curable composition using a thermal polymerization initiator, the heating temperature is preferably 40 to 250°C, and the heating time is preferably 5 minutes to 24 hours. When the heating temperature is high, it is preferable to shorten the heating time, and when the heating temperature is low, it is preferable to lengthen the heating time.

[0079] [Adhesive Sheet] The adhesive sheet of this embodiment has an adhesive layer made of the adhesive of this embodiment described above. The adhesive layer and adhesive sheet of this embodiment are flexible and exhibit excellent low-temperature folding durability, with no change in appearance even when repeatedly folded at least 200,000 times at a bending radius of 2.5 mm at a temperature below freezing (e.g., −20° C.).

[0080] The pressure-sensitive adhesive sheet can be produced, for example, by the following method. First, a curable composition (diluted with an organic solvent as necessary) is applied to one or both sides of a substrate sheet, and then dried. Alternatively, the curable composition may be melted by heating and extrusion laminated onto the substrate sheet using a T-die or the like. If necessary, a release sheet may be attached to the curable composition on the substrate sheet. Next, a pressure-sensitive adhesive layer is formed on the substrate sheet, and the curable composition on the substrate sheet is cured by the curing method described above, thereby obtaining a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer.

[0081] The PSA sheet may also be a double-sided PSA sheet having no substrate sheet (substrate-less), in which a PSA layer is formed on one side of the release sheet and a release sheet is also attached to the other side of the PSA layer. When in use, the PSA sheet is attached to an adherend by peeling the release sheet from the PSA layer.

[0082] Examples of the substrate sheet include synthetic resin (e.g., polyester such as polyethylene terephthalate (PET), polyimide, etc.) sheets; metal foils such as aluminum, copper, iron, etc.; paper such as fine paper and glassine paper; woven fabrics made of glass fiber, natural fiber, synthetic fiber, etc.; and nonwoven fabrics. The substrate sheet may be a single layer or a multi-layer body made of two or more types of the same or different materials.

[0083] Examples of the release sheet include a synthetic resin sheet, paper, cloth, nonwoven fabric, etc. made of the same material as the above-mentioned base sheet, which has been subjected to a release treatment (for example, silicone treatment).

[0084] The method for applying the curable composition is not particularly limited, and examples thereof include roll coating, die coating, gravure coating, comma coating, and screen printing.

[0085] The thickness of the adhesive layer is preferably 10 to 1000 μm, more preferably 15 to 250 μm, and even more preferably 20 to 100 μm, from the viewpoint of good adhesiveness and impact resistance, and taking into consideration the effect on the dimensions of the adherend.

[0086] [Laminate] The laminate of this embodiment has a flexible member and a pressure-sensitive adhesive layer formed on the flexible member and made of the pressure-sensitive adhesive of this embodiment. The flexible member is attached to an adherend by the pressure-sensitive adhesive layer to form a laminate. The pressure-sensitive adhesive of this embodiment has small residual strain, excellent impact resistance, and excellent low-temperature bending durability, and is therefore suitable for use in producing a laminate including a flexible member. The laminate of this embodiment is also flexible.

[0087] The flexible member may be, for example, a member constituting a flexible display panel, and may be at least one selected from the group consisting of a surface protection panel, an optical film, a touch panel, and a display panel body. The pressure-sensitive adhesive of the present embodiment is also suitable as an optically clear pressure-sensitive adhesive (OCA) or the like applied to such flexible members.

[0088] Examples of surface protection panels include thin cover glass and cover films. Optical films have optical functions, and examples thereof include polarizing films, retardation films, optical filters, anti-reflection films, near-infrared cut films, and electromagnetic wave shielding films. Touch panels include, for example, thin glass or plastic substrates on which touch sensors are mounted. Examples of display panel bodies include organic EL display panels.

[0089] [Flexible Display] The flexible display of this embodiment includes the laminate of this embodiment described above. As described above, the laminate of this embodiment is flexible and suitable for flexible displays, and is particularly suitable for foldable displays.

[0090] The present invention will be described in detail below with reference to examples. The present invention is not limited to the following examples, and various modifications are possible within the scope of the present invention.

[0091] [Synthesis of (meth)acrylic resins and urethane (meth)acrylates] Various (meth)acrylic resins and urethane (meth)acrylates used in the production of curable compositions were synthesized. Details of the various raw materials used are as follows. HEA: 2-hydroxyethyl acrylate 2EHA: 2-ethylhexyl acrylate BA: n-butyl acrylate EMA: ethyl methacrylate AIBN: 2,2'-azobisisobutyronitrile PPG: polypropylene glycol P1: "Preminol S 4011", manufactured by AGC Inc., number of functional groups (f): 2, number average molecular weight (Mn): 10,000 P2: "Preminol S 4015", manufactured by AGC Inc., f: 2, Mn: 15,000 P3: "Preminol S 3011", manufactured by AGC Inc., f: 3, Mn: 10,000 P4: "Preminol S 3025", manufactured by AGC Inc., f: 3, Mn: 24,000 P5: "Preminol S P6: "Preminol S 1011", manufactured by AGC Inc., f: 1, Mn: 10,000 P7: "Preminol S 4013F", manufactured by AGC Inc., f: 2, Mn: 12,000 AOI: 2-isocyanatoethyl acrylate; "Karendz AOI", manufactured by Resonac Co., Ltd. IPDI: isophorone diisocyanate Kalcol: decyl alcohol; "Kalcol (registered trademark) 1098", manufactured by Kao Corporation Omnirad 184: 1-hydroxycyclohexyl phenyl ketone; "Omnirad (registered trademark) 184", manufactured by IGM Resins B.V. Omnirad 754: a mixture of 2-(2-oxo-2-phenylacetoxyethoxy)ethyl oxyphenylacetate and 2-(2-hydroxyethoxy)ethyl oxyphenylacetate; "Omnirad (registered trademark) 754", manufactured by IGM Resins B.V.

[0092] Synthesis Example 1 Synthesis of (meth)acrylic resins 104 parts by mass of ethyl acetate, 20 parts by mass of acetone, 0.01 part by mass of AIBN as a polymerization initiator, and each monomer shown in Table 1 (total 100 parts by mass) were charged into a reaction vessel equipped with a stirrer and a cooler, and the mixture was heated to reflux at 80° C. After 1 hour, 20 parts by mass of ethyl acetate and 0.01 part of AIBN were added dropwise over 2 hours to obtain solutions of (meth)acrylic resins (A1) and (A2).

[0093] The weight average molecular weight (Mw) and glass transition temperature (Tg) of each (meth)acrylic resin obtained in Synthesis Example 1 are shown in Table 1. The Mw and Tg of the (meth)acrylic resin were determined as follows.

[0094] (Weight-average molecular weight (Mw)) Measurement was performed by gel permeation chromatography (GPC) under the following measurement conditions. In Table 1, values ​​are expressed with two significant digits. <Measurement conditions> - Instrument used: "HLC-8320GPC", manufactured by Tosoh Technosystems Corporation - Column used: The following two types of columns were connected in series: "TSKgel (registered trademark) GMHXL", manufactured by Tosoh Corporation, three columns; "TSKgel (registered trademark) G2000HXL", manufactured by Tosoh Corporation, one column - Column temperature: 40°C - Detector: Refractive index (RI) detector - Eluent: Tetrahydrofuran - Flow rate: 0.8 mL / min - Sample concentration: 0.5% by mass - Sample injection volume: 100 μL - Standard sample: Polystyrene

[0095] (Glass Transition Temperature (Tg)) The resin solution obtained by synthesis was applied to a polyester release sheet and dried, and the resulting laminate was repeatedly laminated to form a coating film with a thickness of approximately 650 μm. The dynamic viscoelasticity of the coating film was measured under the following measurement conditions, and the maximum peak temperature of the loss tangent tanδ (= loss modulus G" / storage modulus G') was taken as the glass transition temperature (Tg). <Measurement Conditions> - Instrument used: "DVA-225", manufactured by IT Measurement Control Co., Ltd. - Deformation mode: shear - Strain: 0.1% - Measurement temperature: -80 to 60°C - Heating rate: 3°C / min - Measurement frequency: 1 Hz

[0096]

[0097] Synthesis Example 2 Synthesis of Urethane (Meth)acrylate (1) PPG and AOI (isocyanate index 100) were charged into a reaction vessel equipped with a stirrer and a nitrogen inlet tube in accordance with the respective blending compositions shown in Table 2 for urethane (meth)acrylates (B1) to (B5) and (C1), and the mixtures were reacted at 70°C for 3 hours in the presence of 0.008 parts by mass of bismuth 2-ethylhexanoate. Next, 0.03 ppm by mass of 2,5-di-tert-butylhydroquinone was added to obtain urethane (meth)acrylates (B1) to (B5) and (C1), respectively.

[0098] (Synthesis Example 3) Synthesis of Urethane (Meth)acrylate (2) In a reaction vessel equipped with a stirrer and a nitrogen inlet tube, PPG and IPDI were charged in the respective blending compositions shown in Table 2 for urethane (meth)acrylates (D1) and (D2). The mixture was reacted at 70°C for 4 hours in the presence of 0.025 parts by mass of dibutyltin dilaurate. Then, HEA and Kalcol, as well as 0.05 parts by mass of 2,6-di-tert-butylcresol as a polymerization inhibitor, were added. The mixture was reacted at 60°C until the isocyanate group content reached 0% by mass. Next, 0.03 ppm by mass of 2,5-di-tert-butylhydroquinone was added to obtain urethane (meth)acrylates (D1) and (D2), respectively. The isocyanate group content was quantified by back titration using an indicator titration method in accordance with Method A of JIS K 1603-1:2007.

[0099] The weight average molecular weight (Mw), glass transition temperature (Tg), and viscosity of each urethane (meth)acrylate obtained in Synthesis Examples 2 and 3 are shown in Table 2. The number average molecular weight (Mn) of PPG and the Mw of the urethane (meth)acrylate were determined by the same measurement method as for the Mw of the (meth)acrylic resin described above. In Table 2, the Mn of the PPG is expressed to two significant digits, and the Mw of the urethane (meth)acrylate is expressed to three significant digits. The Tg and viscosity of the urethane (meth)acrylate were measured as follows:

[0100] (Glass transition temperature (Tg)) A mixed solution of 100 parts by mass of urethane (meth)acrylate and 4 parts by mass of Omnirad 184 was prepared. The mixed solution was applied to a polyester (polyethylene terephthalate; PET) release sheet using a doctor blade, and the coated sheet was irradiated with ultraviolet light (cumulative irradiation dose 3 J / cm ２ The coating was cured using a high-pressure mercury lamp (80 W, height 18 cm, conveyor speed 1.5 m / min x 3 passes; the same applies below). The coating was laminated by repeating this process to form a coating film with a thickness of approximately 1,200 μm. The dynamic viscoelasticity of the coating film was measured in the same manner as for the (meth)acrylic resin described above, and Tg was determined.

[0101] (Viscosity) Measurement was performed using an E-type viscometer ("RE85U", manufactured by Toki Sangyo Co., Ltd., 25°C).

[0102]

[0103] [Preparation of Curable Compositions] A (meth)acrylic resin and a urethane (meth)acrylate were mixed according to the formulation shown in Table 3, and 0.25 parts by mass of Omnirad 184 and 1.50 parts by mass of Omnirad 754 were added as photopolymerization initiators to prepare curable compositions of Examples 1 to 13. Examples 1 to 11 are working examples, and Examples 12 and 13 are comparative examples.

[0104] [Evaluation of Pressure-Sensitive Adhesive Properties] The evaluation results of the curable compositions of each example for glass transition temperature (Tg), bending durability, residual strain, and impact resistance are shown in Table 3. Details of each evaluation item are as follows.

[0105] (Glass transition temperature (Tg)) The curable composition was applied to a PET release sheet using a doctor blade, and the composition was cured by UV irradiation. This procedure was repeated to form a pressure-sensitive adhesive layer having a thickness of approximately 1,200 μm. The dynamic viscoelasticity of the pressure-sensitive adhesive layer was measured in the same manner as for the above-mentioned (meth)acrylic resin coating film, and Tg was determined.

[0106] (Low-Temperature Bending Durability) A curable composition was applied to a PET release sheet using a doctor blade and cured by ultraviolet irradiation to form a pressure-sensitive adhesive layer approximately 25 μm thick. The pressure-sensitive adhesive layer was peeled from the PET release sheet, and a polyimide film (50 μm thick) was attached to one side and a corona-treated PET sheet (50 μm thick) was attached to the other side to prepare a laminate test specimen (width 50 mm, length 100 mm, thickness 125 nm). A low-temperature repeated bending test was performed on the test specimen under the following test conditions. <Test Conditions> - Equipment used: Planar body no-load U-shaped extension tester "DLDM111LH", manufactured by Yuasa System Co., Ltd. - Test temperature: -20°C - Inner surface of bending: polyimide film side - Bending radius: 1.5 mm - Bending speed: 60 times / min

[0107] The appearance of the test specimen in the repeated bending test (whitening and cracking of the pressure-sensitive adhesive layer, peeling and lifting of the laminate, etc.) was visually observed to evaluate the adhesiveness and low-temperature bending durability according to the following evaluation criteria: <Evaluation criteria> A: 200,000 or more bending times without change in appearance B: 100,000 or more bending times but less than 200,000 times without change in appearance C: Less than 100,000 times without change in appearance A rating of A or B can be said to indicate good adhesiveness and low-temperature bending durability of the pressure-sensitive adhesive layer.

[0108] (Residual strain) The curable composition was sandwiched between a soda-lime glass stage and a measuring spindle ("Disposable Plate D-PP20 / AL / S07", manufactured by Anton Paar) in a gap of 0.2 mm in width. Under a nitrogen gas atmosphere at 35°C, the curable composition was irradiated with light from a mercury-xenon lamp ("Spot Cure (registered trademark) SP-9", manufactured by Ushio Inc.; illuminance 100 mW / cm) installed below the stage. ２) and cured under ultraviolet light for 5 minutes to obtain a pressure-sensitive adhesive sample. The spindle position was automatically adjusted to prevent stress from occurring in the normal direction of the spindle during curing of the curable composition. While irradiating with ultraviolet light, a 2% dynamic shear strain was applied for 30 minutes using a rheometer (Physica MCR301, manufactured by Anton Paar), and the strain was removed and the residual strain was measured 30 minutes later. Residual strain was evaluated according to the following evaluation criteria, with the strain before the dynamic shear strain application being set at 0% (reference). <Evaluation Criteria> A: 0.1% or less B: More than 0.1% A rating of A indicates excellent shape recovery even after the external force on the pressure-sensitive adhesive is removed.

[0109] (Impact Resistance) A curable composition was applied to a PET release sheet using a doctor blade and cured by ultraviolet irradiation to form a 25 μm thick adhesive layer. The adhesive layer was peeled from the PET release sheet, and polyimide films (50 μm thick) were attached to both sides of the adhesive layer to produce a laminate (adhesive layer thickness: 25 μm). The laminate was placed on pressure-sensitive paper placed on a steel plate, and an impact test was performed by dropping a stainless steel ball (5 g) from a height of 5 cm from the laminate.

[0110] After the impact test, the impact marks of the ball recorded on the pressure-sensitive paper were visually inspected, and the impact resistance was evaluated according to the following evaluation criteria: <Evaluation criteria> A: No impact marks B: One impact mark C: Two or more impact marks A rating of A or B indicates good impact resistance.

[0111]

[0112] As shown in Table 3, it was confirmed that the pressure-sensitive adhesive of this embodiment has a low glass transition temperature, excellent low-temperature bending durability, small residual strain, and excellent impact resistance.

Claims

1. A curable composition comprising a (meth)acrylic resin and a first urethane (meth)acrylate, wherein the first urethane (meth)acrylate is a urethane reaction product of a polyether polyol and a monoisocyanate having a (meth)acryloyloxy group, and has a polyoxypropylene group and two or more (meth)acryloyloxy groups per molecule.

2. The curable composition according to claim 1, wherein the content of the first urethane (meth)acrylate is 10 to 100 parts by mass per 100 parts by mass of the (meth)acrylic resin.

3. The curable composition according to claim 1, wherein the weight average molecular weight of the first urethane (meth)acrylate is 5,000 to 200,000.

4. The curable composition according to claim 1, further comprising a second urethane (meth)acrylate having one (meth)acryloyloxy group per molecule.

5. The curable composition according to claim 4, wherein the weight average molecular weight of the second urethane (meth)acrylate is 5,000 to 200,000.

6. The curable composition according to claim 1, wherein the (meth)acrylic resin has a weight average molecular weight of 100,000 to 3,000,000.

7. A pressure-sensitive adhesive which is a cured product of the curable composition according to any one of claims 1 to 6.

8. The pressure-sensitive adhesive according to claim 7, wherein the glass transition temperature of the cured product is -35°C or lower.

9. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to claim 7.

10. A laminate comprising: a flexible member; and an adhesive layer formed on the flexible member and comprising the adhesive according to claim 7.

11. The laminate according to claim 10, wherein the flexible member is at least one selected from the group consisting of a surface protection panel, an optical film, a touch panel, and a display panel body.

12. A flexible display comprising the laminate according to claim 10.

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