Adhesive, adhesive sheet, laminate, and display

Abstract

The problem of the present invention is solved by an adhesive comprising a specific acrylic copolymer (A), an isocyanate compound (B), and a metal chelate compound (C), the adhesive after curing satisfying all of (1) to (3). (1) 3.0 × 104 Pa < G'(-20) < 4.0 × 105 Pa; (2) 5 < G'(-20) / G'(200) < 17; (3) 2 < tanδ (-20) / tanδ (200) < 6.5. In the abovementioned formulas, G'(-20) represents the storage elastic modulus at -20°C and 1 Hz, G'(200) represents the storage elastic modulus at 200°C and 1 Hz, tanδ (-20) represents the loss tangent at -20°C and 1 Hz, and tanδ (200) represents the loss tangent at 200°C and 1 Hz, respectively.

Description

Adhesive, adhesive sheet, laminate and display

[0001] The present disclosure relates to a pressure-sensitive adhesive suitable for forming a laminate including a light-transmitting substrate, a pressure-sensitive adhesive layer, and a polarizing plate, a pressure-sensitive adhesive sheet, and a laminate having the pressure-sensitive adhesive layer. The laminate is suitable for use in displays.

[0002] Thin image display devices such as liquid crystal displays and organic EL displays typically have a laminated structure including an image-forming layer such as a liquid crystal layer or an organic EL layer, and an optical film or a cover panel. Adhesives are generally used to bond the various layers constituting the image display device. For example, a transparent conductive film used in a touch panel is laminated to a member such as a support glass or a support film via an adhesive layer. Furthermore, a polarizing plate film used in an image device is attached to a liquid crystal module or an organic EL module via an adhesive layer. In this way, the various components of the image display device are attached and fixed by the adhesive layer.

[0003] Furthermore, while flat displays using glass substrates have been mainstream as the image display devices, in recent years, flexible displays using flexible substrates such as plastics, such as foldable displays and rollable displays, have been developed. Compared to conventional flat displays using glass substrates, such flexible displays have various advantages such as being lighter, thinner, more flexible, and more aesthetically pleasing.

[0004] The pressure-sensitive adhesive layer has traditionally been required to have the property of not foaming or peeling in high-temperature environments or high-temperature, high-humidity environments, but in recent years, further functionality has been required, and flexibility has become necessary for flexible displays. For example, in the case of a foldable display, flexibility refers to the suitability (flexibility) for adapting to the bending of the display. Generally, the flexibility requires a property (dynamic flexibility) that does not cause foaming, lifting, or peeling when repeatedly bent.

[0005] Patent Document 1 discloses a pressure-sensitive adhesive containing an acrylic polymer and a radically polymerizable compound, while Patent Document 2 discloses a pressure-sensitive adhesive containing two types of acrylic polymers.

[0006] JP 2023-89937 A International Publication No. 2023 / 068009

[0007] In recent years, in order to meet the increasing demands on displays, adhesives used are required to have even stricter durability than before. In particular, for foldable displays, in addition to the property of not causing foaming, lifting, or peeling when repeatedly bent (dynamic flexibility), they also need the property of not causing foaming, lifting, or peeling when the bent state is maintained for a long time (static flexibility). Furthermore, for rollable displays, the adhesive must be able to handle the winding of the display (windability) so that it can be used in rollable displays. The windability requires the property of not causing foaming, lifting, or peeling when the rolled state is maintained for a long time.

[0008] Furthermore, while previously this flexibility was a required quality only at room temperature, with the spread of displays, flexibility in low-temperature environments such as those in extremely cold regions, and high-temperature environments such as those in extremely hot regions or inside automobiles under the blazing sun, is now also becoming necessary.

[0009] In contrast, conventional pressure-sensitive adhesive sheets currently do not satisfy the heat resistance and moist heat resistance at levels that are practically problem-free, and the flexibility such as bendability and rollability. Furthermore, flexibility requires dynamic bendability, static bendability, and rollability depending on the display configuration, and although it is possible to satisfy these flexibilities individually, it is difficult to satisfy them all at the same time. In addition, the current situation is that pressure-sensitive adhesive sheets do not satisfy the dynamic bendability, static bendability, and rollability in high-temperature environments and high-temperature, high-humidity environments.

[0010] An object of the present disclosure is to provide a pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, a laminate thereof, and a display that are excellent in transparency and also have satisfactory heat resistance, moist heat resistance, flexibility, and windability.

[0011] As a result of extensive investigations, the present inventors have found that the problems of the present invention can be solved in the following aspect, and have thus completed the present invention. That is, an embodiment of the present disclosure solves the problems by an adhesive comprising an acrylic copolymer (A), an isocyanate compound (B), and a metal chelate compound (C), wherein the acrylic copolymer (A) is a copolymer of a monomer mixture containing the following monomers (a-1), (a-2), and (a-3), and wherein the adhesive after curing satisfies all of the following (1) to (3): (a-1) a (meth)acrylic acid alkyl ester monomer having an alkyl group having 8 to 12 carbon atoms; (a-2) a monomer having a hydroxyl group; and (a-3) a monomer that forms a chelate crosslink with a metal compound. (1) 3.0 × 10 ４ Pa<G'(-20)<4.0×10 ５ Pa (2) 5<G'(-20) / G'(200)<17 (3) 2<tan δ(-20) / tan δ(200)<6.5 In the above formula, G'(-20) represents the storage modulus at -20°C and 1 Hz. G'(200) represents the storage modulus at 200°C and 1 Hz. tan δ(-20) represents the loss tangent at -20°C and 1 Hz. tan δ(200) represents the loss tangent at 200°C and 1 Hz.

[0012] Another embodiment of the present disclosure is the above-mentioned pressure-sensitive adhesive, wherein the acrylic copolymer (A) contains, relative to 100% by mass of the monomer mixture, 20 to 98% by mass of the monomer (a-1), 0.2 to 2% by mass of the monomer (a-2), and 0.2 to 5% by mass of the monomer (a-3).

[0013] Another embodiment of the present disclosure is the above-mentioned pressure-sensitive adhesive, which contains 0.5 to 5 mass% of the isocyanate compound (B) and 0.2 to 2 mass% of the metal chelate compound (C) relative to 100 mass% of the acrylic copolymer (A1).

[0014] Another embodiment of the present disclosure is the pressure-sensitive adhesive, wherein the pressure-sensitive adhesive has a gel fraction of 60 to 90 mass % after curing.

[0015] Another embodiment of the present disclosure is a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer, which is a cured product of the pressure-sensitive adhesive, is sandwiched between release films.

[0016] Moreover, an embodiment of the present disclosure is a laminate comprising a light-transmitting substrate, a pressure-sensitive adhesive layer, and a polarizing plate, wherein the pressure-sensitive adhesive layer is a cured product of the pressure-sensitive adhesive.

[0017] Another embodiment of the present disclosure is a display comprising the laminate and an optical element.

[0018] The present disclosure provides a pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, and a laminate using the pressure-sensitive adhesive sheet, which are excellent in transparency and also have heat resistance, moist heat resistance, flexibility, and roll-up properties. Furthermore, by using the pressure-sensitive adhesive sheet and laminate of the present disclosure, a display with excellent visibility and contrast is provided.

[0019] 1 is a schematic cross-sectional view partially showing a pressure-sensitive adhesive sheet according to the present disclosure; 2 is a schematic cross-sectional view partially showing a laminate, which is an example of use of a pressure-sensitive adhesive sheet according to the present disclosure; 3 is a schematic cross-sectional view partially showing a display, which is an example of use of a pressure-sensitive adhesive sheet according to the present disclosure.

[0020] Hereinafter, examples of the configurations of the pressure-sensitive adhesive, pressure-sensitive adhesive sheet, laminate, and display of the present disclosure will be described, but the present disclosure is not limited to these.

[0021] The terms used in this specification are defined below. (Meth)acrylic acid ester includes acrylic acid ester and methacrylic acid ester. Monomer refers to an ethylenically unsaturated group-containing monomer. Adherend refers to the object to which the PSA sheet is attached. In this disclosure, sheet, film, and tape are synonymous terms. Furthermore, in this specification, (a-1) (meth)acrylic acid alkyl ester monomers having an alkyl group containing 8 to 12 carbon atoms, (a-2) monomers having a hydroxyl group, (a-3) monomers that form chelate crosslinks with metal compounds, and (a-4) other monomers other than (a-1), (a-2), and (a-3) may be abbreviated as monomer (a-1), monomer (a-2), monomer (a-3), and monomer (a-4), respectively. Furthermore, acrylic copolymer (A), isocyanate compound (B), metal compound (C), and other crosslinking agent (D) other than (B) and (C) may be abbreviated as copolymer (A), compound (B), compound (C), and other crosslinking agent (D), respectively. Unless otherwise noted, the various components appearing in this specification may be used independently either alone or in combination of two or more.

[0022] In this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the range's lower and upper limits.

[0023] <<Adhesive>> The adhesive of the present disclosure contains a specific acrylic copolymer (A), an isocyanate compound (B), and a metal chelate compound (C), and the adhesive after curing satisfies all of the following (1) to (3): (1) 3.0 × 10 ４ Pa<G'(-20)<4.0×10 ５ Pa (2) 5<G'(-20) / G'(200)<17 (3) 2<tan δ(-20) / tan δ(200)<6.5 In the above formula, G'(-20) represents the storage modulus at -20°C and 1 Hz. G'(200) represents the storage modulus at 200°C and 1 Hz. tan δ(-20) represents the loss tangent at -20°C and 1 Hz. tan δ(200) represents the loss tangent at 200°C and 1 Hz.

[0024] <Acrylic Copolymer (A)> The acrylic copolymer (A) is a copolymer of a monomer mixture containing at least (a-1), (a-2), and (a-3), and the monomer mixture may contain a monomer (a-4) as needed: (a-1) a (meth)acrylic acid alkyl ester monomer having an alkyl group with 8 to 12 carbon atoms; (a-2) a monomer having a hydroxyl group; (a-3) a monomer that forms a chelate crosslink with a metal compound; and (a-4) a monomer other than (a-1), (a-2), and (a-3).

[0025] Monomer (a-1) is a (meth)acrylic acid alkyl ester monomer having an alkyl group containing 8 to 12 carbon atoms, and specific examples thereof include n-octyl (meth)acrylate, 2-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, and dodecyl (meth)acrylate. Among these monomers (a-1), n-octyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred because they can particularly impart stress relaxation properties and adhesion, resulting in improved flexibility.

[0026] The acrylic copolymer (A) contains the monomer (a-1), which gives it a long-chain alkyl group in the side chain, allowing the polymers to be appropriately entangled with each other, imparting stress relaxation properties and adhesion to the substrate, and as a result, greatly improving flexibility.

[0027] The monomer (a-1) is preferably contained in an amount of 20 to 98% by mass, more preferably 40 to 90% by mass, based on 100% by mass of the monomer mixture. A content of 20% by mass or more can impart sufficient stress relaxation properties and improve flexibility. Furthermore, a content of 98% by mass or less can maintain flexibility.

[0028] [Monomer (a-2)] Monomer (a-2) is a monomer having a hydroxyl group, and specific examples thereof include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc. Among these monomers (a-2), use of 2-hydroxyethyl (meth)acrylate is preferred because it can particularly impart cohesive strength, thereby improving heat resistance and moist heat resistance.

[0029] The acrylic copolymer (A) contains the monomer (a-2), which gives it a hydroxyl group in its side chain, which allows it to form a crosslinked structure with the isocyanate compound (B) described below and impart cohesive strength, thereby significantly improving heat resistance and moist heat resistance.

[0030] The monomer (a-2) is preferably contained in an amount of 0.2 to 2% by mass, more preferably 0.4 to 1.5% by mass, based on 100% by mass of the monomer mixture. A content of 0.2% by mass or more can impart sufficient cohesiveness and improve heat resistance and moist heat resistance. Furthermore, a content of 2% by mass or less can maintain heat resistance and moist heat resistance.

[0031] [Monomer (a-3)] Monomer (a-3) is a monomer that forms a chelate crosslink with a metal compound, and examples thereof include carboxyl group-containing monomers and monomers containing α-hydrogen in the molecule. Here, α-hydrogen refers to a hydrogen bonded to the carbon adjacent to the carbonyl group. Specific examples include carboxyl group-containing monomers such as (meth)acrylic acid, p-carboxybenzyl acrylate, β-carboxyethyl acrylate, maleic acid, monoethyl maleate, itaconic acid, citraconic acid, and fumaric acid; and monomers containing α-hydrogen in the molecule such as acetylmethyl (meth)acrylate, propionylmethyl (meth)acrylate, 2-oxopropyl (meth)acrylate, oxobutyl (meth)acrylate, 2-butyrylethyl (meth)acrylate, 4-oxohexyl (meth)acrylate, and acetoacetoxyethyl (meth)acrylate. Among these monomers (a-3), (meth)acrylic acid and acetoacetoxyethyl (meth)acrylate are preferred because they are particularly capable of imparting cohesion, thereby improving winding properties.

[0032] The acrylic copolymer (A) contains the monomer (a-3), which gives the copolymer a substituent in the side chain that forms a crosslink with a metal compound, thereby forming a crosslinked structure with the metal compound (C) described below and imparting cohesive force, thereby significantly improving winding properties.

[0033] The content of monomer (a-3) is preferably 0.2 to 5% by mass, more preferably 0.5 to 3% by mass, based on 100% by mass of the monomer mixture. A content of 0.2% by mass or more can impart sufficient cohesion and improve winding properties. Furthermore, a content of 5% by mass or less can maintain winding properties.

[0034] [Monomer (a-4)] Monomer (a-4) is a monomer other than monomers (a-1), (a-2), and (a-3). Examples of monomer (a-4) include (meth)acrylic acid alkyl ester monomers other than monomer (a-1), monomers having an epoxy group, monomers having an amino group, monomers having an alkyleneoxy group, and vinyl monomers. In terms of compatibility with monomer (a-1), (meth)acrylic acid alkyl ester monomers other than monomer (a-1) are preferred.

[0035] Examples of (meth)acrylic acid alkyl ester monomers other than monomer (a-1) include (meth)acrylic acid alkyl ester monomers having an alkyl group of 1 to 7 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, and heptyl (meth)acrylate, and (meth)acrylic acid alkyl ester monomers having an alkyl group of 13 or more carbon atoms, such as octadecyl (meth)acrylate.

[0036] Examples of the monomer having an epoxy group include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, and 6-methyl-3,4-epoxycyclohexylmethyl (meth)acrylate.

[0037] Examples of the monomer having an amino group include (meth)acrylic acid monoalkylamino esters such as monomethylaminoethyl (meth)acrylate, monoethylaminoethyl (meth)acrylate, monomethylaminopropyl (meth)acrylate, and monoethylaminopropyl (meth)acrylate.

[0038] Examples of the monomer having an alkyleneoxy group include a monomer represented by the following general formula (1) and a monomer represented by the following general formula (2).

[0039]

[0040]

[0041] In the general formula (1) and the general formula (2), R １ , R ２ are each independently a hydrogen atom or a methyl group, n and m are integers representing a repeating unit, and 1≦n≦25, 1≦m≦25, preferably 1≦n≦13, 1≦m≦5.

[0042] Commercially available products of the monomer represented by the general formula (1) include, for example, methoxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.; in the above formula (1), R １ is a hydrogen atom, n=1), methoxydiethylene glycol acrylate (Osaka Organic Chemical Industry Co., Ltd.: in the above formula (1), R １ is a hydrogen atom, n=2), methoxytriethylene glycol acrylate (Osaka Organic Chemical Industry Co., Ltd.: in the above formula (1), R １ is a hydrogen atom, n=3), methoxypolyethylene glycol #400 acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.; in the above formula (1), R １ is a hydrogen atom, n=9), methoxypolyethylene glycol #600 acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.; in the above formula (1), R １ is a hydrogen atom, n=13), methoxypolyethylene glycol #1000 acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.; in the above formula (1), R １ is a hydrogen atom, n=23), methoxydiethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R １ is a methyl group, n=2), methoxytriethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R １ is a methyl group, n=3), methoxytetraethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.; in the above formula (1), R １ is a methyl group, n=4), methoxypolyethylene glycol #400 methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.; in the above formula (1), R １ is a hydrogen atom, n=9), methoxypolyethylene glycol #600 methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.; in the above formula (1), R １is a hydrogen atom, n=13), methoxypolyethylene glycol #1000 methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.; in the above formula (1), R １ is a hydrogen atom, n=23).

[0043] Commercially available products of the monomer represented by the general formula (2) include, for example, methoxytripropylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.; in the above formula (2), R １ is a hydrogen atom, m=3), methoxytripropylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (2), R １ is a methyl group, m = 3)

[0044] Examples of the vinyl monomer include vinyl acetate, vinyl crotonate, styrene, and acrylonitrile.

[0045] When the monomer mixture contains the monomer (a-4), the monomer mixture preferably contains 100% by mass, and more preferably 5 to 40% by mass. When the content is 5% by mass or more, the cohesive strength is further improved. When the content is 40% by mass or less, the adhesion is further improved.

[0046] [Production of Acrylic Copolymer (A)] The copolymer (A) can be produced by polymerizing a monomer mixture. Although known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization are possible, solution polymerization is preferred. Examples of solvents used in solution polymerization include acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, and cyclohexanone. The polymerization temperature is preferably a boiling point reaction at 60 to 120°C. The polymerization time is preferably about 5 to 12 hours.

[0047] The polymerization initiator used in the polymerization is preferably a radical polymerization initiator. Radical polymerization initiators are generally peroxides and azo compounds. Examples of peroxides include dialkyl peroxides such as di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, and 2,5-di(t-butylperoxy)hexyne-3; peroxy esters such as t-butyl peroxybenzoate, t-butyl peroxyacetate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, and methylcyclohexanone peroxide; Examples of the peroxyketals include 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and n-butyl-4,4-bis(t-butylperoxy)valerate; hydroperoxides such as cumene hydroperoxide, diisopropylbenzene hydroperoxide, and 2,5-dimethylcyclohexane-2,5-dihydroperoxide; diacyl peroxides such as benzoyl peroxide, decanoyl peroxide, lauroyl peroxide, and 2,4-dichlorobenzoyl peroxide; and peroxydicarbonates such as bis(t-butylcyclohexyl)peroxydicarbonate.

[0048] Examples of the azo compound include 2,2'-azobisbutyronitrile such as 2,2'-azobisisobutyronitrile (abbreviation: AIBN) and 2,2'-azobis(2-methylbutyronitrile); 2,2'-azobisvaleronitrile such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile); 2,2'-azobispropionitrile such as 2,2'-azobis(2-hydroxymethylpropionitrile); and 1,1'-azobis-1-alkanenitrile such as 1,1'-azobis(cyclohexane-1-carbonitrile).

[0049] The polymerization initiator is preferably used in an amount of 0.01 to 10 parts by mass, more preferably 0.1 to 2 parts by mass, based on 100 parts by mass of the monomer mixture.

[0050] [Weight average molecular weight (Mw)] The weight average molecular weight of the acrylic copolymer (A) is preferably 600,000 to 1,800,000, and more preferably 800,000 to 1,200,000. When it is in the range of 600,000 to 1,800,000, the cohesive strength is further improved, and the moist heat resistance and heat resistance are further improved. Specific methods for measuring the weight average molecular weight are described in the Examples section.

[0051] <Isocyanate Compound (B)> The isocyanate compound (B) can impart cohesive strength to the pressure-sensitive adhesive layer by reacting with the hydroxyl group of the copolymer (A), thereby highly improving flexibility.

[0052] The isocyanate compound (B) is an isocyanate having two or more isocyanate groups. Examples of the isocyanate compound include isocyanate monomers such as aromatic polyisocyanates, aliphatic polyisocyanates, araliphatic polyisocyanates, and alicyclic polyisocyanates, as well as biuret, nurate, and adduct forms thereof.

[0053] Examples of aromatic polyisocyanates include 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, and 4,4',4"-triphenylmethane triisocyanate.

[0054] Examples of aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (also known as HMDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0055] Examples of the aromatic aliphatic polyisocyanate include ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate.

[0056] Examples of alicyclic polyisocyanates include 3-isocyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI, isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanatemethyl)cyclohexane.

[0057] The biuret compound is a self-condensation product having a biuret bond formed by self-condensation of an isocyanate monomer, such as a biuret compound of hexamethylene diisocyanate.

[0058] The nurate derivative is a trimer of an isocyanate monomer, such as a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, or a trimer of tolylene diisocyanate.

[0059] The adduct is a bifunctional or higher isocyanate compound obtained by reacting an isocyanate monomer with a bifunctional or higher low-molecular-weight active hydrogen-containing compound. Examples of the adduct include a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with tolylene diisocyanate, a compound obtained by reacting trimethylolpropane with xylylene diisocyanate, a compound obtained by reacting trimethylolpropane with isophorone diisocyanate, and a compound obtained by reacting 1,6-hexanediol with hexamethylene diisocyanate.

[0060] The isocyanate compound (B) is preferably a trifunctional isocyanate compound from the viewpoint of forming a sufficient crosslinked structure. The isocyanate compound is more preferably an adduct or nurate, which is a reaction product of an isocyanate monomer and a trifunctional low-molecular-weight active hydrogen-containing compound. Specifically, the isocyanate compound is preferably a trimethylolpropane adduct of hexamethylene diisocyanate, a nurate of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, a nurate of tolylene diisocyanate, a trimethylolpropane adduct of isophorone diisocyanate, or a nurate of isophorone diisocyanate, and more preferably a trimethylolpropane adduct of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, or a trimethylolpropane adduct of isophorone diisocyanate. Among these, a trimethylolpropane adduct of tolylene diisocyanate and a nurate of tolylene diisocyanate are preferred from the viewpoint of flexibility.

[0061] The isocyanate compound (B) is preferably contained in an amount of 0.5 to 5% by mass, more preferably 0.5 to 3% by mass, relative to 100% by mass of the copolymer (A). A content of 0.5% by mass or more can impart cohesive strength and highly improve flexibility. Furthermore, a content of 5% by mass or less can maintain flexibility. Furthermore, the ratio (NCO / OH) of the number of moles of isocyanate groups contained in the isocyanate compound (B) to the number of moles of hydroxyl groups contained in the acrylic copolymer (A) is preferably 0.5 to 3, more preferably 0.5 to 2. A ratio of 0.5 or more can achieve sufficient cohesive strength, while a ratio of 3 or less is preferred because it facilitates achieving both cohesive strength and flexibility. Typically, pressure-sensitive adhesives used in image display devices use isocyanate compounds to impart cohesive strength. However, to prevent a decrease in adhesion due to crosslinking, it is common to use only small amounts of isocyanate compounds (approximately 0.4 or less in terms of molar ratio). For this reason, it may be difficult to achieve both high levels of flexibility and windability. On the other hand, in the pressure-sensitive adhesive of the present disclosure, even when a large amount of an isocyanate compound is used, a decrease in adhesion can be suppressed, and therefore, both flexibility and windability due to crosslinking can be achieved at a high level.

[0062] <Metal chelate compound (C)> The metal chelate compound (C) reacts with a substituent that forms a crosslink with a metal compound contained in the copolymer (A), thereby improving the cohesive force of the pressure-sensitive adhesive layer and imparting cohesive force, thereby highly improving winding properties.

[0063] Examples of the metal chelate compound (C) include the coordination compound of polyvalent metals such as aluminum, iron, copper, zinc, titanium, nickel, magnesium, and zirconium with acetylacetone or ethyl acetoacetate. Examples of the metal compound include aluminum ethyl acetoacetate diisopropylate, aluminum trisacetylacetonate, aluminum bisethyl acetoacetate monoacetylacetonate, aluminum alkyl acetoacetate diisopropylate, iron trisacetylacetonate, copper bisacetylacetonate, zinc bisacetylacetonate, titanium tetraacetylacetonate, nickel bisacetylacetonate, magnesium bisacetylacetonate, and zirconium tetraacetylacetonate. Among these metal chelate compounds (C), aluminum compounds and zinc compounds are preferred from the viewpoint of cohesive strength and coloring, and aluminum ethyl acetoacetate diisopropylate, aluminum trisacetylacetonate, and zinc bisacetylacetonate are more preferred.

[0064] The metal chelate compound (C) is preferably contained in an amount of 0.2 to 2% by mass, more preferably 0.2 to 1.5% by mass, based on 100% by mass of the copolymer (A). A content of 0.2% by mass or more can impart cohesive strength and significantly improve winding properties. Furthermore, a content of 2% by mass or less can maintain winding properties.

[0065] The pressure-sensitive adhesive of the present disclosure may further contain a crosslinking agent (D) other than the compounds (B) and (C). The inclusion of the crosslinking agent (D) can improve durability. Examples of the crosslinking agent (D) include an epoxy compound, an aziridine compound, and a carbodiimide compound.

[0066] Examples of epoxy compounds include glycerin diglycidyl ether, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidylaminophenylmethane.

[0067] Examples of the aziridine compound include N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxite), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane, and 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate].

[0068] The carbodiimide compound is preferably a high-molecular-weight polycarbodiimide produced by a decarboxylation condensation reaction of a diisocyanate compound in the presence of a carbodiimidization catalyst. Commercially available high-molecular-weight polycarbodiimides are preferably the Carbodilite series manufactured by Nisshinbo Industries, Inc. Among these, Carbodilite V-03, 07, and 09 are preferred due to their excellent compatibility with organic solvents.

[0069] The content of the other crosslinking agent (D) is preferably 0.05 to 2% by mass, and more preferably 0.1 to 1% by mass, based on 100% by mass of the copolymer (A). When the content is 0.05% by mass or more, the cohesive strength is further improved, and when it is 2% by mass or less, the adhesion is further improved.

[0070] <Organic Silane Compound> The pressure-sensitive adhesive of the present disclosure can further contain an organic silane compound. By containing an organic silane, adhesion to an adherend can be improved. Examples of the organic silane compound include alkoxysilane compounds having a (meth)acryloxy group, such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropyltripropoxysilane, 3-(meth)acryloxypropyltributoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane; alkoxysilane compounds having a vinyl group, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinylmethyldimethoxysilane, and vinylmethyldiethoxysilane; Alkoxysilane compounds having an amino group such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltripropoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane; alkoxysilane compounds having a mercapto group such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltripropoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylmethyldiethoxysilane; alkoxysilane compounds having an epoxy group, such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyltripropoxysilane, 3-glycidoxypropyltributoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane;Tetraalkoxysilane compounds such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane; 3-chloropropyltrimethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, styryltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate, 3-isocyanatepropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, hexamethyldisilazane, and silicone resins having an alkoxysilyl group in the molecule;

[0071] The organic silane compound is preferably used in an amount of 0.01 to 2.0% by mass, more preferably 0.05 to 1.0% by mass, based on 100% by mass of the copolymer (A).

[0072] The pressure-sensitive adhesive of the present disclosure may contain various resins, oils, softeners, dyes, pigments, antioxidants, UV absorbers, weather stabilizers, plasticizers, fillers, antioxidants, antistatic agents, and the like as optional components, as long as the problem can be solved.

[0073] <<Properties of Pressure-Sensitive Adhesive>> A cured product of the pressure-sensitive adhesive of the present disclosure satisfies all of the following (1) to (3): (1) 3.0 × 10 ４ Pa<G'(-20)<4.0×10 ５ Pa (2) 5<G'(-20) / G'(200)<17 (3) 2<tan δ(-20) / tan δ(200)<6.5 In the above formula, G'(-20) represents the storage modulus at -20°C and 1 Hz. G'(200) represents the storage modulus at 200°C and 1 Hz. tan δ(-20) represents the loss tangent at -20°C and 1 Hz. tan δ(200) represents the loss tangent at 200°C and 1 Hz.

[0074] <Storage Modulus and Loss Factor> The storage modulus and loss factor of a pressure-sensitive adhesive are determined by viscoelasticity measurement at a frequency of 1 Hz. The storage modulus corresponds to the energy stored as elastic energy when a material deforms, and is an index of hardness. In other words, the higher the storage modulus value, the harder the pressure-sensitive adhesive, and the lower the storage modulus value, the softer it is. The loss factor is the value obtained by dividing the loss modulus, which corresponds to the energy diffused to the outside as loss energy when a material deforms, by the storage modulus, and a higher loss factor indicates higher stress relaxation properties. Details of the measurement method are described in the Examples section.

[0075] The cured product of the pressure-sensitive adhesive of the present disclosure has a storage modulus at −20° C. and 1 Hz (hereinafter sometimes abbreviated as G′(−20)) of 3.0×10 ４ Pa<G'(-20)<4.0×10 ５ Pa, 3.0 × 10 ４ Pa<G'(-20)<3.0×10 ５ It is preferable that G'(-20) is 3.0 x 10 ４ When G'(-20) is greater than 4×10 Pa, the rigidity in a low temperature environment is improved, and the flexibility and windability are improved. ５ When the modulus is smaller than Pa, the adhesiveness is improved, and the flexibility and windability are improved.

[0076] Furthermore, in the cured product of the pressure-sensitive adhesive of the present disclosure, the storage modulus at -20°C and 1 Hz (hereinafter sometimes abbreviated as G'(-20)) divided by the storage modulus at 200°C and 1 Hz (hereinafter sometimes abbreviated as G'(200)) is preferably such that G'(-20) / G'(200) is 5 < G'(-20) / G'(200) < 17, and such that G'(-20) / G'(200) is 5 < G'(-20) / G'(200) < 15. When G'(-20) / G'(200) is greater than 5, rigidity in low-temperature environments is improved, and when G'(-20) / G'(200) is less than 17, cohesion in high-temperature environments is improved, thereby imparting durability.

[0077] Furthermore, in the cured product of the pressure-sensitive adhesive of the present disclosure, tan δ(-20) / tan δ(200), which is the value obtained by dividing the loss factor at -20°C and 1 Hz (hereinafter sometimes abbreviated as tan δ(-20)) by the loss factor at 200°C and 1 Hz (hereinafter sometimes abbreviated as tan δ(200)), preferably satisfies the following relationship: 2 < tan δ(-20) / tan δ(200) < 6.5, and 2 < tan δ(-20) / tan δ(200) < 5. When tan δ(-20) / tan δ(200) is greater than 2, stress relaxation properties in low-temperature environments are improved, and when tan δ(-20) / tan δ(200) is less than 6.5, flexibility in high-temperature environments is improved, thereby imparting adhesion.

[0078] The cured product of the pressure-sensitive adhesive of the present disclosure has a storage modulus and loss factor within specific ranges, thereby exhibiting the flexibility required for foldable displays and the winding ability required for rollable displays.

[0079] <Gel Fraction> The cured product of the pressure-sensitive adhesive of the present disclosure preferably has a gel fraction of 60 to 90% by mass, more preferably 60 to 80% by mass. A gel fraction of 60% by mass or more improves the cohesive strength of the pressure-sensitive adhesive, resulting in a tough pressure-sensitive adhesive layer and improved durability, while a gel fraction of 90% by mass or less improves the stress relaxation properties of the pressure-sensitive adhesive, resulting in a flexible pressure-sensitive adhesive layer and improved adhesion.

[0080] [Method for Measuring Gel Fraction] The gel fraction can be determined as the amount of insoluble matter in a solvent such as ethyl acetate. Specifically, as represented by the following formula 1, the gel fraction is determined as the mass fraction (unit: mass%) of the insoluble matter after immersing a pressure-sensitive adhesive layer in ethyl acetate at 50°C for one day relative to the pressure-sensitive adhesive layer before immersion. (Formula 1) Gel fraction (mass%) = (Y / X) x 100 X = mass (g) of the pressure-sensitive adhesive layer before immersion Y = mass (g) of the pressure-sensitive adhesive layer after immersion Generally, the gel fraction of a polymer is equal to the degree of crosslinking, and the more crosslinked portions in the polymer, the higher the gel fraction. The gel fraction (amount of crosslinked structure introduced) can be adjusted to a desired range by the method for introducing the crosslinked structure, the type and amount of curing agent, etc.

[0081] "Adhesive Sheet" The adhesive sheet of the present disclosure is an adhesive sheet that is suitably used to form an adhesive layer in a laminate consisting of a light-transmitting substrate and an adhesive layer, i.e., the adhesive sheet of the present disclosure is suitably used to bond light-transmitting substrates. Figure 1 shows an example of a schematic cross-sectional view partially illustrating the adhesive sheet of the present disclosure. In Figure 1, 1 is an adhesive layer 1, and 2 is a release film.

[0082] As shown in FIG. 1 , the pressure-sensitive adhesive sheet of the present disclosure has a configuration in which release films are formed on both sides of a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer sandwiched between the release films is a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive of the present disclosure, which contains an acrylic copolymer (A), an isocyanate compound (B), and a metal compound (C).

[0083] <Release Film> The release film is not particularly limited, but a transparent plastic substrate can be suitably used. Examples of materials for the transparent plastic substrate include polyesters such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), and plastic materials such as polycarbonate, triacetyl cellulose, polysulfone, polyarylate, and polycycloolefin. The plastic materials can be used alone or in combination of two or more.

[0084] As the release film, among the above-mentioned transparent plastic substrates, a transparent plastic substrate having excellent heat resistance, i.e., a transparent plastic substrate that is suppressed or prevented from deforming under severe conditions such as high temperature, high temperature and high humidity, etc. PET film or sheet is particularly suitable as the transparent plastic substrate.

[0085] The thickness of the transparent plastic substrate is not particularly limited, but is preferably, for example, 10 to 200 μm, and more preferably 25 to 150 μm.

[0086] The release film may have either a single layer or multiple layers. The surface of the transparent substrate may be subjected to an appropriate surface treatment, for example, a physical treatment such as corona discharge treatment or plasma treatment, or a chemical treatment such as a primer treatment.

[0087] <Production of Pressure-Sensitive Adhesive Sheet> The pressure-sensitive adhesive sheet of the present disclosure can be produced according to a typical pressure-sensitive adhesive sheet production method. For example, it can be produced by a method in which a pressure-sensitive adhesive is applied to the release-treated surface of a release film so that the thickness after application is a predetermined thickness, dried to form a pressure-sensitive adhesive layer, and then a release film is attached, or a method in which a pressure-sensitive adhesive is applied to the release-treated surfaces of two release films so that the thickness after application is a predetermined thickness, dried to form two pressure-sensitive adhesive layers, and then each pressure-sensitive adhesive layer is attached.

[0088] The drying conditions can be set depending on the blending and thickness of the raw material composition, the types and amounts of the organic peroxide and curing agent, and the like, and can be, for example, 3 minutes in an atmosphere of 90 to 110°C.

[0089] The thickness of the pressure-sensitive adhesive layer is not particularly limited, and is preferably 10 to 500 μm, more preferably 50 to 200 μm, for example. When the thickness of the pressure-sensitive adhesive layer is 10 to 500 μm, sufficient cohesive strength is easily obtained, and high levels of heat resistance, moist heat resistance, flexibility, and windability can be achieved at the same time, which is preferable.

[0090] When applying the adhesive, a conventional coater such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, or spray coater can be used.

[0091] The pressure-sensitive adhesive sheet may be in the form of a rolled pressure-sensitive adhesive tape, which is obtained by cutting the sheet to a suitable width and winding it into a roll.

[0092] "Laminate" The laminate of the present disclosure comprises a light-transmitting substrate, a pressure-sensitive adhesive layer, and a polarizing plate, and the pressure-sensitive adhesive layer is formed from a cured product of the pressure-sensitive adhesive of the present disclosure.

[0093] The laminate of the present disclosure is formed from a pressure-sensitive adhesive sheet that has excellent transparency, heat resistance, moist heat resistance, flexibility, and windability, and therefore has excellent transparency, heat resistance, moist heat resistance, flexibility, and windability.

[0094] An example of a schematic cross-sectional view partially illustrating a laminate, which is an example of use of the pressure-sensitive adhesive sheet of the present disclosure, is shown in Figure 2. In Figure 2, 3 is a light-transmitting substrate (cover panel), 1 is a pressure-sensitive adhesive layer, and 1 and 4 are polarizing plates.

[0095] In the laminate shown in Fig. 2, a light-transmitting substrate (cover panel) is attached to a polarizing plate via a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive of the present disclosure. In this way, the pressure-sensitive adhesive sheet of the present disclosure can be used in a form in which a transparent pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive is attached to the light-transmitting substrate (cover panel) and the polarizing plate.

[0096] The light-transmitting substrate (cover panel) is not particularly limited, but a transparent plastic substrate can be suitably used. Examples of materials for the transparent plastic substrate include acrylic resins such as polyethylene terephthalate (PET) and polymethyl methacrylate (PMMA), and plastic materials such as polycarbonate, polycycloolefin, and polyimide. The plastic materials can be used alone or in combination of two or more.

[0097] As the light-transmitting substrate (cover panel), among the above-mentioned transparent plastic substrates, a transparent plastic substrate having excellent heat resistance, i.e., a transparent plastic substrate that is suppressed or prevented from deforming under severe conditions such as high temperature, high temperature and high humidity, etc. Polyethylene terephthalate (PET), polycycloolefin, and polyimide are particularly suitable as transparent plastic substrates.

[0098] The thickness of the light-transmitting substrate (cover panel) is not particularly limited, but is preferably, for example, 100 to 2000 μm, and more preferably 200 to 1000 μm.

[0099] "Display" A display includes the laminate of the present disclosure and an optical element. The optical element is not particularly limited, and examples thereof include a liquid crystal element and an organic EL element.

[0100] The display of the present disclosure has a laminate that is excellent in transparency, heat resistance, moist heat resistance, flexibility and windability, and is therefore excellent in transparency, heat resistance, moist heat resistance, flexibility and windability.

[0101] Figure 3 shows an example of a schematic cross-sectional view partially illustrating a display, which is an example of use of the pressure-sensitive adhesive sheet of the present disclosure. In Figure 3, 3 is a light-transmitting substrate (cover panel), 1 is pressure-sensitive adhesive layer 1, 4 is a polarizing plate, 5 is pressure-sensitive adhesive layer 2, 6 is a barrier layer such as silicon nitride, 7 is an organic EL layer, 8 is a support such as polyimide, and 9 is an organic EL cell. It should be noted that the configuration of the display is not limited to that shown in Figure 3.

[0102] In the display shown in FIG. 3 , a light-transmitting substrate (cover panel) is attached to a polarizing plate via a pressure-sensitive adhesive layer (pressure-sensitive adhesive layer 1) made of the pressure-sensitive adhesive of the present disclosure, and is further attached to an organic EL cell via a pressure-sensitive adhesive layer for the polarizing plate (pressure-sensitive adhesive layer 2). In this way, the pressure-sensitive adhesive sheet of the present disclosure can be used in a form in which a transparent pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive is attached to the light-transmitting substrate (cover panel) and the polarizing plate, and the laminate is further attached to the organic EL cell via the pressure-sensitive adhesive layer for the polarizing plate. For example, in FIG. 3 , the pressure-sensitive adhesive of the present disclosure can be used for both pressure-sensitive adhesive layer 1 and pressure-sensitive adhesive layer 2. Generally, when pressure-sensitive adhesive layer 1 and pressure-sensitive adhesive layer 2 are compared, the pressure-sensitive adhesive layer 1 has higher quality requirements, while the pressure-sensitive adhesive of the present disclosure is preferably used for pressure-sensitive adhesive layer 1 because of its excellent adhesion and bondability to the substrate. In this case, the pressure-sensitive adhesive for forming pressure-sensitive adhesive layer 2 may be the pressure-sensitive adhesive of the present disclosure or a conventionally known pressure-sensitive adhesive.

[0103] The uses of the display are not particularly limited, but examples include organic EL televisions, organic EL smartphones, organic EL tablets, and organic EL smart watches.

[0104] Next, further details will be explained with reference to examples, but the present disclosure is not limited thereto. In the examples, unless otherwise specified, "parts" means "parts by mass", "%" means "% by mass", and "RH" means relative humidity. The blending amounts in the tables are in parts by mass. Note that blank spaces in the tables indicate that no blending was performed. Note that the methods for measuring the weight average molecular weight of the acrylic copolymer (A) and the storage modulus and loss factor of the pressure-sensitive adhesive are as follows.

[0105] <Measurement of Weight Average Molecular Weight> The weight average molecular weight (Mw) of the acrylic copolymer (A) can be measured using a GPC "LC-GPC system" manufactured by Shimadzu Corporation, and the weight average molecular weight (Mw) can be determined by conversion using polystyrene of known molecular weight as a standard substance. Apparatus name: LC-GPC system "Prominence" manufactured by Shimadzu Corporation Column: Four GMHXL columns manufactured by Tosoh Corporation and one HXL-H column manufactured by Tosoh Corporation were connected together. Mobile phase solvent: tetrahydrofuran Flow rate: 1.0 ml / min Column temperature: 40°C

[0106] <Measurement of storage modulus and loss factor> The storage modulus is measured by using a measurement sample made by laminating the cured pressure-sensitive adhesive to a thickness of approximately 1.0 mm and performing viscoelasticity measurement under the following conditions using a "Discovery HR-2 (DHR-2)" manufactured by TA Instrument-Waters LLC. From the measurement results, the storage modulus and loss factor at 0°C and 150°C can be read. (Measurement conditions) Deformation mode: torsion Measurement frequency: 1 Hz Heating rate: 10°C / min Jig shape: parallel plate 8.0 mmφ

[0107] <Production Example of Acrylic Copolymer (A)> (Copolymer (A-1)) A reaction vessel (hereinafter simply referred to as the "reaction vessel") equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen inlet tube was charged with 18 parts of 2-ethylhexyl acrylate (EHA) as monomer (a-1), 1 part of 2-hydroxyethyl acrylate (HEA) as monomer (a-2), 1 part of acrylic acid as monomer (a-3), 80 parts of butyl acrylate as monomer (a-4), and 0.2 parts of 2,2'-azobisisobutyronitrile (hereinafter simply referred to as "AIBN") as an initiator, and the atmosphere in the reaction vessel was replaced with nitrogen gas. Thereafter, the mixture was heated to 60°C while stirring under a nitrogen atmosphere to initiate the reaction. Thereafter, the reaction solution was reacted at 60°C for 4 hours. After completion of the reaction, the mixture was cooled and diluted with ethyl acetate to obtain a copolymer (A-1) solution with a non-volatile content of 30%. The weight average molecular weight of the resulting copolymer (A-1) was 1,200,000.

[0108] (Copolymers (A-2 to A-12, A'-1 to A'-3)) Copolymers (A-2 to A-10, A'-1 to A'-3) were produced in the same manner as in the production of acrylic copolymer (A-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Table 1.

[0109] The weight average molecular weights (Mw) of the resulting copolymers (A-1 to 12, A'-1 to 3) are shown in Table 1.

[0110]

[0111] The abbreviations in the table are as follows: (Monomer (a-1)) EHA: 2-ethylhexyl acrylate (alkyl group has 8 carbon atoms) nOA: n-octyl acrylate (alkyl group has 8 carbon atoms) DOA: dodecyl acrylate (alkyl group has 12 carbon atoms) (Monomer (a-2)) HEA: 2-hydroxyethyl acrylate HEMA: 2-hydroxyethyl methacrylate (Monomer (a-3)) AA: acrylic acid AAEM: acetoacetoxyethyl methacrylate (Monomer (a-4)) BA: butyl acrylate (alkyl group has 4 carbon atoms) MA: methyl acrylate (alkyl group has 1 carbon atom)

[0112] Example 1 Preparation of Pressure-Sensitive Adhesive 100 parts of the nonvolatile content of the acrylic copolymer (A-1) were blended with 1.2 parts of a trimethylolpropane adduct of tolylene diisocyanate (TDITMP) as the isocyanate compound (B) and 1 part of aluminum ethyl acetoacetate diisopropylate (ALEADI) as the metal compound (C), and the mixture was stirred to obtain a pressure-sensitive adhesive.

[0113] <Production of Pressure-Sensitive Adhesive Sheet> The obtained pressure-sensitive adhesive was coated onto a 50 μm-thick release film (polyethylene terephthalate (PET), "E7004", silicone-based release layer, manufactured by Toyobo Co., Ltd.) so that the thickness after drying would be 50 μm, and the coated film was dried at 100°C for 3 minutes to form a pressure-sensitive adhesive layer. Next, one side of a 38 μm-thick release film (polyethylene terephthalate, "SP-PET3811", silicone-based release layer, manufactured by Lintec Corporation) was bonded to this pressure-sensitive adhesive layer to produce a "release sheet / pressure-sensitive adhesive layer / release sheet" laminate. The obtained laminate was then aged for 3 days in a 40°C environment to obtain a pressure-sensitive adhesive sheet.

[0114] Examples 2 to 18, Comparative Examples 1 to 12 As shown in Tables 2 and 3, pressure-sensitive adhesive sheets were obtained in the same manner as in Example 1, except that the types and blending amounts (parts by mass) of the copolymer and curing agent were changed.

[0115]

[0116]

[0117] The abbreviations in the table are as follows: <Isocyanate compounds (B)> TDITMP: trimethylolpropane adduct of tolylene diisocyanate TDIIN: nurate of tolylene diisocyanate HDITMP: trimethylolpropane adduct of hexamethylene diisocyanate <Metal chelate compounds (C)> ALEADI: aluminum ethyl acetoacetate diisopropylate ALTAA: aluminum trisacetylacetonate ZNBAA: zinc bisacetylacetonate <Other crosslinks (D)> TGXDA: N,N,N',N'-tetraglycidyl-m-xylylenediamine HMBTAP: 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate] <Organic silane compounds> GPTMS: 3-glycidoxypropyltrimethoxysilane

[0118] <<Measurement and Evaluation of Physical Properties of Pressure-Sensitive Adhesive Sheet>> Using the obtained pressure-sensitive adhesive sheet, the storage modulus and loss factor were measured, and G'(-20), G'(-20) / G'(200), and tan δ(-20) / tan δ(200) were calculated. The gel fraction, transparency, heat resistance, moist heat resistance, dynamic flex resistance, static flex resistance, and windability were evaluated using the following methods. The results are shown in Tables 2, 3, and 4.

[0119] <Gel Fraction> The obtained pressure-sensitive adhesive sheet was cut into a size of 25 mm wide x 100 mm long. One release film was peeled off from the cut pressure-sensitive adhesive sheet, and the sheet was attached to a 200 mesh sheet measuring 50 mm wide x 120 mm long, the mass of which had been measured in advance. Next, the other release film was peeled off, and the mesh was folded so that the adhesive was facing inward to prevent the adhesive from being exposed. The pressure-sensitive adhesive wrapped in the mesh was immersed in approximately 50 mL of ethyl acetate at 50°C for 1 day, allowing the sol component of the pressure-sensitive adhesive to elute out of the mesh. After immersion, the pressure-sensitive adhesive wrapped in the mesh was removed, dried at 100°C for 1 hour, and allowed to cool for approximately 20 minutes, after which the dry mass was measured. The gel fraction of the pressure-sensitive adhesive was calculated using the following formula: Gel Fraction (mass%) = (Y / X) x 100, where X = mass (g) of the pressure-sensitive adhesive layer before immersion and Y = mass (g) of the pressure-sensitive adhesive layer after immersion.

[0120] <Preparation of Test Pressure-Sensitive Adhesive Sheet> The 38 μm-thick release film was peeled off from the obtained pressure-sensitive adhesive sheet, and the exposed pressure-sensitive adhesive layer was attached to a 50 μm-thick PET film (T60, manufactured by Toray Industries, Inc.) using a laminator in an atmosphere of 23° C. and 50% RH to prepare a test pressure-sensitive adhesive sheet consisting of PET film / pressure-sensitive adhesive layer / release film.

[0121] <Transparency> The test pressure-sensitive adhesive sheet was cut into a size of 112 mm wide x 200 mm long (equivalent to a 9-inch display). The release film was peeled off from the cut test pressure-sensitive adhesive sheet, and the exposed pressure-sensitive adhesive layer was attached to an alkali-free glass plate (EN-A1: manufactured by Asahi Glass Co., Ltd.) using a laminator in an atmosphere of 25°C and 50% RH, and the haze was measured. The haze was measured using a Turbidimeter NDH5000W manufactured by Nippon Denshoku Industries Co., Ltd. The evaluation criteria were as follows. [Evaluation criteria] ○: Haze is less than 1.0 (good). ×: Haze is 1.0 or more (poor).

[0122] <Heat Resistance and Moist Heat Resistance> The release film was peeled off from a separately prepared test pressure-sensitive adhesive sheet, and the exposed pressure-sensitive adhesive layer was attached to a polarizing plate (layer structure: triacetyl cellulose film / polyvinyl alcohol film / cycloolefin film) using a laminator in an atmosphere of 25°C and 50% RH to obtain a test laminate consisting of PET film / pressure-sensitive adhesive layer / polarizing plate. Next, as a heat resistance test, the test laminate was left at 105°C for 500 hours, cooled in an atmosphere of 25°C and 50% RH, and then visually evaluated for bubble formation and lifting and peeling of the test laminate under the following conditions. Furthermore, as an evaluation of moist heat resistance, the test laminate was left at 60°C and 95% RH for 500 hours, cooled in an atmosphere of 25°C and 50% RH, and then visually evaluated for bubble formation and lifting and peeling of the pressure-sensitive adhesive sheet under the following conditions. Heat resistance and moist heat resistance were evaluated based on the following three-level evaluation criteria. [Evaluation criteria] ⊚: No bubbles, lifting or peeling are observed, and there is no practical problem. ○: Bubbles, lifting or peeling are observed in less than 5 places, but there is no practical problem. ×: Bubbles, lifting or peeling are observed in 5 or more places, and there is a practical problem.

[0123] <Dynamic Flex Resistance: Flex Resistance [1], [2], [3]> The release film was peeled off from a separately prepared test pressure-sensitive adhesive sheet, and the exposed pressure-sensitive adhesive layer was attached to a polarizing plate (layer structure: triacetyl cellulose film / polyvinyl alcohol film / cycloolefin film) using a laminator at 25°C and 50% RH to obtain a test laminate consisting of a PET film / pressure-sensitive adhesive layer / polarizing plate. The test laminate was then subjected to a normal test (flex resistance [1]) at 25°C and 50% RH, a heat resistance test (flex resistance [2]) at 85°C, and a moist heat resistance test (flex resistance [3]) at 60°C and 95% RH. The conditions were set so that the inner diameter (diameter) when bent was 6 mm using a bending tester (manufactured by Yuasa System Co., Ltd.), and 300,000 cycles were repeated, with one cycle consisting of bending and 180° release. Dynamic flex resistance was evaluated based on the appearance after the test from the following perspectives. Appearance: The test laminate was visually evaluated for the presence or absence of bubbles and the presence or absence of lifting or peeling of the pressure-sensitive adhesive layer under the following conditions. [Evaluation criteria] ⊚: No bubbles, lifting, or peeling was observed, and there was no practical problem. ○: There were bubbles, lifting, or peeling in less than five places, but there was no practical problem. ×: There were bubbles, lifting, or peeling in five or more places, and there was a practical problem.

[0124] <Static Bending Resistance: Bending Resistance [1], [2], [3]> The release film was peeled off from a separately prepared test pressure-sensitive adhesive sheet, and the exposed pressure-sensitive adhesive layer was attached to a polarizing plate (layer structure: triacetyl cellulose film / polyvinyl alcohol film / cycloolefin film) using a laminator at 25°C and 50% RH to obtain a test laminate consisting of a PET film / pressure-sensitive adhesive layer / polarizing plate. The test laminate was then subjected to a normal test (bending resistance [1]) at 25°C and 50% RH, a heat resistance test (bending resistance [2]) at 85°C, and a moist heat resistance test (bending resistance [3]) at 60°C and 95% RH. The test specimen was held in a bent state with a bending radius of 3 mm and a bending angle of 180° for 240 hours using a planar body no-load U-shaped stretch tester, with the polarizing plate side facing inward. Static bending resistance was evaluated based on the appearance after the test, according to the following criteria. Appearance: The test laminate was visually evaluated for the presence or absence of bubbles and the presence or absence of lifting or peeling of the pressure-sensitive adhesive layer under the following conditions. [Evaluation criteria] ⊚: No bubbles, lifting, or peeling was observed, and there was no practical problem. ○: There were bubbles, lifting, or peeling in less than five places, but there was no practical problem. ×: There were bubbles, lifting, or peeling in five or more places, and there was a practical problem.

[0125] <Windability> The release film was peeled off from a separately prepared test pressure-sensitive adhesive sheet, and the exposed pressure-sensitive adhesive layer was attached to a polarizing plate (layer structure: triacetyl cellulose film / polyvinyl alcohol film / cycloolefin film) using a laminator in an atmosphere of 25°C and 50% RH to obtain a test laminate consisting of PET film / pressure-sensitive adhesive layer / polarizing plate. The test laminate was then wound around a metal rod with a radius of 3 mm, with the PET side of the test piece facing inward, in the longitudinal direction to form a roll, and then secured in place with three ties using string. For the winding test, the rolled test laminate was kept in an atmosphere of 25°C and 50% RH for 240 hours. The windability was evaluated by the appearance after the test based on the following criteria. Appearance: The test laminate was visually evaluated for the presence or absence of bubbles and the presence or absence of lifting or peeling of the pressure-sensitive adhesive layer under the following conditions. [Evaluation Criteria] ⊚: No bubbles, lifting, or peeling were observed, and there were no practical problems. ◯: Air bubbles, lifting, or peeling is observed in less than 5 places, but there is no practical problem. ×: Air bubbles, lifting, or peeling is observed in 5 or more places, and there is a practical problem.

[0126]

[0127] The abbreviations in the table are as follows: Layer structure of test pressure-sensitive adhesive sheet and test laminate [A]: PET film / pressure-sensitive adhesive layer / glass [B]: PET film / pressure-sensitive adhesive layer / polarizing plate Test conditions Bending resistance [1]: 25°C, 50% RH atmosphere Bending resistance [2]: 85°C atmosphere Bending resistance [3]: 60°C, 95% RH atmosphere

[0128] The results in Table 4 confirm that the pressure-sensitive adhesive sheets of Examples 1 to 18 were excellent in transparency, heat resistance, moist heat resistance, flexibility, and windability. This demonstrates that laminates and displays using pressure-sensitive adhesive sheets according to the present disclosure are excellent in transparency, heat resistance, moist heat resistance, and flexibility. Furthermore, displays according to the present disclosure also had excellent visibility and contrast. On the other hand, the pressure-sensitive adhesive sheets of Comparative Examples 1 to 12 were unable to satisfy all of the above properties.

[0129] Although the present invention has been described with reference to the above-mentioned several embodiments, the present invention is not limited to these several embodiments. Various modifications can be made to the configuration and details of the present invention within the scope of the present invention.

[0130] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-188434 filed on November 2, 2023, and the subject matter described in Japanese Patent Application No. 2024-108589 filed on July 5, 2024, the entire disclosures of which are incorporated herein by reference.

[0131] REFERENCE SIGNS LIST 1 Pressure-sensitive adhesive layer 1, 2 Release film, 3 Light-transmitting substrate (cover panel), 4 Polarizing plate, 5 Pressure-sensitive adhesive layer 2, 6 Barrier layer, 7 Organic EL layer, 8 Support, 9 Organic EL cell

Claims

1. An adhesive comprising an acrylic copolymer (A), an isocyanate compound (B) and a metal chelate compound (C), wherein the acrylic copolymer (A) is a copolymer of a monomer mixture containing the following monomers (a-1), (a-2) and (a-3), and wherein the adhesive after curing satisfies all of the following (1) to (3): (a-1) a (meth)acrylic acid alkyl ester monomer having an alkyl group with 8 to 12 carbon atoms; (a-2) a monomer having a hydroxyl group; (a-3) a monomer that forms a chelate crosslink with a metal compound; (1) 3.0 x 10 ４ Pa<G'(-20)<4.0×10 ５ Pa (2) 5<G'(-20) / G'(200)<17 (3) 2<tan δ(-20) / tan δ(200)<6.5 In the above formula, G'(-20) is the storage modulus at -20°C and 1 Hz. G'(200) is the storage modulus at 200°C and 1 Hz. tan δ(-20) is the loss tangent at -20°C and 1 Hz. tan δ(200) is the loss tangent at 200°C and 1 Hz.

2. The pressure-sensitive adhesive according to claim 1, wherein the acrylic copolymer (A) contains, based on 100% by mass of the monomer mixture, 20 to 98% by mass of monomer (a-1), 0.2 to 2% by mass of monomer (a-2), and 0.2 to 5% by mass of monomer (a-3).

3. The pressure-sensitive adhesive according to claim 1, comprising 0.5 to 5 mass% of an isocyanate compound (B) and 0.2 to 2 mass% of a metal chelate compound (C) relative to 100 mass% of the acrylic copolymer (A).

4. The adhesive according to claim 1, wherein the gel fraction of the adhesive after curing is 60 to 90 mass %.

5. An adhesive sheet comprising an adhesive layer, which is a cured product of the adhesive according to any one of claims 1 to 4, sandwiched between release films.

6. A laminate comprising a light-transmitting substrate, an adhesive layer, and a polarizing plate, the adhesive layer being a cured product of the adhesive according to any one of claims 1 to 4.

7. A display comprising the laminate according to claim 6 and an optical element.

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