Adhesive, adhesive sheet, laminate, and flexible display

Abstract

To provide an adhesive and an adhesive sheet having excellent transparency and also having heat resistance and moisture heat resistance and capable of achieving both flexibility and windability.SOLUTION: There is provided an adhesive which contains an acrylic copolymer (A) comprising a (meth)acrylic acid alkyl ester monomer having an alkyl group having 1 to 4 carbon atoms, a (meth)acrylic acid alkyl ester monomer having an alkyl group having 6 to 12 carbon atoms, a monomer having a hydroxyl group and a monomer having a carboxy group, a tackifier resin (B) which is a saturated aliphatic hydrocarbon compound having at least one alicyclic structure in the molecule and a curing agent (C). The storage modulus of the adhesive at -20°C, 25°C and 60°C at 1 Hz is 1×105 to 1×106 Pa, 4×104 to 1×105 Pa and 1×104 to 4×104 Pa, respectively. The loss modulus at 1 Hz of the adhesive at -20°C and 60°C is 1.0 to 3.0 and 0.2 to 1.0, respectively.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive for forming a laminate including a support film, a pressure-sensitive adhesive layer, and a metal plate, a pressure-sensitive adhesive sheet, and a laminate having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive sheet. The laminate is used for a flexible display. [Background technology]

[0002] In recent years, input devices that combine an image display device such as a liquid crystal display (LCD) or an organic electroluminescence (organic EL) display (OLED) with a touch panel have become widespread. The transparent conductive film used in the touch panel is laminated to a member such as a support glass or a display film via an adhesive layer. In addition, the polarizing plate film used in the image device is attached to the liquid crystal module or the organic EL module via an adhesive layer. In this way, each member of the image display device is attached and fixed by the adhesive layer.

[0003] Flat displays using glass substrates have been mainstream as image display devices, but 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 having better designability.

[0004] In such flexible displays, the flexible organic EL used is thin to provide foldability and rollability, and to reinforce the strength of the flexible organic EL, a back plate comprising a support film, an adhesive layer, a metal plate, an adhesive layer, and a support film in that order is attached to the bottom of the organic EL via the adhesive layer. 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, flexibility has also become necessary. For example, in the case of a foldable display, flexibility refers to the suitability (flexibility) of the display to accommodate bending so that it can be used in the foldable display. Generally, flexibility requires a property (dynamic flexibility) that does not cause foaming, lifting, or peeling when repeatedly bent.

[0005] In order to solve these problems, Patent Document 1 discloses a pressure-sensitive adhesive sheet containing a resin syrup produced by partial polymerization of a (meth)acrylate monomer and a photoinitiator, in which the storage modulus of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is 1.0 × 10 at 25°C and 1 Hz. 6 ~1.0×10 7 Patent Document 2 discloses an optically transparent adhesive sheet characterized by the fact that the adhesive is Pa. Patent Document 2 also discloses an adhesive containing a styrene-isobutylene-styrene (SIBS) rubber, an alicyclic epoxy compound, and a photoinitiator. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2020-517800 [Patent Document 2] Patent Publication No. 2021-14563 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in recent years, in order to respond to the ever-increasing durability of displays, stricter flexibility is required than ever before, and in addition to dynamic flexibility, properties that do not cause bubbling, lifting, or peeling when maintained in a bent state for a long period of time (static flexibility) are also required. Furthermore, for rollable displays, suitability for winding up the display (windability) is required so that it can be used in rollable displays. Generally, windability requires properties that do not cause bubbling, lifting, or peeling when maintained in a rolled state for a long period of time.

[0008] Furthermore, while previously this flexibility was a required quality only at room temperature, with the spread of flexible displays, flexibility in low-temperature environments such as those in extremely cold regions, as well as in 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 to this, conventional pressure-sensitive adhesive sheets currently do not satisfy the requirements for heat resistance and moist heat resistance at levels that are practically acceptable, and flexibility such as bendability and windability. Furthermore, flexibility requires dynamic bending, static bending, and rollability depending on the display configuration. Although it is possible to satisfy these flexibility requirements individually, it is difficult to satisfy them all at the same time. In addition, the current situation is that dynamic bending, static bending, and rollability cannot be satisfied in high-temperature environments or high-temperature, high-humidity environments.

[0010] An object of the present invention is to provide a pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, a laminate thereof, and a flexible display that are excellent in transparency and can achieve all of heat resistance, moist heat resistance, flexibility, and windability. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have found that the problems of the present invention can be solved in the following aspects. The present invention has been completed based on the findings. That is, the present invention provides a composition comprising an acrylic copolymer (A), a tackifier resin (B), and a curing agent (C), The acrylic copolymer (A) is a copolymer of a monomer mixture containing all of the following monomers (a-1) to (a-4): The tackifier resin (B) is a saturated aliphatic hydrocarbon compound having at least one alicyclic structure in the molecule, and The problems are solved by a pressure-sensitive adhesive which satisfies all of the following (1) to (8): (a-1) (Meth)acrylic acid alkyl ester monomers having an alkyl group containing 1 to 4 carbon atoms (a-2) (Meth)acrylic acid alkyl ester monomers having an alkyl group with 6 to 12 carbon atoms (a-3) Monomers having a hydroxyl group (a-4) Monomers having a carboxy group (1) In 100% by mass of the monomer mixture, the mass % of (a-1) is less than the mass % of (a-2). (2) In 100% by mass of the monomer mixture, the value (a-3) / (a-4) obtained by dividing the mass% of (a-3) by the mass% of (a-4) is 0.01<(a-3) / (a-4)<6 (3) The total mass% of (a-1) and (a-2) is greater than the total mass% of (a-3) and (a-4) in 100% by mass of the monomer mixture. (4) The storage modulus of the adhesive at -20°C and 1 Hz is 1 x 10 5 ~1×10 6 Pa (5) The storage modulus of the adhesive at 25°C and 1 Hz is 4 x 10 4 ~1×10 5 Pa (6) The storage modulus of the adhesive at 60°C and 1 Hz is 1 x 10 4 ~4×10 4 Pa (7) The loss coefficient of the adhesive at -20°C and 1 Hz is 1.0 to 3.0 (8) The loss coefficient of the adhesive at 60°C and 1 Hz is 0.2 to 1.0 [Effects of the Invention]

[0012] The present invention 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 can further achieve heat resistance, moist heat resistance, flexibility, and windability. Furthermore, by using the pressure-sensitive adhesive sheet and laminate of the present invention, a flexible display with excellent visibility and contrast can be provided. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view partially illustrating the pressure-sensitive adhesive sheet (for constituting a back plate) of the present invention. [Figure 2] 1 is a schematic cross-sectional view partially illustrating the pressure-sensitive adhesive sheet (for fixing a back plate) of the present invention. [Figure 3] FIG. 1 is a schematic cross-sectional view partially illustrating a laminate (back plate), which is an example of the use of the pressure-sensitive adhesive sheet of the present invention. [Figure 4] FIG. 1 is a schematic cross-sectional view partially illustrating a display, which is an example of the use of the pressure-sensitive adhesive sheet of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Examples of the configurations of the pressure-sensitive adhesive, pressure-sensitive adhesive sheet, laminate, and display of the present invention will be described below, but the present invention is not limited to these.

[0015] The terms used in this specification are defined below. (Meth)acrylic acid ester includes acrylic acid ester and methacrylic acid ester. Monomer is an ethylenically unsaturated group-containing monomer. Adherend refers to the object to which the pressure-sensitive adhesive sheet is attached. In the present invention, sheet, film, and tape are synonymous terms. In addition, in this specification, (a-1) the (meth)acrylic acid alkyl ester monomer having 1 to 4 carbon atoms, (a-2) the (meth)acrylic acid alkyl ester monomer having 6 to 12 carbon atoms, (a-3) the monomer having a hydroxyl group, (a-4) the monomer having a carboxy group, and the acrylic copolymer (A) may be abbreviated as monomer (a-1), monomer (a-2), monomer (a-3), monomer (a-4), monomer (a-5), and copolymer (A), respectively. Unless otherwise noted, the various components appearing in this specification may be used independently either alone or in combination of two or more.

[0016] In this specification, a numerical range specified using "to" is intended to include the numerical values ​​before and after "to" as the range's lower and upper limits.

[0017] "Adhesive" The pressure-sensitive adhesive of the present invention comprises an acrylic copolymer (A), a tackifier resin (B), and a curing agent (C), The acrylic copolymer (A) is a copolymer of a monomer mixture containing all of the following monomers (a-1) to (a-4): The tackifier resin (B) is a saturated aliphatic hydrocarbon compound having at least one alicyclic structure in the molecule, and Meet all of the following (1) to (8). (a-1) (Meth)acrylic acid alkyl ester monomer having 1 to 4 carbon atoms (a-2) (Meth)acrylic acid alkyl ester monomer having 6 to 12 carbon atoms (a-3) Monomers having a hydroxyl group (a-4) Monomers having a carboxy group (1) In 100% by mass of the monomer mixture, the mass % of (a-1) is less than the mass % of (a-2). (2) In 100% by mass of the monomer mixture, the value (a-3) / (a-4) obtained by dividing the mass% of (a-3) by the mass% of (a-4) is 0.01<(a-3) / (a-4)<6 (3) The total mass% of (a-1) and (a-2) is greater than the total mass% of (a-3) and (a-4) in 100% by mass of the monomer mixture. (4) The storage modulus at -20°C and 1 Hz is 1×10 5 ~1×10 6 Pa (5) The reservoir elastic modulus at 25°C and 1 Hz is 4 x 10 4 ~1×10 5 Pa (6) The elastic modulus of the reservoir at 60°C and 1 Hz is 1 x 10 4 ~4×10 4 Pa (7) Loss factor at -20℃ and 1Hz is 1.0 to 3.0 (8) Loss factor at 60℃ and 1Hz is 0.2 to 1.0

[0018] <Acrylic copolymer (A)> The acrylic copolymer (A) is a copolymer of a monomer mixture containing at least all of the monomers (a-1) to (a-4), and the monomer mixture may contain the monomer (a-5) as needed. (a-1) (Meth)acrylic acid alkyl ester monomer having an alkyl group with 1 to 4 carbon atoms (a-2) (Meth)acrylic acid alkyl ester monomers having an alkyl group with 6 to 12 carbon atoms (a-3) Monomers having a hydroxyl group (a-4) Monomers having a carboxy group (a-5) Other monomers other than (a-1) to (a-4)

[0019] [Monomer (a-1)] Monomer (a-1) is a (meth)acrylic acid alkyl ester monomer having an alkyl group having 1 to 4 carbon atoms in the molecule, and specific examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and t-butyl (meth)acrylate. By including the monomer (a-1), the cohesive strength of the pressure-sensitive adhesive is improved, a strong pressure-sensitive adhesive layer is obtained, and adhesive strength can be improved. Of these monomers (a-1), methyl (meth)acrylate and butyl (meth)acrylate are preferred from the viewpoint of cohesive strength and adhesive strength.

[0020] The content of the monomer (a-1) is preferably 2 to 40% by mass, more preferably 5 to 30% by mass, based on 100% of the monomer mixture. A content of 2% by mass or more makes it easier to obtain sufficient cohesive strength. A content of 40% by mass or less is also preferred, as it makes it easier to achieve both cohesive strength and stress relaxation properties.

[0021] [Monomer (a-2)] Monomer (a-2) is a (meth)acrylic acid alkyl ester monomer having an alkyl group having 6 to 12 carbon atoms in the molecule, and specific examples thereof include isohexyl (meth)acrylate, heptyl (meth)acrylate, 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. By including the monomer (a-2), the stress relaxation property of the pressure-sensitive adhesive is improved, a flexible pressure-sensitive adhesive layer is obtained, and adhesion strength can be improved. Of these monomers (a-2), 2-ethylhexyl (meth)acrylate and dodecyl (meth)acrylate are preferred from the viewpoints of stress relaxation and adhesive strength.

[0022] These monomers (a-2) can be used alone or in combination of two or more. In particular, it is more preferable to use two or more types of monomers (a-2) in combination from the viewpoint of achieving both adhesiveness and cohesive strength.

[0023] The monomer (a-2) is preferably contained in an amount of 50 to 98% by mass, more preferably 60 to 90% by mass, based on 100% by mass of the monomer mixture. A content of 50% by mass or more is likely to provide sufficient stress relaxation properties. A content of 98% by mass or less is also preferred, as it facilitates achieving both cohesive strength and stress relaxation properties.

[0024] [Monomer (a-3)] The monomer (a-3) is a monomer having a hydroxyl group. The monomer having a hydroxyl group is not limited as long as it has a hydroxyl group in the molecule, and specific examples include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, allyl alcohol, and 3-butene-1-ol. By including the monomer (a-3), the cohesive strength of the pressure-sensitive adhesive is improved, a strong pressure-sensitive adhesive layer is obtained, and adhesive strength can be improved. Of these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred from the viewpoint of cohesive strength and adhesive strength.

[0025] The monomer (a-3) is preferably contained in an amount of 0.01 to 4.0% by mass, more preferably 0.04 to 2.0% by mass, relative to 100% by mass of the monomer mixture. A content of 0.01% by mass or more facilitates obtaining sufficient cohesive strength. A content of 4.0% by mass or less is also preferred, as it facilitates achieving both cohesive strength and stress relaxation properties.

[0026] [Monomer (a-4)] The monomer (a-4) is a monomer having a carboxy group. The carboxy group-containing monomer is not limited as long as it is a monomer having a carboxy group in the molecule, and specific examples include (meth)acrylic acid, p-carboxybenzyl acrylate, β-carboxyethyl acrylate, maleic acid, monoethyl maleate, itaconic acid, citraconic acid, and fumaric acid. By including the monomer (a-4), the cohesive strength of the pressure-sensitive adhesive is improved, a strong pressure-sensitive adhesive layer is obtained, and adhesive strength can be improved. Of these, (meth)acrylic acid is preferred from the viewpoint of cohesive strength and adhesive strength.

[0027] The monomer (a-4) is preferably contained in an amount of 0.1 to 5.0 mass%, more preferably 0.2 to 4.0 mass%, relative to 100 mass% of the monomer mixture. A content of 0.1 mass% or more makes it easier to obtain sufficient cohesive strength. A content of 5.0 mass% or less is also preferred, as it makes it easier to achieve both cohesive strength and stress relaxation properties.

[0028] [Monomer (a-5)] The monomer (a-5) is a monomer other than the monomers (a-1) to (a-4), and the acrylic copolymer (A) of the present invention may further contain the monomer (a-5) in addition to the monomers (a-1) to (a-4). Examples of the monomer (a-5) include (meth)acrylic acid alkyl ester monomers other than the monomers (a-1) to (a-4), (meth)acrylic acid monomers having an epoxy group, (meth)acrylic acid monomers having an amino group, monomers having an alkyleneoxy group, N-substituted (meth)acrylamide monomers, and other vinyl monomers.

[0029] Examples of the (meth)acrylic acid alkyl ester monomer other than the monomers (a-1) to (a-4) include pentyl (meth)acrylate and undecyl (meth)acrylate.

[0030] Examples of the monomer having an epoxy group include glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, and 6-methyl-3,4-epoxycyclohexylmethyl (meth)acrylate.

[0031] 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.

[0032] 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).

[0033] [ka]

[0034] [ka]

[0035] In general formula (1) and general formula (2), R1 and R2 each independently represent a hydrogen atom or a methyl group, n and m represent integers representing repeating units, and 1≦n≦25, 1≦m≦25, preferably 1≦n≦13, 1≦m≦5.

[0036] Commercially available products of the monomer represented by general formula (1) include, for example, methoxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.: in the above formula (1), R1 is a hydrogen atom, n=1), methoxydiethylene glycol acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.: in the above formula (1), R1 is a hydrogen atom, n=2), methoxytriethylene glycol acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.: in the above formula (1), R1 is a hydrogen atom, n=3), methoxypolyethylene glycol #400 acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R1 is a hydrogen atom, n=9), methoxypolyethylene glycol #600 acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R1 is a hydrogen atom, n=13), and methoxypolyethylene glycol #1000 acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R1 is a hydrogen atom, n=2). 3), methoxydiethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R1 is a methyl group, n=2), methoxytriethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R1 is a methyl group, n=3), methoxytetraethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R1 is a methyl group, n=4), methoxypolyethylene glycol #400 methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R1 is a hydrogen atom, n=9), methoxypolyethylene glycol #600 methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R1 is a hydrogen atom, n=13), and methoxypolyethylene glycol #1000 methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R1 is a hydrogen atom, n=23).

[0037] Commercially available products of the monomer represented by general formula (2) include, for example, methoxytripropylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (2), R1 is a hydrogen atom, m=3), and methoxytripropylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (2), R1 is a methyl group, m=3).

[0038] Examples of N-substituted (meth)acrylamide monomers include (meth)acrylamide-based compounds such as N-methylacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-dimethylaminopropyl(meth)acrylamide, diacetoneacrylamide, and N-(butoxymethyl)acrylamide; Examples include compounds containing a heterocycle such as N-vinylpyrrolidone, N-vinylcaprolactam, and acryloylmorpholine.

[0039] Examples of the vinyl monomer include vinyl acetate, vinyl crotonate, styrene, and acrylonitrile.

[0040] The monomer (a-5) preferably comprises 2 to 30% by mass of the monomer mixture, with the content being 100% by mass. When the content is 2% by mass or more, the adhesiveness is further improved. When the content is 30% by mass or less, it is easy to achieve both cohesive strength and adhesiveness, which is preferable.

[0041] The acrylic copolymer (A) satisfies the condition that the mass % of (a-1) is less than the mass % of (a-2) relative to 100 mass % of the monomer mixture constituting the acrylic copolymer (A). By satisfying the condition that the mass % of (a-1) is less than the mass % of (a-2), the stress relaxation property of the pressure-sensitive adhesive can be improved, thereby improving adhesion strength.

[0042] In the acrylic copolymer (A), the value (a-3) / (a-4), obtained by dividing the mass % of (a-3) by the mass % of (a-4) in 100 mass % of the (2) monomer mixture constituting the acrylic copolymer (A), satisfies 0.01 < (a-3) / (a-4) < 6. When 0.01 < (a-3) / (a-4) < 6, the cohesive strength of the pressure-sensitive adhesive is improved, thereby improving adhesive strength.

[0043] In the acrylic copolymer (A), the total mass % of (a-1) and (a-2) is greater than the total mass % of (a-3) and (a-4) in 100% by mass of the monomer mixture constituting the acrylic copolymer (A). By having the total mass % of (a-1) and (a-2) greater than the total mass % of (a-3) and (a-4), the stress relaxation property and cohesive strength of the pressure-sensitive adhesive can be improved, and flexibility can be improved.

[0044] [Production of acrylic copolymer (A)] The copolymer (A) can be produced by polymerizing a monomer mixture containing (a-1) to (a-4). The polymerization can be carried out by known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization, but solution polymerization is preferred. Preferred 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.

[0045] The polymerization initiator used for the polymerization is preferably a radical polymerization initiator, and the radical polymerization initiator is generally a peroxide or an azo compound. 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; Peroxyesters 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; Peroxyketals such as 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; Examples include peroxydicarbonates such as bis(t-butylcyclohexyl) peroxydicarbonate.

[0046] Examples of the azo compounds include 2,2'-azobisbutyronitriles such as 2,2'-azobisisobutyronitrile (abbreviation: AIBN) and 2,2'-azobis(2-methylbutyronitrile); 2,2'-azobisvaleronitriles such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and 2,2'-azobis(2,4-dimethylvaleronitrile); 2,2'-azobispropionitriles, such as 2,2'-azobis(2-hydroxymethylpropionitrile); Examples include 1,1'-azobis-1-alkanenitriles such as 1,1'-azobis(cyclohexane-1-carbonitrile).

[0047] 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.

[0048] [Mass average molecular weight (Mw)] The mass average molecular weight of the copolymer (A) is preferably 800,000 to 1,800,000, more preferably 1,000,000 to 1,500,000. When it is in the range of 800,000 to 1,800,000, the cohesive strength is further improved, and the moist heat resistance and heat resistance are further improved. The mass average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). Details are described in the Examples section.

[0049] <Tackifying resin (B)> The pressure-sensitive adhesive of the present invention contains a tackifier resin (B). The tackifier resin (B) of the present invention is a saturated aliphatic hydrocarbon compound having at least one alicyclic structure in the molecule. When a pressure-sensitive adhesive layer is formed, the tackifier (B) forms high-cohesion domains, thereby achieving the effect of exhibiting high cohesion and high adhesive strength. Furthermore, the presence of at least one alicyclic structure in the molecule improves compatibility with the acrylic polymer (A), allowing high transparency to be obtained and maintaining transparency even when exposed to a high-temperature, high-humidity environment.

[0050] Specific examples of the tackifier resin (B) include hydrogenated hydrocarbon resins such as hydrogenated petroleum resins and hydrogenated terpene resins, and alicyclic acrylic resins. Alicyclic acrylic resins refer to acrylic resins having at least one alicyclic structure in the molecule.

[0051] Examples of hydrogenated petroleum resins include C5 hydrogenated petroleum resins, C9 hydrogenated petroleum resins, C5 / C9 hydrogenated petroleum resins, and styrene hydrogenated petroleum resins. C5 hydrogenated petroleum resins are obtained by adding hydrogen atoms to the unsaturated double bonds of an aliphatic resin obtained by separating and purifying a C5 fraction obtained from petroleum naphtha. C9 hydrogenated petroleum resins are obtained by adding hydrogen atoms to the unsaturated double bonds of an aromatic resin obtained by separating and purifying a C9 fraction obtained from petroleum naphtha. C5 / C9 hydrogenated petroleum resins are obtained by adding hydrogen atoms to the unsaturated double bonds of an aromatic aliphatic resin obtained by separating, mixing, copolymerizing, and purifying a C5 fraction and a C9 fraction. Styrenic hydrogenated petroleum resins are obtained by adding hydrogen atoms to the unsaturated double bonds of a styrene resin obtained by separating, purifying, and polymerizing a styrene fraction obtained from petroleum naphtha.

[0052] The hydrogenated terpene resin is a general term for, for example, polyterpene resin, terpene phenol resin, aromatic terpene resin, etc., and hydrogen atoms are added to the unsaturated double bonds in these resins.

[0053] Examples of C5 hydrogenated petroleum resins include Eastac C100 and Eastac C115W (manufactured by Eastman Chemical Co.). Examples of C9 hydrogenated petroleum resins include Arkon P-90, Arkon P-100, Arkon P-125, Arkon P-140, Arkon M-90, Arkon M-115, and Arkon M-135 (manufactured by Arakawa Chemical Co.). Examples of C5 / C9 hydrogenated petroleum resins include Imave S-100, Imave S-110, Imave P-100, and Imave P-140 (manufactured by Idemitsu Kosan Co., Ltd.). Examples of styrene hydrogenated petroleum resins include FTR6100, FTR6110, FTR6125, FTR7080, FTR7100, and FTR7125 (manufactured by Mitsui Chemicals, Inc.). Examples of hydrogenated terpene resins include Clearon P-105, Clearon P-125, Clearon M-105, Clearon P-115, and YS Polystar TH130 (manufactured by Yasuhara Chemical Co., Ltd.).

[0054] Of these hydrogenated hydrocarbon resins, Eastac C100 is a C5 hydrogenated petroleum resin, Alcon M-90 is a C9 hydrogenated petroleum resin, and FTR6100 is a styrene hydrogenated petroleum resin, which are particularly preferred from the viewpoint of durability.

[0055] Examples of the alicyclic acrylic resin include those commercially available under the trade names VS-1028, VS-1029, ATF-2242, and ATF-2133 (manufactured by Seiko PMC Corporation), as well as (B-1 to B-3) described in the Examples below.

[0056] Of these alicyclic acrylic resins, VS-1028, ATF-2242, and (B-1 to B-3) are particularly preferable from the viewpoint of durability.

[0057] The alicyclic acrylic resin can be produced by polymerizing a monomer mixture containing an alicyclic monomer. The polymerization method and polymerization initiator described in the section on production of the acrylic copolymer (A) can be used.

[0058] Examples of the alicyclic monomer include acrylates having an alicyclic structure, such as isobornyl acrylate, cyclohexyl acrylate, dicyclopentanyl acrylate, cyclododecyl acrylate, methylcyclohexyl acrylate, and trimethylcyclohexyl acrylate; Examples thereof include methacrylic acid esters having an alicyclic structure such as isobornyl methacrylate, cyclohexyl methacrylate, dicyclopentanyl methacrylate, cyclododecyl methacrylate, methylcyclohexyl methacrylate, and trimethylcyclohexyl methacrylate.

[0059] Among these alicyclic monomers, isobornyl acrylate, cyclohexyl acrylate, and isobornyl methacrylate are preferred from the viewpoints of substrate adhesion and durability in a high-temperature atmosphere or a high-temperature, high-humidity atmosphere. The alicyclic monomers can be used alone or in combination of two or more.

[0060] The alicyclic monomer preferably accounts for 40 to 90% by weight, more preferably 60 to 90% by weight, of the 100% by weight of the monomer mixture. A content of 5% by weight or more further improves adhesion to substrates. Furthermore, a content of 40% by weight or less achieves high levels of both cohesive strength and stress relaxation.

[0061] These tackifier resins (B) can be used alone or in combination of two or more.

[0062] The tackifier resin (B) is preferably contained in an amount of 2 to 50 parts by mass, more preferably 5 to 30 parts by mass, per 100 parts by mass of the copolymer (A). When the content is 2 parts by mass or more, heat resistance and adhesion are further improved, and when it is 50 parts by mass or less, adhesive performance can be maintained.

[0063] <Curing agent (C)> The pressure-sensitive adhesive of the present invention contains a curing agent (C), which reacts with the hydroxyl groups and / or carboxyl groups of the copolymer (A) to improve the cohesive strength of the pressure-sensitive adhesive layer, thereby improving durability and stain resistance.

[0064] Examples of the curing agent (C) include an isocyanate compound, an epoxy compound, an aziridine compound, a carbodiimide compound, and a metal chelate. Among these, it is preferable to use an isocyanate compound as the curing agent (C) since this can improve adhesiveness and durability.

[0065] The isocyanate compound is an isocyanate having two or more isocyanate groups. Preferred 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] From the viewpoint of forming a sufficient crosslinked structure, the isocyanate compound is preferably a trifunctional isocyanate compound. 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. 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.

[0074] 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.

[0075] Examples of the aziridine compound include N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxite), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, and 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane.

[0076] The carbodiimide compound is preferably a high-molecular-weight polycarbodiimide produced by decarboxylation condensation of a diisocyanate compound in the presence of a carbodiimide catalyst. Commercially available high-molecular-weight polycarbodiimides are preferably the Carbodilite series from Nisshinbo Industries, Inc. Among these, Carbodilite V-03, 07, and 09 are preferred due to their excellent compatibility with organic solvents.

[0077] Preferred metal chelates are coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium with acetylacetone or ethyl acetoacetate. Examples of metal chelates include aluminum ethyl acetoacetate diisopropylate, aluminum trisacetylacetonate, aluminum bisethyl acetoacetate monoacetylacetonate, and aluminum alkyl acetoacetate diisopropylate.

[0078] The curing agent (C) is preferably contained in an amount of 0.02 to 4.0 parts by mass, more preferably 0.04 to 1.0 part by mass, per 100 parts by mass of the copolymer (A). A content of 0.02 part by mass or more further improves the cohesive strength, and a content of 4.0 parts by mass or less is preferred because it is easier to achieve both cohesive strength and flexibility.

[0079] <Organosilane compounds> The pressure-sensitive adhesive of the present invention may further contain an organosilane compound. 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; Examples include 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 alkoxysilyl groups in the molecule.

[0080] The organosilane compound is preferably used in an amount of 0.01 to 2.0 parts by mass, more preferably 0.05 to 1.0 part by mass, per 100 parts by mass of the copolymer (A).

[0081] The pressure-sensitive adhesive of the present invention may contain various resins, oils, softeners, dyes, pigments, antioxidants, ultraviolet absorbers, weather stabilizers, plasticizers, fillers, antioxidants, antistatic agents, and the like as optional components, as long as the problem can be solved.

[0082] <Storage modulus and loss tangent> The storage modulus and loss tangent of a pressure-sensitive adhesive are determined by viscoelasticity measurement at a frequency of 1 Hz. The loss tangent is the ratio of the storage modulus to the loss modulus, or loss modulus / storage modulus. The storage modulus corresponds to the portion of the material that is stored as elastic energy when it deforms, and is an index of the degree 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. Details of the measurement method are described in the Examples section.

[0083] The loss modulus corresponds to the portion of energy lost due to internal friction when a material deforms, and indicates the degree of viscosity. The larger the loss factor, expressed as the ratio of storage modulus to loss modulus, or loss modulus / storage modulus, the more viscous the material tends to be, the more liquid-like the deformation behavior becomes, and the smaller the rebound resilience tends to be. In other words, the higher the loss tangent, the greater the stress relaxation ability of the adhesive, and the lower the storage modulus, the greater the rigidity of the adhesive.

[0084] <Storage modulus> The pressure-sensitive adhesive for flexible displays of the present invention has a storage modulus at −20° C. and 1 Hz (hereinafter sometimes abbreviated as G′(−20)) of 1×10 5 ~1×10 6 Pa, 2 x 10 5 ~9×10 5 It is more preferable that G'(-20) is 1×10 Pa. 5 When G'(-20) is 1×10 Pa or more, the stiffness in a low temperature environment is improved, and the flexibility and windability are improved. 6 When the viscosity is not more than 1 Pa, the adhesiveness is improved, and the flexibility and winding properties are improved.

[0085] The pressure-sensitive adhesive for flexible displays of the present invention has a storage modulus at 25°C and 1 Hz (hereinafter sometimes abbreviated as G'(25)) of 4 x 10 4 ~1×10 5 Pa, 4 x 10 4 ~8×10 4 It is more preferable that G'(25) is 4×10 Pa. 4 When G'(25) is 1×10 Pa or more, the workability is improved. 5 When it is not more than Pa, the adhesive strength is improved.

[0086] The pressure-sensitive adhesive for flexible displays of the present invention has a storage modulus at 60°C and 1 Hz (hereinafter sometimes abbreviated as G'(60)) of 1 x 10 4 ~4×10 4 Pa, 2 x 10 4 ~4×10 4Pa. G'(60) is preferably 1×10 4 When G'(60) is 4×10 Pa or more, the rigidity in a high temperature environment is improved, and the flexibility and windability are improved. 4 When the molecular weight is 100 Pa or less, flexibility in a high-temperature environment is improved, and bending property and winding property are improved.

[0087] <Loss tangent> The pressure-sensitive adhesive for flexible displays of the present invention has a loss tangent (hereinafter sometimes abbreviated as tan δ(-20)) at -20°C and 1 Hz of 1.0 to 3.0, and more preferably 1.0 to 2.5. Generally, polymer materials are subject to wear and breakage when subjected to physical deformation such as bending or winding. After extensive research, the inventors have found that tan δ(-20) is correlated with the coating strength of the pressure-sensitive adhesive under physical deformation. That is, when tan δ(-20) is 1.0 or more, stress relaxation upon application of physical deformation is improved, and bending and winding properties are improved. When tan δ(-20) is 3.0 or less, rigidity upon application of physical deformation is improved, and bending and winding properties are improved.

[0088] The pressure-sensitive adhesive for flexible displays of the present invention has a loss tangent (hereinafter sometimes abbreviated as tan δ(60)) at 60°C and 1 Hz of 0.2 to 1.0, and more preferably 0.2 to 0.6. When tan δ(60) is 0.2 or more, stress relaxation in a low-temperature environment is improved, and bending and winding properties are improved. When tan δ(60) is 1.0 or less, rigidity in a low-temperature environment is improved, and bending and winding properties are improved.

[0089] The pressure-sensitive adhesive for flexible displays of the present invention has a storage modulus and loss tangent within specific ranges, thereby exhibiting the flexibility required for foldable displays and the winding properties required for rollable displays.

[0090] <Gel fraction> The pressure-sensitive adhesive for flexible displays of the present invention 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 strong 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.

[0091] [Gel fraction measurement method] 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, it is determined as the mass fraction (unit: mass%) of the insoluble matter after immersing the pressure-sensitive adhesive layer in ethyl acetate at 50°C for 1 day relative to the pressure-sensitive adhesive layer before immersion. (Formula 1) Gel fraction (mass%) = (Y / X) × 100 X = mass of adhesive layer before immersion (g) Y = mass of adhesive layer after immersion (g) 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 (the 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.

[0092] "Adhesive sheet" The pressure-sensitive adhesive sheet of the present invention is used to form the pressure-sensitive adhesive layer in a laminate (back plate) having a support film, a pressure-sensitive adhesive layer, a metal plate, a pressure-sensitive adhesive layer, and a support film in this order, i.e., the pressure-sensitive adhesive sheet of the present invention is used to bond the support film and the metal plate. An example of a schematic cross-sectional view partially illustrating the pressure-sensitive adhesive sheet (for use in a backplate) of the present invention is shown in Figure 1. In Figure 1, 1 is pressure-sensitive adhesive layer 1 or 2, 2 is a release film, and 3 is a support film. The pressure-sensitive adhesive of the present invention can be used for pressure-sensitive adhesive layer 1 or 2, and the same pressure-sensitive adhesive or different pressure-sensitive adhesives may be used for each.

[0093] As shown in Figure 1, the adhesive sheet (for backplate construction) of the present invention has a configuration in which a release film is formed on one side of an adhesive layer and a support film is formed on the other side of the release film, and the adhesive layer formed between the release film and the support film is an adhesive layer formed from the adhesive of the present invention.

[0094] The pressure-sensitive adhesive sheet of the present invention can also be used as a pressure-sensitive adhesive layer for fixing the back plate to the organic EL layer. An example of a schematic cross-sectional view partially illustrating the pressure-sensitive adhesive sheet (for fixing a backplate) of the present invention is shown in Figure 2. In Figure 2, 4 is a pressure-sensitive adhesive layer 3, and 2 is a release film.

[0095] As shown in Figure 2, the adhesive sheet (for fixing a backplate) of the present invention has a configuration in which release films are formed on both sides of an adhesive layer, and the adhesive layer formed between the release films is an adhesive layer formed from the adhesive of the present invention.

[0096] <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.

[0097] Among the transparent plastic substrates described above, 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., can be preferably used as the release film. As the transparent plastic substrate, a PET film or sheet is particularly preferred.

[0098] The thickness of the transparent plastic substrate is not particularly limited, and is, for example, preferably from 10 to 200 μm, more preferably from 25 to 150 μm.

[0099] 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 a corona discharge treatment or a plasma treatment, or a chemical treatment such as a primer treatment.

[0100] <Support film> The support film is not particularly limited, but a plastic substrate can be suitably used. Examples of the material for the 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.

[0101] Among the plastic substrates mentioned above, it is preferable to use a plastic substrate having excellent heat resistance, i.e., a plastic substrate that is suppressed or prevented from deforming under severe conditions such as high temperature, high temperature and high humidity, etc. As the support film, polyethylene terephthalate (PET), polycycloolefin, and polyimide are particularly preferable.

[0102] The thickness of the support film is not particularly limited, and is, for example, preferably 10 to 200 μm, more preferably 200 to 100 μm.

[0103] <Manufacturing of adhesive sheets> The pressure-sensitive adhesive sheet of the present invention can be produced by a conventional pressure-sensitive adhesive sheet production method. For example, the pressure-sensitive adhesive of the present invention (hereinafter sometimes simply referred to as "pressure-sensitive adhesive") can be directly applied to the release-treated surface of a release film so that the thickness after drying is a predetermined thickness to form a pressure-sensitive adhesive layer, and then a support film or a release film is attached to the pressure-sensitive adhesive layer, or the pressure-sensitive adhesive can be applied to the support film so that the thickness after drying is a predetermined thickness, and then the release-treated surface of the release film is attached to the pressure-sensitive adhesive layer.

[0104] The thickness of the adhesive layer is not particularly limited and is, for example, preferably 10 to 200 μm, more preferably 15 to 100 μm. When the thickness of the adhesive layer is 10 to 200 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.

[0105] 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.

[0106] 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.

[0107] "Laminate" The laminate (back plate) of the present invention comprises a support film, a pressure-sensitive adhesive layer, a metal plate, a pressure-sensitive adhesive layer, and a support film in this order, and the pressure-sensitive adhesive layer is formed using the pressure-sensitive adhesive sheet of the present invention.

[0108] The laminate of the present invention is formed from a pressure-sensitive adhesive sheet having excellent transparency, heat resistance, moist heat resistance, flexibility and windability, and therefore has excellent transparency, heat resistance, moist heat resistance, flexibility and windability.

[0109] An example of a schematic cross-sectional view partially illustrating a laminate (back plate), which is an example of the use of the pressure-sensitive adhesive of the present invention, is shown in Figure 3. In Figure 3, 3 is a support film, 1 is a pressure-sensitive adhesive layer 1, 5 is a metal plate, 1 is a pressure-sensitive adhesive layer 2, and 3 is a support film.

[0110] In the laminate shown in Fig. 3, a support film is attached to both sides of a metal plate via a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive of the present invention. In this way, the pressure-sensitive adhesive sheet of the present invention can be used in a form in which the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive is attached to the support film and the metal plate.

[0111] The metal plate is not particularly limited, but a metal substrate can be suitably used. Examples of the material for the metal substrate include pure metals such as copper, iron, lead, platinum, and aluminum, and alloy metal materials such as stainless steel.

[0112] As the metal plate, among the above-mentioned metal substrates, a metal substrate having excellent durability, i.e., a metal substrate in which deformation is suppressed or prevented under severe conditions such as high temperature, high temperature and high humidity, etc. Copper and stainless steel are particularly suitable as the metal substrate. "display" The display comprises the laminate of the present invention and an optical element. The optical element is not particularly limited, and examples thereof include a liquid crystal element and an organic EL element.

[0113] The display of the present invention has a laminate excellent in transparency, heat resistance, moist heat resistance, flexibility and winding ability, and is therefore excellent in transparency, heat resistance, moist heat resistance, flexibility and winding ability.

[0114] Fig. 4 shows an example of a schematic cross section partially illustrating a display, which is an example of the use of the pressure-sensitive adhesive sheet of the present invention. In Fig. 4, 6 is an organic EL module, 4 is a pressure-sensitive adhesive layer 3, 3 is a support film, 1 is a pressure-sensitive adhesive layer 1, 5 is a metal plate, 1 is a pressure-sensitive adhesive layer 2, 3 is a support film, 7 is a support, and 8 is a back plate. Note that the configuration of the display is not limited to that shown in Fig. 4.

[0115] In the display shown in Fig. 4, a support film is attached to both sides of a metal plate via adhesive layers (adhesive layers 1 and 2) made of the adhesive of the present invention, and is further attached to an organic EL module via an adhesive layer (adhesive layer 3) made of the adhesive of the present invention. In this way, the adhesive sheet of the present invention can be used in a form in which a laminate formed by adhesive layers made of the adhesive being attached to a support film and a metal plate is further attached to an organic EL module via an adhesive layer made of the adhesive. For example, in FIG. 4, the pressure-sensitive adhesive of the present invention can be used in any of pressure-sensitive adhesive layer 1, pressure-sensitive adhesive layer 2 and pressure-sensitive adhesive layer 3. Generally, when comparing adhesive layer 1, adhesive layer 2, and adhesive layer 3, the quality requirements for the adhesive layers are higher for adhesive layer 1 and adhesive layer 2, and the adhesive of the present invention has good adhesion and bondability to the substrate, so it is preferably used for adhesive layer 1 and adhesive layer 2. In this case, the adhesive for forming adhesive layer 3 may be the adhesive of the present invention, or a conventionally known adhesive may be used.

[0116] There are no particular limitations on the uses of the displays, but examples include OLED televisions, OLED smartphones, OLED tablets, and OLED smartwatches. [Example]

[0117] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these. 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. Blank spaces in the tables indicate that no ingredients were blended. The method for measuring the mass average molecular weight of the copolymer is as follows.

[0118] <Measurement of mass average molecular weight of copolymer> The mass average molecular weight (Mw) can be measured using a GPC "LC-GPC system" manufactured by Shimadzu Corporation, and the mass average molecular weight (Mw) can be determined by conversion using polystyrene of known molecular weight as a standard substance. Device name: Shimadzu Corporation, LC-GPC system "Prominence" Columns: 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: 1.0ml / min Column temperature: 40℃

[0119] <Production example of acrylic copolymer> (Acrylic copolymer (A-1)) A reaction vessel (hereafter simply referred to as the "reaction vessel") equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube was charged with 20 parts of butyl acrylate (BA) as monomer (a-1), 78.98 parts of 2-ethylhexyl acrylate (EHA) as monomer (a-2), 0.02 parts of 2-hydroxyethyl acrylate as monomer (a-3), 1 part of acrylic acid as monomer (a-4), and 0.2 parts of 2,2'-azobisisobutyronitrile (hereafter simply referred to as "AIBN") as an initiator. The atmosphere inside the reaction vessel was then replaced with nitrogen gas. The mixture was then heated to 50°C with stirring under a nitrogen atmosphere to initiate the reaction. The reaction solution was then reacted at 50°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 nonvolatile content of 30% and a viscosity of 8000 mPa·s. The resulting copolymer (A-1) had a mass average molecular weight of 1,000,000.

[0120] (Acrylic copolymers (A-2 to A-15, A'-1 to A'-8) Copolymers (A-2 to A-15, A'-1 to A'-8) were produced in the same manner as the production of acrylic copolymer (A-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Tables 1 and 2.

[0121] Tables 1 and 2 show the mass average molecular weights (Mw) of the resulting copolymers (A-1 to A-15, A'-1 to A'-8).

[0122] <Production example of alicyclic acrylic resin (tackifying resin)> (Alicyclic acrylic resin (B-1)) A reaction vessel (hereafter simply referred to as the "reaction vessel") equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube was charged with 20 parts of butyl acrylate, 80 parts of cyclohexyl acrylate, acrylic acid, 100 parts of toluene, 5 parts of thioglycerol, and 0.5 parts of 2,2'-azobisisobutyronitrile (hereafter referred to as AIBN). The air in the reaction vessel was then purged with nitrogen gas. The mixture was then heated to 110°C with stirring under a nitrogen atmosphere to initiate the reaction. The reaction solution was then allowed to react at reflux temperature for 7 hours. After completion of the reaction, the mixture was cooled and diluted with ethyl acetate to obtain an alicyclic acrylic resin (B-1) solution with a nonvolatile content of 50% and a viscosity of 1000 mPa·s. The resulting alicyclic acrylic resin (B-1) had a mass-average molecular weight of 20,000.

[0123] (Alicyclic acrylic resins (B-2, B-3) and acrylic resin (B'-1)) Alicyclic acrylic resins (B-2, B-3) and acrylic resin (B'-1) were produced in the same manner as in the production of alicyclic acrylic resin (B-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Table 3.

[0124] Table 3 shows the mass average molecular weights (Mw) of the obtained alicyclic acrylic resins (B-1 to B-3) and acrylic resin (B'-1).

[0125] [Table 1] [Table 2] [Table 3]

[0126] The abbreviations in the table are as follows: (Monomer (a-1)) BA: Butyl acrylate (alkyl group carbon number: 4) MA: Methyl acrylate (alkyl group carbon number 1) (Monomer (a-2)) EHA: 2-ethylhexyl acrylate (alkyl group carbon number: 8) DOA: Dodecyl acrylate (alkyl group carbon number: 12) (Monomer (a-3)) HEA: 2-hydroxyethyl acrylate HBA: 4-hydroxybutyl acrylate (Monomer (a-4)) AA: acrylic acid MAA: methacrylic acid (Monomer (a-5)) MEA: 2-methoxyethyl acrylate (a monomer in which R1 is a hydrogen atom and n=1 in general formula (1)) NVP: N-vinylpyrrolidone (alicyclic monomer) CHA: Cyclohexyl acrylate IBXA: Isobornyl acrylate

[0127] Example 1 <Preparation of adhesive> For 100 parts of the nonvolatile content of the acrylic copolymer (A-1), 5 parts of an acrylic compound (B-1) was used as the tackifier resin (B), 0.5 parts of an adduct of tolylene diisocyanate and trimethylolpropane (C-1) was used as the curing agent (C), and 0.1 parts of 3-glycidoxypropyltrimethoxysilane (S-1) was used as the organic silane compound. Ethyl acetate was then added to the mixture to make the nonvolatile content 20%, and the mixture was stirred to obtain an adhesive.

[0128] <Manufacturing of adhesive sheets> (Manufacturing of adhesive sheets (Fig. 1)) The resulting adhesive was coated onto a 50 μm-thick release film (polyethylene terephthalate (PET), "E7004", silicone-based release layer, manufactured by Toyobo Co., Ltd.) to a dry thickness of 20 μm, and dried at 110°C for 3 minutes to form an adhesive layer. Next, one side of a 38 μm-thick support film (polyethylene terephthalate, "Lumirror T-60", manufactured by Toray Industries, Inc.) was bonded to this adhesive layer, producing a "release film / adhesive layer / support film" laminate. The resulting laminate was then aged for 1 week at 25°C and 55% RH to obtain an adhesive sheet [1].

[0129] <Manufacturing of adhesive sheets> (Manufacturing of adhesive sheets (Fig. 2)) The resulting adhesive was coated onto a 50 μm-thick release film (polyethylene terephthalate (PET), "E7004", silicone-based release layer, manufactured by Toyobo Co., Ltd.) to a dry thickness of 50 μm, and dried at 110°C for 3 minutes to form an 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 adhesive layer to produce a "release film / adhesive layer / release film" laminate. The resulting laminate was then aged for 1 week at 25°C and 55% RH to obtain an adhesive sheet [2].

[0130] (Examples 2 to 21, Comparative Examples 1 to 18) As shown in Table 4, adhesive sheets [1] and [2] were obtained in the same manner as in Example 1, except that the types and amounts (parts by mass) of the copolymer, tackifier resin, and curing agent were changed.

[0131] <<Measurement and evaluation of adhesive sheet properties>> The resulting pressure-sensitive adhesive sheets were evaluated for gel fraction, storage modulus, and loss tangent. The results are shown in Table 4. The following transparency, heat resistance, moist heat resistance, dynamic bending resistance, static bending resistance, and winding properties were also evaluated. The results are shown in Table 5.

[0132] <Gel fraction> The resulting adhesive sheet [2] was cut into a size of 25 mm wide x 100 mm long. One release film was removed from the cut 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 removed, and the mesh was folded so that the adhesive was facing inward to prevent the adhesive from being exposed. The mesh-wrapped adhesive was immersed in approximately 50 mL of ethyl acetate at 23°C for 7 days, allowing the adhesive sol component to elute out of the mesh. After immersion, the mesh-wrapped adhesive was removed, dried at 100°C for 1 hour, and allowed to cool for approximately 20 minutes before measuring the dry mass. The gel fraction of the adhesive was calculated using the following formula: (Formula 1) Gel fraction (mass%) = (Y / X) × 100 X = mass of adhesive layer before immersion (g) Y = mass of adhesive layer after immersion (g)

[0133] <Storage modulus, loss modulus, loss tangent> The dried adhesive was laminated to a thickness of about 1.0 mm to prepare a measurement sample. Viscoelasticity measurements were performed using a "Discovery HR-2 (DHR-2)" manufactured by TA Instrument-Waters LLC. under the following conditions, and the storage modulus and loss tangent at -20°C, 25°C, and 60°C were read from the measurement results. (Measurement conditions) Deformation mode: Torsion Measurement frequency: 1Hz Heating rate: 10°C / min Jig shape: Parallel plate 8.0mmφ

[0134] [Table 4]

[0135] The abbreviations in the table are as follows: <Tackifying resin> B-1: Alicyclic acrylic resin (compound of Synthesis Example B-1) B-2: Alicyclic acrylic resin (compound of Synthesis Example B-2) B-3: Alicyclic acrylic resin (compound of Synthesis Example B-3) B-4: Alicyclic acrylic resin (VS-1028, manufactured by Seiko PMC Co., Ltd.) B-5: Alicyclic acrylic resin (ATF-2242, manufactured by Seiko PMC Corporation) B-6: C5 hydrogenated petroleum resin (Eastac C100, manufactured by Eastman Chemical Company) B-7: C9 hydrogenated petroleum resin (Alcon M90, manufactured by Arakawa Chemical Industries, Ltd.) B-8: Styrenic hydrogenated petroleum resin (FTR6100, manufactured by Mitsui Chemicals) B'-1: Acrylic compound (compound of Synthesis Example B'-1) B'-2: Rosin-based compound (Pine Crystal KE-359, manufactured by Arakawa Chemical Industries, Ltd.) B'-3: Styrene-based compound (Arastar 700, manufactured by Arakawa Chemical Industries, Ltd.) B'-4: Terpene compound (Tamanol 901, manufactured by Arakawa Chemical Industries, Ltd.) <Curing agent> C-1: Trimethylolpropane adduct of tolylene diisocyanate C-4: Trimethylolpropane adduct of hexamethylene diisocyanate C-3: Trimethylolpropane adduct of xylylene diisocyanate C-4: N,N,N',N'-tetraglycidyl-m-xylylenediamine C-5: 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane <Organosilane compounds> S-1: 3-glycidoxypropyltrimethoxysilane

[0136] <Transparency> The adhesive sheet [1] was cut into a size of 112 mm wide x 200 mm long (corresponding to a 9-inch display) to prepare a test adhesive sheet 1 consisting of a PET film / adhesive layer / release film. The release film was peeled off from this test pressure-sensitive adhesive sheet 1, 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 (bad).

[0137] <Heat resistance and moisture and heat resistance> The release film was peeled off from a separately prepared test adhesive sheet 1, and the exposed adhesive layer was attached to an alkali-free glass plate (EN-A1: manufactured by Asahi Glass Co., Ltd.) using a laminator at 25°C and 50% RH to obtain a test laminate consisting of PET film / adhesive layer / alkali-free glass. Next, as a heat resistance test, the test laminate was left at 105°C for 500 hours, cooled at 25°C and 50% RH, and then visually evaluated for bubble formation and lifting or 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 at 25°C and 50% RH, and then visually evaluated for bubble formation and lifting or peeling of the 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 was observed, and there was no problem in practical use. ◯: Bubbles, lifting, and peeling are observed in less than five places, but this does not pose a problem in practical use. ×: Air bubbles, floating or peeling were observed in 5 or more places, and there was a problem in practical use.

[0138] <Dynamic flex resistance: flex resistance [1], [2], [3]> The release film was peeled off from a separately prepared test adhesive sheet 1, and the exposed adhesive layer was attached to both sides of an aluminum plate (120 mm wide x 220 mm long x 0.5 mm thick) at 25°C and 50% RH using a laminator to obtain a test laminate consisting of PET film / adhesive layer / aluminum plate / adhesive / PET film. The test laminate was then subjected to a normal test (flex resistance) at 25°C and 50% RH [1], a heat test (flex resistance) at 85°C [2], and a moist heat test (flex resistance) at 60°C and 95% RH [3]. The conditions were set so that the inner diameter (diameter) when bent was 6 mm, and 300,000 cycles were performed, with each cycle consisting of bending and unbending 180°. Dynamic bending was evaluated based on the appearance after the test according to the following criteria. Appearance: The test laminate was visually inspected for the presence of bubbles and the presence or absence of lifting or peeling of the adhesive layer under the following conditions. [Evaluation criteria] ⊚: No bubbles, lifting or peeling was observed, and there was no problem in practical use. ◯: Bubbles, lifting, and peeling are observed in less than five places, but this does not pose a problem in practical use. ×: Air bubbles, floating or peeling were observed in 5 or more places, and there was a problem in practical use.

[0139] <Static bending resistance: Flexing resistance [1], [2], [3]> The release film was peeled off from a separately prepared test adhesive sheet 1, and the exposed adhesive layer was attached to both sides of an aluminum plate (120 mm wide x 220 mm long x 0.5 mm thick) at 25°C and 50% RH using a laminator to obtain a test laminate consisting of PET film / adhesive layer / aluminum plate / adhesive / PET film. The test laminate was then subjected to a normal test (flex resistance) at 25°C and 50% RH [1], a heat test (flex resistance) at 85°C [2], and a moist heat test (flex resistance) at 60°C and 95% RH [3]. The specimen was bent with the polarizing plate side facing inward at a 3 mm bend radius and 180° bend angle for 240 hours using a planar, no-load U-shaped stretch tester. Static bending was evaluated by visual appearance after the test according to the following criteria: Appearance: The test laminate was visually inspected for the presence of bubbles and the presence or absence of lifting or peeling of the adhesive layer under the following conditions. [Evaluation criteria] ⊚: No bubbles, lifting or peeling was observed, and there was no problem in practical use. ◯: Bubbles, lifting, and peeling are observed in less than five places, but this does not pose a problem in practical use. ×: Air bubbles, floating or peeling were observed in 5 or more places, and there was a problem in practical use.

[0140] <Winding ability> The release film was peeled off from a separately prepared test adhesive sheet 1, and the exposed adhesive layer was attached to both sides of an aluminum plate (120 mm wide x 220 mm long x 0.5 mm thick) using a laminator at 25°C and 50% RH to obtain a test laminate consisting of PET film / adhesive layer / aluminum plate / adhesive / PET film. The test laminate was then wound around a 3 mm radius metal rod in the longitudinal direction, with the PET side of the test piece facing inward, to form a roll, which was then secured in place by tying it in three places with string. For the winding test, the rolled test laminate was kept at 25°C and 50% RH for 240 hours. Static bending was evaluated based on the appearance after the test, according to the following criteria: Appearance: The test laminate was visually inspected for the presence of bubbles and the presence or absence of lifting or peeling of the adhesive layer under the following conditions. [Evaluation criteria] ⊚: No bubbles, lifting or peeling was observed, and there was no problem in practical use. ◯: Bubbles, lifting, and peeling are observed in less than five places, but this does not pose a problem in practical use. ×: Air bubbles, floating or peeling were observed in 5 or more places, and there was a problem in practical use.

[0141] [Table 5]

[0142] The abbreviations for the layer configurations and test conditions in Table 5 are as follows: Layer structure of test adhesive sheet and test laminate [A]: PET film / adhesive layer / glass [B]: PET film / adhesive layer / metal plate / adhesive layer / PET film Test conditions Bending resistance [1]: 25°C, 50% relative humidity Bending resistance [2]; 85℃ atmosphere Bending resistance [3]: 60°C, 95% relative humidity atmosphere

[0143] The results in Tables 4 and 5 confirm that the pressure-sensitive adhesive sheets of Examples 1 to 21 were excellent in transparency, heat resistance, moist heat resistance, flexibility, and windability. This demonstrates that the laminates and displays using the pressure-sensitive adhesive sheets of the present invention are excellent in transparency, heat resistance, moist heat resistance, and flexibility. Furthermore, the displays of the present invention also had excellent visibility and contrast. On the other hand, the pressure-sensitive adhesive sheets of Comparative Examples 1 to 18 were unable to satisfy all of the above properties. [Explanation of symbols]

[0144] 1 Adhesive layer 1 or adhesive layer 2 2 Release film 3 Support film 4 Adhesive layer 3 5 metal plates 6 Organic EL module 7 Support 8 Backplate

Claims

1. The composition comprises an acrylic copolymer (A), a tackifier resin (B), and a curing agent (C), The acrylic copolymer (A) is a copolymer of a monomer mixture containing all of the following monomers (a-1) to (a-4): The tackifier resin (B) is a saturated aliphatic hydrocarbon compound having at least one alicyclic structure in the molecule, and A pressure-sensitive adhesive characterized by satisfying all of the following (1) to (8): (a-1) (Meth)acrylic acid alkyl ester monomers having an alkyl group with 1 to 4 carbon atoms (a-2) (Meth)acrylic acid alkyl ester monomers having an alkyl group with 6 to 12 carbon atoms (a-3) Monomer having a hydroxyl group (a-4) Monomer having a carboxy group (1) The mass % of (a-1) is less than the mass % of (a-2) in 100 mass % of the monomer mixture. (2) The value (a-3) / (a-4) obtained by dividing the mass% of (a-3) by the mass% of (a-4) in 100 mass% of the monomer mixture is 0.01<(a-3) / (a-4)<6 (3) The total mass% of (a-1) and (a-2) is greater than the total mass% of (a-3) and (a-4) in 100% by mass of the monomer mixture. (4) The storage modulus of the adhesive at −20° C. and 1 Hz is 1×10 ５ ~1 x 10 ６ Pa (5) The storage modulus of the adhesive at 25°C and 1 Hz is 4 x 10 ４ ~1 x 10 ５ Pa (6) The storage modulus of the adhesive at 60°C and 1 Hz is 1 x 10 ４ ~4 x 10 ４ Pa (7) The loss factor of the adhesive at -20°C and 1 Hz is 1.0 to 3.0 (8) The loss factor of the adhesive at 60°C and 1 Hz is 0.2 to 1.0

2. The pressure-sensitive adhesive according to claim 1, comprising 2 to 50 parts by mass of a tackifier resin (B) relative to 100 parts by mass of the acrylic copolymer (A).

3. The pressure-sensitive adhesive according to claim 1 or 2, characterized in that the gel fraction is 60 to 90 mass %.

4. The pressure-sensitive adhesive according to any one of claims 1 to 3, wherein the curing agent (C) is an isocyanate compound.

5. A pressure-sensitive adhesive sheet comprising, in this order, a pressure-sensitive adhesive layer which is a cured product of the pressure-sensitive adhesive according to any one of claims 1 to 4, and a support film.

6. A laminate comprising a support film, an adhesive layer, a metal plate, an adhesive layer and a support film in this order, wherein the adhesive layer is a cured product of the adhesive according to any one of claims 1 to 4.

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

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