JP7740002B2 - Adhesive, adhesive sheet, laminate, and flexible display - Google Patents

Description

The present invention relates to a laminate having an adhesive, an adhesive sheet, and an adhesive layer formed from the adhesive sheet, for forming a laminate including a support film, an adhesive layer, and a metal plate. The laminate is used for flexible displays.

In recent years, input devices that combine an image display device, such as a liquid crystal display (LCD) or an organic electroluminescent (organic EL) display (OLED), with a touch panel have become popular. The transparent conductive film used in the touch panel is laminated to components such as support glass or a display film via an adhesive layer. In addition, the polarizing 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 component of the image display device is attached and fixed by the adhesive layer.

While flat displays using glass substrates have been the mainstream of image display devices, in recent years flexible displays such as foldable displays and rollable displays using flexible substrates such as plastic have been developed. Compared to conventional flat displays using glass substrates, these flexible displays offer various advantages, such as being lighter, thinner, and more flexible, as well as being more aesthetically pleasing.

In such flexible displays, the flexible organic EL used is thin to provide foldability and rollability, and in order 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 this 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.

To solve these problems, Patent Document 1 discloses an optically transparent adhesive sheet that contains a resin syrup produced by partially polymerizing a (meth)acrylate monomer and a photoinitiator, wherein the storage modulus of the adhesive layer of the adhesive sheet is 1.0×10 ⁶ to 1.0×10 ⁷ Pa at 25° C. and 1 Hz. Patent Document 2 also discloses an adhesive that contains a styrene-isobutylene-styrene (SIBS) rubber, an alicyclic epoxy compound, and a photoinitiator.

Japanese Patent Application Laid-Open No. 2020-517800 Japanese Patent Application Laid-Open No. 2021-14563

However, in recent years, in order to meet the ever-increasing demands for higher durability in displays, stricter flexibility is required, and in addition to dynamic flexibility, static flexibility is also required, which means that no bubbling, lifting, or peeling occurs when the display is maintained in a bent state for an extended period of time. Furthermore, for rollable displays, the display must be able to be rolled up (windability), allowing it to be used in rollable displays. Generally, windability requires that no bubbling, lifting, or peeling occurs when the display is maintained in a rolled state for an extended period of time.

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 found in extremely cold regions, as well as high-temperature environments such as those found in extremely hot regions or inside automobiles under the blazing sun, is now also becoming necessary.

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.

The present invention aims to provide an adhesive, an adhesive sheet, and a laminate thereof, as well as a flexible display, that are excellent in transparency and also have heat resistance, moist heat resistance, flexibility, and rollability.

As a result of extensive research, the present inventors have found that the problems of the present invention can be solved by the following aspects, and have thus completed the present invention.
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 that satisfies 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) monomers having a hydroxyl group; and (a-4) monomers 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 x 10 ⁵ to 1 x 10 ⁶ Pa.
(5) The storage modulus of the adhesive at 25°C and 1 Hz is 4 x 10 ⁴ to 1 x 10 ⁵ Pa.
(6) The storage modulus of the adhesive at 60°C and 1 Hz is 1 x 10 ⁴ to 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

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 excellent in visibility and contrast can be provided.

1 is a schematic cross-sectional view partially illustrating a pressure-sensitive adhesive sheet (for forming a back plate) of the present invention. 1 is a schematic cross-sectional view partially illustrating the pressure-sensitive adhesive sheet (for fixing a back plate) of the present invention. FIG. 1 is a schematic cross-sectional view partially illustrating a laminate (back plate), which is an example of use of the pressure-sensitive adhesive sheet of the present invention. 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.

The following describes examples of the configurations of the pressure-sensitive adhesive, pressure-sensitive adhesive sheet, laminate, and display of the present invention, but the present invention is not limited to these.

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.

In this specification, numerical ranges specified using "~" are intended to include the numbers before and after "~" as the lower and upper limits of the range.

"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
All of the following (1) to (8) are met.
(a-1) (meth)acrylic acid alkyl ester monomers having 1 to 4 carbon atoms; (a-2) (meth)acrylic acid alkyl ester monomers having 6 to 12 carbon atoms; (a-3) monomers having a hydroxyl group; and (a-4) monomers 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 at -20°C and 1 Hz is 1 x 10 ⁵ to 1 x 10 ⁶ Pa.
(5) The reservoir elastic modulus at 25°C and 1 Hz is 4 x 10 ⁴ to 1 x 10 ⁵ Pa.
(6) The elastic modulus of the reservoir at 60°C and 1 Hz is 1 x 10 ⁴ to 4 x 10 ⁴ Pa.
(7) Loss factor at -20°C and 1 Hz is 1.0 to 3.0
(8) Loss factor at 60°C and 1 Hz is 0.2 to 1.0

<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 necessary.
(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) monomers having a hydroxyl group; (a-4) monomers having a carboxy group; (a-5) other monomers other than (a-1) to (a-4).

[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.

Monomer (a-1) is preferably contained in an amount of 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. Furthermore, a content of 40% by mass or less is preferred, as it makes it easier to achieve both cohesive strength and stress relaxation properties.

[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.

These monomers (a-2) can be used alone or in combination of two or more. In particular, using two or more types of monomers (a-2) in combination is more preferable from the viewpoint of achieving both adhesion and cohesion.

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 makes it easier to achieve sufficient stress relaxation properties. Furthermore, a content of 98% by mass or less is preferred, as it makes it easier to achieve both cohesive strength and stress relaxation properties.

[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 is a monomer having a hydroxyl group in the molecule, and specific examples thereof 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.

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 makes it easier to obtain sufficient cohesive strength. A content of 4.0% by mass or less is also preferred, as it makes it easier to achieve both cohesive strength and stress relaxation properties.

[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 thereof 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.

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

[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.

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

Examples of monomers 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.

Examples of monomers 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.

Examples of monomers having an alkyleneoxy group include monomers represented by the following general formula (1) or general formula (2):

In general formula (1) and general formula (2), R ₁ and R ₂ 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.

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), R ₁ is a hydrogen atom, n=1), methoxydiethylene glycol acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.: in the above formula (1), R ₁ is a hydrogen atom, n=2), methoxytriethylene glycol acrylate (manufactured by 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), and methoxypolyethylene glycol #1000 acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R 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 ₁ is a hydrogen atom, n=13), and methoxypolyethylene glycol #1000 methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above formula (1), R ₁ is a hydrogen atom, n=23).

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

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.

Examples of vinyl monomers include vinyl acetate, vinyl crotonate, styrene, and acrylonitrile.

Monomer (a-5) preferably comprises 2 to 30% by mass of the monomer mixture, with the monomer mixture containing 100% by mass. A content of 2% by mass or more further improves adhesion. Furthermore, a content of 30% by mass or less is preferred, as it makes it easier to achieve both cohesive strength and adhesion.

The acrylic copolymer (A) satisfies the following formula: The mass percentage of (a-1) < the mass percentage of (a-2) in 100 mass% of the monomer mixture constituting the acrylic copolymer (A). By satisfying the formula: (a-1) < (a-2), the stress relaxation properties of the pressure-sensitive adhesive are improved, thereby improving adhesion.

In the acrylic copolymer (A), the value (a-3)/(a-4), obtained by dividing the mass percentage of (a-3) by the mass percentage 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.

In the acrylic copolymer (A), the total mass percentage of (a-1) and (a-2) is greater than the total mass percentage of (a-3) and (a-4) based on 100% by mass of the monomer mixture constituting the acrylic copolymer (A). By having the total mass percentage of (a-1) and (a-2) greater than the total mass percentage of (a-3) and (a-4), the stress relaxation properties and cohesive strength of the adhesive are improved, resulting in improved flexibility.

[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.

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.

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'-azobispropionitriles such as 2,2'-azobis(2-hydroxymethylpropionitrile);
Examples include 1,1'-azobis-1-alkanenitriles such as 1,1'-azobis(cyclohexane-1-carbonitrile).

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, per 100 parts by mass of the monomer mixture.

[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.

<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 a high-cohesion domain, 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.

Specific examples of tackifier resins (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 that have at least one alicyclic structure within the molecule.

Examples of hydrogenated petroleum resins include C5-based hydrogenated petroleum resins, C9-based hydrogenated petroleum resins, C5/C9-based hydrogenated petroleum resins, and styrene-based hydrogenated petroleum resins. C5-based hydrogenated petroleum resins are obtained by adding hydrogen atoms to the unsaturated double bonds of an aliphatic resin obtained by separating and purifying the C5 fraction obtained from petroleum naphtha. C9-based hydrogenated petroleum resins are obtained by adding hydrogen atoms to the unsaturated double bonds of an aromatic resin obtained by separating and purifying the C9 fraction obtained from petroleum naphtha. C5/C9-based 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 then purifying the C5 fraction and the 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 the styrene fraction obtained from petroleum naphtha.

Hydrogenated terpene resin is a general term for, for example, polyterpene resin, terpene phenol resin, and aromatic terpene resin, in which hydrogen atoms are added to the unsaturated double bonds.

Examples of C5 hydrogenated petroleum resins include Eastac C100 and Eastac C115W (manufactured by Eastman Chemical Company). Examples of C9 hydrogenated petroleum resins include Arcon P-90, Arcon P-100, Arcon P-125, Arcon P-140, Arcon M-90, Arcon M-115, and Arcon M-135 (manufactured by Arakawa Chemical Co., Ltd.). 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.).

Of these hydrogenated hydrocarbon resins, Eastack 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 standpoint of durability.

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 those (B-1 to B-3) described in the examples below.

Of these alicyclic acrylic resins, VS-1028, ATF-2242, and (B-1 to B-3) are particularly preferred from the standpoint of durability.

Alicyclic acrylic resins can be produced by polymerizing a monomer mixture containing an alicyclic monomer. The polymerization methods and polymerization initiators described in the section on production of acrylic copolymer (A) can be used.

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.

Of these alicyclic monomers, isobornyl acrylate, cyclohexyl acrylate, and isobornyl methacrylate are preferred from the standpoints of substrate adhesion and durability in high-temperature or high-temperature, high-humidity environments. These alicyclic monomers can be used alone or in combination of two or more types.

The alicyclic monomer preferably accounts for 40 to 90% by weight, and 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 substrate adhesion. Furthermore, a content of 40% by weight or less achieves high levels of both cohesive strength and stress relaxation.

These tackifying resins (B) can be used alone or in combination of two or more types.

The tackifier resin (B) is preferably contained in an amount of 2 to 50 parts by mass, and more preferably 5 to 30 parts by mass, per 100 parts by mass of copolymer (A). A content of 2 parts by mass or more further improves heat resistance and adhesion, while a content of 50 parts by mass or less maintains adhesive performance.

<Curing agent (C)>
The pressure-sensitive adhesive of the present invention contains a curing agent (C). The curing agent (C) 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.

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.

The isocyanate compound is an isocyanate having two or more isocyanate groups. Examples of preferred isocyanate compounds include isocyanate monomers such as aromatic polyisocyanates, aliphatic polyisocyanates, araliphatic polyisocyanates, and alicyclic polyisocyanates, as well as their biuret, nurate, and adduct forms.

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.

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.

Examples of aromatic aliphatic polyisocyanates 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.

Examples of alicyclic polyisocyanates include 3-isocyanatomethyl-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(isocyanatomethyl)cyclohexane.

The biuret compound is a self-condensation product having a biuret bond formed by the self-condensation of an isocyanate monomer. An example of a biuret compound is the biuret compound of hexamethylene diisocyanate.

The nurate derivative is a trimer of an isocyanate monomer. Examples include a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, and a trimer of tolylene diisocyanate.

The adduct is a difunctional or higher isocyanate compound obtained by reacting an isocyanate monomer with a difunctional or higher low-molecular-weight active hydrogen-containing compound. Examples of adducts 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.

From the viewpoint of forming a sufficient crosslinked structure, trifunctional isocyanate compounds are preferred. More preferred isocyanate compounds are adducts and nurates, which are reaction products of an isocyanate monomer and a trifunctional low-molecular-weight active hydrogen-containing compound. Preferred isocyanate compounds are trimethylolpropane adducts of hexamethylene diisocyanate, nurates of hexamethylene diisocyanate, trimethylolpropane adducts of tolylene diisocyanate, nurates of tolylene diisocyanate, trimethylolpropane adducts of isophorone diisocyanate, and nurates of isophorone diisocyanate, and more preferred are trimethylolpropane adducts of hexamethylene diisocyanate, trimethylolpropane adducts of tolylene diisocyanate, and trimethylolpropane adducts of isophorone diisocyanate.

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.

Examples of aziridine compounds 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.

Preferably, the carbodiimide compound is a high-molecular-weight polycarbodiimide produced by the decarboxylation condensation reaction 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. Among these, Carbodilite V-03, 07, and 09 are preferred due to their excellent compatibility with organic solvents.

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.

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

<Organosilane Compound>
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 of the silane 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 an alkoxysilyl group in the molecule.

The organic silane 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 copolymer (A).

The adhesive of the present invention can contain optional components such as various resins, oils, softeners, dyes, pigments, antioxidants, UV absorbers, weather stabilizers, plasticizers, fillers, antioxidants, and antistatic agents, as long as the problem can be solved.

<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 stored as elastic energy when a material 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.

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 stronger the tendency for viscosity, the more liquid-like the deformation behavior, and the smaller the rebound elastic energy. In other words, the higher the loss tangent, the greater the stress relaxation ability of the adhesive, and the lower the storage modulus value, the greater the rigidity of the adhesive.

<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 x 10 ⁵ to 1 x 10 ⁶ Pa, and more preferably 2 x 10 ⁵ to 9 x 10 ⁵ Pa. When G'(-20) is 1 x 10 ⁵ Pa or more, the rigidity in a low temperature environment is improved, and the flexibility and winding properties are improved. When G'(-20) is 1 x 10 ⁶ Pa or less, the adhesion is improved, and the flexibility and winding properties are improved.

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 to 1 x 10 ⁵ Pa, and more preferably 4 x 10 ⁴ to 8 x 10 ⁴ Pa. When G'(25) is 4 x 10 ⁴ Pa or more, processability is improved. When G'(25) is 1 x 10 ⁵ Pa or less, adhesive strength is improved.

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 to 4 x 10 ⁴ Pa, preferably 2 x 10 ⁴ to 4 x 10 ⁴ Pa. When G'(60) is 1 x 10 ⁴ Pa or more, the rigidity in a high temperature environment is improved, and the flexibility and winding properties are improved. When G'(60) is 4 x 10 ⁴ Pa or less, the flexibility in a high temperature environment is improved, and the flexibility and winding properties are improved.

<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 present inventors have found that tan δ(-20) correlates 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.

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 low-temperature environments is improved, and flexibility and winding properties are improved. When tan δ(60) is 1.0 or less, rigidity in low-temperature environments is improved, and flexibility and winding properties are improved.

The 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.

<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.

[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, the gel fraction 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 (g) of the adhesive layer before immersion
Y = mass (g) of the 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 (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.

"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) comprising 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 configuration) of the present invention is shown in Figure 1. In Figure 1, 1 denotes pressure-sensitive adhesive layer 1 or 2, 2 denotes a release film, and 3 denotes 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.

As shown in Figure 1, the pressure-sensitive adhesive sheet (for use in a backplate) of the present invention has a configuration in which a release film is formed on one side of a pressure-sensitive adhesive layer and a support film is formed on the other side of the release film, and the pressure-sensitive adhesive layer formed between the release film and the support film is a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive of the present invention.

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 back plate) of the present invention is shown in Fig. 2. In Fig. 2, 4 denotes a pressure-sensitive adhesive layer 3, and 2 denotes a release film.

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

<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.

Of the transparent plastic substrates mentioned above, those with excellent heat resistance, i.e., those that are suppressed or prevented from deforming under harsh conditions such as high temperature or high temperature and humidity, are suitable for use as release films. PET films or sheets are particularly suitable as transparent plastic substrates.

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

The release film may be either a single layer or a multi-layer structure. The surface of the transparent substrate may be subjected to an appropriate surface treatment, such as a physical treatment such as corona discharge treatment or plasma treatment, or a chemical treatment such as a primer treatment.

<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.

Among the plastic substrates mentioned above, those with excellent heat resistance, i.e., plastic substrates that are suppressed or prevented from deforming under harsh conditions such as high temperature or high temperature and humidity, are preferred. Polyethylene terephthalate (PET), polycycloolefin, and polyimide are particularly suitable as support films.

The thickness of the support film is not particularly limited, but is preferably 10 to 200 μm, and more preferably 200 to 100 μm.

<Production of Pressure-Sensitive Adhesive Sheet>
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.

The thickness of the adhesive layer is not particularly limited, but is preferably 10 to 200 μm, and more preferably 15 to 100 μm. An adhesive layer thickness of 10 to 200 μm is preferred because it is easy to obtain sufficient cohesive strength and can achieve a high level of heat resistance, moist heat resistance, flexibility, and windability.

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.

The adhesive sheet may be in the form of a rolled adhesive tape, which is obtained by cutting it to an appropriate width and winding it into a roll.

"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.

The laminate of the present invention is formed from an 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.

Figure 3 shows a schematic cross-sectional view of a laminate (back plate), an example of the use of the adhesive of the present invention. In Figure 3, 3 is a support film, 1 is adhesive layer 1, 5 is a metal plate, 1 is adhesive layer 2, and 3 is a support film.

In the laminate shown in Figure 3, a support film is attached to both sides of a metal plate via an adhesive layer 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 the adhesive layer formed from the adhesive is attached to the support film and metal plate.

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

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.

The display of the present invention has a laminate 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.

Figure 4 shows a schematic cross-sectional view of a portion of a display, which is an example of the use of the adhesive sheet of the present invention. In Figure 4, 6 is an organic EL module, 4 is adhesive layer 3, 3 is a support film, 1 is adhesive layer 1, 5 is a metal plate, 1 is 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 Figure 4.

In the display shown in Fig. 4, a support film is attached to both sides of a metal plate via pressure-sensitive adhesive layers (pressure-sensitive adhesive layers 1 and 2) made of the pressure-sensitive adhesive of the present invention, and is further attached to an organic EL module via a pressure-sensitive adhesive layer (pressure-sensitive adhesive layer 3) 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 a laminate is formed by attaching a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive to a support film and a metal plate, and the laminate is further attached to an organic EL module via a pressure-sensitive adhesive layer formed from the pressure-sensitive 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 pressure-sensitive adhesive layer 1, pressure-sensitive adhesive layer 2, and pressure-sensitive adhesive layer 3, the quality requirements for the pressure-sensitive adhesive layers are higher for pressure-sensitive adhesive layer 1 and pressure-sensitive adhesive layer 2, and the pressure-sensitive adhesive of the present invention has good adhesion and bondability to the substrate, and is therefore preferably used for pressure-sensitive adhesive layer 1 and pressure-sensitive adhesive layer 2. In this case, the pressure-sensitive adhesive for forming pressure-sensitive adhesive layer 3 may be the pressure-sensitive adhesive of the present invention, or a conventionally known pressure-sensitive adhesive may be used.

There are no particular restrictions on the uses of the display, but examples include OLED televisions, OLED smartphones, OLED tablets, and OLED smartwatches.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In the examples, unless otherwise specified, "parts" means "parts by mass", "%" means "% by mass", and "RH" means relative humidity. In addition, the blending amounts in the tables are in parts by mass. Note that blank spaces in the tables indicate that no blending was performed.
The method for measuring the mass average molecular weight of the copolymer is as follows.

<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: 1.0 ml/min Column temperature: 40°C

<Production Example of Acrylic Copolymer>
(Acrylic Copolymer (A-1))
A reaction vessel (hereinafter 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 (hereinafter simply referred to as "AIBN") as an initiator, and the atmosphere inside the reaction vessel was replaced with nitrogen gas. The mixture was then heated to 50°C while 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 8,000 mPa·s. The mass average molecular weight of the resulting copolymer (A-1) was 1,000,000.

(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 in 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.

The mass average molecular weights (Mw) of the resulting copolymers (A-1 to A-15, A'-1 to A'-8) are shown in Tables 1 and 2.

<Production Example of Alicyclic Acrylic Resin (Tackifying Resin)>
(Alicyclic acrylic resin (B-1))
A reaction vessel (hereinafter 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 (hereinafter referred to as AIBN), and the air in the reaction vessel was replaced 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 reacted 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 1,000 mPa·s. The resulting alicyclic acrylic resin (B-1) had a mass average molecular weight of 20,000.

(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.

The mass average molecular weights (Mw) of the obtained alicyclic acrylic resins (B-1 to B-3) and acrylic resin (B'-1) are shown in Table 3.

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 of general formula (1) where R ₁ is a hydrogen atom and n=1)
NVP: N-vinylpyrrolidone (alicyclic monomer)
CHA: cyclohexyl acrylate IBXA: isobornyl acrylate

Example 1
<Preparation of Adhesive>
A pressure-sensitive adhesive was obtained by blending and stirring 100 parts of the nonvolatile content of the acrylic copolymer (A-1) with 5 parts of an acrylic compound (B-1) as a tackifier resin (B), 0.5 parts of an adduct of tolylene diisocyanate and trimethylolpropane (C-1) as a curing agent (C), and 0.1 parts of 3-glycidoxypropyltrimethoxysilane (S-1) as an organic silane compound, and further mixing ethyl acetate so that the nonvolatile content was 20%.

<Production of adhesive sheet> (Production of adhesive sheet shown in FIG. 1)
The obtained 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 20 μm, and the coated film was 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 to prepare a "release film/adhesive layer/support film" laminate. Next, the obtained laminate was aged for 1 week under conditions of a temperature of 25°C and 55% RH to obtain an adhesive sheet [1].

<Production of adhesive sheet> (Production of adhesive sheet shown in FIG. 2)
The obtained 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 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 obtained laminate was then aged for 1 week under conditions of a temperature of 25°C and 55% RH to obtain an adhesive sheet [2].

(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.

<<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 property were also evaluated. The results are shown in Table 5.

<Gel fraction>
The resulting adhesive sheet [2] was cut into a size of 25 mm wide x 100 mm long. One release film was peeled off 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 peeled off, 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 sol component of the adhesive 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, after which the dry mass was measured. The gel fraction of the adhesive was calculated using the following formula:
(Formula 1)
Gel fraction (mass%)=(Y/X)×100
X = mass (g) of the adhesive layer before immersion
Y = mass (g) of the adhesive layer after immersion

<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 under the following conditions using a "Discovery HR-2 (DHR-2)" manufactured by TA Instrument-Waters LLC, 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: 1 Hz
Temperature rise rate: 10°C/min Jig shape: parallel plate 8.0mmφ

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, Inc.)
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 <organic silane compound>
S-1: 3-glycidoxypropyltrimethoxysilane

<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 are as follows.
[Evaluation criteria]
○: Haze is less than 1.0 (good).
×: Haze is 1.0 or more (bad).

<Heat resistance and moist 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 in a 25°C and 50% RH atmosphere, 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 in a 25°C and 50% RH atmosphere, 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 were observed in less than five places, but this did not pose a problem in practical use.
×: The occurrence of bubbles, lifting or peeling was observed in 5 or more places, and there was a problem in practical use.

<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) 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 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 bending and 180 ° opening being one cycle. Dynamic flexibility was evaluated based on the appearance after the test from the following perspectives.
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 were observed in less than five places, but this did not pose a problem in practical use.
×: The occurrence of bubbles, lifting or peeling was observed in 5 or more places, and there was a problem in practical use.

<Static bending resistance: bending 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) as a metal plate 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 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 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 was evaluated based on the appearance after the test from the following perspectives.
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 were observed in less than five places, but this did not pose a problem in practical use.
×: The occurrence of bubbles, lifting or peeling was observed in 5 or more places, and there was a problem in practical use.

<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 (width 120 mm x length 220 mm x thickness 0.5 mm) 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. Next, the test laminate was wound around a metal rod with a radius of 3 mm, with the PET side of the test piece facing inward, in the long direction, and then rolled up. The rolled test laminate was then tied and secured in place with string in three places. For the winding test, the rolled test laminate was kept at 25 ° C and 50% RH for 240 hours. The static flexibility was evaluated based on the appearance after the test from the following perspectives.
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 were observed in less than five places, but this did not pose a problem in practical use.
×: The occurrence of bubbles, lifting or peeling was observed in 5 or more places, and there was a problem in practical use.

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

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 indicates 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 could not satisfy all of the above properties.

1. Pressure-sensitive adhesive layer 1 or pressure-sensitive adhesive layer 2
2 Release film 3 Support film 4 Pressure-sensitive adhesive layer 3
5 Metal plate 6 Organic EL module 7 Support 8 Back plate

Claims (7)

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) monomers having a hydroxyl group; and (a-4) monomers 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 x 10 ⁵ to 1 x 10 ⁶ Pa.
(5) The storage modulus of the adhesive at 25°C and 1 Hz is 4 x 10 ⁴ to 1 x 10 ⁵ Pa.
(6) The storage modulus of the adhesive at 60°C and 1 Hz is 1 x 10 ⁴ to 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 The adhesive according to claim 1, characterized in that it contains 2 to 50 parts by mass of tackifier resin (B) per 100 parts by mass of the acrylic copolymer (A). The adhesive according to claim 1 or 2, characterized in that the gel fraction is 60 to 90% by mass. The pressure-sensitive adhesive according to any one of claims 1 to 3, wherein the curing agent (C) is an isocyanate-based compound. An adhesive sheet comprising, in this order, an adhesive layer that is a cured product of the adhesive according to any one of claims 1 to 4, and a support film. A laminate comprising, in this order, a support film, an adhesive layer, a metal plate, an adhesive layer, and a support film, wherein the adhesive layer is a cured product of the adhesive described in any one of claims 1 to 4. A flexible display comprising the laminate of claim 6 and an optical element.