WO2024101201A1

WO2024101201A1 - Adhesive, adhesive sheet, laminate, and display

Info

Publication number: WO2024101201A1
Application number: PCT/JP2023/039110
Authority: WO
Inventors: 克哲福田
Original assignee: ａｒｔｉｅｎｃｅ株式会社; トーヨーケム株式会社
Priority date: 2022-11-09
Filing date: 2023-10-30
Publication date: 2024-05-16
Also published as: JP2024069009A; JP7398033B1

Abstract

The purpose of the present disclosure is to provide an adhesive, an adhesive sheet, a laminate, and a display which have excellent transparency, heat resistance, heat and humidity resistance, flexibility, and rollability. The above problem is solved by an adhesive characterized by containing an acrylic copolymer (A1), an acrylic copolymer (A2), and a crosslinker (B), wherein the SP value, glass transition temperature, and weight average molecular weight of the acrylic copolymer (A1), and the SP value, glass transition temperature, and weight average molecular weight of the acrylic copolymer (A2) satisfy specific requirements.

Description

Adhesive, adhesive sheet, laminate, and display

The present disclosure relates to an adhesive for forming a laminate including a light-transmitting substrate, an adhesive layer, and a polarizing plate, an adhesive sheet, and a laminate having an adhesive layer formed by the adhesive sheet. The laminate is used for displays.

Thin image display devices such as liquid crystal displays and organic EL displays usually have a layered structure that includes image forming layers such as a liquid crystal layer and an organic EL layer, and covering layers such as an optical film and a cover panel. Adhesives are generally used to bond the various layers that make up an image display device. For example, transparent conductive films used in touch panels are laminated to members such as support glass and support film via an adhesive layer. Polarizing plate films used in image devices are attached to modules such as liquid crystal modules and organic EL modules via an adhesive layer. In this way, the various components of the image display device are attached and fixed by the adhesive layer.

Furthermore, while flat displays using glass substrates were 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. Such flexible displays have various advantages over conventional flat displays using glass substrates, such as being lightweight, thin, and flexible, as well as having excellent design.

The adhesive layer has traditionally been required to have the property of not foaming or peeling in high temperature or high temperature/high humidity environments, but in recent years, further functionality has become necessary, and flexibility has become necessary for flexible displays. For example, in the case of a foldable display, flexibility means the ability to accommodate bending of the display (flexibility). In general, flexibility requires the property of not foaming, lifting, or peeling when repeatedly bent (dynamic flexibility).

In order to solve these problems, Patent Document 1 discloses an adhesive that has a urethane polymer chain and an acrylic polymer chain. Furthermore, Patent Document 2 discloses an adhesive that contains a base agent and an ionic compound, and has a storage modulus within a specific range after curing.

JP 2021-161433 A JP 2022-115914 A

However, in recent years, in order to keep up with the increasing durability of displays, the adhesives used are required to have even stricter durability than before. In particular, for foldable displays, in addition to the property of not causing foaming, lifting or peeling when repeatedly bent (dynamic flexibility), the adhesive must also have the property of not causing foaming, lifting or peeling when the bent state is maintained for a long period of time (static flexibility). Furthermore, for rollable displays, the adhesive must be suitable for rolling up the display (windability) so that it can be used in rollable displays. In terms of windability, the adhesive must have the property of not causing foaming, lifting or peeling when the rolled state is maintained for a long period of time.

Furthermore, while previously this flexibility was a required quality only at room temperature, with the spread of displays, flexibility is now also required 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 and inside automobiles under the blazing sun.

In contrast, conventional pressure-sensitive adhesive sheets may not be able to satisfy the heat resistance and moist heat resistance, and flexibility such as bendability and windability, at a level that does not pose any practical problems.
In addition, flexibility is required to have dynamic bending properties, static bending properties, and rollability depending on the display configuration. However, even if flexibility can be satisfied individually, it is often difficult to satisfy all properties at the same time. In addition, in a high temperature environment or a high temperature and high humidity environment, it is often even more difficult to satisfy all of the dynamic bending properties, static bending properties, and rollability.

The present disclosure aims to provide an adhesive, an adhesive sheet, and a laminate thereof, as well as a display, that are excellent in transparency and can achieve both heat resistance, moist heat resistance, and flexibility and rollability.

As a result of extensive investigations, the present inventors have found that the problems of the present disclosure can be solved in the following aspect, and have thus completed the present disclosure.
That is, in one embodiment, the above-mentioned problem is solved by a pressure-sensitive adhesive comprising an acrylic copolymer (A1), an acrylic copolymer (A2), and a crosslinking agent (B), and satisfying all of the following (1) to (5):
(1) SP(A1)>SP(A2), and 0.50<|SP(A1)-SP(A2)|<1.60
(2) Tg(A1)<Tg(A2), and 100<|Tg(A1)-Tg(A2)|<180
(3) Mw(A1) is 500,000 to 2,000,000 (4) Mw(A2) is 5,000 to 100,000 (5) 10<Mw(A1)/Mw(A2)<80
Here, in the above formula,
SP(A1) is the SP value of the acrylic copolymer (A1); SP(A2) is the SP value of the acrylic copolymer (A2); Tg(A1) is the glass transition temperature of the acrylic copolymer (A1); Tg(A2) is the glass transition temperature of the acrylic copolymer (A2); Mw(A1) is the weight average molecular weight of the acrylic copolymer (A1); Mw(A2) is the weight average molecular weight of the acrylic copolymer (A2); |SP(A1)-SP(A2)| is the absolute value of the difference between SP(A1) and SP(A2); |Tg(A1)-Tg(A2)| is the absolute value of the difference between Tg(A1) and Tg(A2); and Mw(A1)/Mw(A2) is the value obtained by dividing Mw(A1) by Mw(A2).

Also, one embodiment is the above-mentioned pressure-sensitive adhesive, characterized in that the acrylic copolymer (A1) is a copolymer of a monomer mixture containing the following monomer (a-1) and monomer (a-2), and the acrylic copolymer (A2) is a copolymer of a monomer mixture containing the following monomer (a-3) and monomer (a-4).
(a-1) (meth)acrylic acid alkyl ester monomers having an alkyl group with 8 to 12 carbon atoms (excluding monomer (a-3) below)
(a-2) Monomers having one or more polar groups selected from monomers having a hydroxyl group and monomers having a carboxy group; (a-3) (meth)acrylic acid cycloalkyl ester monomers having a cycloalkyl group; (a-4) Monomers having an amino group.

In one embodiment, the acrylic copolymer (A1) contains 25 to 99% by mass of the monomer (a-1) and 0.1 to 4% by mass of the monomer (a-2) in 100% by mass of a monomer mixture;
The pressure-sensitive adhesive is characterized in that the acrylic copolymer (A2) contains 25 to 99 mass% of the monomer (a-3) and 0.1 to 4 mass% of the monomer (a-4) based on 100 mass% of the monomer mixture.

In one embodiment, the pressure-sensitive adhesive contains 1 to 30 parts by mass of the acrylic copolymer (A2) per 100 parts by mass of the acrylic copolymer (A1).

In one embodiment, the acrylic copolymer (A1) has a weight average molecular weight of 800,000 to 1,500,000, and the acrylic copolymer (A2) has a weight average molecular weight of 20,000 to 80,000.

In one embodiment, the above pressure-sensitive adhesive has a gel fraction of 60 to 90% by mass.

In one embodiment, the crosslinking agent (B) is an isocyanate compound.

Another aspect is an adhesive sheet having an adhesive layer that is a cured product of the above adhesive.

Another embodiment is a laminate comprising a light-transmitting substrate, an adhesive layer, and a polarizing plate, the adhesive layer being a cured product of the adhesive.

Another aspect is a display comprising the laminate and an optical element.

The present disclosure makes it possible to provide a pressure-sensitive adhesive, a pressure-sensitive adhesive sheet, and a laminate using the pressure-sensitive adhesive sheet that are excellent in transparency and further capable of achieving heat resistance, moist heat resistance, flexibility, and rollability.
Furthermore, by using the pressure-sensitive adhesive sheet and laminate of the present disclosure, a display with excellent visibility and contrast can be provided.

1 is a schematic cross-sectional view partially illustrating a pressure-sensitive adhesive sheet according to the present disclosure. FIG. 2 is a schematic cross-sectional view partially illustrating a laminate, which is an example of use of the pressure-sensitive adhesive sheet of the present disclosure. FIG. 2 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 disclosure.

Below, examples of the configurations of the adhesive, adhesive sheet, laminate, and display of the present disclosure are described, but are not limited to these.

The terms used in this specification are defined. (Meth)acrylic acid ester includes acrylic acid ester and methacrylic acid ester. That is, (meth)acrylic acid ester may mean either acrylic acid ester or methacrylic acid ester, or may mean both. The monomer in the monomers (a-1) to (a-4) described below means an ethylenically unsaturated group-containing monomer. The adherend refers to a counterpart to which the pressure-sensitive adhesive sheet is attached. In this specification, the terms sheet, film, and tape are synonymous.
In this specification, (a-1) (meth)acrylic acid alkyl ester monomers having an alkyl group of 8 to 12 carbon atoms, (a-2) monomers having one or more polar groups selected from monomers having a hydroxyl group and monomers having a carboxy group, (a-3) (meth)acrylic acid cycloalkyl ester monomers having a cycloalkyl group, (a-4) monomers having an amino group, (a-5) other monomers other than (a-1) to (a-4), acrylic copolymer (A1), and acrylic copolymer (A2) may be abbreviated as monomer (a-1), monomer (a-2), monomer (a-3), monomer (a-4), monomer (a-5), copolymer (A1), and copolymer (A2), respectively.
Unless otherwise noted, the various components appearing in this specification may be used independently as a single type or as a combination of two or more types.

In this specification, a numerical range specified using "to" is intended to include the numerical values before and after "to" as the lower and upper limit values of the range.
In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples.

"Adhesive"
The pressure-sensitive adhesive of the present disclosure is a pressure-sensitive adhesive comprising an acrylic copolymer (A1), an acrylic copolymer (A2), and a crosslinking agent (B), and satisfying all of the following (1) to (5):
(1) SP(A1)>SP(A2), and 0.50<|SP(A1)-SP(A2)|<1.60
(2) Tg(A1)<Tg(A2), and 100<|Tg(A1)-Tg(A2)|<180
(3) Mw(A1) is 500,000 to 2,000,000 (4) Mw(A2) is 5,000 to 100,000 (5) 10<Mw(A1)/Mw(A2)<80
Here, in the above formula,
SP(A1) is the SP value of the acrylic copolymer (A1); SP(A2) is the SP value of the acrylic copolymer (A2); Tg(A1) is the glass transition temperature of the acrylic copolymer (A1); Tg(A2) is the glass transition temperature of the acrylic copolymer (A2); Mw(A1) is the weight average molecular weight of the acrylic copolymer (A1); Mw(A2) is the weight average molecular weight of the acrylic copolymer (A2); |SP(A1)-SP(A2)| is the absolute value of the difference between SP(A1) and SP(A2); |Tg(A1)-Tg(A2)| is the absolute value of the difference between Tg(A1) and Tg(A2); and Mw(A1)/Mw(A2) is the value obtained by dividing Mw(A1) by Mw(A2).

<Acrylic Copolymer (A1) and Acrylic Copolymer (A2)>
The acrylic copolymer (A1) and the acrylic copolymer (A2) can be copolymers of a monomer mixture selected from the monomers described below. Specific examples of the monomer include (meth)acrylic acid alkyl ester monomers, (meth)acrylic acid cycloalkyl ester monomers having a cycloalkyl group, monomers having an aromatic ring, monomers having a hydroxyl group, monomers having a carboxyl group, monomers having an epoxy group, monomers having an amino group, monomers having an alkyleneoxy group, monomers having an amide group, and other vinyl monomers.

Specific examples of (meth)acrylic acid alkyl ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 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, undecyl (meth)acrylate, and dodecyl (meth)acrylate.

Examples of (meth)acrylic acid cycloalkyl ester monomers having a cycloalkyl group include cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, trimethylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

Examples of monomers having an aromatic ring include phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, biphenyl (meth)acrylate, and styrene.

Examples of monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and hydroxycyclohexyl (meth)acrylate.

Monomers having a carboxy group include (meth)acrylic acid, p-carboxybenzyl acrylate, β-carboxyethyl acrylate, maleic acid, monoethyl maleate, itaconic acid, citraconic acid, and fumaric acid.

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 monoalkylamino esters of (meth)acrylic acid 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 monomers represented by the following 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, and n and m each represent an integer representing a repeating unit, and 1≦n≦25 and 1≦m≦25. Here, n and m preferably represent 1≦n≦13 and 1≦m≦5, respectively.
Commercially available products of the monomer represented by the general formula (1) include, for example, methoxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.: in the above general formula (1), R ₁ is a hydrogen atom, n=1), methoxydiethylene glycol acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.: in the above general formula (1), R ₁ is a hydrogen atom, n=2), methoxytriethylene glycol acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.: in the above general formula (1), R ₁ is a hydrogen atom, n=3), methoxypolyethylene glycol #400 acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above general formula (1), R ₁ is a hydrogen atom, n=9), methoxypolyethylene glycol #600 acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above general 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 general formula (1), R _{methoxydiethylene} glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above general formula (1), R ₁ is a methyl group, n = 2); methoxytriethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above general formula (1), R ₁ is a methyl group, n = 3); methoxytetraethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above general formula (1), R ₁ is a methyl group, n = 4); methoxypolyethylene glycol #400 methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above general formula (1), R ₁ is a hydrogen atom, n = 9); methoxypolyethylene glycol #600 methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above general 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 general formula (1), R ₁ is a hydrogen atom, n = 23).

Commercially available products of the monomer represented by the general formula (2) include, for example, methoxytripropyleneglycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above general formula (2), _R2 is a hydrogen atom, m=3) and methoxytripropyleneglycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: in the above general formula (2), _R2 is a methyl group, m=3).

Examples of monomers having an amide group include (meth)acrylamide-based compounds ((meth)acrylamide monomers) such as N-methyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, diacetone(meth)acrylamide, and N-(butoxymethyl)(meth)acrylamide; and compounds containing heterocycles (amide monomers) such as N-vinylpyrrolidone, N-vinylcaprolactam, and acryloylmorpholine.

Other vinyl monomers include, for example, vinyl acetate, vinyl crotonate, and acrylonitrile.

The acrylic copolymer (A1) preferably contains a (meth)acrylic acid alkyl ester monomer among the above monomers, and particularly preferably contains a (meth)acrylic acid alkyl ester monomer (a-1) having an alkyl group with a carbon number of 8 to 12. However, the monomer (a-1) does not include the monomer (a-3) described below in which the alkyl group is a cycloalkyl group.
More specifically, as the monomer (a-1), 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, and dodecyl (meth)acrylate are preferred from the viewpoints of stress relaxation and adhesion.

The monomer (a-1) is preferably contained in an amount of 25 to 99% by mass, and more preferably 40 to 99% by mass, of the 100% by mass of the monomer mixture constituting the acrylic copolymer (A1). When the content of monomer (a-1) is 25% by mass or more, sufficient stress relaxation properties are easily obtained. Furthermore, when the content of monomer (a-1) is 99% by mass or less, it is easy to achieve both cohesive strength and stress relaxation properties.

These monomers (a-1) 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-1) in combination from the viewpoint of achieving both adhesion and cohesive strength.

The acrylic copolymer (A1) preferably contains a monomer having a polar group, and in particular, it preferably contains one or more types of polar group-containing monomers (a-2) selected from monomers having a hydroxyl group and monomers having a carboxyl group. More specifically, 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and (meth)acrylic acid are preferred as monomer (a-2) from the viewpoints of cohesive strength and adhesive strength.

The monomer (a-2) is preferably contained in an amount of 0.1 to 4 mass% and more preferably 0.4 to 3 mass% of the 100 mass% monomer mixture constituting the acrylic copolymer (A1). When the content of monomer (a-2) is 0.1 mass% or more, it is easy to obtain sufficient cohesive strength. Also, when the content of monomer (a-2) is 4 mass% or less, it is easy to achieve both cohesive strength and stress relaxation properties.

Of the above monomers, the acrylic copolymer (A2) preferably contains a (meth)acrylic acid cycloalkyl ester monomer (a-3) having a cycloalkyl group. More specifically, from the viewpoint of cohesive strength and adhesive strength, cyclohexyl (meth)acrylate and isobornyl (meth)acrylate are preferred as monomer (a-3).

The monomer (a-3) is preferably contained in an amount of 25 to 99% by mass, and more preferably 40 to 99% by mass, of the 100% by mass of the monomer mixture constituting the acrylic copolymer (A2). When the content of monomer (a-3) is 25% by mass or more, it is easy to obtain sufficient cohesive strength. Also, when the content of monomer (a-3) is 99% by mass or less, it is easy to achieve both cohesive strength and stress relaxation properties.

The acrylic copolymer (A2) preferably contains, among the above monomers, a monomer (a-4) having an amino group. More specifically, as the monomer (a-4), monomethylaminoethyl (meth)acrylate, monoethylaminoethyl (meth)acrylate, 2-dimethylaminoethyl (meth)acrylate, and 2-diethylaminoethyl (meth)acrylate are preferred from the viewpoint of cohesive strength and adhesive strength.

The monomer (a-4) is preferably contained in an amount of 0.1 to 4 mass% and more preferably 0.4 to 3 mass% of the 100 mass% monomer mixture constituting the acrylic copolymer (A2). When the content of monomer (a-4) is 0.1 mass% or more, it is easy to obtain sufficient cohesive strength. Also, when the content of monomer (a-4) is 4 mass% or less, it is easy to achieve both cohesive strength and stress relaxation properties.

Each acrylic copolymer may also contain monomer (a-5), which is a monomer other than monomers (a-1) to (a-4). As monomer (a-5), the above-mentioned monomers having an aromatic ring, monomers having an epoxy group, monomers having an alkyleneoxy group, monomers having an amide group, other vinyl monomers, etc. may be used. The content ratio of monomer (a-5) in 100% by mass of the monomer mixture constituting each acrylic copolymer can be appropriately set within a range in which the effects of the present disclosure can be obtained, and is not particularly limited.

<Calculation of solubility parameter (SP value) of acrylic copolymer>
Next, the SP value of each of the acrylic copolymers (A1) and (A2) will be described. In the present disclosure, the SP value of the acrylic copolymer is calculated by the following formula 3. For the SP value of the monomer constituting the acrylic copolymer, refer to the calculation method of Fedors ["Polymer Engineering and Science", Vol. 14, No. 2 (1974), pp. 148-154].

[Formula 3]
δ=(ΣΔe ₁ M ₁ + Δe ₂ M ₂ + . . . Δe _n M _n )/(ΣΔv ₁ M ₁ + Δv ₂ M ₂ + . . . Δv _n M _n ) ^1/2
[In the formula, δ is the solubility parameter (SP value) of the acrylic copolymer (A1) and the acrylic copolymer (A2), Δe _i (i=1, 2, . . . n) is the molar evaporation energy of the monomer i constituting the acrylic copolymer, Δv _i (i=1, 2, . . . n) is the molar volume of the monomer i constituting the acrylic copolymer, and M _i (i=1, 2, . . . n) is the molar fraction of the monomer i constituting the acrylic copolymer in the total monomer components.]
Here, the unit of the solubility parameter is (cal/mol) ^1/2 .

In the pressure-sensitive adhesive of the present disclosure, SP(A1), which is the SP value of acrylic copolymer (A1), and SP(A2), which is the SP value of acrylic copolymer (A2), are SP(A1)>SP(A2), and the absolute value of the difference between SP(A1) and SP(A2), |SP(A1)-SP(A2)|, is 0.50<|SP(A1)-SP(A2)|<1.60. Here, it is preferable that the absolute value of the difference between SP(A1) and SP(A2) is 0.60<|SP(A1)-SP(A2)|<1.30.
The pressure-sensitive adhesive of the present disclosure contains two types of acrylic copolymers with different SP values, with the high-polarity acrylic copolymer (A1) improving adhesion to a high-polarity adherend, and the low-polarity acrylic copolymer (A2) improving adhesion to a low-polarity adherend. When |SP(A1)-SP(A2)| is greater than 0.50, adhesion to low-polarity and high-polarity adherends can be improved, and when |SP(A1)-SP(A2)| is less than 1.60, transparency can be maintained.

<Calculation of Glass Transition Temperature (Tg) of Acrylic Copolymer>
Next, the Tg of each of the acrylic copolymer (A1) and the acrylic copolymer (A2) will be described. In this disclosure, the Tg of the acrylic copolymer is calculated based on the Tg of the homopolymer of each monomer by the Fox formula represented by the following formula 4. The Tg of the homopolymer of the monomer constituting the acrylic copolymer is the value described in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989). For monomers not described in the Polymer Handbook, the catalog value of the monomer manufacturer is adopted.

[Formula 4]
Fox formula: 1/Tg = _W1 / _Tg1 + _W1 / _Tg1 + ... _Wn / _Tgn )
[In the formula, Tg is the glass transition temperature (Tg) of the acrylic copolymer (A1) or acrylic copolymer (A2) (to be calculated), Tg _i (i = 1, 2, ... n) is the glass transition temperature (Tg) when a homopolymer of monomer i constituting the acrylic copolymer (for calculating Tg) is formed, and W _i (i = 1, 2, ... n) represents the mass fraction of monomer i constituting the acrylic copolymer (for calculating Tg) in the total monomer components.]
Here, the unit of the glass transition temperature is (K).

In the pressure-sensitive adhesive of the present disclosure, Tg(A1), which is the Tg of the acrylic copolymer (A1), and Tg(A2), which is the Tg of the acrylic copolymer (A2), are Tg(A1)<Tg(A2), and the absolute value of the difference between Tg(A1) and Tg(A2), |Tg(A1)-Tg(A2)|, is 100<|SP(A1)-SP(A2)|< 180. Here, it is preferable that the absolute value of the difference between Tg(A1) and Tg(A2) is 120<|SP(A1)-SP(A2)|< 160.
The pressure-sensitive adhesive of the present disclosure contains two types of acrylic copolymers with different Tg, the low Tg acrylic copolymer (A1) improves adhesion to an adherend, and the high Tg acrylic copolymer (A2) improves durability. When |Tg(A1)-Tg(A2)| is greater than 100, adhesion and durability can be improved, and when it is less than 180, transparency can be maintained.

<Measurement of weight average molecular weight (Mw) of acrylic copolymer>
Next, the Mw of each of the acrylic copolymer (A1) and the acrylic copolymer (A2) will be described. In the present disclosure, the Mw of the acrylic copolymer is a value measured in terms of polystyrene by gel permeation chromatography (GPC). Specifically, it can be determined as a weight average molecular weight conversion value using a GPC "LC-GPC system" manufactured by Shimadzu Corporation, with polystyrene of known molecular weight as a standard substance.
Device name: Shimadzu Corporation, LC-GPC system "Prominence"
Column: Four GMHXL columns manufactured by Tosoh Corporation and one HXL-H column manufactured by Tosoh Corporation were connected together.
Mobile phase solvent: tetrahydrofuran Flow rate: 1.0 ml/min Column temperature: 40° C.

The weight-average molecular weight of the acrylic copolymer (A1) is 500,000 to 2,000,000, and preferably 800,000 to 1,500,000. When the weight-average molecular weight of the acrylic copolymer (A1) is in the range of 500,000 to 2,000,000, the cohesive strength is improved, and the moist heat resistance and heat resistance are improved.

The weight-average molecular weight of the acrylic copolymer (A2) is 5,000 to 100,000, and preferably 20,000 to 80,000. When the weight-average molecular weight of the acrylic copolymer (A2) is in the range of 5,000 to 100,000, the adhesion is improved, and the flexibility and winding properties are also improved.

In the pressure-sensitive adhesive of the present disclosure, Mw(A1)/Mw(A2), which is the value obtained by dividing Mw(A1), the weight average molecular weight of acrylic copolymer (A1), by Mw(A2), the weight average molecular weight of acrylic copolymer (A2), is 10<Mw(A1)/Mw(A2)<80. Here, it is preferable that the value obtained by dividing Mw(A1) by Mw(A2) is 20<Mw(A1)/Mw(A2)<70. The pressure-sensitive adhesive of the present disclosure contains two types of acrylic copolymers with different Mw, and the acrylic copolymer (A1), which is a high Mw acrylic copolymer, improves durability, and the acrylic copolymer (A2), which is a low Mw acrylic copolymer, improves anchoring to an adherend. When Mw(A1)/Mw(A2) is greater than 10, durability and anchoring to the adherend can be improved, and when it is less than 80, poor durability due to bleed-out of the low Mw acrylic copolymer (A2) can be suppressed.

<Mixing Ratio of Acrylic Copolymer (A1) and Acrylic Copolymer (A2)>
The pressure-sensitive adhesive of the present disclosure preferably contains 1 to 30 parts by mass, more preferably 2 to 20 parts by mass, of the acrylic copolymer (A2) per 100 parts by mass of the acrylic copolymer (A1). When the content of the acrylic copolymer (A2) is 1 part by mass or more, the adhesion to the adherend and durability can be further improved. When the content is 30 parts by mass or less, flexibility, bending property and winding property can be easily maintained.

[Production of acrylic copolymer]
The copolymer (A1) and the copolymer (A2) can be produced by polymerizing a monomer mixture containing monomers (a-1) and (a-2) and a monomer mixture containing monomers (a-3) and (a-4), respectively.
As the polymerization method, known polymerization methods such as solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, etc. can be applied, but solution polymerization is preferred. As the solvent used in solution polymerization, for example, acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, cyclohexanone, etc. are preferred.
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 in the polymerization is preferably a radical polymerization initiator, and the radical polymerization initiator is generally a peroxide or an azo compound.
Examples of the peroxide 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 of the peroxydicarbonate 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'-azobispropionitrile such as 2,2'-azobis(2-hydroxymethylpropionitrile);
Examples of the compound 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.

<Crosslinking Agent (B)>
The pressure-sensitive adhesive of the present disclosure contains a crosslinking agent (B). The crosslinking agent (B) reacts with a polar group (e.g., a hydroxyl group and/or a carboxyl group) of the copolymer (A1) to improve the cohesive strength of the pressure-sensitive adhesive layer, and to improve durability and stain resistance.

Examples of the crosslinking agent (B) 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 crosslinking agent (B) since it is easy to improve adhesion and durability.

As the isocyanate compound, an isocyanate having two or more isocyanate groups can be used. As the isocyanate compound, for example, isocyanate monomers such as aromatic polyisocyanates, aliphatic polyisocyanates, araliphatic polyisocyanates, alicyclic polyisocyanates, etc., as well as their biuret forms, nurate forms, and adduct forms are preferred.

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, 4,4',4"-triphenylmethane triisocyanate, etc.

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), 1,4-bis(isocyanatomethyl)cyclohexane, etc.

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

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

The adduct is a bifunctional or higher isocyanate compound formed 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.

The isocyanate compound is preferably a trifunctional isocyanate compound from the viewpoint of forming a sufficient crosslinked structure. The isocyanate compound is more preferably an adduct or nurate, which is a reaction product between an isocyanate monomer and a trifunctional low-molecular-weight active hydrogen-containing compound. The isocyanate compound is more 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 particularly preferably a trimethylolpropane adduct of hexamethylene diisocyanate, a trimethylolpropane adduct of tolylene diisocyanate, or a trimethylolpropane adduct 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.

The carbodiimide compound is preferably a high molecular weight polycarbodiimide produced by a decarboxylation condensation reaction of a diisocyanate compound in the presence of a carbodiimide catalyst. The commercially available high molecular weight polycarbodiimide is preferably the Carbodilite series from Nisshinbo Industries. Among these, Carbodilite V-03, 07, and 09 (trade names) are preferred because of their excellent compatibility with organic solvents.

The metal chelate is preferably a coordination compound of a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, or zirconium with acetylacetone or ethyl acetoacetate. Examples of the metal chelate include aluminum ethyl acetoacetate diisopropylate, aluminum trisacetylacetonate, aluminum bisethyl acetoacetate monoacetylacetonate, and aluminum alkyl acetoacetate diisopropylate.

The crosslinking agent (B) is preferably contained in an amount of 0.02 to 4.0 parts by mass, and more preferably 0.04 to 1.0 parts by mass, per 100 parts by mass of the total of copolymer (A1) and copolymer (A2). When the content of crosslinking agent (B) is 0.02 parts by mass or more, the cohesive strength is further improved, and when it is 4.0 parts by mass or less, it is preferable because it becomes easier to achieve both cohesive strength and flexibility.

<Organosilane Compound>
The pressure-sensitive adhesive of the present disclosure may further contain an organosilane compound. By containing an organosilane, the adhesiveness to an adherend can be further improved.
Examples of the organic silane compound include alkoxysilane compounds having a (meth)acryloxy group, such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropyltripropoxysilane, 3-(meth)acryloxypropyltributoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane;
Alkoxysilane compounds having a vinyl group, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinylmethyldimethoxysilane, and vinylmethyldiethoxysilane;
alkoxysilane compounds having an amino group, such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltripropoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane;
Alkoxysilane compounds having a mercapto group, such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltripropoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylmethyldiethoxysilane;
alkoxysilane compounds having an epoxy group, such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyltripropoxysilane, 3-glycidoxypropyltributoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane;
tetraalkoxysilane compounds such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane;
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 the total of copolymer (A1) and copolymer (A2).

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

<Gel Fraction>
The pressure-sensitive adhesive of the present disclosure preferably has a gel fraction of 60 to 90% by mass, more preferably 60 to 80% by mass. When the gel fraction is 60% by mass or more, the cohesive strength of the pressure-sensitive adhesive is improved, a strong pressure-sensitive adhesive layer is easily obtained, and durability is improved, whereas when the gel fraction is 90% by mass or less, the stress relaxation property of the pressure-sensitive adhesive is improved, a soft pressure-sensitive adhesive layer is easily obtained, and adhesion is improved.

[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 5, the gel fraction is determined as the mass fraction (unit: mass%) of the insoluble matter after the pressure-sensitive adhesive layer is immersed in ethyl acetate at 50° C. for 1 day relative to the pressure-sensitive adhesive layer before immersion.
(Equation 5)
Gel fraction (mass%)=(Y/X)×100
X = mass (g) of the adhesive layer before immersion
Y = mass of the adhesive layer after immersion (g)
In general, the gel fraction of a polymer is equal to the degree of crosslinking, and the more crosslinked parts in the polymer, the higher the gel fraction. The gel fraction (amount of crosslinked structure introduced) can be adjusted to a desired range by the method of introducing the crosslinked structure, the type and amount of the curing agent, etc.

"Adhesive sheet"
The pressure-sensitive adhesive sheet of the present disclosure is a pressure-sensitive adhesive sheet used to form the pressure-sensitive adhesive layer in a laminate including at least a light-transmitting substrate and a pressure-sensitive adhesive layer, that is, the pressure-sensitive adhesive sheet of the present disclosure can be used to bond a light-transmitting substrate. The laminate preferably includes the light-transmitting substrate, the pressure-sensitive adhesive layer, and a polarizing plate. The pressure-sensitive adhesive sheet is a cured product of the pressure-sensitive adhesive of the present disclosure.
An example of a schematic cross-sectional view partially illustrating a pressure-sensitive adhesive sheet according to the present disclosure is shown in Fig. 1. In Fig. 1, reference numeral 1 denotes a first pressure-sensitive adhesive layer which is a cured product of the pressure-sensitive adhesive according to the present disclosure, and reference numeral 2 denotes a release film.

The adhesive sheet of the present disclosure shown in Figure 1 has a configuration in which release films 2 are formed on both sides of an adhesive layer (first adhesive layer 1) as shown in Figure 1. Here, the first adhesive layer 1 formed between the release films 2 is an adhesive layer formed from a mixture of the above-mentioned acrylic copolymer (A1), acrylic copolymer (A2), and crosslinking agent (B).

<Release film>
The release film is not particularly limited, but a transparent plastic substrate can be suitably used. Examples of the material of 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 kinds.

Among the transparent plastic substrates mentioned above, a transparent plastic substrate with excellent heat resistance, i.e., a transparent plastic substrate in which deformation is suppressed or prevented under harsh conditions such as high temperature or high temperature and humidity, can be preferably used as the release film. 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 in the form of 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.

<Production of Pressure-Sensitive Adhesive Sheet>
The adhesive sheet of the present disclosure can be manufactured according to the manufacturing method of a normal adhesive sheet.For example, it can be manufactured by directly coating the acrylic copolymer (A1), the acrylic copolymer (A2) and the crosslinking agent (B) (hereinafter, may be simply described as "adhesive") on the release treatment surface of the release film so that the thickness after drying is a predetermined thickness, forming an adhesive layer, and then attaching the release film, or by coating the adhesive on the release treatment surface of two release films so that the thickness after drying is a predetermined thickness, forming two adhesive layers, and then attaching each adhesive layer, etc.

The thickness of the adhesive layer is not particularly limited, and is preferably, for example, 10 to 500 μm, and more preferably 50 to 200 μm. When the thickness of the adhesive layer is 10 to 500 μm, sufficient cohesive strength is easily obtained, and it is preferable that heat resistance, moist heat resistance, flexibility, and rollability can be highly compatible.

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 by cutting it to an appropriate width and winding it into a roll.

"Laminate"
The laminate of the present disclosure includes a light-transmitting substrate, a pressure-sensitive adhesive layer, and a polarizing plate, and the pressure-sensitive adhesive layer is formed using the pressure-sensitive adhesive sheet of the present disclosure.

The laminate of the present disclosure is formed from an adhesive sheet that has excellent transparency, heat resistance, moist heat resistance, flexibility and rollability, and therefore has excellent transparency, heat resistance, moist heat resistance, flexibility and rollability.

FIG. 2 shows an example of a schematic cross-sectional view partially illustrating a laminate, which is an example of the use of the adhesive sheet of the present disclosure. In FIG. 2, reference numeral 3 indicates a light-transmitting substrate (cover panel), reference numeral 1 indicates a first adhesive layer, and reference numeral 4 indicates a polarizing plate.

In the laminate shown in FIG. 2, a light-transmitting substrate (cover panel) 3 is attached to a polarizing plate 4 via a first adhesive layer 1 made of the adhesive of the present disclosure. In this manner, the adhesive sheet of the present disclosure can be used in a form in which a transparent adhesive layer formed from the adhesive is attached to the light-transmitting substrate (cover panel) and the polarizing plate.

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

As the light-transmitting substrate (cover panel), among the transparent plastic substrates mentioned above, transparent plastic substrates with excellent heat resistance, that is, transparent plastic substrates in which deformation is suppressed or prevented under harsh conditions such as high temperature or high temperature and high humidity, can be preferably used. As transparent plastic substrates, polyethylene terephthalate (PET), polycycloolefin, and polyimide are particularly suitable.

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

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

The display disclosed herein has a laminate with excellent transparency, heat resistance, moist heat resistance, flexibility and rollability, and therefore has excellent transparency, heat resistance, moist heat resistance, flexibility and rollability.

FIG. 3 shows an example of a schematic cross-sectional view partially illustrating a display, which is an example of the use of the adhesive sheet of the present disclosure. In FIG. 3, reference numeral 3 denotes a light-transmitting substrate (cover panel), reference numeral 1 denotes a first adhesive layer, reference numeral 4 denotes a polarizing plate, reference numeral 5 denotes a second adhesive layer, reference numeral 6 denotes a barrier layer such as silicon nitride, reference numeral 7 denotes an organic EL layer, reference numeral 8 denotes a support such as polyimide, and reference numeral 10 denotes an organic EL cell. Note that the configuration of the display of the present disclosure is not limited to that shown in FIG. 3.

In the display shown in Fig. 3, a light-transmitting substrate (cover panel) 3 is attached to a polarizing plate via an adhesive layer (first adhesive layer 1) made of the adhesive of the present disclosure, and is further attached to an organic EL cell via an adhesive layer for a polarizing plate (second adhesive layer 5). In this way, the adhesive sheet of the present disclosure can be used in a form in which a transparent adhesive layer (reference numeral 1) formed from the adhesive of the present disclosure is attached to a light-transmitting substrate (cover panel) 3 and a polarizing plate 4, and the laminate is further attached to an organic EL cell 10 via an adhesive layer for a polarizing plate 5.
For example, in FIG. 3 , the pressure-sensitive adhesive of the present disclosure can be used only in the first pressure-sensitive adhesive layer 1 , or can be used in both the first pressure-sensitive adhesive layer 1 and the second pressure-sensitive adhesive layer 5 .
In general, when comparing the first pressure-sensitive adhesive layer with the second pressure-sensitive adhesive layer, the first pressure-sensitive adhesive layer has higher required quality, and the pressure-sensitive adhesive of the present disclosure has good adhesion and bonding to the substrate, so it is preferable to use the pressure-sensitive adhesive of the present disclosure for the first pressure-sensitive adhesive layer. In this case, the pressure-sensitive adhesive for forming the second pressure-sensitive adhesive layer may be the pressure-sensitive adhesive of the present disclosure or a conventionally known pressure-sensitive adhesive.

　There are no particular limitations on how the displays can be used, but examples include OLED televisions, OLED smartphones, OLED tablets, and OLED smartwatches.

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

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

<Production Example of Acrylic Copolymer>
(Acrylic Copolymer (A1-1))
A reaction vessel (hereinafter simply referred to as "reaction vessel") equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen inlet tube was charged with 30 parts of 2-ethylhexyl acrylate (EHA), 67 parts of butyl acrylate (BA), 2 parts of 2-hydroxyethyl acrylate (HEA), 1 part of acrylic acid (AA), and 0.2 parts of 2,2'-azobisisobutyronitrile (hereinafter simply referred to as "AIBN") as an initiator, and the atmosphere in the reaction vessel was replaced with nitrogen gas. Then, the mixture was heated to 60°C while stirring under a nitrogen atmosphere to start the reaction. Then, the reaction solution was reacted at 60°C for 4 hours. After the reaction was completed, the mixture was cooled and diluted with ethyl acetate to obtain a copolymer (A1-1) solution with a non-volatile content of 30%. The weight average molecular weight of the obtained copolymer (A1-1) was 1.8 million.

(Acrylic Copolymers (A1-2 to A1-12, A'1-1, A'1-2)
Copolymers (A1-2 to A1-12, A'1-1, A'1-2) were produced in the same manner as in the production of the acrylic copolymer (A1-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Table 1.

(Acrylic Copolymer (A2-1))
A reaction vessel (hereinafter simply referred to as "reaction vessel") equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen inlet tube was charged with 5 parts of butyl acrylate (BA), 95 parts of isobornyl acrylate (IBXA), and 2 parts of AIBN as an initiator, and the atmosphere in the reaction vessel was replaced with nitrogen gas. Then, the mixture was heated to 60°C while stirring under a nitrogen atmosphere to start the reaction. Then, the reaction solution was reacted at 60°C for 4 hours. After the reaction was completed, the mixture was cooled and diluted with ethyl acetate to obtain a copolymer (A2-1) solution with a non-volatile content of 30%. The weight average molecular weight of the obtained copolymer (A2-1) was 50,000.

(Acrylic Copolymers (A2-1 to A2-6, A'2-1, A'2-2)
Copolymers (A2-2 to A2-6, A'2-1, A'2-2) were produced in the same manner as in the production of the acrylic copolymer (A2-1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Table 2.

The solubility parameters (SP values), weight average molecular weights (Mw), and glass transition temperatures (Tg) of the resulting copolymers (A1-1 to A1-12, A'1-1, A1'-2, A2-1 to A2-6, A'2-1, A'2-2) are shown in Tables 1 and 2. The SP values and Tg were measured by the methods described above.

The abbreviations in the table are as follows.
EHA: 2-ethylhexyl acrylate (alkyl group has 8 carbon atoms)
OA: octyl acrylate (alkyl group carbon number: 8)
DOA: dodecyl acrylate (alkyl group carbon number: 12)
BA: butyl acrylate (alkyl group carbon number: 4)
MA: methyl acrylate (alkyl group carbon number 1)
MMA: Methyl methacrylate (alkyl group carbon number 1)
MEA: 2-methoxyethyl acrylate (a monomer represented by the general formula (1), where R ₁ is a hydrogen atom and n=1)
IBXA: isobornyl acrylate (monomer having a cycloalkyl group)
IBXMA: isobornyl methacrylate (monomer having a cycloalkyl group)
HEA: 2-hydroxyethyl acrylate HBA: 4-hydroxybutyl acrylate AA: acrylic acid MAA: methacrylate Am: acrylamide DM: 2-dimethylaminoethyl methacrylate

Example 1
<Preparation of Adhesive>
A pressure-sensitive adhesive was obtained by mixing and stirring 1 part of acrylic copolymer (A2-1), 0.20 parts of an adduct of tolylene diisocyanate and trimethylolpropane (B-1) as a crosslinking agent (B), 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% with respect to 100 parts of the acrylic copolymer (A1-1).

<Production of Pressure-Sensitive Adhesive Sheet>
The obtained adhesive was applied 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 dried at 100° 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 sheet/adhesive layer/release sheet" laminate. Next, the obtained laminate was aged in a 40° C. environment for 1 week to obtain an adhesive sheet.

(Examples 2 to 15, Comparative Examples 1 to 10)
As shown in Table 3, pressure sensitive adhesives and pressure sensitive adhesive sheets were obtained in the same manner as in Example 1, except that the types and amounts (parts by mass) of the copolymer and crosslinking agent were changed.

The abbreviations in the table are as follows.
<Crosslinking Agent (B)>
B-1: Trimethylolpropane adduct of tolylene diisocyanate B-2: Trimethylolpropane adduct of hexamethylene diisocyanate B-3: Trimethylolpropane adduct of xylylene diisocyanate B-4: N,N,N',N'-tetraglycidyl-m-xylylenediamine B-5: 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane <organic silane compound>
S-1: 3-glycidoxypropyltrimethoxysilane

<<Measurement and evaluation of physical properties of adhesive sheets>>
The obtained pressure-sensitive adhesive sheet was evaluated for gel fraction, and the following properties: transparency, heat resistance, moist heat resistance, dynamic bending resistance, static bending resistance, and winding property. The results are shown in Tables 3 and 4.

<Preparation of Test Adhesive Sheet>
The 38 μm-thick release film was peeled off from the obtained adhesive sheet, and the exposed adhesive layer was attached to a 50 μm-thick PET film (T60, manufactured by Toray Industries, Inc.) using a laminator at 23° C. and a relative humidity of 50%, to produce a test adhesive sheet I consisting of PET film/adhesive layer/release film.

<Gel Fraction>
The obtained adhesive sheet was cut into a size of 25 mm wide x 100 mm long. One release film of the cut adhesive sheet was peeled off, and the sheet was attached to a 200 mesh of 50 mm wide x 120 mm long, whose mass had been measured in advance. Next, the other release film was peeled off, and the mesh was folded so that the adhesive was on the inside so that the adhesive was not exposed. The adhesive wrapped in the mesh was immersed in about 50 mL of ethyl acetate at 23 ° C for 7 days, and the sol component of the adhesive was dissolved out of the mesh. After immersion, the adhesive wrapped in the mesh was taken out, dried at 100 ° C for 1 hour, and allowed to cool for about 20 minutes, and then the dry mass was measured. The gel fraction of the adhesive was calculated by the following formula.
Gel fraction (mass%)=((X−Y)/X)×100
X = mass (g) of the adhesive layer before immersion
Y = mass of the adhesive layer after immersion (g)

<Transparency>
Test adhesive sheet I was cut to a size of 112 mm wide x 200 mm long (corresponding to a 9-inch display) to prepare test adhesive sheet II consisting of a PET film/adhesive layer/release film.
The release film was peeled off from this test pressure-sensitive adhesive sheet II, 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% relative humidity, and the haze was measured. The haze was measured using a Turbidimeter NDH5000W (product name) manufactured by Nippon Denshoku Industries Co., Ltd. The evaluation criteria were as follows.
[Evaluation criteria]
A: HAZE is less than 1.0 (good).
B: HAZE is 1.0 or more (poor).

<Heat resistance/humid heat resistance>
The release film was peeled off from the test adhesive sheet II prepared separately, and the exposed adhesive layer was attached to a polarizing plate (layer structure: triacetyl cellulose film/polyvinyl alcohol film/cycloolefin film) using a laminator at 25 ° C. and 50% relative humidity to obtain a test laminate consisting of a PET film/adhesive layer/polarizing plate. Next, as a heat resistance test, the laminate was left for 500 hours under conditions of 105 ° C., cooled at 25 ° C. and 50% relative humidity, and then visually evaluated for the generation of bubbles and the lifting and peeling of the test laminate under the following conditions. In addition, as an evaluation of moist heat resistance, the test laminate was left for 500 hours at 60 ° C. and 95% relative humidity, cooled at 25 ° C. and 50% relative humidity, and then visually evaluated for the generation of bubbles and the lifting and peeling of the adhesive sheet under the following conditions. Heat resistance and moist heat resistance were evaluated based on the following three-stage evaluation criteria.
[Evaluation criteria]
AA: No air bubbles, floating or peeling was observed, and there was no problem in practical use.
A: Air bubbles, lifting or peeling is observed in less than five places, but this does not cause any problems in practical use.
B: Air bubbles, lifting or peeling was observed in 5 or more places, and the product was problematic for practical use.

<Dynamic flex resistance: flex resistance [1], [2], [3]>
The release film was peeled off from the test adhesive sheet II prepared separately, and the exposed adhesive layer was attached to a polarizing plate (layer structure: triacetyl cellulose film / polyvinyl alcohol film / cycloolefin film) using a laminator at 25 ° C. and 50% relative humidity to obtain a test laminate consisting of a PET film / adhesive layer / polarizing plate. Next, the test laminate was subjected to a normal test of bending resistance [1] at 25 ° C. and 50% relative humidity, a heat resistance test of bending resistance [2] at 85 ° C., and a moist heat resistance test of bending resistance [3] at 60 ° C. and 95% relative humidity. The conditions were set so that the inner diameter (diameter) when folded by a folding tester (manufactured by Yuasa System Co., Ltd.) was 6 mm, and 300,000 cycles were repeated, with folding and opening at 180 ° as one cycle. The dynamic bending property was evaluated from the following viewpoints regarding the appearance after the test.
Appearance: The test laminate was visually inspected for the presence or absence of air bubbles and the presence or absence of lifting or peeling of the adhesive layer under the following conditions.
[Evaluation criteria]
AA: No air bubbles, floating or peeling was observed, and there was no problem in practical use.
A: Air bubbles, lifting or peeling is observed in less than five places, but this does not cause any problems in practical use.
B: Air bubbles, lifting or peeling was observed in 5 or more places, and the product was problematic for practical use.

<Static bending resistance: bending resistance [1], [2], [3]>
The release film was peeled off from the test adhesive sheet II prepared separately, and the exposed adhesive layer was attached to a polarizing plate (layer structure: triacetyl cellulose film / polyvinyl alcohol film / cycloolefin film) at 25 ° C. and 50% relative humidity using a laminator to obtain a test laminate consisting of a PET film / adhesive layer / polarizing plate. Next, the test laminate was subjected to bending resistance [1] at 25 ° C. and 50% relative humidity as a normal test, bending resistance [2] at 85 ° C. as a heat resistance test, and bending resistance [3] at 60 ° C. and 95% relative humidity as a moist heat resistance test, respectively, by a planar body unloaded U-shaped stretch tester, with the polarizing plate side of the test piece facing inward, and held in a bent state with a bending radius of 3 mm and a bending angle of 180 ° for 240 hours. The static bending property was evaluated from the following viewpoints regarding the appearance after the test.
Appearance: The test laminate was visually inspected for the presence or absence of air bubbles and the presence or absence of lifting or peeling of the adhesive layer under the following conditions.
[Evaluation criteria]
AA: No air bubbles, floating or peeling was observed, and there was no problem in practical use.
A: Air bubbles, lifting or peeling is observed in less than five places, but this does not cause any problems in practical use.
B: Air bubbles, lifting or peeling was observed in 5 or more places, and the product was problematic for practical use.

<Windability>
The release film was peeled off from the test adhesive sheet II prepared separately, and the exposed adhesive layer was attached to a polarizing plate (layer structure: triacetyl cellulose film/polyvinyl alcohol film/cycloolefin film) using a laminator at 25 ° C. and 50% relative humidity to obtain a test laminate consisting of a PET film/adhesive layer/polarizing plate. Next, the test laminate was wound in the long side direction around a metal rod with a radius of 3 mm, with the PET side of the test piece facing inward, and then rolled into a roll, and fixed by tying at three places with a string. As a winding test, the roll-shaped test laminate was kept in an atmosphere of 25 ° C. and 50% relative humidity for 240 hours. The winding property was evaluated from the following viewpoints of appearance after the test.
Appearance: The test laminate was visually inspected for the presence or absence of air bubbles and the presence or absence of lifting or peeling of the adhesive layer under the following conditions.
[Evaluation criteria]
AA: No air bubbles, floating or peeling was observed, and there was no problem in practical use.
A: Air bubbles, lifting or peeling is observed in less than five places, but this does not cause any problems in practical use.
B: Air bubbles, lifting or peeling was observed in 5 or more places, and the product was problematic for practical use.

Layer structure of test pressure-sensitive adhesive sheet and test laminate [A]: PET film/pressure-sensitive adhesive layer/glass [B]: PET film/pressure-sensitive adhesive layer/polarizing plate Test conditions Bending resistance [1]: 25° C., 50% relative humidity environment Bending resistance [2]: 85° C. environment Bending resistance [3]: 60° C., 95% relative humidity environment

From the results in Table 4, it was confirmed that the pressure-sensitive adhesive sheets of Examples 1 to 15 were excellent in heat resistance, moist heat resistance, flexibility, and windability, in addition to transparency. This demonstrated that the laminate and display using the pressure-sensitive adhesive sheet of the present disclosure were excellent in transparency, heat resistance, moist heat resistance, and flexibility. Furthermore, the display of the present disclosure also had excellent visibility and contrast.
On the other hand, the pressure-sensitive adhesive sheets of Comparative Examples 1 to 10 could not satisfy all of the above characteristics.

This application claims priority based on Japanese Patent Application No. 2022-179756, filed November 9, 2022, the entire disclosure of which is incorporated herein by reference.

1: First pressure-sensitive adhesive layer 2: Release film 3: Light-transmitting substrate (cover panel)
4 Polarizing plate 5 Second adhesive layer 6 Barrier layer 7 Organic EL layer 8 Support 9 Organic EL cell

Claims

A pressure-sensitive adhesive comprising an acrylic copolymer (A1), an acrylic copolymer (A2), and a crosslinking agent (B), and satisfying all of the following (1) to (5):
(1) SP(A1)>SP(A2), and 0.50<|SP(A1)-SP(A2)|<1.60
(2) Tg(A1)<Tg(A2), and 100<|Tg(A1)-Tg(A2)|<180
(3) Mw(A1) is 500,000 to 2,000,000 (4) Mw(A2) is 5,000 to 100,000 (5) 10<Mw(A1)/Mw(A2)<80
Here, in the above formula,
SP(A1) is the SP value of the acrylic copolymer (A1); SP(A2) is the SP value of the acrylic copolymer (A2); Tg(A1) is the glass transition temperature of the acrylic copolymer (A1); Tg(A2) is the glass transition temperature of the acrylic copolymer (A2); Mw(A1) is the weight average molecular weight of the acrylic copolymer (A1); Mw(A2) is the weight average molecular weight of the acrylic copolymer (A2); |SP(A1)-SP(A2)| is the absolute value of the difference between SP(A1) and SP(A2); |Tg(A1)-Tg(A2)| is the absolute value of the difference between Tg(A1) and Tg(A2); and Mw(A1)/Mw(A2) is the value obtained by dividing Mw(A1) by Mw(A2).
The pressure-sensitive adhesive according to claim 1, wherein the acrylic copolymer (A1) is a copolymer of a monomer mixture containing the following monomer (a-1) and the following monomer (a-2), and the acrylic copolymer (A2) is a copolymer of a monomer mixture containing the following monomer (a-3) and the following monomer (a-4).
(a-1) (meth)acrylic acid alkyl ester monomers having an alkyl group with 8 to 12 carbon atoms (excluding monomer (a-3) below)
(a-2) Monomers having one or more polar groups selected from monomers having a hydroxyl group and monomers having a carboxy group; (a-3) (meth)acrylic acid cycloalkyl ester monomers having a cycloalkyl group; (a-4) Monomers having an amino group.
The acrylic copolymer (A1) contains, in 100% by mass of the monomer mixture,
The monomer (a-1) is 25 to 99% by mass, and the monomer (a-2) is 0.1 to 4% by mass.
Including,
The acrylic copolymer (A2) contains, in 100% by mass of the monomer mixture,
The monomer (a-3) is 25 to 99% by mass, and the monomer (a-4) is 0.1 to 4% by mass.
The adhesive according to claim 2 , comprising:
The pressure-sensitive adhesive according to any one of claims 1 to 3, comprising 1 to 30 parts by mass of the acrylic copolymer (A2) per 100 parts by mass of the acrylic copolymer (A1).
The adhesive according to any one of claims 1 to 4, characterized in that the weight average molecular weight of the acrylic copolymer (A1) is 800,000 to 1,500,000, and the weight average molecular weight of the acrylic copolymer (A2) is 20,000 to 80,000.
The adhesive according to any one of claims 1 to 5, characterized in that the gel fraction is 60 to 90% by mass.
The adhesive according to any one of claims 1 to 6, characterized in that the crosslinking agent (B) is an isocyanate compound.
An adhesive sheet having an adhesive layer that is a cured product of the adhesive according to any one of claims 1 to 7.
A laminate comprising a light-transmitting substrate, an adhesive layer, and a polarizing plate, the adhesive layer being a cured product of the adhesive according to any one of claims 1 to 7.
A display comprising the laminate of claim 9 and an optical element.