JP7338829B2 - PSA COMPOSITION FOR FOLDABLE DISPLAY AND OPTICAL MEMBER FOR FOLDABLE DISPLAY - Google Patents

Description

TECHNICAL FIELD The present invention relates to an adhesive composition for foldable displays and an optical member for foldable displays.

2. Description of the Related Art In recent years, mobile electronic devices called so-called foldable devices (also called “flexible devices”), such as curved devices and foldable devices, are becoming popular. Along with this popularization, pressure-sensitive adhesive compositions having properties suitable for use in foldable devices have been developed.

For example, Patent Document 1 discloses a pressure-sensitive adhesive for an optical film containing a (meth)acrylic ester copolymer (A), wherein the (meth)acrylic ester copolymer (A) is (a1) an alkyl 9.9% by mass or more and 99.9% by mass or less of the (meth)acrylic acid ester monomer-derived structural unit; and (a2) 0.1% by mass or more and 15% by mass of the (meth)acrylic monomer-derived structural unit having an amide group %; (a3) 0% by mass or more and 19.9% by mass or less of structural units derived from a functional group-containing monomer that is a (meth) acrylic acid ester monomer that does not have a plurality of radically polymerizable functional groups; and (a4) the above ( 0% by mass or more and 90% by mass or less of structural units derived from (meth)acrylate monomers other than a1), (a2), and (a3), and the above (a1), (a2), (a3), and the total amount of the constituent units derived from (a4) is 100% by mass, and the (meth)acrylate copolymer (A) has a glass transition temperature of −70° C. or more and −58° C. or less, and A pressure-sensitive adhesive for optical films having a weight average molecular weight of more than 1,000,000 and 2,500,000 or less is disclosed.
Further, for example, in Patent Document 2, the ratio of the structural units derived from (meth)acrylic acid alkyl ester monomers and all structural units to the total mass is 10% by mass to 50% by mass, and the hydroxyl group is A (meth)acrylic polymer (A) containing structural units derived from a monomer having a structural unit derived from a (meth)acrylic acid alkyl ester monomer, and a ratio of all structural units to the total mass of 10 A (meth)acrylic oligomer (B) having a mass% to 50% by mass, containing structural units derived from a monomer having a hydroxyl group, and having a weight average molecular weight (Mw) of 2500 or more and 10000 or less. and at least one of the (meth)acrylic polymer (A) and the (meth)acrylic oligomer (B) further contains at least one selected from an amino group, an amide group, and an alkoxy group as a polar group. The (meth)acrylic polymer (A) or the (meth)acrylic oligomer (B) containing a structural unit derived from a polar group-containing monomer and containing a structural unit derived from the polar group-containing monomer. Suitable for sheet-like optical members, wherein the ratio of structural units derived from polar group-containing monomers in each is 6% by mass to 50% by mass with respect to the total mass of all structural units of the polymer or oligomer. An adhesive composition is disclosed.

JP 2017-95653 A Japanese Unexamined Patent Application Publication No. 2013-32428

Foldable devices are often stored in a folded state. In the folded device, stress due to folding concentrates on the adhesive layer at the folded portion. In general, when a foldable device is left in a high-temperature environment, defects such as whitening, foaming, and peeling occur due to stress on the adhesive layer in the folded state rather than the unfolded state. It's easy to do. However, the pressure-sensitive adhesive layer formed from a conventional pressure-sensitive adhesive composition tends to be inferior in high-temperature durability in a folded state, even though it is excellent in high-temperature durability in an unfolded state. For this reason, for example, an adhesive composition used for laminating a foldable display and an optical member (hereinafter also referred to as "adhesive composition for foldable display") has high-temperature durability in an unfolded state. In addition, it is required to be able to form a pressure-sensitive adhesive layer that is excellent in high-temperature durability in a folded state.

In addition, since foldable devices are repeatedly unfolded and folded, the pressure-sensitive adhesive composition for foldable displays is required to form a pressure-sensitive adhesive layer with excellent bending resistance at room temperature. In general, to improve the bending resistance of the adhesive layer, it is conceivable to increase the stress relaxation property of the adhesive layer. It tends to lose power. In order to increase the adhesive strength of the adhesive layer, it is effective to increase the cohesive strength of the adhesive layer. It is not possible to improve the bending resistance at. As a method for enhancing the stress relaxation property of the adhesive layer without lowering the adhesive force, for example, a method using a low-molecular-weight polymer (so-called oligomer) is conceivable. However, when a pressure-sensitive adhesive composition containing a high-molecular-weight polymer (so-called polymer) as a main ingredient contains an oligomer, the oligomer bleeds out due to the poor compatibility between the polymer and the oligomer, and the pressure-sensitive adhesive layer is formed. It may accumulate on the folded part. Defects such as whitening are likely to occur when the oligomer accumulates at the bent portions of the pressure-sensitive adhesive layer.

As described above, it has been difficult to improve both the bending resistance at room temperature and the adhesive strength in addition to the high-temperature durability in the folded state, in the pressure-sensitive adhesive composition for foldable displays.

Regarding the above point, Patent Documents 1 and 2 do not mention at all about increasing the durability of the pressure-sensitive adhesive layer when the foldable device is left in a high-temperature environment in a folded state. Moreover, in Patent Documents 1 and 2, no attention is paid to improving both the bending resistance and adhesive strength at room temperature.

As described above, it has been difficult to improve both the bending resistance at room temperature and the adhesive strength in addition to the high-temperature durability in the folded state, in the pressure-sensitive adhesive composition for foldable displays.

The problem to be solved by the present invention is to provide a pressure-sensitive adhesive composition for foldable displays, which is excellent in bending resistance at room temperature and high-temperature durability in a folded state, and which can form a pressure-sensitive adhesive layer exhibiting good adhesive strength. It is also an object of the present invention to provide an optical member for a foldable display comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for a foldable display.

Specific means for solving the problems include the following aspects.
<1> A structural unit (a1) derived from a monomer having a hydroxyl group, a structural unit (a2) derived from a monomer having a carboxy group, and a structural unit derived from a (meth)acrylic acid alkyl ester monomer The content of the structural unit (a1) containing (a3) and derived from the monomer having a hydroxyl group is in the range of 1.5% by mass or more and 20% by mass or less with respect to all structural units, and the weight a (meth)acrylic copolymer (A) having an average molecular weight of 1,000,000 or more;
Containing a structural unit (b1) derived from a monomer having a hydroxyl group, the content of the structural unit (b1) derived from the monomer having a hydroxyl group is 3% by mass or more and 40% by mass with respect to all structural units. a (meth)acrylic copolymer (B) having a weight average molecular weight within the range of 2500 or more and 10000 or less;
and an isocyanate-based cross-linking agent,
A foldable in which the content of the (meth)acrylic copolymer (B) is in the range of 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic copolymer (A) An adhesive composition for displays.
<2> In the (meth)acrylic copolymer (A), the structural unit (a1) derived from the monomer having a hydroxyl group relative to the structural unit (a2) derived from the monomer having a carboxy group The pressure-sensitive adhesive composition for foldable displays according to <1>, wherein the content ratio [structural unit (a1)/structural unit (a2)] is 1.0 or more on a molar basis.
<3> The adhesive composition for a foldable display according to <1> or <2>, wherein the (meth)acrylic copolymer (A) has a glass transition temperature of less than -50°C.
<4> An optical member for a foldable display comprising an adhesive layer formed from the adhesive composition for a foldable display according to any one of <1> to <3>.

According to the present invention, a pressure-sensitive adhesive composition for a foldable display capable of forming a pressure-sensitive adhesive layer having excellent bending resistance at room temperature and high-temperature durability in a folded state and exhibiting good adhesive strength, and the above-mentioned Provided is an optical member for a foldable display comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for a foldable display.

Specific embodiments of the present invention will be described in detail below. However, the present invention is by no means limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the purpose of the present invention.

In this specification, the numerical range indicated using "to" means a range including the numerical values before and after "to" as the minimum and maximum values, respectively.
In the numerical ranges described stepwise in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the upper limit or lower limit of the numerical range described in other steps. . Moreover, in the numerical ranges described in this specification, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the values shown in the examples.
In the present specification, a combination of two or more preferred aspects is a more preferred aspect.
In the present specification, the amount of each component means the total amount of the multiple types of substances unless otherwise specified when there are multiple types of substances corresponding to each component.

As used herein, the term "(meth)acrylic copolymer" means that the content of structural units derived from a monomer having a (meth)acryloyl group is the total structural units [i.e., (meth)acrylic copolymer total structural units of the polymer] is 50% by mass or more.

As used herein, the term "adhesive composition" means a liquid or paste substance before completion of the cross-linking reaction.
As used herein, the term "adhesive layer" means a film made of a substance after the crosslinking reaction in the adhesive composition has been completed.

As used herein, "(meth)acrylic" is a term that includes both "acrylic" and "methacrylic", and "(meth)acrylate" is a term that includes both "acrylate" and "methacrylate". , "(meth)acryloyl" is a term encompassing both "acryloyl" and "methacryloyl".

As used herein, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

In this specification, the molecular weight when there is a molecular weight distribution means the weight average molecular weight (Mw).

As used herein, "room temperature" means 25°C ± 5°C.

In the present specification, the term "excellent folding resistance" means having excellent properties that can suppress defects such as whitening that may occur when the unfolded state and the folded state are repeated in a foldable display. do.

In this specification, the specific (meth)acrylic copolymer (A) and the specific (meth)acrylic copolymer (B) are collectively referred to as "specific (meth)acrylic copolymer".

[Adhesive composition for foldable display]
The pressure-sensitive adhesive composition for a foldable display of the present invention (hereinafter also simply referred to as "pressure-sensitive adhesive composition") comprises a structural unit (a1) derived from a monomer having a hydroxyl group and a monomer having a carboxy group. The content of the structural unit (a1) derived from the hydroxyl group-containing monomer containing the structural unit (a2) derived from and the structural unit (a3) derived from the (meth)acrylic acid alkyl ester monomer is A (meth) acrylic copolymer (A) having a weight average molecular weight of 1,000,000 or more in the range of 1.5% by mass or more and 20% by mass or less with respect to all structural units [hereinafter referred to as “specific (meth ) is also referred to as “acrylic copolymer (A)”. ] and a structural unit (b1) derived from a monomer having a hydroxyl group, and the content of the structural unit (b1) derived from the monomer having a hydroxyl group is 3% by mass or more with respect to all structural units. (Meth)acrylic copolymer (B) having a weight average molecular weight of 40% by mass or less and a weight average molecular weight of 2500 or more and 10000 or less [hereinafter referred to as “specific (meth)acrylic copolymer (B) ” is also called. ] and an isocyanate-based cross-linking agent, and the content of the (meth)acrylic copolymer (B) is 3 parts by mass with respect to 100 parts by mass of the (meth)acrylic copolymer (A) part or more and 50 parts by mass or less.
ADVANTAGE OF THE INVENTION According to the adhesive composition of this invention, the adhesive layer which is excellent in bending resistance at room temperature, high-temperature durability in the folded state, and shows favorable adhesive force can be formed.
Although the reason why the pressure-sensitive adhesive composition of the present invention can exhibit such effects is not clear, the present inventors speculate as follows. However, the following assumptions are not intended to limit the interpretation of the pressure-sensitive adhesive composition of the present invention, but are explained as an example.

The pressure-sensitive adhesive composition of the present invention contains a high-molecular-weight specific (meth)acrylic copolymer (A) and a low-molecular-weight specific (meth)acrylic copolymer (B) as a main ingredient. Since the specific (meth)acrylic copolymer (B) has a low molecular weight, it is considered to enter the interior of the high molecular weight specific (meth)acrylic copolymer (A). Inside the specific (meth)acrylic copolymer (A), the specific (meth)acrylic copolymer (B) contains a structural unit (b1) derived from a monomer having a hydroxyl group, so the specific ( A crosslinked structure is formed by the reaction between the hydroxyl group of the meth)acrylic copolymer (B) and the isocyanate group of the isocyanate crosslinking agent. When a cross-linked structure is formed by the specific (meth)acrylic copolymer (B) inside the specific (meth)acrylic copolymer (A), the cohesive force of the pressure-sensitive adhesive layer increases, and the adhesive strength increases. As the pressure-sensitive adhesive layer becomes high, the specific (meth)acrylic copolymer (B) is less likely to bleed out, and the specific (meth)acrylic copolymer (B) accumulates in the bent portion of the pressure-sensitive adhesive layer. Since it is suppressed, it is considered that the pressure-sensitive adhesive layer is less prone to floating, whitening, etc., which cause peeling and the like.
On the other hand, the specific (meth)acrylic copolymer (A) contains a structural unit (a1) derived from a monomer having a hydroxyl group, a structural unit (a2) derived from a monomer having a carboxy group, and the like, It has a hydroxyl group and a carboxy group that react with the isocyanate group of the isocyanate-based cross-linking agent. The content of the structural unit (a1) derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer (A) is within the specific range, and the specific (meth)acrylic copolymer (B) In, the content of the structural unit (b1) derived from a monomer having a hydroxyl group is within a specific range, so that the isocyanate group of the isocyanate cross-linking agent is higher than the hydroxyl group of the specific (meth)acrylic copolymer (A) Also, it is believed that the specific (meth)acrylic copolymer (B) preferentially reacts with the hydroxyl group to form a crosslinked structure, and the specific (meth)acrylic copolymer (B) gives priority to the crosslinked structure By forming, the crosslinked structure due to the specific (meth)acrylic copolymer (A) has a sparse crosslink density and is considered to be a pressure-sensitive adhesive layer having stress relaxation.However, the specific (meth)acrylic Since the copolymer (A) has a carboxy group with a high cross-linking rate with an isocyanate group, even if the cross-linked structure by the specific (meth)acrylic copolymer (B) is preferentially formed, the specific (meth) It is believed that the formation of a cross-linked structure by the acrylic copolymer (A) is not suppressed.In addition, in the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition of the present invention, for example, a specific (meth)acrylic copolymer ( A) - isocyanate cross-linking agent - specific (meth) acrylic copolymer (B) - isocyanate cross-linking agent - specific (meth) acrylic copolymer (A), specific (meth) acrylic copolymer It is presumed that a crosslinked structure is formed in which the coalescence (A) is crosslinked via the specific (meth)acrylic copolymer (B).
From the above, it is presumed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention has excellent bending resistance at room temperature and high-temperature durability in a folded state, and exhibits good adhesive strength. be.

[Specific (meth)acrylic copolymer (A)]
The pressure-sensitive adhesive composition of the present invention comprises a structural unit (a1) derived from a monomer having a hydroxyl group, a structural unit (a2) derived from a monomer having a carboxy group, and a (meth)acrylic acid alkyl ester monomer Including the structural unit (a3) derived from the body, the content of the structural unit (a1) derived from a monomer having a hydroxyl group is in the range of 1.5% by mass or more and 20% by mass or less with respect to all structural units and a (meth)acrylic copolymer (A) [that is, a specific (meth)acrylic copolymer (A)] having a weight average molecular weight of 1,000,000 or more.

<Structural Unit (a1) Derived from a Monomer Having a Hydroxyl Group>
The specific (meth)acrylic copolymer (A) contains a structural unit (a1) derived from a monomer having a hydroxyl group.
The hydroxyl group of the structural unit (a1) derived from the hydroxyl group-containing monomer crosslinks with the isocyanate group of the isocyanate-based crosslinking agent.

As used herein, the term “structural unit derived from a monomer having a hydroxyl group” means a structural unit formed by addition polymerization of a monomer having a hydroxyl group.

The type of hydroxyl group-containing monomer is not particularly limited.
Specific examples of monomers having a hydroxyl group include 2-hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4- Hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1 -dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3- Hydroxyhexyl (meth)acrylate, N-hydroxyethyl (meth)acrylamide and the like.
As the monomer having a hydroxyl group, for example, hydroxyalkyl (meth)acrylate is preferable from the viewpoint of good copolymerizability with the (meth)acrylic acid alkyl ester monomer.
Further, as a monomer having a hydroxyl group, for example, from the viewpoint of good compatibility with (meth)acrylic acid alkyl ester monomers and good reactivity with isocyanate-based cross-linking agents, , preferably a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 1 to 5 carbon atoms, more preferably a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms, 2-hydroxyethyl acrylate, At least one selected from the group consisting of 2-hydroxyethyl methacrylate and 2-hydroxypropyl acrylate is more preferred.

The specific (meth)acrylic copolymer (A) may contain only one type of structural unit (a1) derived from a monomer having a hydroxyl group, or may contain two or more types.

The content of the structural unit (a1) derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer (A) is The range is 1.5% by mass or more and 20% by mass or less, preferably 1.5% by mass or more and 15% by mass or less, more preferably 3% by mass or more and 15% by mass or less. It is preferably in the range of 3% by mass or more and 13% by mass or less, and particularly preferably in the range of 5% by mass or more and 10% by mass or less.
The content of the structural unit (a1) derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer (A) is based on the total structural units of the specific (meth)acrylic copolymer (A) When the content is 1.5% by mass or more, there is a tendency that a pressure-sensitive adhesive layer having excellent high-temperature durability in a folded state can be formed.
The content of the structural unit (a1) derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer (A) is based on the total structural units of the specific (meth)acrylic copolymer (A) When the content is 20% by mass or less, there is a tendency that a pressure-sensitive adhesive layer having excellent bending resistance at room temperature and high-temperature durability in a folded state can be formed.

In the specific (meth)acrylic copolymer (A), the content ratio of the structural unit (a1) derived from a monomer having a hydroxyl group to the structural unit (a2) derived from a monomer having a carboxy group [structural unit (a1)/structural unit (a2)] is not particularly limited, but is, for example, preferably 0.8 or more, more preferably 1.0 or more, and 1.5 or more on a molar basis. is more preferable, and 3.0 or more is particularly preferable.
In the specific (meth)acrylic copolymer (A), the content ratio of the structural unit (a1) derived from a monomer having a hydroxyl group to the structural unit (a2) derived from a monomer having a carboxy group is mol As a standard, when it is 0.8 or more, there is a tendency that a pressure-sensitive adhesive layer having excellent high-temperature durability in a folded state can be formed.
Further, in the specific (meth)acrylic copolymer (A), the content ratio of the structural unit (a1) derived from a monomer having a hydroxyl group to the structural unit (a2) derived from a monomer having a carboxy group is , on a molar basis, is preferably 12.5 or less, more preferably 10.0 or less, and even more preferably 8.0 or less.
In the specific (meth)acrylic copolymer (A), the content ratio of the structural unit (a1) derived from a monomer having a hydroxyl group to the structural unit (a2) derived from a monomer having a carboxy group is mol As a standard, when it is 12.5 or less, there is a tendency that a pressure-sensitive adhesive layer having excellent bending resistance at room temperature and high-temperature durability in a folded state can be formed.

<Structural Unit (a2) Derived from Monomer Having Carboxy Group>
The specific (meth)acrylic copolymer (A) contains a structural unit (a2) derived from a monomer having a carboxy group.
The carboxy group of the structural unit (a2) derived from a monomer having a carboxy group is crosslinked with the isocyanate group of the isocyanate cross-linking agent.

As used herein, the term "structural unit derived from a monomer having a carboxy group" means a structural unit formed by addition polymerization of a monomer having a carboxy group.

The type of monomer having a carboxy group is not particularly limited.
Specific examples of monomers having a carboxy group include acrylic acid, methacrylic acid, crotonic acid , maleic acid, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate [ For example, ω-carboxy-polycaprolactone (n≈2) monoacrylate], succinic acid ester (eg, 2-acryloyloxyethyl-succinic acid), and the like.
As the monomer having a carboxy group, for example, at least one selected from the group consisting of acrylic acid and ω-carboxy-polycaprolactone monoacrylate from the viewpoint of good reactivity with an isocyanate-based cross-linking agent. preferable.

The specific (meth)acrylic copolymer (A) may contain only one type of structural unit (a2) derived from a monomer having a carboxy group, or may contain two or more types.

Although the content of the structural unit (a2) derived from a monomer having a carboxy group in the (meth)acrylic copolymer (A) is not particularly limited, for example, the specific (meth)acrylic copolymer (A ) is preferably in the range of 0.5% by mass or more and 4% by mass or less, more preferably in the range of 0.5% by mass or more and 3.5% by mass or less. It is more preferably in the range of 5% by mass or more and 3% by mass or less, and particularly preferably in the range of 0.5% by mass or more and 1.5% by mass or less.
The content of the structural unit (a2) derived from the monomer having a carboxy group in the specific (meth)acrylic copolymer (A) is the total structural units of the specific (meth)acrylic copolymer (A) On the other hand, when it is 0.5% by mass or more, there is a tendency that a pressure-sensitive adhesive layer having excellent high-temperature durability in a folded state can be formed.
The content of the structural unit (a2) derived from a monomer having a carboxy group in the specific (meth)acrylic copolymer (A) is 4 with respect to the total structural units of the specific (meth)acrylic copolymer When the amount is not more than % by mass, there is a tendency that a pressure-sensitive adhesive layer having excellent bending resistance at room temperature and high-temperature durability in a folded state can be formed.

<Structural unit (a3) derived from (meth)acrylic acid alkyl ester monomer>
The specific (meth)acrylic copolymer (A) contains a structural unit (a3) derived from a (meth)acrylic acid alkyl ester monomer.
The structural unit (a3) derived from the (meth)acrylic acid alkyl ester monomer contributes to the adjustment of adhesive strength.

In the present specification, "a structural unit derived from a (meth)acrylic acid alkyl ester monomer" means a structural unit formed by addition polymerization of a (meth)acrylic acid alkyl ester monomer.
In addition, the "(meth)acrylic acid alkyl ester monomer" in the present specification does not include a (meth)acrylic acid alkyl ester monomer having at least one of a hydroxyl group and a carboxy group.

The type of (meth)acrylic acid alkyl ester monomer is not particularly limited.
As the (meth)acrylic acid alkyl ester monomer, an unsubstituted (meth)acrylic acid alkyl ester monomer is preferable.
The alkyl group of the (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic.
The number of carbon atoms in the alkyl group is preferably 1 to 18, more preferably 1 to 12, for example, from the viewpoint of adhesive strength.

Specific examples of (meth) acrylic acid alkyl ester monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, s-butyl (meth) acrylates, t-butyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate and the like.

The (meth)acrylic acid alkyl ester monomer is preferably at least one selected from the group consisting of 2-ethylhexyl acrylate and i-octyl acrylate, more preferably 2-ethylhexyl acrylate or i-octyl acrylate, and 2-ethylhexyl. Acrylates are more preferred.
When the (meth)acrylic acid alkyl ester monomer is at least one selected from the group consisting of 2-ethylhexyl acrylate and i-octyl acrylate, the bending resistance at room temperature and the high temperature durability in the folded state are improved. There is a tendency that an excellent pressure-sensitive adhesive layer can be formed.

The specific (meth)acrylic copolymer (A) may contain only one type of structural unit (a3) derived from a (meth)acrylic acid alkyl ester monomer, or may contain two or more types. .

Although the content of the structural unit (a3) derived from the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic copolymer (A) is not particularly limited, for example, the specific (meth)acrylic copolymer It is preferably 50% by mass or more, more preferably 50% by mass or more and 97.5% by mass or less, and 65% by mass or more and 97.5% by mass, based on the total structural units of the polymer (A). % or less, and particularly preferably 75 mass % or more and 97.5 mass % or less.
Here, the content of the structural unit (a3) derived from the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic copolymer (A) is the specific (meth)acrylic copolymer (A ) is 50% by mass or more with respect to all structural units of (meth)acrylic acid alkyl ester monomer, the structural unit (a3) derived from the specific (meth)acrylic copolymer (A) It means that it is contained as a main component of the constituent structural units.

<Other structural units>
The specific (meth)acrylic copolymer (A) may contain structural units other than the above-described structural units (so-called other structural units) as long as the effects of the present invention are exhibited.

Examples of monomers constituting other structural units include (meth)acrylates having an aromatic ring represented by benzyl (meth)acrylate and phenoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate and ethoxyethyl Alkoxyalkyl (meth)acrylates typified by (meth)acrylates, styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and aromatic monovinyls typified by vinyltoluene, acrylonitrile and methacrylates. vinyl cyanides typified by lonitrile; and vinyl esters typified by vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate. Various derivatives of these monomers are also included.

<<Glass transition temperature of specific (meth)acrylic copolymer (A)>>
The glass transition temperature (also referred to as "Tg") of the specific (meth)acrylic copolymer (A) is preferably less than -50°C, and is preferably in the range of -75°C or more and less than -50°C. It is more preferably in the range of -75°C or higher and -53°C or lower, and particularly preferably in the range of -75°C or higher and -55°C or lower.
When the glass transition temperature of the specific (meth)acrylic copolymer (A) is less than −50° C., there is a tendency to form a pressure-sensitive adhesive layer having excellent bending resistance at room temperature and high-temperature durability in a folded state. be.

The glass transition temperature of the specific (meth)acrylic copolymer (A) is the absolute temperature (unit: K; hereinafter the same) obtained by calculation from the following formula 1 is the Celsius temperature (unit: ° C.; hereinafter the same ).
1/Tg=m1/Tg1+m2/Tg2+...+m(k-1)/Tg(k-1)+mk/Tgk (Formula 1)

In Formula 1, Tg1, Tg2, . Each represents the glass transition temperature expressed in absolute temperature. m1, m2, . +m(k−1)+mk=1.
The absolute temperature can be converted to a Celsius temperature by subtracting 273 from the absolute temperature, and the Celsius temperature can be converted to an absolute temperature by adding 273 to the Celsius temperature.

As used herein, the term "glass transition temperature expressed as an absolute temperature when a homopolymer is used" refers to a glass transition temperature expressed as an absolute temperature of a homopolymer produced by polymerizing the monomer alone. means temperature.
The glass transition temperature of the homopolymer was measured using a differential scanning calorimeter (DSC) [model number: EXSTAR6000, Seiko Instruments Inc.] under the conditions of a measurement sample of 10 mg and a heating rate of 10°C/min in a nitrogen stream. The inflection point of the measured DSC curve is taken as the glass transition temperature of the homopolymer.

The "glass transition temperature represented by the Celsius temperature when converted to a homopolymer" of representative monomers is -76 ° C. for 2-ethylhexyl acrylate (2EHA) and -10 ° C. for 2-ethylhexyl methacrylate (2EHMA). , n-butyl acrylate (n-BA) is −57° C., n-butyl methacrylate (n-BMA) is 21° C., t-butyl acrylate (t-BA) is 41° C., t-butyl methacrylate (t-BMA) is 107°C, i-butyl methacrylate (i-BMA) is 48°C, methyl acrylate (MA) is 5°C, methyl methacrylate (MMA) is 103°C, isobornyl methacrylate (IBXMA) is 155°C, isobornyl acrylate (IBXA ) is 96 ° C, ethyl acrylate (EA) is -27 ° C, methacrylic acid is 185 ° C, 4-hydroxybutyl acrylate (4HBA) is -39 ° C, 2-hydroxyethyl acrylate (2HEA) is -15 ° C, 2-hydroxy Ethyl methacrylate (2HEMA) is 55 ° C., 2-hydroxypropyl acrylate (2HPA) is -7 ° C., acrylic acid (AA) is 163 ° C., i-octyl acrylate (i-OA) is -75 ° C., dimethylaminoethyl methacrylate ( DM) is 18° C., ω-carboxy-polycaprolactone (n≈2) monoacrylate is −30° C., and 2-acryloyloxyethyl-succinic acid is −40° C.

The glass transition temperature of the specific (meth)acrylic copolymer (A) can be appropriately adjusted, for example, by using two or more monomers having different glass transition temperatures when converted to homopolymers.

<<Weight average molecular weight of specific (meth)acrylic copolymer (A)>>
The weight average molecular weight (also referred to as "Mw") of the specific (meth)acrylic copolymer (A) is 1 million or more, preferably in the range of 1 million or more and 2 million or less, and 1.1 million or more and 1.9 million. It is more preferably in the range of 10,000 or less, and further preferably in the range of 1,200,000 to 1,800,000.
When the weight-average molecular weight of the specific (meth)acrylic copolymer is 1,000,000 or more, there is a tendency that a pressure-sensitive adhesive layer having excellent high-temperature durability in a folded state can be formed.

The weight average molecular weight of the specific (meth)acrylic copolymer (A) is a value measured by the following method. Specifically, it is measured according to the following (1) to (3).
(1) A solution of the specific (meth)acrylic copolymer (A) is applied to release paper and dried at 100° C. for 1 minute to obtain a film-like specific (meth)acrylic copolymer (A).
(2) Using the film-like specific (meth)acrylic copolymer (A) obtained in (1) above and tetrahydrofuran, a sample solution having a solid content concentration of 0.2% by mass is obtained. The term "solid content concentration" as used herein means the mass ratio of the specific (meth)acrylic copolymer (A) in the sample solution.
(3) Using gel permeation chromatography (GPC), the weight average molecular weight of the specific (meth)acrylic copolymer (A) is measured as a standard polystyrene equivalent value under the following conditions.

~Conditions~
Measuring device: high-speed GPC [model number: HLC-8220 GPC, Tosoh Corporation]
Detector: Differential refractometer (RI) [built into HLC-8220, Tosoh Corporation]
Column: Four TSK-GEL GMHXL [Tosoh Corporation] connected in series Column temperature: 40°C
Eluent: Tetrahydrofuran Injection volume of sample solution: 100 μL
Flow rate: 0.8 mL/min

The weight average molecular weight of the specific (meth)acrylic copolymer (A) can be adjusted to the desired value by adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, etc. can be the value of

<<Specific (meth)acrylic copolymer (A) content>>
The content of the specific (meth)acrylic copolymer (A) in the pressure-sensitive adhesive composition of the present invention is not particularly limited. It is preferably in the range of 99% by mass or less, more preferably in the range of 75% by mass or more and 95.5% by mass or less, and even more preferably in the range of 80% by mass or more and 93.5% by mass or less. .
When the content of the specific (meth)acrylic copolymer (A) in the pressure-sensitive adhesive composition of the present invention is 65% by mass or more with respect to the total solid content in the pressure-sensitive adhesive composition, the bending resistance at room temperature There is a tendency to form a pressure-sensitive adhesive layer that is superior in terms of durability and high-temperature durability in a folded state.
When the content of the specific (meth)acrylic copolymer (A) in the pressure-sensitive adhesive composition of the present invention is 96.99% by mass or less with respect to the total solid content in the pressure-sensitive adhesive composition, more favorable It tends to be able to form an adhesive layer that exhibits adhesive strength.
As used herein, "total solid content in the pressure-sensitive adhesive composition" means the total mass of the pressure-sensitive adhesive composition when the pressure-sensitive adhesive composition does not contain a solvent. When included, it means the mass of the residue after removing the solvent from the pressure-sensitive adhesive composition.

[Specific (meth)acrylic copolymer (B)]
The pressure-sensitive adhesive composition of the present invention contains a structural unit (b1) derived from a monomer having a hydroxyl group, and the content of the structural unit (b1) derived from a monomer having a hydroxyl group is is in the range of 3% by mass or more and 40% by mass or less, and the weight average molecular weight is in the range of 2500 or more and 10000 or less (B) [i.e., a specific (meth)acrylic copolymer coalescence (B)].
In addition, the content of the specific (meth)acrylic copolymer (B) in the pressure-sensitive adhesive composition of the present invention is 3 parts by mass or more with respect to 100 parts by mass of the specific (meth)acrylic copolymer (A). The range is 50 parts by mass or less.

<Structural Unit (b1) Derived from Monomer Having Hydroxyl Group>
The specific (meth)acrylic copolymer (B) contains a structural unit (b1) derived from a monomer having a hydroxyl group.
The hydroxyl group of the structural unit (b1) derived from the hydroxyl group-containing monomer crosslinks with the isocyanate group of the isocyanate-based crosslinking agent.

The type of hydroxyl group-containing monomer is not particularly limited.
Since specific examples of the hydroxyl group-containing monomer are the same as those of the hydroxyl group-containing monomer in the specific (meth)acrylic copolymer (A), description thereof is omitted here.
As the monomer having a hydroxyl group, for example, when the specific (meth)acrylic copolymer (B) contains a structural unit (b3) derived from a (meth)acrylic acid alkyl ester monomer described later, ( Hydroxyalkyl (meth)acrylates are preferred from the viewpoint of good copolymerizability with meth)acrylic acid alkyl ester monomers, and from the viewpoint of good compatibility with (meth)acrylic acid alkyl ester monomers. , And, from the viewpoint of good reactivity with an isocyanate-based cross-linking agent, a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 1 to 5 carbon atoms is more preferable, and a hydroxyalkyl having 2 to 4 carbon atoms A hydroxyalkyl (meth)acrylate having a group is more preferred, and at least one selected from the group consisting of 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate is particularly preferred.

The specific (meth)acrylic copolymer (B) may contain only one type of structural unit (b1) derived from a monomer having a hydroxyl group, or may contain two or more types.

The content of the structural unit (b1) derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer (B) is is in the range of 3% by mass or more and 40% by mass or less, preferably in the range of 3% by mass or more and 30% by mass or less, more preferably in the range of 5% by mass or more and 30% by mass or less, and 5% by mass % or more and 25 mass % or less, and particularly preferably 10 mass % or more and 20 mass % or less.
The content of structural units (b1) derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer (B) is based on the total structural units of the specific (meth)acrylic copolymer (B) When the content is 3% by mass or more, there is a tendency that a pressure-sensitive adhesive layer having excellent high-temperature durability in a folded state can be formed.
The content of structural units (b1) derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer (B) is based on the total structural units of the specific (meth)acrylic copolymer (B) When the content is 40% by mass or less, there is a tendency that a pressure-sensitive adhesive layer having excellent bending resistance at room temperature and high-temperature durability in a folded state and exhibiting good adhesive strength can be formed.

<Structural unit (b2) derived from (meth)acrylic acid alkyl ester monomer>
The specific (meth)acrylic copolymer (B) preferably contains a structural unit (b2) derived from a (meth)acrylic acid alkyl ester monomer.
The structural unit (b2) derived from the (meth)acrylic acid alkyl ester monomer contributes to the adjustment of adhesive strength.

The type of (meth)acrylic acid alkyl ester monomer is not particularly limited.
As the (meth)acrylic acid alkyl ester monomer, an unsubstituted (meth)acrylic acid alkyl ester monomer is preferable.
The alkyl group of the (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic.
The number of carbon atoms in the alkyl group is preferably 1 to 18, more preferably 1 to 12, for example, from the viewpoint of adhesive strength.

Specific examples of the (meth)acrylic acid alkyl ester monomer are the same as the specific examples of the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic copolymer (A), so they are described here. is omitted.

The (meth)acrylic acid alkyl ester monomer is, for example, preferably at least one selected from the group consisting of i-butyl methacrylate and t-butyl methacrylate, more preferably i-butyl methacrylate or t-butyl methacrylate, and t -Butyl methacrylate is more preferred.
When the (meth)acrylic acid alkyl ester monomer is the above monomer, the compatibility between the specific (meth)acrylic copolymer (A) and the specific (meth)acrylic copolymer (B) is enhanced. tend to be better. Moreover, the above monomer has a moderately high glass transition temperature, and tends to make the cohesive force of the pressure-sensitive adhesive layer formed more moderate.

When the specific (meth)acrylic copolymer (B) contains the structural unit (b2) derived from the (meth)acrylic acid alkyl ester monomer, the structure derived from the (meth)acrylic acid alkyl ester monomer It may contain only one type of unit (b2), or may contain two or more types.

When the specific (meth)acrylic copolymer (B) contains a structural unit (b2) derived from a (meth)acrylic acid alkyl ester monomer, the (meth)acrylic copolymer (B) in the specific (meth)acrylic copolymer (B) ) The content of the structural unit (b2) derived from the acrylic acid alkyl ester monomer is not particularly limited, but for example, 60 mass with respect to all structural units of the specific (meth)acrylic copolymer (B) % or more and 97 mass % or less, more preferably 70 mass % or more and 97 mass % or less, still more preferably 75 mass % or more and 95 mass % or less, and 80 mass % % or more and 90 mass % or less is particularly preferable.

<Other structural units>
The specific (meth)acrylic copolymer (B) may contain structural units other than the above-described structural units (so-called other structural units) as long as the effects of the present invention are exhibited.

Examples of monomers constituting other structural units include (meth)acrylates having an aromatic ring represented by benzyl (meth)acrylate and phenoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate and ethoxyethyl Alkoxyalkyl (meth)acrylates typified by (meth)acrylates, styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and aromatic monovinyls typified by vinyltoluene, acrylonitrile and methacrylates. vinyl cyanides typified by lonitrile; and vinyl esters typified by vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate. Various derivatives of these monomers are also included.
Further, specific examples of monomers constituting other structural units include monomers having a carboxy group. Specific examples of the monomer having a carboxy group are the same as the specific examples of the monomer having a carboxy group in the specific (meth)acrylic copolymer, so description thereof is omitted here. However, the specific (meth)acrylic copolymer (B) should not contain a structural unit derived from a monomer having a carboxy group, from the viewpoint of facilitating the formation of a pressure-sensitive adhesive layer with more moderate cohesion. is preferred.

<<Glass transition temperature of specific (meth)acrylic copolymer (B)>>
The glass transition temperature (Tg) of the specific (meth)acrylic copolymer (B) is preferably 40°C or higher, more preferably in the range of 40°C or higher and 130°C or lower, and 45°C or higher and 120°C. The following range is more preferable, and a range of 45° C. or higher and 110° C. or lower is particularly preferable.
When the glass transition temperature of the specific (meth)acrylic copolymer (B) is 40° C. or higher, there is a tendency that a pressure-sensitive adhesive layer exhibiting better adhesive strength can be formed.

The glass transition temperature of the specific (meth)acrylic copolymer (B) is a value calculated by the same method as the method for calculating the glass transition temperature of the specific (meth)acrylic copolymer (A) described above. be.

The glass transition temperature of the specific (meth)acrylic copolymer (B) can be appropriately adjusted, for example, by using two or more monomers having different glass transition temperatures when converted to homopolymers.

<<Weight average molecular weight of specific (meth)acrylic copolymer (B)>>
The weight average molecular weight (Mw) of the specific (meth)acrylic copolymer (B) is in the range of 2500 to 10000, preferably in the range of 2500 to 9000, and in the range of 2500 to 8000. It is more preferably in the range of 3000 or more and 8000 or less, and particularly preferably in the range of 4000 or more and 8000 or less.
When the weight average molecular weight of the specific (meth)acrylic copolymer (B) is 2500 or more, there is a tendency that a pressure-sensitive adhesive layer exhibiting good adhesive strength can be formed.
When the weight average molecular weight of the specific (meth)acrylic copolymer (B) is 10000 or less, the adhesive exhibits excellent bending resistance at room temperature and high temperature durability in a folded state, and exhibits good adhesive strength. It tends to be able to form an agent layer.

The weight average molecular weight (Mw) of the specific (meth)acrylic copolymer (B) is determined by the same method as the method for measuring the weight average molecular weight (Mw) of the specific (meth)acrylic copolymer (A) described above. is a value measured by

The weight average molecular weight of the specific (meth)acrylic copolymer (B) can be adjusted to the desired value by adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, etc. can be the value of

<<Content of specific (meth)acrylic copolymer (B)>>
The content of the specific (meth)acrylic copolymer (B) in the pressure-sensitive adhesive composition of the present invention is 3 parts by mass or more and 50 parts by mass with respect to 100 parts by mass of the specific (meth)acrylic copolymer (A). parts by mass or less, preferably in the range of 3 to 40 parts by mass, more preferably in the range of 5 to 30 parts by mass, and in the range of 5 to 25 parts by mass. More preferably, it is particularly preferably in the range of 10 parts by mass or more and 20 parts by mass or less.
When the content of the specific (meth)acrylic copolymer (B) in the pressure-sensitive adhesive composition of the present invention is 3 parts by mass or more with respect to 100 parts by mass of the specific (meth)acrylic copolymer (A) , tend to be able to form a pressure-sensitive adhesive layer exhibiting good adhesion.
When the content of the specific (meth)acrylic copolymer (B) in the pressure-sensitive adhesive composition of the present invention is 50 parts by mass or less with respect to 100 parts by weight of the specific (meth)acrylic copolymer (A) , there is a tendency that a pressure-sensitive adhesive layer having excellent bending resistance at room temperature and high-temperature durability in a folded state can be formed.

[Method for producing specific (meth)acrylic copolymer]
The method for producing the specific (meth)acrylic copolymer is not particularly limited.
The specific (meth)acrylic copolymer is obtained by polymerizing the above-described monomers by a known polymerization method represented by, for example, a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, and a bulk polymerization method. can be manufactured by
As the polymerization method, the solution polymerization method is preferable because the processing steps are relatively simple and can be performed in a short period of time when preparing the pressure-sensitive adhesive composition of the present invention after production.

In the solution polymerization method, generally, a predetermined organic solvent, monomers, a polymerization initiator, and optionally a chain transfer agent are charged in a polymerization tank, and stirred at the reflux temperature of the organic solvent in a nitrogen stream. Heat and react for several hours while stirring. In this case, at least part of the organic solvent, monomer, polymerization initiator and/or chain transfer agent may be added sequentially.

Organic solvents used in the polymerization reaction include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, alcohol compounds and the like.
More specific examples of the organic solvent used during the polymerization reaction include benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic hydrocarbon compounds typified by aromatic naphtha, fats typified by n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and turpentine. or alicyclic hydrocarbon compounds, ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate. Ester compounds, acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and ketone compounds represented by methyl cyclohexanone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl Ethers and glycol ether compounds typified by diethylene glycol monobutyl ether, and methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t- Alcohol compounds represented by butyl alcohol are mentioned.

In the production of the specific (meth)acrylic copolymer, it is preferable to use an organic solvent that is unlikely to cause chain transfer during the polymerization reaction of aromatic hydrocarbon compounds, ester compounds, ketone compounds, etc. In particular, the specific (meth)acrylic It is preferable to use at least one selected from the group consisting of ethyl acetate, toluene, and methyl ethyl ketone from the viewpoint of the solubility of the system copolymer, the ease of the polymerization reaction, and the like.

At the time of the polymerization reaction, only one kind of organic solvent may be used, or two or more kinds thereof may be used.

Examples of the polymerization initiator include organic peroxides, azo compounds, and the like, which are used in ordinary solution polymerization methods.
Examples of organic peroxides include t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, carbonate, t-butyl peroxypivalate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-amylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α-cumylperoxycyclohexyl)propane, 2,2-bis(4,4 -di-t-butylperoxycyclohexyl)butane, and 2,2-bis(4,4-di-t-octylperoxycyclohexyl)butane.
Examples of azo compounds include 2,2'-azobisisobutyronitrile [AIBN], 2,2'-azobis(2,4-dimethylvaleronitrile) [ABVN], 2,2'-azobis(4- methoxy-2,4-dimethylvaleronitrile), 1,1′-azobis(cyclohexane-1-carbonitrile), and 2,2′-azobis(isobutyrate)dimethyl.
In producing the specific (meth)acrylic copolymer, it is preferable to use a polymerization initiator that does not cause a graft reaction during the polymerization reaction, and particularly preferably an azo compound.

At the time of the polymerization reaction, only one type of polymerization initiator may be used, or two or more types may be used.

The amount of the polymerization initiator to be used is not particularly limited, and can be appropriately set according to, for example, the molecular weight of the desired specific (meth)acrylic copolymer.

If necessary, a chain transfer agent may be used in the production of the specific (meth)acrylic copolymer.
Examples of chain transfer agents include cyanoacetic acid, cyanoacetic acid alkyl ester compounds having 1 to 8 carbon atoms, bromoacetic acid, bromoacetic acid alkyl ester compounds having 1 to 8 carbon atoms, α-methylstyrene, anthracene, phenanthrene, and fluorene. , and aromatic compounds represented by 9-phenylfluorene, aromatic nitro compounds represented by p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and p-nitrotoluene, benzoquinone and Benzoquinone derivatives typified by 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives typified by tributylborane, carbon tetrabromide, carbon tetrachloride, 1,1,2,2-tetrabromoethane Halogenated hydrocarbon compounds typified by , tribromoethylene, trichlorethylene, bromotrichloromethane, tribromomethane, and 3-chloro-1-propene; aldehyde compounds typified by chloral and furaldehyde; alkyls having 1 to 18 carbon atoms; Mercaptan compounds, aromatic mercaptan compounds represented by thiophenol and toluene mercaptan, mercaptoacetic acid, alkyl ester compounds of mercaptoacetic acid having 1 to 10 carbon atoms, hydroxyalkyl mercaptan compounds having 1 to 12 carbon atoms, and pinene and terpinolene Representative terpene compounds are mentioned.

When a chain transfer agent is used in the production of the specific (meth)acrylic copolymer, the amount of the chain transfer agent used is not particularly limited. It can be set as appropriate.

The polymerization temperature is not particularly limited, and can be appropriately set according to, for example, the molecular weight of the desired specific (meth)acrylic copolymer.

[Isocyanate-based cross-linking agent]
The pressure-sensitive adhesive composition of the present invention contains an isocyanate-based cross-linking agent.
As used herein, the term "isocyanate-based cross-linking agent" refers to a compound having two or more isocyanate groups in the molecule (so-called polyisocyanate compound).

There are no particular restrictions on the polyisocyanate compound.
Polyisocyanate compounds include aromatic polyisocyanate compounds such as xylylene diisocyanate (XDI), diphenylmethane diisocyanate, triphenylmethane triisocyanate, and tolylene diisocyanate (TDI), hexamethylene diisocyanate (HMDI), and pentamethylene diisocyanate (PDI). , isophorone diisocyanate, and aliphatic or alicyclic polyisocyanate compounds such as hydrogenated products of aromatic polyisocyanate compounds.
Further, the polyisocyanate compound may be a dimer, trimer, or pentamer of the polyisocyanate compound, an adduct of the polyisocyanate compound and a polyol compound such as trimethylolpropane, or a biuret of the polyisocyanate compound. And so on.

A commercial item can be used as an isocyanate type crosslinking agent.
Examples of commercially available isocyanate cross-linking agents include "Coronate (registered trademark) HX", "Coronate (registered trademark) HL-S", "Coronate (registered trademark) L", "Coronate (registered trademark) L-45E ", "Coronate (R) 2031", "Coronate (R) 2030", "Coronate (R) 2234", "Coronate (R) 2785", "Aquanate (R) 200", and " Aquanate (registered trademark) 210” [above, Tosoh Corporation], “Sumidule (registered trademark) N3300”, “Desmodur (registered trademark) N3400”, and “Sumidule (registered trademark) N-75” [ Sumika Covestro Urethane Co., Ltd.], "Duranate (registered trademark) E-405-80T", "Duranate (registered trademark) AE700-100", "Duranate (registered trademark) 24A-100", and "Duranate (registered trademark) TSE-100” [Asahi Kasei Corporation], and “Takenate (registered trademark) D-110N”, “Takenate (registered trademark) D-120N”, “Takenate (registered trademark) M-631N ”, “MT-Olestar (registered trademark) NP1200”, and “STABIO (registered trademark) XD-340N” [all manufactured by Mitsui Chemicals, Inc.].

The pressure-sensitive adhesive composition of the present invention may contain only one type of isocyanate-based cross-linking agent, or may contain two or more types.

The content of the isocyanate-based cross-linking agent in the pressure-sensitive adhesive composition of the present invention is not particularly limited. It is preferably in the range of 0.01 part by mass or more and 1 part by mass or less, and even more preferably in the range of 0.01 part by mass or more and 0.45 part by mass or less. , 0.05 parts by mass or more and 0.15 parts by mass or less.
When the content of the isocyanate-based cross-linking agent in the pressure-sensitive adhesive composition of the present invention is 0.005 parts by mass or more with respect to 100 parts by mass of the specific (meth)acrylic copolymer (A), There is a tendency to form a pressure-sensitive adhesive layer that is more excellent in high temperature durability.
When the content of the isocyanate-based cross-linking agent in the pressure-sensitive adhesive composition of the present invention is 5 parts by mass or less with respect to 100 parts by mass of the specific (meth)acrylic copolymer (A), bending resistance at room temperature and It tends to be possible to form a pressure-sensitive adhesive layer with excellent high-temperature durability in a folded state.

[Tackifying resin]
The pressure-sensitive adhesive composition of the present invention can further contain a tackifying resin (so-called tackifier).
When the pressure-sensitive adhesive composition of the present invention further contains a tackifying resin, it tends to form a pressure-sensitive adhesive layer exhibiting better adhesion.

In the present invention, the "tackifier resin" means a polymer having a property of imparting tackiness by blending and having a molecular weight of less than 10,000 (preferably in the range of 500 or more and less than 10,000).
The tackifying resin in the present invention does not include the specific (meth)acrylic copolymer (B) described above.

There are no particular restrictions on the tackifying resin.
Examples of tackifier resins include terpene phenol resins, aromatic modified terpene resins, styrene resins, rosin resins, and the like.
Among these, at least one selected from the group consisting of terpene phenol resins and rosin resins is preferable as the tackifying resin.
A terpene phenol resin is a copolymer of a terpene compound and a phenol compound.
Specific examples of terpene phenol resins include monocyclic monoterpene compounds typified by α-pinene, β-pinene, and dipentene (limonene), and phenol, cresol, and phenol compounds typified by bisphenol A. polymers.
A rosin resin is an ester resin derived from rosin acid as a main component.
Specific examples of rosin resins include rosin compounds represented by abietic acid, neoabietic acid, parastric acid, etc., diol compounds having a rosin skeleton obtained by reacting hydrogenated rosin with diglycidyl ether, and hydrogenated rosin. A diol compound is mentioned.

A commercially available product can be used as the tackifying resin.
Examples of commercially available tackifying resins include "YS Polyster U115", "YS Polyster U130", "YS Polyster T80", "YS Polyster T100", "YS Polyster T115" and "YS Polyster T115" manufactured by Yasuhara Chemical Co., Ltd. Polyster T130", "YS Polyster TH30", "YS Polyster TH130", "YS Polyster T145", "YS Polyster T160", "YS Polyster S145", "YS Polyster G125", "YS Polyster G150", "YS Polyster N125" ”, “YS Polyster K125”, “YS Polyster K140”, and “YS Resin CP”, and Arakawa Chemical Industries Co., Ltd. “Pine Crystal KE-359”, “Pine Crystal D-6011”, “Tamanol 803L” , and “Tamanol 901” (both of which are trade names).

When the pressure-sensitive adhesive composition of the present invention contains a tackifier, it may contain only one tackifier, or may contain two or more tackifiers.

When the pressure-sensitive adhesive composition of the present invention contains a tackifier, the content of the tackifier in the pressure-sensitive adhesive composition of the present invention is not particularly limited. For example, the specific (meth)acrylic copolymer (A) With respect to 100 parts by mass, it is preferably in the range of 1 to 20 parts by mass, more preferably in the range of 3 to 15 parts by mass, and in the range of 5 to 10 parts by mass. is more preferable.
When the content of the tackifier in the pressure-sensitive adhesive composition of the present invention is 1 part by mass or more with respect to 100 parts by mass of the specific (meth)acrylic copolymer (A), the adhesive exhibits better adhesive strength. It tends to be able to form an agent layer.
When the content of the tackifier in the pressure-sensitive adhesive composition of the present invention is 20 parts by mass or less with respect to 100 parts by mass of the specific (meth)acrylic copolymer (A), the optical Properties (for example, light transmittance) tend to be more improved.

[Organic solvent]
The pressure-sensitive adhesive composition of the present invention may contain an organic solvent, for example, from the viewpoint of improving coatability.
Examples of the organic solvent include those similar to those used in the polymerization reaction of the specific (meth)acrylic copolymer described above.

When the pressure-sensitive adhesive composition of the present invention contains an organic solvent, it may contain only one type of organic solvent, or may contain two or more types.

When the pressure-sensitive adhesive composition of the present invention contains an organic solvent, the content of the organic solvent is not particularly limited and can be appropriately set according to the purpose.

[Other ingredients]
The pressure-sensitive adhesive composition of the present invention may, if necessary, contain components other than the components described above (so-called other components) within a range that does not impair the effects of the present invention.
Other components include polymers other than specific (meth)acrylic copolymers, crosslinking catalysts, antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbers), and the like. be done.

When the pressure-sensitive adhesive composition of the present invention contains other components, the content of the other components can be appropriately set within the range in which the effects of the present invention are exhibited.

<Gel fraction after cross-linking>
The gel fraction of the pressure-sensitive adhesive composition of the present invention after cross-linking (so-called gel fraction of the pressure-sensitive adhesive layer) is preferably 45 mass % or more, and is in the range of 45 mass % or more and 90 mass % or less. is more preferably in the range of 50% by mass or more and 90% by mass or less, and particularly preferably in the range of 50% by mass or more and 80% by mass or less.
When the gel fraction of the pressure-sensitive adhesive composition after cross-linking is 45% by mass or more, the pressure-sensitive adhesive layer tends to be more excellent in high-temperature durability in a folded state.

As used herein, the "gel fraction after cross-linking of the pressure-sensitive adhesive composition" is the solvent-insoluble fraction measured using ethyl acetate as an extraction solvent. Specifically, the gel fraction after cross-linking of the pressure-sensitive adhesive composition is measured according to the following (1) to (4).
(1) About 0.15 g of the adhesive composition after cross-linking (i.e., the adhesive layer) is attached to a 250-mesh wire mesh (100 mm × 100 mm) whose mass is accurately measured with a precision balance, and the gel leaks. The wire mesh is folded 5 times with the attached adhesive layer facing inward so that it is not exposed, and this is used as a sample. After that, the mass is accurately measured with a precision balance.
(2) The obtained sample is immersed in 80 mL of ethyl acetate for 3 days.
(3) A sample is taken out, washed with a small amount of ethyl acetate, and dried at 120° C. for 24 hours. After that, the mass is accurately measured with a precision balance.
(4) Calculate the gel fraction by the following formula.
Gel fraction (unit: mass%) = (ZX)/(YX) x 100
However, X is the weight of the wire mesh (unit: g), Y is the weight of the wire mesh with the adhesive layer attached before immersion (unit: g), and Z is the weight of the wire mesh with the adhesive layer attached, dried after immersion. (unit: g).

<Application>
The pressure-sensitive adhesive composition of the present invention is suitable for foldable displays.
The pressure-sensitive adhesive composition of the present invention is excellent in bending resistance at room temperature and high-temperature durability in a folded state, and can form a pressure-sensitive adhesive layer exhibiting good adhesive strength. Since the effect of the pressure-sensitive adhesive composition of the present invention is more exhibited, it is preferable to use it for bonding to a member.

[Optical components for foldable displays]
The optical member for foldable displays of the present invention (hereinafter also simply referred to as "optical member") comprises a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention.
The pressure-sensitive adhesive layer included in the optical member of the present invention is a pressure-sensitive adhesive layer formed from the above-described pressure-sensitive adhesive composition of the present invention, and has excellent bending resistance at room temperature and high-temperature durability in a folded state, Moreover, since the foldable display to which the optical member of the present invention is applied exhibits good adhesive strength, even when it is repeatedly folded at room temperature or left in a folded state in a high-temperature environment, whitening or foaming occurs at the folded portion. , there is a tendency that defects such as peeling are unlikely to occur.

The optical member is not particularly limited, and includes, for example, members constituting devices (so-called optical devices) such as image display devices and input devices, and members used in these devices.
Specific examples of optical members include polarizing plates, AG (Anti-Glare) polarizing plates, wave plates, retardation plates including wave plates such as 1/2 and 1/4 wave plates, viewing angle compensation films, optical compensation films, and luminance enhancement. Films, light guide plates, reflective films, antireflection films, transparent conductive films such as ITO (Indium-Tin Oxide) films, prism sheets, lens sheets, diffusion plates, and the like.
Materials for optical components include polyester-based resin, acetate-based resin, polyethersulfone-based resin, polycarbonate-based resin, polyamide-based resin, polyimide-based resin, polyolefin-based resin, acrylic-based resin, vinyl chloride-based resin, ABS (acrylonitrile Butadiene Styrene) resin, fluorine-based resin, and the like.

The thickness of the pressure-sensitive adhesive layer in the optical member of the present invention is not particularly limited, and can be appropriately set according to, for example, the types of the optical member and foldable display, the materials of the optical member and foldable display, and the like. In general, the thickness of the adhesive layer is in the range of 1 μm to 100 μm, preferably 5 μm to 50 μm, more preferably 10 μm to 30 μm.

The optical member of the present invention can be produced by a known method.
As a known method, for example, the pressure-sensitive adhesive composition of the present invention is applied to the release-treated surface of a release film to form a coating film. Next, by drying the formed coating film, an adhesive film is formed on the release film. Next, there is a method of producing an optical member of the present invention having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention by transferring the formed pressure-sensitive adhesive film onto an optical member and curing the film.
As another method, for example, the pressure-sensitive adhesive composition of the present invention is applied to the release-treated surface of a release film to form a coating film. Next, by drying the formed coating film, an adhesive film is formed on the release film. Then, the exposed surface of the formed adhesive film is overlaid with the release-treated surface of a separately prepared release film to prepare a double-sided pressure-sensitive adhesive sheet without a substrate. Next, the pressure-sensitive adhesive film of the double-sided pressure-sensitive adhesive sheet thus produced is cured to form a pressure-sensitive adhesive layer. Next, peel off one of the release films and transfer the exposed pressure-sensitive adhesive layer onto the optical member, thereby producing the optical member of the present invention provided with the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention. is mentioned.
As another method, for example, the pressure-sensitive adhesive composition of the present invention is applied onto an optical member to form a coating film. Next, by drying the formed coating film, an adhesive film is formed on the optical member. Next, there is a method of producing the optical member of the present invention provided with an adhesive layer formed from the adhesive composition of the present invention by curing the formed adhesive film.
The drying conditions include, for example, a hot air dryer at 70° C. to 120° C. for 1 minute to 3 minutes.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples. The present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

[Production of (meth)acrylic polymer A]
[Production Example A-1]
Into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, a reflux condenser, and a sequential dropping device, 2-ethylhexyl acrylate [2EHA; acrylic acid alkyl ester monomer, Tg as a homopolymer: -76 ° C.] 79 parts by mass, acrylic acid [AA; monomer having a carboxy group, Tg when used as a homopolymer: 163 ° C.] 1 part by mass, 2-hydroxyethyl acrylate [2HEA; monomer having a hydroxyl group Tg: −15° C. as a homopolymer]20 parts by mass and 50 parts by mass of ethyl acetate were added and mixed, and then the air in the reactor was replaced with nitrogen gas. Then, while stirring the mixture in the reactor, the temperature of the mixture was raised to 72° C. (reflux temperature), and then 2,2′-azobis(2,4-dimethylvaleronitrile) [ABVN; polymerization initiator] A mixed solution of 0.02 parts by mass and 40 parts by mass of ethyl acetate was successively added, and after the addition was completed, the mixture was maintained for 6 hours to obtain a polymerization reaction product. The obtained polymerization reaction product was diluted with ethyl acetate to obtain a solution of (meth)acrylic polymer A-1 having a solid content concentration of 15% by mass.

The term "solid content concentration" as used herein means the mass proportion of the (meth)acrylic polymer A-1 in the solution of the (meth)acrylic polymer A-1.
The same applies to each solution of (meth)acrylic polymers A-2 to A-18 below.

[Production Examples A-2 to A-18]
In Production Examples A-2 to A-18, the monomer composition of the (meth)acrylic polymer A was changed to the monomer composition shown in Table 1, and the amount of organic solvent used and the polymerization initiator By adjusting at least one of the amounts used, the weight average molecular weight (Mw) of the (meth)acrylic polymer A was adjusted to the weight average molecular weight (Mw) shown in Table 1, except that Production Example A- 1 to obtain solutions of (meth)acrylic polymers A-2 to A-18 having a solid content concentration of 15% by mass.

(Meth) acrylic polymers A-1 to A-18 monomer composition (unit: mass%), glass transition temperature (Tg) [unit: ° C.], and weight average molecular weight (Mw) [unit: ten thousand ( In the table, it is written as “×10 ⁴ ”)] is shown in Table 1.
Further, in the (meth)acrylic polymers A-1 to A-18, the content ratio on a molar basis of structural units derived from a monomer having a hydroxyl group with respect to structural units derived from a monomer having a carboxy group ( In the table, "hydroxyl group-containing monomer/carboxy group-containing monomer") is shown in Table 1.

The glass transition temperature (Tg) of the (meth)acrylic polymers A-1 to A-18 is the same as the method for calculating the glass transition temperature (Tg) of the specific (meth)acrylic copolymer (A) described above. calculated by the method of
The weight average molecular weight (Mw) of the (meth)acrylic polymers A-1 to A-18 is the same as the method for measuring the weight average molecular weight (Mw) of the specific (meth)acrylic copolymer (A) described above. It was measured by the method of

Among the (meth)acrylic polymers A obtained above, the (meth)acrylic polymers A-1 to A-9 and A-11 to A-14 are the specific (meth)acrylic polymers in the present invention. It corresponds to the system copolymer (A).

Details of each monomer listed in Table 1 are as shown below.
<(Meth)acrylic acid alkyl ester monomer>
"2EHA": 2-ethylhexyl acrylate [Tg as a homopolymer: -76°C]
"2EHMA": 2-ethylhexyl methacrylate [Tg as a homopolymer: -10°C]
"n-BA": n-butyl acrylate [Tg as a homopolymer: -57°C]
"i-OA": i-octyl acrylate [Tg as a homopolymer: -75°C]
<Monomer having a carboxy group>
"AA": acrylic acid [Tg when used as a homopolymer: 163 ° C.]
"M-5300": ω-carboxy-polycaprolactone (n≈2) monoacrylate [Tg as a homopolymer: -30°C]
<Monomer having a hydroxyl group>
"2HEA": 2-hydroxyethyl acrylate [Tg as a homopolymer: -15°C]
"2HEMA": 2-hydroxyethyl methacrylate [Tg as a homopolymer: 55°C]
"2HPA": 2-hydroxypropyl acrylate [Tg as a homopolymer: -7°C]

In Table 1, "-" described in the column of monomer composition means that the corresponding monomer in that column was not blended. In addition, "-" described in other columns means that there is no corresponding value in that column.
In Table 1, "glass transition temperature" is indicated as "Tg", and "weight average molecular weight" is indicated as "Mw".

[Production of (meth)acrylic polymer B]
[Production Example B-1]
A reactor equipped with a thermometer, a stirrer, a reflux condenser, and a sequential dropping device was charged with 106 parts by mass of ethyl acetate, heated, and refluxed at 80° C. (reflux temperature) for 10 minutes. Then, with the temperature in the reactor kept at the reflux temperature, 240 parts by mass of t-butyl methacrylate [t-BMA; methacrylic acid alkyl ester monomer, Tg when used as homopolymer: 107° C. Amount equivalent to 60% by mass with respect to all structural units of the meth)acrylic polymer B-1], and 2-hydroxyethyl methacrylate [2HEMA; a monomer having a hydroxyl group, Tg when used as a homopolymer : 55° C.] 400 parts by mass of a monomer mixture containing 160 parts by mass [an amount equivalent to 40% by mass with respect to all structural units of (meth)acrylic polymer B-1], and 80.6 parts by mass of ethyl acetate A mixed solution of parts by mass and 51.4 parts by mass of dimethyl 2,2′-azobis(isobutyrate) was sequentially added over 180 minutes, and after the addition was completed, the mixture was held for 180 minutes to obtain a polymerization reaction product. . The obtained polymerization reaction product was diluted with ethyl acetate to obtain a solution of (meth)acrylic polymer B-1 having a solid content concentration of 62% by mass.

The term "solid content concentration" as used herein means the mass ratio of the (meth)acrylic polymer B-1 in the solution of the (meth)acrylic polymer B-1.
The same applies to each solution of (meth)acrylic polymers B-2 to B-18 below.

[Production Examples B-2 to B-18]
In Production Examples B-2 to B-18, the monomer composition of the (meth)acrylic polymer B was changed to the monomer composition shown in Table 2, and the amount of organic solvent used and the polymerization initiator By adjusting at least one of the amounts used, the weight average molecular weight (Mw) of the (meth)acrylic polymer B was adjusted to the weight average molecular weight (Mw) shown in Table 2, except that Production Example B- 1 to obtain respective solutions of (meth)acrylic polymers B-2 to B-18 having a solid content concentration of 62% by mass.

(Meth) acrylic polymers B-1 to B-18 monomer composition (unit: mass%), glass transition temperature (Tg) [unit: ° C.], and weight average molecular weight (Mw) [unit: ten thousand ( In the table, it is written as “×10 ⁴ ”)] is shown in Table 2.

The glass transition temperature (Tg) of the (meth)acrylic polymers B-1 to B-18 is the same as the method for calculating the glass transition temperature (Tg) of the specific (meth)acrylic copolymer (A) described above. calculated by the method of
The weight average molecular weight (Mw) of the (meth)acrylic polymers B-1 to B-18 is the same as the method for measuring the weight average molecular weight (Mw) of the specific (meth)acrylic copolymer (A) described above. It was measured by the method of

Among the (meth)acrylic polymers B obtained above, the (meth)acrylic polymers B-1 to B-6 and B-8 to B-13 are the specific (meth)acrylic polymers in the present invention. It corresponds to the system copolymer (B).

Details of each monomer listed in Table 2 are as shown below.
<(Meth)acrylic acid alkyl ester monomer>
"i-BMA": i-butyl methacrylate [Tg when used as a homopolymer: 48 ° C.]
"t-BMA": t-butyl methacrylate [Tg as a homopolymer: 107°C]
<Monomer having a carboxy group>
"AA": acrylic acid [Tg when used as a homopolymer: 163 ° C.]
<Monomer having a hydroxyl group>
"2HEA": 2-hydroxyethyl acrylate [Tg as a homopolymer: -15°C]
"2HEMA": 2-hydroxyethyl methacrylate [Tg as a homopolymer: 55°C]

In Table 2, "-" described in the column of monomer composition means that the corresponding monomer in that column was not blended.
In Table 2, "glass transition temperature" is simply indicated as "Tg", and "weight average molecular weight" is simply indicated as "Mw".

[Preparation of adhesive composition]
[Example 1]
(Meth) 100 parts by mass of acrylic polymer A-1 solution (solid content conversion value), 20 parts by mass of (meth) acrylic polymer B-3 solution (solid content conversion value), and a cross-linking agent [product Name: Sumidule (registered trademark) N-75, biuret-modified hexamethylene diisocyanate compound, isocyanate-based cross-linking agent, Sumika Covestro Urethane Co., Ltd.] 0.1 parts by mass (solid content conversion value), and By mixing, the adhesive composition of Example 1 was obtained.

[Examples 2 to 13]
In Example 1, except that the composition of the adhesive composition was changed to the composition shown in Table 3, the same operation as in Example 1 was performed to obtain each adhesive composition of Examples 2 to 13.

[Examples 14 to 24]
In Example 1, except that the composition of the adhesive composition was changed to the composition shown in Table 4, the same operation as in Example 1 was performed to obtain each adhesive composition of Examples 14 to 24.

[Examples 25 to 40]
In Example 1, except that the composition of the adhesive composition was changed to the composition shown in Table 5, the same operation as in Example 1 was performed to obtain each adhesive composition of Examples 25 to 40.

[Comparative Examples 1 to 14]
In Example 1, except that the composition of the adhesive composition was changed to the composition shown in Table 6, the same operation as in Example 1 was performed to obtain each adhesive composition of Comparative Examples 1 to 14.

[Measurement of gel fraction]
Using the adhesive compositions of Examples 1 to 40 and Comparative Examples 1 to 14, the gel fraction after cross-linking (that is, the gel fraction of the adhesive layer) was measured. Specifically, it was measured by the following method.
A pressure-sensitive adhesive is applied to the surface-treated surface of a release film [trade name: Film Bina (registered trademark) 100E-0010N023, Fujimori Industry Co., Ltd.] that has been surface-treated with a silicone-based release agent so that the thickness after drying is 20 μm. The composition was applied to form a coating film.
Then, the formed coating film was dried using a hot air circulating dryer under drying conditions of a drying temperature of 100° C. and a drying time of 1 minute to form an adhesive film on the release film.
Next, the exposed surface of the adhesive film was superimposed on the surface-treated surface of a separately prepared release film [trade name: Film Binner (registered trademark) 100E-0010N023, Fujimori Industry Co., Ltd.], and then the atmosphere temperature was 25. C. and 50% RH for 168 hours and allowed to cure to promote the cross-linking reaction to produce a substrate-free pressure-sensitive adhesive sheet having a configuration of release film/adhesive layer/release film. .

Using the pressure-sensitive adhesive layer peeled off from the obtained pressure-sensitive adhesive sheet, the gel fraction was measured according to the following (1) to (4). The results are shown in Tables 3-6.
(1) About 0.15 g of the adhesive layer is attached to a 250-mesh wire mesh (100 mm x 100 mm) whose mass is accurately measured with a precision balance, and the attached adhesive layer is placed inside so that the gel content does not leak. Then, the wire mesh is folded 5 times and used as a sample. After that, the mass is accurately measured with a precision balance.
(2) The obtained sample is immersed in 80 mL of ethyl acetate for 3 days.
(3) A sample is taken out, washed with a small amount of ethyl acetate, and dried at 120° C. for 24 hours. After that, the mass is accurately measured with a precision balance.
(4) Calculate the gel fraction by the following formula.
Gel fraction (unit: mass%) = (ZX)/(YX) x 100
However, X is the weight of the wire mesh (unit: g), Y is the weight of the wire mesh with the adhesive layer attached before immersion (unit: g), and Z is the weight of the wire mesh with the adhesive layer attached, dried after immersion. (unit: g).

[evaluation]
The adhesive compositions of Examples 1-40 and Comparative Examples 1-14 were evaluated as follows. The results are shown in Tables 3-6.

<Preparation of sample for evaluation test>
A pressure-sensitive adhesive is applied to the surface-treated surface of a release film [trade name: Film Bina (registered trademark) 100E-0010N023, Fujimori Industry Co., Ltd.] that has been surface-treated with a silicone-based release agent so that the thickness after drying is 20 μm. The composition was applied to form a coating film. Then, the formed coating film was dried using a hot air circulating dryer under drying conditions of a drying temperature of 100° C. and a drying time of 1 minute to form an adhesive film on the release film. Next, the exposed surface of the adhesive film was overlaid on a polyethylene terephthalate (PET) film [trade name: Teijin Tetoron HPE, thickness: 50 μm, Teijin DuPont Co., Ltd.], and then the atmosphere temperature was 25 ° C., 50% By standing for 168 hours in a RH environment and curing, the cross-linking reaction progresses, and an evaluation test sample having a configuration of release film / adhesive layer / PET film (hereinafter, "PET with adhesive layer" ) was produced.

1. Adhesion PET with an adhesive layer was cut into a size of 25 mm x 150 mm.
Next, the release film of the cut PET with an adhesive layer (structure: release film/adhesive layer/PET film) is peeled off, and the surface of the adhesive layer exposed by peeling is attached to a stainless steel plate (so-called SUS). After being superimposed on the surface of a polyimide (PI) film [trade name: Kapton (registered trademark) 100H, Dupont Toray Co., Ltd.] and then pressed with a 2 kg roller, a sample for adhesive strength evaluation was obtained. . This adhesive force evaluation sample was allowed to stand for 24 hours in an environment of an ambient temperature of 25° C. and 50% RH.
Then, using a single column type material testing machine (model number: STA-1225) of A&D Co., Ltd. as a measuring device, under the conditions of an atmosphere temperature of 25 ° C. and 50% RH, a peeling speed of 300 mm / min. Then, the adhesive force (unit: N/25 mm) was measured when PET with an adhesive layer (constitution: adhesive layer/PET film) was peeled off from the PI film at 180° in the long side (150 mm) direction. Then, the adhesive strength was evaluated according to the following evaluation criteria.
If the evaluation result was "A", "B", or "C", it was judged that there was no practical problem.

-Evaluation criteria-
A: The adhesive strength is 10 N/25 mm or more.
B: The adhesive strength is 6 N/25 mm or more and less than 10 N/25 mm.
C: The adhesive strength is 3 N/25 mm or more and less than 6 N/25 mm.
D: The adhesive strength is less than 3N/25mm.

2. Bending Resistance at Room Temperature PET with an adhesive layer was cut into a size of 25 mm×150 mm.
Next, the release film of the cut PET with an adhesive layer (constitution: release film/adhesive layer/PET film) is peeled off, and the surface of the adhesive layer exposed by peeling is covered with a polyimide (PI) film [trade name: Kapton]. (registered trademark) 100H, manufactured by Toray DuPont Co., Ltd.], and pressed with a roller of 2 kg to obtain a bending test sample (hereinafter referred to as "Sample X").
A test was conducted in which the operation of folding the sample X with a radius of curvature (R) of 5 mm and then completely unfolding it was repeated 100 times in an environment of an ambient temperature of 25°C. Then, immediately after the end of the test, 1 hour after the end of the test, and 24 hours after the end of the test, the bent portion of Sample X was observed using a loupe, and the bending resistance at room temperature was evaluated according to the following evaluation criteria. .
If the evaluation result was "A", "B", or "C", it was judged that there was no practical problem.

-Evaluation criteria-
A: No change was observed.
B: Whitening was slightly observed immediately after the end of the test, but disappeared 1 hour after the end of the test.
C: Whitening was slightly observed immediately after the end of the test, and did not disappear 1 hour after the end of the test, but disappeared 24 hours after the end of the test.
D: Remarkable whitening was observed immediately after the test was completed, and did not disappear even 24 hours after the test was completed.
E: Remarkable whitening was confirmed immediately after the end of the test, did not disappear even 24 hours after the end of the test, and peeling was also confirmed 24 hours after the end of the test.

3. High Temperature Durability in Folded State PET with an adhesive layer was cut into a size of 25 mm×150 mm.
Next, the release film of the cut PET with an adhesive layer (constitution: release film/adhesive layer/PET film) is peeled off, and the surface of the adhesive layer exposed by peeling is covered with a polyimide (PI) film [trade name: Kapton]. (registered trademark) 100H, manufactured by Toray DuPont Co., Ltd.], and pressed with a 2 kg roller to obtain a bending test sample (hereinafter referred to as "Sample Y").
After bending the sample Y with a radius of curvature (R) of 5 mm, a test was conducted in which the bent state was allowed to stand still for 168 hours in an environment at an ambient temperature of 100°C. Immediately after the end of the test, the folded sample Y was completely unfolded and allowed to stand in an environment with an ambient temperature of 25°C. Then, immediately after the end of the test, 1 hour after the end of the test, and 24 hours after the end of the test, the bent portion of Sample Y was observed using a loupe, and the high-temperature durability in the bent state was evaluated according to the following evaluation criteria. evaluated.
If the evaluation result was "A", "B", or "C", it was judged that there was no practical problem.

-Evaluation criteria-
A: No change was observed.
B: At least one of whitening and foaming was slightly observed immediately after the end of the test, but all disappeared 1 hour after the end of the test.
C: At least one of whitening and foaming was slightly observed immediately after the end of the test, and had not disappeared 1 hour after the end of the test, but all disappeared 24 hours after the end of the test.
D: Immediately after the end of the test, at least one of whitening and foaming was remarkably observed, and did not disappear even 24 hours after the end of the test.
E: Immediately after the end of the test, at least one of whitening and foaming was observed remarkably, did not disappear even 24 hours after the end of the test, and peeling was also observed 24 hours after the end of the test.

Details of the components listed in Tables 3-6 are as shown below.
[Crosslinking agent]
<Isocyanate-based cross-linking agent>
"Sumidule N-75" [trade name, biuret-modified hexamethylene diisocyanate compound, Sumika Covestro Urethane Co., Ltd.]
"Takenate D-110N" [trade name, xylylene diisocyanate compound, Mitsui Takeda Chemicals Co., Ltd.]
<Epoxy cross-linking agent>
"TETRAD-X" (trade name, Mitsubishi Gas Chemical Company, Inc.)
"Sumidur", "Takenate" and "TETRAD" are registered trademarks.

[Other ingredients]
<Tackifying resin>
"YS Polyster TH130" [trade name, terpene phenolic resin, Yasuhara Chemical Co., Ltd.]
"YS Polyster TH30" [trade name, terpene phenolic resin, Yasuhara Chemical Co., Ltd.]
"YS Polyster T80" [trade name, terpene phenolic resin, Yasuhara Chemical Co., Ltd.]
"YS Polyster T100" [trade name, terpene phenolic resin, Yasuhara Chemical Co., Ltd.]
"YS Polyster T115" [trade name, terpene phenolic resin, Yasuhara Chemical Co., Ltd.]
“YS Resin CP” [trade name, terpene resin, Yasuhara Chemical Co., Ltd.]
"Pine Crystal D-6011" [trade name, rosin resin, Arakawa Chemical Industries, Ltd.]
"Pine Crystal KE-359" [trade name, rosin resin, Arakawa Chemical Industries, Ltd.]

In Tables 3 to 6, "-" means that the component corresponding to that column was not blended.
In Tables 3 to 6, the numerical values described in the column of "mixture amount" are all solid content conversion values.

As shown in Tables 3-5, it was confirmed that the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Examples 1-40 exhibited good adhesive strength. Moreover, the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Examples 1 to 40 were excellent in bending resistance at room temperature. Moreover, the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Examples 1 to 40 were excellent in high-temperature durability in a folded state.

On the other hand, as shown in Table 6, the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Comparative Examples 1 to 14 had adhesive strength, bending resistance at room temperature, and high-temperature durability in a folded state. One or more were inferior.
In addition, the (meth)acrylic polymer B contains a structural unit derived from a monomer having a carboxy group instead of a structural unit derived from a monomer having a hydroxyl group, formed from the pressure-sensitive adhesive composition of Comparative Example 14. The pressure-sensitive adhesive layer thus formed was inferior in adhesive strength and high-temperature durability in a folded state. It is considered that the isocyanate group of the isocyanate-based cross-linking agent reacts with the carboxyl group of the (meth)acrylic polymer B before entering into to form a cross-linked structure.

Claims (3)

Structural unit (a1) derived from a monomer having a hydroxyl group, structural unit (a2) derived from a monomer having a carboxy group, and structural unit (a3) derived from a (meth)acrylic acid alkyl ester monomer and the content of the structural unit (a1) derived from the monomer having a hydroxyl group is in the range of 1.5% by mass or more and 20% by mass or less with respect to all structural units, and the unit having a carboxy group The content of the structural unit (a2) derived from the polymer is in the range of 0.5% by mass or more and 3% by mass or less with respect to all structural units, the glass transition temperature is −55° C. or less, and the weight a (meth)acrylic copolymer (A) having an average molecular weight of 1,000,000 or more;
Containing a structural unit (b1) derived from a monomer having a hydroxyl group, the content of the structural unit (b1) derived from the monomer having a hydroxyl group is 3% by mass or more and 40% by mass with respect to all structural units. a (meth)acrylic copolymer (B) having a weight average molecular weight within the range of 2500 or more and 10000 or less;
and an isocyanate-based cross-linking agent,
A foldable in which the content of the (meth)acrylic copolymer (B) is in the range of 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the (meth)acrylic copolymer (A) An adhesive composition for displays. In the (meth)acrylic copolymer (A), the content ratio of the structural unit (a1) derived from the monomer having a hydroxyl group to the structural unit (a2) derived from the monomer having a carboxy group is , on a molar basis, is 1.0 or more. An optical member for a foldable display, comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for a foldable display according to claim 1 or 2 .