JP2022142666A - Adhesive composition and optical member with adhesive layer - Google Patents

Abstract

To provide an adhesive composition which can form an adhesive layer excellent in high-temperature durability and has excellent coating properties and to provide an optical member with an adhesive layer comprising an adhesive layer excellent in high-temperature durability.SOLUTION: There are provided: an adhesive composition which comprises a (meth)acrylic-based copolymer containing a constitutional unit derived from a (meth)acrylic acid alkyl ester monomer, a constitutional unit derived from a monomer having a carboxy group and a constitutional unit derived from a polyfunctional (meth)acrylic acid ester monomer in which the content ratio of a constitutional unit derived from the polyfunctional (meth)acrylic acid ester monomer is 0.001 to 0.05 mass% based on the total constitutional units and a crosslinking agent, wherein the content of the crosslinking agent is 0.05 pt.mass or more based on 100 pts.mass of the (meth)acrylic-based copolymer; and an optical member with an adhesive layer.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present disclosure relates to an adhesive composition and an optical member with an adhesive layer.

2. Description of the Related Art Many mobile electronic devices such as mobile phones and mobile terminals incorporate a liquid crystal display device. Generally, a liquid crystal display device includes a liquid crystal cell in which a liquid crystal layer is sandwiched between two glass substrates, and polarizing plates arranged on both sides of the liquid crystal cell. From the viewpoint of ensuring the visibility of the liquid crystal display device, the liquid crystal cell and the polarizing plate are generally bonded together via a pressure-sensitive adhesive layer formed of an acrylic pressure-sensitive adhesive.

For example, in Patent Document 1, a monomer having a weight-average molecular weight of 900,000 to 3,000,000 and having an alicyclic structure as a monomer unit constituting the polymer is disclosed as a pressure-sensitive adhesive suitable for optical members such as polarizing plates. A (meth)acrylic acid ester polymer (A) containing a cross-linking agent (B) and an active energy ray-curable component (C) which is a polyfunctional acrylate monomer having a molecular weight of less than 1000. A pressure-sensitive adhesive obtained by curing the composition by irradiation with an active energy ray, wherein the content of the active energy ray-curable component (C) in the pressure-sensitive adhesive composition is equal to the (meth)acrylic acid ester weight A pressure-sensitive adhesive is disclosed which is 1 to 20 parts by mass per 100 parts by mass of coalescence (A) and has a gel fraction of 30% to 90%.

Japanese Patent No. 6502999

The pressure-sensitive adhesive composition used for optical members such as polarizing plates has a property (hereinafter referred to as It is required to be able to form a pressure-sensitive adhesive layer excellent in "high temperature durability").
In general, pressure-sensitive adhesive compositions are required to have excellent coatability.

An object to be solved by an embodiment of the present disclosure is to provide a PSA composition that can form a PSA layer with excellent high-temperature durability and that has excellent coatability.
A problem to be solved by another embodiment of the present disclosure is to provide an optical member with a pressure-sensitive adhesive layer that has a pressure-sensitive adhesive layer that is excellent in high-temperature durability.

Specific means for solving the problems include the following aspects.
<1> A structural unit derived from a (meth)acrylic acid alkyl ester monomer, a structural unit derived from a monomer having a carboxy group, and a structural unit derived from a polyfunctional (meth)acrylate monomer and the content of structural units derived from the polyfunctional (meth)acrylic acid ester monomer is 0.001% by mass to 0.05% by mass with respect to all structural units (meth)acrylic a copolymer;
a cross-linking agent;
including
The pressure-sensitive adhesive composition, wherein the content of the cross-linking agent is 0.05 parts by mass or more relative to 100 parts by mass of the (meth)acrylic copolymer.
<2> The pressure-sensitive adhesive composition according to <1>, wherein the polyfunctional (meth)acrylate monomer is a bifunctional (meth)acrylate monomer.
<3> The pressure-sensitive adhesive composition according to <1> or <2>, wherein the polyfunctional (meth)acrylate monomer has a molecular weight of 200 or more and less than 1,000.
<4> The (meth)acrylic copolymer has a weight average molecular weight [Mw] of 1,400,000 to 2,200,000, and the ratio [Mz /Mw] is 2.5 to 4.5, the adhesive composition according to any one of <1> to <3>.
<5> The content of structural units derived from the monomer having a carboxy group in the (meth)acrylic copolymer is 0.1 relative to the total structural units of the (meth)acrylic copolymer. The pressure-sensitive adhesive composition according to any one of <1> to <4>, which is 5.0% by mass to 5.0% by mass.
<6> The adhesive composition according to any one of <1> to <5>, wherein the (meth)acrylic copolymer contains a structural unit derived from a monomer having a hydroxyl group.
<7> The content of structural units derived from the monomer having a hydroxyl group in the (meth)acrylic copolymer is 0.1 mass with respect to all structural units of the (meth)acrylic copolymer. % to 3.0% by mass of the pressure-sensitive adhesive composition according to <6>.
<8> an optical member;
a pressure-sensitive adhesive layer provided on the optical member and formed from the pressure-sensitive adhesive composition according to any one of <1> to <7>;
An optical member with an adhesive layer.

According to one embodiment of the present disclosure, there is provided a pressure-sensitive adhesive composition that can form a pressure-sensitive adhesive layer with excellent high-temperature durability and that has excellent coatability.
According to another embodiment of the present disclosure, an optical member with a pressure-sensitive adhesive layer having a pressure-sensitive adhesive layer with excellent high-temperature durability is provided.

Hereinafter, the pressure-sensitive adhesive composition and the pressure-sensitive adhesive layer-attached optical member of the present disclosure will be described in detail. Although the description of requirements set forth below may be made based on representative embodiments of the present disclosure, the present disclosure is not limited to such embodiments, and is within the scope of the purposes of the present disclosure. , can be implemented with appropriate changes.

In the present disclosure, a numerical range indicated using "to" means a range including the numerical values described before and after "to" as lower and upper limits, respectively.
In the numerical ranges described step by step in the present disclosure, upper or lower limits described in a certain numerical range may be replaced with upper or lower limits of other numerical ranges described step by step. In addition, in the numerical ranges described in the present disclosure, upper or lower limits described in a certain numerical range may be replaced with values shown in Examples.

In the present disclosure, a combination of two or more preferred aspects is a more preferred aspect.
In the present disclosure, when there are multiple substances corresponding to each component in the adhesive composition, the amount of each component in the adhesive composition is the above amount present in the adhesive composition unless otherwise specified. It means the total amount of multiple substances.

In the present disclosure, the "(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 50% by mass or more of the total constituent units].

In the present disclosure, "(meth)acrylic" is a term that includes both "acrylic" and "methacrylic", "(meth)acrylate" is a term that includes both "acrylate" and "methacrylate", "(Meth)acryloyl" is a term that includes both "acryloyl" and "methacryloyl".

In this disclosure, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

[Adhesive composition]
The pressure-sensitive adhesive composition of the present disclosure includes a structural unit derived from a (meth) acrylic acid alkyl ester monomer, a structural unit derived from a monomer having a carboxy group, and a polyfunctional (meth) acrylic acid ester monomer and the content of structural units derived from the polyfunctional (meth) acrylic acid ester monomer is 0.001% by mass to 0.05% by mass with respect to all structural units. A certain (meth)acrylic copolymer [hereinafter also referred to as “specific (meth)acrylic copolymer”. ] and a cross-linking agent, and the content of the cross-linking agent is 0.05 parts by mass or more with respect to 100 parts by mass of the (meth)acrylic copolymer.
The pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer with excellent high-temperature durability, and has excellent coatability.
Although it is not clear why the pressure-sensitive adhesive composition of the present disclosure can exhibit such effects, 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 disclosure, but are explained as an example.

The (meth)acrylic copolymer contained in the pressure-sensitive adhesive composition of the present disclosure contains structural units derived from polyfunctional (meth)acrylic acid ester monomers. Polyfunctional (meth)acrylic acid ester monomers have many reactive sites and are highly reactive monomers. Crosslinking between meth)acrylic acid ester monomers tends to occur easily, and the z-average molecular weight [Mz] of the (meth)acrylic copolymer tends to increase. A high Mz means that the proportion of high molecular weight substances in the total polymer is high. It is believed that the higher the proportion of high molecular weight substances in the total polymer, the more complicated the entanglement of polymer chains, and the higher the modulus of elasticity of the pressure-sensitive adhesive layer formed. When the elastic modulus of the pressure-sensitive adhesive layer is moderately high, phenomena such as foaming, lifting, and peeling tend not to occur even when the pressure-sensitive adhesive layer is exposed to a high-temperature environment. In the pressure-sensitive adhesive composition of the present disclosure, since the (meth)acrylic copolymer contains a specific ratio or more of structural units derived from polyfunctional (meth)acrylic acid ester monomers, the proportion of high molecular weight in the total polymer increases moderately, and the entanglement between polymer chains becomes moderately complicated. Therefore, it is considered that the elastic modulus of the pressure-sensitive adhesive layer to be formed is moderately high. In addition, the (meth)acrylic copolymer contained in the pressure-sensitive adhesive composition of the present disclosure includes, in addition to structural units derived from polyfunctional (meth)acrylic acid ester monomers, (meth)acrylic acid alkyl ester monomers It contains a structural unit derived from a body and a structural unit derived from a monomer having a carboxyl group, which is a crosslinkable functional group. Since the pressure-sensitive adhesive composition of the present disclosure contains a cross-linking agent in a specific proportion or more with respect to the (meth)acrylic copolymer, the formed pressure-sensitive adhesive layer is considered to have a moderately high elastic modulus. From the above, it is presumed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure is excellent in high temperature durability.

As described above, when a polyfunctional (meth)acrylic acid ester monomer is used as a raw material monomer, the proportion of high molecular weight substances in the total polymer tends to increase. When the proportion of high molecular weight substances in the total polymer is high, the viscosity of the pressure-sensitive adhesive composition may increase and the coatability may deteriorate. Since the pressure-sensitive adhesive composition of the present disclosure has a relatively low content of structural units derived from polyfunctional (meth)acrylic acid ester monomers in the (meth)acrylic copolymer, polyfunctional (meth)acrylic acid Viscosity increase due to cross-linking between ester monomers is less likely to occur. Therefore, the adhesive composition of the present disclosure is presumed to have excellent coatability.

With respect to the present disclosure, in Patent Document 1 (Japanese Patent No. 6502999; hereinafter the same), a (meth)acrylic acid ester polymer, a polyfunctional acrylate monomer, and a pressure-sensitive adhesive composition containing a cross-linking agent are irradiated with ultraviolet rays. By irradiating (UV) and curing, it is possible to form a pressure-sensitive adhesive layer that does not cause significant lifting or peeling even when exposed to an environment of 80°C. However, according to the adhesive composition described in Patent Document 1, both cross-linking between polyfunctional acrylate-based monomers and cross-linking between the cross-linkable functional groups in the (meth)acrylic acid ester polymer and the cross-linking agent is performed, the elastic modulus of the formed pressure-sensitive adhesive layer becomes excessively high. Therefore, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition described in Patent Document 1 is excessively hard and tends to peel off when exposed to a higher temperature environment (for example, 105°C). Conceivable.

By the way, an optical member such as a polarizing plate may contract or expand when the temperature changes, thereby generating stress. If the generated stress is not relieved, the stress remains in the pressure-sensitive adhesive layer. If the stress remaining in the pressure-sensitive adhesive layer becomes non-uniform, for example, light leakage may occur in a liquid crystal display device, causing a phenomenon of whitening, that is, a so-called white spot.
In contrast, according to the pressure-sensitive adhesive composition of the present disclosure, it is possible to form a pressure-sensitive adhesive layer that does not easily cause white spots even when exposed to a high-temperature (for example, 105° C.) environment.

In general, optical members provided with adhesive layers (so-called optical members with adhesive layers) are stacked and stored. When stacking the pressure-sensitive adhesive layer-attached optical members, foreign matter may be caught between the stacked pressure-sensitive adhesive layer-attached optical members. If a foreign object is caught, the pressure-sensitive adhesive layer may be dented, leaving a mark (so-called dent).
On the other hand, according to the adhesive composition of the present disclosure, it is possible to form a pressure-sensitive adhesive layer that is less prone to dents and has excellent dent resistance.

[Specific (meth)acrylic copolymer]
The pressure-sensitive adhesive composition of the present disclosure includes a structural unit derived from a (meth) acrylic acid alkyl ester monomer, a structural unit derived from a monomer having a carboxy group, and a polyfunctional (meth) acrylic acid ester monomer and the content of structural units derived from the polyfunctional (meth) acrylic acid ester monomer is 0.001% by mass to 0.05% by mass with respect to all structural units. A certain (meth)acrylic copolymer [that is, a specific (meth)acrylic copolymer] is included.
The pressure-sensitive adhesive composition of the present disclosure may contain only one type of specific (meth)acrylic copolymer, or may contain two or more types.

<Structural unit derived from (meth)acrylic acid alkyl ester monomer>
The specific (meth)acrylic copolymer contains structural units derived from (meth)acrylic acid alkyl ester monomers.
The structural unit derived from the (meth)acrylic acid alkyl ester monomer can contribute to the adjustment of the adhesive strength of the adhesive layer.

In the present disclosure, "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 disclosure includes a monomer corresponding to a monomer having a carboxy group and a monomer corresponding to a polyfunctional (meth)acrylic acid ester monomer. Body is not included.

The type of (meth)acrylic acid alkyl ester monomer is not particularly limited.
The (meth)acrylic acid alkyl ester monomer is preferably an unsubstituted (meth)acrylic acid alkyl ester monomer.
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, for example, preferably 1-22, more preferably 1-18, even more preferably 1-12.

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, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate.
The (meth)acrylic acid alkyl ester monomer is preferably, for example, at least one selected from n-butyl acrylate (n-BA) and methyl acrylate (MA), more preferably n-butyl acrylate (n-BA). preferable.

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

Although the content of structural units derived from (meth)acrylic acid alkyl ester monomers in the specific (meth)acrylic copolymer is not particularly limited, for example, all structural units of the specific (meth)acrylic copolymer is preferably 50% by mass or more, more preferably 50% by mass to 99.9% by mass, even more preferably 65% by mass to 99.8% by mass, and 80% by mass to More preferably, it is 99.7% by mass.
Here, the fact that the content of structural units derived from (meth)acrylic acid alkyl ester monomers is 50% by mass or more with respect to all structural units of the specific (meth)acrylic copolymer means that (meth) ) means that a structural unit derived from an acrylic acid alkyl ester monomer is contained as a main component of a structural unit constituting a specific (meth)acrylic copolymer.

<Structural Unit Derived from Monomer Having Carboxy Group>
The specific (meth)acrylic copolymer contains structural units derived from a monomer having a carboxy group.
When the specific (meth)acrylic copolymer contains a structural unit derived from a monomer having a carboxy group, the high-temperature durability of the pressure-sensitive adhesive layer formed can be improved. In addition, when the specific (meth)acrylic copolymer contains a structural unit derived from a monomer having a carboxy group, the dent resistance of the pressure-sensitive adhesive layer formed can be improved.

In the present disclosure, "a 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.
Note that the "monomer having a carboxy group" in the present disclosure does not include a monomer corresponding to a polyfunctional (meth)acrylic acid ester monomer.

The type of monomer having a carboxy group is not particularly limited.
Examples of monomers having a carboxy group include monomers having at least one carboxy group and an ethylenically unsaturated group in one molecule.
The type of ethylenically unsaturated group is not particularly limited.
Specific examples of ethylenically unsaturated groups include vinyl groups, allyl groups, vinylphenyl groups, (meth)acrylamide groups, and (meth)acryloyl groups.
A (meth)acryloyl group is preferred as the ethylenically unsaturated group.

Specific examples of monomers having a carboxy group include acrylic acid (AA), methacrylic acid (MAA), crotonic acid, maleic anhydride, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, and ω-carboxy-polycaprolactone. mono(meth)acrylates [e.g. ω-carboxy-polycaprolactone (n≈2) monoacrylate], succinate esters (e.g. 2-acryloyloxyethyl-succinic acid), vinyl formate, vinyl acetate, vinyl propionate, and vinyl neodecanoate;
As the monomer having a carboxy group, for example, acrylic acid (AA) is preferable from the viewpoint of good reactivity with a cross-linking agent (especially an isocyanate-based cross-linking agent).

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

The content of structural units derived from a monomer having a carboxy group in the specific (meth)acrylic copolymer is not particularly limited. , preferably 0.05% by mass to 7.0% by mass, more preferably 0.1% by mass to 5.0% by mass, and 0.3% by mass to 3.0% by mass is more preferable, and 0.5% by mass to 2.0% by mass is particularly preferable.
The content of structural units derived from a monomer having a carboxy group in the specific (meth)acrylic copolymer is 0.05% by mass or more relative to the total structural units of the specific (meth)acrylic copolymer. When there is, the high-temperature durability of the formed pressure-sensitive adhesive layer tends to be more excellent. Further, the content of structural units derived from a monomer having a carboxy group in the specific (meth)acrylic copolymer is 0.05% by mass with respect to the total structural units of the specific (meth)acrylic copolymer. When it is above, the pressure-sensitive adhesive layer to be formed tends to be more excellent in dent resistance.
The content of structural units derived from a monomer having a carboxy group in the specific (meth)acrylic copolymer is 7.0% by mass or less with respect to the total structural units of the specific (meth)acrylic copolymer. With this, there is a tendency to form a pressure-sensitive adhesive layer that is less likely to cause white spots even when exposed to a high-temperature environment.

<Structural Unit Derived from Polyfunctional (Meth)Acrylic Acid Ester Monomer>
The specific (meth)acrylic copolymer contains a structural unit derived from a polyfunctional (meth)acrylic acid ester monomer, and the content of the structural unit derived from the polyfunctional (meth)acrylic acid ester monomer is 0.001% by mass to 0.05% by mass with respect to all structural units.

In the present disclosure, "structural unit derived from a polyfunctional (meth)acrylic acid ester monomer" means a structural unit formed by addition polymerization of a polyfunctional (meth)acrylic acid ester monomer.

In the present disclosure, "polyfunctional (meth)acrylic acid ester monomer" means a (meth)acrylate compound having two or more (meth)acryloyl groups in one molecule.

The polyfunctional (meth) acrylic acid ester monomer may be a bifunctional (meth) acrylic acid ester monomer, may be a trifunctional (meth) acrylic acid ester monomer, or may be a tetrafunctional or higher may be a (meth)acrylic acid ester monomer.
Examples of polyfunctional (meth)acrylate monomers include, from the viewpoint of coating properties of the pressure-sensitive adhesive composition, bifunctional (meth)acrylate monomers and trifunctional (meth)acrylate monomers. It is preferably at least one selected from the group consisting of monomers, and more preferably at least one selected from bifunctional (meth)acrylic acid ester monomers.

The type of polyfunctional (meth)acrylic acid ester monomer is not particularly limited.
Examples of polyfunctional (meth)acrylate monomers include 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol diacrylate, neopentyl glycol di(meth)acrylate, dimethylol-tricyclo Decane di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butylethylpropanediol (meth)acrylate, 3-methyl-1,5-pentanediol diacrylate, dimethylol-tricyclodecanedi Bifunctional (meth)acrylate compounds such as acrylates, EO adduct diacrylate of bisphenol A, PO adduct diacrylate of bisphenol A, neopentyl glycol/hydroxypivalic acid ester diacrylate, trimethylolpropane tri(meth)acrylate, tri Trifunctional (meth)acrylate compounds such as methylolethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, glycerin propoxytriacrylate, pentaerythritol tetra(meth)acrylate, sorbitol tetra( meth) acrylate, ditrimethylolpropane tetra (meth) acrylate and other tetrafunctional (meth) acrylate compounds, sorbitol penta (meth) acrylate, dipentaerythritol penta (meth) acrylate and other pentafunctional (meth) acrylate compounds, and di Examples include hexafunctional (meth)acrylate compounds such as pentaerythritol hexa(meth)acrylate and sorbitol hexa(meth)acrylate.

The molecular weight of the polyfunctional (meth) acrylic acid ester monomer is not particularly limited, but for example, it is preferably in the range of 150 or more and less than 1200, more preferably in the range of 200 or more and less than 1000, 300 or more and 800 A range of less than is more preferable.
Polyfunctional (meth)acrylate monomers tend to have high reactivity during polymerization when the molecular weight is low, and low reactivity during polymerization when the molecular weight is high. When the reactivity of the polyfunctional (meth)acrylic acid ester monomer during polymerization is moderately low, the coating properties of the pressure-sensitive adhesive composition tend to improve, and the polyfunctional (meth)acrylic acid ester monomer When the reactivity of the polymer during polymerization is moderately high, the formed pressure-sensitive adhesive layer tends to have improved high-temperature durability.
When the molecular weight of the polyfunctional (meth)acrylic acid ester monomer is 150 or more, the coating properties of the pressure-sensitive adhesive composition tend to be more excellent.
When the molecular weight of the polyfunctional (meth)acrylic acid ester monomer is less than 1200, the pressure-sensitive adhesive layer formed tends to be more excellent in high-temperature durability.

A commercial item can be used as a polyfunctional (meth)acrylic acid ester monomer.
Examples of commercially available polyfunctional (meth)acrylic acid ester monomers include "A-400" [trade name, chemical name: polyethylene glycol #400 diacrylate, molecular weight: 522, manufactured by Shin-Nakamura Chemical Co., Ltd. ], “Viscoat #195” [trade name, chemical name: 1,4-butanediol diacrylate, molecular weight: 198, manufactured by Osaka Organic Chemical Industry Co., Ltd.], “A-1000” [trade name, chemical name: polyethylene Glycol #1000 diacrylate, molecular weight: 1138, manufactured by Shin-Nakamura Chemical Co., Ltd.] and “Light acrylate TMP-A” [trade name, chemical name: trimethylolpropane triacrylate, molecular weight: 298, Kyoeisha Chemical Co., Ltd. made].

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

The content of structural units derived from polyfunctional (meth)acrylic acid ester monomers in the specific (meth)acrylic copolymer is 0.00% with respect to all structural units of the specific (meth)acrylic copolymer. 001% by mass to 0.05% by mass.
The content of structural units derived from polyfunctional (meth)acrylic acid ester monomers in the specific (meth)acrylic copolymer is 0.001 with respect to all structural units of the specific (meth)acrylic copolymer When it is at least 10% by mass, the pressure-sensitive adhesive layer to be formed tends to have excellent high-temperature durability. Further, the content of structural units derived from polyfunctional (meth) acrylic acid ester monomers in the specific (meth)acrylic copolymer is 0 with respect to all structural units of the specific (meth)acrylic copolymer. When it is 0.001% by mass or more, the pressure-sensitive adhesive layer formed tends to be excellent in dent resistance.
From this point of view, the content of structural units derived from polyfunctional (meth)acrylic acid ester monomers in the specific (meth)acrylic copolymer is the total structural units of the specific (meth)acrylic copolymer. is 0.001% by mass or more, preferably 0.005% by mass or more, more preferably 0.01% by mass or more, more preferably 0.015% by mass or more, A content of 0.02% by mass or more is particularly preferable.
The content of structural units derived from polyfunctional (meth)acrylic acid ester monomers in the specific (meth)acrylic copolymer is 0.05 with respect to all structural units of the specific (meth)acrylic copolymer When it is at most % by mass, the adhesive composition tends to have excellent coatability.
From this point of view, the content of structural units derived from polyfunctional (meth)acrylic acid ester monomers in the specific (meth)acrylic copolymer is the total structural units of the specific (meth)acrylic copolymer. is 0.05% by mass or less, preferably 0.045% by mass or less, more preferably 0.04% by mass or less, and further preferably 0.035% by mass or less, It is particularly preferably 0.03% by mass or less.

<Structural Unit Derived from Monomer Having Hydroxyl Group>
The specific (meth)acrylic copolymer preferably contains a structural unit derived from a monomer having a hydroxyl group.
When the specific (meth)acrylic copolymer contains a structural unit derived from a monomer having a hydroxyl group, the high-temperature durability of the pressure-sensitive adhesive layer formed can be further improved.

In the present disclosure, "a 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.
Monomers having hydroxyl groups include, for example, monomers having at least one hydroxyl group and an ethylenically unsaturated group in one molecule.
The type of ethylenically unsaturated group is not particularly limited.
Specific examples of ethylenically unsaturated groups include vinyl groups, allyl groups, vinylphenyl groups, (meth)acrylamide groups, and (meth)acryloyl groups.
A (meth)acryloyl group is preferred as the ethylenically unsaturated group.

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, glycerin mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, and poly (ethylene glycol-propylene glycol) mono ( meth)acrylates.
As the monomer having a hydroxyl group, for example, hydroxyalkyl (meth)acrylate is preferable from the viewpoint of good copolymerizability with other monomers, and good compatibility with other monomers. And from the viewpoint of good reactivity with a cross-linking agent (especially an isocyanate-based cross-linking agent), a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 1 to 5 carbon atoms is More preferred are hydroxyalkyl (meth)acrylates having a hydroxyalkyl group with 2 to 4 carbon atoms, and particularly preferred is 2-hydroxyethyl acrylate (2HEA).

When the specific (meth)acrylic copolymer contains a structural unit derived from a monomer having a hydroxyl group, it may contain only one type of structural unit derived from a monomer having a hydroxyl group, or two or more types. may contain.

When the specific (meth)acrylic copolymer contains a structural unit derived from a monomer having a hydroxyl group, the content of the structural unit derived from the monomer having a hydroxyl group in the specific (meth)acrylic copolymer is , Although not particularly limited, for example, it is preferably 0.05% by mass to 5.0% by mass, and 0.1% by mass to 3.0% by mass, based on the total structural units of the specific (meth)acrylic copolymer. It is more preferably 0% by mass, still more preferably 0.2% by mass to 2.0% by mass, and particularly preferably 0.3% by mass to 1.0% by mass.
The content of structural units derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer is 0.05% by mass or more with respect to all structural units of the specific (meth)acrylic copolymer. , the high-temperature durability of the pressure-sensitive adhesive layer formed tends to be more excellent. Further, the content of structural units derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer is 0.2% by mass or more with respect to all structural units of the specific (meth)acrylic copolymer. , the resulting pressure-sensitive adhesive layer tends to be more excellent in dent resistance in addition to high-temperature durability.
The content of structural units derived from a monomer having a hydroxyl group in the specific (meth)acrylic copolymer is 5.0% by mass or less with respect to the total structural units of the specific (meth)acrylic copolymer. , there is a tendency to form a pressure-sensitive adhesive layer that is less likely to cause white spots even when exposed to a high-temperature environment.

<Other structural units>
The specific (meth)acrylic copolymer is the aforementioned structural unit, i.e., the essential structural unit (meth)acrylic acid alkyl ester monomer, as long as it does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure. A structural unit derived from, a structural unit derived from a monomer having a carboxy group, a structural unit derived from a polyfunctional (meth) acrylic acid ester monomer, and a monomer having a hydroxyl group which is an arbitrary structural unit Structural units other than structural units derived from the body (so-called other structural units) may be included.

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.

When the specific (meth)acrylic copolymer contains other structural units, it may contain only one type of other structural units, or may contain two or more types thereof.

When the specific (meth)acrylic copolymer contains other structural units, the content of the other structural units in the specific (meth)acrylic copolymer is not particularly limited. It can be appropriately set according to the purpose within a range that does not impair the effect.

<<Molecular weight of specific (meth)acrylic copolymer>>
- Weight average molecular weight [Mw] -
Mw of the specific (meth)acrylic copolymer is not particularly limited, but for example, it is preferably 800,000 to 2,500,000, more preferably 1,000,000 to 2,400,000, and 1,200,000 to 2,300,000 is more preferable, and 1,400,000 to 2,200,000 is particularly preferable.
When the Mw of the specific (meth)acrylic copolymer is 800,000 or more, the pressure-sensitive adhesive layer to be formed tends to be more excellent in high-temperature durability.
When the Mw of the specific (meth)acrylic copolymer is 2,500,000 or less, the viscosity of the pressure-sensitive adhesive composition does not become too high, so that the pressure-sensitive adhesive composition tends to have better coatability.

-z average molecular weight [Mz]-
Mz of the specific (meth)acrylic copolymer is not particularly limited, but for example, it is preferably 3.3 million to 10 million, more preferably 3.5 million to 9.9 million, and 3.7 million to 9.7 million. is more preferable, and 4,000,000 to 9,500,000 is particularly preferable.
When the Mz of the specific (meth)acrylic copolymer is 3,300,000 or more, the pressure-sensitive adhesive layer to be formed tends to be more excellent in high-temperature durability. Further, when the Mz of the specific (meth)acrylic copolymer is 3,300,000 or more, the pressure-sensitive adhesive layer to be formed tends to be more excellent in dent resistance.
When the Mz of the specific (meth)acrylic copolymer is 10,000,000 or less, the pressure-sensitive adhesive composition tends to have more excellent coatability.

-Ratio [Mz/Mw] of z-average molecular weight [Mz] to weight-average molecular weight [Mw]-
Mz/Mw in the specific (meth)acrylic copolymer is preferably 2.1 to 8.5, more preferably 2.5 to 6.5, and 2.5 to 5.5. more preferably 2.5 to 4.5.
When Mz/Mw in the specific (meth)acrylic copolymer is 2.1 or more, the pressure-sensitive adhesive layer to be formed tends to be more excellent in high-temperature durability. Further, when Mz/Mw in the specific (meth)acrylic copolymer is 2.1 or more, the pressure-sensitive adhesive layer to be formed tends to be more excellent in dent resistance.
When the Mz/Mw of the specific (meth)acrylic copolymer is 8.5 or less, the pressure-sensitive adhesive composition tends to have more excellent coatability.

The aspect of Mw and Mz/Mw in the specific (meth)acrylic copolymer is preferably an aspect in which Mw is 1.4 million to 2.2 million and Mz/Mw is 2.5 to 8.5, and Mw is 1.4 million to 2.2 million, and Mz / Mw is more preferably 2.5 to 6.5, Mw is 1.4 million to 2.2 million, and Mz / Mw is 2.5 to 5 0.5 is more preferable, and an embodiment in which Mw is 1.4 million to 2.2 million and Mz/Mw is 2.5 to 4.0 is particularly preferable.
When the aspects of Mw and Mz/Mw in the specific (meth)acrylic copolymer are the above aspects, the pressure-sensitive adhesive layer formed tends to have better high-temperature durability, and the pressure-sensitive adhesive composition can be coated. The workability tends to be better.

Mw and Mz of the specific (meth)acrylic copolymer are values obtained by the following methods. Specifically, it is obtained according to the following (1) to (3).
(1) A solution of the specific (meth)acrylic copolymer is applied to release paper and dried at 100° C. for 1 minute to obtain a film-like specific (meth)acrylic copolymer.
(2) Using the film-like specific (meth)acrylic copolymer 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 in the sample solution.
(3) Using gel permeation chromatography (GPC), the Mw and Mz of the specific (meth)acrylic copolymer are obtained as standard polystyrene equivalent values under the following conditions.

Here, when there are Ni polymers with a molecular weight of Mi, Mw and Mz are calculated by the following equations.
Mw=Σ(Mi ² ×Ni)/Σ(Mi×Ni)
Mz = Σ(Mi ³ ×Ni)/Σ(Mi ² ×Ni)

~Conditions~
Measuring device: high-speed GPC [model number: HLC-8220 GPC, manufactured by Tosoh Corporation]
Detector: Differential refractometer (RI) [built into HLC-8220, manufactured by Tosoh Corporation]
Column: 4 columns of TSKgel GMH _XL [manufactured by Tosoh Corporation] used Column temperature: 40°C
Eluent: Tetrahydrofuran Injection volume of sample solution: 100 μL
Flow rate: 0.8 mL/min

The Mw and Mz of the specific (meth)acrylic copolymer are determined by adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, etc. when polymerizing the monomers. A desired value can be obtained by adjusting.

<<Specific (meth)acrylic copolymer content>>
The content of the specific (meth)acrylic copolymer in the adhesive composition of the present disclosure is not particularly limited, but for example, 70% by mass to 99.95% by mass with respect to the total solid content in the adhesive composition %, more preferably 75% by mass to 99.9% by mass, even more preferably 80% by mass to 99.7% by mass, and 85% by mass to 99.5% by mass. is particularly preferred.
In the present disclosure, "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, and the pressure-sensitive adhesive composition contains a solvent. In some cases, it means the mass of the residue after removing the solvent from the pressure-sensitive adhesive composition.
In the present disclosure, "solvent" means water and organic solvents.

[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 in that 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 disclosure after production.

In the solution polymerization method, generally, a predetermined organic solvent, monomers, polymerization initiator, and optional chain transfer agent are charged in a polymerization vessel, and the reaction is performed, for example, at the reflux temperature of the organic solvent in a nitrogen stream. , with stirring for several hours. In this case, the organic solvent, the monomer, the polymerization initiator, and, if necessary, at least part of the chain transfer agent may be added successively.

Examples of the organic solvent used during the polymerization reaction include aromatic hydrocarbon compounds, aliphatic hydrocarbon compounds, alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds.
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 Ethyl acetate is preferably used 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.

Polymerization initiators include, for example, organic peroxides and azo compounds used in common solution polymerization methods.
Specific examples of organic peroxides include t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propylperoxydicarbonate, di-2-ethylhexylperoxy Dicarbonate, 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.
Specific 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.

[Crosslinking agent]
The adhesive composition of the present disclosure contains a cross-linking agent. In addition, the content of the cross-linking agent in the adhesive composition of the present disclosure is 0.05 parts by mass or more with respect to 100 parts by mass of the specific (meth)acrylic copolymer.

The type of cross-linking agent is not particularly limited.
Examples of cross-linking agents include isocyanate-based cross-linking agents, epoxy-based cross-linking agents, and metal chelate-based cross-linking agents.
Among these, the isocyanate-based cross-linking agent is preferable as the cross-linking agent.

In the present disclosure, "isocyanate-based cross-linking agent" refers to a compound having two or more isocyanate groups in one molecule (so-called polyisocyanate compound). The term "epoxy-based cross-linking agent" refers to a compound having two or more epoxy groups in one molecule (so-called bifunctional or higher epoxy compound). Moreover, the “metal chelate-based cross-linking agent” refers to a metal chelate compound that functions as a cross-linking agent.

The type of isocyanate-based cross-linking agent is not particularly limited.
Examples of isocyanate-based cross-linking agents include aromatic polyisocyanate compounds such as xylylene diisocyanate (XDI), diphenylmethane diisocyanate, triphenylmethane triisocyanate, tolylene diisocyanate (TDI), hexamethylene diisocyanate (HMDI), and pentamethylene diisocyanate (PDI). , isophorone diisocyanate, an aliphatic polyisocyanate compound such as a hydrogenated product of an aromatic polyisocyanate compound, or an alicyclic polyisocyanate compound.
Examples of isocyanate-based cross-linking agents include dimers, trimers, or pentamers of the above polyisocyanate compounds, adducts of the above polyisocyanate compounds and polyol compounds such as trimethylolpropane, and biuret of the above polyisocyanate compounds. Also included is the body.

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) 2037", "Coronate (R) 2234", "Coronate (R) 2785", "Aquanate (R) 200", and " AQUANATE (registered trademark) 210” [manufactured by Tosoh Corporation], “Sumidule (registered trademark) N3300”, “Desmodur (registered trademark) N3400”, and “Sumidule (registered trademark) N75” [above , manufactured by 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” [manufactured by 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” (manufactured by Mitsui Chemicals, Inc.).

The type of epoxy-based cross-linking agent is not particularly limited.
Specific examples of epoxy-based cross-linking agents include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol di glycidyl ether, 1,6-hexanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, resorcin diglycidyl ether, 2, 2-dibromoneopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, adipate diglycidyl ester, phthalate diglycidyl ester, tris(glycidyl) isocyanurate, tris(glycidyl) sidoxyethyl)isocyanurate, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-1,3-benzenedi(methanamine).

A commercially available product can be used as the epoxy-based cross-linking agent.
Commercially available examples of epoxy-based cross-linking agents include "TETRAD (registered trademark)-X" and "TETRAD (registered trademark)-C" (manufactured by Mitsubishi Gas Chemical Company, Inc.).

The type of metal chelate-based cross-linking agent is not particularly limited.
Examples of metal chelate-based cross-linking agents include aluminum chelate compounds represented by aluminum monoacetylacetonate bis(ethylacetoacetate), aluminum tris(ethylacetoacetate), and aluminum tris(acetylacetonate), titanium chelate compounds, Zirconium chelate compounds as well as cobalt chelate compounds are included.

A commercial item can be used as a metal chelate type crosslinking agent.
Examples of commercially available metal chelate-based cross-linking agents include Alumichelate A [trade name, chemical name: aluminum tris (acetylacetonate), manufactured by Kawaken Fine Chemicals Co., Ltd.], Alumichelate D [trade name, chemical name: aluminum monoacetylacetonate bis(ethylacetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.], and ALCH-TR [trade name, chemical name: aluminum tris(ethylacetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.]. be done.

The pressure-sensitive adhesive composition of the present disclosure may contain only one cross-linking agent, or may contain two or more cross-linking agents.

The content of the cross-linking agent in the adhesive composition of the present disclosure is 0.05 parts by mass or more with respect to 100 parts by mass of the specific (meth)acrylic copolymer.
When the content of the cross-linking agent in the pressure-sensitive adhesive composition of the present disclosure is 0.05 parts by mass or more with respect to 100 parts by mass of the specific (meth)acrylic copolymer, the high-temperature durability of the formed pressure-sensitive adhesive layer tend to be superior.
From such a viewpoint, the content of the cross-linking agent in the adhesive composition of the present disclosure is 0.05 parts by mass or more with respect to 100 parts by mass of the specific (meth)acrylic copolymer, and 0.1 mass parts parts by mass or more, more preferably 0.2 parts by mass or more, still more preferably 0.3 parts by mass or more, and particularly preferably 0.4 parts by mass or more.
The upper limit of the content of the cross-linking agent in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited. It is preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less, and particularly preferably 2.0 parts by mass or less.
When the content of the cross-linking agent in the pressure-sensitive adhesive composition of the present disclosure is 5.0 parts by mass or less with respect to 100 parts by mass of the specific (meth)acrylic copolymer, whitening occurs even when exposed to a high-temperature environment. There is a tendency that a pressure-sensitive adhesive layer that is less likely to come off can be formed.

〔Silane coupling agent〕
The adhesive composition of the present disclosure may contain a silane coupling agent.
When the pressure-sensitive adhesive composition of the present disclosure contains a silane coupling agent, the adhesiveness of the formed pressure-sensitive adhesive layer to glass can be further improved. Therefore, when the adherend is glass, the high-temperature durability of the formed pressure-sensitive adhesive layer can be further improved.

The type of silane coupling agent is not particularly limited.
Silane coupling agents include, for example, vinyltrimethoxysilane, vinyltriethoxysilane, and silane compounds containing polymerizable unsaturated groups represented by 3-methacryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3 -thiol group-containing silane compounds represented by mercaptopropyltriethoxysilane and 3-mercaptopropyldimethoxymethylsilane, 3-glycidoxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane Epoxy group-containing silane compounds represented by 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyl Examples include amino group-containing silane compounds typified by dimethoxysilane, and tris-(3-trimethoxysilylpropyl)isocyanurate.

A commercial item can be used as a silane coupling agent.
Examples of commercially available silane coupling agents include "KBM-402", "KBM-403" and "X-41-1053" (manufactured by Shin-Etsu Chemical Co., Ltd.).

When the pressure-sensitive adhesive composition of the present disclosure contains a silane coupling agent, it may contain only one silane coupling agent, or may contain two or more silane coupling agents.

When the pressure-sensitive adhesive composition of the present disclosure contains a silane coupling agent, the content of the silane coupling agent is not particularly limited. It is preferably from 1 part by mass to 1 part by mass, more preferably from 0.1 part by mass to 0.8 part by mass, and even more preferably from 0.1 part by mass to 0.5 part by mass.
When the content of the silane coupling agent in the adhesive composition of the present disclosure is within the above range with respect to 100 parts by mass of the specific (meth)acrylic copolymer, when the adherend is glass, The pressure-sensitive adhesive layer to be formed tends to be more excellent in high-temperature durability.

〔Organic solvent〕
The adhesive composition of the present disclosure may contain an organic solvent.
The pressure-sensitive adhesive composition of the present disclosure can further improve coatability when it contains an organic solvent.
Examples of the organic solvent include those similar to those used in the above-described polymerization reaction of the specific (meth)acrylic copolymer.

When the pressure-sensitive adhesive composition of the present disclosure 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 disclosure 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 disclosure may optionally contain components other than the components described above (so-called other components) as long as the effects are not impaired.
Other components include polymers other than specific (meth)acrylic copolymers, crosslinking catalysts, tackifiers, antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbers ), and various additives such as antistatic agents.

When the pressure-sensitive adhesive composition of the present disclosure contains other components, the content of the other components can be appropriately set within a range that does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure.

<<Gel fraction after cross-linking>>
The gel fraction after crosslinking of the pressure-sensitive adhesive composition of the present disclosure (so-called gel fraction of the pressure-sensitive adhesive layer) is not particularly limited; %, more preferably 60% by mass to 90% by mass, and particularly preferably 70% by mass to 90% by mass.
When the pressure-sensitive adhesive composition of the present disclosure has a gel fraction of 50% by mass or more after cross-linking, the formed pressure-sensitive adhesive layer tends to have better high-temperature durability.

In the present disclosure, the “gel fraction after cross-linking of the pressure-sensitive adhesive composition” means the percentage of solvent-insoluble matter 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 (that is, the adhesive layer) is applied to a 250-mesh wire mesh (100 mm × 100 mm) whose mass is accurately measured using a precision balance, and the gel content is The wire mesh is folded five times with the attached adhesive layer inside so as not to leak, and the sample is obtained. The mass of the sample is then accurately measured using 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. Next, the mass of the dried sample is accurately measured using 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 to which the pressure-sensitive adhesive layer is attached before immersion (unit: g), and Z is the pressure-sensitive adhesive dried after immersion. It is the mass (unit: g) of the wire mesh to which the layer is attached.

<<Usage>>
Applications of the pressure-sensitive adhesive composition of the present disclosure are not particularly limited.
The pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer with excellent high-temperature durability, and has excellent coatability. In addition, the pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer with excellent dent resistance.
Since the pressure-sensitive adhesive composition of the present disclosure has the properties as described above, it is suitable for use in, for example, attaching optical members to adherends (for so-called optical members).
Furthermore, the pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer that does not easily cause white spots even when exposed to a high-temperature environment. preferred. Specific applications include, for example, applications for attaching a polarizing plate to a liquid crystal cell (specifically, a glass substrate of a liquid crystal cell), applications for attaching a polarizing plate to an optical film such as a retardation film, and the like. be done.

[Optical member with adhesive layer]
The pressure-sensitive adhesive layer-carrying optical member of the present disclosure includes an optical member, and a pressure-sensitive adhesive layer provided on the optical member and formed from the above-described pressure-sensitive adhesive composition of the present disclosure. That is, in the pressure-sensitive adhesive layer-carrying optical member of the present disclosure, the optical member and the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure are laminated.
Since the pressure-sensitive adhesive layer-carrying optical member of the present disclosure includes the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure, it has excellent high-temperature durability. In addition, since the pressure-sensitive adhesive layer-carrying optical member of the present disclosure includes the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure, white spots are less likely to occur even when exposed to a high-temperature environment. Moreover, since the optical member with an adhesive layer of the present disclosure includes the adhesive layer formed from the adhesive composition of the present disclosure, it is excellent in dent resistance.

The optical member in the pressure-sensitive adhesive layer-attached optical member of the present disclosure is not particularly limited.
The optical member includes, for example, members constituting devices such as image display devices and input devices (so-called optical devices), or members used in these devices.
Specific examples of optical members include polarizing plates, AG (Anti-Glare) polarizing plates, wave plates, retardation plates including 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 the optical member include polyolefin resins (eg, polyethylene and polypropylene), polyester resins (eg, polyethylene terephthalate (PET)), acetate resins (eg, triacetyl cellulose resin), polyether sulfone resins, Resins such as polycarbonate-based resins, polyamide-based resins, polyimide-based resins, acrylic-based resins, vinyl chloride-based resins, ABS (Acrylonitrile Butadiene Styrene) resins, and fluorine-based resins can be used.

A polarizing plate is preferable as the optical member in the pressure-sensitive adhesive layer-attached optical member of the present disclosure.
The polarizing plate includes at least a polarizer, and may be a single polarizer or a laminate of a polarizer and a protective film. That is, the polarizing plate may have a one-layer structure with a polarizer alone, a two-layer structure with a protective film on one side of the polarizer, or a three-layer structure with protective films on both sides of the polarizer. There may be.
When the optical member in the pressure-sensitive adhesive layer-attached optical member of the present disclosure is a polarizing plate, the layer configuration includes, for example, pressure-sensitive adhesive layer/polarizer, pressure-sensitive adhesive layer/polarizer/protective film, pressure-sensitive adhesive layer/protective film/ A polarizer/protective film and an adhesive layer/protective film/polarizer are included. Further, between the polarizer and the protective film, between the protective film and the pressure-sensitive adhesive layer, and between the polarizer and the pressure-sensitive adhesive layer, a retardation film (e.g., an optical functional layer represented by an EWV layer , an adhesive layer, and an easy-adhesion layer).
Polarizers include, for example, polyvinyl alcohol (PVA) films.
Protective films include, for example, triacetylcellulose (TAC) films, polycycloolefin (COP) films, polyethylene terephthalate (PET) films, and acrylic films.

The thickness of the pressure-sensitive adhesive layer included in the pressure-sensitive adhesive layer-attached optical member of the present disclosure is not particularly limited.
The thickness of the pressure-sensitive adhesive layer is appropriately set according to, for example, the material and shape of the adherend.
The thickness of the adhesive layer is generally 1 μm to 100 μm, preferably 5 μm to 50 μm, more preferably 10 μm to 30 μm.

The "thickness of the adhesive layer" in the present disclosure means the average thickness of the adhesive layer.
The average thickness of the adhesive layer is a value measured by the following method.
The thickness direction of the adhesive layer WHEREIN: The arithmetic mean value of the thickness of the adhesive layer measured at ten randomly selected places is calculated|required, and let the obtained value be an average thickness of an adhesive layer. The thickness of the pressure-sensitive adhesive layer is measured using a thickness gauge.

The exposed pressure-sensitive adhesive layer in the pressure-sensitive adhesive layer-attached optical member of the present disclosure may be protected with a release film.
The release film is not particularly limited as long as it can be easily peeled off from the adhesive layer. is mentioned.
Examples of resin films include polyester films typified by polyethylene terephthalate (PET) films.
Examples of release agents include silicone-based release agents (eg, silicone), wax-based release agents (eg, paraffin wax), fluorine-based release agents (eg, fluorine-based resins), and the like.
The release film protects the surface of the pressure-sensitive adhesive layer until the optical member with the pressure-sensitive adhesive layer is put to practical use, and is peeled off during use.

[Method for producing an optical member with an adhesive layer]
The method for producing the pressure-sensitive adhesive layer-attached optical member of the present disclosure is not particularly limited.
The pressure-sensitive adhesive layer-carrying optical member of the present disclosure can be produced by a known method.
Examples of the method for producing the pressure-sensitive adhesive layer-attached optical member of the present disclosure include the following methods. A coating film is formed on the release film by applying the pressure-sensitive adhesive composition of the present disclosure to the easily peelable surface of the release 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 brought into contact with the optical member and pressed to transfer the adhesive film to the optical member, thereby forming the adhesive film on the optical member. Next, the formed adhesive film is cured to form an adhesive layer. As described above, the optical member with a pressure-sensitive adhesive layer of the present disclosure is obtained.

Another method for producing the pressure-sensitive adhesive layer-attached optical member of the present disclosure includes, for example, the following method. A coating film is formed on the release film by applying the pressure-sensitive adhesive composition of the present disclosure to the easily peelable surface of the release film. Next, by drying the formed coating film, an adhesive film is formed on the release film. Next, the exposed surface of the adhesive film thus formed is superimposed on the easily peelable treated surface of a separately prepared release film, and then pressure-bonded to prepare a double-sided pressure-sensitive adhesive sheet having no 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, one of the two release films included in the double-sided pressure-sensitive adhesive sheet is peeled off, and the exposed pressure-sensitive adhesive layer is brought into contact with the optical member and pressed to transfer the pressure-sensitive adhesive layer to the optical member. As described above, the optical member with a pressure-sensitive adhesive layer of the present disclosure is obtained.

Another method for producing the pressure-sensitive adhesive layer-attached optical member of the present disclosure includes, for example, the following method. A coating film is formed on the optical member by applying the adhesive composition of the present disclosure to one surface of the optical member. Next, by drying the formed coating film, an adhesive film is formed on the optical member. Next, the formed adhesive film is cured to form an adhesive layer. As described above, the optical member with a pressure-sensitive adhesive layer of the present disclosure is obtained.

The method of applying the pressure-sensitive adhesive composition is not particularly limited.
Examples of the method of applying the adhesive composition include known methods using a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, knife coater, spray coater, bar coater, applicator, and the like.
The coating amount of the pressure-sensitive adhesive composition is not particularly limited, and is appropriately set, for example, according to the thickness of the pressure-sensitive adhesive layer to be formed.

A method for drying the coating film is not particularly limited.
Methods for drying the coating film include, for example, natural drying, heat drying, hot air drying, and vacuum drying.
The drying temperature and drying time of the coating film are not particularly limited, and are appropriately set according to the thickness of the coating film, the amount of the organic solvent in the coating film, and the like.
An example of the drying conditions includes conditions of drying at 70° C. to 120° C. for 30 seconds to 180 seconds using a hot air dryer.

Curing is carried out for 2 to 7 days in an environment of, for example, an ambient temperature of 20° C. to 50° C. and a relative humidity of 45% to 55% (that is, 45% RH to 55% RH).

EXAMPLES The pressure-sensitive adhesive composition and the like of the present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples as long as the gist thereof is not exceeded.

[Preparation of adhesive composition]
[Example 1]
Into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, 98.4 parts by mass of n-butyl acrylate [n-BA; acrylic acid alkyl ester monomer], 2-hydroxyethyl acrylate [2HEA; monomer having hydroxyl group] 0.6 parts by mass, acrylic acid [AA; monomer having carboxy group] 1.0 parts by mass, polyethylene glycol #400 diacrylate [trade name: A-400, new Nakamura Kagaku Kogyo Co., Ltd.] [polyfunctional acrylate monomer] 0.025 parts by mass and ethyl acetate [organic solvent] 66.7 parts by mass were mixed to obtain a mixture. The inside was replaced with nitrogen.
Then, the mixture in the reactor was heated to 70° C. with stirring, and then 0.5% of 2,2′-azobis(2,4-dimethylvaleronitrile) [ABVN; polymerization initiator] was added to the mixture in the reactor. 02 parts by mass and 115.0 parts by mass of ethyl acetate were successively added, and after the addition was completed, the polymerization reaction was completed for 6 hours to obtain a solution containing a polymer. Next, the obtained solution containing the polymer was diluted with ethyl acetate to a solid content concentration of 13.5% by mass, and then cooled to obtain a solution of a (meth)acrylic copolymer.

The term "solid content concentration" as used herein means the mass ratio of the (meth)acrylic copolymer in the solution of the (meth)acrylic copolymer. The same applies to each solution of the (meth)acrylic copolymer produced below.

100 parts by mass of the solution of the (meth)acrylic copolymer obtained above (solid content conversion value), and Coronate (registered trademark) L-45E as a cross-linking agent [trade name, tolylene diisocyanate (TDI) and tri Adduct with methylolpropane (TMP), solid content concentration: 45% by mass, manufactured by Tosoh Corporation] 0.4 parts by mass (solid content conversion value), and KBM-403 [trade name, chemical Name: 3-glycidoxypropyltriethoxysilane, solid content concentration: 100% by mass, manufactured by Shin-Etsu Chemical Co., Ltd.] 0.3 parts by mass and an appropriate amount of ethyl acetate are sufficiently mixed to obtain a solid content concentration was adjusted to 8% by mass to obtain a pressure-sensitive adhesive composition of Example 1.

[Examples 2 to 14]
In Example 1, the same operation as in Example 1 was performed except that the composition of the adhesive composition was changed to the composition shown in Table 1, and each of Examples 2 to 14 having a solid content concentration of 8% by mass An adhesive composition was obtained.

[Examples 15 to 25]
In Example 1, the same operation as in Example 1 was performed except that the composition of the adhesive composition was changed to the composition shown in Table 2, and each of Examples 15 to 25 having a solid content concentration of 8% by mass An adhesive composition was obtained.

[Comparative Examples 1 to 5]
In Example 1, the same operation as in Example 1 was performed except that the composition of the adhesive composition was changed to the composition shown in Table 3, and each of Comparative Examples 1 to 5 having a solid content concentration of 8% by mass An adhesive composition was obtained.

Weight-average molecular weight (Mw) of (meth)acrylic copolymer [unit: 10,000 (indicated as “×10 ⁴ ” in the table)], z-average molecular weight (Mz) of (meth)acrylic copolymer [ Unit: 10,000 (indicated as “×10 ⁴ ” in the table)], and the ratio (Mz/Mw) between the z-average molecular weight (Mz) and the weight-average molecular weight (Mw) in the (meth)acrylic copolymer Shown in Tables 1-3.
The weight-average molecular weight (Mw) and z-average molecular weight (Mz) of the (meth)acrylic copolymer are the weight-average molecular weight (Mw) and z-average molecular weight (Mz) of the specific (meth)acrylic copolymer described above. It was obtained by the same method as

In Tables 1 to 3, "-" means that the component corresponding to that column is not included.

Details of each monomer described in Tables 1 to 3 are as shown below.
<(Meth)acrylic acid alkyl ester monomer>
"n-BA": n-butyl acrylate "MA": methyl acrylate <monomer having a hydroxyl group>
"2HEA": 2-hydroxyethyl acrylate <monomer having a carboxy group>
"AA": acrylic acid <polyfunctional (meth) acrylic acid ester monomer>
-Bifunctional (meth)acrylic acid ester monomer-
"A-400" [trade name, chemical name: polyethylene glycol #400 diacrylate, molecular weight: 522, manufactured by Shin-Nakamura Chemical Co., Ltd.]
“Viscoat #195” [trade name, chemical name: 1,4-butanediol diacrylate, molecular weight: 198, manufactured by Osaka Organic Chemical Industry Co., Ltd.]
"A-1000" [trade name, chemical name: polyethylene glycol #1000 diacrylate, molecular weight: 1138, manufactured by Shin-Nakamura Chemical Co., Ltd.]
-Trifunctional (meth)acrylic acid ester monomer-
"TMP-A" [trade name: light acrylate TMP-A, chemical name: trimethylolpropane triacrylate, molecular weight: 298, manufactured by Kyoeisha Chemical Co., Ltd.]

Details of each cross-linking agent described in Tables 1 to 3 are as shown below.
<Isocyanate-based cross-linking agent>
"Coronate L-45E" [trade name, tolylene diisocyanate compound [adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP)], solid content concentration: 45% by mass, manufactured by Tosoh Corporation]
“Takenate D-110N” [trade name, xylylene diisocyanate compound [adduct of xylylene diisocyanate (XDI) and trimethylolpropane (TMP)], solid content concentration: 75% by mass, manufactured by Mitsui Chemicals, Inc.]
“Sumidur N75” [trade name, hexamethylene diisocyanate compound [biuret form of hexamethylene diisocyanate (HMDI)], solid content concentration: 75% by mass, manufactured by Sumika Covestro Urethane Co., Ltd.]
<Epoxy cross-linking agent>
“TETRAD-X” [trade name, solid content concentration: 75% by mass, manufactured by Mitsubishi Gas Chemical Company, Inc.]
<Metal chelate-based cross-linking agent>
“Aluminum chelate A” [trade name, chemical name: aluminum tris (acetylacetonate), manufactured by Kawaken Fine Chemicals Co., Ltd.]
"Coronate", "Takenate", "Sumidure" and "TETRAD" are all registered trademarks.

Details of each silane coupling agent listed in Tables 1 to 3 are as shown below.
“KBM-403” [trade name, chemical name: 3-glycidoxypropyltriethoxysilane, epoxy group-containing silane compound, solid content concentration: 100% by mass, manufactured by Shin-Etsu Chemical Co., Ltd.]
"X-41-1053" [trade name, epoxy group-containing silane compound, solid content concentration: 100% by mass, manufactured by Shin-Etsu Chemical Co., Ltd.]

[Preparation of polarizing plate with adhesive layer]
The pressure-sensitive adhesive composition was applied onto the surface-treated surface of a release film [type: MRF, thickness: 38 μm, manufactured by Mitsubishi Chemical Corporation] that had been surface-treated with a silicone-based release agent to form a coating film. The amount of the pressure-sensitive adhesive composition to be applied was such that the thickness of the pressure-sensitive adhesive film, which will be described later, was 25 μm.
Next, air at 100° C. was blown to the formed coating film using a hot air circulating dryer at a wind speed of 3 m/sec for 60 seconds to form an adhesive film having a thickness of 25 μm on the release film.
Next, the exposed surface of the formed adhesive film and the surface of one TAC layer of a polarizing plate having a structure of triacetyl cellulose (TAC) layer/polyvinyl alcohol (PVA) layer containing a polarizer/TAC layer are overlapped. After lamination, the release film/adhesive layer/polarizing plate (TAC layer/PVA layer/TAC layer ) was prepared.

[Preparation of film with adhesive layer]
The pressure-sensitive adhesive composition was applied onto the surface-treated surface of a release film [type: MRF, thickness: 38 μm, manufactured by Mitsubishi Chemical Corporation] that had been surface-treated with a silicone-based release agent to form a coating film. The amount of the pressure-sensitive adhesive composition to be applied was such that the thickness of the pressure-sensitive adhesive film, which will be described later, was 25 μm.
Next, air at 100° C. was blown to the formed coating film using a hot air circulating dryer at a wind speed of 3 m/sec for 60 seconds to form an adhesive film having a thickness of 25 μm.
Next, the exposed surface of the formed adhesive film and the surface-treated surface of a separately prepared release film [type: MRF, thickness: 38 μm, manufactured by Mitsubishi Chemical Corporation] are laminated together, and then the atmosphere temperature The film was allowed to stand in an environment of 23° C. and 50% RH for 7 days to cure the adhesive film, thereby producing a film with an adhesive layer having a structure of release film/adhesive layer/release film.

[evaluation]
1. Gel Fraction The gel fraction was measured according to the following (1) to (4) using the adhesive layer separated from the adhesive layer-attached film prepared above.
The results are shown in Tables 4 and 5.
(1) About 0.15 g of the adhesive layer is attached to a 250-mesh wire mesh (100 mm × 100 mm) whose mass is accurately measured using a precision balance, and the attached adhesive layer is removed so that the gel content does not leak. Turn inside and fold the wire mesh 5 times to make a sample. The mass of the sample is then accurately measured using 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. Next, the mass of the dried sample is accurately measured using 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 to which the pressure-sensitive adhesive layer is attached before immersion (unit: g), and Z is the pressure-sensitive adhesive dried after immersion. It is the mass (unit: g) of the wire mesh to which the layer is attached.

2. Coatability The pressure-sensitive adhesive composition prepared above is applied to the surface-treated surface of a release film [type: MRF, thickness: 38 μm, manufactured by Mitsubishi Chemical Corporation] that has been surface-treated with a silicone-based release agent. Using an applicator [model number: SA202, manufactured by Tester Sangyo Co., Ltd.], coating was performed at a speed of 2 m/min to 3 m/min. The surface of the coated product after coating was visually observed to confirm the presence or absence and extent of coating streaks (so-called streak-like patterns caused by coating). Then, the applicability of the pressure-sensitive adhesive composition was evaluated according to the following evaluation criteria.
The results are shown in Tables 4 and 5.
In the following evaluation criteria, "A", "B", "C", and "D" are practically acceptable levels, and "A" is most preferred.

-Evaluation criteria-
A: No coating streaks were observed on the surface of the coated product.
B: Almost no coating streaks were observed at the edges of the surface of the coated product.
C: Coating streaks were slightly observed at the edges of the surface of the coated product, but within the allowable range.
D: Coating streaks were slightly observed from the edge to the center of the surface of the coated product, but within the allowable range.
E: A large number of coating streaks were observed from the edge to the center of the surface of the coated product, which was outside the allowable range.

3. High Temperature Durability The pressure-sensitive adhesive layer-attached polarizing plate prepared above was cut into a size of 62 mm×110 mm. Next, the release film of the cut polarizing plate with an adhesive layer is peeled off, and the surface of the adhesive layer exposed by peeling is overlapped with the surface of the adherend described in Table 4 or Table 5. After that, the laminator is placed. A sample for high-temperature durability evaluation was produced by crimping using the same.
Next, the prepared sample for evaluation of high temperature durability was placed in a constant temperature vessel maintained at 105° C. and allowed to stand still for 500 hours. After the settling time had passed, the sample for high-temperature durability evaluation was taken out from the thermostat, and the appearance was visually observed to confirm the presence and degree of foaming, lifting, and peeling. Then, the high-temperature durability of the pressure-sensitive adhesive layer was evaluated according to the following evaluation criteria.
Evaluation results are shown in Tables 4 and 5.
In the following evaluation criteria, "A", "B", and "C" are practically acceptable levels, and "A" is most preferred.

-Evaluation criteria-
A: No foaming, floating, or peeling was observed.
B: Almost no foaming, lifting, or peeling was observed.
C: Slight foaming, floating, and peeling were observed, but within the allowable range.
D: A lot of foaming, floating, and peeling were confirmed, and it was out of the allowable range.

4. White spots Two polarizing plates with adhesive layers prepared as described above were cut into a size of 62 mm x 110 mm to obtain a test piece X and a test piece Y, respectively. Next, the release films of the test piece X and the test piece Y are peeled off, and the surface of the pressure-sensitive adhesive layer exposed by peeling is subjected to In-Plane-Switching (IPS) so that the absorption axes of the respective test pieces are orthogonal. After being superimposed on both sides of the liquid crystal panel, they were pressure-bonded using a laminator to prepare a sample for white spot evaluation.
Next, autoclave treatment (treatment temperature: 50° C., treatment pressure: 5 kg/cm ² , treatment time: 20 minutes) was performed on the produced white spot evaluation sample. After the autoclave treatment, the white spot evaluation sample was allowed to stand under an atmosphere temperature of 23° C. and 50% RH for 24 hours, and then left under an atmosphere temperature of 105° C. for 500 hours. Next, in an environment with an ambient temperature of 23° C. and 50% RH, the white spot evaluation sample after standing was placed on the backlight of a liquid crystal monitor and visually observed to confirm the presence and degree of white spots. . Then, white spots were evaluated according to the following evaluation criteria.
The results are shown in Tables 4 and 5.
In the following evaluation criteria, "A", "B", "C", and "D" are practically acceptable levels, and "A" is most preferred.

-Evaluation criteria-
A: White spots were not observed at all.
B: Almost no white spots were observed.
C: White spots were very slightly observed.
D: White spots were slightly observed, but within the allowable range.
E: A lot of white spots were observed, and it was out of the allowable range.

5. Hit Mark Resistance Fifty sheets of the pressure-sensitive adhesive layer-attached polarizing plate prepared above were cut into a size of 100 mm×110 mm and used as a test piece. Next, 50 test pieces were stacked so that the surface on the release film side faced up to prepare a sample for evaluation of dent resistance.
Next, a weight of 1 kg was placed on a 30 mm×30 mm area on the prepared sample for dent resistance evaluation, and the sample was allowed to stand for 3 hours in an environment of an ambient temperature of 23° C. and 50% RH. The surface of the release film side of the sample for evaluation of dent resistance after standing is observed using a laser microscope manufactured by Keyence Corporation (model number: VK-X200), and the dent resistance is evaluated according to the following evaluation criteria. did.
The results are shown in Tables 4 and 5.
In the following evaluation criteria, "A", "B", and "C" are practically acceptable levels, and "A" is most preferred.

-Evaluation criteria-
A: The depth of the dent was in the range of 0 μm or more and less than 1 μm.
B: The depth of the dent was in the range of 1 μm or more and less than 3 μm.
C: The depth of the dent was in the range of 3 μm or more and less than 5 μm.
D: The depth of the dent was 5 μm or more.

In Table 4, "-" means that evaluation corresponding to that column was not performed.
Details of the adherends listed in Table 4 and/or Table 5 are as follows.
“Glass” [soda glass, manufactured by Matsunami Glass Industry Co., Ltd.]
"BASUS" [stainless steel plate, trade name: SUS304, manufactured by Paltec Co., Ltd.]
“PET” [polyethylene terephthalate film, trade name: Teijin (registered trademark) Tetoron (registered trademark) film HPE, thickness: 50 μm, manufactured by Teijin Film Solutions Co., Ltd.]
“Polyimide” [polyimide film, trade name: Kapton (registered trademark) 100H, thickness: 25 μm, manufactured by DuPont-Toray Co., Ltd.]

As shown in Table 4, the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Examples 1 to 25 were excellent in high temperature durability. Moreover, the adhesive compositions of Examples 1 to 25 were excellent in coatability.
Furthermore, it was confirmed that the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Examples 1 to 25 are less likely to cause white spots even when exposed to a high-temperature environment. Moreover, it was confirmed that the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Examples 1 to 25 were excellent in dent resistance.

On the other hand, as shown in Table 5, the adhesive formed from the adhesive composition of Comparative Example 1 in which the (meth)acrylic copolymer does not contain a structural unit derived from a polyfunctional (meth)acrylic acid ester monomer It was confirmed that the adhesive layers were inferior in high-temperature durability to the adhesive layers formed from the adhesive compositions of Examples.
Although the (meth)acrylic copolymer contains structural units derived from polyfunctional (meth)acrylic acid ester monomers, the content of structural units derived from polyfunctional (meth)acrylic acid ester monomers is Regarding the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 3, which is less than 0.001% by mass based on the structural unit, compared with the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the example, It was confirmed that the high temperature durability was inferior. It was also confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 3 was inferior in dent resistance to the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Examples.
The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 2, in which the content of the cross-linking agent is less than 0.05 parts by mass with respect to 100 parts by mass of the (meth)acrylic copolymer, is the pressure-sensitive adhesive layer of the example. It was confirmed that the high-temperature durability was inferior to that of the pressure-sensitive adhesive layer formed from the composition.
The pressure-sensitive adhesive composition of Comparative Example 4, in which the content of structural units derived from polyfunctional (meth)acrylic acid ester monomers in the (meth)acrylic copolymer exceeds 0.05% by mass with respect to all structural units was confirmed to be inferior in coatability as compared with the pressure-sensitive adhesive compositions of Examples.
The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 5, in which the (meth)acrylic copolymer does not contain a structural unit derived from a monomer having a carboxy group, was formed from the pressure-sensitive adhesive composition of Example. It was confirmed that the high-temperature durability was inferior to that of the pressure-sensitive adhesive layer formed on the substrate. In addition, it was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 5 was inferior in dent resistance to the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Examples.

Claims (8)

a structural unit derived from a (meth)acrylic acid alkyl ester monomer, a structural unit derived from a monomer having a carboxy group, and a structural unit derived from a polyfunctional (meth)acrylic acid ester monomer, and , a (meth)acrylic copolymer in which the content of structural units derived from the polyfunctional (meth)acrylic acid ester monomer is 0.001% by mass to 0.05% by mass with respect to all structural units When,
a cross-linking agent;
including
The pressure-sensitive adhesive composition, wherein the content of the cross-linking agent is 0.05 parts by mass or more relative to 100 parts by mass of the (meth)acrylic copolymer. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the polyfunctional (meth)acrylic acid ester monomer is a bifunctional (meth)acrylic acid ester monomer. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the polyfunctional (meth)acrylic acid ester monomer has a molecular weight in the range of 200 or more and less than 1,000. The (meth)acrylic copolymer has a weight average molecular weight [Mw] of 1,400,000 to 2,200,000, and the ratio [Mz/Mw] of the z average molecular weight [Mz] to the weight average molecular weight [Mw]. is 2.5 to 4.5, the pressure-sensitive adhesive composition according to any one of claims 1 to 3. The content of structural units derived from the monomer having a carboxy group in the (meth)acrylic copolymer is 0.1 mass% to the total structural units of the (meth)acrylic copolymer. The pressure-sensitive adhesive composition according to any one of claims 1 to 4, which is 5.0% by mass. The pressure-sensitive adhesive composition according to any one of claims 1 to 5, wherein the (meth)acrylic copolymer contains a structural unit derived from a monomer having a hydroxyl group. The content of structural units derived from the monomer having a hydroxyl group in the (meth)acrylic copolymer is 0.1% by mass to 3 with respect to the total structural units of the (meth)acrylic copolymer. 7. The pressure-sensitive adhesive composition according to claim 6, which is 0% by mass. an optical member;
a pressure-sensitive adhesive layer provided on the optical member and formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 7;
An optical member with an adhesive layer.