JP7298086B2 - Adhesive composition for polarizing plate and polarizing plate with adhesive layer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pressure-sensitive adhesive composition for polarizing plates and a pressure-sensitive adhesive layer-attached polarizing plate.

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 via an adhesive layer formed of an acrylic adhesive.

A polarizing plate is usually constructed by laminating members having different contraction rates. Therefore, the polarizing plate may warp due to changes in temperature and/or humidity, and air bubbles, peeling, and the like may occur at the interface between the polarizing plate and the pressure-sensitive adhesive layer.
Moreover, when the temperature and/or humidity change, the polarizing plate tends to shrink or expand, and stress may be generated. 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.
Furthermore, in bonding the liquid crystal cell and the polarizing plate, a bonding error may occur. If a lamination error occurs, it is necessary to re-laminate.
Therefore, the pressure-sensitive adhesive used for bonding the liquid crystal cell and the polarizing plate has a property (so-called durability) capable of suppressing bubbles and peeling that may occur when exposed to a high-temperature environment or a high-temperature and high-humidity environment. It is required to be able to form a pressure-sensitive adhesive layer having the property of suppressing the generation of white spots and the property of being easily reapplied without contaminating the liquid crystal cell (so-called reworkability).

In response to such demands, for example, Patent Document 1 discloses a pressure-sensitive adhesive for polarizing films that can sufficiently prevent the occurrence of peeling, air bubbles, and white spots and has excellent reworkability and recyclability. As an agent composition, an acrylic copolymer containing a specific amount of a repeating unit having a carboxy group and a repeating unit having a hydroxy group in the molecule, having a weight average molecular weight of a specific value or more, and a glass transition temperature of a specific value or less. A pressure-sensitive adhesive composition for polarizing films is disclosed that contains coalescence, a specific amount of a polyisocyanate compound, and a specific amount of a silane coupling agent having a specific structure.

By the way, in recent years, in the polarizing plate, an EWV (excellent wide view) layer is further provided on the triacetyl cellulose (TAC) layer provided on the polarizer to increase the viewing angle of the liquid crystal display device. Tend. The EWV layer usually contains a discotic liquid crystal compound.
For example, Patent Document 2 discloses a polarizing plate with an optical compensation film having an adhesive layer containing a (meth)acrylic polymer, an optical compensation film containing a discotic liquid crystal compound, and a polarizer.

Japanese Patent Application Laid-Open No. 2004-224873 JP 2009-258660 A

In general, the EWV layer has extremely poor adhesion to the pressure-sensitive adhesive layer. Therefore, when the polarizing plate provided with the EWV layer (the polarizing plate with the EWV layer; hereinafter also referred to as "EWV polarizing plate") is peeled off, the pressure-sensitive adhesive layer formed on the surface of the EWV layer is attached to the surface. There is a problem that it is easily transferred to an adherent (for example, a glass substrate of a liquid crystal cell).
In order to improve the reworkability of the EWV polarizing plate, for example, it is conceivable to increase the amount of the cross-linking agent blended in the pressure-sensitive adhesive composition forming the pressure-sensitive adhesive layer. When the amount of the cross-linking agent blended in the pressure-sensitive adhesive composition increases, the cross-linking agent that does not contribute to cross-linking interacts with the EWV layer, thereby improving the adhesion between the pressure-sensitive adhesive layer and the EWV layer, thereby improving the reworkability. can be improved.
On the other hand, when the amount of the cross-linking agent blended into the pressure-sensitive adhesive composition is too large, the resulting pressure-sensitive adhesive layer will have low flexibility due to an increase in the cross-linking density of the pressure-sensitive adhesive layer. If the pressure-sensitive adhesive layer has low flexibility, it cannot sufficiently follow the expansion and contraction of the base material due to changes in temperature and/or humidity, which may lead to deterioration in durability.
As described above, it has been difficult to form a pressure-sensitive adhesive layer excellent in both durability and reworkability in the pressure-sensitive adhesive composition used for the EWV polarizing plate.

The problem to be solved by the present invention is to provide a pressure-sensitive adhesive composition for a polarizing plate and a pressure-sensitive adhesive layer-attached polarizing plate that can form a pressure-sensitive adhesive layer that is excellent in durability and reworkability and that hardly causes white spots. That is.

Specific means for solving the problems include the following aspects.
<1> a structural unit a derived from a monomer (A) having a hydroxyl group;
a structural unit b derived from a monomer (B) having at least one group selected from the group consisting of a group having a tertiary carbon atom, a group having an alicyclic structure, and a group having an aromatic ring;
and a structural unit c which is a structural unit derived from the (meth)acrylic acid alkyl ester monomer (C) and which is different from the structural unit a and the structural unit b,
The content of the structural unit a is 0.05% by mass to 0.4% by mass relative to all structural units, and the content of the structural unit b is 10% by mass to 30% by mass relative to all structural units. % and a (meth)acrylic copolymer having a weight average molecular weight of 200,000 to 2,000,000,
a polyisocyanate compound;
and a silane coupling agent,
The molar equivalent ratio of the amount of isocyanate groups in the polyisocyanate compound to the total amount of hydroxyl groups, carboxyl groups, and amino groups in the (meth)acrylic copolymer is 0.5 to 5.0,
A pressure-sensitive adhesive composition for a polarizing plate having a gel fraction of 45% by mass to 80% by mass after cross-linking.

<2> The pressure-sensitive adhesive composition for a polarizing plate according to <1>, wherein the gel fraction after cross-linking is 60% by mass to 80% by mass.
<3> The pressure-sensitive adhesive composition for a polarizing plate according to <1> or <2>, wherein the content of the structural unit a is 0.05% by mass to 0.25% by mass based on the total structural units.
<4> The pressure-sensitive adhesive composition for a polarizing plate according to any one of <1> to <3>, wherein the content of the structural unit b is 10% by mass to 20% by mass based on all structural units.
<5> The pressure-sensitive adhesive composition for polarizing plate according to any one of <1> to <4>, further comprising a crosslinking catalyst.
<6> The pressure-sensitive adhesive composition for polarizing plate according to any one of <1> to <5>, wherein the monomer (B) is t-butyl acrylate.

<7> a polarizing plate;
a layer disposed on the polarizing plate and having a contact angle with water of 90° or more;
A pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition for a polarizing plate according to any one of <1> to <6>, disposed on the surface of the layer having a contact angle with water of 90° or more; ,
A polarizing plate with an adhesive layer.
<8> The pressure-sensitive adhesive layer-attached polarizing plate according to <7>, wherein the layer having a contact angle with water of 90° or more is a layer containing a discotic liquid crystal compound.

ADVANTAGE OF THE INVENTION According to this invention, the adhesive composition for polarizing plates and the polarizing plate with an adhesive layer which can form the adhesive layer which is excellent in durability and reworkability and does not generate a white spot easily are provided.

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

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

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

As used herein, the term "adherend" means an object that is in contact with the pressure-sensitive adhesive layer on the side opposite to the polarizing plate during use. When used for a plate (that is, an EWV polarizing plate), the glass substrate of a liquid crystal cell can be the adherend.
In the present specification, the term "substrate" refers to, for example, a polarizing plate, and the term "substrate" is used to distinguish from the term "adherend".

In the present invention, "durability" means that when exposed to a high temperature and high humidity (e.g., 65 ° C., 95% RH) environment, peeling does not easily occur, and in a high temperature (e.g., 95 ° C.) environment. The ability to suppress foaming when exposed.
In the present invention, "reworkability" refers to the ease of peeling during re-sticking work, for example, when peeling off from the adherend, the pressure-sensitive adhesive layer does not transfer to the adherend (so-called adhesive residue). , means that it can be reapplied. The more excellent the reworkability, the easier the re-sticking work can be performed.

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

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

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

[Adhesive composition for polarizing plate]
The pressure-sensitive adhesive composition for a polarizing plate of the present invention (hereinafter also simply referred to as "pressure-sensitive adhesive composition") has a structural unit a derived from a monomer (A) having a hydroxyl group and a tertiary carbon atom. A structural unit b derived from a monomer (B) having at least one group selected from the group consisting of a group having an alicyclic structure and a group having an aromatic ring, and a (meth)acrylic acid alkyl ester unit a structural unit derived from the polymer (C) and different from the structural unit a and the structural unit b; 0.05% by mass to 0.4% by mass, the content of the structural unit b is 10% by mass to 30% by mass with respect to all structural units, and the weight average molecular weight is 200,000 to 200 A (meth)acrylic copolymer [hereinafter also referred to as a “specified (meth)acrylic copolymer”. ], a polyisocyanate compound, and a silane coupling agent, and the number of isocyanate groups in the polyisocyanate compound with respect to the total amount of hydroxyl groups, carboxy groups, and amino groups in the (meth)acrylic copolymer The molar equivalent ratio of the amounts is 0.5 to 5.0, and the gel fraction after cross-linking is 45% to 80% by weight.
ADVANTAGE OF THE INVENTION According to the adhesive composition of this invention, the adhesive layer which is excellent in reworkability and durability and is hard to generate a white spot can be formed.
Although the reason why the pressure-sensitive adhesive composition of the present invention can exhibit such effects is not clear, the present inventors speculate as follows. However, the following assumptions are not intended to limit the interpretation of the pressure-sensitive adhesive composition of the present invention, but are explained as an example.

In general, the reworkability of the pressure-sensitive adhesive layer can be improved by increasing the amount of the cross-linking agent blended in the pressure-sensitive adhesive composition forming the pressure-sensitive adhesive layer. This is because when the amount of the cross-linking agent blended in the pressure-sensitive adhesive composition increases, the cross-linking agent that does not contribute to cross-linking interacts with the substrate, and the adhesion between the pressure-sensitive adhesive layer and the substrate improves. Conceivable.
On the other hand, if the amount of the cross-linking agent blended in the pressure-sensitive adhesive composition is too large, the resulting pressure-sensitive adhesive layer will have reduced flexibility due to an increase in cross-linking density. If the adhesive layer has low flexibility, the adhesive layer cannot sufficiently follow expansion and contraction of the base material due to changes in temperature and/or humidity. Therefore, the durability of the pressure-sensitive adhesive layer is lowered.
In contrast, with the pressure-sensitive adhesive composition of the present invention, by appropriately controlling the cross-linking reaction, it is possible to form a pressure-sensitive adhesive layer that is excellent in both durability and reworkability and that hardly causes white spots.

Specifically, the pressure-sensitive adhesive composition of the present invention contains a specific (meth)acrylic copolymer, a polyisocyanate compound, and a silane coupling agent.
In the pressure-sensitive adhesive composition of the present invention, a crosslinking reaction between the hydroxyl group of the structural unit a derived from the monomer (A) having a hydroxyl group contained in the specific (meth)acrylic copolymer and the isocyanate group of the polyisocyanate compound progresses, a pressure-sensitive adhesive layer is formed. Since the specific (meth)acrylic copolymer contains a specific amount of structural unit b derived from the monomer (B) having a bulky molecular structure in addition to the specific amount of structural unit a, the monomer (B ) due to steric hindrance caused by the molecular structure of (A), the crosslinking reaction between the hydroxyl group of the structural unit a derived from the monomer (A) and the isocyanate group of the polyisocyanate compound is moderately inhibited, and the crosslink density becomes excessively high. is suppressed. As a result, the crosslink density of the pressure-sensitive adhesive layer becomes moderately high.
Further, in the adhesive composition of the present invention, the molar equivalent ratio of the amount of isocyanate groups in the polyisocyanate compound to the total amount of hydroxyl groups, carboxyl groups and amino groups in the (meth)acrylic copolymer is 0.5. When it is up to 5.0, sufficient cross-linking is achieved even though the amount of hydroxyl groups in the specific (meth)acrylic copolymer is small, and the cross-linking density of the pressure-sensitive adhesive layer is moderately high. Furthermore, since polyisocyanate compounds that do not contribute to cross-linking are not generated excessively, the pressure-sensitive adhesive layer exhibits appropriate flexibility. A pressure-sensitive adhesive layer exhibiting moderate flexibility can sufficiently follow the expansion and contraction of the base material due to changes in temperature and humidity.
Further, the (meth)acrylic copolymer contained in the adhesive composition of the present invention has a weight average molecular weight of 200,000 or more, and a gel fraction after crosslinking of 45% to 80% by mass. By doing so, the cohesive force of the pressure-sensitive adhesive layer is in a more appropriate range.
As described above, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention is presumed to have excellent durability and reworkability and to hardly generate white spots because the cross-linking reaction is appropriately controlled. be done.

In contrast to the pressure-sensitive adhesive composition of the present invention, the pressure-sensitive adhesive described in Patent Document 2 (JP-A-2009-258660) is the total amount of carboxy groups, hydroxyl groups, and amino groups in the (meth)acrylic copolymer. Due to the very low molar equivalent ratio of the amount of isocyanate groups in the isocyanate compound to the amount of isocyanate groups, sufficient crosslink density cannot be obtained. For this reason, it is considered that the reworkability of the formed pressure-sensitive adhesive layer is significantly inferior.

Each component of the pressure-sensitive adhesive composition of the present invention will be described below.

[Specific (meth)acrylic copolymer]
The (meth)acrylic copolymer (that is, the specific (meth)acrylic copolymer) contained in the pressure-sensitive adhesive composition of the present invention is a structural unit a derived from the monomer (A) having a hydroxyl group, A structural unit b derived from a monomer (B) having at least one group selected from the group consisting of a group having a tertiary carbon atom, a group having an alicyclic structure, and a group having an aromatic ring; and a structural unit c which is a structural unit derived from the meth)acrylic acid alkyl ester monomer (C) and which is different from the structural unit a and the structural unit b, and the content of the structural unit a is the total structural unit 0.05% by mass to 0.4% by mass based on the unit, the content of the structural unit b is 10% by mass to 30% by mass based on the total structural units, and the weight average molecular weight is 20 10,000 to 2,000,000.

<Structural Unit a Derived from Monomer (A) Having a Hydroxyl Group>
The specific (meth)acrylic copolymer contains a structural unit a derived from the monomer (A) having a hydroxyl group. Also, the content of the structural unit a in the specific (meth)acrylic copolymer is 0.05% by mass to 0.4% by mass with respect to all structural units.
The hydroxyl group of the structural unit a derived from the monomer (A) having a hydroxyl group can be crosslinked with the isocyanate group of the polyisocyanate compound described below. Therefore, in the pressure-sensitive adhesive composition of the present invention, the hydroxyl group of the structural unit a derived from the monomer (A) having a hydroxyl group contained in the specific (meth)acrylic copolymer and the isocyanate of the polyisocyanate compound described later A pressure-sensitive adhesive layer is formed by the progress of the cross-linking reaction with the groups.

In the present specification, "structural unit a derived from the monomer (A) having a hydroxyl group" means a structural unit a formed by addition polymerization of the monomer (A) having a hydroxyl group.

There are no particular restrictions on the type of monomer (A) having a hydroxyl group.
Specific examples of the monomer (A) having a hydroxyl group include 2-hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 3-hydroxypropyl (meth)acrylate. , 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl -3-hydroxyhexyl (meth)acrylate, N-hydroxyethyl (meth)acrylamide and the like.
Among these, as the monomer (A) having a hydroxyl group, for example, the compatibility and copolymerizability with the monomer (B) and the (meth)acrylic acid alkyl ester monomer (C) described later are higher. At least one selected from the group consisting of 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate from the viewpoint of being good and having better reactivity with the polyisocyanate compound described later. is preferred.

The specific (meth)acrylic copolymer may contain only one type of structural unit a, or may contain two or more types.

The content of the structural unit a in the specific (meth)acrylic copolymer (that is, the ratio; hereinafter the same) is 0.05% by mass with respect to the total structural units of the specific (meth)acrylic copolymer. ~0.4% by mass.
When the content of the structural unit a in the specific (meth)acrylic copolymer is 0.05% by mass or more with respect to the total structural units of the specific (meth)acrylic copolymer, the crosslink density of the pressure-sensitive adhesive layer is appropriate. Therefore, the pressure-sensitive adhesive layer tends to be excellent in durability.
When the content of the structural unit a in the specific (meth)acrylic copolymer is 0.4% by mass or less with respect to the total structural units of the specific (meth)acrylic copolymer, the pressure-sensitive adhesive layer is crosslinked. By containing an appropriate amount of a non-contributing cross-linking agent, the substrate represented by the EWV layer interacts with the pressure-sensitive adhesive layer to exhibit good adhesion. Therefore, the pressure-sensitive adhesive layer tends to be excellent in reworkability. In addition, since the pressure-sensitive adhesive layer has appropriate flexibility and relieves stress, white spots are less likely to occur.

In addition, the content of the structural unit a in the specific (meth)acrylic copolymer is such that, for example, when exposed to a high-temperature environment, air bubbles are less likely to occur at the interface between the adherend and the pressure-sensitive adhesive layer. Therefore, it is 0.05% by mass or more, preferably 0.1% by mass or more, and more preferably 0.15% by mass or more, based on the total structural units of the specific (meth)acrylic copolymer.
Further, the content of the structural unit a in the specific (meth)acrylic copolymer is, for example, from the viewpoint that white spots are less likely to occur, with respect to all structural units of the specific (meth)acrylic copolymer, It is 0.4% by mass or less, preferably 0.35% by mass or less, more preferably 0.3% by mass or less, even more preferably 0.25% by mass or less, and particularly preferably 0.2% by mass or less.
The content of the structural unit a in the specific (meth)acrylic copolymer is, for example, from the viewpoint of improving the durability of the pressure-sensitive adhesive layer and suppressing the occurrence of white spots, the total amount of the specific (meth)acrylic copolymer is It is preferably 0.1% by mass to 0.35% by mass, more preferably 0.1% by mass to 0.3% by mass, and even more preferably 0.15% by mass to 0.25% by mass, relative to the structural unit.

<Structural unit b derived from monomer (B) having at least one group selected from the group consisting of a group having a tertiary carbon atom, a group having an alicyclic structure, and a group having an aromatic ring>
The specific (meth)acrylic copolymer is a monomer having at least one group selected from the group consisting of a group having a tertiary carbon atom, a group having an alicyclic structure, and a group having an aromatic ring ( It contains a structural unit b derived from B). Also, the content of the structural unit b in the specific (meth)acrylic copolymer is 10% by mass to 30% by mass with respect to all structural units.

In the present specification, "a group having a tertiary carbon atom, a group having an alicyclic structure, and a group having an aromatic ring derived from a monomer (B) having at least one group selected from the group consisting of The structural unit b” is a group having a tertiary carbon atom, a group having an alicyclic structure, and a group having an aromatic ring. It means a structural unit b formed by polymerization.

There are no particular restrictions on the type of group having a tertiary carbon atom.
Groups having tertiary carbon atoms include t-butyl groups.
Monomers having a t-butyl group include t-butyl acrylate, t-butylstyrene, t-butylacrylamide and the like.
A preferred monomer having a t-butyl group is t-butyl acrylate.

The type of group having an alicyclic structure is not particularly limited.
Examples of groups having an alicyclic structure include cycloalkyl groups.
The cycloalkyl group includes an isobornyl group, a cyclohexyl group and the like.
As the monomer having an isobornyl group, isobornyl acrylate is preferred.
Cyclohexyl acrylate is preferred as the monomer having a cyclohexyl group.

There are no particular restrictions on the type of group having an aromatic ring.
An aryl group, an arylalkyl group, etc. are mentioned as a group which has an aromatic ring.
The aryl group includes a phenyl group, a naphthyl group and the like.
Arylalkyl groups include, for example, benzyl groups.
Among these, at least one selected from a phenyl group and a benzyl group is preferable as the group having an aromatic ring.
Phenoxyethyl acrylate is preferred as the monomer having a phenyl group.
Benzyl acrylate is preferred as the monomer having a benzyl group.

A particularly preferred monomer (B) is t-butyl acrylate.
When the monomer (B) is t-butyl acrylate, the reaction between the hydroxyl group of the structural unit a derived from the hydroxyl group-containing monomer (A) and the isocyanate group of the polyisocyanate compound described below is more moderately inhibited. , the crosslink density of the pressure-sensitive adhesive layer can be adjusted more appropriately.

The specific (meth)acrylic copolymer may contain only one type of structural unit b, or may contain two or more types.

The content of the structural unit b in the specific (meth)acrylic copolymer is 10% by mass to 30% by mass, and 10% by mass to 25% by mass with respect to the total structural units of the specific (meth)acrylic copolymer. % by mass is preferable, 10% by mass to 20% by mass is more preferable, and 15% by mass to 20% by mass is even more preferable.
Monomer (B) is a monomer having a bulky molecular structure.
When the content of the structural unit b in the specific (meth)acrylic copolymer is 10% by mass or more with respect to the total structural units of the specific (meth)acrylic copolymer, the molecule of the monomer (B) Due to the steric hindrance caused by the structure, the crosslinking reaction between the hydroxyl group of the structural unit a derived from the monomer (A) having a hydroxyl group and the isocyanate group of the polyisocyanate compound described below is moderately inhibited, and the crosslink density becomes excessively high. can prevent it from happening. As a result, the crosslink density of the pressure-sensitive adhesive layer becomes moderately high. Therefore, the pressure-sensitive adhesive layer tends to be excellent in durability while maintaining excellent reworkability.
When the content of the structural unit b in the specific (meth)acrylic copolymer is 30% by mass or less with respect to the total structural units of the specific (meth)acrylic copolymer, the specific (meth)acrylic copolymer The combination does not become too hard, and the pressure-sensitive adhesive layer has appropriate flexibility. Therefore, the pressure-sensitive adhesive layer tends to be less prone to white spots.

<Structural unit c which is a structural unit derived from (meth)acrylic acid alkyl ester monomer (C) and which is different from structural unit a and structural unit b>
The specific (meth)acrylic copolymer contains a structural unit c which is a structural unit derived from the (meth)acrylic acid alkyl ester monomer (C) and which is different from the structural units a and b.
Structural unit c contributes to the adjustment of the adhesive strength of the adhesive layer.

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

If the (meth)acrylic acid alkyl ester monomer (C) is a (meth)acrylic acid alkyl ester monomer different from the monomers (A) and (B) described above, There are no particular restrictions.
As the (meth)acrylic acid alkyl ester monomer, an unsubstituted (meth)acrylic acid alkyl ester monomer is preferable.
The alkyl group of the (meth)acrylic acid alkyl ester monomer may be linear, branched or cyclic.
In addition, the number of carbon atoms in the alkyl group is preferably in the range of 1 to 18, more preferably in the range of 1 to 12, from the viewpoint of the adhesive strength to the adherend and adhesion to the substrate of the pressure-sensitive adhesive layer to be formed. .

(Meth) acrylic acid alkyl ester monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, s-butyl (meth) acrylate, t -butyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate and the like.
Among these, the (meth)acrylic acid alkyl ester monomer (C) is selected from methyl acrylate and n-butyl acrylate, for example, from the viewpoint that it is easy to adjust the cohesive force and adhesive force of the adhesive layer. is preferably at least one, more preferably n-butyl acrylate.

The specific (meth)acrylic copolymer may contain only one type of structural unit c, or may contain two or more types.

The content of the structural unit c in the specific (meth)acrylic copolymer is preferably 50% by mass or more, more preferably 60% by mass or more, based on the total structural units of the specific (meth)acrylic copolymer. 70% by mass or more is more preferable, and 80% by mass or more is particularly preferable.
The upper limit of the content of the structural unit c in the specific (meth)acrylic copolymer is not particularly limited. is preferred.

<Structural Unit Derived from Monomer Having Carboxy Group>
The specific (meth)acrylic copolymer may contain structural units derived from a monomer having a carboxy group.
As used herein, the term "structural unit derived from a monomer having a carboxy group" means a structural unit formed by addition polymerization of a monomer having a carboxy group.

There are no particular restrictions on the type of monomer having a carboxy group.
Specific examples of monomers having a carboxy group include acrylic acid (AA), methacrylic acid (MAA), crotonic acid , maleic acid, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, and ω-carboxy-polycaprolactone. mono(meth)acrylates (eg, ω-carboxy-polycaprolactone (n≈2) monoacrylate), succinic acid esters (eg, 2-acryloyloxyethyl-succinic acid), and the like.

When the specific (meth)acrylic copolymer contains a structural unit derived from a monomer having a carboxy group, it may contain only one type of structural unit derived from a monomer having a carboxy group. It may contain more than seeds.

By the way, carboxyl groups can corrode metals. When a pressure-sensitive adhesive composition containing a (meth)acrylic copolymer having a large proportion of structural units that
From such a point of view, the specific (meth)acrylic copolymer does not contain structural units derived from monomers having a carboxy group, or contains structural units derived from monomers having a carboxy group. It is preferable that the ratio is more than 0% by mass and 1.0% by mass or less, and does not contain a structural unit derived from a monomer having a carboxy group, or a structure derived from a monomer having a carboxy group It is more preferable that the unit content is more than 0% by mass and 0.5% by mass or less, and does not contain a structural unit derived from a monomer having a carboxy group, or a monomer having a carboxy group It is more preferable that the content of structural units derived from is more than 0% by mass and 0.2% by mass or less, and it is particularly preferable that no structural units derived from a monomer having a carboxy group are contained.

<Structural Unit Derived from Monomer Having Amino Group>
The specific (meth)acrylic copolymer may contain structural units derived from a monomer having an amino group.
As used herein, the term "structural unit derived from a monomer having an amino group" means a structural unit formed by addition polymerization of a monomer having an amino group.

The amino group can crosslink with the isocyanate group of the polyisocyanate compound described below.
In addition, the "amino group" here refers to a primary amino group or a secondary amino group.
There are no particular restrictions on the type of monomer having a primary amino group.
Specific examples of monomers having a primary amino group include acrylamide and methacrylamide.
Specific examples of monomers having a secondary amino group include N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-methoxyethyl(meth)acrylamide and the like.

When the specific (meth)acrylic copolymer contains a structural unit derived from a monomer having an amino group, it may contain only one type of structural unit derived from a monomer having an amino group. It may contain more than seeds.

<Other structural units>
The specific (meth)acrylic copolymer has the structural units described above, that is, the structural unit a, the structural unit b, and the structural unit c, and optionally Structural units (so-called other structural units) other than arbitrary structural units that may be contained (that is, structural units derived from a monomer having a carboxy group and structural units derived from a monomer having an amino group) may contain

There are no particular restrictions on the types of monomers that constitute other structural units.
Examples of monomers constituting other structural units include alkoxyalkyl (meth)acrylates typified by methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; cyanide typified by acrylonitrile and methacrylonitrile; and vinyl esters typified by vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate.
In addition, various derivatives of these monomers can be mentioned as monomers constituting other structural units.
Further, monomers constituting other structural units include monomers having functional groups such as glycidyl groups, amide groups, N-substituted amide groups, and tertiary amino groups.

Specific examples of monomers having a glycidyl group include glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, glycidyl vinyl ether, 3,4-epoxycyclohexyl vinyl ether, and glycidyl (meth)allyl ether. , 4-hydroxybutyl acrylate glycidyl ether, and 3,4-epoxycyclohexyl (meth)allyl ether.

Specific examples of monomers having an amide group or N-substituted amide group include acrylamide, methacrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-methoxymethyl(meth)acrylamide , N-ethoxymethyl (meth)acrylamide, N-propoxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N-tert-butylacrylamide, N-octylacrylamide, dimethylacrylamide, diethylacrylamide, isopropylacrylamide, and Diacetone acrylamide may be mentioned.

Specific examples of monomers having a tertiary amino group include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and dimethylaminopropyl (meth)acrylamide.

<<Weight average molecular weight of specific (meth)acrylic copolymer>>
The weight average molecular weight (Mw) of the specific (meth)acrylic copolymer is 200,000 to 2,000,000, preferably 500,000 to 2,000,000, more preferably 1,000,000 to 1,800,000, and further preferably 1,500,000 to 1,800,000. preferable.
When the weight average molecular weight (Mw) of the specific (meth)acrylic copolymer is 200,000 or more, the cohesive force of the pressure-sensitive adhesive layer falls within an appropriate range. Therefore, during reworking, cohesive failure of the pressure-sensitive adhesive layer does not occur, and adhesive residue on the substrate and/or the adherend is less likely to occur. In addition, when exposed to a high-temperature environment, air bubbles are less likely to form at the interface between the adherend and the adhesive layer, and when exposed to a high-temperature and high-humidity environment, the adhesion between the adherend and the adhesive layer is suppressed. It becomes difficult for peeling to occur at the interface between the
When the weight average molecular weight (Mw) of the specific (meth)acrylic copolymer is 2,000,000 or less, the viscosity of the pressure-sensitive adhesive composition does not become too high, so that the pressure-sensitive adhesive composition can be applied satisfactorily.

The weight average molecular weight (Mw) of the specific (meth)acrylic copolymer is a value measured by the following method. Specifically, it is measured according to the following (1) to (3).
(1) A solution of the specific (meth)acrylic copolymer is applied to release paper and dried at 100° C. for 2 minutes 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.
(3) Using gel permeation chromatography (GPC), measure the weight average molecular weight (Mw) of the specific (meth)acrylic copolymer as a standard polystyrene equivalent value under the following conditions.

~Conditions~
Measuring device: high-speed GPC (model number: HLC-8220 GPC, Tosoh Corporation)
Detector: Differential refractometer (RI) (built into HLC-8220, Tosoh Corporation)
Column: Four TSK-GEL GMHXL (Tosoh Corporation) connected in series Column temperature: 40°C
Eluent: Tetrahydrofuran Sample concentration: 0.2% by mass
Injection volume: 100 μL
Flow rate: 0.6 mL/min

The content of the specific (meth)acrylic copolymer in the pressure-sensitive adhesive composition of the present invention is the total solid content in the pressure-sensitive adhesive composition, from the viewpoint that it is easy to adjust the cohesive strength and adhesive strength of the pressure-sensitive adhesive layer. 50% by mass to 99% by mass is preferable.
As used herein, the term "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 volatile component such as a solvent. When the composition contains a volatile component such as a solvent, it means the mass of the residue after removing the volatile component such as the solvent from the pressure-sensitive adhesive composition.

[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 can be produced by polymerizing monomers by a known polymerization method represented by, for example, solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization.
Among these, solution polymerization is preferable as the polymerization method because the processing steps are relatively simple and can be performed in a short period of time when preparing the pressure-sensitive adhesive composition of the present invention after production.

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

Organic solvents used in the polymerization reaction include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, alcohol compounds and the like.
More specific examples of the organic solvent used during the polymerization reaction include benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic hydrocarbons 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 hydrocarbons, ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate. Esters, acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, ketones 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 ethers 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- Alcohols typified by butyl alcohol can be mentioned.
At the time of the polymerization reaction, one kind of these organic solvents may be used alone, or two or more kinds thereof may be mixed and used.

In the production of the specific (meth)acrylic copolymer, it is preferable to use organic solvents such as aromatic hydrocarbons, esters, ketones, etc., which are unlikely to cause chain transfer during the polymerization reaction. Ethyl acetate, toluene, methyl ethyl ketone, and the like are preferably used from the viewpoint of the solubility of the system copolymer, ease of polymerization reaction, and the like.

Examples of the polymerization initiator include organic peroxides, azo compounds, and the like, which are used in ordinary solution polymerization.
Examples of organic peroxides include t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, carbonate, t-butyl peroxypivalate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-amylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α-cumylperoxycyclohexyl)propane, 2,2-bis(4,4 -di-t-butylperoxycyclohexyl)butane, and 2,2-bis(4,4-di-t-octylperoxycyclohexyl)butane.
Examples of azo compounds include 2,2'-azobisisobutyronitrile [AIBN], 2,2'-azobis(2,4-dimethylvaleronitrile) [ABVN], 2,2'-azobis(4- methoxy-2,4-dimethylvaleronitrile), 1,1′-azobis(cyclohexane-1-carbonitrile), and 2,2′-azobis(isobutyrate)dimethyl.

In the production of 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 azobis polymerization initiator.

The amount of the polymerization initiator to be used is not particularly limited, and is appropriately set according to the molecular weight of the desired specific (meth)acrylic copolymer.
For example, the amount of polymerization initiator used is preferably 0.001 part by mass to 0.1 part by mass with respect to 100 parts by mass of the total amount of monomers constituting the specific (meth)acrylic copolymer. 0.005 parts by weight to 0.05 parts by weight is more preferred.

In the production of the specific (meth)acrylic copolymer, a chain transfer agent may be used, if necessary, as long as the objects and effects of the present invention are not impaired.
Examples of chain transfer agents include cyanoacetic acid, cyanoacetic acid alkyl esters having 1 to 8 carbon atoms, bromoacetic acid, bromoacetic acid alkyl esters 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 derivatives typified by benzoquinone and 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives typified by tributylborane, carbon tetrabromide, carbon tetrachloride, 1,1,2,2- Halogenated hydrocarbons typified by tetrabromoethane, tribromoethylene, trichlorethylene, bromotrichloromethane, tribromomethane, and 3-chloro-1-propene; aldehydes typified by chloral and furaldehyde; 18 alkyl mercaptans, aromatic mercaptans represented by thiophenol and toluene mercaptan, mercaptoacetic acid, alkyl esters of mercaptoacetic acid having 1 to 10 carbon atoms, hydroxyalkyl mercaptans having 1 to 12 carbon atoms, and pinene and terpenes represented by terpinolene.

When using a chain transfer agent in the production of the specific (meth)acrylic copolymer, the amount of the chain transfer agent used is not particularly limited, depending on the molecular weight of the desired specific (meth)acrylic copolymer , are set accordingly.
For example, the amount of chain transfer agent used may be 0.005 parts by mass to 1.0 parts by mass with respect to 100 parts by mass of the total amount of monomers constituting the specific (meth)acrylic copolymer. can.

The polymerization temperature is not particularly limited, and is appropriately set according to the molecular weight of the desired specific (meth)acrylic copolymer.
For example, the polymerization temperature is preferably 30°C to 120°C, more preferably 50°C to 100°C, even more preferably 60°C to 80°C.

[Polyisocyanate compound]
The pressure-sensitive adhesive composition of the invention contains a polyisocyanate compound.
A polyisocyanate compound has two or more isocyanate groups in its molecule and functions as a cross-linking agent.

Polyisocyanate compounds include aromatic polyisocyanate compounds such as xylylene diisocyanate (XDI), diphenylmethane diisocyanate, triphenylmethane triisocyanate, and tolylene diisocyanate (TDI), hexamethylene diisocyanate (HMDI), and pentamethylene diisocyanate (PDI). , isophorone diisocyanate, and aliphatic or alicyclic polyisocyanate compounds such as hydrogenated products of the above-described aromatic polyisocyanate compounds.
Further, the polyisocyanate compound may be a dimer, trimer, or pentamer of the polyisocyanate compound, an adduct of the polyisocyanate compound and a polyol compound such as trimethylolpropane, or a biuret of the polyisocyanate compound. And so on.
Among these, tolylene diisocyanate (TDI) is preferable as the polyisocyanate compound, for example, from the viewpoint that it is easy to adjust the gel fraction after cross-linking to 45% by mass or more.

A commercial item can be used as a polyisocyanate compound.
Examples of commercially available polyisocyanate compounds include "Coronate (registered trademark) HX", "Coronate (registered trademark) HL-S", "Coronate (registered trademark) L", and "Coronate (registered trademark) L-45E". , "Coronate (registered trademark) 2031", "Coronate (registered trademark) 2030", "Coronate (registered trademark) 2234", "Coronate (registered trademark) 2785", "Aquanate (registered trademark) 200", and "Aqua Nate (registered trademark) 210” [above, Tosoh Corporation], “Sumidule (registered trademark) N3300”, “Desmodur (registered trademark) N3400”, and “Sumidule (registered trademark) N-75” [above , 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) Registered trademark) TSE-100” [Asahi Kasei Corporation], and “Takenate (registered trademark) D-110N”, “Takenate (registered trademark) D-120N”, “Takenate (registered trademark) M-631N” , “MT-Olestar (registered trademark) NP1200”, and “STABIO (registered trademark) XD-340N” [all of which are manufactured by Mitsui Chemicals, Inc.].

The pressure-sensitive adhesive composition of the present invention may contain only one type of polyisocyanate compound, or may contain two or more types.

The pressure-sensitive adhesive composition of the present invention is the molar equivalent ratio of the amount of isocyanate groups in the polyisocyanate compound to the total amount of carboxy groups, hydroxyl groups, and amino groups in the specific (meth)acrylic copolymer described above [poly molar amount of isocyanate groups in the isocyanate compound/total molar amount of carboxy groups, hydroxyl groups, and amino groups in the specific (meth)acrylic copolymer] is 0.5 to 5.0, and 0.5 to 4 0.0 is preferred, 0.5 to 3.0 is more preferred, 0.5 to 2.0 is even more preferred, and 0.7 to 1.5 is particularly preferred.
In the adhesive composition of the present invention, the molar amount of isocyanate groups in the polyisocyanate compound/the total molar amount of carboxy groups, hydroxyl groups, and amino groups in the specific (meth)acrylic copolymer is 0.5 or more. As a result, although the amount of hydroxyl groups in the specific (meth)acrylic copolymer is small, sufficient cross-linking is achieved and the cross-linking density of the pressure-sensitive adhesive layer is moderately high. Therefore, the pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer having excellent durability while maintaining excellent reworkability.
On the other hand, in the adhesive composition of the present invention, the molar amount of isocyanate groups in the polyisocyanate compound/the total molar amount of carboxy groups, hydroxyl groups, and amino groups in the specific (meth)acrylic copolymer is 5.0 or less. As a result, excessive polyisocyanate compounds that do not contribute to cross-linking are not produced. As a result, the pressure-sensitive adhesive layer does not become too hard and exhibits appropriate flexibility, so that it can sufficiently follow expansion and contraction of the base material due to changes in temperature and humidity. Therefore, the pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer with excellent durability.

The molar equivalent ratio of the amount of isocyanate groups in the polyisocyanate compound to the total amount of carboxy groups, hydroxyl groups, and amino groups in the specific (meth)acrylic copolymer [molar amount of isocyanate groups in the polyisocyanate compound / specific ( The total molar amount of carboxy groups, hydroxyl groups and amino groups in the meth)acrylic copolymer] is determined by the following formulas (1) to (3). In the following calculation formula, the molar amount of isocyanate groups in the polyisocyanate compound is expressed as "NCO amount", and the total molar amount of carboxy groups, hydroxyl groups, and amino groups in the specific (meth)acrylic copolymer is referred to as "total amount of functional groups".

NCO amount (unit: mmol/solid content 100 g)
= [Isocyanate group content in polyisocyanate compound (unit: mass%)/solid content of polyisocyanate compound (unit: mass%) x blending amount of polyisocyanate compound (unit: g)]/formula weight of isocyanate group (Unit: g/mol) x 1000 (1)

Total functional group amount (unit: mmol/solid content 100 g)
= [content of structural units derived from monomers having carboxy groups in the specific (meth)acrylic copolymer (unit: % by mass)/molecular weight of structural units derived from monomers having carboxy groups ( Unit: g / mol) × number of carboxy groups in the structural unit derived from the monomer having a carboxy group (valence) × 1000] + [monomer having a hydroxyl group in the specific (meth)acrylic copolymer Content of structural units derived from the body (unit: mass%) / molecular weight of structural units derived from monomers having hydroxyl groups (units: g / mol) × structural units derived from monomers having hydroxyl groups Number of hydroxyl groups (valence) × 1000] + [content of structural units derived from monomers having amino groups in the specific (meth)acrylic copolymer (unit: mass%) / units having amino groups Molecular weight (unit: g/mol) of a structural unit derived from a monomer x number of amino groups in a structural unit derived from a monomer having an amino group (valence) x 1000] (2)

Molar equivalent ratio of the amount of isocyanate groups in the polyisocyanate compound to the total amount of carboxy groups, hydroxyl groups, and amino groups in the specific (meth)acrylic copolymer = NCO amount/total functional group amount (3)

〔Silane coupling agent〕
The adhesive composition of the present invention contains a silane coupling agent.
When the pressure-sensitive adhesive composition of the present invention contains a silane coupling agent, a pressure-sensitive adhesive layer with excellent durability can be formed.

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)ethyltrimethoxy Epoxy group-containing silane compounds represented by silane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, and N Amino group-containing silane compounds typified by -(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-isocyanatopropyltriethoxysilane, and tris-(3-trimethoxysilylpropyl)isocyanurate. .

A commercial item can be used as a silane coupling agent.
Commercially available silane coupling agents include, for example, Shin-Etsu Chemical Co., Ltd. "KBM-1003", "KBE-1003", and "KBM-503" (all trade names). Saturated group-containing silane compounds, Shin-Etsu Chemical Co., Ltd. "KBM-803", "KBM-802", "X-41-1810", "X-41-1805", and "X-41-1818" ( Thiol group-containing silane compounds represented by all product names), Shin-Etsu Chemical Co., Ltd. "KBM-903", "KBM-603", "KBM-573", and "KBM-602" (all product names) name), an isocyanate group-containing silane compound represented by "KBE-9007N" (trade name) of Shin-Etsu Chemical Co., Ltd., "KBM-9659" of Shin-Etsu Chemical Co., Ltd. (trade name), and "KBM-403", "KBM-303", "KBM-402", "KBE-402", "KBE" of Shin-Etsu Chemical Co., Ltd. -403", "X-41-1053", and "X-41-1056" (all trade names).

The pressure-sensitive adhesive composition of the present invention may contain only one type of silane coupling agent, or may contain two or more types.

The content of the silane coupling agent in the pressure-sensitive adhesive composition of the present invention is not particularly limited. It is preferably 0.05 to 1 part by mass, and even more preferably 0.05 to 0.5 part by mass.
When the content of the silane coupling agent in the pressure-sensitive adhesive composition of the present invention is within the above range, the durability of the formed pressure-sensitive adhesive layer can be further improved.

[Crosslinking catalyst]
The pressure-sensitive adhesive composition of the present invention may further contain a cross-linking catalyst.
When the pressure-sensitive adhesive composition of the present invention further contains a cross-linking catalyst, the cross-linking reaction is performed more appropriately even if the monomer (B) having a bulky molecular structure is included, resulting in a pressure-sensitive adhesive having a more moderate cross-linking density. It can form layers. Therefore, the durability and reworkability of the pressure-sensitive adhesive layer tend to be more excellent.

The cross-linking catalyst is not particularly limited.
Crosslinking catalysts include, for example, 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, and 2,3-dihydro-1H-pyrrolo[1,2-a]benz Imidazole compounds typified by imidazole, organometallic compounds typified by dioctyltin dilaurate and 1,3-diacetoxytetrabutylstannoxane, and tertiary amines typified by triethylenediamine and N-methylmorpholine compound.

A commercially available product can be used as the cross-linking catalyst.
Examples of commercially available cross-linking catalysts include "Curesol (registered trademark) 1B2MZ", "Curesol (registered trademark) 1B2PZ", "Curesol (registered trademark) TBZ" and "Curesol (registered trademark)" manufactured by Shikoku Kasei Co., Ltd. ) 1,2DMZ” (both are trade names).

When the pressure-sensitive adhesive composition of the present invention contains a cross-linking catalyst, it may contain only one cross-linking catalyst, or may contain two or more cross-linking catalysts.

When the pressure-sensitive adhesive composition of the present invention contains a cross-linking catalyst, the content of the cross-linking catalyst in the pressure-sensitive adhesive composition is, for example, 0.01 part by mass to 0.01 part by mass with respect to 100 parts by mass of the specific (meth)acrylic copolymer. 1.5 parts by mass is preferable, 0.05 to 1.0 parts by mass is more preferable, and 0.05 to 0.5 parts by mass is even more preferable.
When the content of the cross-linking catalyst in the pressure-sensitive adhesive composition of the present invention is within the above range, there is a tendency that the curing time can be further shortened.

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

[Other ingredients]
The pressure-sensitive adhesive composition of the present invention may contain components other than the components described above (so-called other components), if necessary, as long as the effects of the present invention are not impaired.
Other components include polymers other than specific (meth)acrylic copolymers, cross-linking agents other than polyisocyanate compounds, antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbing agents), and various additives such as antistatic agents.
From the viewpoint of suppressing excessive cross-linking reaction, the pressure-sensitive adhesive composition of the present invention preferably does not contain a cross-linking agent other than the polyisocyanate compound.

<Gel fraction after cross-linking>
The adhesive composition of the present invention has a gel fraction after crosslinking of 45% by mass to 80% by mass, preferably 55% by mass to 80% by mass, more preferably 60% by mass to 80% by mass, and 65% by mass. ~80% by mass is more preferable, and 70% to 80% by mass is particularly preferable.
When the gel fraction after crosslinking is 45% by mass or more, the cohesive force of the pressure-sensitive adhesive layer is in an appropriate range, and when reworking, cohesive failure of the pressure-sensitive adhesive layer does not occur, and the substrate and / or adhesion Adhesive residue on the body is less likely to occur, and air bubbles are less likely to occur at the interface between the adherend and the pressure-sensitive adhesive layer when exposed to a high-temperature environment. Therefore, the pressure-sensitive adhesive layer tends to be excellent in durability and reworkability.
When the gel fraction after cross-linking is 80% by mass or less, the pressure-sensitive adhesive layer does not become too hard and can sufficiently follow the expansion and contraction of the base material due to changes in temperature and humidity, and tends to be excellent in durability. .

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

[Use of adhesive composition]
The pressure-sensitive adhesive composition of the present invention is suitable for use in attaching a polarizing plate to an adherend. Specific uses include use for attaching a polarizing plate to a liquid crystal cell, use for attaching a polarizing plate to an optical film such as a retardation film, and the like.
Among these, the use of the pressure-sensitive adhesive composition of the present invention, the use particularly required durability and suppression of the occurrence of white spots, that is, the use of affixing a polarizing plate to a liquid crystal cell, the pressure-sensitive adhesive composition of the present invention It is preferable because the effect of the object is exhibited more.

As described above, in general, the EWV layer has extremely poor adhesion to the adhesive layer, so the adhesive layer formed on the surface of the EWV layer is transferred to the adherend (for example, the glass substrate of the liquid crystal cell). Easy to wear. In contrast, the pressure-sensitive adhesive composition of the present invention can form a pressure-sensitive adhesive layer that exhibits good adhesion even to the EWV layer, and is excellent in reworkability. polarizing plate) to an adherend (for example, a glass substrate of a liquid crystal cell).
Examples of glass substrates for liquid crystal cells include soda glass, alkali-free glass, and ITO glass.
When peeling the EWV polarizing plate from the adherend, if peeling occurs at the interface between the EWV layer and the pressure-sensitive adhesive layer, the reworkability is extremely reduced.

[Polarizing plate with adhesive layer]
The pressure-sensitive adhesive layer-attached polarizing plate of the present invention includes a polarizing plate and a pressure-sensitive adhesive layer provided on the polarizing plate and formed from the above-described pressure-sensitive adhesive composition of the present invention.
Since the pressure-sensitive adhesive layer-attached polarizing plate of the present invention includes the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention, it is excellent in reworkability and durability. Further, in the pressure-sensitive adhesive layer-attached polarizing plate of the present invention, white spots are less likely to occur.

The polarizing plate in the present invention 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.

The layer structure of the pressure-sensitive adhesive layer-attached polarizing plate of the present invention includes, for example, pressure-sensitive adhesive layer/polarizer, pressure-sensitive adhesive layer/polarizer/protective film, pressure-sensitive adhesive layer/protective film/polarizer/protective film, and pressure-sensitive adhesive. Layers/protective films/polarizers may be mentioned.
In the pressure-sensitive adhesive layer-attached polarizing plate of the present invention, a retardation film (for example, It may have layers such as an optical functional layer represented by an EWV layer, an adhesive layer, and an easy-adhesion layer.
Further, the outermost surface of the pressure-sensitive adhesive layer-attached polarizing plate may be protected with a release film.

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.

As the release film in contact with the adhesive layer, in order to make it easier to release the release film from the adhesive layer, for example, a fluorine-based resin, paraffin wax, polyester, etc., whose surface has been subjected to an easy-release treatment with a release agent such as silicone, etc. A synthetic resin film of is preferably mentioned.
Examples of the release film for protecting the surface opposite to the pressure-sensitive adhesive layer side include a surface protection film such as a hard-coated polyethylene terephthalate (PET) film.

In a preferred embodiment of the pressure-sensitive adhesive layer-attached polarizing plate of the present invention, a polarizing plate, a layer disposed on the polarizing plate and having a contact angle with water of 90° or more, and the contact angle with water are An embodiment is an adhesive layer-attached polarizing plate comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention and disposed on the surface of the layer having an angle of 90° or more.
In general, a layer having a contact angle with water of 90° or more has extremely poor adhesion to a pressure-sensitive adhesive layer. In contrast, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention exhibits excellent adhesion even to a layer having a contact angle with water of 90° or more, and is excellent in reworkability. It is possible to design a pressure-sensitive adhesive layer-attached polarizing plate in the following manner.

The "contact angle with water" in this specification refers to the contact angle of a water droplet after dropping pure water of 2 μm on the surface of the layer to be measured in an environment with an ambient temperature of 25° C. and leaving it for 30 seconds. It is a value measured using a contact angle meter.
As a measuring device, for example, Drop Master DM-701 (trade name) manufactured by Kyowa Interface Science Co., Ltd. can be used. However, the measuring device is not limited to this.

A layer having a contact angle with water of 90° or more includes, for example, a layer containing a discotic liquid crystal compound (that is, an EWV layer).

The thickness of the pressure-sensitive adhesive layer can be appropriately set according to the type of substrate and adherend, the surface roughness of the substrate and adherend, and the like. Generally, the thickness of the adhesive layer is 1 μm to 100 μm, preferably 5 μm to 50 μm, more preferably 10 μm to 30 μm.

The pressure-sensitive adhesive layer-attached polarizing plate of the present invention can be produced by a known method.
Known methods include, for example, the following methods.
The pressure-sensitive adhesive composition of the present invention is applied to the release-treated surface of the release film to form a coating film. Then, by drying the formed coating film, an adhesive film is formed on the release film. Next, there is a method of producing a polarizing plate with an adhesive layer by transferring the formed adhesive film onto a polarizing plate and curing it.
Alternatively, the pressure-sensitive adhesive composition of the present invention is applied to the release-treated surface of the release film to form a coating film. Then, by drying the formed coating film, an adhesive film is formed on the release film. Then, the exposed surface of the adhesive film thus formed is overlaid with the release-treated surface of a separate release film to prepare a support-free double-sided adhesive tape. Then, after curing the adhesive film of the produced double-sided adhesive tape, one release film is peeled off, and the exposed adhesive film is transferred onto the polarizing plate, thereby producing a polarizing plate with an adhesive layer. be done.
Alternatively, the pressure-sensitive adhesive composition of the present invention is applied onto a polarizing plate to form a coating film. Next, by drying the formed coating film, an adhesive film is formed on the polarizing plate. Next, there is a method of producing a polarizing plate with an adhesive layer by aging the formed adhesive film.
The drying conditions include, for example, a hot air dryer at 70° C. to 120° C. for 1 minute to 3 minutes.

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

[Production of (meth)acrylic copolymer]
[Production Example 1]
In a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, 84.8 parts by mass of n-butyl acrylate [n-BA; monomer (C)], t-butyl acrylate [t -BA; monomer (B)] 15.0 parts by mass, 2-hydroxylethyl acrylate [2HEA; monomer (A)] 0.2 parts by mass, and ethyl acetate 110 parts by mass were added and mixed, The inside of the reactor was replaced with nitrogen. Then, the mixture in the reactor was heated to 70° C. while stirring, and then 0.02 parts by mass of 2,2′-azobis(2,4-dimethylvaleronitrile) [ABVN; polymerization initiator] and 40 parts of ethyl acetate. Parts by mass of the liquid mixture were successively added and kept for 6 hours to carry out a polymerization reaction. After completion of the polymerization reaction, the mixture was diluted with ethyl acetate to make the solid content 17.5% by mass. Thus, a (meth)acrylic copolymer solution was obtained.
The term "solid content" as used herein means the remaining components after removing volatile components such as the solvent from the solution of the (meth)acrylic copolymer. The same applies to the solutions of (meth)acrylic copolymers obtained in Production Examples 2 to 19 below.

[Production Examples 2 to 10]
In Production Example 1, the same operation as in Production Example 1 was performed, except that the monomer composition of the (meth)acrylic copolymer was changed to the monomer composition shown in Table 1, and the (meth)acrylic A solution of the copolymer was obtained.
The solid content of the obtained (meth)acrylic copolymer solution was in the range of 17.0% by mass to 18.0% by mass.

[Production Examples 11 to 15]
In Production Example 1, the same operation as in Production Example 1 was performed, except that the monomer composition of the (meth)acrylic copolymer was changed to the monomer composition shown in Table 2, and a (meth)acrylic A solution of the copolymer was obtained.
The solid content of the obtained (meth)acrylic copolymer solution was in the range of 17.0% by mass to 18.0% by mass.

[Production Examples 16 to 19]
In Production Example 1, by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used, the weight average molecular weight (Mw) of the (meth)acrylic copolymer was adjusted to the weight average molecular weight shown in Table 2. A solution of a (meth)acrylic copolymer was obtained in the same manner as in Production Example 1, except that (Mw) was changed.
The solid content of the obtained (meth)acrylic copolymer solution is in the range of 45.0% by mass to 46.0% by mass in Production Examples 16 and 17, and 21.5 in Production Example 18. % by mass, and Production Example 19 was 13.2% by mass.

Among the (meth)acrylic copolymers obtained above, the (meth)acrylic copolymers obtained in Production Examples 1 to 5, Production Examples 8, 9, Production Examples 12 to 14, and Production Examples 17 to 19 The acrylic copolymer corresponds to the specific (meth)acrylic copolymer in the present invention.

(Meth) acrylic copolymer monomer composition (unit: mass%), total functional group content (unit: mmol/solid content 100 g), and weight average molecular weight [Mw, unit: 10,000 (in the table, " × 10 ⁴ ”] are shown in Tables 1 and 2.
The weight average molecular weight (Mw) of the (meth)acrylic copolymer was measured by the same method as the measurement method of the weight average molecular weight (Mw) of the specific (meth)acrylic copolymer described above.
In Tables 1 and 2, "-" means that the corresponding monomer was not used.

[Example 1]
-Preparation of adhesive composition-
100 parts by mass (solid content conversion value) of the (meth)acrylic copolymer solution obtained in Production Example 1, and a polyisocyanate compound [trade name: Coronate (registered trademark) L-45E, tolylene diisocyanate (TDI ) and an adduct of trimethylolpropane (TMP), solid content: 45% by mass, isocyanate group content: 7.9% by mass, Tosoh Corporation] 0.40 parts by mass (solid content conversion value), Cross-linking catalyst [trade name: Cursol (registered trademark) 1B2PZ, 1-benzyl-2-phenylimidazole, solid content: 100% by mass, Shikoku Chemical Industry Co., Ltd.] 0.2 parts by mass (solid content conversion value), and silane Coupling agent [trade name: X-41-1810, solid content: 100% by mass, Shin-Etsu Chemical Co., Ltd.] 0.1 part by mass was sufficiently stirred and mixed to obtain an adhesive composition. .
The molar equivalent ratio of the amount of isocyanate groups in the polyisocyanate compound to the total amount of hydroxyl groups, carboxyl groups, and amino groups in the (meth)acrylic copolymer in the obtained pressure-sensitive adhesive composition [isocyanate in the polyisocyanate compound The molar amount of groups/the total molar amount of hydroxyl groups, carboxyl groups and amino groups in the (meth)acrylic copolymer] was 0.97.

The molar equivalent ratio of the amount of isocyanate groups in the polyisocyanate compound with respect to the total amount of hydroxyl groups, carboxyl groups, and amino groups in the (meth)acrylic copolymer is calculated using the formulas (1) to (3) described above. calculated using Specifically, it was calculated as follows.
The polyisocyanate compound Coronate (registered trademark) L-45E has a solid content of 45% by mass and an isocyanate group content of 7.9% by mass. Also, the formula weight of the isocyanate group is 42. Further, the molecular weight of the structural unit derived from 2-hydroxyethyl acrylate, which is a monomer having a hydroxyl group, is 116.

Formula (1)
NCO amount (unit: mmol/solid content 100 g)
= isocyanate group content in polyisocyanate compound (unit: mass%) / solid content of polyisocyanate compound (unit: mass%) × compounding amount of polyisocyanate compound (unit: g) / formula weight of isocyanate group (unit : g/mol) x 1000
= 7.9 (% by mass) / 45 (% by mass) x 0.40 (g) / 42 (g / mol) x 1000 = 1.67

Formula (2)
Total functional group amount (unit: mmol/solid content 100 g)
= [content of structural units derived from a monomer having a hydroxyl group in the (meth)acrylic copolymer (unit: mass%) / molecular weight of a structural unit derived from a monomer having a hydroxyl group (unit: g / mol) × number of hydroxyl groups in a structural unit derived from a monomer having a hydroxyl group (valence) × 1000] + [(meth) composition derived from a monomer having a carboxy group in the acrylic copolymer Unit content (unit: mass %)/molecular weight of structural unit derived from monomer having carboxy group (unit: g/mol) × number of carboxy groups in structural unit derived from monomer having carboxy group number (valence) × 1000] + [content of structural units derived from monomers having amino groups in (meth)acrylic copolymer (unit: mass%) / monomers having amino groups Molecular weight of derived structural unit (unit: g/mol) x number of amino groups in structural unit derived from monomer having amino group (valence) x 1000]
= [0.2 (parts by mass) / 100 (parts by mass) × 100 (%) / 116 (g / mol) × 1 × 1000] = 1.72

Formula (3)
The molar equivalent ratio of the amount of isocyanate groups to the total amount of carboxy groups, hydroxyl groups, and amino groups in the (meth)acrylic copolymer = NCO amount/total functional group amount = 1.67/1.72 = 0.97

-Preparation of polarizing plate with adhesive layer-
Using the pressure-sensitive adhesive composition prepared above, a polarizing plate with a pressure-sensitive adhesive layer was produced as follows. Adhere to the release-treated surface of a release film [trade name: Film Bina (registered trademark) 100E-0010N023, Fujimori Industry Co., Ltd.] that has been treated with a silicone-based release agent for easy release so that the thickness after drying is 20 μm. The agent composition was applied to form a coating film. Then, the formed coating film was dried using a hot air circulating dryer under drying conditions of 100° C. for 1 minute to form an adhesive film on the release film.
Next, an EWV layer-side surface of a polarizing plate with an EWV layer (that is, an EWV polarizing plate) having a laminated structure of EWV layer/triacetylcellulose (TAC) layer/polyvinyl alcohol (PVA) layer/TAC layer, and the peeling The surface of the adhesive film formed on the film and the surface of the adhesive film are laminated together, cured for 168 hours in an environment of an atmospheric temperature of 25 ° C. and 50% RH, and the crosslinking reaction is allowed to proceed, resulting in release film / adhesive layer / polarized light. A pressure-sensitive adhesive layer-attached polarizing plate having a laminate structure of plates was produced.
The contact angle of water on the surface of the EWV layer of the polarizing plate was 97.6°.

[Examples 2 to 18]
-Preparation of adhesive composition-
In Examples 2 to 18, pressure-sensitive adhesive compositions were prepared in the same manner as in Example 1, except that the composition of the pressure-sensitive adhesive composition in Example 1 was changed to the composition shown in Table 3.

-Preparation of polarizing plate with adhesive layer-
Using the pressure-sensitive adhesive composition prepared above, the same operation as in Example 1 was performed to prepare a polarizing plate with a pressure-sensitive adhesive layer.

[Comparative Examples 1 to 12]
-Preparation of adhesive composition-
In Comparative Examples 1 to 12, pressure-sensitive adhesive compositions were prepared in the same manner as in Example 1 except that the composition of the pressure-sensitive adhesive composition in Example 1 was changed to the composition shown in Table 4.

-Preparation of polarizing plate with adhesive layer-
Using the pressure-sensitive adhesive composition prepared above, the same operation as in Example 1 was performed to prepare a polarizing plate with a pressure-sensitive adhesive layer.

[Measurement and evaluation]
1. Measurement of Gel Fraction A release film [trade name: Film Binah (registered trademark) 100E-0010N023, Fujimori Kogyo Co., Ltd.] obtained by subjecting the pressure-sensitive adhesive composition prepared above to an easy-release treatment with a silicone-based release agent. A coating film was formed by coating the release-treated surface so that the thickness after drying was 20 μm. Then, the formed coating film was dried using a hot air circulating dryer under drying conditions of 100° C. for 1 minute to form an adhesive film on the release film.
Next, the surface where the adhesive film was exposed was superimposed on the release-treated surface of a separately prepared release film [trade name: Film Bina (registered trademark) 100E-0010N023, Fujimori Industry Co., Ltd.], and then the atmosphere temperature was 25. C. and 50% RH for 168 hours to allow the cross-linking reaction to proceed, thereby obtaining a substrate-free pressure-sensitive adhesive sheet having a laminate structure of release film/adhesive layer/release film.
Then, the two release films of the pressure-sensitive adhesive sheet were peeled off, and the resulting pressure-sensitive adhesive layer was used to measure the gel fraction after cross-linking of the pressure-sensitive adhesive composition by the method described above.
Tables 3 and 4 show the results.
As for the pressure-sensitive adhesive composition of Comparative Example 10, since the gel fraction after cross-linking did not increase, evaluation tests for durability, reworkability, and voids, which will be described later, could not be performed.

2. Durability (Preparation of samples for durability evaluation)
The pressure-sensitive adhesive layer-attached polarizing plate prepared above was cut so that the long side was at 45° to the absorption axis, and two test pieces each having a size of 50 mm×89 mm (long side) were prepared.
The release film of the test piece was peeled off, and the surface of the adhesive layer exposed by peeling was laminated on one side of soda plate soda glass [Matsunami Glass Industry Co., Ltd.], and crimped using a laminator to form a laminate. made.
An autoclave treatment (temperature: 50° C., pressure: 5 kg/cm ² , treatment time: 20 minutes) was applied to the produced laminate. Next, the laminate after the autoclave treatment was left for 1 hour in an environment of an atmospheric temperature of 23° C. and 50% RH to obtain a sample for durability evaluation.

(Evaluation test)
2-1. Foaming The durability evaluation sample prepared above was left in a high temperature environment at an atmospheric temperature of 95° C. for 500 hours. After standing, the appearance of the durability evaluation sample was visually observed to confirm the presence and degree of foaming. Then, durability under high temperature conditions (95° C.) was evaluated according to the following evaluation criteria.
Tables 3 and 4 show the results.
If the evaluation result is "A" or "B", there is no practical problem.

-Evaluation criteria-
A: No foaming was observed.
B: A little foaming was observed, but it was within the allowable range.
C: Foaming was observed and outside the allowable range.
D: Remarkable foaming was observed.

2-2. Peeling The durability evaluation sample obtained above was allowed to stand for 500 hours in a high-temperature and high-humidity environment at an atmospheric temperature of 65°C and 95% RH. After standing, the appearance of the durability evaluation sample was visually observed to confirm the presence and degree of peeling. Then, durability under high temperature and high humidity conditions (65° C., 95% RH) was evaluated according to the following evaluation criteria.
Tables 3 and 4 show the results.
If the evaluation result is "A" or "B", there is no practical problem.

-Evaluation criteria-
A: Peeling was not recognized at all.
B: A little peeling was observed, but it was within the allowable range.
C: Peeling was observed, outside the allowable range.
D: Remarkable peeling was observed.

3. Reworkability The pressure-sensitive adhesive layer-attached polarizing plate prepared above was cut to prepare a test piece having a size of 25 mm x 75 mm (long side).
The release film was peeled off from the test piece, and the surface of the adhesive layer exposed by peeling was coated with soda plate soda glass [Matsunami Glass Industry Co., Ltd.; hereinafter simply referred to as "glass". ] on one side of the sheet, and press-bonded with a laminator to prepare a laminate.
An autoclave treatment (temperature: 50° C., pressure: 5 kg/cm ² , treatment time: 20 minutes) was applied to the produced laminate. Then, the laminate after the autoclave treatment was left in an environment with an ambient temperature of 50° C. for 96 hours.
After the standing time had passed, 180° peeling was performed at a peeling speed of 300 mm/min in an environment of an ambient temperature of 23°C and 50% RH. The surface of the glass and the surface of the peeled pressure-sensitive adhesive layer were visually observed, and reworkability was evaluated according to the following evaluation criteria.
Tables 3 and 4 show the results.
If the evaluation result is "A" or "B", there is no practical problem.

-Evaluation criteria-
A: The adhesive layer was not transferred to the surface of the glass at all.
B: The adhesive layer was not transferred to the glass surface at all, but the surface of the adhesive layer was rough after peeling.
C: Part of the adhesive layer was transferred to the surface of the glass.
D: The pressure-sensitive adhesive layer was entirely transferred and adhered to the surface of the glass.

4. White spots (preparation of samples for evaluation of white spots)
The pressure-sensitive adhesive layer-attached polarizing plate prepared above was cut to prepare two test pieces each having a size of 62 mm×110 mm (long side).
The release films of the two test pieces are peeled off, and the surface of the adhesive layer exposed by peeling is placed on both sides of a Twisted Nematic (TN) liquid crystal panel so that the absorption axes of each test piece are orthogonal. They were laminated together and pressure-bonded using a laminator to produce a laminate. An autoclave treatment (temperature: 50° C., pressure: 5 kg/cm ² , treatment time: 20 minutes) was applied to the produced laminate. Next, the laminate after the autoclave treatment was left for 24 hours in an environment of an atmospheric temperature of 23° C. and 50% RH to obtain a sample for white spot evaluation.

(Evaluation test)
The white spot evaluation sample prepared as described above was left in an environment with an ambient temperature of 95° C. for 500 hours. After being left standing, the white spot evaluation sample was placed on a backlight of a liquid crystal monitor under an environment of an ambient temperature of 23° C. and 50% RH, and the occurrence and degree of white spots were visually observed. Then, based on the observation results, suppression of generation of white spots was evaluated according to the following evaluation criteria.
Tables 3 and 4 show the results.
In addition, it is preferable that the evaluation result is "A" or "B".

-Evaluation criteria-
A: White spots were not observed at all.
B: White spots were slightly observed, but within the allowable range.
C: White spots were observed and outside the allowable range.
D: Remarkable white spots were observed.

In Tables 3 and 4, "-" means that the corresponding component is not included.
In Tables 3 and 4, the molar amount of isocyanate groups in the polyisocyanate compound is denoted as "NCO amount", and the hydroxyl group, carboxy group, and amino group of the (meth)acrylic copolymer are compared to the total amount of polyisocyanate The molar equivalent ratio of the amount of isocyanate groups possessed by the compound was expressed as "molar equivalent ratio".

Details of the components listed in Tables 3 and 4 are as follows.
<Crosslinking agent>
-Polyisocyanate compound-
"Coronate L-45E" [trade name, Tosoh Corporation]: an adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP), solid content: 45% by mass, isocyanate group content: 7.9 mass%
"Sumidule N-75" [trade name, Sumika Covestro Urethane Co., Ltd.]: biuret type of hexamethylene diisocyanate (HMDI), solid content: 75% by mass, content of isocyanate group: 16.5% by mass
"Takenate D-110N" [trade name, Mitsui Takeda Chemicals Co., Ltd.]: xylylene diisocyanate (XDI), solid content: 75% by mass, content of isocyanate group: 11.5% by mass
-others-
"TETRAD-X" [trade name, Mitsubishi Gas Chemical Co., Ltd.]: epoxy compound

<Silane coupling agent>
"X-41-1810" [trade name, Shin-Etsu Chemical Co., Ltd.]: silane compound containing thiol group, solid content: 100% by mass
"KBM-9659" [trade name, Shin-Etsu Chemical Co., Ltd.]: isocyanurate group-containing silane compound, solid content: 100% by mass
"KBE-9007N" [trade name, Shin-Etsu Chemical Co., Ltd.]: isocyanate group-containing silane compound, solid content: 100% by mass
"KBM-573" [trade name, Shin-Etsu Chemical Co., Ltd.]: amino group-containing silane compound, solid content: 100% by mass
<Crosslinking catalyst>
"Curesol 1B2PZ" [trade name, Shikoku Chemical Industry Co., Ltd.]: 1-benzyl-2-phenylimidazole, solid content: 100% by mass

As shown in Table 3, it was confirmed that the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Examples 1 to 18 were all excellent in durability and reworkability.
Further, it was confirmed that the adhesive layers formed from the adhesive compositions of Examples 1 to 18 were less likely to cause white spots.

On the other hand, as shown in Table 4, the (meth)acrylic copolymer contained in the pressure-sensitive adhesive composition is formed from the pressure-sensitive adhesive composition of Comparative Example 1 that does not contain the structural unit b derived from the monomer (B). It was confirmed that the pressure-sensitive adhesive layer thus formed was inferior in reworkability.
The content of the structural unit b derived from the monomer (B) in the (meth)acrylic copolymer contained in the pressure-sensitive adhesive composition is less than 10% by mass relative to the total structural units of Comparative Example 2. It was confirmed that the pressure-sensitive adhesive layer formed from the adhesive composition was inferior in reworkability.
The pressure-sensitive adhesive of Comparative Example 3 in which the content of the structural unit b derived from the monomer (B) in the (meth)acrylic copolymer contained in the pressure-sensitive adhesive composition exceeds 30% by mass relative to the total structural units. It was confirmed that the pressure-sensitive adhesive layer formed from the composition tends to cause white spots.

The content of the structural unit a derived from the monomer (A) in the (meth)acrylic copolymer contained in the pressure-sensitive adhesive composition is less than 0.05% by mass with respect to all structural units, and the molar equivalent In the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 4 having a ratio of more than 5.0 and a gel fraction of less than 45% by mass, foaming remarkably occurred when exposed to a high-temperature environment. It was confirmed that the durability was inferior.
The content of the structural unit a derived from the monomer (A) in the (meth)acrylic copolymer contained in the pressure-sensitive adhesive composition exceeds 0.4% by mass with respect to all structural units, and is mol It was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 5 having an equivalent ratio of less than 0.5 was inferior in reworkability. Further, it was confirmed that the adhesive layer formed from the adhesive composition of Comparative Example 5 was likely to cause white spots.

Formed from the pressure-sensitive adhesive composition of Comparative Example 6 in which the (meth)acrylic copolymer contained in the pressure-sensitive adhesive composition has a weight average molecular weight of less than 200,000 and a gel fraction of less than 45 mass%. When the adhesive layer was exposed to a high-temperature environment, significant foaming was observed, and when exposed to a high-temperature, high-humidity environment, peeling was observed, confirming that the adhesive layer was inferior in durability. . Furthermore, it was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 6 was also inferior in reworkability.

The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 7 having a molar equivalent ratio of less than 0.5 and a gel fraction of less than 45% by mass was exposed to a high-temperature environment. Foaming was observed, and peeling was observed when exposed to a high-temperature and high-humidity environment, confirming that the durability was poor. Furthermore, it was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 7 was also inferior in reworkability.
The pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Comparative Examples 8, 9, and 11 having a gel fraction of less than 45% by mass significantly foamed when exposed to a high-temperature environment. Moreover, when exposed to a high-temperature and high-humidity environment, marked peeling was observed, confirming that the durability was poor. Furthermore, it was confirmed that the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Comparative Examples 8, 9, and 11 were also inferior in reworkability.

The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 10 containing an epoxy compound instead of the polyisocyanate compound did not have an increased gel fraction and could not be subjected to an evaluation test.
It was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 12 containing no silane coupling agent peeled off when exposed to a high-temperature and high-humidity environment, indicating poor durability. .

Claims (7)

A structural unit a derived from a monomer (A) having a hydroxyl group;
a structural unit b derived from a monomer (B) having at least one group selected from the group consisting of a group having a tertiary carbon atom, a group having an alicyclic structure, and a group having an aromatic ring;
and a structural unit c which is a structural unit derived from the (meth)acrylic acid alkyl ester monomer (C) and which is different from the structural unit a and the structural unit b,
the monomer (B) is t-butyl acrylate,
The content of the structural unit a is 0.05% by mass to 0.4% by mass relative to all structural units, and the content of the structural unit b is 15 % by mass to 30% by mass relative to all structural units. % and a (meth)acrylic copolymer having a weight average molecular weight of 200,000 to 2,000,000,
a polyisocyanate compound;
and a silane coupling agent,
The molar equivalent ratio of the amount of isocyanate groups in the polyisocyanate compound to the total amount of hydroxyl groups, carboxyl groups, and amino groups in the (meth)acrylic copolymer is 0.5 to 5.0,
A pressure-sensitive adhesive composition for a polarizing plate having a gel fraction of 45% by mass to 80% by mass after cross-linking. 2. The pressure-sensitive adhesive composition for a polarizing plate according to claim 1, wherein the gel fraction after cross-linking is 60% by mass to 80% by mass. 3. The pressure-sensitive adhesive composition for a polarizing plate according to claim 1, wherein the content of said structural unit a is 0.05% by mass to 0.25% by mass with respect to all structural units. 4. The pressure-sensitive adhesive composition for a polarizing plate according to claim 1, wherein the content of said structural unit b is 15 % by mass to 20% by mass with respect to all structural units. 5. The pressure-sensitive adhesive composition for a polarizing plate according to any one of claims 1 to 4, further comprising a crosslinking catalyst. a polarizing plate;
a layer disposed on the polarizing plate and having a contact angle with water of 90° or more;
A pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for a polarizing plate according to any one of claims 1 to 5 , disposed on the surface of the layer having a contact angle with water of 90° or more; ,
A polarizing plate with an adhesive layer. 7. The pressure-sensitive adhesive layer-attached polarizing plate according to claim 6 , wherein the layer having a contact angle with water of 90° or more is a layer containing a discotic liquid crystal compound.