JP6886401B2 - Adhesive layer and adhesive composition for polarizing plates - Google Patents

Description

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

The liquid crystal cell has a structure in which a liquid crystal layer is sandwiched between two substrates (eg, a glass plate). A polarizing plate is attached to the surface of the substrate constituting the liquid crystal cell via an adhesive layer. Generally, as a polarizing plate, in order to improve its mechanical properties and optical durability, a structure in which a polarizing element protective film such as a triacetyl cellulose film is laminated on both sides of a polarizing element having a polarizing function is adopted. I came.

In recent years, in response to the demand for lighter weight and thinner polarizing plates, attempts have been made to omit one or both of the polarizing element protective films formed on both sides of the polarizer (see, for example, Patent Document 1). However, in a polarizing plate in which one or both of the polarizing element protective films are omitted, the pressure-sensitive adhesive layer comes into direct contact with the polarizer. A large amount of stress is applied, and problems such as peeling of the adhesive layer are likely to occur. In addition, there is a problem that the stress applied to the pressure-sensitive adhesive layer due to the heat shrinkage of the polarizer becomes large, and birefringence is likely to occur.

Therefore, the pressure-sensitive adhesive for polarizing plates is required to have excellent light leakage prevention and durability. Regarding the problem of light leakage, Patent Document 2 describes a polarizing film having a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition for a polarizing plate containing a large amount of an isocyanate compound, and Patent Document 3 describes positive photoelasticity. A pressure-sensitive adhesive composition for a polarizing plate containing a component having a coefficient is described. However, these documents do not describe providing the pressure-sensitive adhesive layer directly on the polarizer.

Japanese Unexamined Patent Publication No. 2012-128099 Japanese Unexamined Patent Publication No. 2010-090354 Japanese Patent Publication No. 2004-516359

A polarizing plate in which at least one of the polarizing element protective films conventionally formed on both sides of the polarizer is omitted is required to be further excellent in light leakage prevention property and durability. An object of the present invention is applicable to a configuration in which at least one of the polarizer protective films conventionally formed on both sides of the polarizer is omitted, and provides an adhesive layer having excellent light leakage prevention and durability. There is.

The present inventors have diligently studied to solve the above problems. As a result, it has been found that when the (meth) acrylic copolymer described below and a cross-linking agent are used, the above-mentioned pressure-sensitive adhesive layer having excellent light leakage prevention and durability can be formed. That is, the present inventors have found that the above problems can be solved by using a pressure-sensitive adhesive layer for a polarizing plate having the following specific configuration, and have completed the present invention.

The present invention is, for example, the following [1] to [10].
[1] (meth) acrylic acid alkyl ester (a11) derived constituent units of the homopolymer of photoelastic coefficient of ^{-1000 × 10 -12 ~-100 ×} 10 -12 (m 2 / N), and homopolymers light includes a constitutional unit derived from the aromatic ring-containing (meth) acrylic acid ester (a12) of the elastic modulus is ^{+ 500 × 10 -12 ~ + 2000} × 10 -12 (m 2 / N), photoelastic coefficient of -200 × 10 ^-12 Formed from a pressure-sensitive adhesive composition containing a (meth) acrylic copolymer (A1) of ~ + 200 × 10 ^-12 (m ² / N) and an isocyanate-based cross-linking agent (B1) having no aromatic ring. , photoelastic coefficient is ^{-200 × 10 -12 ~ + 200 ×} 10 -12 (m 2 / N), pressure-sensitive adhesive for polarizing plates layer being disposed in direct contact with the polarizer.

[2] The pressure-sensitive adhesive layer for a polarizing plate according to the above [1], wherein the isocyanate-based cross-linking agent (B1) is a hexamethylene diisocyanate-based cross-linking agent.

[3] The above-mentioned [1] or [2], wherein the pressure-sensitive adhesive composition contains 0.05 to 10 parts by mass of an isocyanate-based cross-linking agent (B1) with respect to 100 parts by mass of the copolymer (A1). Adhesive layer for polarizing plate.

[4] Contains ^{a (meth) acrylic copolymer (A2) having a photoelastic coefficient of less than −200 × 10 -12} (m ² / N) and an isocyanate-based cross-linking agent (B2) having an aromatic ring. For polarizing plates, which are formed from a pressure-sensitive adhesive composition, have a photoelastic coefficient of −200 × 10 ^-12 to ^{+200 × 10 -12} (m ² / N), and are arranged in direct contact with a polarizer. Adhesive layer.

[5] The pressure-sensitive adhesive layer for a polarizing plate according to [4] above, wherein the isocyanate-based cross-linking agent (B2) is at least one selected from a tolylene diisocyanate-based cross-linking agent and a xylylene diisocyanate-based cross-linking agent.

[6] The polarizing plate according to the above [4] or [5], wherein the pressure-sensitive adhesive composition contains 2 parts by mass or more of an isocyanate-based cross-linking agent (B2) with respect to 100 parts by mass of the copolymer (A2). Adhesive layer for.

[7] A pressure-sensitive adhesive sheet for a polarizing plate having the pressure-sensitive adhesive layer according to any one of the above [1] to [6].

[8] A polarizing plate with an adhesive layer having a polarizing element and an adhesive layer according to any one of [1] to [6], which is directly laminated on at least one surface of the polarizer.

[9] (meth) acrylic acid alkyl ester (a11) derived constituent units of the homopolymer of photoelastic coefficient of ^{-1000 × 10 -12 ~-100 ×} 10 -12 (m 2 / N), and homopolymers light includes a constitutional unit derived from the aromatic ring-containing (meth) acrylic acid ester (a12) of the elastic modulus is ^{+ 500 × 10 -12 ~ + 2000} × 10 -12 (m 2 / N), photoelastic coefficient of -200 × 10 ^-12 ~ + 200 × 10 ^-12 (m ² / N) (meth) acrylic copolymer (A1) and an isocyanate-based cross-linking agent (B1) having no aromatic ring, according to the above [1]. A pressure-sensitive adhesive composition for a polarizing plate used for forming the pressure-sensitive adhesive layer of the above.

[10] Contains ^{a (meth) acrylic copolymer (A2) having a photoelastic coefficient of less than −200 × 10 -12} (m ² / N) and an isocyanate-based cross-linking agent (B2) having an aromatic ring. , A pressure-sensitive adhesive composition for a polarizing plate used for forming the pressure-sensitive adhesive layer according to the above [4].

According to the present invention, it is applicable to a configuration in which at least one of the polarizing element protective films conventionally formed on both sides of the polarizer is omitted, and an adhesive layer having excellent light leakage prevention and durability is provided. be able to.

Hereinafter, the pressure-sensitive adhesive composition for a polarizing plate, the pressure-sensitive adhesive layer for a polarizing plate, the pressure-sensitive adhesive sheet for a polarizing plate, and the polarizing plate with a pressure-sensitive adhesive layer of the present invention will be described. Hereinafter, the pressure-sensitive adhesive composition for a polarizing plate, the pressure-sensitive adhesive layer for a polarizing plate, and the pressure-sensitive adhesive sheet for a polarizing plate of the present invention are also referred to as "adhesive composition", "adhesive layer", and "adhesive sheet", respectively.

[Adhesive composition for polarizing plate]
The first pressure-sensitive adhesive composition for a polarizing plate of the present invention contains a (meth) acrylic copolymer (A1) ^{having a photoelastic coefficient of −200 × 10 -12} to +200 × 10 ^-12 (m ^{2 / N).} It contains an isocyanate-based cross-linking agent (B1) that does not have an aromatic ring, and is used to form an adhesive layer that is in direct contact with a polarizing element.

By cross-linking a (meth) acrylic copolymer having a photoelastic coefficient in the above range with an isocyanate-based cross-linking agent having no aromatic ring and having a small contribution to the photoelastic coefficient of the pressure-sensitive adhesive layer, the photoelastic coefficient there can be formed a pressure-sensitive adhesive layer in the ^{-200 × 10 -12 ~ + 200 ×} 10 -12 (m 2 / N).

The second pressure-sensitive adhesive composition for a polarizing plate of the present invention contains a (meth) acrylic copolymer (A2) having a ^{photoelastic coefficient of less than −200 × 10 -12} (m ^{2 / N) and an aromatic ring.} It contains an isocyanate-based cross-linking agent (B2) and is used to form a pressure-sensitive adhesive layer in direct contact with a polarizer.

By cross-linking a (meth) acrylic copolymer having a negative photoelastic coefficient with an isocyanate-based cross-linking agent having an aromatic ring that shifts the photoelastic coefficient of the pressure-sensitive adhesive layer to the positive side, the photoelastic coefficient is -200. The pressure-sensitive adhesive layer at × 10 ^{-12 to +200} × 10 -12 (m ² / N) can be formed.

In the present specification, the copolymers (A1) and (A2) are also collectively referred to as "copolymer (A)", and the first and second pressure-sensitive adhesive compositions of the present invention are used, respectively. They are also referred to as "first pressure-sensitive adhesive composition" and "second pressure-sensitive adhesive composition", and these are also collectively referred to as "the pressure-sensitive adhesive composition of the present invention".

In the present specification, acrylics and methacryl are also collectively referred to as "(meth) acrylics". Further, the structural unit derived from a certain monomer A contained in the polymer is also described as "monomer A unit". Further, a certain ester (a) may be referred to as "monomer (a)" for convenience.

Unless otherwise specified in the present specification, the unit of the photoelastic coefficient of the homopolymer, the (meth) acrylic copolymer and the pressure-sensitive adhesive layer formed from each monomer is "× 10 ^-12 m ² / N". is there. Further, for example, ^{-200 × 10 -12 ~ + 200 ×} 10 -12 (m 2 / N) ^{is, -200 × 10 -12 (m 2} / N) or more, + 200 × 10 ^-12 to (m ² / N) or less means. The same applies to other numerical ranges.

The photoelastic modulus of the homopolymer formed from each monomer is determined as follows.
The homopolymer used for measuring the photoelastic coefficient is prepared by the following procedure. A reactor equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen introduction tube is charged with 100 parts by mass of a monomer and 100 parts by mass of an ethyl acetate solvent, and the temperature is raised to 80 ° C. while introducing nitrogen gas. Next, 0.1 part by mass of 2,2'-azobisisobutyronitrile is added, and the polymerization reaction is carried out at 80 ° C. for 6 hours in a nitrogen gas atmosphere. After completion of the reaction, the mixture is diluted with ethyl acetate to prepare a homopolymer solution of the monomer having a solid content concentration of 30% by mass.

The homoholimer solution is applied to the peeled surface of the stripped polyethylene terephthalate film and dried at 90 ° C. for 3 minutes to form a coating film (homopolymer layer) having a dry film thickness of 20 μm. Homopolymer layers with a dry film thickness of 20 μm were bonded together multiple times in a 23 ° C./50% RH environment and treated in an autoclave adjusted to 50 ° C./5 atm for 20 minutes to form a 1.0 mm thick homopolymer layer. To make.

A 1.0 mm thick homopolymer layer is cut into a size of 15 mm × 50 mm, and this is attached to an automatic wavelength scanning ellipsometer (model “M-220”, manufactured by JASCO Corporation) using a jig. , The retardation is measured at a measurement wavelength of 633 nm while changing the stress. The plot when stress is on the horizontal axis and retardation is on the vertical axis is linearly approximated, and the slope is taken as the photoelastic coefficient of the homopolymer formed from the above-mentioned monomer.

For the glass transition temperature (Tg) of the homopolymer formed from each monomer, for example, the value described in Polymer Handbook Fourth Edition (Wiley-Interscience 2003) can be adopted.
For monomers for which Tg is not described in the above document, for example, Tg of a homopolymer synthesized under the following conditions is measured under the following conditions. A reactor equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen introduction tube is charged with 100 parts by mass of a monomer and 100 parts by mass of an ethyl acetate solvent, and the temperature is raised to 80 ° C. while introducing nitrogen gas. Next, 0.1 part by mass of 2,2'-azobisisobutyronitrile is added, and the polymerization reaction is carried out at 80 ° C. for 6 hours in a nitrogen gas atmosphere. The obtained homopolymer is sealed in a simple airtight pan. Using a differential scanning calorimeter (DSC), the temperature is raised at 10 ° C./min under a nitrogen stream to measure the thermal change, and a graph of "heat absorption and calorific value" and "temperature" is drawn and observed at this time. The characteristic variation is the glass transition. For Tg, a value obtained from the DSC curve by the midpoint method is used.

[(Meta) acrylic copolymer (A1)]
The (meth) acrylic copolymer (A1) has a constituent unit derived from the (meth) acrylic acid alkyl ester (a11) having a photoelastic coefficient of -1000 to -100 of the homopolymer and a photoelastic coefficient of +500 for the homopolymer. It has a constituent unit derived from the aromatic ring-containing (meth) acrylic acid ester (a12) of ~ +2000. The copolymer (A1) is, for example, a copolymer obtained by copolymerizing a monomer component containing a monomer (a11) and a monomer (a12).

The monomer component (that is, the raw material monomer component of (A1)) is preferably a polymerizable unsaturated double bond-containing monomer.
The photoelastic modulus of the (meth) acrylic copolymer (A1) is −200 to +200, preferably −100 to +100, and more preferably −70 to +70.

By copolymerizing a monomer (a11) having a negative photoelastic coefficient of a homopolymer and a monomer (a12) having a positive photoelastic coefficient of a homopolymer, a copolymer (A1) having a photoelastic coefficient in the above range is obtained. be able to. By using the copolymer (A1) and the isocyanate-based cross-linking agent (B1) having no aromatic ring, the photoelastic coefficient of the pressure-sensitive adhesive layer can be brought close to the range described later, particularly 0. Light leakage in the polarizing plate can be suppressed.

<< (Meta) Acrylic Acid Alkyl Ester (a11) (Monomer (a11)) >>
The monomer (a11) is a (meth) acrylic acid alkyl ester having a photoelastic modulus of −1000 to -100 of a homopolymer. The monomer having a photoelastic coefficient of the homopolymer of -750 to -150 is preferable, and the monomer having a photoelastic coefficient of -500 to -200 is more preferable.

By using the copolymer (A1) obtained by copolymerizing the monomer (a11) having the photoelastic coefficient in the above range of the homopolymer, the pressure-sensitive adhesive layer is softened and the light leakage prevention property is exhibited. be able to.

The monomer (a11) is preferably a (meth) acrylic acid alkyl ester having a homopolymer Tg of −30 ° C. or lower, and the Tg is more preferably −100 to −30 ° C., still more preferably −70 to −30. ℃.

Examples of the monomer (a11) include compounds in which the photoelastic coefficient of the homopolymer is in the above range among the compounds represented by _{CH 2} = CR ¹ −COOR ^2. In the formula, R ¹ is a hydrogen atom or a methyl group, and R ² is an alkyl group having 1 to 20 carbon atoms. The alkyl group preferably has 2 to 16 carbon atoms, more preferably 4 to 12 carbon atoms.

Examples of the monomer (a11) include n-butyl acrylate (-400; -50), 2-ethylhexyl acrylate (-700; -70), isodecyl methacrylate (-190; -41), and lauryl methacrylate (-460;). -65) can be mentioned. The numerical values in parentheses indicate the photoelastic modulus (× 10 ^-12 m ² / N) on the left side and Tg (° C.) on the right side of the homopolymer formed from each monomer.

The monomer (a11) may be used alone or in combination of two or more. When two or more kinds of monomers (a11) are used, it is preferable that each monomer satisfies the requirements of photoelastic modulus and Tg.

The amount of the monomer (a11) used in 100% by mass of the raw material monomer component of the copolymer (A1) is preferably 50 to 90% by mass, more preferably 55 to 85% by mass, and further preferably 60 to 80% by mass. %. When the amount of the monomer (a11) used is in the above range, the photoelastic coefficient of the obtained copolymer (A1) can be adjusted within the above range, which is preferable.

<< Aromatic ring-containing (meth) acrylic acid ester (a12) (monomer (a12)) >>
The monomer (a12) is an aromatic ring-containing (meth) acrylic acid ester having a photoelastic modulus of +500 to +2000 as a homopolymer. The monomer having a photoelastic coefficient of the homopolymer of +700 to +1950 is preferable, and the monomer having a photoelastic coefficient of +800 to +1900 is more preferable.

By using a copolymer (A1) obtained by copolymerizing a monomer (a12) having a photoelastic modulus in the above range of the homopolymer, appropriate durability can be imparted to the pressure-sensitive adhesive layer.
The monomer (a12) is preferably an aromatic ring-containing (meth) acrylic acid ester having a homopolymer Tg of −50 ° C. or higher, and the Tg is more preferably -40 to 130 ° C., still more preferably -30 to 120 ° C. ℃.

Examples of the monomer (a12) include compounds in which the photoelastic coefficient of the homopolymer is in the above range among the compounds represented by _{CH 2} = CR ^3- COOR ^4. In the formula, R ³ is a hydrogen atom or a methyl group, and R ⁴ is an aromatic ring-containing group. Examples of the aromatic ring-containing group include an aryl group such as a phenyl group, an arylalkyl group such as a benzyl group, and an aryloxyalkyl group such as a phenoxyethyl group. The carbon number of R ⁴ is preferably 6 to 12, more preferably 6 to 10, and even more preferably 7 to 9.

Examples of the monomer (a12) include benzyl acrylate (1840; 6), benzyl methacrylate (1530; 54), and phenoxyethyl acrylate (1830; -22). The numerical values in parentheses indicate the photoelastic modulus (× 10 ^-12 m ² / N) on the left side and Tg (° C.) on the right side of the homopolymer formed from each monomer. In addition, examples of the monomer (a12) include phenyl acrylate, phenyl methacrylate, and phenoxyethyl methacrylate.

The monomer (a12) may be used alone or in combination of two or more. When two or more kinds of monomers (a12) are used, it is preferable that each monomer satisfies the requirements of photoelastic modulus and Tg.

The amount of the monomer (a12) used is preferably 9 to 40% by mass, more preferably 12 to 35% by mass, and further preferably 15 to 30% by mass in 100% by mass of the raw material monomer component of the copolymer (A1). %. When the amount of the monomer (a12) used is in the above range, the photoelastic coefficient of the obtained copolymer (A1) can be adjusted within the above range, which is preferable.

<< Crosslinkable Functional Group-Containing Monomer (a13) >>
The raw material monomer component of the copolymer (A1) preferably further contains a monomer having a crosslinkable functional group capable of reacting with the isocyanate-based crosslinking agent (B1), that is, a crosslinkable functional group-containing monomer (a13). .. That is, it is preferable that the copolymer (A1) further has a structural unit derived from the monomer (a13).

The monomer (a13) preferably has a polymerizable unsaturated double bond.
Examples of the crosslinkable functional group include a hydroxyl group and a carboxyl group. Examples of the monomer (a13) include a hydroxyl group-containing monomer and a carboxyl group-containing monomer.

Examples of the hydroxyl group-containing monomer include hydroxyl group-containing (meth) acrylates, and specifically, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 4-hydroshikibutyl (meth) acrylate. , 6-Hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate and other hydroxyalkyl (meth) acrylates. The number of carbon atoms of the hydroxyalkyl group in the hydroxyalkyl (meth) acrylate is usually 2 to 8, preferably 2 to 6.

Examples of the carboxyl group-containing monomer include β-carboxyethyl (meth) acrylate, 5-carboxypentyl (meth) acrylate, mono (meth) acryloyloxyethyl ester of succinate, and ω-carboxypolycaprolactone mono (meth) acrylate. Carboxyl group-containing (meth) acrylates such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, maleic acid and the like.

The monomer (a13) may be used alone or in combination of two or more.
The amount of the monomer (a13) used in 100% by mass of the raw material monomer component of the copolymer (A1) is preferably more than 0% by mass and 10% by mass or less, more preferably 0.5 to 7% by mass. More preferably, it is 1 to 5% by mass. When the amount of the monomer (a13) used is not more than the above upper limit value, the cross-linking density formed by the copolymer (A1) and the cross-linking agent (B1) does not become too high. When the amount of the monomer (a13) used is not less than the lower limit, the crosslinked structure is effectively formed, and a pressure-sensitive adhesive layer having appropriate strength can be obtained.

<< Other monomers >>
As the raw material monomer component of the copolymer (A1), for example, an alkyl (meth) acrylate, an alkoxyalkyl (meth) acrylate, and an alkoxy other than the above-mentioned monomer (a11) are used as long as the physical properties of the copolymer (A1) are not impaired. Other monomers such as polyalkylene glycol mono (meth) acrylate, alicyclic group-containing (meth) acrylate, amino group-containing monomer, and amide group-containing monomer can also be used. That is, the copolymer (A1) may further have a structural unit derived from other monomers.

Examples of the alkyl (meth) acrylate other than the monomer (a11) include methyl acrylate (600; 8), t-butyl methacrylate (130; 118), n-butyl methacrylate (320; 20), and 2-ethylhexyl methacrylate (2). 420; -10) can be mentioned. The numerical values in parentheses indicate the photoelastic modulus (× 10 ^-12 m ² / N) on the left side and Tg (° C.) on the right side of the homopolymer formed from each monomer.

Examples of the alkoxyalkyl (meth) acrylate include methoxymethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxypropyl (meth) acrylate, and 3-ethoxypropyl (meth) acrylate. Examples thereof include meta) acrylate, 4-methoxybutyl (meth) acrylate, and 4-ethoxybutyl (meth) acrylate.

Examples of the alkoxypolyalkylene glycol mono (meth) acrylate include methoxydiethylene glycol mono (meth) acrylate, methoxydipropylene glycol mono (meth) acrylate, ethoxytriethylene glycol mono (meth) acrylate, and ethoxydiethylene glycol mono (meth) acrylate. Examples thereof include methoxytriethylene glycol mono (meth) acrylate.

Examples of the alicyclic group-containing (meth) acrylate include cyclohexyl (meth) acrylate.
Examples of the amino group-containing monomer include amino group-containing (meth) acrylates such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate.

Examples of the amide group-containing monomer include (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, and N-hexyl (meth) acrylamide.

The other monomers may be used alone or in combination of two or more.
The total amount of the other monomers used in 100% by mass of the raw material monomer component of the copolymer (A1) is not particularly limited as long as the photoelastic coefficient of (A1) is within the above range, but is 0 to 10% by mass. It is preferably 0 to 5% by mass, more preferably 0 to 5% by mass.

[(Meta) acrylic copolymer (A2)]
The (meth) acrylic copolymer (A2) is a copolymer having a photoelastic modulus of less than −200, preferably −500 or more and less than −200, and more preferably −300 or more and less than −200. Such a copolymer has, for example, a structural unit derived from a (meth) acrylic acid alkyl ester (a21) having a photoelastic coefficient of less than −200 of a homopolymer, and for example, a monomer component containing the monomer (a21). Is obtained by copolymerizing.

The monomer component (that is, the raw material monomer component of (A2)) is preferably a polymerizable unsaturated double bond-containing monomer.
By using the copolymer (A2) and the isocyanate-based cross-linking agent (B2) having an aromatic ring, the photoelastic coefficient of the pressure-sensitive adhesive layer can be brought close to the range described later, particularly 0, whereby the polarizing plate can be used. It is possible to suppress light leakage in.

<< (Meta) Acrylic Acid Alkyl Ester (a21) (Monomer (a21)) >>
As the monomer (a21), an ester having a homopolymer photoelastic modulus of less than −200 among the above-mentioned (meth) acrylic acid alkyl esters (a11) can be exemplified. The monomer having a photoelastic coefficient of -750 or more and less than -200 of the homopolymer is preferable, and the monomer having a photoelastic coefficient of -500 or more and less than -200 is more preferable.

The monomer (a21) may be used alone or in combination of two or more. When two or more kinds of monomers (a21) are used, it is preferable that each monomer satisfies the requirement of photoelastic modulus.

The amount of the monomer (a21) used is preferably 59 to 99% by mass, more preferably 64 to 98% by mass, and further preferably 69 to 97% by mass in 100% by mass of the raw material monomer component of the copolymer (A2). %. When the amount of the monomer (a21) used is within the above range, the photoelastic coefficient of the obtained copolymer (A2) can be adjusted within the above range, which is preferable.

<< Crosslinkable Functional Group-Containing Monomer (a22) >>
The raw material monomer component of the copolymer (A2) preferably further contains a monomer having a crosslinkable functional group capable of reacting with the isocyanate-based crosslinking agent (B2), that is, a crosslinkable functional group-containing monomer (a22). .. That is, it is preferable that the copolymer (A2) further has a structural unit derived from the monomer (a22).

As the monomer (a22), the above-mentioned crosslinkable functional group-containing monomer (a13) can be exemplified, and the same applies to preferred examples. The monomer (a22) may be used alone or in combination of two or more.

The amount of the monomer (a22) used in 100% by mass of the raw material monomer component of the copolymer (A2) is preferably more than 0% by mass and 10% by mass or less, more preferably 0.5 to 7% by mass. More preferably, it is 1 to 5% by mass. When the amount of the monomer (a22) used is not more than the above upper limit value, the cross-linking density formed by the copolymer (A2) and the cross-linking agent (B2) does not become too high. When the amount of the monomer (a22) used is not less than the lower limit, the crosslinked structure is effectively formed, and a pressure-sensitive adhesive layer having appropriate strength can be obtained.

<< Other monomers >>
As the raw material monomer component of the copolymer (A2), for example, an alkyl (meth) acrylate, an alkoxyalkyl (meth) acrylate, and an alkoxy other than the above-mentioned monomer (a21) are used as long as the physical properties of the copolymer (A2) are not impaired. Other monomers such as polyalkylene glycol mono (meth) acrylate, alicyclic group-containing (meth) acrylate, aromatic ring-containing (meth) acrylate, amino group-containing monomer, and amide group-containing monomer can also be used. That is, the copolymer (A2) may further have a structural unit derived from other monomers.

Examples of these monomers include the respective compounds described in << Other Monomers >> in the column of copolymer (A1). Examples of the aromatic ring-containing (meth) acrylate include phenyl (meth) acrylate, benzyl (meth) acrylate, and phenoxyethyl (meth) acrylate.

However, the (meth) acrylic acid alkyl ester having a photoelastic coefficient of +100 to +1000 for the homopolymer, and the aromatic ring-containing (meth) acrylic acid ester having a photoelastic coefficient of +500 to +2000 for the homopolymer (monomer (a12) described above). The amount of the copolymer (A2) used is preferably adjusted as appropriate from the viewpoint of adjusting the photoelastic coefficient of the copolymer (A2) within the above range.

Examples of the (meth) acrylic acid alkyl ester having a photoelastic coefficient of the homopolymer of +100 to +1000 include methyl acrylate (600), t-butyl methacrylate (130), n-butyl methacrylate (320), and 2-ethylhexyl methacrylate. 420). The numbers in parentheses indicate the photoelastic modulus (× 10 ^-12 m ² / N) of the homopolymer formed from each monomer.

The other monomers may be used alone or in combination of two or more.
The total amount of the other monomers used in 100% by mass of the raw material monomer component of the copolymer (A2) is not particularly limited as long as the photoelastic coefficient of (A2) is within the above range, but is 0 to 35% by mass. It is preferably 0 to 30% by mass, more preferably 0 to 26% by mass.

[Production conditions for (meth) acrylic copolymer (A)]
The production conditions of the (meth) acrylic copolymer (A) are not particularly limited, but the (meth) acrylic copolymer (A) can be produced, for example, by a solution polymerization method. Specifically, a polymerization solvent and a monomer component are charged in a reaction vessel, a polymerization initiator is added, the reaction start temperature is usually set to 40 to 100 ° C., preferably 50 to 90 ° C., and the reaction system is usually set to 40 to 90 ° C. The reaction is carried out at a temperature of 50 to 90 ° C., preferably 70 to 90 ° C. for 2 to 20 hours. The polymerization reaction can be carried out in an atmosphere of an inert gas such as nitrogen gas, for example.

The copolymer (A) is obtained, for example, by copolymerizing the above-mentioned monomer components, but it may be a random copolymer or a block copolymer. Of these, random copolymers are preferred.

Examples of the polymerization solvent include aromatic hydrocarbons such as benzene, toluene and xylene; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane; cyclopentane, cyclohexane and cycloheptane. , Cyclooctane and other alicyclic hydrocarbons; diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, phenylethyl ether, diphenyl ether and other ethers; chloroform, carbon tetrachloride, etc. Halogenized hydrocarbons such as 1,2-dichloroethane and chlorobenzene; esters such as ethyl acetate, propyl acetate, butyl acetate and methyl propionate; ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone and cyclohexanone; N , N-Dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone and other amides; acetonitrile, benzonitrile and other nitriles; dimethylsulfoxide, sulfolane and other sulfoxides. These polymerization solvents may be used alone or in combination of two or more.

Examples of the polymerization initiator include an azo-based initiator and a peroxide-based initiator. Specific examples thereof include azo compounds such as 2,2'-azobisisobutyronitrile and peroxides such as benzoyl peroxide and lauroyl peroxide. Among these, the azo compound is preferable. Examples of the azo compound include 2,2'-azobisisobutyronitrile, 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), and 2,2'-azobis (2-cyclopropyl). Propionitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2-methylbutyronitrile), 1,1'-azobis (cyclohexane-1-carbonitrile) , 2- (Carbamoylazo) isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis ( N, N'-Azobisisobutyamidine), 2,2'-azobis (isobutylamide) dihydrate, 4,4'-azobis (4-cyanopentanoic acid), 2,2'-azobis (2-cyanopropanol), Examples thereof include dimethyl-2,2'-azobis (2-methylpropionate) and 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide]. These polymerization initiators may be used alone or in combination of two or more.

The polymerization initiator is usually in the range of 0.01 to 5 parts by mass, preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the raw material monomer component of the (meth) acrylic copolymer (A). Used in quantity. Further, a polymerization initiator, a chain transfer agent, a monomer component, and a polymerization solvent may be additionally added as appropriate during the above-mentioned polymerization reaction.

[Physical characteristics and content of (meth) acrylic copolymer (A)]
The photoelastic modulus of the (meth) acrylic copolymer (A) is as described above.
The weight average molecular weight (Mw) of the (meth) acrylic copolymer (A) measured by the gel permeation chromatography method (GPC method) is a polystyrene-equivalent value, usually 300,000 to 2,000,000, which is preferable. Is 400,000 to 1.8 million, more preferably 500,000 to 1.5 million. By using the copolymer (A) having Mw in the above range and having the above-mentioned monomer unit, it is possible to easily balance the adhesive force and obtain a pressure-sensitive adhesive composition having a viscosity suitable for coating. Further, by using the copolymer (A) having Mw of 500,000 or more, a pressure-sensitive adhesive layer having higher durability can be obtained.

The molecular weight distribution (Mw / Mn) of the (meth) acrylic copolymer (A) measured by the GPC method is usually 20 or less, preferably 2 to 15, and more preferably 2 to 9.
The glass transition temperature (Tg) of the (meth) acrylic copolymer (A) can be calculated, for example, from the monomer units constituting the copolymer and the content ratio thereof by the Fox formula. For example, the (meth) acrylic copolymer (A) is synthesized so that the glass transition temperature (Tg) determined by the Fox formula is usually −70 to −10 ° C., preferably −60 to −20 ° C. It is preferable to do so. By using the (meth) acrylic copolymer (A) having such a glass transition temperature (Tg), a pressure-sensitive adhesive composition having excellent stress relaxation characteristics and durability and excellent adhesiveness at room temperature can be obtained. be able to.
Fox formula: 1 / Tg = (W ₁ / Tg ₁ ) + (W ₂ / Tg ₂ ) + ... + (W _m / Tg _m )
W ₁ + W ₂ + ... + W _m = 1
In the formula, Tg is the glass transition temperature (K) of the (meth) acrylic copolymer (A), and Tg ₁ , Tg ₂ , ..., Tg _m is the glass transition temperature (K) of the homopolymer composed of each monomer. W ₁ , W ₂ , ..., W _m are the weight fractions of the constituent units derived from each monomer in the copolymer (A). As the weight fraction of the structural unit derived from each monomer, the charging ratio of each monomer to all the monomers at the time of copolymer synthesis can be used.

For the glass transition temperature of the homopolymer composed of each monomer in the Fox formula, for example, the value described in Polymer Handbook Fourth Edition (Wiley-Interscience 2003) can be used. For the monomers for which Tg is not described in the above-mentioned documents, for example, the values obtained by the above-mentioned method are used.

In the first pressure-sensitive adhesive composition, the content of the (meth) acrylic copolymer (A1) is usually 60 to 99.95% by mass in 100% by mass of the solid content excluding the organic solvent in the composition. It is preferably 70 to 99.5% by mass, and particularly preferably 80 to 99.0% by mass. When the content of the (meth) acrylic copolymer (A1) is within the above range, the performance as an adhesive is balanced and the adhesive properties are excellent.

In the second pressure-sensitive adhesive composition, the content of the (meth) acrylic copolymer (A2) is usually 60 to 98.0% by mass in 100% by mass of the solid content excluding the organic solvent in the composition. It is preferably 70 to 96.2% by mass, and particularly preferably 80 to 92.6% by mass. When the content of the (meth) acrylic copolymer (A2) is within the above range, the performance as an adhesive is balanced and the adhesive properties are excellent.

[Crosslinking agent (B)]
The first pressure-sensitive adhesive composition further contains an isocyanate-based cross-linking agent (B1) having no aromatic ring. The second pressure-sensitive adhesive composition further contains an isocyanate-based cross-linking agent (B2) having an aromatic ring.

<< Isocyanate-based cross-linking agent (B1) >>
As the isocyanate-based cross-linking agent (B1), an isocyanate compound having two or more isocyanate groups in one molecule and having no aromatic ring is usually used. By cross-linking the (meth) acrylic copolymer (A1) with a cross-linking agent (B1), a cross-linked product (network polymer) having excellent durability can be formed. Further, by using a cross-linking agent (B1) having no aromatic ring together with a copolymer (A1) having a photoelastic coefficient in the range of -200 to +200, adhesion having a photoelastic coefficient in the range of -200 to +200 A drug layer can be formed.

The number of isocyanate groups of the cross-linking agent (B1) is usually 2 or more, preferably 2 to 8, and more preferably 3 to 6. When the number of isocyanate groups is within the above range, it is preferable in terms of the cross-linking reaction efficiency between the (meth) acrylic copolymer (A1) and the cross-linking agent (B1) and the flexibility of the pressure-sensitive adhesive layer.

Examples of the diisocyanate compound having 2 isocyanate groups in one molecule include aliphatic diisocyanates and alicyclic diisocyanates. Examples of the aliphatic diisocyanate include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, 2,2,4. Examples thereof include aliphatic diisocyanates having 4 to 30 carbon atoms such as −trimethyl-1,6-hexamethylene diisocyanate. Examples of the alicyclic diisocyanate include isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and hydrogenated tetramethylxylylene diisocyanate having 7 to 30 carbon atoms. An alicyclic diisocyanate can be mentioned.

Examples of the isocyanate compound having 3 or more isocyanate groups in one molecule include aliphatic polyisocyanates and alicyclic polyisocyanates.
The cross-linking agent (B1) includes, for example, a multimer (for example, a dimer or a trimer, a biuret, or an isocyanurate) or a derivative (for example, a polymer) of the above-mentioned isocyanate compound having 2 or 3 or more isocyanate groups. Addition reaction products of valent alcohols and two or more molecules of the diisocyanate compound), polymers and the like. Examples of the polyhydric alcohol in the derivative include trihydric or higher alcohols such as trimethylolpropane, glycerin, and pentaerythritol as low molecular weight polyhydric alcohols; and examples of high molecular weight polyhydric alcohols include polyether polyols. Examples thereof include polyester polyols, acrylic polyols, polybutadiene polyols, and polyisoprene polyols.

Examples of such an isocyanate compound include a biuret or isocyanurate form of hexamethylene diisocyanate, a reaction product of trimethylolpropane and hexamethylene diisocyanate (for example, a three-molecule addition of hexamethylene diisocyanate), and a polyether polyisocyanate. Polyester polyisocyanate can be mentioned.

Among the cross-linking agents (B1), hexamethylene diisocyanate-based cross-linking agents are preferable because they can improve aging properties and light leakage prevention properties. Examples of the hexamethylene diisocyanate-based cross-linking agent include hexamethylene diisocyanate and its derivatives, biuret and isocyanurates. Examples of commercially available products include "D-94" manufactured by Soken Chemical Co., Ltd.

The cross-linking agent (B1) may be used alone or in combination of two or more.
In the first pressure-sensitive adhesive composition, the content of the cross-linking agent (B1) is usually 0.05 to 10 parts by mass, preferably 0, based on 100 parts by mass of the (meth) acrylic copolymer (A1). .5 to 8 parts by mass, more preferably 1 to 5 parts by mass. When the content of the cross-linking agent (B1) is within the above range, it is preferable that the durability and the light leakage prevention property can be easily balanced.

<< Isocyanate-based cross-linking agent (B2) >>
As the isocyanate-based cross-linking agent (B2), an isocyanate compound having an aromatic ring and having two or more isocyanate groups in one molecule is usually used. By cross-linking the (meth) acrylic copolymer (A2) with a cross-linking agent (B2), a cross-linked product (network polymer) having excellent durability can be formed. Further, by using a cross-linking agent (B2) having an aromatic ring together with a copolymer (A2) having a photoelastic coefficient in the range of less than -200, a pressure-sensitive adhesive layer having a photoelastic coefficient in the range of -200 to +200 can be obtained. Can be formed.

The number of isocyanate groups of the cross-linking agent (B2) is usually 2 or more, preferably 2 to 8, and more preferably 3 to 6. When the number of isocyanate groups is within the above range, it is preferable in terms of the cross-linking reaction efficiency between the (meth) acrylic copolymer (A2) and the cross-linking agent (B2) and the flexibility of the pressure-sensitive adhesive layer.

Examples of the diisocyanate compound having 2 isocyanate groups in one molecule include aromatic diisocyanates. Examples of the aromatic diisocyanate include aromatic diisocyanates having 8 to 30 carbon atoms such as phenylenediocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, and diphenylpropane diisocyanate.

Examples of the isocyanate compound having 3 or more isocyanate groups in one molecule include aromatic polyisocyanates. Specific examples thereof include 2,4,6-triisocyanate toluene, 1,3,5-triisocyanatebenzene, and 4,4', 4 "-triphenylmethane triisocyanate.

The cross-linking agent (B2) includes, for example, a multimer (for example, a dimer or a trimer, a biuret, or an isocyanurate) or a derivative (for example, a polymer) of the above-mentioned isocyanate compound having 2 or 3 or more isocyanate groups. Addition reaction products of valent alcohols and two or more molecules of the diisocyanate compound), polymers and the like. Examples of the polyhydric alcohol in the derivative include trihydric or higher alcohols such as trimethylolpropane, glycerin, and pentaerythritol as low molecular weight polyhydric alcohols; and examples of high molecular weight polyhydric alcohols include polyether polyols. Examples thereof include polyester polyols, acrylic polyols, polybutadiene polyols, and polyisoprene polyols.

Examples of such an isocyanate compound include a trimer of diphenylmethanediisocyanate, polymethylenepolyphenylpolyisocyanate, a biuret or isocyanurate of tolylene diisocyanate, and reaction formation of trimethylpropane with tolylene diisocyanate or xylylene diisocyanate. Examples thereof include three-molecule additions of tolylene diisocyanate or xylylene diisocyanate, polyether polyisocyanates, and polyester polyisocyanates.

Among the cross-linking agents (B2), at least one selected from a tolylene diisocyanate-based cross-linking agent and a xylylene diisocyanate-based cross-linking agent is preferable because it can improve aging property and light leakage prevention property, and tolylene diisocyanate A system cross-linking agent is more preferable. Examples of the tolylene diisocyanate-based cross-linking agent include tolylene diisocyanate and its derivatives, biuret and isocyanurate. Examples of the xylylene diisocyanate-based cross-linking agent include xylylene diisocyanate and its derivatives, biuret form or isocyanurate form. Examples of commercially available products include "L-45" manufactured by Soken Chemical Co., Ltd.

The cross-linking agent (B2) may be used alone or in combination of two or more.
In the second pressure-sensitive adhesive composition, the content of the cross-linking agent (B2) is usually 2 parts by mass or more, preferably 4 to 30 parts by mass with respect to 100 parts by mass of the (meth) acrylic copolymer (A2). Parts, more preferably 8 to 15 parts by mass. When the content of the cross-linking agent (B2) is in the above range, even a composition containing a copolymer (A2) having a negative photoelastic modulus can form a layer having a photoelastic modulus near 0, and therefore, It is preferable because it is easy to balance durability and light leakage prevention.

<< Other cross-linking agents >>
The first and second pressure-sensitive adhesive compositions contain the above-mentioned cross-linking agent (B1) or other cross-linking agent other than the above-mentioned cross-linking agent (B2), respectively, as long as the photoelastic coefficient of the obtained pressure-sensitive adhesive layer is within the above range. It may be further contained. For example, by using a cross-linking agent that does not significantly shift the photoelastic coefficient of the pressure-sensitive adhesive layer to the plus side together with the above-mentioned cross-linking agent, the durability can be further improved while maintaining the photoelastic coefficient within the range described later. You can also.

The other cross-linking agent is not particularly limited as long as it is a component capable of causing a cross-linking reaction with the cross-linking functional group derived from the cross-linking functional group-containing monomer, and for example, a metal chelate compound (B3) and an epoxy compound (B4). Can be mentioned.

When other cross-linking agents are used in the first and second pressure-sensitive adhesive compositions, the content thereof is preferably 2 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic copolymer (A). It is more preferably 0.01 to 1.5 parts by mass, and further preferably 0.03 to 1 part by mass.

<Metal chelate compound (B3)>
Examples of the metal chelate compound (B3) include polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium and zirconium, as well as alkoxide, acetylacetone and ethyl acetoacetate. Coordinated compounds can be mentioned.

Among these, an aluminum chelate compound is particularly preferable. Specific examples thereof include aluminum isopropylate, aluminum secondary butyrate, aluminum ethyl acetoacetate / diisopropirate, aluminum tris ethyl acetoacetate, and aluminum tris acetyl acetonate. Examples of commercially available products include "M-12AT" manufactured by Soken Chemical Co., Ltd.

The metal chelate compound (B3) may be used alone or in combination of two or more.
The metal chelate compound (B3) crosslinks the (meth) acrylic copolymer (A) by a coordination bond (pseudocrosslink). When the metal chelate compound (B3) is further used as the cross-linking agent, the cross-linking is maintained at room temperature and the polymer exhibits cohesiveness, whereas the cross-linking is partially disintegrated at high temperature and the pressure-sensitive adhesive layer is more excellent. Shows flexibility.

<< Epoxy compound (B4) >>
As the epoxy compound (B4), an epoxy compound having two or more epoxy groups in one molecule is usually used. For example, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,3-bis (N, N-diglycidyl aminomethyl) cyclohexane, N, N, N', N' -Tetraglycidyl-m-xylylene diamine, N, N, N', N'-tetraglycidyl aminophenylmethane, triglycidyl isocyanurate, m-N, N-diglycidyl aminophenyl glycidyl ether, N, N-diglycidyl Examples include truidin and N, N-diglycidyl aniline. Examples of commercially available products include "E-5C" manufactured by Soken Chemical Co., Ltd.

[Silane Coupling Agent (C)]
The pressure-sensitive adhesive composition of the present invention preferably further contains a silane coupling agent (C). The silane coupling agent (C) firmly adheres the pressure-sensitive adhesive layer to an adherend such as a glass plate, and contributes to preventing the polarizing plate from peeling off in a high humidity and heat environment.

Examples of the silane coupling agent (C) include a polymerizable unsaturated group-containing silane coupling agent such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacrypropyltrimethoxysilane; 3-glycidoxypropyltrimethoxysilane. , 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane and other epoxy groups Containing silane coupling agent; amino such as 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane Group-containing silane coupling agent; halogen-containing silane coupling agent such as 3-chloropropyltrimethoxysilane, 3-oxobutanoate-3- (trimethoxysilyl) propyl can be mentioned. Examples of commercially available products include "A-50" manufactured by Soken Chemical Co., Ltd.

In the pressure-sensitive adhesive composition of the present invention, the content of the silane coupling agent (C) is usually 1 part by mass or less, preferably 0 parts by mass, based on 100 parts by mass of the (meth) acrylic copolymer (A). It is 01 to 1 part by mass, more preferably 0.05 to 0.5 part by mass. When the content is within the above range, peeling of the polarizing plate in a high humidity environment and bleeding of the silane coupling agent (C) in a high temperature environment tend to be prevented.

[Antistatic agent (D)]
The antistatic agent (D) can be used, for example, to reduce the surface resistance value of the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention. Examples of the antistatic agent (D) include a surfactant, an ionic compound, and a conductive polymer.

Examples of the surfactant include a cationic surfactant having a cationic group such as a quaternary ammonium salt, an amide quaternary ammonium salt, a pyridium salt, and a primary to tertiary amino group; a sulfonic acid base and a sulfate ester. Anionic surfactants having anionic groups such as bases and phosphate esters; amphoteric surfactants such as alkylbetaines, alkylimidazolinium betaines, alkylamine oxides, amino acid sulfate esters, glycerin fatty acid esters, etc. , Solbitan fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene alkylamine fatty acid esters, N-hydroxyethyl-N-2-hydroxyalkylamines, alkyldiethanolamides and other nonionic surfactants. Be done.

Further, as the surfactant, a reactive emulsifier having a polymerizable group can be mentioned, and a polymer-based surfactant having a high molecular weight of the above-mentioned surfactant or a monomer component containing the reactive emulsifier can also be used.

The ionic compound is composed of a cation portion and an anion portion, and may be in a solid state or a liquid state at room temperature (23 ° C./50% RH).
The cation portion constituting the ionic compound may be either an inorganic cation or an organic cation, or both. As the inorganic cation, alkali metal ion and alkaline earth metal ion are preferable, ^{and Li +} , Na ⁺ and K ⁺ having excellent antistatic properties are more preferable. Examples of the organic cation include pyridinium cation, piperidinium cation, pyrrolidinium cation, pyrolin cation, pyrrole cation, imidazolium cation, tetrahydropyrimidinium cation, dihydropyrimidinium cation, pyrazolium cation, pyrazoli Examples include nium cations, tetraalkylammonium cations, trialkylsulfonium cations, tetraalkylphosphonium cations and derivatives thereof.

The anionic portion constituting the ionic compound is not particularly limited as long as it can form an ionic compound by ionic bonding with the cation moiety. ^{Specifically, F -, Cl -, Br} -, I -, AlCl 4 -, Al 2 Cl 7 -, BF 4 -, PF 6 -, SCN -, ClO 4 -, NO 3 -, CH 3 COO - _{^{, CF 3 COO -, CH 3}} SO 3 -, CF 3 SO 3 -, (CF 3 SO 2) 2 N -, (F 2 SO 2) 2 N -, (CF 3 SO 2) 3 C -, AsF 6 _{^{-, SbF 6 -, NbF 6}} -, TaF 6 -, (CN) 2 N -, C 4 F 9 SO 3 -, (C 2 F 5 SO 2) 2 N -, C 3 F 7 COO - , and (CF _{3 SO 2) (CF 3 CO} ) N - are exemplified. Among these, anions containing fluorine atoms is preferably because it provides a low melting point ionic _{compound, (F 2 SO 2) 2} N - and _{(CF 3 SO 2) 2 N} - is especially preferred.

Examples of the ionic compound include lithium bis (trifluoromethanesulfonyl) imide, lithium bis (difluorosulfonyl) imide, lithium tris (trifluoromethanesulfonyl) methane, potassium bis (trifluoromethanesulfonyl) imide, potassium bis (difluorosulfonyl) imide, and 1 -Ethylpyridinium hexafluorophosphate, 1-butylpyridinium hexafluorophosphate, 1-hexyl-4-methylpyridinium hexafluorophosphate, 1-octyl-4-methylpyridinium hexafluorophosphate, 1-octyl-4-methylpyridinium bis (fluoro) Sulfonyl) imide, 1-octyl-4-methylpyridinium bis (trifluoromethanesulfonyl) imide, tributylmethylammonium bis (fluorosulfonyl) imide, tributylmethylammonium bis (trifluoromethanesulfonyl) imide, (N, N-diethyl-N-) Methyl-N- (2-methoxyethyl) ammonium tetrafluoroborate, N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide, 1-octylpyridinium fluorosphonium imide , 1-octyl-3-methylpyridinium trifluorosulfonium imide is preferred.

Conductive polymers include, for example, polythiophene, polyaniline, polypyrrole and derivatives thereof.
In the pressure-sensitive adhesive composition of the present invention, the content of the antistatic agent (D) is usually 3 parts by mass or less, preferably 0.01 with respect to 100 parts by mass of the (meth) acrylic copolymer (A). It is ~ 3 parts by mass, more preferably 0.05 to 2.5 parts by mass.

[Organic solvent (E)]
The pressure-sensitive adhesive composition of the present invention preferably contains an organic solvent (E) in order to adjust its coatability. Examples of the organic solvent include the solvent exemplified as the polymerization solvent in the column of the production conditions of the (meth) acrylic copolymer (A). For example, a pressure-sensitive adhesive composition can be prepared by mixing a polymer solution containing the (meth) acrylic copolymer (A) and a polymerization solvent obtained by the above-mentioned copolymerization with a cross-linking agent (B). it can. In the pressure-sensitive adhesive composition of the present invention, the content of the organic solvent (E) is usually 50 to 90% by mass, preferably 60 to 85% by mass.

In the present specification, the “solid content” refers to all the components contained in the pressure-sensitive adhesive composition excluding the organic solvent (E), and the “solid content concentration” refers to the pressure-sensitive adhesive composition 100. The ratio of the solid content to the mass%.

[Additive]
In addition to the above components, the pressure-sensitive adhesive composition of the present invention comprises an antioxidant, a light stabilizer, a metal corrosion inhibitor, a pressure-sensitive adhesive, a plasticizer, a cross-linking accelerator, and the above (as long as the effects of the present invention are not impaired. It may contain one or more selected from (meth) acrylic polymers and reworking agents other than A).

[Preparation of adhesive composition for polarizing plate]
The pressure-sensitive adhesive composition of the present invention is prepared by mixing a (meth) acrylic copolymer (A), a cross-linking agent (B), and, if necessary, other components by a conventionally known method. Can be done. For example, a cross-linking agent (B) and, if necessary, other components may be added to a polymer solution containing the polymer obtained when the (meth) acrylic copolymer (A) is synthesized. Be done.

Using the pressure-sensitive adhesive composition of the present invention, a pressure-sensitive adhesive layer is formed on a polarizing plate having a polarizer protective film on only one side of the polarizer and a polarizing plate having no polarizer protective film on both sides of the polarizer. Even when this is done, the light leakage phenomenon can be suppressed. Further, in the present invention, even in a configuration in which the pressure-sensitive adhesive layer is in direct contact with the polarizing element, it is possible to suppress tearing of the pressure-sensitive adhesive layer, peeling of the polarizing plate, and the like in a high-temperature and high-humidity environment.
The above composition is suitable for bonding a substrate constituting a liquid crystal cell and a polarizer.

[Adhesive layer for polarizing plate]
The first pressure-sensitive adhesive layer for a polarizing plate of the present invention is formed from the above-mentioned first pressure-sensitive adhesive composition. The second polarizing plate pressure-sensitive adhesive layer of the present invention is formed from the above-mentioned second pressure-sensitive adhesive composition. The first and second pressure-sensitive adhesive layers are also collectively referred to as "the pressure-sensitive adhesive layer of the present invention".

By using the pressure-sensitive adhesive composition of the present invention, a pressure-sensitive adhesive layer having the following photoelastic properties can be formed. The photoelastic modulus of the pressure-sensitive adhesive layer of the present invention is −200 to +200, preferably −150 to +150, more preferably −100 to +100, and even more preferably −70 to +70. The unit of the photoelastic coefficient is "× 10 ^-12 m ² / N".

The photoelastic coefficient is, for example, bonded to the pressure-sensitive adhesive layers a plurality of times to prepare a laminated body having a thickness of about 1.0 mm, and the laminated body is measured at a measurement wavelength of 633 nm. The details of the measurement conditions are as described in the examples.

Since the pressure-sensitive adhesive layer of the present invention has the above characteristics, it is excellent in light leakage prevention in a high temperature and high humidity environment. Further, since the pressure-sensitive adhesive layer of the present invention has excellent durability, tearing of the pressure-sensitive adhesive layer and peeling of the pressure-sensitive adhesive layer from the polarizing plate are unlikely to occur.

The pressure-sensitive adhesive layer of the present invention has a gel content of preferably 40% by mass or more, more preferably 50 to 97% by mass, still more preferably, from the viewpoint of suppressing distortion of the polarizing plate, cohesive force, adhesive force, and removability. Is 60 to 95% by mass. When the gel fraction is in the above range, the pressure-sensitive adhesive layer exhibits excellent durability. The details of the measurement conditions are as described in the examples.

The pressure-sensitive adhesive layer of the present invention specifically cross-links the (meth) acrylic copolymer (A) with the cross-linking agent (B) by proceeding with the cross-linking reaction in the above-mentioned pressure-sensitive adhesive composition. Obtained by

The conditions for forming the pressure-sensitive adhesive layer are as follows, for example. The pressure-sensitive adhesive composition of the present invention is applied onto a support and varies depending on the type of solvent, but is usually 50 to 150 ° C, preferably 60 to 100 ° C, usually 1 to 10 minutes, preferably 2 to 7. Dry for minutes to remove the solvent and form a coating. The film thickness of the coating film after drying is usually 5 to 75 μm, preferably 10 to 50 μm, and the film thickness of the finally obtained pressure-sensitive adhesive layer is also preferably in the above range. The film thickness can be measured by, for example, a dial thickness gauge.

The pressure-sensitive adhesive layer is preferably formed under the following conditions. After applying the pressure-sensitive adhesive composition of the present invention on a support to form a coating film under the above conditions and, if necessary, attaching a cover film on the coating film, it is usually 3 days or more, preferably 7 to 7 to. It is cured for 10 days in an environment of usually 5 to 60 ° C., preferably 15 to 40 ° C., usually 30 to 70% RH, preferably 40 to 70% RH. When cross-linking is performed under the above-mentioned aging conditions, a cross-linked product (network polymer) can be efficiently formed.

As a method for applying the pressure-sensitive adhesive composition, a known method such as a spin coating method, a knife coating method, a roll coating method, a bar coating method, a blade coating method, a die coating method, a gravure coating method, or the like is used to obtain a predetermined thickness. The method of coating can be used.

Examples of the support and cover film include polyester films such as polyethylene terephthalate (PET); and plastic films such as polyolefin films such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers.

[Adhesive sheet for polarizing plate]
The pressure-sensitive adhesive sheet for a polarizing plate of the present invention has a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention. As the pressure-sensitive adhesive sheet, for example, one of a double-sided pressure-sensitive adhesive sheet having only the pressure-sensitive adhesive layer, a base material, and a double-sided pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layers formed on both sides of the base material, the base material, and the base material. Examples thereof include a single-sided pressure-sensitive adhesive sheet having the above-mentioned pressure-sensitive adhesive layer formed on a surface, and a pressure-sensitive adhesive sheet in which a peel-treated cover film is attached to a surface of the pressure-sensitive adhesive sheet that is not in contact with the base material.

Examples of the base material and the cover film include a polyester film such as polyethylene terephthalate (PET); and a plastic film such as a polyolefin film such as polyethylene, polypropylene, and an ethylene-vinyl acetate copolymer.

The conditions for forming the pressure-sensitive adhesive layer are the same as those described in the column of [Adhesive layer for polarizing plate].
The film thickness of the pressure-sensitive adhesive layer is usually 5 to 75 μm, preferably 10 to 50 μm from the viewpoint of maintaining the pressure-sensitive adhesive performance. The film thickness of the base material and the cover film is not particularly limited, but is usually 10 to 125 μm, preferably 25 to 75 μm.

[Polarizing plate with adhesive layer]
The polarizing plate with a pressure-sensitive adhesive layer of the present invention has a polarizing element and a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention, which is directly laminated on at least one surface of the polarizer. In addition, in this specification, "polarizing plate" is used in the meaning which includes "polarizing film".

As the polarizing plate, a conventionally known polarizing film can be used. For example, a multilayer film having a polarizer itself, a polarizer, and a polarizer protective film arranged on the polarizer can be mentioned. In the present invention, since the pressure-sensitive adhesive layer is arranged in direct contact with the polarizer, for example, the polarizer protective film is arranged on only one side of the polarizer, and the polarizer protective film is not arranged on the other surface. Examples thereof include a configuration in which the polarizer protective film is not arranged on both sides of the polarizer.

Examples of the polarizer include a stretched film obtained by adding a polarizing component to a film made of a polyvinyl alcohol-based resin and stretching the film. Examples of the polyvinyl alcohol-based resin include saponified products of polyvinyl alcohol, polyvinyl formal, polyvinyl acetal, and ethylene-vinyl acetate copolymer. Examples of the polarizing component include iodine and dichroic dyes.

Examples of the polarizer protective film include a film made of a thermoplastic resin. Examples of the thermoplastic resin include cellulose resins such as triacetyl cellulose, polyester resins, polyether sulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins, and cyclic polyolefin resins (norbornene). (Based resin), polyarylate resin, polystyrene resin, polyvinyl alcohol resin, and a mixture of two or more kinds selected from these resins can be mentioned.

The thickness of the polarizing plate is usually 10 to 200 μm, preferably 30 to 100 μm. In the present invention, the polarizing element protective film formed on the polarizer can be omitted, so that the polarizing plate can be made thinner.

In the present invention, the pressure-sensitive adhesive layer is formed in direct contact with the polarizer. The polarizing plate with an adhesive layer of the present invention includes, for example, a structure in which a polarizing element protective film, a polarizer, and the pressure-sensitive adhesive layer are laminated in this order, the pressure-sensitive adhesive layer, the polarizer protective film, the polarizer, and the above. Examples thereof include a structure in which the pressure-sensitive adhesive layer is laminated in this order, and a structure in which the pressure-sensitive adhesive layer, a polarizing element, and the pressure-sensitive adhesive layer are laminated in this order. In these configurations, the cover film described above may be arranged as the outermost layer on the pressure-sensitive adhesive layer.

The method of forming the pressure-sensitive adhesive layer on the surface of the polarizer is not particularly limited, and the method of applying the above-mentioned pressure-sensitive adhesive composition to the surface of the polarizer and drying and aging it, and the method of polarizing the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet for a polarizing plate of the present invention. Examples thereof include a method of attaching or transferring to the surface of a child and aging it. The conditions for drying and aging, the range of gel fraction, etc. are the same as the conditions described in the column of [Adhesive layer for polarizing plate].

The thickness of the pressure-sensitive adhesive layer is usually 5 to 75 μm, preferably 10 to 50 μm. The pressure-sensitive adhesive layer may be formed in contact with the polarizer on at least one surface of the polarizer, and the pressure-sensitive adhesive layer is formed on only one side of the polarizer, and the pressure-sensitive adhesive is formed on both sides of the polarizer. An embodiment in which a layer is formed can be mentioned.

Further, the polarizing plate may be laminated with layers having other functions such as a protective layer, an antiglare layer, a retardation layer, and a viewing angle improving layer.
A liquid crystal element is manufactured by providing the polarizing plate with an adhesive layer of the present invention obtained as described above on the substrate surface of a liquid crystal cell. Here, the liquid crystal cell has a structure in which the liquid crystal layer is sandwiched between two substrates. Examples of the substrate contained in the liquid crystal cell include a glass plate. The thickness of the substrate is usually 0.05 to 3 mm, preferably 0.2 to 1 mm.

Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to these Examples. In the description of the following examples and the like, "parts" means "parts by mass" unless otherwise specified.

[GPC]
The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the (meth) acrylic copolymer were determined by gel permeation chromatography (GPC method) under the following conditions.
-Measuring device: HLC-8320GPC (manufactured by Tosoh Corporation)
-GPC column configuration: The following 4-column column (all manufactured by Tosoh Corporation)
(1) TSKgel HxL-H (guard column)
(2) TSKgel GMHxL
(3) TSKgel GMHxL
(4) TSKgel G2500HxL
・ Flow velocity: 1.0 mL / min
-Column temperature: 40 ° C
-Sample concentration: 1.5% (w / v) (diluted with tetrahydrofuran)
・ Mobile phase solvent: Tetrahydrofuran ・ Standard polystyrene conversion

[Photoelastic coefficient]
The photoelastic modulus of the (meth) acrylic copolymer was measured as follows.
The hollymer solution containing the (meth) acrylic copolymer obtained in the synthetic example was applied to the peeled surface of the peeled polyethylene terephthalate film and dried at 90 ° C. for 3 minutes to obtain a dry film thickness of 20 μm. A coating film (polymer layer) was formed. Polymer layers having a dry film thickness of 20 μm were laminated multiple times in a 23 ° C./50% RH environment and treated in an autoclave adjusted to 50 ° C./5 atm for 20 minutes to prepare a polymer layer having a thickness of 1.0 mm. .. A polymer layer having a thickness of 1.0 mm was cut into a size of 15 mm × 50 mm, and this was attached to an automatic wavelength scanning ellipsometer (model “M-220”, manufactured by JASCO Corporation) using a jig. The retardation was measured at a measurement wavelength of 633 nm while changing the stress. The slope of a straight line when stress is on the horizontal axis and retardation is on the vertical axis is used as the photoelastic modulus of the (meth) acrylic copolymer.

[Synthesis Example 1]
Reactor equipped with stirrer, reflux condenser, thermometer and nitrogen introduction tube, n-butyl acrylate 76.5 parts, phenoxyethyl acrylate 19.0 parts, acrylic acid 1.5 parts, acrylamide 3.0 parts and 100 parts of an ethyl acetate solvent was charged, and the temperature was raised to 80 ° C. while introducing nitrogen gas. Next, 0.1 part of 2,2'-azobisisobutyronitrile was added, and a polymerization reaction was carried out at 80 ° C. for 6 hours in a nitrogen gas atmosphere. After completion of the reaction, the mixture was diluted with ethyl acetate to prepare a polymer solution having a solid content concentration of 30% by mass. The weight average molecular weight (Mw) of the obtained (meth) acrylic copolymer 1 is 800,000, the molecular weight distribution (Mw / Mn) is 7.5, and the photoelastic coefficient is −58 × 10 ^-12 ( It was m ² / N).

[Synthesis Examples 2-3]
The same procedure as in Synthesis Example 1 was carried out except that the monomer components used in the polymerization reaction were changed as shown in Table 1, to prepare a polymer solution having a solid content concentration of 30% by mass. The results are shown in Table 1.

[Example A1]
(1) Preparation of Adhesive Composition With respect to the polymer solution (solid content concentration 30% by mass) obtained in Synthesis Example 1 and 100 parts (solid content) of the (meth) acrylic copolymer contained in the solution. As an isocyanate compound, 2.0 parts (solid content) of "D-94" manufactured by Soken Kagaku Co., Ltd. and 0.2 parts (solid content) of "M-12AT" manufactured by Soken Kagaku Co., Ltd. as a metal chelate compound. As a silane coupling agent, 0.2 part of "A-50" (solid content 100% by mass) manufactured by Soken Kagaku Co., Ltd. was mixed to obtain a pressure-sensitive adhesive composition.

(2) Preparation of Adhesive Sheet The adhesive composition obtained in (1) above is applied onto a peeled polyethylene terephthalate film (PET film) using a doctor blade after defoaming, and at 90 ° C. It was dried for 3 minutes to form a coating film having a dry film thickness of 20 μm. The peeled PET film is further attached to the surface of the coating film opposite to the surface on which the PET film is attached, and allowed to stand for 7 days in a 23 ° C./50% RH environment for aging to obtain two PET films. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a thickness of 20 μm sandwiched between the two was obtained.

(3) Preparation of Polarizing Plate with Adhesive Layer The adhesive composition obtained in (1) above is applied onto a stripped polyethylene terephthalate film (PET film) using a doctor blade after defoaming. , 90 ° C. for 3 minutes to obtain a sheet having a coating film having a dry film thickness of 20 μm. The coating surface of the sheet is in contact with the polyvinyl alcohol film surface of a two-layered (60 μm thick) polarizing plate composed of a polyvinyl alcohol film as a polarizer and a triacetyl cellulose film as a polarizer protective film. A polarizing plate with an adhesive layer having a PET film, a 20 μm-thick adhesive layer, a polarizer, and a polarizer protective film. Got

[Examples B1 to B2, Comparative Examples A1 to A2, B1 to B3]
In Example A1, the pressure-sensitive adhesive composition was the same as in Example A1 except that the polymer solution was changed to the polymer solution obtained in each synthesis example and / or the compounding composition was changed as described in Table 2. A product, a pressure-sensitive adhesive sheet, and a polarizing plate with a pressure-sensitive adhesive layer were obtained.

[Evaluation]
[Gel fraction]
From the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet obtained in Examples and Comparative Examples, about 0.1 g of a pressure-sensitive adhesive was collected in a sampling bottle, 30 mL of ethyl acetate was added, and the mixture was shaken for 4 hours, and then the contents of this sample bottle were 200. The mesh was filtered through a stainless steel wire mesh, and the residue on the wire mesh was dried at 100 ° C. for 2 hours, and the dry weight was measured. The gel fraction of the pressure-sensitive adhesive was determined by the following formula.
-Gel fraction (%) = (dry weight / adhesive collection weight) x 100 (%)

[Photoelastic coefficient]
In the pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples, the PET film was peeled off, and the pressure-sensitive adhesive layers having a thickness of 20 μm were bonded to each other multiple times in a 23 ° C./50% RH environment to adjust the pressure to 50 ° C./5 atm. The treatment was carried out in an autoclave for 20 minutes to prepare a pressure-sensitive adhesive layer having a thickness of 1.0 mm. An adhesive layer with a thickness of 1.0 mm is cut into a size of 15 mm x 50 mm, and this is attached to an automatic wavelength scanning ellipsometer (model "M-220", manufactured by JASCO Corporation) using a jig. The retardation was measured at a measurement wavelength of 633 nm while changing the stress. The slope of a straight line when stress is on the horizontal axis and retardation is on the vertical axis is used as the photoelastic modulus of the pressure-sensitive adhesive layer.

[Light leakage test]
Two polarizing plates with an adhesive (a laminate composed of a PET film / an adhesive layer / a polarizer / a protector protective film) obtained in Examples and Comparative Examples were cut into a size of 310 mm × 385 mm and tested. I made a piece. The PET film is peeled off from the test piece, and a laminator roll is used to form a laminate consisting of an adhesive layer / polarizer / protector protective film so that the polarization axes are orthogonal to each other on both sides of a 0.5 mm thick glass plate. And so that the adhesive layer and the glass plate are in contact with each other. The obtained laminate was held in an autoclave adjusted to 50 ° C./5 atm for 20 minutes to prepare a test plate. This test plate was left to stand for 500 hours under the condition of a temperature of 80 ° C./dry, and light leakage was observed according to the following criteria.
AA: No light leakage was observed BB: Light leakage was slightly observed CC: Light leakage was clearly observed

[Durability test (heat resistance / moisture heat resistance test)]
A polarizing plate with an adhesive layer (a laminate composed of a PET film / an adhesive layer / a polarizer / a protector protective film) obtained in Examples and Comparative Examples was cut into a size of 150 mm × 250 mm, and a test piece was cut into pieces. Created. The PET film is peeled off from the test piece, and a laminate consisting of the pressure-sensitive adhesive layer / polarizer / protector protective film is placed on one side of a glass plate having a thickness of 0.5 mm using a laminator roll, and the pressure-sensitive adhesive layer and the glass plate are placed on one side. I stuck it so that it would come in contact with. The obtained laminate was held in an autoclave adjusted to 50 ° C./5 atm for 20 minutes to prepare a test plate. Two similar test plates were prepared. The test plate is left to stand under a temperature of 80 ° C./dry (heat resistance) or a temperature of 60 ° C./90% humidity (moisture heat resistance) for 500 hours, and has defects (foaming, floating, peeling) according to the following criteria. ) Was observed and evaluated.
AA: No defect BB: Defect area is 5% or less, no problem in practical use CC: Defect area exceeds 5%, there is problem in practical use

D-94: Hexamethylene diisocyanate-based cross-linking agent
(Manufactured by Soken Chemical Co., Ltd., solid content 90% by mass)
-L-45: Tolylene diisocyanate cross-linking agent (manufactured by Soken Chemical Co., Ltd., solid content 45% by mass, ethyl acetate / toluene solution)
-E-5C: Epoxy cross-linking agent
(Manufactured by Soken Chemical Co., Ltd., solid content 5% by mass)
-M-12AT: Aluminum chelate-based cross-linking agent (manufactured by Soken Chemical Co., Ltd., solid content 10% by mass, toluene / acetylacetone solution)
-A-50: Silane coupling agent
(Manufactured by Soken Chemical Co., Ltd., solid content 50% by mass, toluene solution)

Claims (10)

The homopolymer has a photoelastic coefficient of −500 × 10 ^-12 to −200 × 10 ^-12 (m ² / N), which is a structural unit derived from the (meth) acrylic acid alkyl ester (a11), and the photoelastic coefficient of the homopolymer. have a constitutional unit derived from the aromatic ring-containing (meth) acrylic acid ester (a12) of ^{+800 × 10 -12 ~ +1900 × 10} -12 (m 2 / N), the weight average measured by gel permeation chromatography A (meth) acrylic copolymer (A1) having a molecular weight (Mw) of 300,000 to 1.5 million and a photoelastic coefficient of −70 × 10 ^-12 to +70 × 10 ^-12 (m ^{2 / N).}
It is formed from a pressure-sensitive adhesive composition containing an isocyanate-based cross-linking agent (B1) having no aromatic ring.
The photoelastic modulus is −70 × 10 ^{-12 to +70} × 10 -12 (m ² / N).
A pressure-sensitive adhesive layer for a polarizing plate, which is arranged in direct contact with a polarizing element. The pressure-sensitive adhesive layer for a polarizing plate according to claim 1, wherein the isocyanate-based cross-linking agent (B1) is a hexamethylene diisocyanate-based cross-linking agent. The pressure-sensitive adhesive for polarizing plates according to claim 1 or 2, wherein the pressure-sensitive adhesive composition contains 0.05 to 10 parts by mass of an isocyanate-based cross-linking agent (B1) with respect to 100 parts by mass of the copolymer (A1). layer. A (meth) acrylic copolymer (A2) having a photoelastic coefficient of −300 × 10 ^-12 (m ² / N) or more and less than −200 × 10 ^-12 (m ² / N) and an isocyanate having an aromatic ring. Formed from a pressure-sensitive adhesive composition containing a system cross-linking agent (B2),
The photoelastic modulus is -100 x 10 ^{-12 to +70} x 10 -12 (m ² / N).
A pressure-sensitive adhesive layer for a polarizing plate, which is arranged in direct contact with a polarizing element. The pressure-sensitive adhesive layer for a polarizing plate according to claim 4, wherein the isocyanate-based cross-linking agent (B2) is at least one selected from a tolylene diisocyanate-based cross-linking agent and a xylylene diisocyanate-based cross-linking agent. The pressure-sensitive adhesive layer for a polarizing plate according to claim 4 or 5, wherein the pressure-sensitive adhesive composition contains 2 parts by mass or more of an isocyanate-based cross-linking agent (B2) with respect to 100 parts by mass of the copolymer (A2). A pressure-sensitive adhesive sheet for a polarizing plate having the pressure-sensitive adhesive layer according to any one of claims 1 to 6. A polarizing plate with a pressure-sensitive adhesive layer having a polarizing element and a pressure-sensitive adhesive layer according to any one of claims 1 to 6, which is directly laminated on at least one surface of the polarizer. The homopolymer has a photoelastic coefficient of −500 × 10 ^-12 to −200 × 10 ^-12 (m ² / N), which is a structural unit derived from the (meth) acrylic acid alkyl ester (a11), and the photoelastic coefficient of the homopolymer. have a constitutional unit derived from the aromatic ring-containing (meth) acrylic acid ester (a12) of ^{+800 × 10 -12 ~ +1900 × 10} -12 (m 2 / N), the weight average measured by gel permeation chromatography A (meth) acrylic copolymer (A1) having a molecular weight (Mw) of 300,000 to 1.5 million and a photoelastic coefficient of −70 × 10 ^-12 to +70 × 10 ^-12 (m ^{2 / N).}
Contains an isocyanate-based cross-linking agent (B1) that does not have an aromatic ring,
A pressure-sensitive adhesive composition for a polarizing plate used for forming the pressure-sensitive adhesive layer according to claim 1. A (meth) acrylic copolymer (A2) having a photoelastic coefficient of −300 × 10 ^-12 (m ² / N) or more and less than −200 × 10 ^-12 (m ² / N) and an isocyanate having an aromatic ring. Containing a system cross-linking agent (B2),
A pressure-sensitive adhesive composition for a polarizing plate used for forming the pressure-sensitive adhesive layer according to claim 4.