TW201713741A - Adhesive layer for polarizing plate and adhesive composition - Google Patents

Abstract

The present application provides an adhesive layer that can be applied to a structure where at least one surface of a polarizing plate protective film conventionally formed on both surfaces of a polarizer is omitted. In addition, the adhesive layer has excellent light leakage prevention and durability. The solution of the present invention is an adhesive layer for a polarizing plate, which is formed of an adhesive composition. The adhesive composition comprises a (meth)acrylic copolymer having a photoelastic coefficient of from -200*10<SP>-12</SP> to +200*10<SP>-12</SP> (m2/N), and an isocyanate-based cross-linking agent having a photoelasticity coefficient of -200*10<SP>-12</SP> to +200*10<SP>-12</SP> (m2/N), which is free of an aromatic ring. Further, the adhesive layer for a polarizing plate is disposed in direct contact with a polarizer. Moreover, the (meth)acrylic copolymer has structural units of a (meth)acrylic acid alkyl ester, being derived from a homopolymer and having a photoelastic coefficient of from -1000*10<SP>-12</SP> to -100*10<SP>-12</SP> (m2/N), and a (meth) acrylate, being derived from a homopolymer and having a photoelastic coefficient of +500*10<SP>-12</SP> to +2000*10<SP>-12</SP> (m2/N), wherein the (meth)acrylic acid alkyl ester contains an aromatic ring.

Description

Adhesive layer and adhesive composition for polarizing plate

The present invention relates to an adhesive layer for an polarizing plate and an adhesive composition.

The liquid crystal cell has a structure in which two substrates (for example, a glass plate) sandwich a liquid crystal layer. The surface of the substrate constituting the liquid crystal cell is attached to the polarizing plate through the adhesive layer. In general, in order to improve the mechanical properties and optical durability of the polarizing plate, a polarizer protective film such as a cellulose triacetate film is used in a two-layer layer of a polarizing plate having a polarizing function.

In recent years, in order to reduce the weight and thickness of the polarizing plate, it is attempted to omit one or both sides of the polarizer protective film formed on both surfaces of the polarizer (see, for example, Patent Document 1). However, since the polarizing plate of one or both of the polarizer protective films is omitted, since the adhesive layer directly contacts the polarizer, a large stress is applied to the adhesive layer accompanying thermal contraction of the polarizer in a high-temperature, high-humidity heat environment, and it is easy. Adverse conditions such as peeling of the adhesive layer occur. Further, the stress applied to the adhesive layer due to thermal contraction of the polarizer becomes large, and there is a problem that birefringence easily occurs.

Therefore, the adhesive for polarizing plates is required to have excellent light leakage prevention. Sex and durability. In the case of the light leakage, Patent Document 2 discloses a polarizing film having an adhesive layer formed of an adhesive composition for a polarizing plate containing a large amount of an isocyanate compound, and Patent Document 3 discloses a component containing a positive photoelastic coefficient. The polarizing plate is composed of a pressure-sensitive adhesive composition. However, there is no description of the direct placement of the adhesive layer on the polarizer in these documents.

(previous technical literature) (Patent Literature)

Patent Document 1: Japanese Laid-Open Patent Publication No. 2012-128099

Patent Document 2: Japanese Laid-Open Patent Publication No. 2010-090354

Patent Document 3: Japanese Patent Publication No. 2004-516359

The polarizing plate which has been conventionally formed on at least one surface of the polarizer protective film on both surfaces of the polarizer is required to have more excellent light leakage prevention and durability. An object of the present invention is to provide an adhesive layer which can be applied to a configuration in which at least one surface of a polarizer protective film which is conventionally formed on both surfaces of a polarizer is omitted, and which is excellent in light leakage prevention and durability.

The inventors of the present invention have diligently studied to solve the above problems. As a result, it has been found that when the (meth)acrylic copolymer and the crosslinking agent described below are used, the above-mentioned adhesive layer excellent in light leakage prevention and durability can be formed. In other words, the present inventors have found that the above problem can be solved by using an adhesive layer for a polarizing plate having the following specific configuration, and the present invention can be completed. Bright.

The present invention is, for example, the following [1] to [10].

[1] An adhesive layer for a polarizing plate comprising a (meth)acrylic copolymer (A1) having a photoelastic coefficient of -200 × 10 ^-12 to +200 × 10 ^-12 (m ² /N) and not The adhesive composition of the aromatic ring-containing isocyanate crosslinking agent (B1) has a photoelastic coefficient of -200×10 ^-12 to +200×10 ^-12 (m ² /N) and is directly related to the polarizer. Further, the (meth)acrylic copolymer (A1) has a photoelastic coefficient derived from a homopolymer of -1000×10 ^-12 to -100×10 ^-12 (m ² /N) ( a constituent unit of the alkyl methacrylate (a11), and an aromatic ring-containing (meth) having a photoelastic coefficient derived from a homopolymer of +500×10 ^-12 to +2000×10 ^-12 (m ² /N) The constituent unit of the acrylate (a12).

[2] The adhesive layer for a polarizing plate according to the above [1], wherein the isocyanate crosslinking agent (B1) is a hexamethylene diisocyanate crosslinking agent.

[3] The adhesive layer for a polarizing plate according to the above [1], wherein the adhesive composition contains an isocyanate crosslinking agent (B1) with respect to 100 parts by mass of the copolymer (A1). 0.05 to 10 parts by mass.

[4] An adhesive layer for a polarizing plate comprising a (meth)acrylic copolymer (A2) having a photoelastic coefficient of less than -200 × 10 ^-12 (m ² /N), and an isocyanate containing an aromatic ring The adhesive composition of the crosslinking agent (B2) is formed, and the photoelastic coefficient is -200 × 10 ^-12 to +200 × 10 ^-12 (m ² /N), and is disposed in direct contact with the polarizer.

[5] The adhesive layer for a polarizing plate according to the above [4], wherein the isocyanate crosslinking agent (B2) is selected from the group consisting of toluene diisocyanate crosslinking. At least one of a solvent and a phthalic diisocyanate crosslinking agent.

[6] The adhesive layer for a polarizing plate according to the above [4], wherein the adhesive composition contains an isocyanate crosslinking agent (B2) based on 100 parts by mass of the copolymer (A2). 2 parts by mass or more.

[7] An adhesive sheet for a polarizing plate, which has the adhesive layer according to any one of the above [1] to [6].

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

[9] An adhesive composition for a polarizing plate comprising a (meth)acrylic copolymer (A1) having a photoelastic coefficient of -200 × 10 ^-12 to +200 × 10 ^-12 (m ² /N) and The isocyanate-based crosslinking agent (B1) containing no aromatic ring is used to form the adhesive layer according to the above [1], wherein the (meth)acrylic copolymer (A1) has a source derived from The photoelastic coefficient of the polymer is -1000 × 10 ^-12 to -100 × 10 ^-12 (m ² /N) of the alkyl (meth) acrylate (a11), and the photoelasticity derived from the homopolymer The coefficient is +500×10 ^-12 to +2000×10 ^-12 (m ² /N) of the constituent unit of the aromatic ring-containing (meth) acrylate (a12).

[10] An adhesive composition for a polarizing plate comprising a (meth)acrylic copolymer (A2) having a photoelastic coefficient of less than -200 × 10 ^-12 (m ² /N), and an isocyanate containing an aromatic ring The crosslinking agent (B2) is used to form the adhesive layer described in the above [4].

According to the present invention, an adhesive layer can be provided which can be applied to omit at least one side of a polarizer protective film which has been conventionally formed on both sides of a polarizer The structure is excellent in light leakage prevention and durability.

(Best embodiment of the invention)

Hereinafter, the adhesive composition for a polarizing plate, the adhesive layer for a polarizing plate, the adhesive sheet for a polarizing plate, and a polarizing plate with an adhesive layer will be described. Hereinafter, the adhesive composition for a polarizing plate, the adhesive layer for a polarizing plate, and the 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 adhesive composition for a first 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) and The isocyanate-based crosslinking agent (B1) containing no aromatic ring is used to form an adhesive layer directly in contact with the polarizer.

A photoelastic coefficient can be formed by crosslinking a (meth)acrylic copolymer having a photoelastic coefficient in the above range and an isocyanate-based crosslinking agent which does not contribute to the photoelastic coefficient of the adhesive layer and which does not contain an aromatic ring. Adhesive layer at -200 x 10 ^-12 to +200 x 10 ^-12 (m ² /N).

The adhesive composition for a second polarizing plate of the present invention, which comprises a (meth)acrylic copolymer (A2) having a photoelastic coefficient of less than -200 × 10 ^-12 (m ² /N) and an isocyanate containing an aromatic ring The crosslinking agent (B2) is used to form an adhesive layer directly in contact with the polarizer.

Light can be formed by crosslinking a (meth)acrylic copolymer having a negative photoelastic coefficient to an aromatic ring-containing isocyanate crosslinking agent having a photoelastic coefficient of the adhesive layer on the positive side. An adhesive layer having a modulus of elasticity of from -200 x 10 ^-12 to +200 x 10 ^-12 (m ² /N).

In the present specification, the copolymers (A1) and (A2) may be collectively referred to as "copolymer (A)", and the adhesive compositions for the first and second polarizing plates of the present invention are also referred to as "first". The "adhesive composition" and the "second adhesive composition" are collectively referred to as "the adhesive composition of the present invention".

In the present specification, the collective name of acrylic acid and methacrylic acid is also referred to as "(meth)acrylic acid". Further, the constituent unit derived from a certain monomer A contained in the polymer is also referred to as "monomer A unit". Further, for the sake of convenience, a certain ester (a) may be referred to as "monomer (a)".

In the present specification, the units of the photoelastic coefficient of the homopolymer, the (meth)acrylic copolymer and the adhesive layer formed of the respective monomers are "×10 ^-12 m ² /N" unless otherwise specified. . Moreover, for example, -200 × 10 ^-12 to +200 × 10 ^-12 (m ² /N) means -200 × 10 ^-12 (m ² /N) or more, +200 × 10 ^-12 (m ² /N) The following meaning. The same is true for other numerical ranges.

The photoelastic coefficient of the homopolymer formed from each monomer is determined as follows.

The homopolymer used in the measurement of the photoelastic coefficient was produced by the following procedure. In a reaction apparatus equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas introduction tube, 100 parts by mass of a monomer and 100 parts by mass of an ethyl acetate solvent were charged, and the temperature was raised to 80 ° C while introducing nitrogen gas. Then, 0.1 part by mass of 2,2'-azobisisobutyronitrile was added, and polymerization reaction was carried out for 6 hours at 80 ° C under a nitrogen atmosphere. After the reaction is completed, it is diluted with ethyl acetate to prepare a solid. A homopolymer solution of the above monomer having a concentration of 30% by mass.

The above homopolymer solution was coated on the release-treated surface of the release-treated polyethylene terephthalate film, and dried at 90 ° C for 3 minutes to form a coating film having a dry film thickness of 20 μm (homopolymer layer). ). The homopolymer layers having a dry film thickness of 20 μm were bonded to each other several times in an environment of 23 ° C / 50% RH, and treated in an autoclave adjusted to 50 ° C / 5 atm for 20 minutes to prepare a thickness of 1.0 mm. Polymer layer.

The homopolymer layer having a thickness of 1.0 mm was cut into a size of 15 mm × 50 mm, and this was changed by an automatic wavelength scanning type ellipsometer (model "M-220", manufactured by JASCO Corporation). The hysteresis value was measured at a measurement wavelength of 633 nm. The curve in which the stress is on the horizontal axis and the hysteresis value on the vertical axis is close to a straight line, and the slope is taken as the photoelastic coefficient of the homopolymer formed by the above monomer.

The glass transition temperature (Tg) of the homopolymer formed of each monomer can be, for example, a value described in Polymer Handbook Fourth Edition (Wiley-Interscience 2003).

Further, in the case where the monomer having no Tg is described in the above literature, for example, the Tg of the homopolymer synthesized under the following conditions is measured under the following conditions. In a reaction apparatus equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas introduction tube, 100 parts by mass of a monomer and 100 parts by mass of an ethyl acetate solvent were charged, and the temperature was raised to 80 ° C while introducing nitrogen gas. Then, 0.1 part by mass of 2,2'-azobisisobutyronitrile was added, and polymerization reaction was carried out for 6 hours at 80 ° C under a nitrogen atmosphere. The resulting homopolymer was sealed in a simple sealed pot. The change in heat was measured using a differential scanning calorimeter (DSC) under a nitrogen stream at a temperature of 10 ° C/min. A graph of "heat absorption" and "temperature" is plotted, and the characteristic inflection point observed at this time is the glass transition. Moreover, Tg uses the value obtained from the DSC curve by the midpoint method.

[(Meth)acrylic copolymer (A1)]

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

The monomer component (that is, the raw material monomer component of (A1)) is preferably a monomer containing a polymerizable unsaturated double bond.

The (meth)acrylic copolymer (A1) has a photoelastic coefficient of from -200 to +200, preferably from -100 to +100, more preferably from -70 to +70.

When the monomer (a11) having a photocoelastic coefficient of a homopolymer is negative and the monomer (a12) having a positive photoelastic coefficient of a homopolymer is copolymerized, a copolymer having a photoelastic coefficient in the above range can be obtained (A1). ). By using the copolymer (A1) and the isocyanate crosslinking agent (B1) containing no aromatic ring, the photoelastic coefficient of the adhesive layer can be made close to the range described later, especially close to 0, whereby the polarizing plate can be suppressed. Light leaks.

"Alkyl (meth) acrylate (a11) (monomer (a11)"

The monomer (a11) is a (meth)acrylic acid alkyl ester having a photoelastic coefficient of from -1000 to -100. The photoelastic coefficient of the homopolymer is preferably from 750 to -150 for the above monomers, more preferably from -500 to -200.

The copolymer (A1) obtained by copolymerizing the monomer (a11) having a photoelastic coefficient of the homopolymer in the above range imparts flexibility to the adhesive layer and exhibits light leakage prevention.

The monomer (a11) is preferably an alkyl (meth)acrylate having a Tg of a homopolymer of -30 ° C or less, more preferably -100 to -30 ° C, still more preferably -70 to -30 ° C. .

In the case of the monomer (a11), for example, a compound represented by CH ₂ =CR ¹ -COOR ² may, for example, be a compound having a photoelastic coefficient of the homopolymer in the above range. 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 above alkyl group preferably has 2 to 16 carbon atoms and more preferably 4 to 12 carbon atoms.

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

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 preferred that each monomer meets the conditions of the photoelastic coefficient and Tg.

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

"Aromatic ring-containing (meth) acrylate (a12) (monomer) (a12))

The monomer (a12) is a homopolymer having an aromatic ring-containing (meth) acrylate having a photoelastic coefficient of from +500 to +2000. The above monomer having a photoelastic coefficient of a homopolymer of from +700 to +1950 is preferred, and the above monomer of from +800 to +1900 is more preferably.

When the copolymer (A1) obtained by copolymerizing the monomer (a12) having a photoelastic coefficient of the homopolymer in the above range is used, appropriate durability can be imparted to the adhesive layer.

The monomer (a12) is preferably an aromatic ring-containing (meth) acrylate having a Tg of a homopolymer of -50 ° C or more, and the above Tg is more preferably -40 ° C to 130 ° C, still more preferably -30 ° C. To 120 ° C.

In the case of the monomer (a12), for example, a compound represented by CH ₂ =CR ³ -COOR ⁴ may, for example, be a compound having a photoelastic coefficient of the homopolymer in the above range. In the formula, R ³ is a hydrogen atom or a methyl group, and R ⁴ is a group containing an aromatic ring. 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 from 6 to 12, more preferably from 6 to 10, still more preferably from 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 coefficient and Tg of the homopolymer formed by each monomer, the photoelastic coefficient (×10 ^-12 m ² /N) on the left side, and the Tg (° C.) on the right side. Other 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. on. When two or more types of monomers (a12) are used, it is preferred that each monomer meets the conditions of the photoelastic coefficient and Tg.

The monomer (a12) is preferably used in an amount of from 9 to 40% by mass, more preferably from 12 to 35% by mass, still more preferably from 15 to 30% by mass, based on 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 to the above range.

"Crosslinking functional group-containing monomer (a13)"

The raw material monomer component of the copolymer (A1) further contains a monomer having a crosslinkable functional group reactive with the isocyanate crosslinking agent (B1), that is, a monomer having a crosslinkable functional group (a13) ) is better. That is, the copolymer (A1) is preferably one having a constituent unit derived from the monomer (a13).

The monomer (a13) is preferably 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 a hydroxyl group-containing (meth) acrylate, and specific examples thereof include 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate. A hydroxyalkyl (meth)acrylate such as 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate or 8-hydroxyoctyl (meth)acrylate. The hydroxyalkyl group in the hydroxyalkyl (meth)acrylate has a carbon number of 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(methyl)propenyloxyethyl succinate, and ω- Carboxy polycaprolactone mono(meth)acrylate A carboxyl group-containing (meth) acrylate; acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid.

The monomer (a13) may be used alone or in combination of two or more.

In 100% by mass of the raw material monomer component of the copolymer (A1), the amount of the monomer (a13) used is preferably more than 0% by mass and not more than 10% by mass, more preferably from 0.5 to 7% by mass, still more preferably 1 to 5 mass%. When the amount of the monomer (a13) used is at most the above upper limit value, the crosslinking density formed by the copolymer (A1) and the crosslinking agent (B1) is not excessively high. When the amount of use of the monomer (a13) is at least the above lower limit value, an adhesive layer having an appropriate strength can be obtained due to the effective topography structure.

Other Monomers

In the raw material monomer component of the copolymer (A1), for example, in the range of the physical properties of the copolymer (A1), for example, an alkyl (meth)acrylate other than the above monomer (a11), (methyl) may be used. Alkoxyalkyl acrylate, alkoxy polyalkylene glycol mono (meth) acrylate, alicyclic group-containing (meth) acrylate, amine group-containing monomer, and guanamine-containing monomer, etc. monomer. That is, the copolymer (A1) may further have constituent units derived from other monomers.

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

Examples of the alkoxyalkyl (meth)acrylate include methoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, and 2-ethoxy(meth)acrylate. Ethyl ester, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate and 4-ethyl (meth)acrylate Oxybutyl ester.

Examples of the alkoxypolyalkylene glycol mono(meth)acrylate include methoxydiethylene glycol mono(meth)acrylate, methoxydipropylene glycol mono(meth)acrylate, and ethoxylate. Triethylene glycol mono (meth) acrylate, ethoxy diethylene glycol mono (meth) acrylate and methoxy triethylene glycol mono (meth) acrylate.

Examples of the (meth) acrylate containing an alicyclic group include cyclohexyl (meth)acrylate.

Examples of the amino group-containing monomer include an amino group-containing (meth) acrylate such as dimethylaminoethyl (meth)acrylate or diethylaminoethyl (meth)acrylate.

Examples of the monomer containing a guanamine group include (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl ( Methyl) acrylamide, N-hexyl (meth) acrylamide.

Other single systems may be used alone or in combination of two or more.

In the 100% by mass of the raw material monomer component of the copolymer (A1), the total amount of the other monomer used is not particularly limited as long as the photoelastic coefficient of the above (A1) is within the above range, and is 0 to 10% by mass. Preferably, it is preferably from 0 to 5% by mass.

[(Meth)acrylic copolymer (A2)]

The (meth)acrylic copolymer (A2) is a copolymer having a photoelastic coefficient of less than -200, preferably -500 or more and less than -200, more preferably -300 or more and less than -200. Such a copolymer is, for example, a constituent unit derived from an alkyl (meth)acrylate (a21) having a photoelastic coefficient of less than -200 derived from a homopolymer, and for example, a monomer component containing the above monomer (a21) is copolymerized. Winner.

The monomer component (that is, the raw material monomer component of (A2)) is preferably a monomer containing a polymerizable unsaturated double bond.

By using the copolymer (A2) and using an aromatic ring-containing isocyanate crosslinking agent (B2), the photoelastic coefficient of the adhesive layer can be made close to the range described later, especially close to 0, whereby light leakage of the polarizing plate can be suppressed. .

"Alkyl (meth) acrylate (a21) (monomer (a21))"

In the aspect of the monomer (a21), an ester having a photoelastic coefficient of the above-mentioned (meth)acrylic acid alkyl ester (a11) having a photoelastic coefficient of less than -200 can be exemplified. The above monomer having a photoelastic coefficient of a homopolymer of -750 or more and less than -200 is more preferable, and the above monomer 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 preferred that each monomer meets the conditions of the photoelastic coefficient.

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

"Crosslinking functional group-containing monomer (a22)"

The raw material monomer component of the copolymer (A2) further contains a monomer having a crosslinkable functional group reactive with the isocyanate crosslinking agent (B2), that is, a monomer having a crosslinkable functional group (a22) ) is better. That is, the copolymer (A2) is preferably one having a constituent unit derived from the monomer (a22).

The monomer (a13) having a crosslinkable functional group may be exemplified as the monomer (a22), and preferred examples are also the same. The monomer (a22) may be used alone or in combination of two or more.

In 100% by mass of the raw material monomer component of the copolymer (A2), the amount of the monomer (a22) to be used is preferably more than 0% by mass and not more than 10% by mass, more preferably from 0.5 to 7% by mass, still more preferably 1 to 5 mass%. When the amount of the monomer (a22) used is at most the above upper limit value, the crosslinking density formed by the copolymer (A2) and the crosslinking agent (B2) is not excessively high. When the amount of use of the monomer (a22) is at least the above lower limit value, an adhesive layer having an appropriate strength can be obtained due to the effective topography structure.

Other Monomers

In the raw material monomer component of the copolymer (A2), in the range of the physical properties of the copolymer (A2), for example, an alkyl (meth)acrylate other than the above monomer (a21), (methyl) may be used. Alkoxyalkyl acrylate, alkoxy polyalkylene glycol mono (meth) acrylate, alicyclic group-containing (meth) acrylate, aromatic ring-containing (meth) acrylate, amine group-containing single Other monomers such as a body and a monomer containing a guanamine group. That is, the copolymer (A2) may further have constituent units derived from other monomers.

The monomer aspect can be exemplified in the column of the copolymer (A1). Each compound described in "Other Monomers". Examples of the aromatic ring-containing (meth) acrylate include phenyl (meth) acrylate, benzyl (meth) acrylate, and (meth) propylene phenoxyethyl ester.

However, the homopolymer has a photoelastic coefficient of +100 to +1000 (meth) acrylate and a homopolymer having a photoelastic coefficient of +500 to +2000 (A) containing an aromatic ring (described above) The amount of use of the monomer (a12)) is preferably adjusted as appropriate from the viewpoint that the photoelastic coefficient of the copolymer (A2) is adjusted to the above range.

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

Other single systems may be used alone or in combination of two or more.

In the 100% by mass of the raw material monomer component of the copolymer (A2), the total amount of the other monomer used is not particularly limited as long as the photoelastic coefficient of the above (A2) is within the above range, and is 0 to 35 mass%. Preferably, it is preferably from 0 to 30% by mass, more preferably from 0 to 26% by mass.

[Production conditions of (meth)acrylic copolymer (A)]

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

The copolymer (A) may be obtained by copolymerizing, for example, the above monomer component, and may be a random copolymer or a block copolymer. Among these, a random copolymer is 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 ring; Alicyclic hydrocarbons such as heptane and cyclooctane; diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, Ethers such as alkane, anisole, phenethyl ether and diphenyl ether; halogenated hydrocarbons such as chloroform, carbon tetrachloride, 1,2-dichloroethane and chlorobenzene; ethyl acetate, propyl acetate, butyl acetate Esters such as esters and methyl propionate; ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone and cyclohexanone; N, N-dimethylformamide, N, Amidoxime such as N-dimethylacetamide and N-methylpyrrolidone; nitriles such as acetonitrile and benzonitrile; and anthraquinones such as dimethyl hydrazine and cyclobutyl hydrazine. These polymerization solvents may be used alone or in combination of two or more.

Examples of the polymerization initiator include an azo initiator and a peroxide initiator. Specific examples include azo compounds such as 2,2'-azobisisobutyronitrile, peroxides such as benzamidine peroxide and lauric acid peroxide. Among these, azo compounds are also preferred. Examples of the azo compound include 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and 2,2. '-Azobis(2-cyclopropylpropionitrile), 2,2'-azobis (2,4- Dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2-(aminocarbazinyl) Azo)isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutylphosphonium), 2,2'-azobis(isobutylguanamine) dihydrate, 4,4'-azo Bis(4-cyanovaleric acid), 2,2'-azobis(2-cyanopropanol), dimethyl-2,2'-azobis(2-methylpropionate), 2 , 2'-azobis[2-methyl-N-(2-hydroxyethyl)propanamide]. These polymerization initiators may be used alone or in combination of two or more.

The polymerization initiator is usually used in an amount of from 0.01 to 5 parts by mass, preferably from 0.1 to 3 parts by mass, per 100 parts by mass of the raw material monomer component of the (meth)acryl-based copolymer (A). Further, in the above polymerization reaction, a polymerization initiator, a chain transfer agent, a monomer component, and a polymerization solvent may be appropriately added.

[Physical properties and content of (meth)acrylic copolymer (A)]

The photoelastic coefficient of the (meth)acrylic copolymer (A) is as described above.

The weight average molecular weight (Mw) of the (meth)acrylic copolymer (A) measured by gel permeation chromatography (GPC method) is usually 300,000 to 2,000,000 in terms of polystyrene, preferably 400,000 to 1.8 million, and more preferably 500,000 to 1.5 million. When the copolymer (A) having the above-mentioned monomer unit of Mw in the above range is used, the balance of the adhesive force can be easily obtained, and the viscosity is an adhesive composition suitable for coating. Further, when a copolymer (A) having a Mw of 500,000 or more is used, an 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, More preferably 2 to 9.

The glass transition temperature (Tg) of the (meth)acrylic copolymer (A) can be determined by calculation of the monomer unit constituting the copolymer and the content ratio thereof according to the formula of Fox. For example, the glass transition temperature (Tg) obtained by the formula of Fox is usually -70 to -10 ° C, preferably -60 to -20 ° C, to synthesize the (meth)acrylic copolymer (A). It is better. By using the (meth)acrylic copolymer (A) having such a glass transition temperature (Tg), an adhesive composition excellent in stress relaxation properties and durability and excellent in adhesion at normal temperature can be obtained.

Fox's 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 a glass transition temperature (K) of the (meth)acrylic copolymer (A), and Tg ₁ , Tg ₂ , ..., Tg _m are glass transition temperatures of a homopolymer composed of each monomer ( K), W ₁ , W ₂ , ..., W _m are the weight fractions of the above copolymer (A) derived from the constituent units of the respective monomers. From the aspect of the weight fraction of the constituent units derived from the respective monomers, the packing ratio of each monomer to the total monomer at the time of synthesizing the copolymer can be used.

The glass transition temperature of the homopolymer composed of each monomer in the above formula of Fox can be, for example, a value described in the fourth edition of the Polymer Handbook (Wiley-Interscience 2003). Further, for the monomer having no Tg in the above literature, for example, the value obtained by the above method is used.

In the first adhesive composition, the content of the (meth)acrylic copolymer (A1) is usually 60 to 99.95% by mass, preferably 70, in 100% by mass of the solid content other than the organic solvent in the composition. To 99.5 % by mass, particularly preferably from 80 to 99.0% by mass. When the content of the (meth)acrylic copolymer (A1) is in the above range, the performance as an adhesive is balanced, and the adhesive property is excellent.

In the second adhesive composition, the content of the (meth)acrylic copolymer (A2) is usually from 60 to 98.0% by mass, preferably 70, in 100% by mass of the solid content other than the organic solvent in the composition. It is up to 96.2% by mass, particularly preferably from 80 to 92.6% by mass. When the content of the (meth)acrylic copolymer (A2) is in the above range, the performance as an adhesive is balanced, and the adhesive property is excellent.

[Crosslinking agent (B)]

The first adhesive composition further contains an isocyanate crosslinking agent (B1) which does not contain an aromatic ring. The second adhesive composition further contains an isocyanate-based crosslinking agent (B2) containing an aromatic ring.

Isocyanate Crosslinking Agent (B1)

In the case of the isocyanate-based crosslinking agent (B1), an isocyanate compound having an isocyanate group number of 2 or more and containing no aromatic ring is usually used. When the (meth)acrylic copolymer (A1) is crosslinked by the crosslinking agent (B1), a crosslinked body (mesh polymer) excellent in durability can be formed. Further, by using the aromatic ring-free crosslinking agent (B1) together with the copolymer (A1) having a photoelastic coefficient in the range of -200 to +200, a photoelastic coefficient can be formed in the range of -200 to +200. Adhesive layer.

The number of isocyanate groups of the crosslinking agent (B1) is usually 2 or more, preferably 2 to 8, more preferably 3 to 6. When the number of isocyanate groups is in the above range, the crosslinking reaction effect of the (meth)acrylic copolymer (A1) and the crosslinking agent (B1) The point of the rate and the point of maintaining the softness of the adhesive layer are preferred.

The diisocyanate compound having an isocyanate group number of 2 in one molecule may, for example, be an aliphatic diisocyanate or an alicyclic diisocyanate. Examples of the aliphatic diisocyanate include ethyl diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, and 2-methyl-1,5-. Aliphatic diisocyanate having 4 to 30 carbon atoms such as pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate . Examples of the alicyclic diisocyanate include isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated dimethyl diisocyanate, hydrogenated toluene diisocyanate, and hydrogenated diphenyl. An alicyclic diisocyanate having 7 to 30 carbon atoms such as methyl methane diisocyanate or hydrogenated tetramethyl dimethyl diisocyanate.

The isocyanate compound having an isocyanate group number of 3 or more in one molecule may, for example, be an aliphatic polyisocyanate or an alicyclic polyisocyanate.

Further, as the crosslinking agent (B1), for example, a polymer of the above isocyanate compound having an isocyanate group number of 2 or more (for example, a dimer or a trimer, a biuret, or an isocyanurate) And a derivative (for example, an addition reaction product of a polyhydric alcohol with two or more molecules of the above diisocyanate compound) or a polymer. In the case of the polyol of the above-mentioned derivative, the low molecular weight polyol may, for example, be a trihydric or higher alcohol such as trimethylolpropane, glycerin or neopentyl alcohol; and examples of the high molecular weight polyol include For example: polyether polyols, polyester polyols, acryl-based polyols, polybutylene Diene polyol, polyisoprene polyol.

Examples of such an isocyanate compound include a biuret or hexamethylene diisocyanate, a reaction product of trimethylolpropane and hexamethylene diisocyanate (for example, six). a three-molecular adduct of methylene diisocyanate), a polyether polyisocyanate, a polyester polyisocyanate.

Among the crosslinking agents (B1), a hexamethylene diisocyanate crosslinking agent is preferred from the viewpoint of improving the ripening property and light leakage resistance. Examples of the hexamethylene diisocyanate crosslinking agent include hexamethylene diisocyanate and a derivative thereof, a biuret or an isocyanurate. In addition, as for the commercial item, for example, "D-94" manufactured by Soken Chemical Co., Ltd. can be cited.

The crosslinking agent (B1) may be used singly or in combination of two or more.

The content of the crosslinking agent (B1) in the first adhesive composition is usually 0.05 to 10 parts by mass, preferably 0.5 to 8 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (A1). More preferably, it is 1 to 5 parts by mass. When the content of the crosslinking agent (B1) is in the above range, it is preferable from the viewpoint of easily obtaining a balance between durability and light leakage resistance.

Isocyanate Crosslinking Agent (B2)

In the case of the isocyanate-based crosslinking agent (B2), an isocyanate compound having an aromatic ring having an isocyanate group number of 2 or more in one molecule is usually used. By crosslinking the (meth)acrylic copolymer (A2) via the crosslinking agent (B2), a crosslinked body (mesh polymer) excellent in durability can be obtained. and, By using a crosslinking agent (B2) having an aromatic ring together with a copolymer (A2) having a photoelastic coefficient in the range of less than -200, an adhesive layer having a photoelastic coefficient in the range of -200 to +200 can be formed. .

The number of isocyanate groups of the crosslinking agent (B2) is usually 2 or more, preferably 2 to 8, more preferably 3 to 6. When the number of isocyanate groups is in the above range, it is preferable from the viewpoint of the crosslinking reaction efficiency of the (meth)acrylic copolymer (A2) and the crosslinking agent (B2) and the flexibility of the adhesive layer.

The diisocyanate compound having an isocyanate group number of 2 in one molecule may, for example, be an aromatic diisocyanate. Examples of the aromatic diisocyanate include benzodiisocyanate, toluene diisocyanate, benzodimethyl diisocyanate, naphthalene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, and diphenyl. An aromatic diisocyanate having 8 to 30 carbon atoms such as a propane diisocyanate.

The isocyanate compound having an isocyanate group number of 3 or more in one molecule may, for example, be an aromatic polyisocyanate. Specific examples thereof include 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, and 4,4',4"-triphenylmethane triisocyanate.

Further, as the crosslinking agent (B2), for example, a polymer of the above isocyanate compound having an isocyanate group number of 2 or more (for example, a dimer or a trimer, a biuret, or an isocyanuric acid) may be mentioned. An ester), a derivative (for example, an addition reaction product of a polyhydric alcohol and two or more molecules of the above diisocyanate compound), or a polymer. In the case of the polyhydric alcohol in the above-mentioned derivative, examples of the low molecular weight polyhydric alcohol include a trihydric or higher alcohol such as trimethylolpropane, glycerin or neopentyl alcohol; and as a high molecular weight polyol For example, a polyether polyol, a polyester polyol, an acryl-based polyol, a polybutadiene polyol, and a polyisoprene polyol can be mentioned.

Examples of such an isocyanate compound include a terpolymer of diphenylmethane diisocyanate, a polymethylene polyphenyl polyisocyanate, a biuret or tol cyanide of toluene diisocyanate, and a trishydroxyl group. A reaction product of a propane with toluene diisocyanate or benzodimethyl diisocyanate (for example, a three-molecular adduct of toluene diisocyanate or dimethyl diisocyanate), a polyether polyisocyanate, or a polyester polyisocyanate.

Among the crosslinking agents (B2), at least one selected from the group consisting of a toluene diisocyanate crosslinking agent and a phthalic diisocyanate crosslinking agent is preferable from the viewpoint of improving the ripening property and the light leakage resistance. More preferably, the toluene diisocyanate crosslinking agent is used. Examples of the toluene diisocyanate crosslinking agent include toluene diisocyanate and derivatives thereof, biuret or isocyanurate. Examples of the benzenedimethyl diisocyanate crosslinking agent include benzenedimethyl diisocyanate and a derivative thereof, a biuret or an isocyanurate. In addition, as for the commercial item, for example, "L-45" manufactured by Soken Chemical Co., Ltd. can be cited.

The crosslinking agent (B2) may be used alone or in combination of two or more.

In the second adhesive composition, the content of the crosslinking agent (B2) is usually 2 parts by mass or more, preferably 4 to 30 parts by mass, based on 100 parts by mass of the (meth)acrylic copolymer (A2). It is preferably 8 to 15 parts by mass. When the content of the crosslinking agent (B1) is in the above range, even if the composition of the copolymer (A2) having a negative photoelastic coefficient is included, a layer having a photoelastic coefficient close to 0 can be formed. It is preferable from the viewpoint of easily achieving a balance between durability and light leakage prevention.

Other Crosslinkers

The first and second adhesive compositions may further contain a crosslinking agent other than the crosslinking agent (B1) or the crosslinking agent (B2) as long as the photoelastic coefficient of the obtained pressure-sensitive adhesive layer is within the above range. For example, when the crosslinking agent having the photoelastic coefficient of the adhesive layer not significantly shifted to the positive side is used in combination with the above-mentioned crosslinking agent, the photoelastic coefficient is maintained in the range described later, and the durability can be further improved.

The other crosslinking agent is not particularly limited as long as it is a component capable of initiating a crosslinking reaction with a crosslinkable functional group derived from a crosslinking functional group-containing monomer, and examples thereof include a metal chelate compound ( B3), epoxy compound (B4).

In the first and second adhesive compositions, the content of the other crosslinking agent is usually 2 parts by mass or less, preferably 0.01 to 1.5, per 100 parts by mass of the (meth)acrylic copolymer (A). The part by mass is more preferably 0.03 to 1 part by mass.

<Metal Chelate Compound (B3)>

Examples of the chelating compound (B3) include, for example, alkoxide, acetamidineacetone, and ethyl acetonitrile, and the like, and are coordinated to aluminum, iron, copper, zinc, tin, titanium, nickel, ruthenium, magnesium, vanadium, and chromium. And a compound of a polyvalent metal such as zirconium.

Among these, an aluminum chelate compound is particularly preferred. Specific examples thereof include aluminum isopropylate, aluminum second butyrate, ethyl acetate, aluminum diisopropylate, aluminum triacetate, and aluminum triethylacetonate. Moreover, as for the commercial products, for example, the comprehensive research chemical limited stock "M-12AT" manufactured by the company.

The metal chelate compound (B3) may be used alone or in combination of two or more.

The chelating compound (B3) crosslinks (virtually crosslinks) the (meth)acrylic copolymer (A) by a coordinate bond. When the metal chelate compound (B3) is further used as a crosslinking agent, the crosslinking is maintained at room temperature and the polymer is cohesive, and at a high temperature, a part of the crosslinking crosslinks to make the adhesive layer more excellent. Softness.

Epoxy Compound (B4)

The epoxy compound (B4) is usually an epoxy compound having 2 or more epoxy groups in one molecule. For example, ethylene glycol diepoxypropyl ether, polyethylene glycol diepoxypropyl ether, glycerol diepoxypropyl ether, glycerol triepoxypropyl ether, 1,3-double (N, N) -diepoxypropylaminomethyl)cyclohexane, N,N,N',N'-tetraepoxypropylm-xylylenediamine, N,N,N',N'-tetraepoxypropyl Aminophenyl benzene methane, triglycidyl isocyanate, N,N-diepoxypropylaminophenyl epoxidized propyl ether, N,N-diepoxypropyl toluidine and N,N-diepoxypropyl aniline. In addition, as for the commercial item, for example, "E-5C" manufactured by Soken Chemical Co., Ltd. can be cited.

[Chane coupling agent (C)]

The adhesive composition of the present invention is preferably one which further contains a decane coupling agent (C). The decane coupling agent (C) is used to firmly adhere the adhesive layer to an adherend such as a glass plate, and helps prevent the peeling of the polarizing plate in a high humidity and heat environment.

As the decane coupling agent (C), for example, vinyl three a decane coupling agent containing a polymerizable unsaturated group such as methoxydecane, vinyltriethoxydecane or methacryloxypropyltrimethoxydecane; 3-glycidoxypropyltrimethoxydecane , 3-glycidoxypropyltriethoxydecane, 3-glycidoxypropylmethyldimethoxydecane, 3-glycidoxypropylmethyldiethoxydecane, An epoxy group-containing decane coupling agent such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxydecane; 3-aminopropyltrimethoxydecane, N-(2-aminoethyl) An amine group-containing decane coupling agent such as 3-aminopropyltrimethoxydecane or N-(2-aminoethyl)-3-aminopropylmethyldimethoxydecane; 3-chloropropyl group A halogen-containing decane coupling agent such as trimethoxydecane, and 3-(trimethoxyindenyl)propyl-3-oxybutyrate. In addition, as for the commercial item, for example, "A-50" manufactured by Soken Chemical Co., Ltd. can be cited.

In the adhesive composition of the present invention, the content of the decane coupling agent (C) is usually 1 part by mass or less, preferably 0.01 to 1 part by mass, based on 100 parts by mass of the (meth)acryl-based copolymer (A). More preferably, it is 0.05 to 0.5 part by mass. When the content is in the above range, there is a tendency to prevent peeling of the polarizer in a high-humidity heat environment or bleed out of the decane coupling agent (C) in a high-temperature environment.

[Antistatic agent (D)]

The antistatic agent (D) is, for example, useful for lowering the surface resistance value of the adhesive layer formed by the 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, for example, a 4-stage ammonium salt, a guanamine 4-grade ammonium salt, a pyridinium salt, a cationic surfactant having a cationic group such as a 1st to a third amine group; and a sulfonic acid group; Anionic interfacial activity having an anionic group such as a salt group, a sulfate group or a phosphate group Amphoteric surfactants such as alkylbetaines, alkylimidazolinebetaines, alkylamine oxides, and amino acid sulfates; glycerol fatty acid esters, sorbitan fatty acid esters, polyoxygen extension Nonionic surfactants such as ethylalkylamines, polyoxyethylideneamine fatty acid esters, N-hydroxyethyl-N-2-hydroxyalkylamines, and alkyldiethanolamines.

Further, a reactive emulsifier having a polymerizable group may be used as the surfactant, and a polymer interface activity obtained by polymerizing a monomer component containing the above surfactant or reactive emulsifier may be used. Agent.

The ionic compound is composed of a cationic portion and an anionic portion, and may be either solid or liquid at room temperature (23 ° C / 50% RH).

The cation portion constituting the ionic compound may be either or both of an inorganic cation or an organic cation. The inorganic cation is preferably an alkali metal ion or an alkaline earth metal ion, and more preferably Li ⁺ , Na ⁺ and K ⁺ having excellent antistatic properties. Examples of the organic cation include pyridinium cation, piperidine cation, pyrrolidinium cation, pyrroline cation, pyrrole cation, imidazolium cation, tetrahydropyrimidine cation, dihydropyrimidine cation, pyrazole cation, pyrazoline cation, and tetra. An alkylammonium cation, a trialkylsulfonium cation, a tetraalkylphosphonium cation, and the like.

The anion portion constituting the ionic compound is not particularly limited as long as it can be ion-bonded to the cation portion to form an ionic compound. Specific examples thereof include 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 ^- . Among these, since an anion of a fluorine atom can provide an ionic compound having a low melting point, (F ₂ SO ₂ ) ₂ N ^- and (CF ₃ SO ₂ ) ₂ N ^- are particularly preferable.

In terms of the ionic compound, lithium bis(trifluoromethanesulfonyl) phthalimide, lithium bis(difluorosulfonyl) phthalimide, lithium sulfonate (trifluoromethanesulfonyl) methane, and bis (three) are preferable. Fluoromethanesulfonyl) sulfonium imide, potassium bis(difluorosulfonyl) phthalimide, 1-ethylpyridinium hexafluorophosphate, 1-butylpyridinium hexafluorophosphate, 1-hexyl- 4-methylpyridinium hexafluorophosphate, 1-octyl-4-methylpyridinium hexafluorophosphate, 1-octyl-4-methylpyridinium bis(fluorosulfonyl) quinone imine, 1 -octyl-4-methylpyridinium bis(trifluoromethanesulfonyl) quinone imine, tributylmethylammonium bis(fluorosulfonyl) quinone imine, tributylmethylammonium bis(trifluoromethanesulfonyl)醯imino, (N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate, N,N-diethyl-N-methyl-N -(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl) quinone imine, 1-octylpyridinium fluoroquinone imine, 1-octyl-3-methylpyridinium trifluorofluorene Imine.

Examples of the conductive polymer include polythiophene, polyaniline, polypyrrole, and derivatives thereof.

In the adhesive composition of the present invention, the content of the antistatic agent (D) is usually 3 parts by mass or less, preferably 0.01 to 3 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (A). More preferably, it is 0.05 to 2.5 parts by mass.

[Organic Solvent (E)]

The adhesive composition of the present invention is preferably adjusted for coating properties. Contains organic solvent (E). In the case of the organic solvent, for example, a solvent which is a polymerization solvent is exemplified in the column of the production conditions of the (meth)acrylic copolymer (A). For example, the polymer solution containing the (meth)acrylic copolymer (A) and the polymerization solvent obtained by the above copolymerization and the crosslinking agent (B) can be mixed to prepare an adhesive composition. In the adhesive composition of the present invention, the content of the organic solvent (E) is usually from 50 to 90% by mass, preferably from 60 to 85% by mass.

In the present specification, the "solid content" means all the components after removing the organic solvent (E) from the components contained in the adhesive composition, and the "solid content concentration" means 100% by mass relative to the adhesive composition. The ratio of the above solid parts.

[additive]

The adhesive composition of the present invention may contain, in addition to the above components, an antioxidant composition, a light stabilizer, a metal corrosion inhibitor, a tackifier, a plasticizer, and a crosslinking promotion, within a range not impairing the effects of the present invention. One or two or more kinds of the (meth)acrylic copolymer and the rework agent other than the above (A).

[Modulation of Adhesive Composition for Polarizing Plate]

The adhesive composition of the present invention can be prepared by mixing a (meth)acrylic copolymer (A), a crosslinking agent (B) and, if necessary, other components by a conventional method. For example, a polymer solution containing the polymer obtained by synthesizing the (meth)acrylic copolymer (A) may be blended with a crosslinking agent (B) and other components as necessary.

By using the adhesive composition of the present invention, even on a polarizing plate having a polarizer protective film on only one side of the polarizer, and on both sides of the polarizer When an adhesive layer is formed on a polarizing plate which does not have a polarizer protective film, light leakage can be suppressed. Further, in the present invention, even if the adhesive layer directly contacts the polarizer, the fracture of the adhesive layer and the peeling of the polarizing plate can be suppressed in a high-temperature/high-humidity heat environment.

The above composition is suitable for use in bonding of a substrate constituting a liquid crystal cell and a polarizer.

[Adhesive layer for polarizing plate]

The first adhesive layer for a polarizing plate of the present invention is formed of the above first adhesive composition. The second adhesive layer for a polarizing plate of the present invention is formed of the above second adhesive composition. The first and second adhesive layers may also be referred to as "the adhesive layer of the present invention".

When the adhesive composition of the present invention is used, an adhesive layer having the following photoelastic properties can be formed. The adhesive layer of the present invention has a photoelastic coefficient of -200 to +200, preferably -150 to +150, more preferably -100 to +100, still more preferably -70 to +70. The unit of the photoelastic coefficient is "×10 ^-12 m ² /N".

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

Since the adhesive layer of the present invention has the above characteristics, it is excellent in light leakage prevention in a high-temperature/high-humidity heat environment. Moreover, since the adhesive layer of the present invention is excellent in durability, it is difficult to cause breakage of the adhesive layer and peeling of the adhesive layer from the polarizing plate.

The adhesive layer of the present invention preferably has a gel fraction of 40% by mass or more, more preferably 50 to 97% by mass, from the viewpoints of deformation resistance, cohesive force, adhesion, and removability of the polarizing plate. Preferably, it is 60 to 95% by mass. When the gel fraction is in the above range, the adhesive layer exhibits excellent durability. The details of the measurement conditions are as described in the examples.

The adhesive layer of the present invention can be obtained, for example, by performing a crosslinking reaction in the above adhesive composition, specifically, crosslinking the (meth)acrylic copolymer (A) with a crosslinking agent (B). .

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

The adhesive layer is preferably formed under the following conditions. Applying the adhesive composition of the present invention to a support, forming a coating film under the above conditions, and attaching a cover film to the coating film as needed, usually after 3 days or more, preferably 7 to The aging is carried out in an environment of 10 days, usually 5 to 60 ° C, preferably 15 to 40 ° C, usually 30 to 70% RH, preferably 40 to 70% RH. When cross-linking is carried out under the above-mentioned ripening conditions, the cross-linking (mesh polymer) can be effectively formed.

As the coating method of the adhesive composition, a conventional method such as a spin coating method, a knife coating method, a roll coating method, or a bar coating method can be used. A coating method of a specific thickness is formed by a cloth method, a blade coating method, a die coating method, a gravure coating method, or the like.

Examples of the support 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 or an ethylene-vinyl acetate copolymer.

[Adhesive sheet for polarizing plate]

The adhesive sheet for a polarizing plate of the present invention has an adhesive layer formed of the adhesive composition of the present invention. Examples of the adhesive sheet include, for example, a double-sided adhesive sheet having only the above-mentioned adhesive layer; a double-sided adhesive sheet having a base material and the above-mentioned adhesive layer formed on both surfaces of the base material; and a base material and a side formed on the base material The one-side adhesive sheet of the above adhesive layer; and the adhesive sheet formed by attaching the peeled cover film to the surface of the adhesive layer of the adhesive sheet which is not in contact with the substrate.

Examples of the substrate 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 or an ethylene-vinyl acetate copolymer.

The conditions for forming the adhesive layer are the same as those described in the column of [Adhesive Layer for Polarizing Plate].

The film thickness of the adhesive layer is usually from 5 to 75 μm , preferably from 10 to 50 μm , from the viewpoint of maintaining adhesive properties. The film thickness of the substrate and the cover film is not particularly limited, but is usually 10 to 125 μm , preferably 25 to 75 μm .

[Polarizer with Adhesive Layer]

The polarizing plate with an adhesive layer of the present invention has a polarizer and an adhesive composition of the present invention directly laminated on at least one side of the polarizer The resulting adhesive layer. In the present specification, the "polarizing plate" is used in the sense of including a "polarizing film".

As the polarizing plate, a conventional polarizing film can be used. For example, a polarizer itself, and a multilayer film having a polarizer and a polarizer protective film disposed on the polarizer can be cited. In the present invention, since the adhesive layer is disposed directly in contact with the polarizer, for example, a polarizer protective film is disposed only on one surface of the polarizer, and a polarizer protective film is not disposed on the other surface, and The polarizer protective film is not disposed on both sides of the polarizer.

The polarizing plate may, for example, be a stretched film obtained by stretching a film made of a polyvinyl alcohol-based resin and containing a polarizing component. Examples of the polyvinyl alcohol-based resin include polyvinyl alcohol, polyvinyl formal, polyvinyl acetal, and a saponified product of an ethylene/vinyl acetate copolymer. Examples of the polarizing component include iodine or a dichroic dye.

The polarizer protective film may, for example, be a film made of a thermoplastic resin. Examples of the thermoplastic resin include cellulose resins such as cellulose triacetate, polyester resins, polyether oxime resins, polyfluorene resins, polycarbonate resins, polyamide resins, polyimide resins, and polyolefin resins. (meth)acrylic resin, cyclic polyolefin resin (northene-based resin), polyarylate resin, polystyrene resin, polyvinyl alcohol resin, and two or more kinds selected from the resins mixture.

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

In the present invention, the adhesive layer is formed by directly contacting the polarizer. In the polarizing plate with an adhesive layer of the present invention, for example, a laminated polarizer protective film, a polarizer, and the above-mentioned adhesive layer may be mentioned; the adhesive layer, the polarizer protective film, and the polarizer are sequentially laminated; The adhesive layer is formed; and the adhesive layer, the polarizer, and the adhesive layer are laminated in this order. In these configurations, the cover film may be disposed on the adhesive layer as the outermost layer.

The method of forming the adhesive layer on the surface of the polarizer is not particularly limited, and examples thereof include a method of applying the above-described adhesive composition on the surface of the polarizer to dry and ripen it; and the adhesive sheet for a polarizing plate of the present invention has A method in which an adhesive layer is attached or transferred onto a surface of a polarizer to be matured. The conditions of drying and ripening, and the range of the gel fraction are the same as those described in the column of the [adhesive layer for polarizing plates].

The thickness of the adhesive layer is usually from 5 to 75 μm , preferably from 10 to 50 μm . Further, the pressure-sensitive adhesive layer may be formed by being in contact with the polarizing plate on at least one surface of the polarizing plate, and may be an aspect in which an adhesive layer is formed only on one surface of the polarizing film, and an adhesive layer is formed on both surfaces of the polarizing plate. kind.

Further, the polarizing plate may have a layer having other functions such as a protective layer, an antiglare layer, a retardation layer, and a viewing angle lifting layer.

The polarizing plate of the adhesive layer of the present invention obtained as described above was placed on the surface of the substrate of the liquid crystal cell, whereby a liquid crystal element was produced. Here, the liquid crystal cell has a structure in which two substrates sandwich a liquid crystal layer. Examples of the substrate of the liquid crystal cell include a glass plate. The thickness of the substrate is usually from 0.05 to 3 mm, preferably from 0.2 to 1 mm.

[Examples]

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

[GPC]

The (meth)acrylic copolymer was subjected to colloidal permeation chromatography (GPC method) to obtain a weight average molecular weight (Mw) and a number average molecular weight (Mn) under the following conditions.

. Measuring device: HLC-8320GPC (manufactured by TOSOH Co., Ltd.)

. GPC column structure: the following four columns (all are limited by TOSOH shares) Made by the company)

(1)TSKgel H×L-H (protective column)

(2) TSKgel GMH×L

(3) TSKgel GMH×L

(4)TSKgel G2500H×L

. Flow rate: 1.0mL/min

. Column temperature: 40 ° C

. Sample concentration: 1.5% (w/v) (diluted with tetrahydrofuran)

. Mobile phase solvent: tetrahydrofuran

. Standard polystyrene conversion

[Photoelastic coefficient]

The (meth)acrylic copolymer was measured for photoelastic coefficient in the following manner.

The polymer solution containing the (meth)acrylic copolymer obtained in the synthesis example was applied onto the release-treated surface of the release-treated polyethylene terephthalate film, and dried at 90 ° C for 3 minutes to form a dry film. A film (polymer layer) having a film thickness of 20 μm . The polymer layers having a dry film thickness of 20 μm were laminated to each other at 23 ° C / 50% RH for several times, and treated in an autoclave adjusted to 50 ° C / 5 atm for 20 minutes to prepare a polymer having a thickness of 1.0 mm. Floor. The polymer layer having a thickness of 1.0 mm was cut into a size of 15 mm × 50 mm, and this was mounted on an automatic wavelength scanning ellipsometer (model "M-220"; manufactured by JASCO Corporation), and the stress was measured to determine The hysteresis value was measured at a wavelength of 633 nm. The linear slope when the stress is the horizontal axis and the hysteresis value is the vertical axis is taken as the photoelastic coefficient of the (meth)acrylic copolymer.

[Synthesis Example 1]

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

[Synthesis Examples 2 to 3]

A polymer solution having a solid content concentration of 30% by mass was prepared in the same manner as in Synthesis Example 1, except that the monomer components used in the polymerization reaction were changed to those described in Table 1. The results are presented in Table 1.

[Example A1]

(1) Modulation of adhesive composition

The polymer solution obtained in Synthesis Example 1 (solid content concentration: 30% by mass) and I100 (solid content) of the (meth)acrylic copolymer contained in the solution were used as isocyanate compounds. Manufactured "D-94" 2.0 parts (solid content) and as a metal chelate compound 0.2 parts (solid content) of "M-12AT" manufactured by the company, and 0.2 parts ("100% by mass") of "A-50" manufactured by Zaken Chemical Co., Ltd. as a decane coupling agent, and adhered. Agent composition.

(2) Making of adhesive sheets

On the peeled polyethylene terephthalate film (PET film), the adhesive composition obtained in the above (1) was defoamed, coated with a knife coater, and dried at 90 ° C for 3 minutes. On the other hand, a coating film having a dry film thickness of 20 μm was formed. The peeled PET film was further bonded to the surface of the coating film opposite to the adhesion surface of the PET film, and allowed to stand at 23 ° C / 50% RH for 7 days for aging. An adhesive sheet having an adhesive layer having a thickness of 20 μm sandwiched between two PET films was obtained.

(3) Fabrication of a polarizing plate with an adhesive layer

On the peeled polyethylene terephthalate film (PET film), the adhesive composition obtained in the above (1) was defoamed, coated with a knife coater, and dried at 90 ° C for 3 minutes. A sheet having a coating film having a dry film thickness of 20 μm was obtained. The coating film surface of the sheet and the polyvinyl alcohol film surface of the polarizing plate (thickness: 60 μm) composed of the polyvinyl alcohol film of the polarizer and the cellulose triacetate film of the polarizer protective film are in contact with each other. The method was applied and allowed to stand at 23 ° C / 50% RH for 7 days for ripening. A polarizing plate having an adhesive layer of a PET film, an adhesive layer having a thickness of 20 μm, a polarizing plate, and a polarizer protective film was obtained.

[Examples B1 to B2, Comparative Examples A1 to A2, B1 to B3]

In Example 1, except that the polymer solution was changed to each synthesis example. The adhesive composition, the adhesive sheet, and the polarizing plate with the adhesive layer were obtained in the same manner as in Example A1 except that the polymer solution was changed and the composition was changed to the one shown in Table 2.

[assessment]

[Gel fraction]

From the adhesive layer of the adhesive sheet obtained in the example/comparative example, about 0.1 g of the adhesive was collected in a sample bottle, 30 mL of ethyl acetate was added, and after shaking for 4 hours, the contents of the vial were made of stainless steel of 200 mesh. The metal mesh was filtered, and the residue on the metal mesh was dried at 100 ° C for 2 hours, and the dry weight was measured. The gel fraction of the adhesive was determined by the following formula.

‧gel fraction (%) = (dry weight / adhesive collection weight) × 100 (%)

[Photoelastic coefficient]

In the adhesive sheets obtained in the examples/comparative examples, the adhesive layers having a thickness of 20 μm of the peeled PET film were laminated to each other in a 23° C./50% RH atmosphere, and were adjusted to an autoclave adjusted to 50° C./5 atm. The treatment was carried out for 20 minutes to prepare an adhesive layer having a thickness of 1.0 mm. The adhesive layer having a thickness of 1.0 mm was cut into a size of 15 mm × 50 mm, and this was mounted on an automatic wavelength scanning ellipsometer (model "M-220"; manufactured by JASCO Corporation), and the stress was measured to determine The hysteresis value was measured at a wavelength of 633 nm. The linear slope when the stress is the horizontal axis and the hysteresis value is the vertical axis is taken as the photoelastic coefficient of the adhesive layer.

[Light leakage test]

Two polarizing plates with an adhesive layer obtained in the examples/comparative examples (a laminate of a PET film/adhesive layer/polarizer/polarizer protective film) The test piece was produced by cutting to a size of 310 mm × 385 mm. The PET film is peeled off from the test piece, and the laminated body composed of the adhesive layer/polarizing sheet/polarizing sheet protective film is orthogonal to each other and the adhesive layer is bonded to the glass plate by using a laminating roll. The method is adhered to both sides of a glass plate having a thickness of 0.5 mm. The obtained laminate was kept in an autoclave adjusted to 50 ° C / 5 atm for 20 minutes to prepare a test plate. The test plate was allowed to stand under the conditions of a temperature of 80 ° C / dry for 500 hours, and light leakage was observed on the basis of the following criteria.

AA: No light leakage is observed

BB: I noticed some light leakage

CC: Obviously observed light leakage

[Durability test (heat resistance, heat and humidity resistance test)]

The polarizing plate (PET film/adhesive layer/layer of polarizer/polarizer protective film) with the adhesive layer obtained in the example/comparative example was cut into a size of 150 mm×250 mm to prepare a test piece. The PET film is peeled off from the test piece, and the laminated body composed of the adhesive layer/polarizer/polarizer protective film is laminated on the single side of the glass plate having a thickness of 0.5 mm by the adhesive layer and the glass plate by using a laminating roll. Paste. The obtained laminate was kept in an autoclave adjusted to 50 ° C / 5 atm for 20 minutes to prepare a test plate. Make two identical test plates. The test plate was allowed to stand under the conditions of a temperature of 80 ° C / dry (heat resistance) or under the conditions of a temperature of 60 ° C / humidity of 90% RH (moisture resistance) for 500 hours, and the defects were observed on the following basis (bubble, float) , peeling off) and assessing.

AA: no defect

BB: The defect area is 5% or less, and there is no problem in use.

CC: The defect area exceeds 5%, there is a problem in use.

‧D-94: hexamethylene diisocyanate cross-linking agent (manufactured by Zaken Chemical Co., Ltd.; 90% by mass solid content)

‧L-45: toluene diisocyanate cross-linking agent (manufactured by Soken Chemical Co., Ltd.; solid content 45 mass%, ethyl acetate/toluene solution)

‧E-5C: epoxy crosslinking agent (manufactured by Zaken Chemical Co., Ltd.; solid content 5 mass%)

‧M-12AT: Aluminum chelate crosslinker (manufactured by Zaken Chemical Co., Ltd.; solid content 10% by mass, toluene / acetonitrile acetone solution)

‧A-50: decane coupling agent (manufactured by Zaken Chemical Co., Ltd.; solid content 50% by mass, toluene solution)

Claims (10)

An adhesive layer for a polarizing plate comprising a (meth)acrylic copolymer (A1) having a photoelastic coefficient of -200×10 ^-12 to +200×10 ^-12 (m ² /N) and an aromatic ring-free The adhesive composition of the isocyanate crosslinking agent (B1) is formed, and the photoelastic coefficient is -200×10 ^-12 to +200×10 ^-12 (m ² /N), and is directly connected to the polarizer. Wherein the (meth)acrylic copolymer (A1) has a (meth) group derived from a homopolymer having a photoelastic coefficient of -1000×10 ^-12 to -100×10 ^-12 (m ² /N) a constituent unit of an alkyl acrylate (a11), and an aromatic ring-containing (meth)acrylic acid having a photoelastic coefficient derived from a homopolymer of +500×10 ^-12 to +2000×10 ^-12 (m ² /N) The constituent unit of the ester (a12). The adhesive layer for a polarizing plate according to the first aspect of the invention, wherein the isocyanate crosslinking agent (B1) is a hexamethylene diisocyanate crosslinking agent. The adhesive layer for a polarizing plate according to claim 1 or 2, wherein the adhesive composition contains an isocyanate crosslinking agent (B1) 0.05 to 10 with respect to 100 parts by mass of the copolymer (A1). Parts by mass. An adhesive layer for a polarizing plate comprising an (meth)acrylic copolymer (A2) having a photoelastic coefficient of less than -200×10 ^-12 and an adhesive of an aromatic ring-containing isocyanate crosslinking agent (B2) The composition was formed to have a photoelastic coefficient of -200 × 10 ^-12 to +200 × 10 ^-12 (m ² /N), and was placed in direct contact with the polarizer. An adhesive layer for a polarizing plate according to item 4 of the patent application, The isocyanate crosslinking agent (B2) is at least one selected from the group consisting of a toluene diisocyanate crosslinking agent and a benzodimethyl diisocyanate crosslinking agent. The adhesive layer for a polarizing plate according to the fourth aspect of the invention, wherein the adhesive composition contains 2 parts by mass of the isocyanate crosslinking agent (B2) based on 100 parts by mass of the copolymer (A2). the above. An adhesive sheet for a polarizing plate, which has the adhesive layer according to any one of claims 1 to 6. A polarizing plate with an adhesive layer, comprising a polarizer, and an adhesive layer according to any one of claims 1 to 6 which is directly laminated on at least one side of the polarizer. An adhesive composition for a polarizing plate comprising a (meth)acrylic copolymer (A1) having a photoelastic coefficient of -200×10 ^-12 to +200×10 ^-12 (m ² /N) and containing no fragrance The cyclic isocyanate crosslinking agent (B1) is used to form the adhesive layer according to claim 1, wherein the (meth)acrylic copolymer (A1) has a homopolymer derived from The photoelastic coefficient is -1000×10 ^-12 to -100×10 ^-12 (m ² /N) of the alkyl (meth) acrylate (a11), and the photoelastic coefficient derived from the homopolymer is a constituent unit of an aromatic ring-containing (meth) acrylate (a12) of +500 × 10 ^-12 to +2000 × 10 ^-12 (m ² /N). An adhesive composition for a polarizing plate comprising a (meth)acrylic copolymer (A2) having a photoelastic coefficient of less than -200×10 ^-12 (m ² /N), which is crosslinked with an aromatic ring-containing isocyanate The agent (B2) is used to form the adhesive layer described in claim 4 of the patent application.