CN107924009B - Adhesive layer for polarizing plate and adhesive composition - Google Patents

Abstract

The invention provides an adhesive layer for a polarizing plate, which can be applied to a structure in which at least one of polarizer protective films formed on both surfaces of a polarizer has been omitted in the past, and has excellent light leakage prevention property and durability, and an adhesive layer for a polarizing plate, which comprises a polarizing film having a photoelastic coefficient of-200 × 10^‑12～+200×10^‑12(m²An adhesive composition comprising a (meth) acrylic copolymer and an isocyanate-based crosslinking agent having no aromatic ring, wherein the adhesive layer for polarizing plates has a photoelastic coefficient of-200 × 10^‑12～+200×10^‑12(m²N) and a polarizing element, wherein the (meth) acrylic copolymer has a photoelastic coefficient of-1000 × 10 from a homopolymer^‑12～‑100×10^‑12(m²Structural units of alkyl (meth) acrylates of the formula (I)/N) and a photoelastic coefficient of +500 × 10 from the homopolymer^‑12～+2000×10^‑12(m²Structural units of (meth) acrylates containing aromatic rings.

Description

Adhesive layer for polarizing plate and adhesive composition

Technical Field

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

Background

The liquid crystal cell has a structure in which a liquid crystal layer is sandwiched between two substrates (e.g., glass plates). A polarizing plate is bonded to the surface of a substrate constituting a liquid crystal cell via an adhesive layer. In general, a polarizing plate has a structure in which a polarizing element protective film made of triacetyl cellulose or the like is laminated on both surfaces of a polarizing element having a polarizing function in order to improve mechanical properties and optical durability thereof.

In recent years, there has been a demand for weight reduction and thickness reduction of polarizing plates, and it has been attempted to omit one or both of the polarizer protective films formed on both surfaces of the polarizer (see, for example, patent document 1). However, in the polarizing plate in which one or both of the polarizer protective films are omitted, since the pressure-sensitive adhesive layer is in direct contact with the polarizer, the pressure-sensitive adhesive layer is subjected to a large stress due to thermal shrinkage of the polarizer in a high-temperature, high-humidity and high-temperature environment, and thus defects such as peeling of the pressure-sensitive adhesive layer are likely to occur. Further, there is also a problem that birefringence is likely to occur because stress applied to the adhesive layer is increased due to thermal shrinkage of the polarizing element.

Therefore, the adhesive for polarizing plates is required to have excellent light leakage preventing properties and durability. With respect to the problem of light leakage, patent document 2 describes a polarizing film having an adhesive layer formed of an adhesive composition for a polarizing plate containing a large amount of an isocyanate compound; patent document 3 describes a pressure-sensitive adhesive composition for a polarizing plate containing a component having a positive photoelastic coefficient. However, none of these documents describes that the adhesive layer is directly disposed on the polarizing element.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2012-128099

Patent document 2: japanese patent application laid-open No. 2010-090354

Patent document 3: japanese patent laid-open publication No. 2004-516359

Disclosure of Invention

Technical problem to be solved by the invention

A polarizing plate in which at least one of the polarizer protective films formed on both surfaces of the polarizer has been omitted in the past is required to have more excellent light leakage prevention property and durability. The present invention has been made to solve the above problems, and an object of the present invention is to provide an adhesive layer having excellent light leakage prevention property and durability, which can be applied to a structure in which at least one of polarizer protective films formed on both surfaces of a polarizer has been omitted.

Technical scheme for solving technical problem

The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, it has been found that when a (meth) acrylic copolymer and a crosslinking agent described below are used, the above-mentioned pressure-sensitive adhesive layer having excellent light leakage preventing properties and durability can be formed. That is, the present inventors have found that the above-mentioned technical problem can be solved by using an 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]An adhesive layer for polarizing plate, which comprises a layer containing a material having a photoelastic coefficient of-200 × 10^-12～+200×10^-12(m²An adhesive composition comprising a (meth) acrylic copolymer (A1) of N) and an isocyanate-based crosslinking agent (B1) having no aromatic ring, wherein the photoelastic coefficient of the adhesive layer for polarizing plates is-200 × 10^-12～+200×10^-12(m²N) and a polarizing element, wherein the (meth) acrylic copolymer (A1) has a photoelastic coefficient of-1000 × 10 from a homopolymer^-12～-100×10^-12(m²Structural units of alkyl (meth) acrylates (a11) and a photoelastic coefficient of +500 × 10 from the homopolymer^-12～+2000×10^-12(m²of/N)A structural unit of (meth) acrylate (a12) containing an aromatic ring.

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

[3] The pressure-sensitive adhesive layer for a polarizing plate as described in the above [1] or [2], wherein the pressure-sensitive adhesive composition contains 0.05 to 10 parts by mass of an isocyanate-based crosslinking agent (B1) per 100 parts by mass of the copolymer (A1).

[4]An adhesive layer for polarizing plate, which comprises a layer containing a material having a photoelastic coefficient of less than-200 × 10^-12(m²A (meth) acrylic copolymer (A2) and an aromatic ring-containing isocyanate-based crosslinking agent (B2), and the photoelastic coefficient of the pressure-sensitive adhesive layer for polarizing plates is-200 × 10^-12～+200×10^-12(m²N) and is disposed in direct contact with the polarizing element.

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

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

[7] A pressure-sensitive adhesive sheet for polarizing plates, which comprises the pressure-sensitive adhesive layer according to any one of [1] to [6 ].

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

[9]A method for forming the above [1]]The adhesive composition for a polarizing plate comprising the adhesive layer as described in (1), which has a photoelastic coefficient of-200 × 10^-12～+200×10^-12(m²A (meth) acrylic copolymer (A1) having a photoelastic coefficient of-1000 × 10 from a homopolymer, and an isocyanate-based crosslinking agent (B1) having no aromatic ring^-12～-100×10^-12(m²Structural units of alkyl (meth) acrylates (a11) and a photoelastic coefficient of +500 × 10 from the homopolymer^-12～+2000×10^-12(m²Structural unit of (meth) acrylic ester containing aromatic ring (a 12).

[10]A method for forming the above [4]]The adhesive composition for a polarizing plate comprising the adhesive layer as described in (1), which has a photoelastic coefficient of less than-200 × 10^-12(m²A (meth) acrylic copolymer (A2) of (N) and an aromatic ring-containing isocyanate-based crosslinking agent (B2).

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention can provide an adhesive layer having excellent light leakage prevention properties and durability, which can be applied to a structure in which at least one of the polarizer protective films formed on both surfaces of the polarizer has been omitted in the related art.

Detailed Description

The adhesive composition for polarizing plates, the adhesive layer for polarizing plates, the adhesive sheet for polarizing plates, and the polarizing plate with an adhesive layer of the present invention will be described below. Hereinafter, the adhesive composition for polarizing plates, the adhesive layer for polarizing plates, and the adhesive sheet for polarizing plates of the present invention are also referred to as "adhesive composition", "adhesive layer", and "adhesive sheet", respectively.

[ pressure-sensitive adhesive composition for polarizing plate]

The adhesive composition for the 1 st polarizing plate of the present invention is used for forming an adhesive layer directly contacting with a polarizing element, and the adhesive composition for the 1 st polarizing plate comprises an adhesive having a photoelastic coefficient of-200 × 10^-12～+200×10^-12(m²A (meth) acrylic copolymer (A1) of N) and an isocyanate-based crosslinking agent (B1) containing no aromatic ring.

By crosslinking the (meth) acrylic copolymer having a photoelastic coefficient within the above range with an isocyanate-based crosslinking agent having no aromatic ring and having a small contribution to the photoelastic coefficient of the pressure-sensitive adhesive layer, a film having a photoelastic coefficient of-200 × 10 can be formed^-12～+200×10^-12(m²/N) an adhesive layer.

The adhesive composition for the 2 nd polarizing plate of the present invention is used for forming an adhesive layer directly contacting with a polarizing element, and the adhesive composition for the 2 nd polarizing plate comprises an adhesive layer having a photoelastic coefficient of less than-200 × 10^-12(m²A (meth) acrylic copolymer (A2) of (N) and an aromatic ring-containing isocyanate-based crosslinking agent (B2).

By crosslinking a (meth) acrylic copolymer having a negative photoelastic coefficient with an aromatic ring-containing isocyanate-based crosslinking agent which shifts the photoelastic coefficient of the pressure-sensitive adhesive layer to a positive value, it is possible to form a pressure-sensitive adhesive layer having a photoelastic coefficient of-200 × 10^-12～+200×10^-12(m²/N) an adhesive layer.

In the present specification, the copolymers (a1) and (a2) are collectively referred to as "copolymer (a)", the adhesive compositions for the 1 st and 2 nd polarizing plates of the present invention are also referred to as "1 st adhesive composition" and "2 nd adhesive composition", respectively, and they are collectively referred to as "adhesive composition of the present invention".

In the present specification, acrylic acid and methacrylic acid are collectively referred to as "(meth) acrylic acid". Further, a structural unit derived from a certain monomer a included in the polymer is also referred to as a "monomer a unit". For convenience, the ester (a) is also referred to as "monomer (a)".

In the present specification, unless otherwise specified, 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^-12m²N ". Inaddition, for example, -200 × 10^-12～+200×10^-12(m²/N) represents-200 × 10^-12(m²More than/N) +200 × 10^-12(m²the/N) is as follows. As do other numerical ranges.

The photoelastic coefficient of a homopolymer formed from each monomer was determined in the following manner.

The homopolymer used for the measurement of the photoelastic coefficient was prepared in the following manner. 100 parts by mass of a monomer and 100 parts by mass of an ethyl acetate solvent were charged into a reaction apparatus equipped with a stirrer, a reflux cooler, a thermometer and a nitrogen introduction tube, and the temperature was raised to 80 ℃ while introducing nitrogen. Then, 0.1 part by mass of 2,2' -azobisisobutyronitrile was added, and polymerization was performed at 80 ℃ for 6 hours in a nitrogen atmosphere. After the completion of the reaction, the reaction mixture was diluted with ethyl acetate to obtain a homopolymer solution of the monomer having a solid content of 30% by mass.

The homopolymer solution was applied to the release-treated surface of the polyethylene terephthalate film, and dried at 90 ℃ for 3 minutes to form a coating film (homopolymer layer) having a dry film thickness of 20 μm. The polymer layers having a dry film thickness of 20 μm were laminated to each other in an atmosphere of 23 ℃/50% RH for a plurality of times, and treated in an autoclave adjusted to 50 ℃/5atm for 20 minutes to prepare a polymer layer having a thickness of 1.0 mm.

A homopolymer layer having a thickness of 1.0mm was cut into a size of 15 mm. times.50 mm, and the cut layer was mounted on an automatic wavelength scanning ellipsometer (M220 type, manufactured by Nippon spectral Co., Ltd.) using a jig, and a retardation (retardation) was measured at a measurement wavelength of 633nm while changing the stress. The stress was linearly fitted to a graph having the abscissa and the retardation value as the ordinate, and the slope thereof was used as the photoelastic coefficient of a homopolymer formed from the monomer.

The glass transition temperature (Tg) of the homopolymer formed from each monomer can be determined, for example, by the values described in Polymer handbook (Polymer handbook), fourth edition (Wiley-Interscience 2003).

Further, with respect to the monomers whose Tg is not described in the above documents, for example, the Tg of a homopolymer synthesized under the following conditions is measured under the following conditions. 100 parts by mass of a monomer and 100 parts by mass of an ethyl acetate solvent were charged into a reaction apparatus equipped with a stirrer, a reflux cooler, a thermometer and a nitrogen introduction tube, and the temperature was raised to 80 ℃ while introducing nitrogen. Then, 0.1 part by mass of 2,2' -azobisisobutyronitrile was added, and polymerization was performed at 80 ℃ for 6 hours in a nitrogen atmosphere. The resulting homopolymer was sealed in a simple closed pan. The temperature was increased at 10 ℃/min in a nitrogen gas stream using a Differential Scanning Calorimeter (DSC), the thermal change was measured, a graph of "heat absorption" versus "temperature" was drawn, and the characteristic sharp change observed at this time was taken as the glass transition. Further, Tg is a value obtained from a DSC curve by a midpoint method.

[ (meth) acrylic copolymer (A1)]

The (meth) acrylic copolymer (A1) has a structural unit derived from a homopolymer of an alkyl (meth) acrylate (a11) having a photoelastic coefficient of-1000 to-100 and a structural unit derived from a homopolymer of an aromatic ring-containing (meth) acrylate (a12) having a photoelastic coefficient of +500 to + 2000. For example, the copolymer (a1) is a copolymer obtained by copolymerizing monomer components including the monomer (a11) and the monomer (a 12).

The monomer component (i.e., the raw material monomer component of (a 1)) is preferably a monomer having a polymerizable unsaturated double bond.

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

The copolymer (a1) having a photoelastic coefficient within the above range can be obtained 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. By using the copolymer (a1) and the aromatic ring-free isocyanate-based crosslinking agent (B1), the photoelastic coefficient of the adhesive layer can be made within the range described below, particularly close to zero, whereby light leakage of the polarizing plate can be suppressed.

Alkyl (meth) acrylates (a11) (monomer (a 11)))

The monomer (a11) is an alkyl (meth) acrylate whose homopolymer has a photoelastic coefficient of-1000 to-100. The aforementioned monomer having a photoelastic coefficient of a homopolymer within the range of-750 to-150 is preferable, and the aforementioned monomer within the range of-500 to-200 is more preferable.

By using the copolymer (a1) obtained by copolymerizing the monomer (a11) having a photoelastic coefficient of the homopolymer within the above range, flexibility can be imparted to the pressure-sensitive adhesive layer, and light leakage prevention can be exhibited.

The monomer (a11) is preferably an alkyl (meth) acrylate having a homopolymer Tg of-30 ℃ or lower, and the Tg is more preferably-100 to-30 ℃, and still more preferably-70 to-30 ℃.

The monomer (a11) may, for example, be CH₂＝CR¹-COOR²The compound represented by (A) is a compound in which the photoelastic coefficient of the homopolymer is within the above range. In the formula, R¹Is a hydrogen atom or a methyl group, R²Is an alkyl group having 1 to 20 carbon atoms. The number of carbons of the alkyl group is preferably 2 to 16, more preferably 4 to 12.

Examples of the monomer (a11) include n-butyl acrylate (-400; -50), 2-ethylhexyl acrylate (-700; -70), undecyl methacrylate (-190; -41), and dodecyl methacrylate (-460; -65), and the left side of the parenthesized numerical values indicates the photoelastic coefficient (× 10) of a homopolymer formed from each monomer^-12m²,/N), right side Tg (. degree. C.).

One monomer (a11) may be used alone, or two or more monomers may be used. When two or more monomers (a11) are used, it is preferable that each monomer satisfies the conditions of photoelastic coefficient and Tg.

The amount of the monomer (a11) used is preferably 50 to 90% by mass, more preferably 55 to 85% by mass, and still more preferably 60 to 80% by mass, based on 100% by mass of the raw material monomer component of the copolymer (a 1). When the amount of the monomer (a11) used is within the above range, the photoelastic coefficient of the resulting copolymer (A1) can be adjusted to the above range, which is preferable.

(meth) acrylate (a12) (monomer (a12)) containing aromatic ring

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

By using the copolymer (a1) obtained by copolymerizing the monomer (a12) whose homopolymer photoelastic coefficient is within the above range, appropriate durability can be imparted to the adhesive layer.

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

The monomer (a12) may, for example, be CH₂＝CR³-COOR⁴Of the compounds shownA compound having a photoelastic coefficient within the above range. In the formula, R³Is a hydrogen atom or a methyl group, R⁴Is a group containing aromatic ring. Examples of the aromatic ring-containing group include an aryl group such as a phenyl group, an aralkyl group such as a benzyl group, and an aryloxyalkyl group such as a phenoxyethyl group. R⁴The carbon number of (b) is preferably 6 to 12, more preferably 6 to 10, and further preferably 7 to 9.

Examples of the monomer (a12) include benzyl acrylate (1840; 6), benzyl methacrylate (1530; 54) and phenoxyethyl acrylate (1830; 22). The left side of the parenthesized numerical values indicates the photoelastic coefficient (× 10) of a homopolymer formed from each monomer^-12m²,/N), right side Tg (. degree. C.). Further, as the monomer (a12), phenyl acrylate, phenyl methacrylate, and phenoxyethyl methacrylate may, for example, be mentioned.

One monomer (a12) may be used alone, or two or more monomers may be used. When two or more monomers (a12) are used, it is preferable that each monomer satisfies the conditions of photoelastic coefficient and Tg.

The amount of the monomer (a12) used is preferably 9 to 40% by mass, more preferably 12 to 35% by mass, and still more preferably 15 to 30% by mass, based on 100% by mass of the raw material monomer component of the copolymer (a 1). When the amount of the monomer (a12) used is within the above range, the photoelastic coefficient of the resulting copolymer (A1) can be adjusted to the above range, which is preferable.

Monomers (a13) containing crosslinkable functional groups

The raw material monomer component of the copolymer (a1) preferably further contains a crosslinkable functional group-containing monomer (a13) which is a crosslinkable functional group-containing monomer capable of reacting with the isocyanate-based crosslinking agent (B1). That is, the copolymer (a1) preferably further has a structural unit derived from the monomer (a 13).

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) may 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 specific examples thereof include hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, and 8-hydroxyoctyl (meth) acrylate. The carbon number 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: carboxyl group-containing (meth) acrylates such as β -carboxyethyl (meth) acrylate, 5-carboxypentyl (meth) acrylate, mono (meth) acryloyloxyethyl succinate, and ω -carboxypolycaprolactone mono (meth) acrylate; acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, maleic acid.

One monomer (a13) may be used alone, or two or more monomers may be used.

The amount of the monomer (a13) used is preferably more than 0% by mass and 10% by mass or less, more preferably 0.5 to 7% by mass, and still more preferably 1 to 5% by mass, based on 100% by mass of the raw material monomer component of the copolymer (a 1). If the amount of the monomer (a13) used is not more than the above upper limit, the crosslink density formed by the copolymer (A1) and the crosslinking agent (B1) does not become excessively high. When the amount of the monomer (a13) used is not less than the lower limit, a crosslinked structure can be efficiently formed, and a pressure-sensitive adhesive layer having an appropriate strength can be obtained.

Other monomers

As the raw material monomer component of the copolymer (a1), other monomers such as alkyl (meth) acrylate, alkoxyalkyl (meth) acrylate, alkoxypolyalkylene glycol mono (meth) acrylate (アルコキシポリアルキレングリコールモノ (メタ) アクリレート), alicyclic group-containing (meth) acrylate, amino group-containing monomer, and amide group-containing monomer other than the above-mentioned monomer (a11) may be used within a range not impairing the physical properties of the copolymer (a 1). That is, the copolymer (A1) may have a structural unit derived from another monomer.

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-methacrylic acidEthylhexyl ester (420; -10) with respect to the values in parentheses, the left hand side indicates the photoelastic coefficient (× 10) of the homopolymer formed from the respective monomer^-12m²,/N), right side Tg (. degree. C.).

Examples of the alkoxyalkyl (meth) acrylate include methoxymethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxypropyl (meth) acrylate, 3-ethoxypropyl (meth) 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, ethoxydiethylene glycol mono (meth) acrylate and methoxytriethylene glycol mono (meth) acrylate.

Examples of the (meth) acrylate having an alicyclic group 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.

One or more of the other monomers may be used alone.

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 the (A1) is within the above range, but is preferably 0 to 10% by mass, and more preferably 0 to 5% by mass.

[ (meth) acrylic copolymer (A2)]

The (meth) acrylic copolymer (A2) is preferably 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 has, for example, a structural unit derived from a homopolymer of an alkyl (meth) acrylate (a21) having a photoelastic coefficient of less than-200, and can be obtained, for example, by copolymerizing a monomer component containing the monomer (a 21).

The monomer component (i.e., the raw material monomer component of (a 2)) is preferably a monomer having a polymerizable unsaturated double bond.

By using the copolymer (a2) and the aromatic ring-containing isocyanate-based crosslinking agent (B2), the photoelastic coefficient of the adhesive layer can be made within the range described below, particularly close to zero, whereby light leakage of the polarizing plate can be suppressed.

Alkyl (meth) acrylates (a21) (monomer (a 21)))

Examples of the monomer (a21) include the alkyl (meth) acrylate (a11) in which the photoelastic coefficient of the homopolymer is less than-200. The aforementioned monomer having a photoelastic coefficient of a homopolymer of from-750 to less than-200 is preferable, and the aforementioned monomer having a photoelastic coefficient of from-500 to less than-200 is more preferable.

One monomer (a21) may be used alone, or two or more monomers may be used. When two or more monomers (a21) are used, it is preferable that each monomer satisfies the condition of photoelastic coefficient.

The amount of the monomer (a21) used is preferably 59 to 99% by mass, more preferably 64 to 98% by mass, and still more preferably 69 to 97% by mass, based on 100% by mass of the raw material monomer component of the copolymer (a 2). When the amount of the monomer (a21) used is within the above range, the photoelastic coefficient of the resulting copolymer (A2) can be adjusted to the above range, which is preferable.

Monomers (a22) containing crosslinkable functional groups

The raw material monomer component of the copolymer (a2) preferably further contains a crosslinkable functional group-containing monomer (a22) which is a crosslinkable functional group-containing monomer capable of reacting with the isocyanate-based crosslinking agent (B2). That is, the copolymer (a2) preferably further has a structural unit derived from the monomer (a 22).

The monomer (a22) is exemplified by the above-mentioned monomer (a13) having a crosslinkable functional group, and the same is preferred. One monomer (a22) may be used alone, or two or more monomers may be used.

The amount of the monomer (a22) used is preferably more than 0% by mass and 10% by mass or less, more preferably 0.5 to 7% by mass, and still more preferably 1 to 5% by mass, based on 100% by mass of the raw material monomer component of the copolymer (a 2). If the amount of the monomer (a22) used is not more than the above upper limit, the crosslink density formed by the copolymer (A2) and the crosslinking agent (B2) does not become excessively high. When the amount of the monomer (a22) used is not less than the lower limit, a crosslinked structure can be efficiently formed, and a pressure-sensitive adhesive layer having an appropriate strength can be obtained.

Other monomers

As the raw material monomer component of the copolymer (a2), other monomers such as alkyl (meth) acrylates other than the above-mentioned monomer (a21), alkoxyalkyl (meth) acrylates, alkoxypolyalkylene glycol mono (meth) acrylates (アルコキシポリアルキレングリコールモノ (メタ) アクリレート), alicyclic group-containing (meth) acrylates, aromatic ring-containing (meth) acrylates, amino group-containing monomers, and amide group-containing monomers can be used within a range not impairing the physical properties of the copolymer (a 2). That is, the copolymer (A2) may have a structural unit derived from another monomer.

Examples of these monomers include the compounds described in "other monomers" in the section of copolymer (A1). Examples of the aromatic ring-containing (meth) acrylate include phenyl (meth) acrylate, benzyl (meth) acrylate, and phenoxyethyl (meth) acrylate.

However, from the viewpoint of adjusting the photoelastic coefficient of the copolymer (a2) within the above range, it is preferable to appropriately adjust the amounts of the alkyl (meth) acrylate having a photoelastic coefficient of a homopolymer of +100 to +1000 and the aromatic ring-containing (meth) acrylate having a photoelastic coefficient of a homopolymer of +500 to +2000 (the monomer (a 12)).

Examples of the alkyl (meth) acrylate having a photoelastic coefficient of a homopolymer of +100 to +1000 include methyl acrylate (600), t-butyl methacrylate (130), n-butyl methacrylate (320) and 2-ethylhexyl methacrylate (420). The values in parentheses indicate the photoelastic of the homopolymer formed from the respective monomerCoefficient of performance (× 10)^-12m²/N)。

One or more of the other monomers may be used alone.

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 preferably 0 to 35% by mass, more preferably 0 to 30% by mass, and still more preferably 0 to 26% by mass.

Production conditions of [ (meth) acrylic acid-based copolymer (A)]

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

The copolymer (a) can be obtained by, for example, copolymerizing the monomer components described above, and may be a random copolymer or a block copolymer. Among them, random copolymers are preferable.

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; alicyclic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane, and cyclooctane; ethers such as diethyl ether, diisopropyl ether, 1, 2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, phenetole, and diphenyl ether; halogenated hydrocarbons such as chloroform, carbon tetrachloride, 1, 2-dichloroethane, chlorobenzene, and the like; 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; amides such as N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone; nitriles such as acetonitrile and benzonitrile; sulfoxides such as dimethyl sulfoxide and sulfolane. These polymerization solvents may be used alone or in combination of two or more.

Examples of the polymerization initiator include azo initiators and peroxide initiators. Specifically, the azo compound may, for example, be 2,2' -azobisisobutyronitrile, or the peroxide may, for example, be benzoyl peroxide or lauroyl peroxide. Among them, azo compounds are preferred. Among them, azo compounds are preferred. Examples of the azo compound include 2,2' -azobisisobutyronitrile, 2' -azobis (4-methoxy-2, 4-dimethylvaleronitrile), 2' -azobis (2-cyclopropylpropionitrile), 2' -azobis (2, 4-dimethylvaleronitrile), 2' -azobis (2-methylbutyronitrile), 1' -azobis (cyclohexane-1-carbonitrile), 2- (carbamoylazo) isobutyronitrile, 2-phenylazo-4-methoxy-2, 4-dimethylvaleronitrile, dihydrochloride of 2,2' -azobis (2-amidinopropane), 2' -azobis (N, N ' -dimethyleneisobutyramidine), 2' -azobis (isobutyramide) dihydrate, 2' -azobis (isobutyramide) dihydrate, 4,4 '-azobis (4-cyanovaleric acid), 2' -azobis (2-cyanopropanol), dimethyl-2, 2 '-azobis (2-methylpropionate), 2' -azobis [ 2-methyl-N- (2-hydroxyethyl) propionamide ]. These polymerization initiators may be used singly or in combination of two or more.

The polymerization initiator is used in an amount of usually 0.01 to 5 parts by mass, preferably 0.1 to 3 parts by mass, based on 100 parts by mass of the raw material monomer component of the (meth) acrylic copolymer (a). In the polymerization reaction, a polymerization initiator, a chain transfer agent, a monomer component, and a polymerization solvent may be added as appropriate.

Physical Properties and content of [ (meth) acrylic acid-based copolymer (A)]

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

The weight average molecular weight (M) of the (meth) acrylic copolymer (A) measured by gel permeation chromatography (GPC method)_w) The polystyrene equivalent value is usually 30 to 200 ten thousand, preferably 40 to 180 ten thousand, and more preferably 50 to 150 ten thousand. By using the copolymer (a) having Mw within the above range and having the above monomer unit, the balance of adhesive force can be easily obtained, and an adhesive composition having a viscosity suitable for coating can be formed. Furthermore, by using M_wWith 50 ten thousand or more of the copolymer (A), a pressure-sensitive adhesive layer having higher durability can be obtained.

Molecular weight distribution (M) of (meth) acrylic copolymer (A) measured by GPC method_w/Mn) 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 calculated from, for example, the monomer units constituting the copolymer and the content ratio thereof according to the Fox equation. For example, the (meth) acrylic copolymer (A) is preferably synthesized under the condition that the glass transition temperature (Tg) obtained from the Fox formula is usually-70 to-10 ℃ and preferably-60 to-20 ℃. By using the (meth) acrylic copolymer (a) having such a glass transition temperature (Tg), an adhesive composition having excellent stress relaxation properties and durability and excellent adhesiveness at room temperature can be obtained.

Fox equation: 1/Tg ═ W₁/Tg₁)+(W₂/Tg₂)+……+(W_m/Tg_m)

W₁+W₂+……+W_m＝1

Wherein Tg is the glass transition temperature (K) of the (meth) acrylic copolymer (A), Tg₁、Tg₂、……、Tg_mIs the glass transition temperature (K), W, of a homopolymer composed of the monomers₁、W₂、……、W_mThe weight fraction in the above copolymer (A) is a structural unit derived from each monomer. As the weight fraction of the structural unit derived from each monomer, the charge ratio of each monomer to the whole monomers at the time of copolymer synthesis can be used.

The glass transition temperature of the homopolymer composed of the monomers in the above Fox formula can be, for example, a value described in Polymer Handbook (Polymer Handbook), fourth edition (Wiley-Interscience 2003). For the monomer having a Tg not described in the above document, for example, a value obtained by the above method can be used.

The content of the (meth) acrylic copolymer (A1) in the adhesive composition 1 is usually 60 to 99.95% by mass, preferably 70 to 99.5% by mass, and particularly preferably 80 to 99.0% by mass, based on 100% by mass of the solid content excluding the organic solvent in the composition. When the content of the (meth) acrylic copolymer (a1) is within the above range, the balance of the performance as an adhesive can be achieved and the adhesive properties are excellent.

The content of the (meth) acrylic copolymer (A2) in the adhesive composition of claim 2 is usually 60 to 98.0% by mass, preferably 70 to 96.2% by mass, and particularly preferably 80 to 92.6% by mass, based on 100% by mass of the solid content excluding the organic solvent in the composition. When the content of the (meth) acrylic copolymer (a2) is within the above range, the balance of the performance as an adhesive can be achieved and the adhesive properties are excellent.

[ crosslinking agent (B)]

The adhesive composition 1 further contains an isocyanate-based crosslinking agent (B1) containing no aromatic ring. The 2 nd adhesive composition further contains an aromatic ring-containing isocyanate-based crosslinking agent (B2).

Isocyanate crosslinking agent (B1)

As the isocyanate-based crosslinking agent (B1), an isocyanate compound having no aromatic ring and having an isocyanate group of 2 or more in 1 molecule is generally used. By crosslinking the (meth) acrylic copolymer (a1) with the crosslinking agent (B1), a crosslinked product (network polymer) having excellent durability can be formed. Further, by using a crosslinking agent (B1) containing no aromatic ring together with the copolymer (A1) having a photoelastic coefficient in the range of-200 to +200, a pressure-sensitive 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 (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 efficiency of the crosslinking reaction between the (meth) acrylic copolymer (A1) and the crosslinking agent (B1) and in terms of flexibility of the adhesive layer.

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

Examples of the isocyanate compound having 3 or more isocyanate groups in 1 molecule include aliphatic polyisocyanates and alicyclic polyisocyanates.

Examples of the crosslinking agent (B1) include polymers (e.g., dimers, trimers, biurets, and isocyanurates) of the above-mentioned isocyanate compounds having an isocyanate group of 2 or more, derivatives (e.g., addition reaction products of a polyol and 2 or more molecules of the above-mentioned diisocyanate compounds), and polymers. Examples of the polyol in the derivative include trihydric or higher alcohols such as trimethylolpropane, glycerol and pentaerythritol; examples of the high molecular weight polyol include polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol and polyisoprene polyol.

Examples of such isocyanate compounds include biuret or isocyanurate of hexamethylene diisocyanate, reaction products of trimethylolpropane and hexamethylene diisocyanate (for example, three-molecule adducts of hexamethylene diisocyanate), polyether polyisocyanates, and polyester polyisocyanates.

Among the crosslinking agents (B1), hexamethylene diisocyanate based crosslinking agents are preferable in terms of improving the aging property and light leakage prevention property. Examples of the hexamethylene diisocyanate-based crosslinking agent include hexamethylene diisocyanate and its derivatives, biuret compounds, and isocyanurate compounds. Further, the commercially available product may, for example, be "D-94" manufactured by Suyamo chemical company (Dayamo chemical Co., Ltd.).

One kind of the crosslinking agent (B1) may be used alone, or two or more kinds may be used.

The content of the crosslinking agent (B1) in the adhesive composition 1 is usually 0.05 to 10 parts by mass, preferably 0.5 to 8 parts by mass, and more preferably 1 to 5 parts by mass, based on 100 parts by mass of the (meth) acrylic copolymer (a 1). When the content of the crosslinking agent (B1) is within the above range, the balance between durability and light leakage preventing property is easily obtained, and therefore, the content is preferable.

Isocyanate crosslinking agent (B2)

As the isocyanate-based crosslinking agent (B2), an aromatic ring-containing isocyanate compound having an isocyanate group of 2 or more in 1 molecule is generally used. By crosslinking the (meth) acrylic copolymer (a2) with the crosslinking agent (B2), a crosslinked product (network polymer) having excellent durability can be formed. Further, by using the aromatic ring-containing crosslinking agent (B2) together with the copolymer (A2) having a photoelastic coefficient of less than-200, a pressure-sensitive 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, and more preferably 3 to 6. When the number of isocyanate groups is within the above range, it is preferable in terms of efficiency of the crosslinking reaction between the (meth) acrylic copolymer (A2) and the crosslinking agent (B2) and in terms of flexibility of the adhesive layer.

The diisocyanate compound having 2 isocyanate groups in 1 molecule may, for example, be an aromatic diisocyanate. Examples of the aromatic diisocyanate include aromatic diisocyanates having 8 to 30 carbon atoms such as phenylene diisocyanate, toluene diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, and diphenyl propane diisocyanate.

The isocyanate compound having 3 or more isocyanate groups in 1 molecule may, for example, be an aromatic polyisocyanate. Specifically, 2,4, 6-triisocyanate toluene, 1,3, 5-triisocyanate benzene, and 4,4',4 ″ -triphenylmethane triisocyanate may, for example, be mentioned.

Examples of the crosslinking agent (B2) include polymers (e.g., dimers, trimers, biurets, and isocyanurates) of the above-mentioned isocyanate compounds having an isocyanate group of 2 or more, derivatives (e.g., addition reaction products of a polyol and 2 or more molecules of the above-mentioned diisocyanate compounds), and polymers. Examples of the polyol in the derivative include trihydric or higher alcohols such as trimethylolpropane, glycerol and pentaerythritol; examples of the high molecular weight polyol include polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol and polyisoprene polyol.

Examples of such isocyanate compounds include trimers of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanates, biuret or isocyanurate of toluene diisocyanate, reaction products of trimethylolpropane with toluene diisocyanate or xylylene diisocyanate (e.g., three-molecule adducts of toluene diisocyanate or xylylene diisocyanate), polyether polyisocyanates, and polyester polyisocyanates.

Among the crosslinking agents (B2), at least one selected from the group consisting of toluene diisocyanate-based crosslinking agents and xylylene diisocyanate-based crosslinking agents is preferable in terms of improvement of curability and light leakage prevention, and toluene diisocyanate-based crosslinking agents are more preferable. Examples of the toluene diisocyanate-based crosslinking agent include toluene diisocyanate and its derivatives, biuret compounds, and isocyanurate compounds. Examples of the xylylene diisocyanate-based crosslinking agent include xylylene diisocyanate and its derivatives, biuret compounds and isocyanurate compounds. Further, as a commercially available product, for example, "L-45" manufactured by Soken chemical Co.

One kind of the crosslinking agent (B2) may be used alone, or two or more kinds may be used.

The content of the crosslinking agent (B2) in the adhesive composition 2 is usually 2 parts by mass or more, preferably 4 to 30 parts by mass, and more preferably 8 to 15 parts by mass, per 100 parts by mass of the (meth) acrylic copolymer (a 2). When the content of the crosslinking agent (B2) is within the above range, even a composition containing the copolymer (A2) having a negative photoelastic coefficient can form a layer having a photoelastic coefficient close to zero, and therefore, the composition is preferable in that the balance between durability and light leakage prevention property can be easily obtained.

Other crosslinking Agents

Each of the 1 st and 2 nd adhesive compositions may further contain the above-mentioned crosslinking agent (B1) or a crosslinking agent other than the above-mentioned crosslinking agent (B2) as long as the photoelastic coefficient of the resulting adhesive layer is within the above-mentioned range. For example, by using a crosslinking agent which does not significantly shift the photoelastic coefficient of the pressure-sensitive adhesive layer to the positive value side in combination with the above crosslinking agent, the durability can be further improved while maintaining the photoelastic coefficient within the range described below.

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

When another crosslinking agent is used in the 1 st and 2 nd adhesive compositions, the content of the crosslinking agent is preferably 2 parts by mass or less, more preferably 0.01 to 1.5 parts by mass, and still more preferably 0.03 to 1 part by mass, per 100 parts by mass of the (meth) acrylic copolymer (a).

<Metal chelate (B3)>

Examples of the metal chelate compound (B3) include compounds in which a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, or zirconium is coordinated, such as alkoxide, acetylacetone, or ethyl acetoacetate.

Among them, aluminum chelate compounds are particularly preferable. Specifically, the aluminum isopropoxide, aluminum sec-butoxide, ethyl aluminum diisopropyl acetoacetate, ethyl aluminum triacetylacetate, and aluminum triacetylacetonate may be mentioned. Further, examples of commercially available products include "M-12 AT" manufactured by Soken chemical Co.

One metal chelate compound (B3) may be used alone, or two or more metal chelate compounds may be used.

The metal chelate compound (B3) crosslinks the (meth) acrylic copolymer (a) by a coordinate bond (pseudo-crosslinking). When a metal chelate (B3) is further used as a crosslinking agent, the crosslinking is maintained at room temperature, the polymer exhibits cohesiveness, and at high temperature, the crosslinking is partially released, so that the pressure-sensitive adhesive layer exhibits more excellent flexibility.

Epoxy Compound (B4)

As the epoxy compound (B4), an epoxy compound having an epoxy group number of 2 or more in 1 molecule is generally used. Examples thereof may include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol triglycidyl ether, 1, 3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N, N ', N' -tetraglycidylmethylenem-xylylenediamine, N, N, N ', N' -tetraglycidylaminophenylmethane, triglycidyl isocyanurate, m-N, N-diglycidylaminophenylglycidyl ether, N, N-diglycidyltoluidine and N, N-diglycidylaniline. Further, examples of commercially available products include "E-5C" manufactured by Soken chemical Co.

[ silane coupling agent (C)]

The adhesive composition of the present invention preferably further contains a silane coupling agent (C). The silane coupling agent (C) strongly bonds the pressure-sensitive adhesive layer to an adherend such as a glass plate, and contributes to preventing peeling of the polarizing plate in a high-humidity and high-heat environment.

Examples of the silane coupling agent (C) include: silane coupling agents containing polymerizable unsaturated groups such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane; epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane and 2- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane; amino group-containing silane coupling agents such as 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane and N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane; halogen-containing silane coupling agents such as 3-chloropropyltrimethoxysilane, and 3-oxobutanoic acid-3- (trimethoxysilyl) propyl ester. Further, examples of commercially available products include "A-50" manufactured by Soken chemical Co.

In the adhesive composition of the present invention, the content of the silane coupling agent (C) is usually 1 part by mass or less, preferably 0.01 to 1 part by mass, and more preferably 0.05 to 0.5 part by mass, based on 100 parts by mass of the (meth) acrylic copolymer (a). When the content is within the above range, the peeling of the polarizing plate in a high-humidity environment or the bleeding of the silane coupling agent (C) in a high-temperature environment tends to be prevented.

[ antistatic agent (D)]

The antistatic agent (D) can be used, for example, for the purpose of reducing 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 surfactants, ionic compounds, and conductive polymers.

Examples of the surfactant include: quaternary ammonium salts, amide quaternary ammonium salts, pyridinium salts, cationic surfactants having cationic groups such as primary amino groups to tertiary amino groups, and the like; anionic surfactants having anionic groups such as sulfonate, sulfate, and phosphate groups; amphoteric surfactants such as alkylbetaines, alkylimidazolium betaines, alkyl amine peroxides, and amino acid sulfates; nonionic surfactants such as fatty acid glycerides, sorbitan fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene alkylamine fatty acid esters, N-hydroxyethyl-N-2-hydroxyalkylamines, and alkyldiethanolamides.

The surfactant may be a reactive emulsifier having a polymerizable group, and a polymer surfactant obtained by increasing the molecular weight of a monomer component containing the surfactant or the reactive emulsifier may be used.

The ionic compound is composed of a cationic moiety and an anionic moiety, and can be in any one of a solid state and a liquid state at room temperature (23 ℃/50% RH).

The cationic moiety constituting the ionic compound may be either an inorganic cation or an organic cation, or both. The inorganic cation is preferably an alkali metal ion or an alkaline earth metal ion, and more preferably Li having excellent antistatic properties⁺、Na⁺And K⁺. As is provided withExamples of the organic cation include a pyridinium cation, a piperidine cation, a pyrrolidone cation, a pyrroline cation, a pyrrole cation, an imidazolium cation, a tetrahydropyrimidine cation, a dihydropyrimidine cation, a pyrazole cation, a dihydropyrazole cation (ピラゾリニウムカチオン), a tetraalkylammonium cation, a trialkylsulfonium cation, a tetraalkylphosphine cation, and derivatives thereof.

The anionic moiety constituting the ionic compound is not particularly limited as long as it is capable of forming an ionic compound by ionic bonding with the cationic moiety. Specifically, F-, Cl-, Br-, I-, AlCl₄ ^-、Al₂Cl₇ ^-、BF₄ ^-、PF₆ ^-、SCN^-、ClO₄ ^-、NO₃ ^-、CH₃COO^-、CF₃COO^-、CH₃SO₃ ^-、CF₃SO₃ ^-、(CF₃SO₂)₂N^-、(F₂SO₂)₂N^-、(CF₃SO₂)₃C^-、AsF₆ ^-、SbF₆ ^-、NbF₆ ^-、TaF₆ ^-、(CN)₂N^-、C₄F₉SO₃ ^-、(C₂F₅SO₂)₂N^-、C₃F₇COO^-And (CF)₃SO₂)(CF₃CO)N^-. Among these, anions containing a fluorine atom are preferable because of ionic compounds capable of providing a low melting point, and (F) is particularly preferable₂SO₂)₂N^-And (CF)₃SO₂)₂N^-。

The ionic compound is preferably lithium bistrifluoromethanesulfonimide, lithium tris (trifluoromethanesulfonyl) methane, potassium bistrifluoromethanesulfonimide, 1-ethylpyridinium hexafluorophosphate, 1-butylpyridinium hexafluorophosphate, 1-hexyl-4-methylpyridinium hexafluorophosphate, 1-octyl-4-methylpyridinium bistrifluorosulfonimide, 1-octyl-4-methylpyridinium bistrifluoromethanesulfonimide, tributylmethylammonium bistrifluoromethanesulfonimide, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium tetrafluoroborate, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium tetrafluoroborate Bis (trifluoromethanesulfonyl) imide, 1-octyl pyridine fluorosulfide (1- オクチルピリジニウムフルオロスホニウムイミド), 1-octyl-3-methylpyridine, trifluoromethanesulfonimide (トリフルオロスルホニウムイミド).

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, and more preferably 0.05 to 2.5 parts by mass, based on 100 parts by mass of the (meth) acrylic copolymer (a).

[ organic solvent (E)]

The pressure-sensitive adhesive composition of the present invention preferably contains an organic solvent (E) for adjusting the coatability thereof. Examples of the organic solvent include solvents listed in the section of "production conditions of (meth) acrylic copolymer (a)", as polymerization solvents. For example, the pressure-sensitive adhesive composition can be prepared by mixing a polymer solution containing the (meth) acrylic copolymer (a) and the polymerization solvent obtained by the above copolymerization with the crosslinking agent (B). In the 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, "solid content" means all components except the organic solvent (E) among the components contained in the binder composition, and "solid content concentration" means a ratio of the solid content to 100 mass% of the binder composition.

[ additive agent]

The adhesive composition of the present invention may contain, in addition to the above components, one or more selected from an antioxidant, a light stabilizer, a metal corrosion inhibitor, a tackifier, a plasticizer, a crosslinking accelerator, a (meth) acrylic polymer other than the above (a), and a rework agent (リワーク agent) within a range not to impair the effects of the present invention.

[ preparation of adhesive composition for polarizing plate]

The adhesive composition of the present invention can be prepared by mixing the (meth) acrylic copolymer (a), the crosslinking agent (B), and other components used as needed by a conventionally known method. For example, the crosslinking agent (B) and other components used as needed may be blended in a polymer solution containing the polymer obtained in the synthesis of the (meth) acrylic copolymer (A).

By using the pressure-sensitive adhesive composition of the present invention, the light leakage phenomenon can be suppressed even when the pressure-sensitive adhesive layer is formed on a polarizing plate having a polarizing element protective film only on one surface of a polarizing element and a polarizing plate having no polarizing element protective film on both surfaces of a polarizing element. In the present invention, even in a structure in which the pressure-sensitive adhesive layer is in direct contact with the polarizing element, the pressure-sensitive adhesive layer can be prevented from being broken, and the polarizing plate can be prevented from being peeled off in a high-temperature, high-humidity environment.

The adhesive composition is suitable for use in bonding a substrate constituting a liquid crystal cell to a polarizing element.

[ pressure-sensitive adhesive layer for polarizing plate]

The adhesive layer for the 1 st polarizing plate of the present invention is formed from the 1 st adhesive composition. The adhesive layer for the 2 nd polarizing plate of the present invention is formed from the 2 nd adhesive composition. The 1 st and 2 nd adhesive layers are also collectively referred to as "adhesive layers of the invention".

The pressure-sensitive adhesive layer of the present invention has a photoelastic coefficient of-200 to +200, preferably-150 to +150, more preferably-100 to +100, and still more preferably-70 to + 70. the unit of the photoelastic coefficient is "× 10^-12m²/N”。

The photoelastic coefficient is obtained, for example, by bonding the pressure-sensitive adhesive layers to each other a plurality of times to produce a laminate having a thickness of about 1.0mm, and measuring the laminate at a measurement wavelength of 633 nm. The detailed measurement conditions are described in examples.

The pressure-sensitive adhesive layer of the present invention has the above properties and is excellent in light leakage prevention property under a high-temperature, high-humidity environment. Further, since the pressure-sensitive adhesive layer of the present invention is excellent in durability, the pressure-sensitive adhesive layer is less likely to be broken or peeled from the polarizing plate.

The pressure-sensitive adhesive layer of the present invention has a gel fraction of preferably 40 mass% or more, more preferably 50 to 97 mass%, and even more preferably 60 to 95 mass%, from the viewpoint of suppressing warpage, cohesive force, adhesive force, and removability of the polarizing plate. If the gel fraction is within the above range, the adhesive layer exhibits excellent durability. The detailed measurement conditions are described in examples.

The pressure-sensitive adhesive layer of the present invention can be obtained, for example, by carrying out a crosslinking reaction in the above-mentioned pressure-sensitive adhesive composition, specifically, by crosslinking the (meth) acrylic polymer (a) with the crosslinking agent (B).

The conditions for forming the adhesive layer are, for example, as follows. The adhesive composition of the present invention is applied to a support at a temperature that varies depending on the type of solvent, but the solvent is usually dried at 50 to 150 ℃ and preferably 60 to 100 ℃ for usually 1 to 10 minutes and preferably 2 to 7 minutes to remove the solvent, thereby forming a coating film. The thickness of the dried coating film is usually 5 to 75 μm, preferably 10 to 50 μm, and the thickness of the finally obtained adhesive layer is preferably within the above range. The film thickness can be measured, for example, by a rotary dial thickness gauge (ダイヤルシックネスゲージ).

The adhesive layer is preferably formed under the following conditions. The adhesive composition of the present invention is applied to a support to form a coating film under the above conditions, and after a cover film is attached to the coating film as required, the coating film is cured in an environment of usually 5 to 60 ℃, preferably 15 to 40 ℃, and usually 30 to 70% RH, preferably 40 to 70% RH for usually 3 days or longer, preferably 7 to 10 days. When crosslinking is carried out under the above-mentioned curing conditions, a crosslinked material (network polymer) can be efficiently formed.

As a coating method of the adhesive composition, a known method can be used, and for example, a coating method of forming a predetermined thickness by spin coating, knife coating, roll coating, bar coating, blade coating, die coating, gravure coating, or the like can be used.

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

[ pressure-sensitive adhesive sheet for polarizing plate]

The adhesive sheet for polarizing plates of the present invention has an adhesive layer formed from the adhesive composition of the present invention. Examples of the pressure-sensitive adhesive sheet include a double-sided pressure-sensitive adhesive sheet having only the pressure-sensitive adhesive layer, a double-sided pressure-sensitive adhesive sheet having a substrate and the pressure-sensitive adhesive layers formed on both sides of the substrate, a single-sided pressure-sensitive adhesive sheet having a substrate and the pressure-sensitive adhesive layer formed on one side of the substrate, and a pressure-sensitive adhesive sheet in which a cover film subjected to a peeling treatment is attached to the surface of the pressure-sensitive adhesive layer not in contact with the substrate.

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

The conditions for forming the pressure-sensitive adhesive layer were the same as those described in the section of [ pressure-sensitive adhesive layer for polarizing plate ].

The 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 adhesive layer-equipped polarizing plate of the present invention has a polarizing element and an adhesive layer formed of the adhesive composition of the present invention directly laminated on at least one side of the polarizing element. In the present specification, the term "polarizing plate" is used to include "polarizing film".

As the polarizing plate, a heretofore known polarizing film can be used. Examples thereof include the polarizing element itself, and a multilayer film having a polarizing element and a polarizing element protective film disposed on the polarizing element. In the present invention, since the pressure-sensitive adhesive layer is disposed so as to be in direct contact with the polarizing element, examples thereof include a structure in which a polarizing element protective film is disposed only on one surface of the polarizing element and no polarizing element protective film is disposed on the other surface, and a structure in which no polarizing element protective film is disposed on both surfaces of the polarizing element.

Examples of the polarizing element include a stretched film obtained by stretching a film made of a polyvinyl alcohol resin after containing a polarizing component therein. Examples of the polyvinyl alcohol resin include polyvinyl alcohol, polyvinyl formal, polyvinyl acetal, and saponified ethylene-vinyl acetate copolymer. Examples of the polarizing component include iodine and dichroic dyes.

The polarizing element protective film may be made of a thermoplastic resin, for example. 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, cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures of two or more selected from these resins.

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

In the present invention, the pressure-sensitive adhesive layer is formed so as to be in direct contact with the polarizing element. Examples of the polarizing plate with an adhesive layer of the present invention include the following: a polarizer protective film, a polarizer, and the adhesive layer are laminated in this order; a structure in which the adhesive layer, the polarizing element protective film, the polarizing element, and the adhesive layer are laminated in this order; the pressure-sensitive adhesive layer, the polarizing element, and the pressure-sensitive adhesive layer are laminated in this order. In these structures, the above-described cover film may also be disposed on the adhesive layer as the outermost layer.

The method for forming the adhesive layer on the surface of the polarizing element is not particularly limited, and examples thereof include a method in which the adhesive composition is applied to the surface of the polarizing element, and then dried and cured, and a method in which the adhesive layer of the adhesive sheet for polarizing plate of the present invention is attached to or transferred to the surface of the polarizing element and then cured. The drying and curing conditions, the range of gel fraction, and the like are the same as those described in the column of [ pressure-sensitive adhesive layer for polarizing plate ].

The thickness of the adhesive layer is usually 5 to 75 μm, preferably 10 to 50 μm. The pressure-sensitive adhesive layer may be formed on at least one surface of the polarizing element so as to be in contact with the polarizing element, and examples thereof include a form in which the pressure-sensitive adhesive layer is formed only on one surface of the polarizing element and a form in which the pressure-sensitive adhesive layer is formed on both surfaces of the polarizing element.

Further, a layer having another function such as a protective layer, an antiglare layer, a retardation layer, or a viewing angle improving layer may be laminated on the polarizing plate.

The adhesive layer-attached polarizing plate of the present invention obtained in the above manner was disposed on the substrate surface of the liquid crystal cell to produce a liquid crystal cell. The liquid crystal cell has a structure in which a liquid crystal layer is sandwiched between two substrates. Examples of the substrate having liquid crystal cells include a glass plate. The thickness of the substrate is usually 0.05 to 3 mm, preferably 0.2 to 1 mm.

Examples

The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the following description of examples and the like, "part" means "part 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) under the following conditions.

The measurement device: HLC-8320GPC (produced by Tosoh corporation of China, Inc.; Chinese character "DONG ソー"))

The composition of the GPC column: the following 4 pillars (all produced by Tosoh corporation)

(1) TSKgel HxL-H (guard column)

(2)TSKgel GMHxL

(3)TSKgel GMHxL

(4)TSKgel G2500HxL

Flow rate: 1.0 ml/min

Column temperature: 40 deg.C

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

Mobile phase solvent: tetrahydrofuran (THF)

Conversion to standard polystyrene

[ photoelastic coefficient]

For the (meth) acrylic copolymer, the photoelastic coefficient was measured in the following manner.

The homopolymer solution containing the (meth) acrylic copolymer obtained in the synthesis example was applied to the release-treated surface of the polyethylene terephthalate film, and dried at 90 ℃ for 3 minutes to form a coating film (polymer layer) having a dry film thickness of 20 μm. The polymer layers having a dry film thickness of 20 μm were laminated to each other in an atmosphere of 23 ℃/50% RH for a plurality of times, and treated in an autoclave adjusted to 50 ℃/5atm for 20 minutes to prepare a polymer layer having a thickness of 1.0 mm. A polymer layer having a thickness of 1.0mm was cut into a size of 15mm × 50mm, and mounted on an automatic wavelength scanning ellipsometer (M220 type, manufactured by Nippon spectral Co., Ltd.) using a jig, and the retardation value was measured at a measurement wavelength of 633nm while changing the stress. The photoelastic coefficient of the (meth) acrylic copolymer was determined as the slope of a straight line with the stress on the horizontal axis and the retardation on the vertical axis.

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 charged into a reaction apparatus equipped with a stirrer, a reflux cooler, a thermometer and a nitrogen introduction tube, and the temperature was raised to 80 ℃ while introducing nitrogen. Then, 0.1 part of 2,2' -azobisisobutyronitrile was added to conduct polymerization at 80 ℃ for 6 hours in a nitrogen atmosphere. After the reaction, the reaction mixture was diluted with ethyl acetate to obtain a solid content ofA 30 mass% polymer solution the resulting (meth) acrylic copolymer 1 had a weight average molecular weight (Mw) of 80 ten thousand, a molecular weight distribution (Mw/Mn) of 7.5, and a photoelastic coefficient of-58 × 10^-12(m²/N)。

[ Synthesis examples 2 to 3]

Synthesis was carried out in the same manner as in Synthesis example 1 except that the monomer components used in the polymerization reaction were changed to those shown in Table 1, to obtain a polymer solution having a solid content concentration of 30% by mass. The results are shown in Table 1.

[ Table 1]

TABLE 1

Example A1]

(1) Preparation of adhesive composition

An adhesive composition was obtained by mixing the polymer solution (solid content concentration: 30 mass%) obtained in synthesis example 1 with 2.0 parts (solid content) of "D-94" manufactured by seiko chemical corporation as an isocyanate compound, 0.2 parts (solid content) of "M-12 AT" manufactured by seiko chemical corporation as a metal chelate, and 0.2 parts of "a-50" (solid content: 100 mass%) manufactured by seiko chemical corporation as a silane coupling agent, with respect to 1100 parts (solid content) of the (meth) acrylic copolymer contained in the solution.

(2) Production of adhesive sheet

The pressure-sensitive adhesive composition obtained in (1) above was defoamed on a polyethylene terephthalate film (PET film) subjected to a peeling treatment, then applied by a doctor blade, and dried at 90 ℃ for 3 minutes to form a coating film having a dry film thickness of 20 μm. The peeled PET film was further bonded to the reverse side of the adhesion surface of the above PET film coated with the film, and the film was left to stand for 7 days at 23 ℃/50% RH to be cured, thereby obtaining an adhesive sheet having an adhesive layer of 20 μm thickness sandwiched between 2 PET films.

(3) Production of polarizing plate with adhesive layer

The pressure-sensitive adhesive composition obtained in (1) above was defoamed on a polyethylene terephthalate film (PET film) subjected to a peeling treatment, then applied by a doctor blade, and dried at 90 ℃ for 3 minutes to form a sheet having a coating film with a dry film thickness of 20 μm. The film-coated surface of the sheet was bonded to one surface of a polyvinyl alcohol film of a polarizing plate having a two-layer structure (thickness: 60 μm) comprising a polyvinyl alcohol film as a polarizer and a triacetyl cellulose film as a polarizer protective film, and the sheet was left to stand at 23 ℃/50% RH for 7 days to be cured, thereby obtaining a polarizing plate with an adhesive layer comprising a PET film, an adhesive layer having a thickness of 20 μm, a polarizer and a polarizer protective film.

Examples B1 to B2, comparative examples A1 to A2, and B1 to B3]

An adhesive composition, an adhesive sheet, and an adhesive layer-attached polarizing plate were obtained in the same manner as in example a1, except that the polymer solution in example a1 was changed to the polymer solution obtained in each synthesis example, and/or the blend composition was changed to the content described in table 2.

[ evaluation of]

[ gel fraction]

About 0.1g of the adhesive was collected from the adhesive layer of the adhesive sheet obtained in the examples and comparative examples, placed in a sample bottle, 30mL of ethyl acetate was added thereto, the mixture was shaken for 4 hours, the content of the sample bottle was filtered through a 200-mesh stainless steel wire mesh, and the residue on the wire mesh was dried at 100 ℃ for 2 hours, and then the dry weight was measured. The gel fraction of the adhesive was determined according to the following formula.

Gel fraction (%) ═ (dry weight/adhesive collection weight) × 100 (%)

[ photoelastic coefficient]

The adhesive sheets obtained in examples and comparative examples were peeled from each other by peeling off the PET film, and adhesive layers having a thickness of 20 μm were bonded to each other in an atmosphere of 23 ℃/50% RH for a plurality of times, and treated in an autoclave adjusted to 50 ℃/5atm for 20 minutes to obtain an adhesive layer having a thickness of 1.0 mm. An adhesive layer having a thickness of 1.0mm was cut into a size of 15mm × 50mm, and mounted on an automatic wavelength scanning ellipsometer (M-220 type, manufactured by japan spectrographic corporation) using a jig, and the retardation value was measured at a measurement wavelength of 633nm while changing the stress. The photoelastic coefficient of the adhesive layer was determined as the slope of a straight line with the stress on the abscissa and the retardation on the ordinate.

[ light leakage test]

The 2 adhesive-attached polarizing plates (laminate composed of PET film/adhesive layer/polarizing element protective film) obtained in examples and comparative examples were cut into dimensions of 310 mm × 385 mm, and test pieces were prepared. The PET film was peeled off from the test piece, and a laminate composed of an adhesive layer/a polarizing element protective film was bonded to both sides of a glass plate having a thickness of 0.5 mm by a laminating roller so that the polarizing axes were orthogonal to each other and the adhesive layer was in contact with the glass plate. The obtained laminate was held in an autoclave adjusted to 50 ℃/5atm for 20 minutes to prepare a test piece. The test piece was left at a temperature of 80 ℃ C/dry for 500 hours, and light leakage was observed according to the following criteria.

AA: no light leakage was observed

BB: little light leakage was observed

CC: significant light leakage was observed

[ durability test (Heat resistance-Wet Heat resistance test)]

The pressure-sensitive adhesive layer-attached polarizing plates (laminate composed of PET film/pressure-sensitive adhesive layer/polarizing element protective film) obtained in examples and comparative examples were cut into a size of 150 mm × 250 mm, and test pieces were prepared. The PET film was peeled off from the test piece, and a laminate composed of an adhesive layer/a polarizing element protective film was bonded to one surface of a glass plate having a thickness of 0.5 mm by a laminating roller so that the adhesive layer was in contact with the glass plate. The obtained laminate was held in an autoclave adjusted to 50 ℃/5atm for 20 minutes to prepare a test piece. 2 identical test pieces were prepared. The test sheet was left to stand at 80 ℃ for 500 hours for drying (heat resistance) or at 60 ℃ for 90% RH (humidity resistance), and defects (foaming, lifting, and peeling) were observed and evaluated according to the following criteria.

AA: defect free

BB: the defect area is less than 5 percent, and the practical use is not influenced

CC: the defect area exceeds 5 percent, and the practical use is influenced

[ Table 2]

D-94: hexamethylene diisocyanate crosslinking agent

(manufactured by Soken chemical Co., Ltd., solid content 90% by mass)

L-45: toluene diisocyanate crosslinking agent

(produced by Soken chemical Co., Ltd., solid content 45% by mass, ethyl acetate/toluene solution)

E-5C: epoxy resin crosslinking agent

(5% by mass of solid content, manufactured by Soken chemical Co., Ltd.)

M-12 AT: aluminum chelate crosslinking agent (10% by mass solid content, toluene/acetylacetone solution, available from Sokka chemical Co., Ltd.)

A-50: silane coupling agent

(50% by mass of solid content, toluene solution, manufactured by Soken chemical Co., Ltd.)

Claims (10)

1. An adhesive layer for polarizing plate, which comprises a layer containing a material having a photoelastic coefficient of-200 × 10^-12～+200×10^-12(m²An adhesive composition comprising a (meth) acrylic copolymer (A1) of N) and an isocyanate-based crosslinking agent (B1) having no aromatic ring, wherein the photoelastic coefficient of the adhesive layer for polarizing plates is-200 × 10^-12～+70×10^-12(m²N) and a polarizing element, wherein the (meth) acrylic copolymer (A1) has a photoelastic coefficient of-1000 × 10 from a homopolymer^-12～-100×10^-12(m²Structural units of alkyl (meth) acrylates (a11) and ofThe photoelastic coefficient of the homopolymer was +500 × 10^-12～+2000×10^-12(m²Structural unit of (meth) acrylic ester containing aromatic ring (a 12).

2. The adhesive layer for polarizing plates according to claim 1, wherein the isocyanate-based crosslinking agent (B1) is a hexamethylene diisocyanate-based crosslinking agent.

3. The adhesive layer for a polarizing plate according to claim 1 or 2, wherein the adhesive composition contains 0.05 to 10 parts by mass of an isocyanate-based crosslinking agent (B1) per 100 parts by mass of the copolymer (a 1).

4. An adhesive layer for polarizing plate, which comprises a layer containing a material having a photoelastic coefficient of less than-200 × 10^-12(m²A (meth) acrylic copolymer (A2) and an aromatic ring-containing isocyanate-based crosslinking agent (B2), and the photoelastic coefficient of the pressure-sensitive adhesive layer for polarizing plates is-200 × 10^-12～+70×10^-12(m²N) and is disposed in direct contact with the polarizing element.

5. The adhesive layer for a polarizing plate according to claim 4, wherein the isocyanate-based crosslinking agent (B2) is at least one selected from the group consisting of a toluene diisocyanate-based crosslinking agent and a xylylene diisocyanate-based crosslinking agent.

6. The adhesive layer for a polarizing plate according to claim 4 or 5, wherein the adhesive composition contains 2 parts by mass or more of an isocyanate-based crosslinking agent (B2) per 100 parts by mass of the copolymer (A2).

7. An adhesive sheet for a polarizing plate, which comprises the adhesive layer according to any one of claims 1 to 6.

8. An adhesive layer-equipped polarizing plate having a polarizing element and the adhesive layer according to any one of claims 1 to 6 directly laminated on at least one surface of the polarizing element.

9. An adhesive composition for polarizing plate for forming the adhesive layer of claim 1, comprising a photoelastic coefficient of-200 × 10^-12～+200×10^-12(m²A (meth) acrylic copolymer (A1) having a photoelastic coefficient of-1000 × 10 from a homopolymer, and an isocyanate-based crosslinking agent (B1) having no aromatic ring^-12～-100×10^-12(m²Structural units of alkyl (meth) acrylates (a11) and a photoelastic coefficient of +500 × 10 from the homopolymer^-12～+2000×10^-12(m²Structural unit of (meth) acrylic ester containing aromatic ring (a 12).

10. An adhesive composition for polarizing plate for forming the adhesive layer of claim 4, comprising a photoelastic coefficient of less than-200 × 10^-12(m²A (meth) acrylic copolymer (A2) of (N) and an aromatic ring-containing isocyanate-based crosslinking agent (B2).