WO2016072201A1 - Adhesive composition for polarizing plates and polarizing plate having adhesive layer - Google Patents

Abstract

[Problem] To provide an adhesive composition for polarizing plates that: contains a crosslinking agent and a (meth) acrylic copolymer obtained by polymerization of a (meth) acrylate alkyl ester; and is capable of forming an adhesive layer having excellent durability and light-leakage prevention characteristics. [Solution] An adhesive composition for polarizing plates, characterized by containing a (meth) acrylic copolymer (A) and a crosslinking agent (B), said (meth) acrylic copolymer (A) being obtained by copolymerization of monomer components including a (meth) acrylate alkyl ester (a1) having a homopolymer photoelastic coefficient of -1,000 × 10^-12 - -100 × 10^-12 (m²/N), a (meth) acrylate alkyl ester (a2) having a homopolymer photoelastic coefficient of +100 × 10^-12 - +1,000 × 10^-12 (m²/N), and a crosslinking functional group-containing monomer (a3).

Description

Adhesive composition for polarizing plate and polarizing plate with adhesive layer

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

The liquid crystal cell has a structure in which a liquid crystal layer is sandwiched between two substrates (eg, a glass plate). A polarizing plate is attached to the surface of the substrate constituting the liquid crystal cell via an adhesive layer. In recent years, liquid crystal cells have been used for vehicles, outdoor instruments, PC displays, televisions, and the like, and the usage environment has become very severe.

In particular, under high temperature and high humidity environment, stress concentrates due to thermal contraction of the polarizing plate, induces birefringence of the polarizing plate, and the adhesive itself is oriented due to stress concentration, resulting in birefringence and stress concentration. Light leakage occurs at the edge, and the display quality deteriorates. In such an environment, problems such as tearing of the pressure-sensitive adhesive layer and peeling of the polarizing plate are likely to occur. Therefore, the polarizing plate adhesive is required to have excellent light leakage prevention and durability.

Patent Document 1 discloses that a pressure-sensitive adhesive for a polarizing plate is obtained by adding an epoxy crosslinking agent and an isocyanate compound to an acrylic polymer having a weight average molecular weight and a molecular weight distribution in a specific range, which is copolymerized with a carboxyl group-containing monomer. A technique for improving the durability and the light leakage prevention property is described.

Patent Document 2 discloses a pressure-sensitive adhesive for polarizing plates obtained from a pressure-sensitive adhesive composition containing a (meth) acrylic polymer obtained by copolymerizing a monomer mainly composed of alkoxyethyl (meth) acrylate. In addition, a technique for improving durability and preventing light leakage is described by adjusting the photoelastic coefficient of the pressure-sensitive adhesive for polarizing plates within a certain range.

Patent Document 3 discloses an alkyl (meth) acrylate (a1) having a branched alkyl group having 8 to 24 carbon atoms at the ester end and an alkyl (meth) acrylate having a linear alkyl group having 8 to 24 carbon atoms at the ester end. A pressure-sensitive adhesive containing a (meth) acrylic polymer obtained by polymerizing a monomer component containing (a2) is described. However, there is no mention of the above-described problem of light leakage when the pressure-sensitive adhesive is used for polarizing plates.

JP 2010-196003 A JP 2012-067275 A JP 2013-194170 A

In the prior art, depending on the weight average molecular weight and molecular weight distribution of the (meth) acrylic copolymer, the copolymerization amount of the aromatic ring-containing monomer constituting the (meth) acrylic copolymer, the addition amount of the isocyanate crosslinking agent, etc. The photoelastic coefficient of the adhesive is adjusted to improve the light leakage prevention property. On the other hand, if the photoelastic coefficient can be adjusted by the (meth) acrylic acid alkyl ester constituting the (meth) acrylic copolymer, the choice of monomers that contribute to the adjustment of the photoelastic coefficient will expand, and the design of the adhesive It is advantageous in that the width of can be increased.

An object of the present invention is to prevent light leakage and durability in a pressure-sensitive adhesive composition for a polarizing plate containing a (meth) acrylic copolymer obtained by polymerizing an alkyl (meth) acrylate and a crosslinking agent. It is providing the adhesive composition for polarizing plates which can form the adhesive layer excellent in these.

The present inventors diligently studied to solve the above problems. As a result, it has been found that when a specific (meth) acrylic copolymer is used and a crosslinking agent is used, a pressure-sensitive adhesive layer excellent in the light leakage prevention property and durability described above can be formed. .

That is, the present inventors have found that the above problems can be solved by using a polarizing plate pressure-sensitive adhesive composition having the following specific configuration, and have completed the present invention.

The present invention includes, for example, the following [1] to [11].

[1] (A) (meth) acrylic acid alkyl ester (a1) having a photoelastic coefficient of the homopolymer of −1000 × 10 ⁻¹² to −100 × 10 ⁻¹² (m ² / N), the photoelastic coefficient of the homopolymer Obtained by copolymerizing a monomer component containing (meth) acrylic acid alkyl ester (a2) having a crosslinkable functional group-containing monomer (a3) of + 100 × 10 ⁻¹² to + 1000 × 10 ⁻¹² (m ² / N) A pressure-sensitive adhesive composition for a polarizing plate, comprising the obtained (meth) acrylic copolymer and (B) a crosslinking agent.

[2] The Tg of the homopolymer of the (meth) acrylic acid alkyl ester (a1) is −30 ° C. or lower, and the Tg of the homopolymer of the (meth) acrylic acid alkyl ester (a2) is −20 ° C. or higher. The pressure-sensitive adhesive composition for polarizing plates according to [1].

[3] In the above [1] or [2], the photoelastic coefficient of the (meth) acrylic copolymer (A) is −150 × 10 ⁻¹² to + 150 × 10 ⁻¹² (m ² / N). The adhesive composition for polarizing plates as described.

[4] The pressure-sensitive adhesive composition for a polarizing plate according to any one of [1] to [3], wherein the crosslinking agent (B) comprises an isocyanate compound (B1).

[5] The pressure-sensitive adhesive composition for polarizing plate according to [4], wherein the isocyanate compound (B1) is at least one selected from a xylylene diisocyanate crosslinking agent and a hexamethylene diisocyanate crosslinking agent.

[6] The pressure-sensitive adhesive composition for polarizing plates according to any one of [1] to [5], which is used for forming a pressure-sensitive adhesive layer in direct contact with a polarizer.

[7] A polarizing plate pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of [1] to [6].

[8] The pressure-sensitive adhesive layer for a polarizing plate according to [7], wherein the photoelastic coefficient is −150 × 10 ⁻¹² to + 150 × 10 ⁻¹² (m ² / N).

[9] A pressure-sensitive adhesive sheet for polarizing plate having the pressure-sensitive adhesive layer according to [7] or [8].

[10] A polarizing plate with an adhesive layer having a polarizing plate and the adhesive layer according to [7] or [8] laminated on at least one surface of the polarizing plate.

[11] A polarizing plate with an adhesive layer having the adhesive layer according to [7] or [8], which is directly laminated on at least one surface of a polarizer.

According to the present invention, in a pressure-sensitive adhesive composition for a polarizing plate containing a (meth) acrylic copolymer obtained by polymerizing a (meth) acrylic acid alkyl ester and a crosslinking agent, light leakage prevention and durability It is possible to provide a pressure-sensitive adhesive composition for polarizing plates capable of forming a pressure-sensitive adhesive layer excellent in the above.

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

[Adhesive composition for polarizing plate]
The pressure-sensitive adhesive composition for polarizing plates of the present invention contains a (meth) acrylic copolymer (A) and a crosslinking agent (B) described below. The composition may contain at least one selected from a silane coupling agent (C) and an antistatic agent (D) as necessary, and may contain an organic solvent (E).

[(Meth) acrylic copolymer (A)]
The (meth) acrylic copolymer (A) includes a (meth) acrylic acid alkyl ester (a1) having a homopolymer photoelastic coefficient of −1000 to −100 and a homopolymer photoelastic coefficient of +100 to +1000 ( It is a copolymer of monomer components containing a (meth) acrylic acid alkyl ester (a2) and a crosslinkable functional group-containing monomer (a3), and is obtained by copolymerizing the monomer components. The copolymer (A) is usually composed of a structural unit derived from (meth) acrylic acid alkyl ester (a1), a structural unit derived from (meth) acrylic acid alkyl ester (a2), and a crosslinkable functional group-containing monomer ( and a structural unit derived from a3).

In the present specification, unless otherwise specified, the unit of the photoelastic coefficient of the homopolymer comprising the above (a1) or (a2) is “× 10 ⁻¹² m ² / N”. In addition, (a1), (a2) and (a3) are also referred to as “monomer (a1)”, “monomer (a2)” and “monomer (a3)”, respectively.

In this specification, acrylic and methacryl are collectively referred to as “(meth) acryl”. Moreover, the structural unit derived from a certain monomer A contained in the polymer is also referred to as “monomer A unit”.

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

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

The homopolymer solution is applied to the release-treated surface of the release-treated polyethylene terephthalate film and dried at 90 ° C. for 3 minutes to form a coating film (homopolymer layer) having a dry film thickness of 20 μm. The homopolymer layers having a dry film thickness of 20 μm are bonded together several times in an environment of 23 ° C./50% RH, and processed in an autoclave at 50 ° C./5 atm for 20 minutes to produce a homopolymer layer having a thickness of 1.0 mm.

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

As the glass transition temperature (Tg) of the homopolymer formed from each monomer, a value described in Polymer Handbook Fourth Edition (Wiley-Interscience 2003) is adopted.

<< (Meth) acrylic acid alkyl ester (a1) >>
Monomer (a1) is a (meth) acrylic acid alkyl ester having a homopolymer photoelastic coefficient of −1000 to −100. The monomer having a photoelastic coefficient of homopolymer in the range of −750 to −150 is preferable, and the monomer in the range of −500 to −200 is more preferable.

By using the copolymer (A) obtained by copolymerizing the monomer (a1) having a photoelastic coefficient of the homopolymer in the above range, the pressure-sensitive adhesive layer is given softness and the effect of suppressing the warpage of the polarizing plate is obtained. Can be expressed.

The monomer (a1) is preferably a (meth) acrylic acid alkyl ester having a homopolymer Tg of −30 ° C. or less, and the Tg is more preferably −100 to −30 ° C., further preferably −70 to −30. ° C.

As the monomer (a1), for example, among compounds represented by CH ₂ ═CR ¹ —COOR ² , compounds having a homopolymer photoelastic coefficient in the above range can be mentioned. In the formula, R ¹ is a hydrogen atom or a methyl group, and R ² is an alkyl group having 1 to 20 carbon atoms. The alkyl group preferably has 2 to 16 carbon atoms, and more preferably 4 to 12 carbon atoms.

Examples of the monomer (a1) include n-butyl acrylate (-400; -50), 2-ethylhexyl acrylate (-700; -70), isodecyl methacrylate (-190; -41), lauryl methacrylate (-460; -65). The numerical values in parentheses indicate the photoelastic coefficient (× 10 ⁻¹² m ² / N) on the left side and the Tg (° C.) on the right side of the homopolymer formed from each monomer.

Monomers (a1) may be used alone or in combination of two or more. When using 2 or more types of monomers (a1), it is preferable that each monomer satisfy | fills the requirements of a photoelastic coefficient and Tg.

In 100% by mass of the monomer component forming the copolymer (A), the amount of the monomer (a1) used is preferably 10% by mass or more and less than 90% by mass, more preferably 14.9 to 85% by mass, and still more preferably. Is 35 to 59.5% by mass. When the amount of the monomer (a1) used is in the above range, it is preferable in that the photoelastic coefficient of the obtained copolymer (A) can be adjusted to the range described later.

<< (Meth) acrylic acid alkyl ester (a2) >>
The monomer (a2) is a (meth) acrylic acid alkyl ester having a homopolymer photoelastic coefficient of +100 to +1000. The monomer having a photoelastic coefficient of the homopolymer in the range of +100 to +800 is preferable, and the monomer in the range of +150 to +600 is more preferable.

Appropriate durability can be imparted to the pressure-sensitive adhesive layer by using the copolymer (A) obtained by copolymerizing the monomer (a2) having a photoelastic coefficient of the homopolymer in the above range. By using the copolymer (A) obtained by copolymerizing a methacrylic acid alkyl ester as the monomers (a1) and (a2), the heat and moisture resistance of the pressure-sensitive adhesive layer can be further improved.

The monomer (a2) is preferably a (meth) acrylic acid alkyl ester having a homopolymer Tg of −20 ° C. or more, and the Tg is more preferably −20 to 150 ° C., further preferably −15 to 100 ° C. is there.

As the monomer (a2), for example, among compounds represented by CH ₂ ═CR ³ —COOR ⁴ , compounds having a homopolymer photoelastic coefficient in the above range can be mentioned. In the formula, R ³ is a hydrogen atom or a methyl group, and R ⁴ is an alkyl group having 1 to 15 carbon atoms. The alkyl group preferably has 1 to 12 carbon atoms, and more preferably 1 to 10 carbon atoms.

Examples of the monomer (a2) include t-butyl methacrylate (130; 118), n-butyl methacrylate (320; 20), and 2-ethylhexyl methacrylate (420; -10). The numerical values in parentheses indicate the photoelastic coefficient (× 10 ⁻¹² m ² / N) on the left side and the Tg (° C.) on the right side of the homopolymer formed from each monomer.

Monomer (a2) may be used alone or in combination of two or more. When using 2 or more types of monomers (a2), it is preferable that each monomer satisfy | fills the requirements of a photoelastic coefficient and Tg.

In 100% by mass of the monomer component forming the copolymer (A), the amount of the monomer (a2) used is preferably 10% by mass or more and less than 90% by mass, more preferably 14.9 to 85% by mass, and still more preferably. Is 40 to 64.5% by mass. When the amount of the monomer (a2) used is in the above range, it is preferable in that the photoelastic coefficient of the obtained copolymer (A) can be adjusted to the range described later.

<< Crosslinkable functional group-containing monomer (a3) >>
The monomer component forming the copolymer (A) further includes a monomer having a crosslinkable functional group capable of reacting with the crosslinker (B), that is, a crosslinkable functional group-containing monomer (a3).

Examples of the monomer (a3) include a hydroxyl group-containing monomer, an acid group-containing monomer, an amino group-containing monomer, an amide group-containing monomer, a nitrogen-based heterocyclic ring-containing monomer, and a cyano group-containing monomer. In this specification, examples of the acid group include a carboxyl group, an acid anhydride group, a phosphoric acid group, and a sulfuric acid group.

Examples of the hydroxyl group-containing monomer include a hydroxyl group-containing (meth) acrylate, and specific examples include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate. And hydroxyalkyl (meth) acrylates such as 6-hydroxyhexyl (meth) acrylate and 8-hydroxyoctyl (meth) acrylate. The number of carbon atoms of the hydroxyalkyl group in the hydroxyalkyl (meth) acrylate is usually 2 to 8, preferably 2 to 6.

Examples of the carboxyl group-containing monomer include β-carboxyethyl (meth) acrylate, 5-carboxypentyl (meth) acrylate, mono (meth) acryloyloxyethyl ester succinate, and ω-carboxypolycaprolactone mono (meth) acrylate. Carboxyl group-containing (meth) acrylates such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid. Examples of the acid anhydride group-containing monomer include maleic anhydride and itaconic anhydride. Examples of the phosphate group-containing monomer include (meth) acrylic monomers having a phosphate group in the side chain, and examples of the sulfate group-containing monomer include (meth) acrylic monomers having a sulfate group in the side chain.

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. Examples of the nitrogen heterocycle-containing monomer include vinyl pyrrolidone, acryloyl morpholine, and vinyl caprolactam. Examples of the cyano group-containing monomer include cyano (meth) acrylate and (meth) acrylonitrile.

The monomer (a3) is preferably at least one selected from a hydroxyl group-containing monomer, a carboxyl group-containing monomer, and an amide group-containing monomer from the viewpoint of crosslinkability with the crosslinking agent (B). However, monomers having a carboxyl group and / or an amide group are excluded from the hydroxyl group-containing monomer. Moreover, the monomer which has a hydroxyl group and / or a carboxyl group is remove | excluded from an amide group containing monomer.

Monomer (a3) may be used alone or in combination of two or more.

In 100% by mass of the monomer component forming the copolymer (A), the amount of the monomer (a3) used is preferably more than 0% by mass and 10% by mass or less, more preferably 0.1 to 8% by mass, More preferably, it is 0.5 to 5% by mass. When the amount of the monomer (a3) used is less than or equal to the above upper limit, the crosslinking density formed by the copolymer (A) and the crosslinking agent (B) does not become too high, and an adhesive layer excellent in stress relaxation properties is obtained. can get. When the usage-amount of a monomer (a3) is more than the said lower limit, a crosslinked structure is formed effectively and the adhesive layer which has appropriate intensity | strength at normal temperature is obtained.

《Other monomers》
Examples of the monomer component that forms the copolymer (A) include alkyl (meth) acrylates and alkoxyalkyls other than the monomer (a1) and monomer (a2) as long as the physical properties of the copolymer (A) are not impaired. Other (meth) acrylic acid esters such as (meth) acrylate, alkoxypolyalkylene glycol mono (meth) acrylate, alicyclic group or aromatic ring-containing (meth) acrylate can also be used. That is, the copolymer (A) may further have a structural unit derived from the other (meth) acrylic acid ester.

Examples of the alkoxyalkyl (meth) acrylate include methoxymethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxypropyl (meth) acrylate, 3-ethoxypropyl ( And (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 alicyclic group or aromatic ring-containing (meth) acrylate include cyclohexyl (meth) acrylate, benzyl (meth) acrylate, and phenyl (meth) acrylate.

Moreover, as a monomer component which forms a copolymer (A), it is a range which does not impair the physical property of a copolymer (A), For example, copolymerizable monomers, such as a styrene-type monomer and vinyl acetate, are used. You can also. That is, the copolymer (A) may further have a structural unit derived from the copolymerizable monomer.

Examples of the styrenic monomer include styrene; methyl styrene, dimethyl styrene, trimethyl styrene, propyl styrene, butyl styrene, hexyl styrene, heptyl styrene, octyl styrene, and other alkyl styrenes; fluorostyrene, chlorostyrene, bromostyrene, Halogenated styrene such as dibromostyrene and iodinated styrene; nitrostyrene, acetylstyrene, and methoxystyrene.

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

In 100% by mass of the monomer component forming the copolymer (A), the total amount of other monomers (eg, other (meth) acrylic acid ester, copolymerizable monomer) used is 0 to 10% by mass. Preferably, it is 0 to 5% by mass.

In the prior art, it was common to adjust the photoelastic coefficient of the entire polymer using an aromatic ring-containing monomer. On the other hand, in the present invention, the photoelastic coefficient of the whole polymer is adjusted mainly by the monomers (a1) and (a2) which are alkyl (meth) acrylates. For this reason, the monomer which adjusts the photoelastic coefficient of the whole polymer is not restricted to an aromatic ring containing monomer, The choice of designing an adhesive can be expanded from the point that various (meth) acrylic acid alkylesters can be used. For example, it is advantageous in that the adjustment of the photoelastic coefficient of the polymer and the adjustment of Tg are compatible.

<< Production conditions for (meth) acrylic copolymer (A) >>
Although the manufacturing conditions of a (meth) acrylic-type copolymer (A) are not specifically limited, For example, it can manufacture by a solution polymerization method. Specifically, a polymerization solvent and a monomer component are charged into a reaction vessel, a polymerization initiator is added in an inert gas atmosphere such as nitrogen gas, and the reaction start temperature is usually 40 to 100 ° C., preferably 50 to 80 ° C. The reaction system is maintained at a temperature of usually 50 to 90 ° C., preferably 70 to 90 ° C., and allowed to react for 4 to 20 hours.

The copolymer (A) is obtained, for example, by copolymerizing monomer components including the monomers (a1) to (a3) described above, but may be a random copolymer or a block copolymer. Among these, a random copolymer is preferable.

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

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

The polymerization initiator is usually in the range of 0.01 to 5 parts by mass, preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the monomer component forming the (meth) acrylic copolymer (A). Used in quantity. Moreover, you may add suitably a polymerization initiator, a chain transfer agent, a monomer component, and a polymerization solvent during the said polymerization reaction.

<< Physical properties and content of (meth) acrylic copolymer (A) >>
The photoelastic coefficient of the (meth) acrylic copolymer (A) is preferably −150 to +150, more preferably −100 to +100, and further preferably −70 to +70. The unit of the photoelastic coefficient is 10 ⁻¹² m ² / N.

A copolymer (A) having a photoelastic coefficient in the above range is obtained by copolymerizing the monomer (a1) having a negative photoelastic coefficient of the homopolymer and the monomer (a2) having a positive photoelastic coefficient of the homopolymer. be able to. By using such a copolymer (A) and making the photoelastic coefficient of the pressure-sensitive adhesive layer close to the range described below, particularly close to 0, light leakage in the polarizing plate can be suppressed.

The weight average molecular weight (Mw) measured by the gel permeation chromatography (GPC) method of the (meth) acrylic copolymer (A) is usually 300,000 to 2,000,000 in terms of polystyrene, preferably 40 It is 10,000 to 1,800,000, more preferably 500,000 to 1,500,000. By using the copolymer (A) having Mw in the above range and having the above monomer unit, it is easy to balance the adhesive force, and a pressure-sensitive adhesive composition suitable for coating can be obtained. Moreover, an adhesive layer with higher durability can be obtained by using the copolymer (A) having an Mw of 500,000 or more.

The molecular weight distribution (Mw / Mn) measured by the GPC method of the (meth) acrylic copolymer (A) is usually 20 or less, preferably 3 to 15, more preferably 5 to 10.

The glass transition temperature (Tg) of the (meth) acrylic copolymer (A) can be calculated by, for example, the Fox formula from the monomer units constituting the copolymer and the content ratio thereof. For example, the (meth) acrylic copolymer (A) is synthesized so that the glass transition temperature (Tg) determined by the Fox equation is usually −70 to −10 ° C., preferably −60 to −20 ° C. It is preferable. By using the (meth) acrylic copolymer (A) having such a glass transition temperature (Tg), a pressure-sensitive adhesive composition excellent in stress relaxation characteristics and durability and having excellent adhesiveness at room temperature is obtained. be able to.

Fox formula:
_{1 / Tg = (W 1 /} Tg 1) + (W 2 / Tg 2) + ... + (W m / Tg m)
W ₁ + W ₂ + ... + W _m = 1
In the formula, Tg is the glass transition temperature (unit: K) of the (meth) acrylic copolymer (A), and Tg ₁ , Tg ₂ ,..., Tg _m are the glass transition temperatures of homopolymers composed of the respective monomers ( Unit: K), and W ₁ , W ₂ ,..., W _m are weight fractions of the structural units derived from the respective monomers in the copolymer (A). As the weight fraction of the structural unit derived from each monomer, the charging ratio of each monomer to the total monomers at the time of copolymer synthesis can be used.

As the glass transition temperature of the homopolymer composed of each monomer in the Fox formula, for example, a value described in Polymer Handbook Fourth Edition (Wiley-Interscience 2003) can be used.

In the pressure-sensitive adhesive composition of the present invention, the content of the (meth) acrylic copolymer (A) is usually 60 to 99.99% by mass in 100% by mass of the solid content excluding the organic solvent in the composition. The amount is preferably 70 to 99.95% by mass, particularly preferably 80 to 99.90% by mass. When the content of the (meth) acrylic copolymer (A) is in the above range, the performance as an adhesive is balanced and the adhesive properties are excellent.

[Crosslinking agent (B)]
The pressure-sensitive adhesive composition of the present invention further contains a crosslinking agent (B).

The crosslinking agent (B) is particularly limited as long as it is a component capable of causing a crosslinking reaction with the crosslinking functional group derived from the crosslinking functional group-containing monomer (a3) of the (meth) acrylic copolymer (A). Although not mentioned, for example, an isocyanate compound (B1), a metal chelate compound (B2), and an epoxy compound (B3) are mentioned, and it is preferable that the above (B1) is included.

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

In the pressure-sensitive adhesive composition of the present invention, the content of the crosslinking agent (B) is usually 0.01 to 5 parts by mass, more preferably 0, relative to 100 parts by mass of the (meth) acrylic copolymer (A). .05 to 2.5 parts by mass, more preferably 0.1 to 1 part by mass. When the content is within the above range, it is preferable in terms of easy balance between durability and stress relaxation characteristics.

<< Isocyanate compound (B1) >>
As the isocyanate compound (B1), an isocyanate compound having 2 or more isocyanate groups in one molecule is usually used. A crosslinked body (network polymer) can be formed by crosslinking the (meth) acrylic copolymer (A) with the isocyanate compound (B1).

The number of isocyanate groups in the isocyanate compound (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 from the viewpoint of the crosslinking reaction efficiency between the (meth) acrylic copolymer (A) and the isocyanate compound (B1) and the flexibility of the pressure-sensitive adhesive layer.

Examples of the diisocyanate compound having 2 isocyanate groups in one molecule include aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate. Aliphatic diisocyanates include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, 2,2,4-trimethyl And aliphatic diisocyanates having 4 to 30 carbon atoms such as -1,6-hexamethylene diisocyanate. Examples of alicyclic diisocyanates include alicyclic rings having 7 to 30 carbon atoms such as isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and hydrogenated tetramethylxylylene diisocyanate. Group diisocyanates. Examples of the aromatic diisocyanate include aromatic diisocyanates having 8 to 30 carbon atoms such as phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, and diphenylpropane diisocyanate.

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

Examples of the isocyanate compound (B1) include multimers (for example, dimers or trimers, biurets, isocyanurates), derivatives (for example, many) of the above isocyanate compounds having 2 or 3 or more isocyanate groups. Addition reaction product of a dihydric alcohol and two or more molecules of a diisocyanate compound), and a polymer. Examples of the polyhydric alcohol in the derivative include trivalent or higher alcohols such as trimethylolpropane, glycerin and pentaerythritol as low molecular weight polyhydric alcohols; high molecular weight polyhydric alcohols such as polyether polyols, Examples include polyester polyol, acrylic polyol, polybutadiene polyol, and polyisoprene polyol.

Examples of such isocyanate compounds include diphenylmethane diisocyanate trimer, polymethylene polyphenyl polyisocyanate, hexamethylene diisocyanate or tolylene diisocyanate biuret or isocyanurate, trimethylolpropane and tolylene diisocyanate or xylylene diisocyanate. Reaction product (for example, a trimolecular adduct of tolylene diisocyanate or xylylene diisocyanate), a reaction product of trimethylolpropane and hexamethylene diisocyanate (for example, a trimolecular adduct of hexamethylene diisocyanate), a polyether polyisocyanate, Polyester polyisocyanate is mentioned.

Among the isocyanate compounds (B1), at least one selected from a xylylene diisocyanate crosslinking agent and a hexamethylene diisocyanate crosslinking agent is preferable in that it can improve aging properties and light leakage resistance. A crosslinking agent is more preferred.

Examples of the xylylene diisocyanate crosslinking agent include xylylene diisocyanate and derivatives thereof, biuret or isocyanurate. Examples of the hexamethylene diisocyanate-based crosslinking agent include hexamethylene diisocyanate and derivatives thereof, biuret bodies, and isocyanurate bodies.

The isocyanate compound (B1) may be used alone or in combination of two or more.

<< Metal chelate compound (B2) >>
Examples of the metal chelate compound (B2) include polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium, alkoxide, acetylacetone, and ethyl acetoacetate. Examples include a coordinated compound.

Among these, an aluminum chelate compound (M-12AT manufactured by Soken Chemical Co., Ltd.) is particularly preferable. Specific examples include aluminum isopropylate, aluminum secondary butyrate, aluminum ethyl acetoacetate / diisopropylate, aluminum trisethyl acetoacetate, and aluminum trisacetylacetonate.

The metal chelate compound (B2) may be used alone or in combination of two or more.

The metal chelate compound (B2) crosslinks the (meth) acrylic copolymer (A) by coordination bond (pseudocrosslinking). When the metal chelate compound (B2) is used as the cross-linking agent (B), the cross-linking is maintained at room temperature, and the polymer exhibits cohesiveness. Shows greater flexibility.

<< Epoxy compound (B3) >>
As the epoxy compound (B3), an epoxy compound having 2 or more epoxy groups in one molecule is usually used. For example, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N, N ′, N ′ -Tetraglycidyl-m-xylylenediamine, N, N, N ', N'-tetraglycidylaminophenylmethane, triglycidyl isocyanurate, mN, N-diglycidylaminophenyl glycidyl ether, N, N-diglycidyl Examples include toluidine and N, N-diglycidylaniline.

[Silane coupling agent (C)]
The pressure-sensitive adhesive composition of the present invention preferably further contains a silane coupling agent (C). A silane coupling agent (C) contributes to the point which adheres an adhesive layer firmly to adherends, such as a glass plate, and prevents peeling of a polarizing plate in a high-humidity heat environment.

Examples of the silane coupling agent (C) include polymerizable unsaturated group-containing silane coupling agents such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane; 3-glycidoxypropyltrimethoxysilane Epoxy groups such as 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane Containing silane coupling agent; amino such as 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane Group-containing silane coupling Grayed agent; 3-chloropropyl trimethoxysilane halogen-containing silane coupling agent and the like.

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

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

Examples of the surfactant include cationic surfactants having cationic groups such as quaternary ammonium salts, amide quaternary ammonium salts, pyridium salts, primary to tertiary amino groups; sulfonate groups, sulfate esters Anionic surfactants having an anionic group such as a base or a phosphate ester base; amphoteric surfactants such as alkylbetaines, alkylimidazolinium betaines, alkylamine oxides, amino acid sulfates, glycerin fatty acid esters Nonionic surfactants such as sorbitan fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene alkylamine fatty acid esters, N-hydroxyethyl-N-2-hydroxyalkylamines and alkyldiethanolamides It is done.

In addition, a reactive emulsifier having a polymerizable group is also exemplified as the surfactant, and a polymer surfactant obtained by increasing the molecular weight of the monomer component containing the above surfactant or reactive emulsifier can also be used.

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

The cation portion constituting the ionic compound may be either an inorganic cation or an organic cation, or both. As the inorganic cation, alkali metal ions and alkaline earth metal ions are preferable, and Li ⁺ , Na ⁺ and K ⁺ having excellent antistatic properties are more preferable. Examples of organic cations include pyridinium cation, piperidinium cation, pyrrolidinium cation, pyrroline cation, pyrrole cation, imidazolium cation, tetrahydropyrimidinium cation, dihydropyrimidinium cation, pyrazolium cation, pyrazoli Examples thereof include a nium cation, a tetraalkylammonium cation, a trialkylsulfonium cation, a tetraalkylphosphonium cation, and derivatives thereof.

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

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

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

In the pressure-sensitive adhesive composition of the present invention, the content of the antistatic agent (D) is usually 3 parts by mass or less, preferably 0.01 to 100 parts by mass with respect to 100 parts by mass of the (meth) acrylic copolymer (A). 3 parts by mass, more preferably 0.05 to 2.5 parts by mass.

[Organic solvent (E)]
The pressure-sensitive adhesive composition of the present invention preferably contains an organic solvent (E) in order to adjust its applicability. As an organic solvent, the polymerization solvent demonstrated in the column of the (meth) acrylic-type copolymer (A) is mentioned. For example, the pressure-sensitive adhesive composition can be prepared by mixing the polymer solution containing the (meth) acrylic copolymer (A) and the polymerization solvent obtained by the above copolymerization and the crosslinking agent (B). it can. In the pressure-sensitive adhesive composition of the present invention, the content of the organic solvent (E) is usually 50 to 90% by mass, preferably 60 to 85% by mass.

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

[Additive]
In addition to the above components, the pressure-sensitive adhesive composition of the present invention includes an antioxidant, a light stabilizer, a metal corrosion inhibitor, a tackifier, a plasticizer, a crosslinking accelerator, You may contain the 1 type (s) or 2 or more types selected from the (meth) acrylic-type polymer and rework agents other than A).

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

Using the pressure-sensitive adhesive composition of the present invention, a pressure-sensitive adhesive layer was formed on a polarizing plate having a polarizer protective film only on one side of the polarizer and on a polarizing plate having no polarizer protective film on both sides of the polarizer. In particular, warpage of the polarizing plate and the substrate and light leakage can be suppressed. In the present invention, even when the pressure-sensitive adhesive layer is in direct contact with the polarizer, tearing of the pressure-sensitive adhesive layer, peeling of the polarizing plate, and the like can be suppressed under a high temperature and high humidity environment.

The pressure-sensitive adhesive composition of the present invention is suitable for use in bonding a substrate constituting a liquid crystal cell and a polarizing plate. In particular, even when the thickness of the glass plate constituting the thinned liquid crystal cell is as small as about 0.05 to 1 mm, it is suitable for bonding the substrate and the polarizing plate.

The gel fraction of the pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition of the present invention is preferably 40% by mass or more, more preferably 50 to 95% by mass, and further preferably 55 to 90% by mass. The said gel fraction is a value measured about the adhesive extract | collected, for example by the conditions of an Example description.

[Adhesive layer for polarizing plate]
The pressure-sensitive adhesive layer for polarizing plates of the present invention is formed from the above-mentioned pressure-sensitive adhesive composition. By using the pressure-sensitive adhesive composition of the present invention, a pressure-sensitive adhesive layer having the following photoelastic properties can be formed.

The photoelastic coefficient of the pressure-sensitive adhesive layer of the present invention is preferably −150 to +150, more preferably −100 to +100, and further preferably −70 to +70. The unit of the photoelastic coefficient is 10 ⁻¹² m ² / N.

The photoelastic coefficient is measured at a measurement wavelength of 633 nm, for example, by laminating the pressure-sensitive adhesive layers a plurality of times to produce a laminate having a thickness of about 1.0 mm. Details of the measurement conditions are as described in the examples.

Since the pressure-sensitive adhesive layer of the present invention has the above properties, it has excellent light leakage prevention properties even in a high temperature and high humidity environment. Moreover, the pressure-sensitive adhesive layer of the present invention is excellent in hardness at normal temperature and has improved workability. For example, when the pressure-sensitive adhesive layer is cut, adhesion of the pressure-sensitive adhesive to the cutting blade, stringing of the pressure-sensitive adhesive layer, and the like are prevented. Moreover, since the adhesive layer of this invention has sufficient softness | flexibility in a high temperature environment, it can fully relieve | moderate the stress resulting from the thermal contraction (dimensional change) of a polarizer. For this reason, even if it exposes to a high temperature environment, the curvature of a to-be-adhered body is reduced, and a tear of an adhesive layer and peeling of an adhesive layer from a polarizing plate do not generate | occur | produce easily.

The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention has a gel fraction of preferably 40% by mass or more, more preferably from the viewpoints of distortion suppression, cohesive strength, adhesive strength, and removability of the polarizing plate. 50 to 95% by mass, more preferably 55 to 90% by mass. When the gel fraction is in the above range, the pressure-sensitive adhesive layer exhibits excellent durability.

The pressure-sensitive adhesive layer of the present invention specifically cross-links the (meth) acrylic copolymer (A) with the cross-linking agent (B) by, for example, advancing the crosslinking reaction in the above-mentioned pressure-sensitive adhesive composition. Is obtained.

The conditions for forming the pressure-sensitive adhesive layer are, for example, as follows. The pressure-sensitive adhesive composition of the present invention is applied on a support and varies depending on the type of solvent, but is usually 50 to 150 ° C., preferably 60 to 100 ° C., usually 1 to 10 minutes, preferably 2 to 7 minutes. Then, the solvent is removed and a coating film is formed. The film thickness of the dried coating film is usually 5 to 75 μm, preferably 10 to 50 μm.

The pressure-sensitive adhesive layer is preferably formed under the following conditions. After applying the pressure-sensitive adhesive composition of the present invention on a support and applying a cover film on the coating film formed under the above conditions, usually 3 days or more, preferably 7 to 10 days, usually 5 to 60 ° C., It is preferably cured in an environment of 15 to 40 ° C., usually 30 to 70% RH, preferably 40 to 70% RH. When crosslinking is performed under the aging conditions as described above, a crosslinked body (network polymer) can be efficiently formed.

As a method for applying the pressure-sensitive adhesive composition, a predetermined thickness is obtained by a known method such as spin coating, knife coating, roll coating, bar coating, blade coating, die coating, or gravure coating. Thus, a method of applying and drying can be used.

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

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

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

The conditions for forming the pressure-sensitive adhesive layer are the same as the conditions described in the column “Plastic 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 adhesive performance. 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.

[Polarizing plate with adhesive layer]
The polarizing plate with an adhesive layer of this invention has a polarizing plate and the adhesive layer formed from the adhesive composition of this invention laminated | stacked on the at least one surface of the said polarizing plate. In this specification, “polarizing plate” is used to include “polarizing film”.

One embodiment of the polarizing plate with the pressure-sensitive adhesive layer of the present invention has a pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition of the present invention, which is directly laminated on at least one surface of a polarizer.

As the polarizing plate, a conventionally known polarizing film can be used. For example, the multilayer film which has polarizer itself, a polarizer, and the polarizer protective film arrange | positioned on a polarizer is mentioned. In the present invention, the pressure-sensitive adhesive layer may be disposed in direct contact with the polarizer. For example, the polarizer protective film is disposed only on one surface of the polarizer, and the polarizer protective film is disposed on the other surface. A configuration without a polarizer protective film on both sides of the polarizer.

Examples of the polarizer include a stretched film obtained by stretching a film made of a polyvinyl alcohol-based resin 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.

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

The thickness of the polarizing plate is usually 10 to 200 μm, preferably 50 to 100 μm. In this invention, since the polarizer protective film formed on a polarizer can be abbreviate | omitted, a polarizing plate can also be made thin.

As a polarizing plate with an adhesive layer of the present invention, for example, a configuration in which a polarizer protective film, a polarizer, and the adhesive layer are laminated in this order, a polarizer protective film, a polarizer, a polarizer protective film, and the above A configuration in which the pressure-sensitive adhesive layer is laminated in this order, a configuration in which the pressure-sensitive adhesive layer, the polarizer protective film, the polarizer and the pressure-sensitive adhesive layer are laminated in this order, the pressure-sensitive adhesive layer and the polarizer protective film, Examples include a configuration in which a polarizer, a polarizer protective film, and the pressure-sensitive adhesive layer are laminated in this order, and a configuration in which the pressure-sensitive adhesive layer, the polarizer, and the pressure-sensitive adhesive layer are laminated in this order. In these structures, the cover film mentioned above may be arrange | positioned as an outermost layer on the adhesive layer.

The method for forming the pressure-sensitive adhesive layer on the surface of the polarizing plate (eg, polarizer) is not particularly limited, and the method of applying the pressure-sensitive adhesive composition directly on the surface of the polarizing plate using a bar coater and drying and aging the present invention, And a method of transferring and aging the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet for polarizing plates to the surface of the polarizing plate. The conditions for drying and aging, the range of the gel fraction, and the like are the same as the conditions described in the section of [PSA layer for polarizing plate].

The thickness of the pressure-sensitive adhesive layer is usually 5 to 75 μm, preferably 10 to 50 μm, in terms of dry film thickness. In addition, the adhesive layer should just be formed in at least one surface of a polarizing plate, the aspect in which an adhesive layer is formed only in the single side | surface of a polarizing plate, the aspect in which an adhesive layer is formed in both surfaces of a polarizing plate Is mentioned.

The polarizing plate may be laminated with layers having other functions such as a protective layer, an antiglare layer, a retardation layer, and a viewing angle improving layer.

A liquid crystal element is produced by providing the polarizing plate with an adhesive layer of the present invention obtained as described above on the substrate surface of the liquid crystal cell. Here, the liquid crystal cell has a structure in which a liquid crystal layer is sandwiched between two substrates.

Examples of the substrate of the liquid crystal cell include a glass plate. The thickness of the substrate is usually 0.05 to 3 mm, preferably 0.2 to 1 mm. In this invention, by using the said adhesive composition, even when an adhesive layer is laminated | stacked directly on a polarizer, the curvature of a polarizing plate and a board | substrate can be suppressed. Therefore, even when the thickness of the substrate is small (eg, 1 mm or less, preferably 0.2 to 1 mm), the above-mentioned pressure-sensitive adhesive composition can be suitably used for bonding the polarizing plate and the substrate.

Hereinafter, the present invention will be described more specifically based on 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]
About the (meth) acrylic-type copolymer, the weight average molecular weight (Mw) and the number average molecular weight (Mn) were calculated | required on condition of the following by the gel permeation chromatography method (GPC method).
・ Measurement device: HLC-8320GPC (manufactured by Tosoh Corporation)
-GPC column configuration: The following four columns (all manufactured 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 ° C
Sample concentration: 1.5% (w / v) (diluted with tetrahydrofuran)
・ Mobile phase solvent: Tetrahydrofuran ・ Standard polystyrene conversion [photoelastic coefficient]
For the (meth) acrylic copolymer, the photoelastic coefficient was measured as follows.

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

[Synthesis Example 1]
A reactor equipped with a stirrer, reflux condenser, thermometer and nitrogen inlet tube was charged with 39 parts of lauryl methacrylate, 56 parts of 2-ethylhexyl methacrylate, 5 parts of 2-hydroxyethyl methacrylate and 100 parts of ethyl acetate solvent, and nitrogen gas The temperature was raised to 80 ° C. while introducing. Next, 0.1 part of 2,2′-azobisisobutyronitrile was added, and a polymerization reaction was performed at 80 ° C. for 6 hours in a nitrogen gas atmosphere. After completion of the reaction, it was diluted with ethyl acetate to prepare a polymer solution having a solid content concentration of 30% by mass. The obtained (meth) acrylic copolymer A1 has a weight average molecular weight (Mw) of 910,000, a molecular weight distribution (Mw / Mn) of 6.2, and a photoelastic coefficient of 50.1 × 10 ^−12. (M ² / N).

[Synthesis Examples 2 to 5]
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 as described in Table 1. The results are shown in Table 1.

[Example 1]
(1) Preparation of pressure-sensitive adhesive composition For the polymer solution obtained in Synthesis Example 1 (solid content concentration 30% by mass) and 100 parts (solid content) of (meth) acrylic copolymer A1 contained in the solution As an isocyanate compound, 0.2 part (solid content) of “TD-75” (solid content: 75% by mass, ethyl acetate solution) manufactured by Soken Chemical Co., Ltd. and Shin-Etsu Chemical Co., Ltd. A pressure-sensitive adhesive composition was obtained by mixing 0.2 parts of “KBM-403” (solid content: 100% by mass).

(2) Preparation of pressure-sensitive adhesive sheet On the polyethylene terephthalate film (PET film) subjected to release treatment, the pressure-sensitive adhesive composition obtained in the above (1) was applied using a doctor blade after removing bubbles, and at 90 ° C. The film was dried for 3 minutes to form a coating film having a dry film thickness of 20 μm. Two PET films were obtained by further laminating the peeled PET film on the surface of the coating film opposite to the surface on which the PET film was applied, and leaving it to stand for aging in a 23 ° C./50% RH environment for 7 days. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a thickness of 20 μm sandwiched between the layers was obtained.

(3) Preparation of polarizing plate with pressure-sensitive adhesive layer On the peeled polyethylene terephthalate film (PET film), the pressure-sensitive adhesive composition obtained in (1) above was applied using a doctor blade after removing bubbles. And dried at 90 ° C. for 3 minutes to obtain a sheet having a coating film having a dry film thickness of 20 μm. The coating film surface of the sheet is in contact with the polyvinyl alcohol film surface of the polarizing plate having a two-layer structure (thickness 60 μm) composed of a polyvinyl alcohol film as a polarizer and a triacetyl cellulose film as a polarizer protective film. A polarizing plate with an adhesive layer having a PET film, an adhesive layer having a thickness of 20 μm, a polarizer, and a polarizer protective film, which is allowed to stand for aging at 23 ° C./50% RH for 7 days. Got.

[Examples 2 and 3, Comparative Examples 1 and 2]
In Example 1, except that the polymer solution was changed to the polymer solution obtained in each synthesis example, and the blending composition was changed as described in Table 2, the same procedure as in Example 1 was followed. A sheet and a polarizing plate with an adhesive layer were obtained.

[Evaluation]
[Gel fraction]
About 0.1 g of the pressure-sensitive adhesive was collected in a sampling bottle from the pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples, and 30 mL of ethyl acetate was added and shaken for 4 hours. The contents of the sample bottle were made of 200 mesh stainless steel. The mixture was filtered through a wire mesh, the residue on the wire mesh was dried at 100 ° C. for 2 hours, and the dry weight was measured. The gel fraction of the pressure-sensitive adhesive was determined by the following formula.
Gel fraction (%) = (Dry weight / Adhesive sampling weight) × 100 (%)
[Photoelastic coefficient]
In the pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples, the pressure-sensitive adhesive layers having a thickness of 20 μm were bonded together in an environment of 23 ° C./50% RH several times and treated with an autoclave at 50 ° C./5 atm for 20 minutes. A pressure-sensitive adhesive layer having a thickness of 1.0 mm was produced. The pressure-sensitive adhesive layer is cut into a size of 15 mm × 50 mm, and this is attached to an automatic wavelength scanning ellipsometer (model “M-220”, manufactured by JASCO Corporation) using a jig. The measurement was performed at a measurement wavelength of 633 nm while changing. The slope when the stress is plotted on the horizontal axis and the retardation is plotted on the vertical axis is the photoelastic coefficient of the pressure-sensitive adhesive layer.

[Durability Test (Heat and Moisture Resistance Test)]
The polarizing plate with a pressure-sensitive adhesive layer obtained in the examples and comparative examples (laminated body composed of PET film / pressure-sensitive adhesive layer / polarizer / polarizer protective film) was cut into a size of 150 mm × 250 mm, and the test piece was cut. Created. The PET film is peeled from the test piece, and a laminate composed of an adhesive layer / polarizer / polarizer protective film is laminated on one side of a 0.5 mm thick glass plate using a laminator roll. I stuck it so that it touched. The obtained laminate was held in an autoclave adjusted to 50 ° C./5 atm for 20 minutes to prepare a test plate. Two similar test plates were prepared. The test plate is allowed to stand for 500 hours under conditions of a temperature of 80 ° C. (heat resistance) or a temperature of 60 ° C./90% humidity (humidity heat resistance), and the occurrence of foaming, floating and peeling is observed according to the following criteria. And evaluated.

AA: Appearance defects such as foaming, floating, and peeling were not observed. BB: Appearance defects such as foaming, floating, and peeling were slightly observed. CC: Appearance defects such as foaming, floating, and peeling were clearly observed. [Light leakage test]
Two polarizing plates with adhesive (PET film / adhesive layer / polarizer / polarizer protective film laminate) obtained in Examples and Comparative Examples were cut into a size of 310 mm × 385 mm and tested. Created a piece. The PET film is peeled from the test piece, and a laminate composed of an adhesive layer / polarizer / polarizer protective film is laminated on both sides of a 0.5 mm thick glass plate using a laminator roll so that the polarization axes are orthogonal to each other. And it stuck so that an adhesive layer and a glass plate might contact | connect. The obtained laminate was held in an autoclave adjusted to 50 ° C./5 atm for 20 minutes to prepare a test plate. This test plate was allowed to stand for 500 hours at a temperature of 80 ° C., and light leakage was observed according to the following criteria.

AA: No light leakage was observed BB: Light leakage was slightly observed CC: Light leakage was clearly observed [workability (cutting property)]
Thirty of the pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples were cut with a Thomson blade of 50 mm × 50 mm using a Thomson punching machine. Immediately after cutting, the shape of the end portion was observed, and it was determined that AA was the case where no protrusion of glue, crushing of the end portion, or loss of the adhesive layer was found in one of the 30 sheets, and CC was observed.

TD-75: trimethylolpropane modified xylylene diisocyanate (manufactured by Soken Chemical Co., Ltd., solid content 75% by mass, ethyl acetate solution)
・ KBM-403: 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.)

Claims (11)

1. (A) (meth) acrylic acid alkyl ester (a1) having a homopolymer photoelastic coefficient of −1000 × 10 ⁻¹² to −100 × 10 ⁻¹² (m ² / N), and the homopolymer has a photoelastic coefficient of + 100 × 10 ⁻¹² to + 1000 × 10 ⁻¹² (m ² / N) (meth) acrylic acid alkyl ester (a2) and a monomer component containing a crosslinkable functional group-containing monomer (a3) were obtained by copolymerization ( A (meth) acrylic copolymer;
   (B) A pressure-sensitive adhesive composition for a polarizing plate, comprising a crosslinking agent.
2. The Tg of the homopolymer of the (meth) acrylic acid alkyl ester (a1) is -30 ° C or lower, and the Tg of the homopolymer of the (meth) acrylic acid alkyl ester (a2) is -20 ° C or higher. 2. The pressure-sensitive adhesive composition for polarizing plate according to 1.
3. The pressure-sensitive adhesive for a polarizing plate according to claim 1 or 2, wherein the (meth) acrylic copolymer (A) has a photoelastic coefficient of -150 × 10 ^-12 to + 150 × 10 ^-12 (m ² / N). Agent composition.
4. The pressure-sensitive adhesive composition for a polarizing plate according to any one of claims 1 to 3, wherein the crosslinking agent (B) comprises an isocyanate compound (B1).
5. The pressure-sensitive adhesive composition for a polarizing plate according to claim 4, wherein the isocyanate compound (B1) is at least one selected from a xylylene diisocyanate crosslinking agent and a hexamethylene diisocyanate crosslinking agent.
6. The pressure-sensitive adhesive composition for a polarizing plate according to any one of claims 1 to 5, which is used for forming a pressure-sensitive adhesive layer in direct contact with a polarizer.
7. A pressure-sensitive adhesive layer for a polarizing plate formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 6.
8. The pressure-sensitive adhesive layer for a polarizing plate according to claim 7, wherein the photoelastic coefficient is −150 × 10 ⁻¹² to + 150 × 10 ⁻¹² (m ² / N).
9. A pressure-sensitive adhesive sheet for a polarizing plate comprising the pressure-sensitive adhesive layer according to claim 7 or 8.
10. The polarizing plate with an adhesive layer which has a polarizing plate and the adhesive layer of Claim 7 or 8 laminated | stacked on the at least one surface of the said polarizing plate.
11. The polarizing plate with the adhesive layer which has an adhesive layer of Claim 7 or 8 directly laminated | stacked on the at least one surface of the polarizer.