JPWO2016072199A1 - Adhesive composition for polarizing plate and polarizing plate with adhesive layer - Google Patents

Abstract

[PROBLEMS] A pressure-sensitive adhesive layer that can be applied to a configuration in which at least one of the polarizer protective films usually formed on both sides of a polarizer is omitted, can suppress bending of the liquid crystal cell, and has excellent durability. Provided is a pressure-sensitive adhesive composition for a polarizing plate capable of forming a film. [Solution] 30% by mass or more and less than 90% by mass of a methacrylic acid alkyl ester (a1) having a homopolymer glass transition temperature of less than −30 ° C., and a homopolymer having a glass transition temperature of −30 ° C. or more ( (meth) obtained by copolymerizing a monomer component containing a2) in an amount of 10% by mass or more and less than 70% by mass and a crosslinkable functional group-containing monomer (a3) in an amount of more than 0% by mass and 10% by mass or less. A pressure-sensitive adhesive composition for a polarizing plate, which comprises an acrylic copolymer and (B) a crosslinking agent, and is used for forming a pressure-sensitive adhesive layer in direct contact with a polarizer.

Description

  The present invention relates to a pressure-sensitive adhesive composition for polarizing plates, 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 (for example, glass plates). A polarizing plate is attached to the surface of the substrate constituting the liquid crystal cell via an adhesive layer. Conventionally, in order to improve mechanical properties and optical durability, a polarizing plate generally has a structure in which a polarizer protective film such as a triacetyl cellulose film is laminated on both sides of a polarizer having a polarizing function. Has been.

  In recent years, with the thinning of the liquid crystal cell and the thinning of the polarizing plate, the warpage of the liquid crystal cell in a high temperature and high humidity environment has become a major problem. As a cause of the warp of the liquid crystal cell, for example, the conventional pressure-sensitive adhesive layer has low stress relaxation characteristics, and the stress due to thermal contraction (dimensional change) of the polarizer cannot be sufficiently relaxed.

  On the other hand, it has been attempted to omit the polarizer protective film formed on both surfaces of the polarizer in response to the demand for thinning the polarizing plate. However, in a polarizing plate that does not have a polarizer protective film, since the pressure-sensitive adhesive layer is in direct contact with the polarizer, a large stress is applied to the pressure-sensitive adhesive layer due to thermal contraction of the polarizer in a high-temperature and high-humidity environment. In addition to warping of the liquid crystal cell, problems such as tearing of the pressure-sensitive adhesive layer and peeling of the polarizing plate are likely to occur.

  Patent Document 1 was obtained by polymerizing a monomer component containing 19 to 99.5% by mass of an alkyl (meth) acrylate having a branched alkyl group having 10 to 24 carbon atoms at the terminal of the ester group (meth). A pressure-sensitive adhesive containing an acrylic polymer is described. However, no particular mention is made of the above-described warpage problem when the polarizer protective film is omitted and the pressure-sensitive adhesive layer is directly laminated on the polarizer.

  Patent Document 2 is an adhesive polarizing plate having a polarizing plate and an adhesive layer provided on the polarizing plate, the polarizing plate having a transparent protective film only on one side of the polarizer, The structure provided in the polarizer of the side which does not have the said transparent protective film is described for the adhesive layer. However, no particular mention is made of the problem of warpage associated with the omission of the transparent protective film.

JP 2012-246477 A JP 2012-247574 A

  An object of the present invention is an adhesive that can be applied to a configuration in which at least one of the polarizer protective films usually formed on both sides of the polarizer is omitted, and can suppress the bending (bending) of the liquid crystal cell and has excellent durability. It is providing the adhesive composition for polarizing plates which can form an agent layer.

  The present inventors diligently studied to solve the above problems. As a result, when a specific (meth) acrylic copolymer is used and a crosslinking agent is used, the above-described liquid crystal cell can be prevented from warping (bending) and a pressure-sensitive adhesive layer having excellent durability can be formed. I found that I can do it.

  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 [5].

  [1] (A) Alkyl methacrylate having a glass transition temperature of homopolymer of less than −30 ° C. and an alkyl methacrylate (a1) of 30% by mass to less than 90% by mass, and a homopolymer having a glass transition temperature of −30 ° C. or more. It was obtained by copolymerizing a monomer component containing the ester (a2) in an amount of 10% by mass or more and less than 70% by mass and the crosslinkable functional group-containing monomer (a3) in an amount of more than 0% by mass and 10% by mass or less ( A pressure-sensitive adhesive composition for polarizing plates, which comprises a (meth) acrylic copolymer and (B) a crosslinking agent, and is used for forming a pressure-sensitive adhesive layer in direct contact with a polarizer.

  [2] A pressure-sensitive adhesive layer for a polarizing plate formed from the pressure-sensitive adhesive composition according to [1].

[3] The storage elastic modulus at 23 ° C. is 0.10 MPa or more, the storage elastic modulus at 85 ° C. is 0.05 MPa or less, and the storage elastic modulus at a certain temperature T ° C. is stored at G ′ _T and T + 1 ° C. When the elastic modulus is G ′ _{T + 1} , the temperature T is in the range of 23 to 50 ° C., and always satisfies G ′ _T / G ′ _{T + 1} <1.07. Adhesive layer.

  [4] A pressure-sensitive adhesive sheet for polarizing plate having the pressure-sensitive adhesive layer according to [2] or [3].

  [5] A polarizing plate with an adhesive layer having the adhesive layer according to [2] or [3], which is directly laminated on at least one surface of a polarizer.

  ADVANTAGE OF THE INVENTION According to this invention, the adhesion which can suppress the curvature (bending) of a liquid crystal cell applicable to the structure by which at least one of the polarizer protective film normally formed on both surfaces of a polarizer was abbreviate | omitted, and was excellent in durability. The adhesive composition for polarizing plates which can form an agent layer can be provided. Moreover, the adhesive layer for polarizing plates formed from the said composition, the adhesive sheet for polarizing plates which has the said adhesive layer, and the polarizing plate with an adhesive layer which has the said adhesive layer can be provided.

  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 of the present invention 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) has a glass transition temperature (Tg) of homopolymer of methacrylic acid alkyl ester (a1) having a glass transition temperature of less than −30 ° C. of 30% by mass or more and less than 90% by mass. The amount of the methacrylic acid alkyl ester (a2) having a temperature (Tg) of −30 ° C. or more of 10% by mass or more and less than 70% by mass and the crosslinkable functional group-containing monomer (a3) of more than 0% by mass and 10% by mass or less. The monomer component is a copolymer obtained by copolymerizing the monomer component. The copolymer (A) is usually a structural unit derived from an alkyl methacrylate ester (a1), a structural unit derived from an alkyl methacrylate ester (a2), and a structural unit derived from a crosslinkable functional group-containing monomer (a3). And have.

  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”. In addition, (a1), (a2) and (a3) are also referred to as “monomer (a1)”, “monomer (a2)” and “monomer (a3)”, respectively.

  As the glass transition temperature (Tg) of the homopolymer of (meth) acrylic acid alkyl ester, the value described in Polymer Handbook Fourth Edition (Wiley-Interscience 2003) is adopted.

<< Methacrylic acid alkyl ester (a1) >>
The monomer (a1) is an alkyl methacrylate having a homopolymer Tg of less than −30 ° C. The monomer having a Tg of the homopolymer in the range of −80 to −40 ° C. is preferable, and the monomer in the range of −70 to −50 ° C. is more preferable.

  By using the copolymer (A) obtained by copolymerizing the monomer (a1) having a Tg of less than −30 ° C. of the homopolymer, appropriate stress relaxation characteristics can be imparted to the pressure-sensitive adhesive layer.

Examples of the monomer (a1), for example, of CH ₂ = C (CH ₃₎ compounds represented by -COOR ^1, Tg of homopolymer include compounds is less than -30 ° C.. In the formula, R ¹ is an alkyl group having 6 to 18 carbon atoms. The alkyl group preferably has 6 to 14 carbon atoms, and more preferably 8 to 14 in view of obtaining a hydrophobic pressure-sensitive adhesive layer capable of preventing moisture from entering the polarizer.

  Examples of the monomer (a1) include isooctyl methacrylate (−45 ° C.), isodecyl methacrylate (−41 ° C.), lauryl methacrylate (−65 ° C.), and tetradecyl methacrylate (−72 ° C.). The numerical value in parenthesis shows Tg of the homopolymer of each monomer.

  When a (meth) acrylic copolymer containing a structural unit derived from a methacrylic acid alkyl ester having a low homopolymer Tg is used, appropriate stress relaxation characteristics can be imparted to the pressure-sensitive adhesive layer. In addition, when a long chain alkyl group of methacrylic acid alkyl ester is used, hydrophobicity can be imparted in addition to stress relaxation characteristics. For example, by using the monomer (a1) having a long-chain alkyl group, the storage elastic modulus at 85 ° C. is 0.05 MPa or less, the flexibility is high, and the hydrophobicity is capable of preventing moisture from entering the polarizer. There exists a tendency to obtain the adhesive layer which has.

  A monomer (a1) may be used individually by 1 type, and may use 2 or more types.

  In 100% by mass of the monomer component forming the copolymer (A), the amount of the monomer (a1) used is 30% by mass or more and less than 90% by mass, preferably 30 to 70% by mass, more preferably 30 to 50% by mass. %. When the usage-amount of a monomer (a1) exists in the said range, it is preferable at the point (the balance of a softness | flexibility and rigidity) that the storage elastic modulus of the adhesive layer obtained can be adjusted to the range mentioned later.

<< alkyl methacrylate (a2) >>
The monomer (a2) is an alkyl methacrylate having a homopolymer Tg of −30 ° C. or higher. The monomer having a Tg of homopolymer at -30 to 30 ° C is preferable, and the monomer at -20 to 0 ° C is more preferable.

  By using the copolymer (A) obtained by copolymerizing the monomer (a2) having a homopolymer Tg of −30 ° C. or more, suitable processability can be imparted to the pressure-sensitive adhesive layer.

Examples of the monomer (a2), for example, of CH ₂ = C (CH ₃₎ a compound represented by -COOR ^2, include compounds Tg of the homopolymer is -30 ° C. or higher. In the formula, R ² is an alkyl group having 1 to 18 carbon atoms. The alkyl group preferably has 1 to 8 carbon atoms, and more preferably 4 to 8 in view of obtaining a hydrophobic pressure-sensitive adhesive layer capable of preventing moisture from entering the polarizer.

  Examples of the monomer (a2) include methyl methacrylate (105 ° C.), ethyl methacrylate (65 ° C.), propyl methacrylate (35 ° C.), isopropyl methacrylate (81 ° C.), tert-butyl methacrylate (118 ° C.), and n-butyl methacrylate. (20 ° C), isobutyl methacrylate (48 ° C), pentyl methacrylate (-5 ° C), hexyl methacrylate (-5 ° C), octyl methacrylate (-20 ° C), 2-ethylhexyl methacrylate (-10 ° C), hexadecyl methacrylate ( 15 ° C.). The numerical value in parenthesis shows Tg of the homopolymer of each monomer.

  When a (meth) acrylic copolymer containing a structural unit derived from a methacrylic acid alkyl ester having a high homopolymer Tg is used, suitable processability can be imparted to the pressure-sensitive adhesive layer. In addition, when the alkyl group of the methacrylic acid alkyl ester has a long chain, hydrophobicity can be imparted in addition to processability. For example, by using the monomer (a2) having a long-chain alkyl group, the adhesive has a storage elastic modulus at 23 ° C. of not less than 0.10 MPa and is hard, and has a hydrophobic property capable of preventing moisture from entering the polarizer. The agent layer tends to be obtained.

  A monomer (a2) may be used individually by 1 type, and may use 2 or more types.

  In 100% by mass of the monomer component forming the copolymer (A), the amount of the monomer (a2) used is 10% by mass or more and less than 70% by mass, preferably 30 to 65% by mass, more preferably 40 to 60% by mass. %. When the usage-amount of a monomer (a2) exists in the said range, it is preferable at the point (the balance of a softness | flexibility and rigidity) that the storage elastic modulus of the adhesive layer obtained can be adjusted to the range mentioned later.

  When the usage ratio of the monomer (a2) increases, the storage elastic modulus of the pressure-sensitive adhesive layer tends to increase, and when the usage ratio of the monomer (a2) decreases, the storage elastic modulus of the pressure-sensitive adhesive layer tends to decrease.

  In the present invention, the methacrylic acid alkyl ester (a1) having a Tg of less than −30 ° C. and the methacrylic acid alkyl ester (a2) having a Tg of −30 ° C. or higher are copolymerized, so that the Tg is less than −30 ° C. Compared with the case of copolymerizing an acrylic acid alkyl ester and an acrylic acid alkyl ester having a Tg of −30 ° C. or higher, this is excellent in that the pressure-sensitive adhesive performance can be expressed while having hydrophobicity.

<< 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, specifically, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate. , Hydroxyalkyl (meth) acrylates such as 6-hydroxyhexyl (meth) acrylate and 8-hydroxyoctyl (meth) acrylate. Carbon number of the hydroxyalkyl group in hydroxyalkyl (meth) acrylate is 2-8 normally, Preferably it is 2-6.

  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 at least selected from a hydroxyl group-containing monomer (however, a hydroxyl group-containing monomer excludes a monomer having a carboxyl group) and a carboxyl group-containing monomer from the viewpoint of crosslinkability with the crosslinking agent (B). One type is preferable, and a hydroxyl group-containing monomer is more preferable.

  A monomer (a3) may be used individually by 1 type, and may use 2 or more types.

  In 100% by mass of the monomer component forming the copolymer (A), the amount of the monomer (a3) used is more than 0% by mass and 10% by mass or less, preferably 2 to 8% by mass, more preferably 4 to 4%. 6% 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》
As a monomer component which forms a copolymer (A), in the range which does not impair the physical property of a copolymer (A), for example, acrylic acid alkylester, alkoxyalkyl (meth) acrylate, alkoxy polyalkylene glycol mono (meth) Other (meth) acrylic acid esters such as 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.

The alkyl acrylate ester is represented by, for example, the formula: CH ₂ ═CH—COOR ³ . In the formula, R ³ is an alkyl group having 1 to 18 carbon atoms. For example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, isooctyl acrylate, Nonyl acrylate, decyl acrylate, undecaacrylate, lauryl acrylate, stearyl acrylate, and isostearyl acrylate may be mentioned.

  Examples of the alkoxyalkyl (meth) acrylate include methoxymethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxypropyl (meth) acrylate, 3-ethoxypropyl ( Examples include 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 the above other monomers (eg, other (meth) acrylic acid ester, copolymerizable monomer) is 0 to 10% by mass. It is preferable that it is 0 to 5% by mass.

<< 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 under 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 ketone Ketones 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), and 2,2′-azobis (2-cyclopropyl). Propionitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile) 2- (carbamoylazo) isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis ( N, N'-dimethyleneisobutylamidine), 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], 2,2'-azobis Isobutylamide) dihydrate, 4,4′-azobis (4-cyanopentanoic acid), 2,2′-azobis (2-cyanopropanol), dimethyl-2,2′-azobis (2-methylpropionate) It is done. These polymerization initiators may be used alone or in combination of two or more.

  A polymerization initiator is 0.01-5 mass parts normally with respect to 100 mass parts of monomer components which form a (meth) acrylic-type copolymer (A), Preferably it exists in the range of 0.1-3 mass parts. 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 weight average molecular weight (Mw) measured by the gel permeation chromatography (GPC) method of the (meth) acrylic copolymer (A) is a polystyrene conversion value, and is usually 400,000 to 1,800,000, preferably 60. It is 10,000 to 1,400,000, more preferably 800,000 to 1,000,000. 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 (the balance of storage elastic modulus (G′1) and (G′2)), It can be set as the adhesive composition of the viscosity suitable for coating.

  The molecular weight distribution (Mw / Mn) measured by the GPC method of the (meth) acrylic copolymer (A) is usually 15 or less, preferably 2 to 10, more preferably 4 to 8.

  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 monomer (a1) and (a2) having a glass transition temperature (Tg) of the homopolymer in the above range are used in combination, and the glass transition temperature (Tg) determined by the Fox equation is usually −70 to −20 ° C., The (meth) acrylic copolymer (A) can be synthesized so that the temperature is preferably −60 to −30 ° C. 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. Preferably it is 70-99.95 mass%, Most preferably, it is 80-99.90 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 carried out, for example, an isocyanate compound (B1), a metal chelate compound (B2), and an epoxy compound (B3) can be mentioned.

  A crosslinking agent (B) may be used individually by 1 type, and may use 2 or more types.

  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). 0.05 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. Examples include aliphatic diisocyanates having 4 to 30 carbon atoms such as -1,6-hexamethylene diisocyanate. Examples of the alicyclic diisocyanate 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), the reaction product of trimethylolpropane and tolylene diisocyanate or xylylene diisocyanate (L-45 manufactured by Soken Chemical Co., Ltd.) TD-75, etc.), isocyanurate of hexamethylene diisocyanate or tolylene diisocyanate (Asahi Kasei Co., Ltd. TSE-100, Nippon Polyurethane Industry Co., Ltd. 2050, etc.) are preferred.

  An isocyanate compound (B1) may be used individually by 1 type, and may use 2 or more types.

<< 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.

  A metal chelate compound (B2) may be used individually by 1 type, and may use 2 or more types.

  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, m-N, 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 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 Agents; halogen-containing silane coupling agents such as 3-chloropropyl trimethoxysilane.

  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 quaternary ammonium salts, amide quaternary ammonium salts, pyridium salts, cationic surfactants having a cationic group such as 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.

  Moreover, the reactive type emulsifier which has a polymeric group is also mentioned as surfactant, The polymeric surfactant which made high molecular weight the monomer component containing said 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-diethyl) N-methyl-N- (2-methoxyethyl) ammonium tetrafluoroborate, N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide, 1-octylpyridinium fluorophospho Nium imide, 1-octyl-3-methylpyridinium, and trifluorosulfonium imide are preferable.

  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.

  The pressure-sensitive adhesive composition of the present invention is suitable for use in bonding a substrate constituting a liquid crystal cell and a polarizer. In particular, even when the thickness of the glass plate constituting the thinned liquid crystal cell is as small as about 0.05 to 1.0 mm, it is suitable for bonding the substrate and the polarizer.

  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 80% by mass, and still more preferably 55 to 70% 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 storage elastic modulus characteristics can be formed.

  The pressure-sensitive adhesive layer of the present invention has a storage elastic modulus (G′1) at 23 ° C. of preferably 0.10 MPa or more, more preferably 0.10 to 0.20 MPa, and particularly preferably 0.10 to 0.15 MPa. Yes; The storage elastic modulus (G′2) at 85 ° C. is preferably 0.05 MPa or less, more preferably 0.01 to 0.04 MPa, and particularly preferably 0.01 to 0.03 MPa.

When the storage elastic modulus at a certain temperature T ° C. is G ′ _T and the storage elastic modulus at T + 1 ° C. is G ′ _{T + 1} , the pressure-sensitive adhesive layer of the present invention has a temperature T of 23 to 50 ° C. It is preferable to always satisfy _T / G ′ _{T + 1} <1.07, and it is more preferable to always satisfy 1 ≦ G ′ _T / G ′ _{T + 1} ≦ 1.06.

  The storage elastic modulus is, for example, a value calculated from a dynamic viscoelastic spectrum measured for the laminate by laminating the adhesive layers a plurality of times to produce a laminate having a thickness of about 1.0 mm. .

  When the storage elastic modulus (G′1) at 23 ° C. is in the above range, the pressure-sensitive adhesive layer of the present invention is excellent in hardness at room 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.

  When the storage elastic modulus (G′2) at 85 ° C. is in the above range, the pressure-sensitive adhesive layer of the present invention has sufficient flexibility in a high temperature environment, and therefore the thermal contraction (dimensions) of the polarizer. The stress caused by (change) can be sufficiently relaxed. For this reason, even if it exposes to a high temperature environment, the curvature of a to-be-adhered body is reduced, and also a tear of an adhesive layer and peeling of an adhesive layer from a polarizer do not occur easily.

Always satisfying G ′ _T / G ′ _{T + 1} <1.07 in the range of 23 to 50 ° C. means that the change in elastic modulus in this temperature range is small and suppresses deformation and protrusion of the pressure-sensitive adhesive layer. be able to.

  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. 50-80 mass%, More preferably, it is 55-70 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 onto a support and varies depending on the type of solvent, but is usually 50 to 150 ° C., preferably 60 to 100 ° C., usually 1 to 10 minutes, preferably 2 to 7 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 apply | coating the adhesive composition of this invention on a support body and sticking a cover film on the coating film formed on the said conditions, normally 3 days or more, Preferably it is 7-10 days, Usually 5-60 degreeC, It is preferably cured under 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); and 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 the cover film include polyester films such as polyethylene terephthalate (PET); and plastic films such as polyolefin films such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer.

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

  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. Although the film thickness of a base material and a cover film is not specifically limited, Usually, 10-125 micrometers, Preferably it is 25-75 micrometers.

[Polarizing plate with adhesive layer]
The polarizing plate with the pressure-sensitive adhesive layer of the present invention has a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention, which is directly laminated on at least one surface of a polarizer. In this specification, “polarizing plate” is used to include “polarizing film”.

  A conventionally well-known polarizing film can be used as a polarizing plate. 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, since the pressure-sensitive adhesive layer is disposed in direct contact with the polarizer, the polarizer protective film is disposed only on one side of the polarizer, and the polarizer protective film is disposed on both sides of the polarizer. There is no configuration.

  As a polarizer, the stretched film obtained by making a film which consists of polyvinyl alcohol-type resins contain a polarizing component, and extending | stretching is mentioned, for example. 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 polarization 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 be reduced in thickness.

  In the present invention, the pressure-sensitive adhesive layer is formed in direct contact with the polarizer. As a polarizing plate with an adhesive layer of the present invention, for example, a polarizer protective film, a polarizer, and the adhesive layer are laminated in this order, the adhesive layer, the polarizer protective film, the polarizer, and the above The structure by which the adhesive layer was laminated | stacked in this order, the structure by which the said adhesive layer, the polarizer, and the said adhesive layer were laminated | stacked in this order are mentioned. 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 polarizer is not particularly limited. The method for applying the pressure-sensitive adhesive composition directly to the surface of the polarizer using a bar coater, drying and aging, the pressure-sensitive adhesive sheet for polarizing plate of the present invention There is a method in which the pressure-sensitive adhesive layer possessed by is transferred to the polarizer surface and aged. 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, as a dry film thickness. The pressure-sensitive adhesive layer only needs to be formed in contact with the polarizer on at least one surface of the polarizer, and the pressure-sensitive adhesive layer is formed only on one side of the polarizer, and the pressure-sensitive adhesive is formed on both sides of the polarizer. The aspect in which a layer is formed is mentioned.

  Moreover, the layer which has other functions, such as a protective layer, a glare-proof layer, a phase difference layer, a viewing angle improvement layer, for example may be laminated | stacked on the said polarizing plate.

  A liquid crystal element is produced by providing the polarizing plate with the pressure-sensitive 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.

  An example of the substrate that the liquid crystal cell has is 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. For this reason, also when the thickness of a board | substrate is small (Example: 1 mm or less, Preferably 0.2-1 mm), the said adhesive composition can be used suitably for bonding of a polarizing plate and a board | substrate.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this 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).
-Measuring 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
[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 had a weight average molecular weight (Mw) of 910,000 and a molecular weight distribution (Mw / Mn) of 6.2.

[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 In addition, 0.2 part (solid content) of “TD-75” (solid content: 75% by mass, ethyl acetate solution) manufactured by Soken Chemical Co., Ltd. as the isocyanate compound, and “Shin-Etsu Chemical Co., Ltd.” as the silane coupling agent A pressure-sensitive adhesive composition was obtained by mixing 0.2 part 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.

[Example 2, Comparative Examples 1-3]
In Example 1, the pressure-sensitive adhesive composition was changed in the same manner as in Example 1 except that the polymer solution was changed to the polymer solution obtained in Synthesis Examples 2 to 5 and the blending composition was changed as described in Table 2. The polarizing plate with an adhesive sheet and an adhesive layer was 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 (%)
[Storage modulus]
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. For the pressure-sensitive adhesive layer having a thickness of 1.0 mm, a dynamic viscoelasticity measurement method (temperature range: −40 to 160 ° C., temperature rising rate: 3.67 ° C.) based on JIS K7244 using “Physica MCR300” manufactured by Anton Paar. / Min, conditions of frequency 1 Hz), the viscoelastic spectrum was measured, and the storage elastic modulus at a temperature of 23 ° C. and 85 ° C., and the maximum value of G ′ _T / G ′ _{T + 1} in the range of 23 to 50 ° C. was determined.

[Measurement of adhesive strength]
The polarizing plate with the pressure-sensitive adhesive layer obtained in Examples and Comparative Examples (laminated body composed of PET film / pressure-sensitive adhesive layer / polarizer / polarizer protective film) was cut into a size of 70 mm × 25 mm, and the test piece was cut. Created. The PET film is peeled from the test piece, and the laminate composed of the pressure-sensitive adhesive layer / polarizer / polarizer protective film is laminated on one side of a 2 mm thick glass plate using a laminator roll. Affixed to touch. The obtained laminate was held in an autoclave adjusted to 50 ° C./5 atm for 20 minutes. Next, after being left in a 23 ° C./50% RH environment for 1 hour, the end of the polarizing plate was pulled at a rate of 300 mm / min in the 90 ° direction with respect to the glass plate surface, and the adhesive strength (peel strength) was measured.

(Water vapor transmission rate)
The water vapor transmission rate was measured as follows according to JIS Z0208. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a thickness of 50 μm was prepared in the same manner as described in the column “(2) Preparation of pressure-sensitive adhesive sheet”. The PET film was peeled from this pressure-sensitive adhesive sheet, and a nonwoven fabric was bonded to both sides of the pressure-sensitive adhesive layer (the obtained laminate was referred to as “sheet A”), and cut according to the diameter of the moisture permeable cup. 10 g of calcium chloride was put in a moisture permeable cup (inner diameter 60 mm), and the cut sheet A, rubber packing, and cover ring were set and fixed with bolts. Under a constant temperature and humidity condition of 40 ° C./90% RH, a moisture permeable cup in which the sheet A or the like was set was put in. After 24 hours, the moisture permeable cup was taken out, and the weight of the moisture permeable cup was weighed (initial weight). The weighed moisture-permeable cup was returned to 40 ° C./90% RH condition, and the weight was weighed every 24 hours. When the increase in mass every 24 hours was within 5%, the water vapor transmission rate was calculated from the last mass change and measurement interval using the following formula.

Water vapor transmission rate [g / m ² / day] = 240 × M / T × S
M: Increased mass (mg) of the last two weighing intervals tested
T: Time of the last two weighing intervals during the test (hours)
S: Transmission area (cm ² )
[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
[Bending test]
The polarizing plate with the pressure-sensitive adhesive layer obtained in Examples and Comparative Examples (laminated body composed of PET film / pressure-sensitive adhesive layer / polarizer / polarizer protective film) was cut into a size of 35 mm × 400 mm (stretching axis direction). A test piece was prepared. A PET film is peeled from a test piece, and a laminate composed of an adhesive layer / polarizer / polarizer protective film is laminated on one surface of a glass plate having a thickness of 0.7 mm and 40 mm × 410 mm using a laminator roll. It stuck so that a layer and a glass plate might contact. The obtained laminate was allowed to stand in a 23 ° C./50% RH environment for 24 hours, and then held in an oven at 60 ° C. for 72 hours. One end was fixed to a wall surface perpendicular to the floor surface, and the amount of lifting at the opposite end was measured with a ruler. The warping (bending) was observed according to the following criteria.

AA: Terminal lift is 3 mm or less BB: Terminal lift is more than 3 mm and less than 5 mm CC: Terminal lift is 5 mm or more
[Processability (Cutability)]
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.

[Adhesive deformation]
Ten polarizing plates with adhesive layers obtained in Examples / Comparative Examples cut into 100 mm × 100 mm were laminated and left to stand for 24 hours with a load of 1 kg from above. The protrusion was observed visually.

AA: No sticking out of the adhesive layer was observed BB: Some sticking out of the adhesive layer was observed CC: Protruding of the adhesive layer was clearly observed

  As a monomer for forming the (meth) acrylic copolymer, (1) As shown in the examples, in the example in which the monomer (a1) and the monomer (a2) are used in the specific ratio, durability, warpage suppression, Excellent in workability and adhesive non-deformability. (2) As shown in Comparative Examples 1 and 2, in an example in which the monomer (a1) and the monomer (a2) are not used in the specific ratio, durability and warpage Inferior in suppression, workability or adhesive non-deformability, (3) As shown in Comparative Example 3, in the case of using an acrylic acid alkyl ester without using a methacrylic acid alkyl ester, water vapor permeability is high (hydrophobicity is low) ), The heat and moisture resistance of the pressure-sensitive adhesive sheet and warpage suppression were inferior.

Claims (5)

(A) 30% by mass or more and less than 90% by mass of a methacrylic acid alkyl ester (a1) having a glass transition temperature of the homopolymer of less than −30 ° C. (Meth) acryl obtained by copolymerizing a monomer component containing 10% by mass or more and less than 70% by mass and a crosslinkable functional group-containing monomer (a3) in an amount of more than 0% by mass and 10% by mass or less. A copolymer,
(B) contains a crosslinking agent,
A pressure-sensitive adhesive composition for polarizing plates, which is used for forming a pressure-sensitive adhesive layer in direct contact with a polarizer.   A pressure-sensitive adhesive layer for a polarizing plate formed from the pressure-sensitive adhesive composition according to claim 1. The storage elastic modulus at 23 ° C. is 0.10 MPa or more,
The storage elastic modulus at 85 ° C. is 0.05 MPa or less, and
Assuming that the storage elastic modulus at a certain temperature T ° C. is G ′ _T and the storage elastic modulus at T + 1 ° C. is G ′ _{T + 1} , G ′ _T / G ′ _{T + 1} < Always satisfies 1.07,
The pressure-sensitive adhesive layer for a polarizing plate according to claim 2.   The adhesive sheet for polarizing plates which has an adhesive layer of Claim 2 or 3.   The polarizing plate with an adhesive layer which has an adhesive layer of Claim 2 or 3 directly laminated | stacked on the at least one surface of the polarizer.