JP6530376B2 - Pressure-sensitive adhesive composition for polarizing plate, pressure-sensitive adhesive sheet and polarizing plate with pressure-sensitive adhesive layer - Google Patents

Description

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

  The liquid crystal cell has a structure in which a liquid crystal layer is sandwiched between two substrates (eg, a glass plate), and a polarizing plate is attached to the surface of the substrate via an adhesive layer. Since the polarizing plate is easily thermally shrunk in a high temperature and high humidity and heat environment, it may lack dimensional stability and may cause warpage in the liquid crystal cell. In recent years, with the reduction in thickness of liquid crystal cells (eg, reduction in thickness of substrates constituting liquid crystal cells) and the reduction in thickness of polarizing plates, warpage of liquid crystal cells under high-temperature, high-humidity heat environment has become a serious problem. The causes of the warpage of the liquid crystal cell include, for example, the inability of the pressure-sensitive adhesive layer to follow the thermal contraction (dimension change) of the polarizing plate and the low stress relaxation property of the pressure-sensitive adhesive layer.

  In addition, in a high temperature and high humidity and heat environment, defects such as foaming at the interface between the polarizing plate and the substrate, tearing of the pressure-sensitive adhesive layer, peeling of the polarizing plate, and the like easily occur. Therefore, high durability is required for the polarizing plate adhesive.

  In general, as a means for suppressing the warpage of the liquid crystal cell, there is mentioned a method using a highly flexible pressure-sensitive adhesive layer which can cope with the dimensional change of the polarizing plate. However, such an adhesive layer lacks cohesion and causes problems such as deterioration in durability and deterioration in processability.

  For example, Patent Document 1 contains a specific (meth) acrylic polymer and an isocyanate-based crosslinking agent with durability, stress relaxation characteristics (warpage of glass) due to dimensional changes of optical members, and removability as subjects. Patent Document 2 discloses a pressure-sensitive adhesive composition for an optical member, which contains a specific copolymer, a metal chelate-based curing agent, and an isocyanate-based curing agent, with reworkability and durability as issues. An adhesive composition is disclosed.

JP, 2006-219526, A JP, 2009-132752, A

  The object of the present invention is to provide a pressure-sensitive adhesive composition for a polarizing plate capable of suppressing a bending (bending) of a liquid crystal cell and capable of forming a pressure-sensitive adhesive layer excellent in durability, and a pressure-sensitive adhesive formed from the composition It is providing the adhesive sheet for polarizing plates which has a layer, and the polarizing plate with an adhesive layer which has the said adhesive layer.

  The present inventors diligently studied to solve the above problems. As a result, when a (meth) acrylic copolymer having a branching degree in a specific range is used and an isocyanate compound and a metal chelate compound are used in combination as a crosslinking agent, warpage (bending) of the liquid crystal cell can be suppressed and It has been found that a pressure-sensitive adhesive layer excellent in durability can be formed. The above-mentioned Patent Documents 1 and 2 do not mention at all such a degree of branching. That is, the present inventors have found that the above-mentioned problems can be solved by using the pressure-sensitive adhesive composition for a polarizing plate having the following specific constitution, and have completed the present invention.

The present invention is, for example, the following [1] to [9].
[1] (A) obtained by copolymerizing a monomer component containing a (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms of an alkyl group and a carboxyl group-containing monomer, and gel permeation chromatography method / multiple angle Contains a (meth) acrylic copolymer having a degree of branching measured by a laser light scattering detector (GPC-MALS) of 0.55 or less, (B1) an isocyanate compound, and (B2) a metal chelate compound The adhesive composition for polarizing plates characterized by the above-mentioned.

  [2] The polarizing plate according to [1], wherein the (meth) acrylic copolymer (A) is a copolymer obtained by the copolymerization in the presence of a peroxide polymerization initiator. Adhesive composition.

  [3] The above-mentioned [1], wherein the weight average molecular weight (Mw) measured by gel permeation chromatography (GPC method) of the (meth) acrylic copolymer (A) is 200,000 to 1,500,000. Or the adhesive composition for polarizing plates as described in [2].

  [4] Any one of the above [1] to [3], wherein the degree of branching measured by GPC-MALS of the (meth) acrylic copolymer (A) is 0.10 to 0.54. The adhesive composition for polarizing plates as described.

  [5] The above [1] to [4], wherein the (meth) acrylic copolymer (A) is a copolymer obtained by further copolymerizing a polar group-containing monomer other than a carboxyl group-containing monomer The pressure-sensitive adhesive composition for a polarizing plate according to any one of the above.

  [6] Any one of the above [1] to [5], wherein the content of the peroxide is 0.1 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic copolymer (A) The adhesive composition for polarizing plates as described in a term.

  [7] The adhesive for polarizing plate according to any one of the above [1] to [6], wherein the gel fraction of the pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition for polarizing plate is 20 to 70% by mass. Agent composition.

  [8] A pressure-sensitive adhesive sheet for a polarizing plate comprising a pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition for a polarizing plate according to any one of the above [1] to [7].

  [9] A polarizing plate, and a pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition for a polarizing plate according to any one of the above [1] to [7] on at least one surface of the polarizing plate. A polarizing plate with a pressure-sensitive adhesive layer characterized by

  According to the present invention, it is possible to suppress the bending (bending) of a liquid crystal cell, and to form a pressure-sensitive adhesive composition for a polarizing plate capable of forming a pressure-sensitive adhesive layer excellent in durability, and a pressure-sensitive adhesive formed from the composition The adhesive sheet for polarizing plates which has a 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 a polarizing plate, the pressure-sensitive adhesive sheet for a polarizing plate, and the polarizing plate with a pressure-sensitive adhesive layer of the present invention will be described. Hereinafter, the pressure-sensitive adhesive composition for polarizing plate of the present invention is simply referred to as "pressure-sensitive adhesive composition", and the pressure-sensitive adhesive sheet for polarizing plate of the present invention is also simply referred to as "pressure-sensitive adhesive sheet".

[Pressure-sensitive adhesive composition for polarizing plate]
The pressure-sensitive adhesive composition for a polarizing plate of the present invention contains a (meth) acrylic copolymer (A), an isocyanate compound (B1) and a metal chelate compound (B2). The pressure-sensitive adhesive composition may optionally contain at least one selected from a silane coupling agent (C), an antistatic agent (D) and an organic solvent (E).

  Hereinafter, the isocyanate compound (B1) and the metal chelate compound (B2) are collectively referred to as "crosslinking agent (B)". In the present invention, the pressure-sensitive adhesive layer is formed by crosslinking the (meth) acrylic copolymer (A) in combination with these crosslinking agents.

[(Meth) acrylic copolymer (A)]
The (meth) acrylic copolymer (A) is a copolymer obtained by copolymerizing a monomer component containing an alkyl group having a carbon number of 4 to 18 (meth) acrylic acid alkyl ester and a carboxyl group-containing monomer It is. Other examples of the monomer component of the copolymer (A) include polar group-containing monomers other than carboxyl group-containing monomers, and other monomers other than these.

  In the present specification, acrylic and methacrylic are also collectively referred to as "(meth) acrylic". Moreover, the structural unit derived from a certain monomer a contained in a polymer is also described as a "monomer a unit."

  The (meth) acrylic copolymer (A) has a branching degree of 0.55 or less, preferably 0, as measured by gel permeation chromatography / multiangle laser light scattering detector (GPC-MALS). And more preferably 0.20 to 0.53, and particularly preferably 0.30 to 0.53. Details of the measurement conditions of the degree of branching are described in the examples.

  The degree of branching is an index showing that it is a branched polymer when it is 0.55 or less and it is a linear polymer when it exceeds 0.55. Moreover, in the branched polymer, when the value of the degree of branching is small, it indicates that the polymer molecule is highly branched and has a highly branched chain, and when the value of degree of branching is large, the polymer molecule is less branched and the low branched chain Indicates having.

  In the (meth) acrylic copolymer (A) having a degree of branching in the above range, (1) many entanglements due to branching between polymer molecules occur around room temperature, and as a result, the molecular weight of the polymer and the pressure-sensitive adhesive Even in the design where the gel fraction of the layer is low, the cohesiveness of the polymer is maintained, and the adhesive property is excellent, the adhesive property, the processability such as punching the adhesive layer, and the storage properties such as the deformation of the adhesive layer and little storage (2) The adhesive layer exhibits excellent flexibility because the entanglement of polymer molecules is partially loosened at high temperature (eg, 60 ° C.), and it is excellent in suppression of bending (bending) of the polarizing plate, The pressure-sensitive adhesive layer exhibits excellent durability due to the entanglement which is partially remaining.

  Regarding the above (1) and (2), in the present invention, the metal chelate compound (B2) is used as a part of the crosslinking agent, and (meth) acrylic copolymer (A) / metal chelate compound (B2) Crosslinks are formed between one another by coordination (pseudocrosslinking). Therefore, the crosslinking is maintained at the room temperature and the polymer exhibits cohesiveness, whereas the crosslinking is partially solved at the high temperature, and the pressure-sensitive adhesive layer exhibits more excellent flexibility.

  About the point by which the curvature of a polarizing plate is suppressed, it is estimated by the following reasons. For example, in the configuration of polarizing plate / pressure-sensitive adhesive layer / adherend, the case of using a glass plate as an adherend will be described as an example. The polarizing plate and the glass plate have different thermal contraction rates, and the polarizing plate usually has a thermal contraction rate (dimension change) larger than that of the glass plate. When the pressure-sensitive adhesive layer lacks flexibility under high temperature and high humidity heat environment, the pressure-sensitive adhesive layer can not follow the dimensional change of the polarizing plate, and the stress can not be relieved by the pressure-sensitive adhesive layer. The stress is concentrated on the glass plate, which causes the glass plate to warp. On the other hand, the pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition of the present invention contains a highly branched polymer, and a metal chelate compound is used as a part of the crosslinking agent. Since the pressure-sensitive adhesive layer can follow the dimensional change of the polarizing plate because stress is partially loosened and the above-mentioned crosslinking is partially solved, stress is not generated and stress is not concentrated on the glass plate . In addition, the polarizing plate can also be thermally shrunk uniformly without anisotropy, and the birefringence of the polarizing plate is not induced. As described above, in the present invention, the pressure-sensitive adhesive layer can absorb and relieve the stress caused by the dimensional change of the polarizing plate, and therefore, the glass plate is not subjected to an excessive stress (load). It is presumed that it leads to the board curb curbing.

  The pressure-sensitive adhesive composition of the present invention has the above-described properties, and thus is suitable for use in laminating a substrate constituting a liquid crystal cell and a polarizing plate. In particular, even in the case where the thickness of the glass plate constituting the thinned liquid crystal cell is as small as about 0.1 to 1.0 mm, it is suitable for use for bonding the substrate and the polarizing plate.

<< (meth) acrylic acid alkyl ester >>
As the (meth) acrylic acid alkyl ester, an alkyl group having 4 to 18 carbon atoms (meth) acrylic acid alkyl ester (CH ₂ = CR ¹ -COOR ² ; R ¹ is a hydrogen atom or a methyl group, R ² Is an alkyl group having 4 to 18 carbon atoms, and the alkyl group preferably has 4 to 12 carbon atoms.

  Examples of (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms of alkyl group include n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, Hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, undeca (meth) acrylate, Examples include lauryl (meth) acrylate, stearyl (meth) acrylate and isostearyl (meth) acrylate. These may be used singly or in combination of two or more.

  The total amount of (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms in the alkyl group in 100% by mass of the monomer component forming the (meth) acrylic copolymer (A) has good adhesion and durability. From the viewpoint of expression, it is preferably 99.8 to 20% by mass, more preferably 99.5 to 30% by mass, and still more preferably 99 to 50% by mass.

As a monomer component of the (meth) acrylic copolymer (A), an alkyl group having 1 to 3 carbon atoms (meth) acrylic acid alkyl ester (CH ₂ 3CR ³ -COOR ⁴ ; R ³ is a hydrogen atom or methyl And R ⁴ is an alkyl group having 1 to 3 carbon atoms.

  Examples of (meth) acrylic acid alkyl ester having 1 to 3 carbon atoms in the alkyl group include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate and isopropyl (meth) acrylate . These may be used singly or in combination of two or more.

  The amount of the (meth) acrylic acid alkyl ester having 1 to 3 carbon atoms in the alkyl group is preferably 60% by mass or less, more preferably 50% by mass or less in 100% by mass of the monomer component, from the viewpoint of stress relaxation properties. More preferably, it is 40 mass% or less.

<< Carboxyl group-containing monomer >>
As a carboxyl group-containing monomer, for example, (meth) acrylic acid β-carboxyethyl, (meth) acrylic acid 5-carboxypentyl, succinic acid mono (meth) acryloyl oxyethyl ester, ω-carboxy polycaprolactone mono (meth) acrylate Etc .; and acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid and maleic acid.

  In the present specification, the carboxyl group-containing monomer also includes a monomer containing an acid anhydride group formed by dehydration condensation of two carboxyl groups, and examples thereof include carboxylic acid anhydrides such as maleic anhydride and itaconic anhydride. Be

The carboxyl group-containing monomer may be used alone or in combination of two or more.
The said carboxyl group contained in a carboxyl group-containing monomer functions as a crosslinkable functional group with an isocyanate compound (B1) and a metal chelate compound (B2). The amount of the carboxyl group-containing monomer to be used is preferably 0.01 to 15% by mass, more preferably 0.05 to 10% by mass, and still more preferably 0.1 to 5% by mass in 100% by mass of the monomer component. For example, the acid value of the (meth) acrylic copolymer (A) is preferably 0.1 to 117 mg KOH / g, more preferably 0.4 to 78 mg KOH / g.

  When the amount of use of the carboxyl group-containing monomer is less than or equal to the above upper limit, the crosslink density formed by the (meth) acrylic copolymer (A) and the crosslinking agent (B) does not become too high. An excellent pressure-sensitive adhesive layer is obtained. A crosslinked structure is effectively formed as the usage-amount of a carboxyl group-containing monomer is more than the said lower limit, and the adhesive layer which has appropriate intensity | strength at normal temperature is obtained.

<< Polar group-containing monomer >>
Examples of polar group-containing monomers include hydroxyl group-containing monomers, acid group-containing monomers other than carboxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, nitrogen-based heterocycle-containing monomers, and cyano group-containing monomers. As the polar group-containing monomer, it is preferable to use a monomer having a polar group (crosslinkable functional group) capable of reacting with the crosslinkable functional group possessed by the crosslinking agent (B).

  The (meth) acrylic copolymer (A) is preferably a copolymer obtained by copolymerizing a polar group-containing monomer other than the carboxyl group-containing monomer with the carboxyl group-containing monomer. Among these, it is preferable to use a hydroxyl group-containing monomer together with the carboxyl group-containing monomer from the viewpoint of improving the adhesion to a substrate with an optical film such as a polarizing plate.

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

  The said hydroxyl group contained in a hydroxyl-containing monomer functions as a crosslinkable functional group with the isocyanate group contained in an isocyanate compound (B1). The amount of the hydroxyl group-containing monomer used is preferably 0 to 15% by mass, more preferably 0.05 to 10% by mass, and still more preferably 0.1 to 7% by mass in 100% by mass of the monomer component. The crosslinking density formed by the (meth) acrylic copolymer (A) and the isocyanate compound (B1) does not become too high when the amount of the hydroxyl group-containing monomer used is not more than the above upper limit, and the stress relaxation characteristics are excellent. An adhesive layer is obtained. A crosslinked structure is effectively formed as the usage-amount of a hydroxyl-containing monomer is more than the said lower limit, and the adhesive layer which has appropriate intensity | strength at normal temperature is obtained.

  In the present specification, examples of the acid group include a phosphate group and a sulfate group. As a phosphoric acid group containing monomer, the (meth) acrylic-type monomer which has a phosphoric acid group in a side chain is mentioned, As a sulfuric acid group containing monomer, the (meth) acrylic-type monomer which has a sulfate group in a side chain is mentioned.

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 nitrogen-based heterocycle-containing monomers include vinyl pyrrolidone, acryloyl morpholine and vinyl caprolactam. Examples of cyano group-containing monomers include cyano (meth) acrylate and (meth) acrylonitrile.
The polar group-containing monomer may be used alone or in combination of two or more.

<< Other monomer >>
The monomer component for forming the (meth) acrylic copolymer (A) is, for example, alkoxyalkyl (meth) acrylate or alkoxypolyalkylene glycol, as long as the physical properties of the (meth) acrylic copolymer (A) are not impaired. Other (meth) acrylic esters may be included, such as mono (meth) acrylates, alicyclic groups or aromatic ring-containing (meth) acrylates.

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

  As alkoxypolyalkylene glycol mono (meth) acrylate, for example, methoxydiethylene glycol mono (meth) acrylate, methoxydipropylene glycol mono (meth) acrylate, ethoxytriethylene glycol mono (meth) acrylate, ethoxydiethylene glycol mono (meth) acrylate, Methoxy triethylene glycol mono (meth) acrylate is mentioned.

  As an alicyclic group or aromatic ring containing (meth) acrylate, a cyclohexyl (meth) acrylate, a benzyl (meth) acrylate, phenyl (meth) acrylate is mentioned, for example.

  The total amount of the other (meth) acrylic acid ester used in the copolymerization is preferably 60% by mass or less, more preferably 40% by mass or less, in 100% by mass of the monomer component.

  In addition, for example, styrene, methylstyrene, dimethylstyrene, trimethylstyrene, propylstyrene, butylstyrene, hexylstyrene, heptylstyrene and octylstyrene, as long as the physical properties of the (meth) acrylic copolymer (A) are not impaired. Styrene-based monomers such as alkylstyrenes, fluorostyrenes, chlorostyrenes, bromostyrenes, dibromostyrenes, iodostyrenes, nitrostyrenes, nitrostyrenes, acetylstyrenes and methoxystyrenes; copolymerizable monomers such as vinyl acetate it can.

The total amount of the copolymerizable monomer used in the copolymerization is preferably 40% by mass or less, and more preferably 20% by mass or less in 100% by mass of the monomer component.
The other monomers may be used alone or in combination of two or more.

<< Production conditions of (meth) acrylic copolymer (A) >>
The (meth) acrylic copolymer (A) is preferably a copolymer obtained by the copolymerization in the presence of a peroxide polymerization initiator. That is, by using a peroxide-based polymerization initiator as the polymerization initiator, a copolymer having a degree of branching in the above range tends to be obtained.

  The (meth) acrylic copolymer (A) can be produced, for example, by a conventionally known polymerization method such as solution polymerization method, bulk polymerization method, emulsion polymerization method, suspension polymerization method, etc. Legal is preferred. Specifically, a polymerization solvent and a monomer component are charged in a reaction vessel, a polymerization initiator is added under an inert gas atmosphere such as nitrogen gas, and the reaction initiation temperature is usually 40 to 100 ° C., preferably 50 to 80 ° C. The reaction is carried out for 4 to 20 hours while maintaining the reaction system at a temperature of usually 50 to 90.degree. C., preferably 70 to 90.degree.

As a peroxide type polymerization initiator, for example,
Di (2-tert-butylperoxyisopropyl) benzene, dicumyl peroxide, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, tert-butylcumyl peroxide, di-tert-hexyl Dialkyl peroxides such as peroxides and di-tert-butyl peroxides (eg compounds represented by R—O—O—R, wherein R in the formula is each independently an alkyl group or an aryl group-substituted alkyl group A compound represented by R-O-O-A-O-O-R, wherein R is each independently an alkyl group or an aryl group-substituted alkyl group, and A is a divalent hydrocarbon group) ;
Diisobutyryl peroxide, di (3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, dibenzoyl peroxide, benzoyl (3-methylbenzoyl) peroxide, di (3-methylbenzoyl) peroxide, Diacyl peroxides such as di (4-methylbenzoyl) peroxide (eg, a compound represented by R-COO-OCO-R, wherein R is each independently an alkyl group or an aryl group);
Di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di (4-tert-butylcyclohexyl) peroxydicarbonate, di (2-ethylhexyl) peroxydicarbonate, di-sec-butylperoxydicarbonate Peroxydicarbonates (eg, compounds represented by R-OCO-O-O-COO-R, wherein R is each independently an alkyl group or a cycloalkyl group);
Kumylperoxy neodecanoate, 1,1,3,3-tetramethylbutylperoxy neodecanoate, tert-hexylperoxyneodecanoate, tert-butylperoxyneodecanoate, tert-butylperone Oxyneoheptanoate, tert-hexylperoxypivalate, tert-butylperoxypivalate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, 2,5-dimethyl-2 5-di (2-ethylhexanoylperoxy) hexane, tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxy-3,5 3,5-trimethylhexanoate, tert-butyl peroxy laurate, tert-hexyl peroxybenzoate, 2,5- Peroxy esters such as dimethyl-2,5-di (benzoylperoxy) hexane, tert-butylperoxyacetate, tert-butylperoxy-3-methylbenzoate, tert-butylperoxybenzoate and the like (example: R ^1- O-O-CO-R compounds represented by ^2, R ¹ in the formula is an alkyl group or an aryl group-substituted alkyl group, R ² is an alkyl group, an aryl group or an aryl group-substituted alkyl group; R- A compound represented by CO-O-O-A-O-O-CO-R, wherein R is each independently an alkyl group or an aryl group, and A is a divalent hydrocarbon group);
Peroxy monocarbonates such as tert-hexyl peroxyisopropyl monocarbonate, tert-butyl peroxyisopropyl monocarbonate, tert-butyl peroxy-2-ethylhexyl monocarbonate etc. (example: R-O-O-COO-R Compounds wherein R in the formula is each independently an alkyl group);
Can be mentioned.

  Among the peroxide type polymerization initiators, peroxy esters are preferable because a highly branched (meth) acrylic copolymer can be obtained, and the peroxide type polymerization initiation represented by the following formula (1) Agents are more preferred.

式（１）中、Ｒ^A〜Ｒ^Fはそれぞれ独立に水素原子、アルキル基またはアリール基であり、高分岐鎖の共重合体が得られることから、好ましくは炭素数１〜１０のアルキル基、フェニル基であり、より好ましくは炭素数１〜８のアルキル基であり、さらに好ましくは炭素数１〜４のアルキル基、特に好ましくは炭素数１〜２のアルキル基である。

In formula (1), R ^{A to} R ^F each independently represent a hydrogen atom, an alkyl group or an aryl group, and a highly branched copolymer is obtained, preferably an alkyl group having 1 to 10 carbon atoms, It is a phenyl group, more preferably an alkyl group having 1 to 8 carbon atoms, still more preferably an alkyl group having 1 to 4 carbon atoms, and particularly preferably an alkyl group having 1 to 2 carbon atoms.

  Among the peroxide type polymerization initiators represented by the formula (1), tert-butyl peroxypivalate, tert-hexyl peroxypivalate, tert-butyl peroxy neodecanoate, tert-butyl peroxyneo Preferably, heptanoate, tert-butylperoxy-2-ethylhexanoate, and cumylperoxyneodecanoate are preferred, and a highly branched copolymer is obtained. Particularly preferred are hexyl peroxypivalate, tert-butyl peroxy neodecanoate, tert-butyl peroxy neoheptanoate, tert-butyl peroxy-2-ethylhexanoate.

A peroxide type polymerization initiator may be used individually by 1 type, and may use 2 or more types. In addition, the addition of the peroxide-based polymerization initiator multiple times during the polymerization is also not limited.
As the polymerization initiator, an azo initiator may be used together with the peroxide initiator as long as the degree of branching is in the above range. As an azo initiator, for example, 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis (2-) Cyclopropylpropionitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbo) Nitrile), 2- (carbamoylazo) isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'- Azobis (N, N′-dimethylene isobutyl amidine), 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], 2,2′-azo Di (isobutylamido) dihydrate, 4,4'-azobis (4-cyanopentanoic acid), 2,2'-azobis (2-cyanopropanol), dimethyl-2,2'-azobis (2-methyl propionate) And azo compounds such as 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide]. One of these polymerization initiators may be used alone, or two or more thereof may be used.

  The peroxide-based polymerization initiator is usually 0.001 to 5 parts by mass, preferably 0.005 to 3 parts by mass, per 100 parts by mass of the monomer component forming the (meth) acrylic copolymer (A). Used in amounts in the range of Moreover, it is preferable not to use an azo initiator, and the amount thereof used is preferably 0.5 parts by mass or less, more preferably 0.2 parts by mass or less, with respect to 100 parts by mass of a peroxide type polymerization initiator. And more preferably 0 parts by mass. However, use for the purpose of reducing residual monomers in the latter half of the reaction is not limited. In addition, during the polymerization reaction, a polymerization initiator, a chain transfer agent, a monomer component, and a polymerization solvent may be added as appropriate.

  As a polymerization solvent used for solution polymerization, for example, aromatic hydrocarbons such as benzene, toluene, xylene and the like; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, n-octane and the like; cyclopentane, Alicyclic hydrocarbons such as cyclohexane, cycloheptane and cyclooctane; diethylether, diisopropylether, 1,2-dimethoxyethane, dibutylether, tetrahydrofuran, dioxane, anisole, phenylethylether, ethers such as diphenylether; chloroform, Halogenated hydrocarbons such as carbon tetrachloride, 1,2-dichloroethane and chlorobenzene; esters such as ethyl acetate, propyl acetate, butyl acetate and methyl propionate; acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone And ketones such as 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. One of these polymerization solvents may be used alone, or two or more thereof may be used.

In the pressure-sensitive adhesive composition of the present invention, the residual ratio (%) after reaction for t time of the peroxide-based polymerization initiator preferably used as a polymerization initiator when producing the (meth) acrylic copolymer (A) Can be obtained by the following equation.
Residual rate (%) = exp (-k _d t) x 100 (%)
Where k _d is the thermal decomposition rate constant and is represented by the Arrhenius equation: k _d = A × exp (−ΔE / RT), where A is a frequency factor and ΔE is the thermal decomposition of the polymerization initiator Activation energy in the reaction, R is a gas constant (8.314 J / mol · K), T is an absolute temperature (K); t is a reaction time.

The frequency factor (A) and the activation energy (ΔE) of the peroxide-based polymerization initiator are determined, for example, the values described in NOF Corporation organic peroxide catalog (10th edition). It can be used. For example, ΔE = 119.1 kJ / mol, A = 6.93 × 10 ¹⁷ hr ⁻¹ for tert-butyl peroxypivalate, ΔE = 118.5 kJ / mol for tert-hexyl peroxypivalate, A = 6.45 × 10 ¹⁷ hr ⁻¹ , and for cumyl peroxy neodecanoate, ΔE = 105.3 kJ / mol, A = 3.94 × 10 ¹⁶ hr ⁻¹ .

Therefore, since the k _d at a predetermined temperature can be calculated, the residual ratio (%) of the peroxide-based polymerization initiator after reaction for a predetermined time t can be calculated according to the above equation. Therefore, the remaining amount of the peroxide-based polymerization initiator contained in the pressure-sensitive adhesive composition can be calculated by the amount of the peroxide-based polymerization initiator used in the above copolymerization and the remaining rate (%).

<< Physical properties and content of (meth) acrylic copolymer (A) >>
The weight average molecular weight (Mw) of the (meth) acrylic copolymer (A) measured by the GPC method is, in terms of polystyrene, usually from 200,000 to 1,500,000, preferably from 400,000 to 1,300,000, more preferably Is 500,000 to 1,100,000. The copolymer (A) has hyperbranched chains even if Mw is in the above range, so that the copolymer (A) chains can be appropriately intertwined with each other, and the durability of the pressure-sensitive adhesive layer And processability does not deteriorate. In particular, when the Mw is 400,000 or more, a highly cohesive pressure-sensitive adhesive layer can be obtained.

The molecular weight distribution (Mw / Mn) of the (meth) acrylic copolymer (A) measured by the GPC method is usually 50 or less, preferably 30 or less, more preferably 20 or less.
The glass transition temperature (Tg) of the (meth) acrylic copolymer (A) can be calculated, for example, from the monomer units constituting the polymer and the content ratio thereof by the Fox equation. For example, the (meth) acrylic copolymer (A) is synthesized such that the glass transition temperature (Tg) determined by the Fox equation is usually −70 to 0 ° C., preferably −60 to −30 ° C. Can. By using the (meth) acrylic copolymer (A) having such a glass transition temperature (Tg), a pressure-sensitive adhesive composition having excellent adhesiveness at normal temperature can be obtained.
Fox's formula: 1 / Tg = (W ₁ / Tg ₁ ) + (W ₂ / Tg ₂ ) +... + (W _m / Tg _m )
W ₁ + W ₂ + ... + W _m = 1
In the formula, Tg is the glass transition temperature of the (meth) acrylic copolymer (A), Tg ₁ , Tg ₂ ,..., Tg _m is the glass transition temperature of the homopolymer comprising each monomer, W ₁ , W ₂ ,..., W _m are weight fractions of the constituent units derived from the respective monomers in the copolymer (A).

  The glass transition temperature of the homopolymer comprising each monomer in the Fox formula can be, for example, the value described in Polymer Handbook Fourth Edition (Wiley-Interscience 1999).

  The content of the (meth) acrylic copolymer (A) in the pressure-sensitive adhesive composition of the present invention is usually 50 to 99.99 in 100% by mass of the solid content excluding the organic solvent (E) in the composition. % By mass, more preferably 60 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 can be balanced, and the adhesive properties are excellent.

[Isocyanate Compound (B1)]
As the isocyanate compound (B1), an isocyanate compound having two 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 of 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 in the above range, it is preferable in terms of the crosslinking reaction efficiency of the (meth) acrylic copolymer (A) and the isocyanate compound (B1) and in terms of maintaining the flexibility of the pressure-sensitive adhesive layer.

  Examples of the diisocyanate compound having 2 isocyanate groups per molecule include aliphatic diisocyanates, alicyclic diisocyanates and aromatic diisocyanates. As aliphatic diisocyanates, ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, 2,2,4-trimethyl isocyanate Aliphatic diisocyanates having 4 to 30 carbon atoms such as 1,6-hexamethylene diisocyanate can be mentioned. Examples of alicyclic diisocyanates include isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethyl xylylene diisocyanate, and the like. Family diisocyanates. Examples of the aromatic diisocyanate include aromatic diisocyanates having 8 to 30 carbon atoms, such as phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthyl diisocyanate, diphenyl ether diisocyanate, diphenyl methane diisocyanate, diphenyl propane diisocyanate, and the like.

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

  In addition, as the isocyanate compound (B1), for example, a multimer (for example, dimer or trimer, biuret body, isocyanurate body), a derivative (for example, many polymers) of the above-mentioned isocyanate compound having two or more isocyanate groups The addition reaction product of a dihydric alcohol and a diisocyanate compound of two or more molecules), and a polymer. Examples of the polyhydric alcohol in the derivative include low molecular weight polyhydric alcohols such as tri- or higher alcohols such as trimethylolpropane, glycerin and pentaerythritol; and high molecular weight polyhydric alcohols such as polyether polyols, Polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols are mentioned.

  As such an isocyanate compound, for example, trimer of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, biuret or isocyanurate of hexamethylene diisocyanate or tolylene diisocyanate, trimethylolpropane and tolylene diisocyanate or xylylene diisocyanate (For example, trimolecular adduct of tolylene diisocyanate or xylylene diisocyanate), reaction product of trimethylolpropane with hexamethylene diisocyanate (for example, trimolecular adduct of hexamethylene diisocyanate), polyether polyisocyanate, Polyester polyisocyanate is mentioned.

Among isocyanate compounds (B1), the reaction product of trimethylolpropane with tolylene diisocyanate or xylylene diisocyanate in that it can improve the aging property and the light leakage performance (L-45 manufactured by Soken Chemical Co., Ltd., Soken Chemical Inc. TD-75 etc.), isocyanurate of hexamethylene diisocyanate or tolylene diisocyanate (TSE-100 manufactured by Asahi Kasei Kogyo Co., Ltd., 2050 manufactured by Nippon Polyurethane Industry Co., Ltd.) is preferable.
The isocyanate compound (B1) may be used singly or in combination of two or more.

[Metal chelate compound (B2)]
In the present invention, the metal chelate compound (B2) is used as a part of the crosslinking agent (B). The metal chelate compound (B2) crosslinks the (meth) acrylic copolymer (A) by coordination bond. Therefore, when the temperature is high, the crosslinking is partially solved, and the pressure-sensitive adhesive layer exhibits more excellent flexibility.

  Examples of the metal chelate compound (B2) include alkoxides, acetylacetone, ethyl acetoacetate and the like with polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium and zirconium. The compound which coordinated is mentioned. Among these, aluminum chelate compounds (M-12AT manufactured by Soken Chemical Co., Ltd.) are particularly preferable. Specific examples thereof include aluminum isopropylate, aluminum secondary butyrate, aluminum ethylacetoacetate / diisopropylate, aluminum trisethylacetoacetate and aluminum trisacetylacetonate.

The metal chelate compound (B2) may be used alone or in combination of two or more.
In the pressure-sensitive adhesive composition of the present invention, the total content of the isocyanate compound (B1) and the metal chelate compound (B2) is usually 0.01 relative to 100 parts by mass of the (meth) acrylic copolymer (A). The amount is 5 to 5 parts by mass, more preferably 0.05 to 2.5 parts by mass, and still more preferably 0.1 to 1 parts by mass. When the content is in the above range, it is preferable from the viewpoint that balance between durability and stress relaxation characteristics can be easily achieved.

  In the pressure-sensitive adhesive composition of the present invention, the content of the metal chelate compound (B2) is usually 10 to 1000 parts by mass, preferably 50 to 600 parts by mass, more preferably 100 parts by mass of the isocyanate compound (B1). Is 100 to 400 parts by mass. When this content is in the above-mentioned range, it is preferable in terms of suppression of bending amount and improvement of adhesion to a substrate with an optical film such as a polarizing plate.

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

  The content of the silane coupling agent (C) in the pressure-sensitive adhesive composition for a polarizing plate of the present invention is usually 1 part by mass or less, preferably 0 based on 100 parts by mass of the (meth) acrylic copolymer (A). 0.01 to 1 part by mass, more preferably 0.05 to 0.5 parts by mass. If the content is in the above range, peeling of the polarizing plate in a high humidity and heat 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 of the pressure-sensitive adhesive composition for a polarizing plate of the present invention. As an antistatic agent (D), surfactant, an ionic compound, a conductive polymer is mentioned, for example.

  As the surfactant, for example, cationic surfactants having cationic groups such as quaternary ammonium salts, amide quaternary ammonium salts, pyridinium salts, primary to tertiary amino groups, etc .; sulfonic acid groups, sulfuric acid 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 etc., glycerin fatty acid esters And nonionic surfactants such as sorbitan fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene alkylamine fatty acid esters, N-hydroxyethyl-N-2-hydroxyalkylamines and alkyl diethanolamides Be

  Moreover, the reaction type emulsifier which has a polymeric group as surfactant is also mentioned, The polymer type surfactant which polymerized the monomer component containing said surfactant or a reactive emulsifier can also be used.

The ionic compound is composed of a cation moiety and an anion moiety, and may be solid or liquid at room temperature (23 ° C./50% RH).
The cation moiety constituting the ionic compound may be either an inorganic cation or an organic cation or both. As an inorganic type cation, an alkali metal ion and an alkaline earth metal ion are preferable, and Li ⁺ , Na ⁺ and K ⁺ having an excellent antistatic property are more preferable. Examples of organic cations include pyridinium cation, piperidinium cation, pyrrolidinium cation, pyrroline cation, pyrrole cation, pyrrole cation, imidazolium cation, tetrahydropyrimidinium cation, dihydropyrimidinium cation, pyrazolium cation, pyrazolinium There may be mentioned cations, tetraalkylammonium cations, trialkylsulfonium cations, tetraalkylphosphonium cations and their derivatives.

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 ⁻ can be mentioned. Among these, anions containing a fluorine atom are preferable because they give low melting point ionic compounds, and (F ₂ SO ₂ ) ₂ N ⁻ and (CF ₃ SO ₂ ) ₂ N ⁻ are particularly preferable.

  As the ionic compound, 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-octyl pyridinium fluorosulfonyl Preferred are aluminum imide, 1-octyl-3-methylpyridinium and trifluorosulfonium imide.

As the conductive polymer, for example, polythiophene, polyaniline, polypyrrole and derivatives thereof can be mentioned.
The content of the antistatic agent (D) in the pressure-sensitive adhesive composition for a polarizing plate of the present invention is usually 3 parts by mass or less, preferably 0. 0 to 100 parts by mass of the (meth) acrylic copolymer (A). It is 0.1 to 3 parts by mass, more preferably 0.05 to 2.5 parts by mass.

[Organic solvent (E)]
The pressure-sensitive adhesive composition of the present invention preferably contains an organic solvent (E) in order to adjust its coatability. As an organic solvent, the polymerization solvent demonstrated by the column of the (meth) acrylic-type copolymer (A) is mentioned. For example, a polymer solution containing a (meth) acrylic copolymer (A) and a polymerization solvent obtained by the above copolymerization, and an isocyanate compound (B1) and a metal chelate compound (B2) are mixed to obtain an adhesive. The composition can be prepared. In the pressure-sensitive adhesive composition of the present invention, the content of the organic solvent is usually 50 to 90% by mass, preferably 60 to 85% by mass.

  In addition, in this specification, "solid content" means all the components except the said organic solvent (E) among the components in an adhesive composition, and "solid content concentration" means the adhesive composition 100. The ratio of said solid content to mass% is said.

[Peroxide]
It is preferable not to mix | blend the peroxide (peroxide system crosslinking agent) as a crosslinking agent with the adhesive composition of this invention. The content of the peroxide, including the residual amount of the peroxide-based polymerization initiator used at the time of synthesis of the (meth) acrylic copolymer (A), is (meth) acrylic copolymer (A) 100. Preferably it is 0.1 mass part or less with respect to mass part, More preferably, it is 0.05 mass part or less, More preferably, it is 0.01 mass part or less. By using an isocyanate compound (B1) and a metal chelate compound (B2) as a crosslinking agent and not using a peroxide crosslinking agent, it is possible to suppress the temporal deterioration of the pressure-sensitive adhesive layer based on the remaining peroxide.

[Additive]
The pressure-sensitive adhesive composition of the present invention may contain, in addition to the above components, an antioxidant, a light stabilizer, a metal corrosion inhibitor, a tackifier, a plasticizer, a crosslinking accelerator, as long as the effects of the present invention are not impaired. You may contain 1 type, or 2 or more types selected from (meth) acrylic-type polymers and rework agents other than A).

[Preparation of pressure-sensitive adhesive composition for polarizing plate]
The pressure-sensitive adhesive composition for a polarizing plate of the present invention comprises a (meth) acrylic copolymer (A), an isocyanate compound (B1), a metal chelate compound (B2), and, if necessary, other components, It can be prepared by mixing according to the method of For example, in the polymer solution containing the polymer obtained when synthesizing the (meth) acrylic copolymer (A), the isocyanate compound (B1) and the metal chelate compound (B2) and other components as needed And compounding.

  The gel fraction of the pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition of the present invention is preferably 20 to 70% by mass, more preferably 24 to 60% by mass, and still more preferably 30 to 55% by mass. The gel fraction is, for example, a value measured for a pressure-sensitive adhesive collected under the conditions described in the examples.

[Adhesive layer]
In the pressure-sensitive adhesive layer of the present invention, for example, the crosslinking reaction in the above-mentioned pressure-sensitive adhesive composition is advanced, and specifically, the (meth) acrylic copolymer (A) is an isocyanate compound (B1) and a metal chelate compound It is obtained by crosslinking with (B2).

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

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

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

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

  The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention preferably has a gel fraction of 20 to 70% by mass, more preferably from the viewpoint of distortion suppression of a polarizing plate, cohesion, adhesion and removability. Is 24 to 60% by mass, more preferably 30 to 55% by mass. Since the (meth) acrylic copolymer (A) has highly branched chains even when the gel fraction is in the above range, the branched chains of the copolymer (A) may be appropriately intertwined with each other There is no deterioration in the durability and processability of the pressure-sensitive adhesive layer. In particular, when the gel fraction is 30% by mass or more, a highly cohesive pressure-sensitive adhesive layer is obtained. When the gel fraction exceeds the above range, the pressure-sensitive adhesive layer may not be able to sufficiently absorb and relieve the stress caused by the dimensional change of the polarizing plate under high temperature and high humidity and heat environment.

[Adhesive sheet for polarizing plate]
The pressure-sensitive adhesive sheet for a polarizing plate of the present invention has a pressure-sensitive adhesive layer formed of the above-described pressure-sensitive adhesive composition for a polarizing plate. As the pressure-sensitive adhesive sheet, for example, a double-sided pressure-sensitive adhesive sheet having only the pressure-sensitive adhesive layer, a double-sided pressure-sensitive adhesive sheet having the substrate and the pressure-sensitive adhesive layer formed on both sides of the substrate, a substrate, and one of the substrates The adhesive sheet in which the single-sided adhesive sheet which has the said adhesive layer formed in the surface and the cover film by which the peeling process was carried out on the surface which is not in contact with the base material of the adhesive layer of these adhesive sheets is mentioned.

  As a base material and a cover film, For example, Polyester film, such as a polyethylene terephthalate (PET); Plastic film, such as polyolefin films, such as polyethylene, a polypropylene, an ethylene-vinyl acetate copolymer, etc. are mentioned.

The formation conditions of the pressure-sensitive adhesive layer are the same as the conditions described in the section of [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 adhesion 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.

[Polarizer with adhesive layer]
The polarizing plate with a pressure-sensitive adhesive layer of the present invention is characterized by having a polarizing plate and a pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition for a polarizing plate of the present invention on at least one surface of the polarizing plate. . In the present specification, “polarizing plate” is used to mean including “polarizing film”.

  A conventionally known polarizing film can be used as the polarizing plate. For example, a multilayer film having a stretched film obtained by adding a polarizing component to a film made of a polyvinyl alcohol resin and stretching the film, and a protective film disposed on the stretched film can be mentioned. Examples of polyvinyl alcohol resins include polyvinyl alcohol, polyvinyl formal, polyvinyl acetal, and saponified ethylene-vinyl acetate copolymer. The polarization component includes, for example, iodine or a dichroic dye. As a protective film, cellulose films, such as a triacetyl cellulose, a polycarbonate film, a polyether sulfone film is mentioned, for example.

The thickness of the polarizing plate is usually 30 to 250 μm, preferably 50 to 200 μm.
There is no particular limitation on the method of forming the pressure-sensitive adhesive layer on the surface of the polarizing plate, and a method of applying and drying the above-mentioned pressure-sensitive adhesive composition directly on the surface of the polarizing plate using a bar coater etc. There is a method of transferring the pressure-sensitive adhesive layer to the surface of the polarizing plate and aging it. 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 [adhesive layer].

  The thickness of the pressure-sensitive adhesive layer formed on the polarizing plate is usually 5 to 75 μm, preferably 10 to 50 μm, in dry thickness. The pressure-sensitive adhesive layer may be formed on at least one surface of the polarizing plate, and the pressure-sensitive adhesive layer may be formed on only one side of the polarizing plate, or the pressure-sensitive adhesive layer may be formed on both sides of the polarizing plate. Can be mentioned.

In addition, layers having other functions such as a protective layer, an antiglare layer, a retardation layer, and a viewing angle improvement layer may be stacked on the polarizing plate.
A liquid crystal element is manufactured by providing the adhesive layer-attached polarizing plate of the present invention obtained as described above on the substrate surface of a liquid crystal cell. Here, the liquid crystal cell has a structure in which a liquid crystal layer is sandwiched between two substrates.

  As a substrate which a liquid crystal cell has, a glass plate is mentioned, for example. The thickness of the substrate is usually 0.1 to 1 mm, preferably 0.15 to 0.8 mm. In the present invention, in particular, warpage of the polarizing plate and the substrate can be suppressed by using the pressure-sensitive adhesive composition. Therefore, even when the thickness of the substrate is small (e.g., 0.8 mm or less, preferably 0.15 to 0.7 mm), the above-mentioned pressure-sensitive adhesive composition is suitably used for bonding the polarizing plate and the substrate. be able to.

  Hereinafter, the present invention will be more specifically described based on examples, but the present invention is not limited to these examples. In the description of the following examples etc., unless otherwise stated, "part" shows a "mass part".

[GPC and GPC-MALS]
For the (meth) acrylic copolymer, the weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured by gel permeation chromatography (multi-angle method) by gel permeation chromatography (GPC method) under the following conditions. The degree of branching was determined by a laser light scattering detector (GPC-MALS) under the following conditions.
-Measuring device: HLC-8320GPC (made by Tosoh Corp.)
・ GPC column configuration: the following 4 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 Detector: DAWN HELEOS (MALS detector) + Optilab rEX (RI detector)
· Standard polystyrene equivalent (when measuring Mw and Mn)

Synthesis Example 1
98.8 parts of n-butyl acrylate, 1 part of 4-hydroxybutyl acrylate, 0.2 parts of acrylic acid, and 100 parts of ethyl acetate solvent in a reaction apparatus equipped with a stirrer, reflux condenser, thermometer and nitrogen inlet tube The temperature was raised to 80.degree. C. while introducing nitrogen gas. Next, 0.1 part of tert-butyl peroxypivalate was added, and a polymerization reaction was performed at 80 ° C. for 6 hours in a nitrogen gas atmosphere. After completion of the reaction, the reaction solution was diluted with ethyl acetate to prepare a polymer solution having a solid concentration of 30% by mass. The weight average molecular weight (Mw) of the obtained (meth) acrylic copolymer A is 700,000, the molecular weight distribution (Mw / Mn) is 7.1, the degree of branching is 0.51, and the acid value is Was 1.6 mg KOH / g.

Synthesis Examples 2 to 12
A polymer solution with a solid concentration of 30% by mass was prepared in the same manner as in Synthesis Example 1 except that the monomer components and the polymerization initiator used for the polymerization reaction were changed as described in Table 1. The results are shown in Table 1.

Example 1
(1) Preparation of adhesive composition The (meth) acrylic polymer solution (solid content concentration: 30% by mass) obtained in Synthesis Example 1 and 100 parts (solid content) of the (meth) acrylic polymer contained in the solution And 0.05 parts (solid content) of “TD-75” (solid content 75% by mass, ethyl acetate solution) manufactured by Soken Chemical Co., Ltd. as an isocyanate compound, and “K-Kanken Co. M-12AT "(solid content: 10% by mass, toluene, acetylacetone solution) 0.14 parts (solid content), and as a silane coupling agent, Shin-Etsu Chemical Co., Ltd." KBM-403 "(solid content: 100%) 0 .2 parts and 1 part of "AS-804" (solid content 100%) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. as an antistatic agent were mixed to obtain a pressure-sensitive adhesive composition.

(2) Preparation of Pressure-Sensitive Adhesive Sheet After foaming, the pressure-sensitive adhesive composition obtained in the above (1) is applied onto a release-treated polyethylene terephthalate film (PET film) using a doctor blade, and 3 It was dried for a minute to form a coating having a dry film thickness of 20 μm. On the opposite side of the coated surface of the PET film to which the PET film is attached, a peeling-treated PET film is further attached, allowed to stand for 7 days in a 23 ° C./50% RH environment, and aged to obtain two PET films. A pressure-sensitive adhesive sheet having a 20 μm-thick pressure-sensitive adhesive layer sandwiched therebetween was obtained.

(3) Preparation of Polarizing Plate with Pressure-Sensitive Adhesive Layer After foaming, the pressure-sensitive adhesive composition obtained in the above (1) is applied onto a release-treated polyethylene terephthalate film (PET film) using a doctor blade, It dried at 90 degreeC for 3 minutes, and obtained the sheet | seat which has a coating film with a dry film thickness of 20 micrometers. The sheet and a polarizing plate (thickness: 110 μm, layer structure: triacetyl cellulose film / polyvinyl alcohol film / triacetyl cellulose film) are laminated so that the coating film and the polarizing plate are in contact with each other, and 23 ° C./50% The mixture was allowed to stand for 7 days under the conditions of RH for aging to obtain a polarizing plate with a pressure-sensitive adhesive layer having a PET film, a pressure-sensitive adhesive layer with a thickness of 20 μm, and a polarizing plate.

[Examples 2-11, Comparative Examples 1-2]
In the same manner as in Example 1 except that the (meth) acrylic polymer solution is changed to the polymer solution obtained in Synthesis Example 2 to 12 and the composition is changed as described in Table 2 in Example 1. A pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet and a polarizing plate with a pressure-sensitive adhesive layer were obtained.

[Evaluation]
[Gel fraction]
About 0.1 g of a pressure-sensitive adhesive is taken from a pressure-sensitive adhesive sheet obtained in Example and Comparative Example in a sampling bottle, and 30 mL of ethyl acetate is added thereto and shaken for 4 hours. The resultant was filtered through a wire mesh, and the residue on the wire mesh was dried at 100 ° C. for 2 hours to determine the dry weight. The gel fraction of the adhesive was determined by the following equation.
・ Gel fraction (%) = (dry weight / adhesive collected weight) x 100 (%)

[Creep value]
The polarizing plate with a pressure-sensitive adhesive layer (laminate consisting of PET film / pressure-sensitive adhesive layer / polarizing plate) obtained in Examples and Comparative Examples is cut into a width of 10 mm × length 100 mm, and the release-treated PET film is peeled off Then, on an alkali-treated glass plate, the pressure-sensitive adhesive layer was bonded so that the pressure-sensitive adhesive layer was in contact with the glass plate, and a bonding area of 10 mm × 10 mm was obtained, to obtain a tackified polarizing plate test piece for evaluation.

  The adhesion-processed polarizing plate test pieces for evaluation were subjected to an autoclave treatment (50 ° C., 5 atm), and left to stand under an atmosphere of 23 ° C./50% RH for 24 hours. Next, the test piece was set in the chamber BOX of the micro creep measuring machine with a length of 15 mm of the fixing chuck portion. The adhesion-processed polarizing plate for evaluation in the test piece is pulled parallel to the bonding surface of the polarizing plate and the glass in the longitudinal direction of the polarizing plate at a tensile load of 800 g and a tensile time of 1000 seconds, and the test is performed. The distance (μm) of the displacement of the bonded portion of the glass plate and the polarizing plate in the piece was measured as a creep value.

[Measurement of adhesive force]
A polarizing plate with a pressure-sensitive adhesive layer (a laminate comprising a PET film / pressure-sensitive adhesive layer / a polarizing plate) obtained in Examples and Comparative Examples was cut into a size of 70 mm × 25 mm to prepare a test piece. The PET film was peeled off from the test piece, and the laminate consisting of the pressure-sensitive adhesive layer / polarizing plate was attached using a laminator roll so that the pressure-sensitive adhesive layer and the glass plate were in contact with one side of a 2 mm-thick glass plate. . The resulting laminate was held in an autoclave adjusted to 50 ° C./5 atm for 20 minutes. Subsequently, after leaving it to stand in a 23 ° C./50% RH environment for 1 hour, the end of the polarizing plate was pulled at a speed of 300 mm / min in the direction of 90 ° with respect to the surface of the glass plate to measure adhesive strength (peel strength).

[Bending (warping)]
The adhesive layer-attached polarizing plate (PET film / adhesive layer / laminated plate laminate) obtained in Examples and Comparative Examples is cut into a size of 35 mm × 400 mm (stretching axis direction) to prepare a test piece did. The PET film is peeled off from the test piece, and using a laminator roll, the pressure-sensitive adhesive layer and the glass plate are laminated on one side of a glass plate with a thickness of 0.7 mm and 40 mm × 410 mm using a pressure-sensitive adhesive layer / polarizing plate. I stuck to touch. The resulting laminate was left 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 perpendicular to the floor surface, and the amount of floating of the opposite end was measured with a ruler. The measurements were carried out immediately after removal from the oven and after 24 hours.

[Durability test]
A polarizing plate with a pressure-sensitive adhesive layer (a laminate comprising a PET film / pressure-sensitive adhesive layer / a polarizing plate) obtained in Examples and Comparative Examples was cut into a size of 150 mm × 250 mm to prepare a test piece. The PET film was peeled off from the test piece, and the laminate consisting of the pressure-sensitive adhesive layer / polarizing plate was attached using a laminator roll so that the pressure-sensitive adhesive layer and the glass plate were in contact with one side of a 2 mm-thick glass plate. . 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 made. The test plate is left for 500 hours under conditions of temperature 80 ° C. (heat resistance) or conditions of temperature 60 ° C./humidity 90% RH (moisture and humidity resistance), and observation of foaming and breakage is observed based on the following criteria: evaluated. Foaming occurs when the cohesion is insufficient and tearing occurs when the stress relaxation is insufficient.

(Foaming)
AA: no foaming was observed at all.
BB: The area of foaming is less than 1% of the whole.
CC: The area of the foam is 1% or more and less than 5% of the whole.
DD: The area of the foam is 5% or more of the whole.

(Rupture)
AA: no tears are seen at all.
BB: The area of fracture is less than 1% of the total.
CC: The area of fracture is 1% or more and less than 5% of the whole.
DD: The area of fracture is 5% or more of the whole.

表２において、過酸化物系重合開始剤量は、以下のようにして算出した。上述した残存率の式：ｅｘｐ（−ｋ_dｔ）×１００（％）から、例えば実施例１では、ｋ_d＝Ａ×ｅｘｐ（−ΔＥ／ＲＴ）、Ａ＝６．９３×１０¹⁷ｈｒ^-1、ΔＥ＝１１９．１ｋＪ／ｍｏｌ、Ｒ＝８．３１４Ｊ／ｍｏｌ・Ｋ、Ｔ＝３５３Ｋ、反応時間ｔ＝６ｈから、上記共重合で使用した過酸化物系重合開始剤の量×残存率（％）により、５×１０^-3質量部と算出した。

In Table 2, the amount of peroxide type polymerization initiator was calculated as follows. Wherein residual ratio described above: from _{exp (-k d t) × 100} (%), in example Example _{1, k d = A × exp} (-ΔE / RT), A = 6.93 × 10 17 hr - ¹ , ΔE = 119.1 kJ / mol, R = 8.314 J / mol · K, T = 353 K, reaction time t = 6 h, the amount of peroxide-based polymerization initiator used in the copolymerization × remaining ratio ( % To calculate 5 × 10 ⁻³ parts by mass.

  In Comparative Examples 1 and 2, a (meth) acrylic copolymer having a branching degree of 0.59 is used. For this reason, in the system (comparative example 1) with a high gel fraction, although bending evaluation after 24 hours is bad (5.0 mm or more) and although foaming was not recognized in durability evaluation, many tears generate | occur | produced. In addition, in the system with a low gel fraction (Comparative Example 2), a large amount of foaming occurred.

  Since the copolymer in Comparative Example 1 is a linear polymer, the cohesive force development depends only on the bond between the crosslinking agent and the functional group in the copolymer. Therefore, it is necessary to set the gel fraction high for maintaining the cohesion. However, when the gel fraction is high, in the system of Comparative Example 1, the stress relaxation property is lowered, so that deterioration in bending and durability (resistance to fracture) is observed.

  On the other hand, in the example, since a (meth) acrylic copolymer having a branching degree of 0.55 or less is used and an isocyanate compound and a metal chelate compound are used in combination as a crosslinking agent, bending evaluation after 24 hours is high ( In the evaluation of durability, the occurrence of foaming and tearing was within an acceptable range.

  By generating a large number of branched chains in the polymer, in addition to the bond between the crosslinker and the functional group in the copolymer, entanglement occurs in the branched portion, so cohesive force is developed even at a low gel fraction. Therefore, at high temperatures, entanglement is relaxed, so bending is good, and a tendency to improve the durability can be seen.

Claims (9)

(A) obtained by copolymerizing a monomer component containing a (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms of an alkyl group and a carboxyl group-containing monomer, and gel permeation chromatography method / multi-angle laser light scattering a detector (GPC-MALS) der degree of branching less than 0.55 as measured by is, acid value Ru 0.1~7.8mgKOH / g der (meth) acrylic copolymer,
(B1) an isocyanate compound,
(B2) containing a metal chelate compound ,
The total content of the isocyanate compound (B1) and the metal chelate compound (B2) is 0.01 to 2.5 parts by mass with respect to 100 parts by mass of the (meth) acrylic copolymer (A) A pressure-sensitive adhesive composition for a polarizing plate, characterized by:   The pressure-sensitive adhesive composition for a polarizing plate according to claim 1, wherein the (meth) acrylic copolymer (A) is a copolymer obtained by the copolymerization in the presence of a peroxide polymerization initiator. .   The weight average molecular weight (Mw) measured by the gel permeation chromatography method (GPC method) of the said (meth) acrylic-type copolymer (A) is 200,000 to 1.5 million of Claim 1 or 2 Adhesive composition for polarizing plate.   The adhesion for polarizing plates of any one of Claims 1-3 whose branching degree measured by GPC-MALS of said (meth) acrylic-type copolymer (A) is 0.10-0.54. Agent composition.   The copolymer according to any one of claims 1 to 4, wherein the (meth) acrylic copolymer (A) is a copolymer obtained by further copolymerizing a polar group-containing monomer other than a carboxyl group-containing monomer. Adhesive composition for polarizing plate.   The polarizing plate according to any one of claims 1 to 5, wherein the content of the peroxide is 0.1 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic copolymer (A). Adhesive composition.   The adhesive composition for polarizing plates of any one of Claims 1-6 whose gel fraction of the adhesive formed from the adhesive composition for polarizing plates is 20-70 mass%.   The adhesive sheet for polarizing plates characterized by having an adhesive layer formed from the adhesive composition for polarizing plates of any one of Claims 1-7.   A pressure-sensitive adhesive comprising a polarizing plate, and a pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition for a polarizing plate according to any one of claims 1 to 7 on at least one surface of the polarizing plate. Layered polarizing plate.