TW201623524A - Adhesive composition for polarizing plate and polarizing plate with adhesive layer - Google Patents

Abstract

The present invention provides an adhesive composition for forming an adhesive layer on a polarizing plate. The adhesive layer may be applied to a structure that at least one polarizer protecting film typically formed on both sides of polarizer is omitted. Moreover, the adhesive layer may inhibit warping (bend) of a liquid crystal cell, and has excellent durability. The present invention provides an adhesive composition for forming an adhesive layer directly on a polarizer. The adhesive composition is characterized by containing (A) (meth) acrylic copolymers and (B) crosslinking agents, wherein the (A) (meth) acrylic copolymers are obtained by copolymerization of monomer compositions, and its degree of branching is 0.55 or less measured by gel permeation chromatography / multi-angle laser light scattering detector (GPC-MALS). In addition, the monomer compositions contain (meth) alkyl acrylates having an alkyl group of 4-18carbon atoms, and monomers having crosslinkable functional groups.

Description

Adhesive composition for polarizing plate and polarizing plate with adhesive layer

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

A liquid crystal cell has a structure in which a liquid crystal layer is sandwiched between two substrates (for example, a glass plate). A polarizing plate is attached to the surface of the substrate constituting the liquid crystal cell via the adhesive layer. In order to improve the mechanical properties and optical durability, the polarizing plate has a structure in which a polarizer protective film such as a cellulose triacetate film is laminated on both sides of a polarizer having a polarizing function.

In recent years, with the reduction in thickness of the liquid crystal cell and the reduction in thickness of the polarizing plate, warpage of the liquid crystal cell in a high-temperature, high-humidity heat environment has become a major problem. The reason for the warpage of the liquid crystal cell is, for example, that the conventional adhesive layer has low stress relaxation characteristics, and the stress caused by thermal contraction (size change) of the polarizer cannot be sufficiently alleviated.

On the other hand, in order to reduce the thickness of the polarizing plate, attempts have been made to omit the polarizing plate protective film formed on both sides of the polarizing plate. However, in a polarizing plate without a protective film, since the adhesive layer is in direct contact with The polarizer, in the high temperature and high humidity environment, with the thermal contraction of the polarizer, a large stress is applied to the adhesive layer, which not only causes warpage of the liquid crystal cell, but also easily causes breakage of the adhesive layer, and the polarizing plate Defects such as peeling.

Patent Document 1 describes that an adhesive composition composed of a specific acrylic polymer and an isocyanate compound is subjected to a crosslinking reaction to obtain an adhesive for an optical member having a gel fraction of 1% or more and 50% or less. Agent. According to Patent Document 1, it is described that the above-described configuration can alleviate the stress caused by the dimensional change of the polarizing film and suppress light leakage. However, the omission of the polarizer protective film is not particularly mentioned.

Patent Document 2 describes an adhesive polarizing plate having a polarizing plate and an adhesive layer provided on the polarizing plate, wherein the polarizing plate has a transparent protective film only on one side of the polarizing plate, and the adhesive layer is It is disposed on a polarizer that does not have the side of the aforementioned transparent protective film. However, the problem of warpage of the liquid crystal cell accompanying the omission of the aforementioned transparent protective film is not particularly mentioned.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-091500

Patent Document 2: Japanese Laid-Open Patent Publication No. 2012-247574

An object of the present invention is to provide a capable of forming the following The adhesive composition for the polarizer of the adhesive layer is applicable to at least one of the polarizer protective films which are usually formed on both sides of the polarizer, and can suppress the warpage of the liquid crystal cell. (bending) and excellent durability.

The inventors of the present invention have carefully studied in order to solve the above problems. As a result, it has been found that when a (meth)acrylic copolymer having a specific degree of branching is used and a crosslinking agent is used, an adhesive layer capable of suppressing warpage (bending) of the liquid crystal cell and having excellent durability can be formed. In the above Patent Documents 1 to 2, the degree of branching is not particularly mentioned.

In other words, the present inventors have found that the above problems can be solved by using an adhesive composition system for a polarizing plate having the following specific constitution, and thus the present invention has been completed.

The present invention is, for example, the following [1] to [8].

[1] An adhesive composition for a polarizing plate for forming an adhesive layer in direct contact with a polarizer, the composition comprising (A) a (meth)acrylic copolymer and (B) a crosslinking agent; Here, the (A) (meth)acrylic copolymer is a monomer containing a (meth)acrylic acid alkyl group having 4 to 18 carbon atoms and a monomer having a crosslinkable functional group. Copolymerized, and the (meth)acrylic copolymer is measured by a gel permeation chromatography/Gel Permeation Chromatography-Multi Angle Light Scattering (GPC-MALS: Gel Permeation Chromatography-Multi Angle Light Scattering) The branching degree is 0.55 or less.

[2] The adhesive composition for a polarizing plate according to the above [1], wherein the (meth)acrylic copolymer (A) is copolymerized by the foregoing in the presence of a peroxide-based polymerization initiator And the copolymer obtained.

[3] The adhesive composition for a polarizing plate according to the above [1], wherein the crosslinking agent (B) comprises at least one selected from the group consisting of an isocyanate compound (B1) and a metal chelate compound (B2). 1 species.

[4] The adhesive composition for a polarizing plate according to any one of the above [1], wherein the adhesive component formed by the adhesive composition for a polarizing plate has a gel fraction exceeding 50% by mass.

[5] An adhesive layer for a polarizing plate, which is formed by the adhesive composition according to any one of the above [1] to [4].

[6] The adhesive layer for a polarizing plate according to the above [5], wherein the storage elastic modulus at 23 ° C is 0.1 MPa or more, and the storage elastic modulus at 85 ° C is 0.05. MPa or less; and, when the storage elastic modulus at a certain temperature T ° C is taken as G' _T and the storage elastic modulus at T+1 ° C is taken as G' _T+1 , the temperature T is 23 to 50. In the range of °C, the system always satisfies G' _T /G' _T+1 <1.07.

[7] An adhesive sheet for a polarizing plate, comprising the adhesive layer according to the above [5] or [6].

[8] A polarizing plate with an adhesive layer, which has an adhesive layer as described in the above [5] or [6], which is laminated directly on at least one side of the polarizer.

According to the present invention, it is possible to provide a glue capable of forming the following The adhesive layer of the polarizing plate of the coating layer is applicable to at least one of the polarizer protective films which are usually formed on both sides of the polarizer, and can suppress the warpage of the liquid crystal cell. (bending) and excellent durability. Further, an adhesive layer for a polarizing plate formed of the above composition, an adhesive sheet for a polarizing plate having the above-mentioned adhesive layer, and a polarizing plate having an adhesive layer of the above-mentioned adhesive layer can be provided.

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

[Adhesive Composition for Polarizing Plate]

The adhesive composition for a polarizing plate of the present invention contains the (meth)acrylic copolymer (A) and the crosslinking agent (B) described below. The composition may contain at least one selected from the group consisting of a decane coupling agent (C) and an antistatic agent (D), and may also contain an organic solvent (E).

[(Meth)acrylic copolymer (A)]

The (meth)acrylic copolymer (A) is a copolymer containing a monomer component obtained by copolymerizing the monomer components; The fraction comprises: an alkyl (meth)acrylate having an alkyl carbon number of 4 to 18, and a monomer having a crosslinkable functional group. The copolymer (A) usually has a constituent unit derived from the above-mentioned (meth)acrylic acid alkyl ester and a constituent unit derived from the above-mentioned crosslinkable functional group-containing monomer.

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

The degree of branching of the copolymer (A) measured by gel permeation chromatography/multi-angle laser light scattering detector (GPC-MALS) is 0.55 or less, preferably 0.10 to 0.54, and particularly preferably 0.20 to 0.53, particularly preferably 0.30 to 0.53.

The degree of branching means the radius of gyration (nm) and molecular weight (g/mol) measured by GPC-MALS, plotted in a double logarithmic chart with the radius of rotation as the vertical axis and the molecular weight as the horizontal axis. The slope of the obtained straight line (hereinafter also referred to as "double logarithmic straight line of radius of rotation and molecular weight"). Theoretically, the straight line molecular system has a slope of one of the aforementioned straight lines, and the smaller the slope, that is, the higher the degree of branching.

The details of the measurement conditions of the branching degree are as described in the examples.

The degree of branching is an index, and when it is 0.55 or less, it shows a branched polymer, and when it exceeds 0.55, it shows a linear polymer. In addition, in the branched polymer, when the value of the branching degree is small, it means that the polymer molecule has many branches and has a high branching chain, and when the value of the branching degree is large, it means a polymer molecule. It has few branches and has a low branching chain.

The copolymer (A) having a branching degree within the above range has the following In two cases: (1) at a room temperature, a large amount of entanglement caused by the branched chains of the polymer molecules is generated, and as a result, the cohesiveness, adhesive properties, and the adhesive layer of the polymer are maintained. (2) At a high temperature (for example, 60 ° C), the entanglement of the polymer molecules is partially relaxed at a high temperature (for example, 60 ° C), so that the workability, the deformation of the adhesive layer, and the bleed out are small, the entanglement of the polymer molecules is partially relaxed. The adhesive layer exhibits excellent flexibility, and is excellent in suppressing warpage (bending) of the adherend accompanying heat shrinkage of the polarizer, and exhibiting the adhesive layer due to the partial entanglement remaining. Excellent durability (for example, heat resistance and moist heat resistance).

The characteristics of suppressing the warpage of the adherend are presumed to be due to the following reasons. For example, in the configuration of the polarizer/adhesive layer/adhered body, a case where a glass plate is used as an adherend will be described as an example. The heat shrinkage ratios of the polarizer and the glass plate are different from each other, and the heat shrinkage ratio (size change) of the polarizer is generally larger than that of the glass plate. When the adhesive layer is lacking in the softness under high temperature and high humidity, the adhesive layer cannot keep up with the size change of the polarizer, and as a result, the stress can not be relieved by the adhesive layer, and the stress is concentrated on the glass plate, thereby causing the glass plate to be warped. song. On the other hand, the adhesive layer formed by using the adhesive composition of the present invention contains a high-branched chain polymer, and the entanglement is partially relaxed in a high-temperature and high-humidity heat environment, so that the adhesive layer can be Keeping up with the dimensional change of the polarizer, no stress is generated and the stress is not concentrated on the glass plate. Further, the polarizer does not cause anisotropy and can be uniformly heat-shrinked without causing birefringence of the polarizer.

As described above, in the present invention, it is presumed that the adhesive layer can alleviate the stress accompanying the change in the size of the polarizer, and therefore does not affect the glass plate. Excessive stress (load) is applied to suppress the warpage of the glass sheet.

Since the adhesive composition of the present invention has the above characteristics, it 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 1 mm or less, it is suitable for use in bonding the substrate to the polarizer.

"Alkyl (meth)acrylate"

The alkyl (meth)acrylate is an alkyl (meth)acrylate having an alkyl carbon number of 4 to 18 (CH ₂ =CR ¹ -COOR ² ; R ¹ is a hydrogen atom or a methyl group, and R ² is a carbon number 4 Here, the alkyl group has a carbon number of from 4 to 12, particularly preferably from 4 to 12.

The alkyl (meth)acrylate having 4 to 18 carbon atoms may, for example, be n-butyl (meth)acrylate, isobutyl (meth)acrylate or tertiary butyl (meth)acrylate, ( Amyl methacrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate Ester, decyl (meth) acrylate, decyl (meth) acrylate, undecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, (meth) acrylate Isostearyl ester. These may be used alone or in combination of two or more.

In the case of forming 100% by mass of the monomer component of the copolymer (A), the amount of the alkyl (meth)acrylate having an alkyl group of 4 to 18 is preferably from the viewpoint of exhibiting good adhesion and durability. It is from 99.8 to 20% by mass, particularly preferably from 99.5 to 30% by mass, more preferably from 99 to 50% by mass.

The monomer component of the copolymer (A) is formed, and an alkyl (meth)acrylate having an alkyl group having 1 to 3 carbon atoms (CH ₂ =CR ³ -COOR ⁴ ; R ³ is a hydrogen atom or a methyl group) may be further used. R ⁴ is an alkyl group having 1 to 3 carbon atoms).

The alkyl (meth)acrylate having an alkyl carbon number of 1 to 3 may, for example, be methyl (meth)acrylate, ethyl (meth)acrylate or n-propyl (meth)acrylate, or (methyl). Isopropyl acrylate. These may be used alone or in combination of two or more.

The amount of the (meth)acrylic acid alkyl ester having an alkyl group having 1 to 3 alkyl groups in the amount of 100% by mass of the monomer component of the copolymer (A) is preferably 60% by mass or less from the viewpoint of stress relaxation. It is preferably 50% by mass or less, more preferably 40% by mass or less.

"Monomers with crosslinkable functional groups"

The monomer component forming the copolymer (A) further comprises a monomer having a crosslinkable functional group reactive with the crosslinking agent (B), that is, a monomer having a crosslinkable functional group.

Examples of the monomer having a crosslinkable functional group include a hydroxyl group-containing monomer, an acid group-containing monomer, an amine group-containing monomer, a mercapto group-containing monomer, and a nitrogen-containing heterocyclic monomer. , a monomer containing a cyano group. In the present specification, examples of the acid group include a carboxyl group, an acid anhydride group, a phosphoric acid group, and a sulfuric acid group.

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

Examples of the carboxyl group-containing monomer include β-carboxyethyl (meth)acrylate, 5-carboxypentyl (meth)acrylate, mono(meth)acryloxyethyl succinate, and ω-carboxyl groups. A carboxyl group-containing (meth) acrylate such as polycaprolactone mono(meth)acrylate; acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, maleic acid or the like. Examples of the acid anhydride group-containing monomer include maleic anhydride and itaconic anhydride. The mono-system containing a phosphate group may, for example, be a (meth)acrylic monomer having a phosphate group in a side chain, and the mono-system containing a sulfate group may, for example, be a (meth)acrylic acid having a sulfate group in a side chain. body.

The amine group-containing monomer may, for example, be an amino group-containing (meth) acrylate such as dimethylaminoethyl (meth)acrylate or diethylamine ethyl (meth)acrylate. Examples of the mercapto group-containing monomer include (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, and N-propyl (A). Base) acrylamide, N-hexyl (meth) acrylamide. Examples of the monomer containing a nitrogen-containing hetero ring include vinyl pyrrolidone, acryloyl morpholine, and vinyl caprolactam. Examples of the cyano group-containing monomer include cyano (meth) acrylate and (meth) acrylonitrile.

The single system containing a crosslinkable functional group may be used alone or in combination of two or more.

The monomer containing the crosslinkable functional group is preferably used in an amount of from 0.01 to 15% by mass, particularly preferably from 0.05 to 10% by mass, more preferably from 0.1 to 5, per 100% by mass of the monomer component of the copolymer (A). quality%. When the amount of the monomer having a crosslinkable functional group is less than or equal to the above upper limit, the copolymer (A) The crosslinking density formed by the crosslinking agent (B) is not excessively high, and an adhesive layer excellent in stress relaxation characteristics can be obtained. When the amount of the monomer having a crosslinkable functional group is at least the above lower limit value, the bonded structure can be effectively formed to obtain an adhesive layer having an appropriate strength at normal temperature.

Other Monomers

The monomer component forming the copolymer (A) may contain, for example, an alkoxyalkyl (meth)acrylate or an alkoxy poly(meth)acrylate, within a range not impairing the physical properties of the copolymer (A). Other (meth) acrylates such as alkylene glycol esters, alicyclic groups or aromatic ring-containing (meth) acrylates. That is, the copolymer (A) may further have a constituent unit derived from the other (meth) acrylate described above.

Examples of the alkoxyalkyl (meth)acrylate include methoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, and 2-ethoxyethyl (meth)acrylate. Ester, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxy (meth)acrylate Butyl ester.

Examples of the mono(meth)acrylic alkoxypolyalkylene glycol esters include methoxybisethylene glycol mono(meth)acrylate, methoxydipropylene glycol mono(meth)acrylate, and mono(A). Ethylene ethoxylated triethylene glycol acrylate, ethoxylated diethylene glycol mono(meth)acrylate, methoxytriethylene glycol mono(meth)acrylate.

Examples of the (meth) acrylate containing an alicyclic group or an aromatic ring include cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and phenyl (meth)acrylate. By using an aromatic ring-containing (meth) acrylate, Improve the light leakage resistance of the adhesive layer.

In 100% by mass of the monomer component of the copolymer (A), the total amount of the other (meth) acrylate is preferably 60% by mass or less, and particularly preferably 40% by mass or less.

Further, the monomer component forming the copolymer (A) may contain, for example, a copolymerizable monomer such as a styrene monomer or vinyl acetate, within a range not impairing the physical properties of the copolymer (A). That is, the copolymer (A) may further have a constituent unit derived from the above-mentioned copolymerizable monomer.

Examples of the styrene monomer include styrene; methyl styrene, dimethyl styrene, trimethyl styrene, propyl styrene, butyl styrene, hexyl styrene, and heptyl styrene. Alkyl styrene such as octyl styrene; halogenated styrene such as fluorostyrene, chlorostyrene, bromostyrene, dibromostyrene, iodine styrene; nitrostyrene, ethyl styrene styrene, methoxy benzene Ethylene and the like.

In 100% by mass of the monomer component of the copolymer (A), the total amount of the above-mentioned copolymerizable monomer is preferably 40% by mass or less, and particularly preferably 20% by mass or less.

The other single system 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 above copolymerization in the presence of a peroxide polymerization initiator. That is, by using a peroxide-based polymerization initiator as a polymerization initiator, There is a tendency to obtain a copolymer having a branching degree within the above range.

The (meth)acrylic copolymer (A) can be produced, for example, by a conventionally known polymerization method such as a solution polymerization method, a bulk polymerization method, an emulsion polymerization method, or a suspension polymerization method. Among these, a solution polymerization method is preferred. Specifically, the polymerization solvent and the monomer component are charged into a reaction vessel, and a polymerization initiator is added under an inert gas atmosphere such as nitrogen to set the reaction initiation temperature to usually 40 to 100 ° C, preferably 50 to The reaction system is maintained at a temperature of usually 50 to 90 ° C, preferably 70 to 90 ° C, at 80 ° C for 4 to 20 hours. Further, in the above polymerization reaction, a polymerization initiator, a chain transfer agent, a monomer component, and a polymerization solvent may be appropriately added.

Examples of the peroxide-based polymerization initiator include bis(2-di-tert-butylperoxyisopropyl)benzene, bis(isopropylphenyl) peroxide, and 2,5-dimethyl- 2,5-di (tertiary butyl peroxy) hexane, tributyl cumyl peroxide, di(tertiary hexyl peroxide), di(tertiary butyl) peroxide, dioxane a base (for example, a compound represented by ROOR, wherein R is independently an alkyl group or an alkyl group substituted with an aryl group; a compound represented by ROOAOOR, wherein R in each case is independently an alkyl group or an aryl group; Substituted alkyl group, A is a divalent hydrocarbon group); bis(isobutyl decyl) peroxide, bis(3,5,5-trimethylhexyl) peroxide, bis(laurel), peroxide (benzhydryl), benzhydryl peroxide (3-methylbenzhydryl), bis(3-methylbenzhydryl) peroxide, bis(4-methylbenzhydryl) peroxide a perylene dihydrazyl group (for example, a compound represented by R-COO-OCO-R, wherein R in the formula is independently an alkyl group or an aryl group); di-n-propyl peroxydicarbonate, peroxidized Diisopropyl carbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, peroxygen a peroxydicarbonate such as di(2-ethylhexyl) dicarbonate or di(tertiary butyl) peroxydicarbonate (for example, a compound represented by R-OCO-OO-COO-R, R is independently alkyl or cycloalkyl); cumene peroxy neodecanoate, 1,1,3,3-tetramethylbutyl peroxy neodecanoate, tertiary neodecanoate Ester, tertiary butyl peroxy neodecanoate, tertiary butyl peroxy neoheptanoate, tertiary hexyl peroxypivalate, tertiary butyl peroxypivalate, peroxy-2-ethyl 1,1,3,3-tetramethylbutyl acid, 2,5-dimethyl-2,5-di(2-ethylhexylperoxy)hexane, peroxy-2-ethyl Tert-butyl hexanoate, tertiary butyl peroxy-2-ethylhexanoate, tertiary butyl peroxy-3,5,5-trimethylhexanoate, tertiary butyl laurate, peroxidation Tert-Benzyl Benzate, 2,5-Dimethyl-2,5-bis(benzhydrylperoxy)hexane, tertiary butyl peroxyacetate, 3-methyl peroxy-3-benzylate Peroxy esters such as butyl ester and butyl peroxybenzylate (for example, a compound represented by R ¹ -OO-CO-R ² wherein R ¹ is an alkyl group or an alkyl group substituted with an aryl group, R ² is an alkyl group, an aryl group or an alkyl group substituted with an aryl group; a compound represented by R-CO-OOAOO-CO-R, wherein R is independently an alkyl group or an aryl group, and A is a divalent hydrocarbon group) ; mono-carbonic acid peroxyesters such as dimethyl peroxyacetate monoisopropylate, butyl peroxycarbonate isopropyl perester, monobutyl butyl carbonate, peroxy-2-ethylhexyl ester (eg: A compound represented by ROO-COO-R wherein R in the formula is independently an alkyl group).

In the peroxide-based polymerization initiator, a peroxy ester is preferred from the viewpoint of obtaining a (meth)acrylic copolymer having a high branched chain, and a peroxide represented by the following formula (1) is particularly preferable. It is a polymerization initiator.

In the formula (1), R ^A to R ^F are each independently a hydrogen atom, an alkyl group or an aryl group, and from the viewpoint of obtaining a copolymer of a highly branched chain, an alkyl group having 1 to 10 carbon atoms is preferable. The phenyl group is particularly preferably an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, particularly preferably an alkyl group having 1 to 2 carbon atoms.

Among the peroxide-based polymerization initiators represented by the formula (1), preferred are tertiary butyl peroxypivalate, tertiary hexyl peroxypivalate, and tertiary butyl peroxy neodecanoate. Peroxidic neoheptanoic acid tert-butyl acrylate, peroxy-2-ethylhexanoate tert-butyl acrylate, peroxyphenyl phthalate, from the viewpoint of obtaining a highly branched chain copolymer, Is peroxidized tertiary butyl pivalate, tertiary hexyl peroxypivalate, tertiary butyl peroxy neodecanoate, tertiary butyl peroxy neoheptate, peroxy-2-ethylhexanoate Tertiary butyl ester.

The peroxide polymerization initiator may be used singly or in combination of two or more. Further, in the polymerization, a plurality of peroxide-based polymerization initiators may be added without limitation.

As the polymerization initiator, an azo-based initiator may be used together with the peroxide-based initiator as long as the degree of branching is within the above range. Azo system The initiator may, for example, be 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-carbonitrile), 2-(aminomercaptoazo)isobutyronitrile, 2-phenylazo-4-methoxy-2,4 - dimethyl valeronitrile, dihydrochloride-2,2'-azobis(2-carboxynylpropane), 2,2'-azobis(N,N'-dimethylene isobutylformamidine , 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propanamide], dihydrated-2,2'-azobis(isobutylamine) , 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-cyanopropanol), dimethyl-2,2'-azobis(2- An azo compound such as methyl propionate). These polymerization initiators may be used alone or in combination of two or more.

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)acryl-based copolymer (A). The amount within the range is used. Further, the azo-based initiator is preferably used, and the amount thereof is preferably 0.5 parts by mass or less, more preferably 0.2 parts by mass or less, more preferably 0.2 parts by mass or less, more preferably 100 parts by mass or less based on the peroxide-based polymerization initiator. 0 parts by mass. However, it is not limited to use in the latter half of the reaction for the purpose of reducing residual monomers.

Examples of the polymerization solvent include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, and n-octane; and cyclopentane, cyclohexane, and cycloheptane. An alicyclic hydrocarbon such as an alkane or a cyclooctane; diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, benzene An ether such as diethyl ether or diphenyl ether; a halogenated hydrocarbon such as chloroform, carbon tetrachloride, 1,2-dichloroethane or chlorobenzene; Ethyl acetate, propyl acetate, butyl acetate, methyl propionate and other esters; acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, cyclohexanone and other ketones; N, N - guanamines such as dimethylformamide, N,N-dimethylacetamide, N,N-methylpyrrolidone; nitriles such as acetonitrile and benzonitrile; dimethyl hydrazine and cycline碸 and other Aachen. These polymerization solvents may be used alone or in combination of two or more.

"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 usually 200,000 to 1,500,000, preferably 400,000 to 130, in terms of polystyrene. 10,000, especially good for 500,000 to 1.1 million. Since the copolymer (A) is a highly branched polymer, the copolymer (A) chains can be appropriately intertwined with each other, and the workability of the adhesive layer does not deteriorate. In particular, when the Mw is 400,000 or more, an adhesive layer having high cohesiveness 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 10 to 40, and particularly preferably 10 to 30.

The glass transition temperature (Tg) of the (meth)acrylic copolymer (A) can be calculated, for example, from the monomer unit constituting the copolymer and the content ratio thereof according to the formula of Fox. For example, the (meth)acrylic copolymer can be synthesized in such a manner that the glass transition temperature (Tg) obtained by the calculation formula according to Fox is usually -70 to 0 ° C, preferably -60 to -30 ° C. (A). By using a (meth)acrylic copolymer (A) having such a glass transition temperature (Tg), an adhesive composition excellent in adhesion at normal temperature can be obtained. Things.

Fox's formula: 1/Tg=(W ₁ /Tg ₁ )+(W ₂ /Tg ₂ )+‧‧‧+(W _m /Tg _m ) W ₁ +W ₂ +‧‧‧+W _m =1

In the formula, Tg is a glass transition temperature (unit: K) of the (meth)acrylic copolymer (A), and Tg ₁ , Tg ₂ , ‧ ‧ and Tg _m are homopolymers composed of each monomer The glass transition temperature (unit: K), W ₁ , W ₂ , ‧ ‧ , W _m is the weight fraction of the constituent unit derived from each monomer in the copolymer (A). The weight fraction of the constituent units derived from the respective monomers can be used for the ratio of the loading of each monomer to the total monomers when the copolymer is synthesized.

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

In the adhesive composition of the present invention, the content of the (meth)acrylic copolymer (A) is usually from 50 to 99.99% by mass based on 100% by mass of the solid content of the organic solvent (E) in the composition. More preferably, it is 60 to 99.95 mass%, and particularly preferably 80 to 99.90 mass%. When the content of the (meth)acrylic copolymer (A) is in the above range, a balance of properties as an adhesive can be obtained, and the adhesive property is excellent.

[Crosslinking agent (B)]

The adhesive composition of the present invention further contains a crosslinking agent (B).

The crosslinking agent (B) is a crosslinkable member which can be derived from a monomer having a crosslinkable functional group which is compatible with the (meth)acrylic copolymer (A). The component capable of causing a crosslinking reaction is not particularly limited, and examples thereof include an isocyanate compound (B1), a metal chelate compound (B2), and an epoxy compound (B3).

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

In the crosslinking agent (B), at least one selected from the group consisting of an isocyanate compound (B1) and a metal chelate compound (B2) is preferably used, and an isocyanate compound (B1) and a metal chelate compound (B2) are preferably used in combination.

With respect to the (meth)acrylic copolymer (A), crosslinking is preferably carried out by crosslinking formed by a covalent bond of the isocyanate compound (B1), and/or by a metal chelate compound ( The virtual crosslink formed by the coordination key of B2).

In the adhesive composition of the present invention, the content of the crosslinking agent (B) is usually 0.01 to 5 parts by mass, particularly preferably 0.05 to 2.5 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (A). More preferably, it is 0.1 to 1 part by mass. When the content is in the above range, it is preferable from the viewpoint of easily obtaining a balance between durability and stress relaxation characteristics.

Isocyanate Compound (B1)

The isocyanate compound (B1) is usually an isocyanate compound having an isocyanate group number of 2 or more in one molecule. By crosslinking the (meth)acrylic copolymer (A) with the isocyanate compound (B1), a crosslinked body (mesh polymer) can be formed.

The isocyanate group number of the isocyanate compound (B1) is usually It is 2 or more, preferably 2 to 8, and particularly preferably 3 to 6. When the number of isocyanate groups is in the above range, it is preferable from the viewpoint of the crosslinking reaction efficiency of the (meth)acrylic copolymer (A) and the isocyanate compound (B1) and the flexibility of the adhesive layer.

The isocyanate compound having an isocyanate group number of 2 in one molecule may, for example, be an aliphatic diisocyanate, an alicyclic diisocyanate or an aromatic diisocyanate. Examples of the aliphatic diisocyanate include ethyl diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, and 3 An aliphatic diisocyanate having 4 to 30 carbon atoms such as methyl-1,5-pentane diisocyanate or 2,2,4-trimethyl-1,6-hexamethylene diisocyanate. Examples of the alicyclic diisocyanate include isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated diphenylmethane diisocyanate, and hydrogen tetramethylate. An alicyclic diisocyanate having 7 to 30 carbon atoms such as xylene diisocyanate. Examples of the aromatic diisocyanate include carbon number such as phenylene diisocyanate, toluene diisocyanate, xylene diisocyanate, naphthalene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, and diphenylpropane diisocyanate. 8 to 30 aromatic diisocyanates.

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

Further, examples of the isocyanate compound (B1) include a polymer (for example, a dimer or a trimer, a biuret or a trimeric isocyanate) of the above isocyanate compound having an isocyanate group number of 2 or more, A derivative (for example, an addition reaction product of a polyhydric alcohol and two or more molecules of a diisocyanate compound), a polymer, or the like. Examples of the polyhydric alcohol in the above-mentioned derivative include a trihydric or higher alcohol such as trimethylolpropane, glycerin or neopentyl alcohol, and examples of the high molecular weight polyhydric alcohol include polyether polyol. Polyester polyol, acrylic polyol, polybutadiene polyol, polyisoprene polyol.

Examples of such an isocyanate compound include a trimer of diphenylmethane diisocyanate, a polymethylene polyphenyl polyisocyanate, a hexamethylene diisocyanate or a toluene diisocyanate or a trimeric isocyanate. a reaction product of trimethylolpropane with toluene diisocyanate or xylene diisocyanate (for example, a three-molecule adduct of toluene diisocyanate or xylene diisocyanate), trimethylolpropane and hexamethylene diisocyanate. A reaction product (for example, a three-molecular adduct of hexamethylene diisocyanate), a polyether polyisocyanate, or a polyester polyisocyanate.

In the isocyanate compound (B1), a reaction product of trimethylolpropane and toluene diisocyanate or xylene diisocyanate is preferred from the viewpoint of improving the ripening property (L-45, manufactured by Soken Chemical Co., Ltd.) Isocyanate of hexamethylene diisocyanate or toluene diisocyanate (TSE-100 manufactured by Asahi Kasei Co., Ltd., 2050 manufactured by Nippon Polyurethane Industry Co., Ltd., etc.).

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

In the adhesive composition of the present invention, the content of the isocyanate compound (B1) is preferably 5 parts by mass or less, more preferably 2.5 parts by mass or less, based on 100 parts by mass of the (meth)acryl-based copolymer (A). It is preferably 1 part by mass or less, and particularly preferably 0.5 part by mass or less. When the content is in the above range, it is preferable from the viewpoint of easily obtaining a balance between durability and stress relaxation characteristics. When the above (B1) is used, the lower limit thereof is, for example, 0.001 part by mass, preferably 0.01 part by mass.

Metal Chelate Compound (B2)

The metal chelate compound (B2) may, for example, be alkoxide, acetamidineacetone or ethyl acetoacetate in aluminum, iron, copper, zinc, tin, titanium, nickel, bismuth, magnesium, vanadium, chromium and A compound obtained by a polyvalent metal such as zirconium or the like.

Among these, it is particularly preferred to be an aluminum chelate compound (M-12AT manufactured by Soken Chemical Co., Ltd.). Specific examples thereof include aluminum isopropoxide, aluminum secondary aluminoxide, ethyl acetate-diisopropyl aluminum, aluminum tris (ethyl acetoacetate), and aluminum triacetate (a1uminum). Tris (acetylacetonate)).

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

The metal chelate compound (B2) crosslinks (virtual crosslinks) the (meth)acrylic copolymer (A) by a coordinate bond. When the metal chelate compound (B2) is used as the cross-linking agent (B), the aforementioned cross-linking is maintained at room temperature In contrast, the polymer is partially cohesive at a high temperature, and the adhesive layer exhibits more excellent flexibility.

In the adhesive composition of the present invention, the content of the metal chelate compound (B2) is preferably 5 parts by mass or less, and particularly preferably 2.5 parts by mass or less based on 100 parts by mass of the (meth)acryl-based copolymer (A). More preferably, it is 1 part by mass or less, and particularly preferably 0.5 part by mass or less. When the content is in the above range, it is preferable from the viewpoint of easily obtaining a balance between durability and stress relaxation characteristics. When the above (B2) is used, the lower limit thereof is, for example, 0.001 part by mass, preferably 0.01 part by mass.

In the adhesive composition of the present invention, when the isocyanate compound (B1) and the metal chelate compound (B2) are used as the crosslinking agent (B), the content of the above (B2) is usually 100 parts by mass based on the above (B1). It is more than 0 parts by mass and is 1000 parts by mass or less, more preferably more than 0 parts by mass and 600 parts by mass or less, more preferably more than 0 parts by mass and 400 parts by mass or less. When the content is in the above range, it is preferable from the viewpoint of suppressing the bending and improving the adhesion between the polarizer and the adhesive layer.

Epoxy Compound (B3)

The epoxy compound (B3) is usually an epoxy compound having two or more epoxy groups in one molecule. For example, ethylene glycol diglycidyl ether, polyethylene glycol diepoxypropyl ether, glycerol diepoxypropyl ether, glycerol triepoxypropyl ether, 1, 3 -Bis(N,N'-diepoxypropylaminomethyl)cyclohexane, N,N,N',N'-tetraepoxypropyl-m-xylenediamine, N,N,N' , N'-tetraepoxypropylaminophenylmethane, trimeric isocyanate ring Oxypropyl propyl ester, m-N,N-diepoxypropylaminophenyl epoxypropyl ether, N,N-diepoxypropyl toluidine, N,N-diepoxypropyl aniline.

In the adhesive composition of the present invention, the content of the epoxy compound (B3) is preferably 2 parts by mass or less, and particularly preferably 1 part by mass or less based on 100 parts by mass of the (meth)acryl-based copolymer (A). More preferably, it is 0.5 mass part or less. When the above (B3) is used, the lower limit thereof is, for example, 0.001 part by mass, preferably 0.01 part by mass.

[decane coupling agent (C)]

The adhesive composition of the present invention preferably further contains a decane coupling agent (C). The decane coupling agent (C) contributes to prevention of peeling in a high-humidity heat environment by adhering the adhesive layer firmly to a adherend such as a glass plate.

Examples of the decane coupling agent (C) include a polymerizable unsaturated group-containing decane coupling agent such as vinyltrimethoxydecane, vinyltriethoxysilane or methacryloxypropyltrimethoxydecane. 3-glycidoxypropyltrimethoxydecane, 3-glycidoxypropyltriethoxydecane, 3-glycidoxypropylmethyldimethoxydecane, 3-ring An epoxy group-containing decane coupling agent such as oxypropoxypropylmethyldiethoxy decane or 2-(3,4-epoxycyclohexyl)ethyltrimethoxydecane; 3-aminopropyltrimethoxy Baseline, N-(2-aminoethyl)-3-aminopropyltrimethoxydecane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxydecane, etc. A halogen-containing decane coupling agent such as an amine group-containing decane coupling agent; 3-chloropropyltrimethoxy decane.

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

[Antistatic agent (D)]

The antistatic agent (D) can be used, for example, to lower the surface resistance value of the adhesive layer formed of the adhesive composition of the present invention. Examples of the antistatic agent (D) include a surfactant, an ionic compound, and a conductive polymer.

Examples of the surfactant include a 4-stage ammonium salt, a guanamine 4-grade ammonium salt, a pyridinium salt, and a cationic surfactant having a cationic group such as a 1st to a third amine group; Anionic surfactants such as an anionic group such as a sulfonate group or a phosphate group; an alkylbetaine, an alkylimidazolium betaine, an alkylamine oxide, an amino acid sulfate, etc. Sexual surfactants, glycerol fatty acid esters, sorbitan fatty acid esters, polyoxyethylidene amines, polyoxyethylene alkylamine fatty acid esters, N-hydroxyethyl-N-2-hydroxyalkane A nonionic surfactant such as a base amine or an alkyl diethanolamine.

Further, as the surfactant, a reactive emulsifier having a polymerizable group may be used, and a polymerization of a monomer component containing the above surfactant or reactive emulsifier may be used. System surfactant.

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

The cation portion constituting the ionic compound may be either or both of an inorganic cation or an organic cation. The inorganic cation is preferably an alkali metal ion or an alkaline earth metal ion, and particularly preferably Li ⁺ , Na ⁺ and K ⁺ having excellent antistatic properties. Examples of the organic cation system include a pyridinium cation, a piperidinium cation, a pyrrolidinium cation, a dihydropyrrole cation, a pyrrole cation, an imidazolium cation, a tetrahydropyrimidinium cation, a dihydropyrimidinium cation, and a pyrazolium cation. And pyrazolinium cations, tetraalkylammonium cations, trialkylsulfonium cations, tetraalkylphosphonium cations and derivatives thereof.

The anion portion constituting the ionic compound is not particularly limited as long as it can be ionically bonded to the cation portion to form an ionic compound. Specific examples thereof include F ^- , Cl ^- , Br ^- , I ^- , AlCl ₄ ^- , Al ₂ Cl ₇ ^- , BF ₄ ^- , PF ₆ ^- , SCN ^- , ClO ₄ ^- , NO ₃ ^- , CH ₃ COO ^- , CF ₃ COO ^- , CH ₃ SO ₃ ^- , CF ₃ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (F ₂ SO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₃ C ^- , AsF ₆ ^- , SbF ₆ ^- , NbF ₆ ^- , TaF ₆ ^- , F(HF) _n ^- , (CN) ₂ N ^- , C ₄ H ₉ SO ₃ ^- , (C ₂ F ₅ SO ₂ ) ₂ N ^- , C ₃ F ₇ COO ^- and (CF ₃ SO ₂ )(CF ₃ CO)N ^- . Among these, an anion containing a fluorine atom is preferred because it can impart an ionic compound having a low melting point, and particularly preferably (F ₂ SO ₂ ) ₂ N ^- and (CF ₃ SO ₂ ) ₂ N ^- .

The ionic compound is preferably lithium bis(trifluoromethanesulfonyl) phthalimide, lithium bis(difluorosulfonyl) ruthenium, lithium tris(trifluoromethanesulfonyl)methane, bis(trifluoromethane) Sulfonyl) sulfinium imide, potassium bis(difluorosulfonyl) sulfinium imide, 1-ethylpyridinium hexafluorophosphate, 1-butylpyridinium hexafluorophosphate, 1-hexyl hexafluorophosphate -4-methylpyridinium salt, hexafluorophosphate 1- Octyl-4-methylpyridinium salt, bis(fluorosulfonyl) quinone imine 1-octyl-4-methylpyridinium salt, bis(trifluoromethanesulfonyl) quinone imine 1-octyl -4-methylpyridinium salt, tetrafluoroboric acid (N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium, bis(trifluoromethanesulfonyl)pyrene Amine N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium, quinone imine 1-octylpyridinium fluoranthene, 1-octyl-3-methylpyridinium , quinone imine trifluorohydrazine.

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

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

[Organic solvent (E)]

In order to adjust the coatability, the adhesive composition of the present invention preferably contains an organic solvent (E). The organic solvent is a polymerization solvent described in the column of the (meth)acrylic copolymer (A). For example, the polymer solution containing the (meth)acrylic copolymer (A) and the polymerization solvent obtained by the above copolymerization may be mixed with the crosslinking agent (B) to prepare an adhesive composition. In the adhesive composition of the present invention, the content of the organic solvent (E) is usually from 50 to 90% by mass, preferably from 60 to 85% by mass.

In the present specification, the term "solid content" means all components after the organic solvent (E) is deducted from the components of the adhesive composition, and the "solid content concentration" means that the solid components are relatively The ratio of the adhesive composition to 100% by mass.

[additive]

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

[Modulation of adhesive composition for polarizing]

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

The gel fraction of the adhesive formed of the adhesive composition of the present invention is preferably more than 50% by mass, more preferably more than 50% by mass and more preferably 80% by mass or less, still more preferably 60% by mass to 75% by mass. The gel fraction is, for example, a value obtained by measuring the adhesive collected under the conditions described in the examples.

[Adhesive layer for polarizing plate]

The adhesive layer for a polarizing plate of the present invention is formed of the above-described adhesive composition. By using the adhesive composition of the present invention, it can be formed to have The adhesive layer that stores the elastic modulus characteristics.

The storage elastic layer of the present invention preferably has a storage elastic modulus (G'1) at 23 ° C of 0.1 MPa or more, particularly preferably 0.1 to 0.2 MPa, particularly preferably 0.1 to 0.15 MPa; and storage at 85 ° C The modulus of elasticity (G'2) is preferably 0.05 MPa or less, more preferably 0.05 to 0.02 MPa, particularly preferably 0.05 to 0.03 MPa.

The adhesive layer of the present invention has a storage elastic modulus at a certain temperature T ° C as G' _T and a storage elastic modulus at T+1 ° C as G' _T+1 at a temperature T of 23 In the range of 50 ° C, the preferred system always satisfies G' _T /G' _T+1 <1.07, and the better system always satisfies 1≦G' _T /G' _T+1 ≦1.05.

The storage elastic modulus is, for example, a result of laminating the pressure-sensitive adhesive layers to each other to form a laminate having a thickness of about 1.0 mm and calculating the dynamic viscoelasticity spectrum measured from the laminate.

When the storage elastic modulus (G'1) at 23 ° C is in the above range, the adhesive layer of the present invention is excellent in hardness at normal temperature and improves workability. For example, when the adhesive layer is cut, it is possible to prevent the adhesive from adhering to the cutting edge or the drawing of the adhesive layer.

By setting the storage elastic modulus (G'2) at 85 ° C to the above range, the adhesive layer of the present invention has sufficient flexibility in a high temperature environment, so that heat shrinkage by the polarizer can be sufficiently alleviated. The stress caused by (dimension change). Therefore, even when exposed to a high temperature environment, the warpage of the adherend can be lowered, and the breakage of the adhesive layer or the peeling of the adhesive layer from the polarizer is less likely to occur.

It is said that G' _T /G' _T+1 <1.07 is always satisfied in the range of 23 to 50 ° C, which means that the change in the elastic modulus in this temperature range is small, and deformation and bleeding of the adhesive layer can be suppressed.

The adhesive layer formed of the adhesive composition of the present invention preferably has a gel fraction of more than 50% by mass from the viewpoint of strain suppression, cohesive force, adhesion, and removability of the polarizing plate, and more preferably exceeds 50% by mass and 80% by mass or less, more preferably 60 to 75% by mass. When the gel fraction is in the above range, the adhesive layer can exhibit excellent durability. Further, even if the gel fraction is in the above range, since the branching chains of the (meth)acrylic copolymer (A) are partially relaxed at a high temperature, the adhesive layer can exhibit excellent stress relaxation properties.

The adhesive layer of the present invention is crosslinked by, for example, performing the crosslinking reaction in the above adhesive composition, specifically, by crosslinking the (meth)acrylic copolymer (A) with the crosslinking agent (B). And get it.

The conditions for forming the adhesive layer are, for example, those described below. The adhesive composition of the present invention is applied to a support, although it varies depending on the kind of the solvent, but is usually 50 to 150 ° C, preferably 60 to 100 ° C, usually dried for 1 to 10 minutes, preferably 2 to dry. The solvent was removed in 7 minutes to form a coating film. The film thickness of the dried coating film is usually from 5 to 75 μm, preferably from 10 to 50 μm.

The adhesive layer is preferably formed by the following conditions. Applying the adhesive composition of the present invention to a support, and attaching a cover film to the coating film formed under the above conditions, usually for 3 days or longer, preferably 7 to 10 days, and Usually at 5 to 60 ° C, preferably 15 to 40 ° C, usually 30 to 70% RH, preferably 40 to 70% RH Maturation. When cross-linking is carried out under the above-mentioned ripening conditions, the cross-linking (network polymer) can be efficiently formed.

The coating method of the adhesive composition can be a generally known method, for example, by a spin coating method, a knife coating method, a roll coating method, a bar coating method, a blade coating method, or a die coating method. A method of applying and drying a method such as a method or a gravure coating method to have a predetermined thickness.

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

[Adhesive sheet for polarizing plate]

The adhesive sheet for a polarizing plate of the present invention has an adhesive layer formed of the above-mentioned adhesive composition. The adhesive sheet may, for example, be a double-sided adhesive sheet having only the above adhesive layer; a double-sided adhesive sheet having a substrate and the above-mentioned adhesive layer formed on both sides of the substrate; and a substrate and a substrate; One side of the adhesive layer on one side of the adhesive sheet; and an adhesive sheet on which the cover film after the release treatment is applied is adhered to the surface of the adhesive layer of the adhesive sheet which is not in contact with the substrate.

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

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

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

[Polarizer with Adhesive Layer]

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

As the polarizing plate, a conventionally known polarizing film can be used. For example, the polarizer itself and a multilayer film having a polarizer and a polarizer protective film disposed on the polarizer can be exemplified. In the present invention, since the adhesive layer is disposed in direct contact with the polarizer, a configuration in which the polarizer protective film is disposed only on one surface of the polarizer, and a polarizer protective film is not disposed on both surfaces of the polarizer The composition.

The polarizing film is, for example, a stretched film obtained by including a polarizing component in a film made of a polyvinyl alcohol-based resin and extending it. Examples of the polyvinyl alcohol-based resin include saponified products of polyvinyl alcohol, polyvinyl formal, polyvinyl acetal, and ethylene-vinyl acetate copolymer. Examples of the polarizing component include iodine or a dichroic dye.

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

The thickness of the polarizing plate is usually from 10 to 200 μm, preferably from 50 to 100 μm. In the present invention, since the polarizer protective film formed on the polarizer can be omitted, the thickness of the polarizing plate can be reduced.

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

The method of forming the adhesive layer on the surface of the polarizer is not particularly limited, and a method of directly applying the above-described adhesive composition to the surface of the polarizer using a bar coater or the like, followed by drying and aging; The method of transferring the adhesive layer of the polarizing plate of the present invention to the surface of the polarizer and aging it is carried out. The conditions for drying and aging, the range of the gel fraction, and the like are the same as those described in the column of [Adhesive Layer for Polarizing Plate].

The thickness of the adhesive layer is usually from 5 to 75 μm, preferably from 10 to 50 μm, in terms of dry film thickness. In addition, the adhesive layer is only The polarizer may be formed by contacting the polarizer on at least one side thereof, and examples thereof include an adhesive layer formed on only one side of the polarizer and an adhesive layer formed on both surfaces of the polarizer. .

Further, on the above polarizing plate, for example, a protective layer, an antiglare layer, a phase difference layer, a viewing angle lifting layer, or the like having other functions may be laminated.

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

The substrate of the liquid crystal cell is, for example, a glass plate. The thickness of the substrate is usually from 0.05 to 3 mm, preferably from 0.2 to 1 mm. In the present invention, by using the above-mentioned adhesive layer, warpage of the polarizing plate and the substrate can be suppressed even if the adhesive layer is directly laminated on the polarizer. Therefore, even when the thickness of the substrate is small (for example, 1 mm or less, preferably 0.2 to 1 mm), the above-mentioned adhesive composition can be preferably used for bonding the polarizing plate to the substrate.

[Examples]

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

[GPC and GPC-MALS]

For the (meth)acrylic copolymer, the weight average molecular weight (Mw) and the amount are determined by gel permeation chromatography (GPC method) under the following conditions. The average molecular weight (Mn) was calculated by a gel permeation chromatography/multi-angle laser light scattering detector (GPC-MALS) under the following conditions to calculate the slope of the double logarithmic straight line of the radius of gyration and the molecular weight, and to obtain the branching degree.

‧Measurement device: HLC-8320GPC (manufactured by Tosoh Co., Ltd.)

‧GPC column structure: The following 4 series column (both made by Tosoh Co., Ltd.)

(1) TSKgel HxL-H (guard column, guard column)

(2) TSKgel GMHxL

(3) TSKgel GMHxL

(4)TSKgel G2500HxL

‧Flow rate: 1.0ml/min

‧column temperature: 40 ° C

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

‧Mobile phase solvent: tetrahydrofuran

‧Detector: DAWN HELEOS (MALS detector) + OptiLab rEE (RI detector)

‧Standard polystyrene conversion (when measuring Mw and Mn)

[Synthesis Example 1]

76.8 parts of n-butyl acrylate, 20 parts of benzyl acrylate, 3 parts of acrylic acid, 0.2 parts of 2-hydroxyethyl acrylate and 100 parts of ethyl acetate solvent were placed in a reaction equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen introduction tube. In the apparatus, the temperature was raised to 80 ° C while introducing nitrogen gas. Next, 0.1 part of butyl peroxypivalate was added, and polymerization was carried out at 80 ° C for 6 hours under a nitrogen atmosphere. After the reaction is completed, it is prepared by diluting with ethyl acetate. A polymer solution having a solid concentration of 30% by mass. The obtained (meth)acrylic copolymer A1 had a weight average molecular weight (Mw) of 670,000, a molecular weight distribution (Mw/Mn) of 13, and a branching degree of 0.48.

[Synthesis Examples 2 to 5]

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

[Example 1] (1) Modulation of adhesive composition

The polymer solution obtained in Synthesis Example 1 (solid content concentration: 30% by mass) and 100 parts (solid content) of the (meth)acrylic copolymer A1 contained in the solution were used as a crosslinking agent. "TD-75" (solid content: 75 mass%, ethyl acetate solution), 0.07 parts (solid content), "M-12AT" 0.2 parts (solid content), and Shin-Etsu as a decane coupling agent 0.2 parts of "KBM-403" (solid content: 100% by mass) manufactured by Chemical Industry Co., Ltd. was mixed to obtain an adhesive composition.

(2) Production of adhesive sheets

The adhesive composition obtained in the above (1) was subjected to defoaming, and then applied to a polyethylene terephthalate film (PET film) subjected to release treatment using a blade coater, and dried at 90 ° C for 3 minutes. On the other hand, a coating film having a dry film thickness of 20 μm was formed. The PET film after the release treatment was further bonded to the surface of the coating film opposite to the bonding surface of the PET film, and allowed to stand in an environment of 23° C./50% RH for 7 days to be aged. An adhesive sheet having an adhesive layer having a thickness of 20 μm held in two PET films.

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

The adhesive composition obtained in the above (1) was subjected to defoaming, and then applied to a polyethylene terephthalate film (PET film) which had been subjected to release treatment using a blade coater, and dried at 90 ° C for 3 minutes. Thus, a sheet having a coating film having a dry film thickness of 20 μm was obtained. The coating film surface of the sheet, the polyvinyl alcohol film as a polarizer, and the cellulose triacetate film as a polarizer protective film The polyvinyl alcohol film of the polarizing plate having a two-layer structure (thickness: 60 μm) was brought into contact with each other, and was allowed to stand in an environment of 23° C./50% RH for 7 days for aging, thereby obtaining a PET film and a thickness. A 20 μm adhesive layer and a polarizer of the polarizer and the adhesive layer of the polarizer protective film.

[Examples 2 to 3, Comparative Examples 1 to 3]

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/or the composition of the formulation was changed as described in Table 2, in the same manner as in Example 1. The adhesive composition, the adhesive sheet, and the polarizing plate with the adhesive layer are obtained.

[assessment] [Gel fraction]

From the adhesive sheets obtained in the examples and the comparative examples, about 0.1 g of the adhesive was collected into the sample bottle, and 30 mL of ethyl acetate was added and shaken for 4 hours, and then the contents of the sample bottle were filtered with a stainless steel gold mesh of 200 mesh, and The residue on the gold mesh was dried at 100 ° C for 2 hours, and the dry weight was measured. The gel fraction of the adhesive was determined by the following formula.

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

[Storage Elastic Modulus]

In the adhesive sheets obtained in the examples and the comparative examples, the adhesive layers having a thickness of 20 μm were adhered to each other in an environment of 23° C./50% RH for several times, and were treated in an autoclave at 50° C./5 atm for 20 minutes. An adhesive layer having a thickness of 1.0 mm was produced. "Physica MCR300" manufactured by Anton Paar Co., Ltd., according to the dynamic viscoelasticity measurement method based on JIS K7244 (temperature range -40 to 160 ° C, temperature rising rate 3.67 ° C / min, frequency 1 Hz), the thickness is 1.0 mm. The adhesive layer was measured for the viscoelastic spectrum, and the storage elastic modulus at temperatures of 23 ° C and 85 ° C and the maximum value of G' _T /G' _T+1 in the range of 23 to 50 ° C were determined.

[Measurement of adhesion]

The polarizing plate with the adhesive layer obtained in the examples and the comparative examples (the laminated body composed of the PET film/adhesive layer/polarizing sheet/polarizing sheet protective film) was cut into a size of 70 mm×25 mm to prepare a test. sheet. The PET film was peeled off from the test piece, and a laminate of the adhesive layer/polarizer/polarizer protective film was applied to the glass plate having a thickness of 2 mm by using a pressure roller so that the adhesive layer was in contact with the glass plate. One side. The obtained laminate was kept in an autoclave adjusted to 50 ° C / 5 atm for 20 minutes. Then, after standing for 1 hour in an environment of 23 ° C / 50% RH, the end portion of the polarizing plate was pulled at a rate of 90° with respect to the glass plate at a speed of 300 mm/min, and the adhesion (peel strength) was measured. .

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

The polarizing plate with the adhesive layer obtained in the examples and the comparative examples (the laminated body composed of the PET film/adhesive layer/polarizing sheet/polarizing sheet protective film) was cut into a size of 150 mm×250 mm to prepare a test. sheet. The PET film is peeled from the test piece, and a product of the adhesive layer/polarizer/polarizer protective film is formed by using a pressure roller to bring the adhesive layer into contact with the glass plate. The layer is attached to one side of a glass plate having a thickness of 0.5 mm. The obtained laminate was held in an autoclave adjusted to 50 ° C / 5 atm for 20 minutes to prepare a test plate. Make two identical test panels. The test plate was placed under conditions of a temperature of 80 ° C (heat resistance) or a temperature of 60 ° C / humidity of 90% RH (moisture resistance) for 500 hours, and foaming, floating, and the like were observed by the following criteria. The production of peeling is performed for evaluation.

‧AA: No appearance defects such as foaming, floating, peeling, etc. were observed

‧BB: Only a few appearances such as foaming, floating, peeling, etc. were observed.

‧CC: Observed obvious appearance such as foaming, floating, peeling, etc.

[Light leakage test]

The polarizing plate (the laminated body composed of the PET film/adhesive layer/polarizer/polarizer protective film) obtained by the two examples of the adhesive layer obtained in the examples and the comparative examples was cut into a size of 310 mm × 385 mm, and was produced. Test strips. The PET film was peeled off from the test piece, and a laminating body composed of an adhesive layer/polarizer/polarizer protective film was attached to the test piece so that the polarizing axes were orthogonal to each other and the adhesive layer was in contact with the glass plate. On both sides of a glass plate with a thickness of 0.5 mm. The obtained laminate was held in an autoclave adjusted to 50 ° C / 5 atm for 20 minutes to prepare a test plate. The test plate was allowed to stand at a temperature of 80 ° C for 500 hours, and observation of light leakage was performed by the following reference.

AA: No light leakage was observed

BB: Only a few light leaks were observed

CC: Observed significant light leakage

[warping (bending) test]

The polarizing plate with the adhesive layer obtained in the examples and the comparative examples (the laminated body composed of the PET film/adhesive layer/polarizing sheet/polarizing sheet protective film) was cut into a size of 35 mm×400 mm to prepare a test. sheet. The PET film was peeled off from the test piece, and a laminate body composed of an adhesive layer/polarizer/polarizer protective film was attached to a thickness of 0.7 mm and 40 mm by using a pressure roller so that the adhesive layer was in contact with the glass plate. One side of a glass plate of ×410 mm. The obtained laminate was placed in an environment of 23 ° C / 50% RH for 24 hours, and then kept in an oven at 60 ° C for 72 hours. The end of the single side was fixed to a wall surface perpendicular to the ground, and the amount of floating at the opposite end was measured by a ruler.

The observation of warpage (bending) was performed by the following criteria.

AA: The floating of the end is 3mm or less

BB: The end floats more than 3mm and is less than 5mm

CC: The floating at the end is 5mm or more

[Processability (cutting)]

The adhesive sheets obtained in the examples and the comparative examples were cut out into 30 pieces using a Thomson cutting machine using a Thomson cutting machine of 50 mm × 50 mm. Immediately after the cutting, the shape of the end portion was observed. In 30 pieces, no oozing or end cracking was observed in one place, and the defect of the adhesive layer was judged as AA, and there was observed. Then it is judged as CC.

[Adhesive deformability]

The polarizing plates of the adhesive layer obtained in the examples and the comparative examples were cut into Ten sheets of 100 mm × 100 mm were laminated, and a load of 1 kg was applied from above and left for 24 hours, and the bleeding of the adhesive layer was visually observed by the following criteria.

AA: No seepage of the adhesive layer was observed

BB: Only a few oozing layers of the adhesive layer were observed.

CC: Obvious bleed out of the adhesive layer was observed

Claims (8)

An adhesive composition for a polarizing plate for forming an adhesive layer in direct contact with a polarizer, the composition comprising (A) a (meth)acrylic copolymer and (B) a crosslinking agent; (A) (meth)acrylic copolymer is a copolymerization of a monomer component containing a (meth)acrylic acid alkyl ester having 4 to 18 carbon atoms and a monomer having a crosslinkable functional group; Further, the (meth)acrylic copolymer has a branching degree of 0.55 or less as measured by a gel permeation chromatography/multi-angle laser light scattering detector (GPC-MALS). The adhesive composition for a polarizing plate according to claim 1, wherein the (meth)acrylic copolymer (A) is copolymerized by the copolymer in the presence of a peroxide polymerization initiator. The copolymer obtained. The adhesive composition for a polarizing plate according to claim 1 or 2, wherein the crosslinking agent (B) contains at least one selected from the group consisting of an isocyanate compound (B1) and a metal chelate compound (B2). . The adhesive composition for a polarizing plate according to the first aspect of the invention, wherein the adhesive composition of the adhesive composition for a polarizing plate has a gel fraction of more than 50% by mass. An adhesive layer for a polarizing plate, which is formed by the adhesive composition according to any one of claims 1 to 4. The adhesive layer for a polarizing plate according to claim 5, wherein the storage elastic modulus at 23 ° C is 0.1 MPa or more, and the storage elastic modulus at 85 ° C is 0.05 MPa or less; when in a storage elastic modulus at a temperature T deg.] C as the G _'T, and at T + storage elastic modulus at 1 ℃ as G' when _{T +. 1,} at a temperature T 23 to 50 deg.] C range, based Always meet G' _T /G' _T+1 <1.07. An adhesive sheet for a polarizing plate, which has the adhesive layer described in claim 5 or 6. A polarizing plate with an adhesive layer having an adhesive layer as described in claim 5 or 6 directly laminated on at least one side of the polarizer.