WO2015141382A1 - Adhesive composition for polarizing plate, adhesive sheet and polarizing plate with adhesive layer - Google Patents

Abstract

[Problem] To provide a polarizing plate adhesive composition which can suppress warping (bending) of liquid crystal cells and which can form an adhesive layer with excellent durability. [Solution] This adhesive composition for a polarizing plate contains (A) a (meth)acrylic copolymer which is obtained by copolymerizing a (meth)acrylate alkyl ester with a 4-18 carbons in an alkyl group and a monomer component containing a polymerizable macromonomer, and which has a branching degree of 0.55 or less, measured by a gel permeation chromatography / multi-angle light scattering (GPC-MALS) detector, and is characterized in that the gel fraction of the adhesive formed from the aforementioned composition is 30 mass% or less.

Description

Adhesive composition for polarizing plate, adhesive layer, adhesive sheet and polarizing plate with adhesive layer

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

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. A polarizing plate is likely to be thermally contracted in a high temperature and high humidity environment, so that it lacks dimensional stability and may cause warpage in a liquid crystal cell. In recent years, with the thinning of liquid crystal cells (eg, thinning of the substrate constituting the liquid crystal cell) and the thinning of the polarizing plate, the warpage of the liquid crystal cell under a high temperature and high humidity environment has become a larger problem. As a cause of the warp of the liquid crystal cell, for example, the pressure-sensitive adhesive layer cannot follow the thermal contraction (dimensional change) of the polarizing plate, and the stress relaxation property of the pressure-sensitive adhesive layer is low.

Also, in a high-temperature, high-humidity environment, problems such as foaming at the interface between the polarizing plate and the substrate, tearing of the pressure-sensitive adhesive layer, and peeling of the polarizing plate are likely to occur. Therefore, high durability is requested | required of the adhesive for polarizing plates.

Generally, as a means for suppressing the warpage of the liquid crystal cell, there is a method of using a highly flexible pressure-sensitive adhesive layer that can cope with a dimensional change of the polarizing plate. However, such a pressure-sensitive adhesive layer has insufficient cohesive force and causes problems such as deterioration of durability and deterioration of workability.

As a solution to the above-mentioned problem, for example, in Patent Document 1, a pressure-sensitive adhesive layer is prepared by subjecting a pressure-sensitive adhesive for an optical film containing a specific (meth) acrylic polymer, a peroxide and an isocyanate compound to a crosslinking reaction. A method of forming is disclosed. In Patent Document 1, a cross-linking method using a thermal decomposition cross-linking reaction with a peroxide and a cross-linking method using a urethane bond formation with an isocyanate-based compound are used in combination, so that stress associated with dimensional change of an optical film can be reduced. On the other hand, it is described that high durability can be maintained while maintaining sufficient stress relaxation characteristics.

However, in the method of Patent Document 1, since the remaining peroxide is decomposed by light or heat and generates radicals in the pressure-sensitive adhesive layer after the crosslinking reaction, the pressure-sensitive adhesive layer deteriorates with time. Sometimes.

Further, Patent Document 2 polymerizes (meth) acrylic monomer, macromonomer, and (meth) acrylate monomer having a crosslinkable functional group for reworkability and durability under high temperature and high humidity conditions. An adhesive composition containing a (meth) acrylic polymer and a curing agent having a functional group that reacts with the crosslinkable functional group and having a gel fraction of 55% to 80% is disclosed. .

However, Patent Document 2 does not describe the suppression of warpage of the liquid crystal cell, and since the gel fraction of the pressure-sensitive adhesive layer is relatively high, it is presumed that the stress relaxation property is also low.

JP 2006-183022 A JP 2010-150400 A

The subject of this invention is the adhesive composition for polarizing plates which can suppress the curvature (bending) of a liquid crystal cell, and can form the adhesive layer excellent in durability, The adhesive formed from the said composition It is providing the polarizing plate with an adhesive layer which has a layer, the adhesive sheet for polarizing plates which has the said adhesive layer, and the said adhesive layer.

The present inventors diligently studied to solve the above problems. As a result, a (meth) acrylic copolymer having a degree of branching in a specific range obtained by copolymerizing a (meth) acrylic acid alkyl ester having an alkyl group with 4 to 18 carbon atoms and a polymerizable macromonomer is obtained. It has been found that, when used, it is possible to form a pressure-sensitive adhesive layer that is capable of suppressing warping (bending) of the liquid crystal cell and having excellent durability while having a low gel fraction. That is, the present inventors have found that the above problems can be solved by using a polarizing plate pressure-sensitive adhesive composition having the following specific configuration, and have completed the present invention.

The present invention includes, for example, the following [1] to [10].
[1] (A) It is obtained by copolymerizing a copolymer component containing an alkyl group (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms and a polymerizable macromonomer, and is a gel permeation chromatography method / A pressure-sensitive adhesive composition for a polarizing plate containing a (meth) acrylic copolymer having a degree of branching of 0.55 or less measured by an angle laser light scattering detector (GPC-MALS), and formed from the composition A pressure-sensitive adhesive composition for polarizing plates, wherein the pressure-sensitive adhesive has a gel fraction of 30% by mass or less.

[2] The (meth) acrylic copolymer (A) is a copolymer obtained by copolymerizing a polar group-containing monomer together with the (meth) acrylic acid alkyl ester and a polymerizable macromonomer. The pressure-sensitive adhesive composition for polarizing plate according to [1].

[3] The pressure-sensitive adhesive composition according to the above [1] or [2], wherein the amount of the polar group-containing monomer used in the copolymerization is 10% by mass or less in 100% by mass of the copolymerization component.

[4] The weight average molecular weight (Mw) measured by the gel permeation chromatography method (GPC method) of the (meth) acrylic copolymer (A) is 200,000 to 1,500,000. [1] The adhesive composition for polarizing plates according to any one of to [3].

[5] The pressure-sensitive adhesive composition for a polarizing plate according to any one of [1] to [4], further comprising (B) a crosslinking agent.

[6] The pressure-sensitive adhesive for polarizing plates according to [5], wherein the crosslinking agent (B) is at least one selected from an isocyanate compound (B1), a metal chelate compound (B2), and an epoxy compound (B3). Composition.

[7] The content of the crosslinking agent (B) is 5 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic copolymer (A), according to the above [5] or [6]. A pressure-sensitive adhesive composition for polarizing plates.

[8] A pressure-sensitive adhesive for polarizing plates, which is formed from the pressure-sensitive adhesive composition for polarizing plates according to any one of [1] to [7], and has a gel fraction of 30% by mass or less. layer.

[9] A pressure-sensitive adhesive sheet for polarizing plates, comprising the pressure-sensitive adhesive layer according to [8].

[10] A polarizing plate with an adhesive layer, characterized by having the polarizing plate and the adhesive layer described in [8] on at least one surface of the polarizing plate.

ADVANTAGE OF THE INVENTION According to this invention, the adhesive composition for polarizing plates which can suppress the curvature (bending) of a liquid crystal cell and can form the adhesive layer excellent in durability, The adhesive formed from the said composition A polarizing plate having a pressure-sensitive adhesive layer, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, and a pressure-sensitive adhesive layer-attached polarizing plate having the pressure-sensitive adhesive layer can be provided.

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

[Adhesive composition for polarizing plate]
The pressure-sensitive adhesive composition for polarizing plates of the present invention contains a (meth) acrylic copolymer (A). The pressure-sensitive adhesive composition preferably further contains a cross-linking agent (B), and if necessary, at least selected from a silane coupling agent (C), an antistatic agent (D), and an organic solvent (E). You may contain 1 type.

The pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition for polarizing plates of the present invention has a gel fraction of 30% by mass or less, preferably 0 to 25% by mass, more preferably 0 to 20% by mass. Even if the gel fraction is within the above range, the copolymer (A) is obtained because the (meth) acrylic copolymer (A) has a highly branched chain derived from the polymerizable macromonomer as described later. The branched chains can be appropriately entangled with each other, and the durability and workability of the pressure-sensitive adhesive layer are not deteriorated. When the gel fraction exceeds the above range, the pressure-sensitive adhesive layer may not be able to sufficiently absorb or relax the stress caused by the dimensional change of the polarizing plate under a high temperature / high humidity heat environment. The said gel fraction is a value measured about the adhesive extract | collected, for example by the conditions of an Example description.

[(Meth) acrylic copolymer (A)]
The (meth) acrylic copolymer (A) is a copolymer obtained by copolymerizing a copolymer component containing a (meth) acrylic acid alkyl ester having an alkyl group having 4 to 18 carbon atoms and a polymerizable macromonomer. It is a coalescence. As a copolymerization component of the copolymer (A), at least one selected from polar group-containing monomers and other monomers other than these may be further used.

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

The (meth) acrylic copolymer (A) has a degree of branching of 0.55 or less, preferably 0 as measured by gel permeation chromatography / multi-angle laser light scattering detector (GPC-MALS). .10 to 0.54, more preferably 0.20 to 0.53, and particularly preferably 0.30 to 0.53. Details of measurement conditions for the degree of branching are described in the examples.

The degree of branching is an index indicating a branched polymer when it is 0.55 or less and a linear polymer when it exceeds 0.55. In a branched polymer, when the degree of branching is small, it indicates that the polymer molecule has many branches and has a high degree of branching, and when the degree of branching is large, the polymer molecule has little branching and low degree of branching. It shows having.

The (meth) acrylic copolymer (A) having a degree of branching in the above range (1) is often entangled due to the branched chain between polymer molecules at about room temperature, resulting in the molecular weight of the polymer and the pressure-sensitive adhesive. Adhesive layer with excellent storability such as adhesive properties, processability such as punching out the adhesive layer, and less deformation and protrusion of the adhesive layer, even in designs with a low gel fraction of the layer (2) At a high temperature (eg, 60 ° C.), the entanglement between the polymer molecules is partially relaxed, so that the pressure-sensitive adhesive layer exhibits excellent flexibility, and is excellent in suppressing warping (bending) of the polarizing plate, Due to the remaining entanglement, the pressure-sensitive adhesive layer exhibits excellent durability.

It is estimated that the reason why the warpage of the polarizing plate is suppressed is as follows. For example, in the configuration of polarizing plate / adhesive layer / adhered body, a case where a glass plate is used as the adherend will be described as an example. The polarizing plate and the glass plate have different heat shrinkage rates, and the polarizing plate usually has a larger heat shrinkage rate (dimensional change) than the glass plate. If the pressure-sensitive adhesive layer lacks flexibility under a high-temperature, high-humidity heat environment, the pressure-sensitive adhesive layer cannot follow the dimensional change of the polarizing plate, and the pressure-sensitive adhesive layer cannot relieve stress. Stress concentrates on the glass plate, which causes warpage of the glass plate. On the other hand, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention contains a highly branched polymer, and the entanglement partly loosens in a high temperature / high humidity environment. Can follow. Therefore, no stress is generated and the stress is not concentrated on the glass plate. Further, the polarizing plate can also be thermally contracted uniformly without anisotropy, and does not induce birefringence of the polarizing plate. As described above, in the present invention, the pressure-sensitive adhesive layer can absorb and relieve the stress accompanying the dimensional change of the polarizing plate, and therefore, no excessive stress (load) is applied to the glass plate. It is presumed that this will lead to suppression of warpage of the plate.

Since the pressure-sensitive adhesive composition of the present invention has the above properties, it is suitable for use in bonding a substrate constituting a liquid crystal cell and a polarizing plate. In particular, even when the thickness of the glass plate constituting the thinned liquid crystal cell is as small as about 0.10 to 1.0 mm, it is suitable for the purpose of bonding the substrate and the polarizing plate.

<< (Meth) acrylic acid alkyl ester >>
As the (meth) acrylic acid alkyl ester, a (meth) acrylic acid alkyl ester having an alkyl group having 4 to 18 carbon atoms (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 the (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms in the alkyl group include, for example, 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 alone or in combination of two or more.

In 100% by mass of the copolymer component forming the (meth) acrylic copolymer (A), the total amount of (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms in the alkyl group is good adhesive strength and durability. From the standpoint of expression, it is preferably 99.7 to 20% by mass, more preferably 99.4 to 30% by mass, and still more preferably 98.7 to 50% by mass.

As a copolymerization component of the (meth) acrylic copolymer (A), a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 3 carbon atoms (CH ₂ ═CR ³ —COOR ⁴ ; R ³ is a hydrogen atom or It is also possible to use a methyl group and R ⁴ is an alkyl group having 1 to 3 carbon atoms.

Examples of the (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 alone or in combination of two or more.

The amount of (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 in 100% by mass of the copolymer component from the viewpoint of stress relaxation characteristics. Or less, more preferably 40% by mass or less.

<Polymerizable macromonomer>
The polymerizable macromonomer is a monomer having a high molecular weight having a polymerizable unsaturated group copolymerizable with the above (meth) acrylic acid alkyl ester.

The polymer chain (main chain) portion constituting the polymerizable macromonomer is not particularly limited as long as it has a polymerizable unsaturated group copolymerizable with the above (meth) acrylic acid alkyl ester. ) It is preferable that a repeating structural unit derived from at least one selected from alkyl acrylate, styrene and acrylonitrile is a main component, and a repeating structural unit derived from (meth) acrylic acid alkyl ester is a main component. Is more preferable. Here, the main component means a content exceeding 50% by mass with respect to the total repeating unit amount.

Among polymerizable macromonomers whose main component is a repeating structural unit derived from (meth) acrylic acid alkyl ester, the polymer chain part is derived from (meth) acrylic acid alkyl ester having 1 to 8 carbon atoms in the alkyl group. A polymer chain mainly composed of repeating structural units is particularly preferred. Examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, and tert-butyl (meth) acrylate.

When the polymer chain part is composed of repeating structural units derived from (meth) acrylic acid alkyl ester, the content of (meth) acrylic acid alkyl ester unit having 1 to 8 carbon atoms in the alkyl group in the polymer chain part Is usually 60% by mass or more, preferably 80% by mass or more. If the content is within this range, it may have a repeating structural unit derived from styrene, acrylonitrile or the like.

The repeating structural unit constituting the polymer chain (main chain) portion may be composed of one type of repeating structural unit or may be composed of two or more types of repeating structural units. In the latter case, the polymer chain portion may be a random copolymer chain, a block copolymer chain, or an alternating copolymer chain.

The polymerizable macromonomer reacts with the above (meth) acrylic acid alkyl ester used as a copolymerization component to form a side chain derived from the macromonomer in the (meth) acrylic copolymer (A). . For this reason, the (meth) acrylic copolymer (A) is a highly branched polymer having a highly branched structure.

The polymerizable unsaturated group possessed by the polymerizable macromonomer is preferably a group having an ethylenically unsaturated double bond, such as a (meth) acryloyl group, an allyl group, a propenyl group, a vinyl group, a vinylidene group, or a vinylene group. (Meth) acryloyl group or vinyl group is preferable, and (meth) acryloyl group is particularly preferable.

The polymerizable unsaturated group may be present at the end of the polymer chain portion or at the side chain, but is preferably present at the end. In addition, the polymerizable unsaturated group may be present only at one end of the polymer chain portion or at both ends. From the viewpoint of stability during polymerization, one of the polymer chain portions may be present. It is preferably present only at the ends.

As the polymerizable macromonomer, a (meth) acrylic macromonomer is preferable. Examples of the (meth) acrylic macromonomer include polymethyl (meth) acrylate, polybutyl (meth) acrylate, and polyisobutyl (meth) acrylate having a (meth) acryloyl group at the terminal. Polymethyl (meth) acrylate having a (meth) acryloyl group is preferred.

The number average molecular weight of the polymerizable macromonomer is usually 500 or more, preferably 1,000 to 10,000, and more preferably 3,000 to 8,000. The number average molecular weight (Mn) of the polymerizable macromonomer is a value in terms of polystyrene measured by gel permeation chromatography.

The glass transition temperature (Tg) of the polymerizable macromonomer is preferably −60 to 150 ° C., more preferably −30 to 130 ° C., from the viewpoint of securing sufficient cohesive force and elastic performance suitable for workability and durability. More preferably, it is 0 to 120 ° C. The glass transition temperature (Tg) of the polymerizable macromonomer can be calculated, for example, from the monomer unit constituting the macromonomer and the content ratio thereof according to the Fox formula described later.

As a commercially available product of the polymerizable macromonomer, for example, as a product manufactured by Toagosei Co., Ltd., a macromonomer (product name) whose terminal functional group is a (meth) acryloyl group and whose polymer chain portion is polymethylmethacrylate. : 45% AA-6, AA-6SR, AA-6), a macromonomer (product name: AB-6) whose polymer chain part is polybutyl acrylate, and a macromonomer whose polymer chain part is polyisobutyl methacrylate ( Product name: AW-6S).

The said polymerizable macromonomer may be used individually by 1 type, and may use 2 or more types.
In 100% by mass of the copolymer component forming the (meth) acrylic copolymer (A), the total amount of the polymerizable macromonomer is usually 0.3 to 20% by mass, preferably 0.5 to 12% by mass, More preferably, it is 0.8 to 10% by mass. When the amount of copolymerization of the macromonomer is within the above range, it is preferable in that the cohesiveness of the copolymer can be obtained. If the amount of macromonomer copolymerization exceeds the above range, the viscosity increase during copolymerization may become severe, and if the viscosity of the coating solution containing the copolymer is too high, good coating properties to the substrate May not be obtained.

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

Among these, from the viewpoint of improving the adhesion of a substrate to an optical film such as a polarizing plate, a monomer whose polar group is a carboxyl group and / or a hydroxyl group is used, that is, selected from a carboxyl group-containing monomer and a hydroxyl group-containing monomer. It is preferable to use at least one kind.

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

A hydroxyl-containing monomer may be used individually by 1 type, and may use 2 or more types.
Examples of the carboxyl group-containing monomer include β-carboxyethyl (meth) acrylate, 5-carboxypentyl (meth) acrylate, mono (meth) acryloyloxyethyl ester succinate, and ω-carboxypolycaprolactone mono (meth) acrylate. Carboxyl group-containing (meth) acrylates such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid. Examples of the acid anhydride group-containing monomer include maleic anhydride and itaconic anhydride. Examples of the phosphate group-containing monomer include (meth) acrylic monomers having a phosphate group in the side chain, and examples of the sulfate group-containing monomer include (meth) acrylic monomers having a sulfate group in the side chain.

For example, the acid value of the (meth) acrylic copolymer (A) is preferably 117 mgKOH / g or less, more preferably 78 mgKOH / g or less.
Examples of the amino group-containing monomer include amino group-containing (meth) acrylates such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate. Examples of the amide group-containing monomer include (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, and N-hexyl (meth) acrylamide. Examples of the nitrogen heterocycle-containing monomer include vinyl pyrrolidone, acryloyl morpholine, and vinyl caprolactam. Examples of the cyano group-containing monomer include cyano (meth) acrylate and (meth) acrylonitrile.

The amount of the polar group-containing monomer used is preferably 10% by mass or less, more preferably 0.1 to 9% by mass, and further preferably 0.5 to 8% by mass in 100% by mass of the copolymer component.
When the use amount of the polar group-containing monomer is not more than the above upper limit value, the crosslinking density formed by the (meth) acrylic copolymer (A) and the crosslinking agent (B) does not become too high, and the stress relaxation property is obtained. An excellent pressure-sensitive adhesive layer is obtained. In the present invention, since a highly branched (meth) acrylic copolymer (A) having a structural unit derived from a (meth) acrylic macromonomer is used, even if the crosslinking density is lowered, that is, an adhesive. Even in a design where the gel fraction of the layer is as low as 30% by mass or less, a pressure-sensitive adhesive layer having high processability, storage property and durability can be obtained.
A polar group containing monomer may be used individually by 1 type, and may use 2 or more types.

《Other monomers》
As a copolymerization component which forms (meth) acrylic-type copolymer (A), in the range which does not impair the physical property of (meth) acrylic-type copolymer (A), for example, alkoxyalkyl (meth) acrylate, alkoxy poly Other (meth) acrylic acid esters such as alkylene glycol mono (meth) acrylates, alicyclic groups or aromatic ring-containing (meth) acrylates can be included.

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

Examples of the alkoxypolyalkylene glycol mono (meth) acrylate include methoxydiethylene glycol mono (meth) acrylate, methoxydipropylene glycol mono (meth) acrylate, ethoxytriethylene glycol mono (meth) acrylate, ethoxydiethylene glycol mono (meth) acrylate, And methoxytriethylene glycol mono (meth) acrylate.

Examples of the alicyclic group or aromatic ring-containing (meth) acrylate include cyclohexyl (meth) acrylate, benzyl (meth) acrylate, and phenyl (meth) acrylate.

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

Further, within the range where the physical properties of the (meth) acrylic copolymer (A) are not impaired, for example, styrene, methylstyrene, dimethylstyrene, trimethylstyrene, propylstyrene, butylstyrene, hexylstyrene, heptylstyrene and octylstyrene. Styrenic monomers such as alkyl styrene, fluoro styrene, chloro styrene, bromo styrene, dibromo styrene, iodinated styrene, nitro styrene, acetyl styrene and methoxy styrene, etc .; copolymerizable monomers such as vinyl acetate can also be used it can.

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

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

The (meth) acrylic copolymer (A) is preferably a copolymer obtained by the above copolymerization in the presence of a polymerization initiator. Examples of the polymerization initiator include azo initiators and peroxide polymerization initiators.

Examples of the azo initiator include 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-carbohydrate) Nitrile), 2- (carbamoylazo) isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′- Azobis (N, N'-dimethyleneisobutylamidine), 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], 2,2'-a Bis (isobutyramide) dihydrate, 4,4′-azobis (4-cyanopentanoic acid), 2,2′-azobis (2-cyanopropanol), dimethyl-2,2′-azobis (2-methylpropionate) And azo compounds such as 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide].

Examples of peroxide polymerization initiators include t-butyl hydroperoxide, cumene hydroxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, and di-i-propyl peroxydicarbonate. , Di-2-ethylhexyl peroxydicarbonate, t-butyl peroxybivalate, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, 2,2-bis (4,4- Di-t-amylperoxycyclohexyl) propane, 2,2-bis (4,4-di-t-octylperoxycyclohexyl) propane, 2,2-bis (4,4-di-α-cumylperoxycyclohexyl) ) Propane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) ) Butane, 2,2-bis (4,4-di -t- octylperoxycarbonyl cyclohexyl), and butane.

These polymerization initiators may be used alone or in combination of two or more.
The polymerization initiator is usually in the range of 0.001 to 5 parts by mass, preferably 0.005 to 3 parts by mass with respect to 100 parts by mass of the copolymer component forming the (meth) acrylic copolymer (A). Used in quantity. Moreover, you may add suitably a polymerization initiator, a chain transfer agent, a copolymerization component, and a polymerization solvent during the said polymerization reaction.

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

<< Physical properties and content of (meth) acrylic copolymer (A) >>
The weight average molecular weight (Mw) measured by the GPC method of the (meth) acrylic copolymer (A) is usually 200,000 to 1,500,000, preferably 400,000 to 1,300,000, more preferably in terms of polystyrene. Is between 500,000 and 1.1 million. Since the copolymer (A) has highly branched chains derived from the polymerizable macromonomer even if Mw is in the above range, the branched chains of the copolymer (A) are appropriately entangled with each other. The durability and workability of the pressure-sensitive adhesive layer are not deteriorated. 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) measured by the GPC method of the (meth) acrylic copolymer (A) 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 by, for example, the Fox formula from the monomer units constituting the polymer and the content ratio thereof. For example, the (meth) acrylic copolymer (A) is synthesized so that the glass transition temperature (Tg) determined by the Fox equation is usually −70 to 0 ° C., preferably −60 to −30 ° C. Can do. By using the (meth) acrylic copolymer (A) having such a glass transition temperature (Tg), a pressure-sensitive adhesive composition having excellent pressure-sensitive adhesive properties at room temperature can be obtained.
Fox formula: 1 / Tg = (W ₁ / Tg ₁ ) + (W ₂ / Tg ₂ ) +... + (W _m / Tg _m )
W ₁ + W ₂ + ... + W _m = 1
In the formula, Tg is a glass transition temperature of the (meth) acrylic copolymer (A), Tg ₁ , Tg ₂ ,..., Tg _m are glass transition temperatures of homopolymers composed of the respective monomers, W ₁ , W ₂ ,..., W _m are weight fractions of the structural units derived from the respective monomers in the copolymer (A).

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

The content of the (meth) acrylic copolymer (A) in the pressure-sensitive adhesive composition of the present invention is usually 50 to 100% by mass in 100% by mass of the solid content excluding the organic solvent (E) in the composition. More preferably, it is 60 to 99.999% by mass, and particularly preferably 80 to 99.99% by mass. When the content of the (meth) acrylic copolymer (A) is in the above range, the performance as an adhesive is balanced and the adhesive properties are excellent.

[Crosslinking agent (B)]
The pressure-sensitive adhesive composition for polarizing plates of the present invention preferably further contains a crosslinking agent (B). The crosslinking agent (B) is not particularly limited as long as it is a component that can be included in the (meth) acrylic copolymer (A) and can cause a crosslinking reaction with a polar group derived from a polar group-containing monomer. , Isocyanate compound (B1), metal chelate compound (B2), and epoxy compound (B3).

In the present invention, since the (meth) acrylic copolymer (A) having a highly branched chain derived from the polymerizable macromonomer is used, the crosslinking agent (B) is not used or only a small amount is used. That is, even in a low design where the gel fraction of the pressure-sensitive adhesive layer is 30% by mass or less, a pressure-sensitive adhesive layer having high processability, storage property and durability can be obtained.

A crosslinking agent (B) may be used individually by 1 type, and may use 2 or more types.
Among the crosslinking agents (B), it is preferable to use an isocyanate compound (B1) and / or a metal chelate compound (B2). It is preferable to form a crosslink by a covalent bond based on the isocyanate compound (B1) and / or a pseudo-crosslink by a coordinate bond based on the metal chelate compound (B2) with respect to the (meth) acrylic copolymer (A). .

In the pressure-sensitive adhesive composition of the present invention, the total content of the crosslinking agent (B) is preferably 5 parts by mass or less, more preferably 2.10 parts by mass with respect to 100 parts by mass of the (meth) acrylic copolymer (A). The amount is 5 parts by mass or less, more preferably 0.001 to 1 part by mass, and particularly preferably 0.01 to 0.5 part by mass. Thus, even if the amount of the crosslinking agent (B) used is small or not used, a pressure-sensitive adhesive layer having excellent adhesiveness, dimensional stability, and durability under a high humidity and heat environment can be realized.

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

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

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

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

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

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

Among isocyanate compounds (B1), the reaction product of trimethylolpropane and tolylene diisocyanate or xylylene diisocyanate (L-45, Soken Chemical Co., Ltd.) TD-75 manufactured by KK), isocyanurate of hexamethylene diisocyanate or tolylene diisocyanate (TSE-100 manufactured by Asahi Kasei Kogyo Co., Ltd., 2050 manufactured by Nippon Polyurethane Co., Ltd.).

An isocyanate compound (B1) may be used individually by 1 type, and may use 2 or more types.
In the pressure-sensitive adhesive composition of the present invention, the content of the isocyanate compound (B1) is preferably 5 parts by mass or less, more preferably 2.5 parts with respect to 100 parts by mass of the (meth) acrylic copolymer (A). It is not more than part by mass, more preferably not more than 1 part by mass, particularly preferably not more than 0.5 part by mass. When the content is within the above range, it is preferable in terms of easy balance between durability and stress relaxation characteristics. The lower limit when using (B1) is, for example, 0.001 part by mass, preferably 0.01 part by mass.

[Metal chelate compound (B2)]
Examples of the metal chelate compound (B2) include polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium, alkoxide, acetylacetone, and ethyl acetoacetate. Examples include a coordinated compound. Among these, an aluminum chelate compound (M-12AT manufactured by Soken Chemical Co., Ltd.) is particularly preferable. Specific examples include aluminum isopropylate, aluminum secondary butyrate, aluminum ethyl acetoacetate / diisopropylate, aluminum trisethyl acetoacetate, and aluminum trisacetylacetonate.

A metal chelate compound (B2) may be used individually by 1 type, and may use 2 or more types.
The metal chelate compound (B2) crosslinks the (meth) acrylic copolymer (A) by coordination bond (pseudocrosslinking). When the metal chelate compound (B2) is used as the cross-linking agent (B), the cross-linking is maintained at room temperature, and the polymer exhibits cohesiveness. Shows greater flexibility.

In the pressure-sensitive adhesive composition of the present invention, the content of the metal chelate compound (B2) is preferably 5 parts by mass or less, more preferably 2.10 parts by mass with respect to 100 parts by mass of the (meth) acrylic copolymer (A). 5 parts by mass or less, more preferably 1 part by mass or less, and particularly preferably 0.5 parts by mass or less. When the content is within the above range, it is preferable in terms of easy balance between durability and stress relaxation characteristics. The lower limit when using the (B2) is, for example, 0.001 part by mass, preferably 0.01 part by mass.

In the pressure-sensitive 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 (B2) is 100 parts by mass of the (B1). On the other hand, it is usually more than 0 parts by mass and 1000 parts by mass or less, more preferably more than 0 parts by mass and 600 parts by mass or less, still more preferably more than 0 parts by mass and 400 parts by mass or less. When the content is within the above range, it is preferable in terms of suppressing the bending amount and improving the adhesion of the substrate to an optical film such as a polarizing plate.

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

In the pressure-sensitive adhesive composition of the present invention, the content of the epoxy compound (B3) is preferably 2 parts by mass or less, more preferably 1 part by mass with respect to 100 parts by mass of the (meth) acrylic copolymer (A). Hereinafter, it is more preferably 0.5 parts by mass or less. The lower limit when using (B3) is, for example, 0.001 part by mass, preferably 0.01 part by mass.

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

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

The content of the silane coupling agent (C) in the pressure-sensitive adhesive composition for polarizing plates of the present invention is usually 1 part by mass or less, preferably 0 with respect to 100 parts by mass of the (meth) acrylic copolymer (A). 0.01 to 1 part by mass, more preferably 0.05 to 0.5 part by mass. When the content is in the above range, peeling of the polarizing plate in a high humidity environment and bleeding of the silane coupling agent (C) in a high temperature environment tend to be prevented.

[Antistatic agent (D)]
An antistatic agent (D) can be used in order to reduce the surface resistance value of the adhesive composition for polarizing plates of this invention, for example. Examples of the antistatic agent (D) include a surfactant, an ionic compound, and a conductive polymer.

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

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

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

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

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

Examples of the conductive polymer include polythiophene, polyaniline, polypyrrole, and derivatives thereof.
The content of the antistatic agent (D) in the pressure-sensitive adhesive composition for polarizing plates of the present invention is usually 3 parts by mass or less, preferably 0.8 parts per 100 parts by mass of the (meth) acrylic copolymer (A). The amount is from 01 to 3 parts by mass, more preferably from 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 in the column of the (meth) acrylic-type copolymer (A) is mentioned. For example, the pressure-sensitive adhesive composition can be prepared by mixing the polymer solution containing the (meth) acrylic copolymer (A) and the polymerization solvent obtained by the above copolymerization and the crosslinking agent (B). it can. In the pressure-sensitive adhesive composition of the present invention, the content of the organic solvent is usually 50 to 90% by mass, preferably 60 to 85% by mass.

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

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

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

(Adhesive layer)
The pressure-sensitive adhesive layer of the present invention can be obtained, for example, by applying and drying the above-mentioned pressure-sensitive adhesive composition; or, specifically, by proceeding with a crosslinking reaction in the above-mentioned pressure-sensitive adhesive composition, specifically (meth) It can be obtained by crosslinking the acrylic copolymer (A) with a crosslinking agent (B).

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

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

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

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

The pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention has a gel fraction of 30% by mass or less, preferably 0 from the viewpoints of distortion suppression of the polarizing plate, cohesion, adhesion, and removability. -25% by mass, more preferably 0-20% by mass. Since the (meth) acrylic copolymer (A) has highly branched chains derived from the polymerizable macromonomer even if the gel fraction is in the above range, the branched chains of the copolymer (A) are They can be appropriately entangled with each other, and the durability and workability of the pressure-sensitive adhesive layer do not deteriorate. When the gel fraction exceeds the above range, the pressure-sensitive adhesive layer may not be able to sufficiently absorb or relax the stress caused by the dimensional change of the polarizing plate under a high temperature / high humidity heat environment.

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

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

The conditions for forming the pressure-sensitive adhesive layer and the gel fraction are the same as the conditions described in the column [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 adhesive performance. The film thickness of the substrate and the cover film is not particularly limited, but is usually 10 to 125 μm, preferably 25 to 75 μm.

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

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

The thickness of the polarizing plate is usually 30 to 250 μm, preferably 50 to 200 μm.
There is no restriction | limiting in particular in the method of forming an adhesive layer in the polarizing plate surface, The method of apply | coating and drying the said adhesive composition directly using a bar coater etc. on the polarizing plate surface, The adhesive sheet for polarizing plates of this invention has A method of transferring the pressure-sensitive adhesive layer to the surface of the polarizing plate and aging is mentioned. The conditions for drying and aging, the range of the gel fraction, and the like are the same as the conditions described in the [Adhesive layer] column.

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 terms of dry film thickness. In addition, the adhesive layer should just be formed in at least one surface of a polarizing plate, the aspect in which an adhesive layer is formed only in the single side | surface of a polarizing plate, the aspect in which an adhesive layer is formed in both surfaces of a polarizing plate Is mentioned.

Moreover, the layer which has other functions, such as a protective layer, a glare-proof layer, a phase difference layer, a viewing angle improvement layer, for example may be laminated | stacked on the said polarizing plate.
A liquid crystal element is produced by providing the polarizing plate with the pressure-sensitive adhesive layer of the present invention obtained as described above on the substrate surface of the liquid crystal cell. Here, the liquid crystal cell has a structure in which a liquid crystal layer is sandwiched between two substrates.

Examples of the substrate of the liquid crystal cell include a glass plate. The thickness of the substrate is usually 0.1 to 1 mm, preferably 0.15 to 0.8 mm. Especially in this invention, the curvature of a polarizing plate and a board | substrate can be suppressed by using the said adhesive composition. Therefore, even when the thickness of the substrate is small (eg, 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 described more specifically based on examples, but the present invention is not limited to these examples. In the following description of Examples and the like, “part” means “part by mass” unless otherwise specified.

[GPC and GPC-MALS]
For the (meth) acrylic copolymer, the gel permeation chromatography method (GPC method) is used to determine the weight average molecular weight (Mw) and the number average molecular weight (Mn) under the following conditions. The degree of branching was determined using a laser light scattering detector (GPC-MALS) under the following conditions.
・ Measurement device: HLC-8320GPC (manufactured by Tosoh Corporation)
-GPC column configuration: The following four columns (all manufactured by Tosoh Corporation)
(1) TSKgel HxL-H (guard column)
(2) TSKgel GMHxL
(3) TSKgel GMHxL
(4) TSKgel G2500HxL
・ Flow rate: 1.0 mL / min
-Column temperature: 40 ° C
Sample concentration: 1.5% (w / v) (diluted with tetrahydrofuran)
・ Mobile phase solvent: Tetrahydrofuran ・ Detector: DAWN HELEOS (MALS detector) + Optilab rEX (RI detector)
・ Standard polystyrene conversion (when measuring Mw and Mn)

[Synthesis Example 1]
In a reactor equipped with a stirrer, reflux condenser, thermometer and nitrogen introduction tube, 98 parts of n-butyl acrylate and a methyl methacrylate macromonomer having a methacryloyl group at the terminal (trade name: AA-6, Toa Gosei Co., Ltd.) Manufactured, Tg: 105 ° C., Mn: 6,000) 1 part, 4-hydroxybutyl acrylate 1 part, and ethyl acetate solvent 100 parts were charged, and the temperature was raised to 80 ° C. while introducing nitrogen gas. Next, 0.1 part of 2,2′-azobisisobutyronitrile was added, and a polymerization reaction was performed at 80 ° C. for 6 hours in a nitrogen gas atmosphere. After completion of the reaction, it was diluted with ethyl acetate to prepare a polymer solution having a solid content concentration of 30% by mass. The obtained (meth) acrylic copolymer A has a weight average molecular weight (Mw) of 700,000, a molecular weight distribution (Mw / Mn) of 7.2, a degree of branching of 0.54, and an acid value. Was 0 mg KOH / g.

[Synthesis Examples 2 to 14]
A polymer solution having a solid content concentration of 30% by mass was prepared in the same manner as in Synthesis Example 1 except that the copolymerization component and the polymerization initiator used in the polymerization reaction were changed as described in Table 1. The results are shown in Table 1.

In Table 1, MMA macromonomer is methyl methacrylate macromonomer having a methacryloyl group at the end (trade name: AA-6, manufactured by Toa Gosei Co., Ltd., Tg: 105 ° C., Mn: 6,000), and BA macromonomer. Represents a butyl acrylate macromonomer having a terminal acryloyl group (trade name: AB-6, manufactured by Toa Gosei Co., Ltd., Tg: -50 ° C., Mn: 6,000).

[Example 1]
(1) Preparation of pressure-sensitive adhesive composition (meth) acrylic polymer solution obtained in Synthesis Example 1 (solid content concentration: 30% by mass) and 100 parts (meth) acrylic polymer contained in the solution (solid content) In contrast, 0.08 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 Shin-Etsu Chemical Co., Ltd. as a silane coupling agent "KBM-403" (solid content 100%) 0.2 parts made by Daiichi Kogyo Seiyaku Co., Ltd. "AS-804" (solid content 100%) 1 part was mixed as an antistatic agent An agent composition was obtained.

(2) Preparation of pressure-sensitive adhesive sheet After removing bubbles, the pressure-sensitive adhesive composition obtained in (1) above was applied onto a polyethylene terephthalate film (PET film) that had been subjected to release treatment using a doctor blade. The film was dried for 30 minutes to form a coating film having a dry film thickness of 20 μm. Two PET films were obtained by further laminating the peeled PET film on the surface of the coating film opposite to the surface on which the PET film was applied, and leaving it to stand for aging in a 23 ° C./50% RH environment for 7 days. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a thickness of 20 μm sandwiched between the layers was obtained.

(3) Preparation of polarizing plate with pressure-sensitive adhesive layer After removing bubbles, the pressure-sensitive adhesive composition obtained in (1) above was applied onto a polyethylene terephthalate film (PET film) subjected to a release treatment using a doctor blade, It dried at 90 degreeC for 3 minute (s), and obtained the sheet | seat which has a coating film with a dry film thickness of 20 micrometers. The sheet and the polarizing plate (thickness: 110 μm, layer structure: triacetyl cellulose film / polyvinyl alcohol film / triacetyl cellulose film) were bonded together so that the coating film and the polarizing plate were in contact with each other, and 23 ° C./50%. The plate was allowed to stand and matured for 7 days under the conditions of RH to obtain a polarizing plate with a pressure-sensitive adhesive layer having a PET film, a pressure-sensitive adhesive layer having a thickness of 20 μm, and a polarizing plate.

[Examples 2 to 14, Comparative Examples 1 to 3]
Example 1 is different from Example 1 except that the (meth) acrylic polymer solution is changed to the polymer solution obtained in Synthesis Examples 2 to 14 and / or the composition is changed as shown in Table 2. Similarly, a pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet, and a polarizing plate with a pressure-sensitive adhesive layer were obtained. In Table 2, “M-12AT” represents “M-12AT” (solid content: 10% by mass, toluene, acetylacetone solution) manufactured by Soken Chemical Co., Ltd., which is a metal chelate compound.

[Evaluation]
[Gel fraction]
About 0.1 g of the pressure-sensitive adhesive was collected in a sampling bottle from the pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples, and 30 mL of ethyl acetate was added and shaken for 4 hours. The contents of the sample bottle were made of 200 mesh stainless steel. The mixture was filtered through a wire mesh, the residue on the wire mesh was dried at 100 ° C. for 2 hours, and the dry weight was measured. The gel fraction of the pressure-sensitive adhesive was determined by the following formula.
Gel fraction (%) = (Dry weight / Adhesive sampling weight) × 100 (%)

[Creep value]
The polarizing plate with a pressure-sensitive adhesive layer obtained in Examples and Comparative Examples (a laminate comprising PET film / pressure-sensitive adhesive layer / polarizing plate) was cut into a width of 10 mm and a length of 100 mm, and the peeled PET film was peeled off. And it bonded together so that the said adhesive layer might contact the said glass plate and it might become a bonding area of 10 mm x 10 mm on the alkali treatment glass plate, and the adhesion processing polarizing plate test piece for evaluation was obtained.

About the adhesion processing polarizing plate test piece for evaluation, it autoclaved (50 degreeC, 5 atm), and left still for 24 hours in 23 degreeC / 50% RH atmosphere. Next, the test piece was set in a chamber BOX of a minute creep measuring machine with a fixing chuck portion having a length of 15 mm. At a tensile load of 800 g and a tensile time of 1000 seconds, the evaluation-treated pressure-sensitive adhesive polarizing plate in the test piece was pulled in parallel with the adhesive surface between the polarizing plate and the glass plate and in the length direction of the polarizing plate, The distance (μm) of the gap between the glass plate and the polarizing plate in the test piece was measured as the creep value.

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

[Bending]
A test piece was prepared by cutting the polarizing plate with the pressure-sensitive adhesive layer (PET film / pressure-sensitive adhesive layer / laminate comprising the polarizing plate) obtained in Examples and Comparative Examples into a size of 35 mm × 400 mm (stretching axis direction). did. The PET film is peeled off from the test piece, and the laminate composed of the pressure-sensitive adhesive layer / polarizing plate is laminated on one side of a glass plate having a thickness of 0.7 mm and 40 mm × 410 mm using a laminator roll. Affixed to touch. The obtained laminate was allowed to stand in a 23 ° C./50% RH environment for 24 hours, and then held in an oven at 60 ° C. for 72 hours. One end was fixed to a wall surface perpendicular to the floor surface, and the amount of lifting at the opposite end was measured with a ruler. Measurements were taken immediately after removal from the oven and after 24 hours.

[Durability test]
A polarizing plate with a pressure-sensitive adhesive layer obtained in Examples and Comparative Examples (a laminate comprising PET film / pressure-sensitive adhesive layer / polarizing plate) was cut into a size of 150 mm × 250 mm to prepare a test piece. The PET film was peeled from the test piece, and a laminate composed of the pressure-sensitive adhesive layer / polarizing plate was attached to one side of a 2 mm thick glass plate so that the pressure-sensitive adhesive layer and the glass plate were in contact with each other using a laminator roll. . The obtained laminate was held in an autoclave adjusted to 50 ° C./5 atm for 20 minutes to prepare a test plate. Two similar test plates were prepared. The test plate is allowed to stand for 500 hours under conditions of a temperature of 80 ° C. (heat resistance) or a temperature of 60 ° C./humidity of 90% RH (humid heat resistance), and the occurrence of foaming and tearing in the adhesive layer according to the following criteria: Was observed and evaluated. Foaming occurs when cohesion is insufficient, and tearing occurs when stress relaxation is insufficient.

(Foam)
-AA: Foaming is not seen at all.
-BB: The area of foaming is less than 5% of the whole.
-CC: The area of foaming is 5% or more of the whole.

(Rupture)
-AA: No tear is seen at all.
-BB: The area of a tear is less than 5% of the whole.
-CC: The area of a tear is 5% or more of the whole.

In the composition of Comparative Example 2, a (meth) acrylic copolymer having a degree of branching of 0.59 is used and the gel fraction is designed to be as high as 57% by mass. However, although foaming was not recognized in the durability evaluation, many tears occurred.

In the composition of Comparative Example 3, a (meth) acrylic copolymer having a degree of branching of 0.59 is used and the gel fraction is designed to be 0% by mass. Occurred.

In the composition of Comparative Example 1, a (meth) acrylic copolymer having a degree of branching of 0.54 is used, but because the gel fraction is designed as high as 65% by mass, bending evaluation after 24 hours is performed. Was not satisfactory (5.0 mm or more), and although no foaming was observed in the durability evaluation, many tears occurred.

On the other hand, the composition of the example uses a (meth) acrylic copolymer having a structural unit derived from a (meth) acrylic macromonomer and having a degree of branching of 0.55 or less, and a gel fraction of 30. Since it was designed at a mass% or less, the bending evaluation after 24 hours was high (3.5 mm or less), and the occurrence of foaming and tearing was in an acceptable range in the durability evaluation.

Claims (10)

1. (A) A gel permeation chromatography method / multi-angle laser beam obtained by copolymerizing a copolymer component containing (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms in the alkyl group and a polymerizable macromonomer A pressure-sensitive adhesive composition for a polarizing plate containing a (meth) acrylic copolymer having a degree of branching of 0.55 or less as measured by a scattering detector (GPC-MALS),
   The pressure-sensitive adhesive composition for polarizing plates, wherein the pressure-sensitive adhesive formed from the composition has a gel fraction of 30% by mass or less.
2. The (meth) acrylic copolymer (A) is a copolymer obtained by further copolymerizing a polar group-containing monomer together with the (meth) acrylic acid alkyl ester and a polymerizable macromonomer. The pressure-sensitive adhesive composition for polarizing plate according to 1.
3. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the amount of the polar group-containing monomer used in the copolymerization is 10% by mass or less in 100% by mass of the copolymerization component.
4. The weight average molecular weight (Mw) measured by a gel permeation chromatography method (GPC method) of the (meth) acrylic copolymer (A) is 200,000 to 1,500,000. The pressure-sensitive adhesive composition for polarizing plate according to claim 1.
5. The pressure-sensitive adhesive composition for polarizing plates according to any one of claims 1 to 4, further comprising (B) a crosslinking agent.
6. The pressure-sensitive adhesive composition for a polarizing plate according to claim 5, wherein the crosslinking agent (B) is at least one selected from an isocyanate compound (B1), a metal chelate compound (B2), and an epoxy compound (B3).
7. The pressure-sensitive adhesive composition for a polarizing plate according to claim 5 or 6, wherein the content of the crosslinking agent (B) is 5 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic copolymer (A). object.
8. A pressure-sensitive adhesive layer for a polarizing plate, which is formed from the pressure-sensitive adhesive composition for a polarizing plate according to any one of claims 1 to 7, and has a gel fraction of 30% by mass or less.
9. A pressure-sensitive adhesive sheet for polarizing plates comprising the pressure-sensitive adhesive layer according to claim 8.
10. A polarizing plate with a pressure-sensitive adhesive layer, comprising the polarizing plate and the pressure-sensitive adhesive layer according to claim 8 on at least one surface of the polarizing plate.