JP2021080421A - Adhesive composition, adhesive, adhesive for polarizing plate, and image display device - Google Patents

Abstract

To provide an adhesive composition forming an adhesive which is excellent in durability under high temperature environment and can achieve reworkability and warpage suppression of a polarizing plate when a glass plate and metal such as a conductive layer used in a liquid crystal cell are formed into an adherend.SOLUTION: An adhesive composition contains an acrylic resin (A), in which the acrylic resin (A) is an acrylic resin obtained by polymerizing a polymerization component containing a polymerizable macromonomer (a1) that is copolymerized with at least two kinds of alkyl (meth)acrylate and has a glass transition temperature of -40 to 100°C.SELECTED DRAWING: None

Description

The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive, a pressure-sensitive adhesive for a polarizing plate, and an image display device. More specifically, the present invention has excellent durability even in a high-temperature environment, and further achieves both reworkability and suppression of warpage of the polarizing plate. It relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive, a pressure-sensitive adhesive for a polarizing plate, and an image display device for forming a possible pressure-sensitive adhesive.

Conventionally, a polarizing plate made of a polyvinyl alcohol-based film or the like to which polarization property is imparted and whose both sides are coated with a protective film is laminated on the surface of a liquid crystal cell in which an oriented liquid crystal component is sandwiched between two glass plates. A liquid crystal display device is manufactured. The lamination of the polarizing plate on the surface of the liquid crystal cell is usually carried out by abutting and pressing the pressure-sensitive adhesive layer provided on the surface of the polarizing plate against the surface of the liquid crystal cell.

The adhesive used for bonding the polarizing plate (protective film) and the liquid crystal cell (glass plate) is, for example, a polarizing plate floating from the liquid crystal cell (glass plate) in a high temperature environment or a high temperature and high humidity environment. Durability is required so that it will not come off or come off.

Further, when a problem such as foreign matter is mixed or misaligned occurs during the bonding of the polarizing plate, it is necessary to peel the polarizing plate from the liquid crystal cell and bond it again. When the polarizing plate is peeled off from the liquid crystal cell, reworkability (removability) is required so that the polarizing plate can be easily peeled off from the liquid crystal cell without causing damage such as a gap change or breakage of the liquid crystal cell.

Further, the polarizing plate lacks dimensional stability because it easily shrinks due to heat in a high temperature and high humidity environment, and the polarizing plate may warp. In recent years, the thickness of the liquid crystal cell has been reduced (eg, the liquid crystal cell has been reduced. With the thinning of the constituent substrates) and the thinning of the polarizing plate, the warp of the liquid crystal cell in a high temperature and high humidity environment has become a bigger problem. Examples of the cause of the warp of the liquid crystal cell include the inability of the pressure-sensitive adhesive layer to follow the heat shrinkage (dimensional change) of the polarizing plate and the low stress relaxation characteristics of the pressure-sensitive adhesive layer.
As described above, the adhesive used for bonding the polarizing plate and the liquid crystal cell is required to have reworkability and warpage suppression in addition to durability.

As a method for improving such reworkability, for example, the (meth) acrylate-based monomer exceeds 94 parts by mass and is 98.9 parts by mass or less, the macromonomer is 1 part by mass or more and 5 parts by mass or less, and a carboxyl group and an amino group. , 0.1 part by mass or more and less than 1 part by mass of a (meth) acrylate-based monomer containing at least one crosslinkable functional group selected from the group consisting of an amide group, a hydroxy group and an acetoacetoxy group (meth). ) A pressure-sensitive adhesive composition containing an acrylic polymer has been proposed (see, for example, Patent Document 1).
Further, as a method for improving warpage suppression, for example, it is obtained by copolymerizing a copolymerization component containing a (meth) acrylic acid alkyl ester having 4 to 18 carbon atoms and a polymerizable macromonomer (meth). Adhesive compositions for polarizing plates containing an acrylic copolymer have been proposed (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2010-150400 International Publication No. 2015/141382

However, the disclosed techniques of Patent Documents 1 and 2 have advantages and disadvantages, and Patent Document 1 does not consider warpage suppression even if improvement in reworkability is observed, while Patent Document 2 improves warpage suppression. However, the reworkability is not satisfactory because the gel fraction is low.
Stress relaxation property is required to suppress warpage, and in order to obtain stress relaxation property, it is common to lower the degree of cross-linking of the adhesive, but lowering the degree of cross-linking tends to worsen the reworkability. Therefore, it is difficult to achieve both warpage suppression and reworkability, and the pressure-sensitive adhesive for polarizing plates is required to have both of these performances.

Therefore, in the present invention, under such a background, for example, when a metal such as a glass plate or a conductive layer used for a liquid crystal cell is used as an adherend, the durability is excellent even in a high temperature environment, and further, rework is performed. It is an object of the present invention to provide a pressure-sensitive adhesive composition, a pressure-sensitive adhesive, a pressure-sensitive adhesive for a polarizing plate, and an image display device for forming a pressure-sensitive adhesive capable of achieving both properties and suppression of warpage of the polarizing plate.

However, as a result of intensive studies in view of such circumstances, in the pressure-sensitive adhesive composition containing the acrylic resin, at least two kinds of copolymerization components are copolymerized as the polymerization components of the acrylic resin. We have found that by using a polymerizable macromonomer having a specific glass transition temperature, an adhesive having excellent durability in a high temperature environment and also having excellent reworkability and warpage suppression can be obtained. The invention was completed.

That is, the present invention is a pressure-sensitive adhesive composition containing an acrylic resin (A), wherein the acrylic resin (A) is copolymerized with at least two types of alkyl (meth) acrylates, and the glass transition temperature is high. The first gist is a pressure-sensitive adhesive composition which is an acrylic resin obtained by polymerizing a polymerization component containing a polymerizable macromonomer (a1) at 40 to 100 ° C.

Further, in the present invention, the pressure-sensitive adhesive composition of the first gist is crosslinked to form the second gist, and the pressure-sensitive adhesive for polarizing plates using the pressure-sensitive adhesive of the second gist is the second gist. This is the gist of 3. Further, the image display device formed by bonding the polarizing plate and the liquid crystal cell with the adhesive of the second gist is the fourth gist.

In a pressure-sensitive adhesive composition containing an acrylic resin, it is common practice to relieve stress, reduce the gel fraction, and reduce the degree of cross-linking in order to suppress warpage, but on the other hand, gel for reworkability. It is necessary to raise the fraction to some extent. However, when a conventional polymerizable macromonomer having a relatively high glass transition temperature is used in a crosslinked state having a relatively high gel fraction, the interaction of side chain entanglement becomes too large, so that the stress relaxation property is lowered. The warp will worsen.
When the gel fraction is high to some extent, for example, when it exceeds 40%, by using a polymerizable macromonomer whose glass transition temperature is in a predetermined temperature range, the cohesive force improvement effect and stress due to the entanglement of side chains are achieved. They found that it is an adhesive that has both relaxation properties and is excellent in both reworkability and warpage suppression.

The present invention is a pressure-sensitive adhesive composition containing an acrylic resin (A), wherein the acrylic resin (A) is copolymerized with at least two types of alkyl (meth) acrylates, and the glass transition temperature is −40. It is an acrylic resin obtained by polymerizing a polymerization component containing a polymerizable macromonomer (a1) at ~ 100 ° C. Therefore, the pressure-sensitive adhesive obtained by using the above-mentioned pressure-sensitive adhesive composition exhibits high durability even in a high-temperature environment, and can achieve both reworkability and warpage suppression. Then, the pressure-sensitive adhesive composition of the present invention can obtain a pressure-sensitive adhesive suitable for various uses, particularly for a polarizing plate.

Hereinafter, the present invention will be described in detail.
In the present invention, "(meth) acrylic" means acrylic or methacrylic, "(meth) acryloyl" means acryloyl or methacryloyl, and "(meth) acrylate" means acrylate or methacrylate. .. The "acrylic resin" is a resin obtained by polymerizing a polymerization component containing at least one (meth) acrylate-based monomer.

The pressure-sensitive adhesive composition of the present invention contains an acrylic resin (A) containing a structural portion derived from a polymerizable macromonomer (a1) having a glass transition temperature in a predetermined range. Hereinafter, each component contained in the pressure-sensitive adhesive composition will be described.

<Acrylic resin (A)>
As described above, the acrylic resin (A) used in the present invention is obtained by polymerizing a polymerization component containing a polymerizable macromonomer (a1). Further, the acrylic resin (A) contains an alkyl (meth) acrylate (a2) in addition to the polymerizable macromonomer (a1) as a polymerization component, preferably a functional group-containing monomer (a3), which is necessary. It contains other copolymerizable monomer (a4) depending on the above.

[Polymerizable macromonomer (a1)]
The polymerizable macromonomer is a high molecular weight monomer having a polymerizable functional group, and in particular, the polymerizable macromonomer (a1) used in the present invention has a polymerizable unsaturated group at the end of the polymer chain. Is preferable.

Further, the polymerizable macromonomer (a1) used in the present invention has a predetermined glass transition temperature.
The glass transition temperature (Tg) of the polymerizable macromonomer is -40 to 100 ° C. from the viewpoint of durability, rework, and suppression of warpage. It is more preferably 0 to 95 ° C, still more preferably 40 to 90 ° C. If the glass transition temperature is too low, durability and reworkability tend to decrease, and if the glass transition temperature is too high, the effect of suppressing warpage tends to decrease.
The glass transition temperature (Tg) of the polymerizable macromonomer (a1) can be calculated, for example, from the monomer units constituting the polymerizable macromonomer (a1) and the content ratio thereof by the Fox formula described later.

The number average molecular weight (Mn) of the polymerizable macromonomer (a1) is preferably 1000 to 200,000 in terms of mechanical properties and durability of the obtained pressure-sensitive adhesive. The lower limit of Mn of the polymerizable macromonomer (a1) is more preferably 2000, still more preferably 3000, and particularly preferably 3500. The upper limit of Mn of the polymerizable macromonomer (a1) is more preferably 100,000, still more preferably 50,000, and particularly preferably 20,000. When Mn is at least the lower limit value, the cohesive force when the acrylic resin (A) is used tends to be improved, and the durability tends to be excellent, which is preferable. On the other hand, if Mn is not more than the upper limit value, the coating suitability of the resin solution is good and a uniform coating film tends to be easily obtained.

The number average molecular weight (Mn) is a number average molecular weight converted to a standard polystyrene molecular weight, and is displayed on a high performance liquid chromatograph (“ACQUITY APC system” manufactured by Waters) with a column: ACQUITY APC XT 450 (molecular weight range: 20000). Measured by using one ACQUITY APC XT 200 (molecular weight range: 3000 to 70000) and two ACQUITY APC XT 45 (molecular weight range: 200 to 5000) in series, for a total of four. The weight average molecular weight is also measured in the same way. Further, the degree of dispersion (weight average molecular weight / number average molecular weight) can be obtained from the number average molecular weight and the weight average molecular weight.

The polymerizable macromonomer (a1) is obtained by copolymerizing a copolymerization component containing at least two kinds of alkyl (meth) acrylates, and the number of alkyl (meth) acrylates used for the copolymerization is usually large. There are 2 to 5 types, preferably 2 to 3 types, and particularly preferably 2 types.

Examples of the alkyl (meth) acrylate include (meth) acrylates having an alkyl group having 1 to 30 carbon atoms, preferably 1 to 26 carbon atoms.

Among the above alkyl (meth) acrylates, (meth) acrylate (a1-1) having an alkyl group having 1 to 4 carbon atoms (preferably, the alkyl group has 1 to 2 carbon atoms) is contained as a copolymerization component. Is preferable from the viewpoint of improving durability and reworkability.

Specific examples of the (meth) acrylate (a1-1) having 1 to 4 carbon atoms in the alkyl group include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and i-. Examples thereof include propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, and methyl (meth) acrylate is preferable.

The glass transition temperature when the alkyl group is a homopolymer of (meth) acrylate (a1-1) having 1 to 4 carbon atoms [hereinafter, abbreviated as the glass transition temperature of (meth) acrylate (a1-1). There is. ] Is usually −50 to 120 ° C., preferably −20 to 110 ° C., and particularly preferably 0 to 105 ° C. If the glass transition temperature is too low, the durability and reworkability tend to decrease, and if the glass transition temperature is too high, the effect of suppressing warpage tends to decrease.

Further, as the copolymerization component of the polymerizable macromonomer (a1), the (meth) acrylate (a1-2) having an alkyl group having 5 to 22 carbon atoms (preferably, the alkyl group has 6 to 14 carbon atoms). Is preferable from the viewpoint of suppressing warpage.

Specific examples of the (meth) acrylate (a1-2) having 5 to 22 carbon atoms in the alkyl group include n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and n-octyl (meth). ) Acrylate, isodecyl (meth) acrylate, tridecyl (meth) acrylate, n-lauryl (meth) acrylate, cetyl (meth) acrylate, n-stearyl (meth) acrylate and the like, among which 2-ethylhexyl (meth) acrylate is used. ) Acrylate, tridecyl (meth) acrylate, n-lauryl (meth) acrylate are preferable.

The glass transition temperature when the alkyl group is a homopolymer of (meth) acrylate (a1-2) having 5 to 22 carbon atoms [hereinafter, abbreviated as the glass transition temperature of (meth) acrylate (a1-2). There is. ] Is usually −80 to 30 ° C., preferably −70 to 0 ° C., and particularly preferably −60 to −10 ° C. If the glass transition temperature is too low, the durability tends to decrease, and if the glass transition temperature is too high, the effect of suppressing warpage tends to decrease.

In particular, as the copolymerization component of the polymerizable macromonomer (a1), the (meth) acrylate (a1-1) having 1 to 4 carbon atoms in the alkyl group and the (meth) having 5 to 22 carbon atoms in the alkyl group. It is preferable to contain acrylate (a1-2) from the viewpoint of high durability, reworkability and suppression of warpage.

Difference in carbon number of alkyl group between (meth) acrylate (a1-1) having 1 to 4 carbon atoms of the alkyl group and (meth) acrylate (a1-2) having 5 to 22 carbon atoms of the alkyl group. Is preferably in the range of 3 to 15 from the viewpoint of high durability, reworkability and suppression of warpage, particularly preferably 4 to 12, and further 7 to 11.

Further, the difference in glass transition temperature between the (meth) acrylate (a1-1) having 1 to 4 carbon atoms in the alkyl group and the (meth) acrylate (a1-2) having 5 to 22 carbon atoms in the alkyl group. The absolute value of is usually 20 ° C. or higher, preferably 50 ° C. or higher, particularly preferably 100 ° C. or higher, from the viewpoint of high durability, reworkability and suppression of warpage. The upper limit is usually 190 ° C.

In the copolymerization component of the polymerizable macromonomer (a1), the (meth) acrylate (a1-1) having 1 to 4 carbon atoms in the alkyl group and the (meth) acrylate having 5 to 22 carbon atoms in the alkyl group. The blending ratio with (a1-2) [(a1-1) / (a1-2)] shows high durability, and is usually 99/1 to 1/1 on a weight basis from the viewpoint of reworkability and suppression of warpage. It is 99, preferably 95/5 to 30/70, and more preferably 90/10 to 60/40.

Further, as the copolymerization component for obtaining the polymerizable macromonomer (a1), the above-mentioned alkyl (meth) acrylate (for example, in the range of 10% by weight or less of the copolymerization component) that does not inhibit the effect of the present invention. Other monomers other than a1-1) and (a1-2) may be contained.

Examples of the other monomers include, for example,
Hydroxy group-containing (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and glycerol (meth) acrylate;
(Meta) acrylic acid, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, 2- (meth) acryloyloxypropyl hexahydrophthalic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxy Propylphthalic acid, 2- (meth) acryloyloxyethyl maleic acid, 2- (meth) acryloyloxypropylmaleic acid, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxypropyl succinic acid, crotonic acid , Acryloyl group-containing vinyl monomer such as fumaric acid, maleic acid, itaconic acid, monomethyl maleate, monomethyl itaconic acid;
An acid anhydride group-containing vinyl monomer such as maleic anhydride and itaconic anhydride;
Epoxy group-containing vinyl-based monomers such as glycisyl (meth) acrylate, glycisyl α-ethyl acrylate, and 3,4-epoxybutyl (meth) acrylate;
Amino group-containing (meth) acrylate-based vinyl monomers such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate;
(Meta) acrylamide, N-t-butyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, diacetone acrylamide, maleic acid amide, maleimide Vinyl-based monomer containing amide group such as;
Vinyl-based monomers such as styrene, α-methylstyrene, vinyltoluene, (meth) acrylonitrile, vinyl chloride, vinyl acetate, and vinyl propionate;
Divinylbenzene, ethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate ) Acrylate, Tripropylene glycol di (meth) acrylate, Trimethylol propantri (meth) acrylate, Allyl (meth) acrylate,
And so on.
The above-mentioned other monomers can be used alone or in combination of two or more.

From the viewpoint of durability, it is preferable that the side chain of the polymerizable macromonomer (a1) has a polar group, and the raw material monomer capable of having the polar group in the side chain includes, for example, a hydroxyl group (meth). ) Consists of acrylate, carboxy group-containing vinyl-based monomer, acid anhydride group-containing vinyl-based monomer, amino group-containing (meth) acrylate-based vinyl-based monomer, and amide group-containing vinyl-based monomer. At least one polar group-containing monomer selected from the group is used, and among the polar group-containing monomers, a hydroxyl group-containing (meth) acrylate is preferable from the viewpoint of durability.

As the polymerizable macromonomer (a1) used in the present invention, the above alkyl (meth) acrylate and the above other monomers are appropriately selected so that the glass transition temperature is within a predetermined range, and these are acrylics described later. It can be obtained by copolymerizing with the same method as the system resin (A).

The content of the polymerizable macromonomer (a1) is preferably 0.1 to 20% by weight, particularly preferably 0.2 to 10% by weight, based on the polymerization component constituting the acrylic resin (A). , More preferably 0.5 to 5% by weight. Within such a content range, high durability is exhibited, and reworkability and suppression of warpage are better.

[Alkyl (meth) acrylate (a2)]
The alkyl (meth) acrylate (a2) is, for example, one in which the alkyl group usually has 1 to 20 carbon atoms (preferably 1 to 18, particularly preferably 1 to 12, still more preferably 1 to 8). Examples thereof include aliphatic alkyl (meth) acrylates, and specific examples thereof include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, and t-. Butyl (meth) acrylate, n-propyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, Examples thereof include cetyl (meth) acrylate and stearyl (meth) acrylate. These may be used alone or in combination of two or more.

Among these alkyl (meth) acrylates (a2), methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, and 2-ethylhexyl are excellent in adhesive properties and stability during polymerization. (Meta) acrylate is preferable, and n-butyl (meth) acrylate is particularly preferable.

The content of the alkyl (meth) acrylate (a2) is preferably 10% by weight or more, particularly preferably 30 to 99.9% by weight, based on the polymerization component constituting the acrylic resin (A). It is more preferably 50 to 98% by weight, and particularly preferably 60 to 95% by weight. If the content is too small, the sticky physical properties and durability tend to decrease.

Further, as a polymerization component constituting the acrylic resin (A), methyl (meth) acrylate, ethyl (meth) acrylate, and n-butyl (meth) are excellent in compatibility with the ionic compound (D) described later. It is preferable that at least one kind of acrylate, preferably n-butyl (meth) acrylate, is contained, and the content thereof is particularly preferably 10% by weight based on the polymerization component constituting the acrylic resin (A). The above is more preferably 30% by weight or more, and particularly preferably 40 to 99.9% by weight.

[Functional group-containing monomer (a3)]
Next, the functional group-containing monomer (a3) will be described.
The functional group-containing monomer (a3) in the present invention refers to a copolymerizable ethylenically unsaturated monomer such as a hydroxyl group-containing monomer, a carboxy group-containing monomer, and a nitrogen atom-containing monomer, and these may be used alone or in combination of two types. The above can be used together. The functional group-containing monomer (a3) excludes the polymerizable macromonomer (a1).

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, and 8-hydroxyoctyl ( Acrylic acid hydroxyalkyl ester such as meta) acrylate, caprolactone-modified monomer such as caprolactone-modified 2-hydroxyethyl (meth) acrylate, oxyalkylene-modified monomer such as diethylene glycol (meth) acrylate and polyethylene glycol (meth) acrylate; 2-acryloy Primary hydroxyl group-containing monomers such as loxyethyl-2-hydroxyethylphthalic acid, N-methylol (meth) acrylamide, hydroxyethyl acrylamide; 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-chloro Secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth) acrylate; 2,2-dimethyl2-hydroxyethyl (meth) acrylate and the like can be mentioned.

Among the above hydroxyl group-containing monomers, a primary hydroxyl group-containing monomer is preferable in terms of excellent reactivity with the cross-linking agent (B) described later, and 2-hydroxyethyl (meth) acrylate is preferable in terms of stability during polymerization. It is preferable to use 4-hydroxybutyl (meth) acrylate because it has a high reactivity with the cross-linking agent (B) and shortens aging. Further, 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate are preferable because they have few impurities such as di (meth) acrylate at the time of monomer preparation, and high purity can be obtained and easy to manufacture.

When the above-mentioned hydroxyl group-containing monomer is prepared and used, or when a commercially available product is used, it is preferable to use one having an impurity di (meth) acrylate content of 0.5% by weight or less, and it is particularly preferable. 0.2% by weight or less, more preferably 0.1% by weight or less, specifically, 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) having a low impurity content as described above. It is particularly preferred to use acrylates.

Examples of the carboxy group-containing monomer include (meth) acrylic acid, dimer acid of acrylic acid such as β-carboxyethyl acrylate, and the like, and among them, in terms of heat resistance and stability during polymerization (meth). ) Acrylic acid is preferable.

Examples of the nitrogen atom-containing monomer include an amino group-containing monomer, an amide group-containing monomer, and other nitrogen atom-containing monomers.

Examples of the amino group-containing monomer include a primary amino group-containing monomer such as aminomethyl (meth) acrylate and aminoethyl (meth) acrylate, and a secondary amino group-containing monomer such as t-butylaminoethyl (meth) acrylate. Examples thereof include tertiary amino group-containing monomers such as ethylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, and diethylaminoethyl (meth) acrylate.
Among the amino group-containing monomers, a tertiary amino group-containing monomer is preferable because it has a high cross-linking promoting effect and a high storage stability of the resin.

Examples of the amide group-containing monomer include (meth) acrylamide; methoxymethyl (meth) acrylamide, ethoxymethyl (meth) acrylamide, propoxymethyl (meth) acrylamide, isopropoxymethyl (meth) acrylamide, and n-butoxymethyl (meth). ) Acrylamide (meth) acrylamide-based monomers such as acrylamide and isobutoxymethyl (meth) acrylamide; Dialkyl (meth) acrylamide-based monomers such as dimethyl (meth) acrylamide and diethyl (meth) acrylamide; N- (hydroxymethyl) acrylamide and the like. Hydroxylamide-containing amide monomer; heterocyclic amide monomer such as (meth) acryloylmorpholin; and the like.

Among the above-mentioned amide group-containing monomers, (meth) acryloylmorpholin, alkoxyalkyl (meth) acrylamide-based monomer, and dialkyl (meth) are used in terms of stability of the resin solution and suppression of migration of the ionic compound (D) described later. Meta) Acrylamide-based monomers are preferred.

The functional group-containing monomer (a3) is preferably at least one of a hydroxyl group-containing monomer and a carboxy group-containing monomer in that it is excellent in reactivity with the cross-linking agent (B) described later, and in particular, a hydroxyl group-containing monomer. It is preferable to use a carboxy group-containing monomer in combination with the above because it can be crosslinked more efficiently.

The molecular weight of the functional group-containing monomer (a3) is preferably 500 or less from the viewpoint of easy cross-linking reaction. The lower limit of the molecular weight is usually 50.

The functional group-containing monomer (a3) is preferably contained in a range of 30% by weight or less with respect to the polymerization component constituting the acrylic resin (A).

Among the functional group-containing monomers (a3), especially when a hydroxyl group-containing monomer is used, the content thereof is 0, with respect to the polymerization component constituting the acrylic resin (A), in terms of durability and reworkability. It is preferably 01 to 30% by weight, more preferably 0.1 to 20% by weight, particularly preferably 1 to 15% by weight, and particularly preferably 3 to 10% by weight.

Among the functional group-containing monomers (a3), especially when a carboxy group-containing monomer is used, the content thereof is 0 with respect to the polymerization component constituting the acrylic resin (A) in terms of durability and reworkability. It is preferably 0.01 to 10% by weight, more preferably 0.1 to 5% by weight. Further, from the viewpoint of corrosion resistance and suppressing hydrolysis of the base material and the adherend, it is preferably 0.5% by weight or less with respect to the polymerization component constituting the acrylic resin (A), and further 0. 2% by weight or less, particularly 0.1% by weight or less is preferable.

Among the functional group-containing monomers (a3), especially when a nitrogen atom-containing monomer is used, the content thereof is 0 with respect to the polymerization component constituting the acrylic resin (A) in terms of durability and hydrolysis suppression. .1 to 10% by weight is preferable, and 0.5 to 5% by weight is more preferable.

[Other copolymerizable monomers (a4)]
The other copolymerizable monomer (a4) is a copolymerizable ethylenically unsaturated monomer, for example, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, 2-hydroxy. Aromatic ring-containing monomers such as -3-phenoxypropyl (meth) acrylate and orthophenylphenoxyethyl (meth) acrylate; cyclohexyl (meth) acrylate, cyclohexyloxyalkyl (meth) acrylate, t-butylcyclohexyloxyethyl (meth) Alicyclic-containing monomers such as acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate; 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2-Butoxyethyl (meth) acrylate, 2-butoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate, Examples include ether chain-containing monomers such as methoxypolyethylene glycol (meth) acrylate, octoxypolyethylene glycol-polypropylene glycol-mono (meth) acrylate, lauroxypolyethylene glycol mono (meth) acrylate, and stearoxypolyethylene glycol mono (meth) acrylate. Be done. These may be used alone or in combination of two or more.

Among these, the point that the refractive index and birefringence can be easily adjusted, and the light leakage resistance (light leakage resistance is backed up after a high temperature or moist heat test when used as an adhesive for attaching a polarizing plate to a liquid crystal cell or the like. The aromatic ring-containing monomer is preferable, and benzyl (meth) acrylate, phenoxy (meth) ethyl acrylate, and phenoxydiethylene glycol (meth) acrylate are particularly preferable in that they are excellent in the ability to prevent light from leaking. An alicyclic-containing monomer is preferable in that the refractive index and birefringence can be easily adjusted and the adhesiveness to a low-polarization adherend (for example, cycloolefin) is excellent.

The content of the other copolymerizable monomer (a4) is preferably 25% by weight or less with respect to the polymerization component constituting the acrylic resin (A) so as not to impair the effects of the present invention.

The acrylic resin (A) used in the present invention is a polymerizable macromonomer (a1), preferably further an alkyl (meth) acrylate (a2), a functional group-containing monomer (a3), and if necessary, other copolymerization. It can be produced by, for example, mixing or dropping such a polymerization component and a polymerization initiator in an organic solvent and polymerizing using a polymerization component in which the sex monomer (a4) is appropriately selected and combined.

The above-mentioned polymerization reaction can be carried out by conventionally known polymerization methods such as solution radical polymerization, suspension polymerization, bulk polymerization and emulsion polymerization. Among these, solution radical polymerization and bulk polymerization are preferable, and solution is particularly preferable. It is a radical polymerization.

Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane, esters such as ethyl acetate and butyl acetate, n-propyl alcohol and isopropyl alcohol. Examples thereof include aliphatic alcohols such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and ketones such as cyclohexanone.

Among these organic solvents, ethyl acetate, acetone, methyl ethyl ketone, butyl acetate, toluene, etc. Methyl isobutyl ketone is preferably used, and ethyl acetate, acetone, and methyl ethyl ketone are particularly preferable. These organic solvents may be used alone or in combination of two or more.
The amount of these organic solvents used is usually 10 to 900 parts by weight with respect to 100 parts by weight of the polymerization component constituting the acrylic resin (A).

Examples of the polymerization initiator used for such solution radical polymerization include 2,2'-azobisisobutyronitrile and 2,2'-azobis-2-methylbutyronitrile, which are ordinary radical polymerization initiators. , 4,4'-azobis (4-cyanovaleric acid), 2,2'-azobis (methylpropionic acid) and other azo initiators, benzoyl peroxide, lauroyl peroxide, di-t-butyl peroxide, cumene Examples thereof include organic peroxides such as hydroperoxide, which can be appropriately selected and used according to the monomer to be used. These polymerization initiators may be used alone or in combination of two or more.
The amount of these polymerization initiators used is usually 0.01 to 5% by weight with respect to the polymerization component.

The acid value of the acrylic resin (A) thus obtained is preferably 30 mgKOH / g or less, particularly preferably 15 mgKOH, from the viewpoints of thermal stability, low metal corrosiveness, and excellent antistatic performance. / G or less, particularly preferably 10 mgKOH / g or less, still more preferably 7 mgKOH / g or less.

Here, the acid value in the present invention is determined by a neutralization titration method or a potentiometric method using potassium hydroxide.

The weight average molecular weight of the acrylic resin (A) is preferably 200,000 to 3,000,000, particularly preferably 400,000 to 2,000,000, still more preferably 600,000 to 1.8 million, and particularly preferably 800,000 to 800,000. It is 1.6 million. If the weight average molecular weight is too small, the durability tends to decrease, and if it is too large, a large amount of diluting solvent is required during production, the drying property decreases, and the residual solvent increases in the pressure-sensitive adhesive layer, resulting in a decrease in durability. Tend to do.

The dispersity (weight average molecular weight / number average molecular weight) of the acrylic resin (A) is preferably 20 or less, particularly preferably 15 or less, and further preferably 10 or less.
If the degree of dispersion is too high, the reworkability and durability tend to decrease. The lower limit of the degree of dispersion is usually 1.

The weight average molecular weight (Mw) is a weight average molecular weight converted to a standard polystyrene molecular weight, and is shown on a high performance liquid chromatograph (“Waters 2695 (main body)” and “Waters 2414 (detector)” manufactured by Waters). Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10 ^7, separation range: 100 to 2 × 10 ^7, theoretical plate number: 10,000 plates / the filler material: styrene - divinylbenzene copolymer, filler particle It is measured by using three pieces (diameter: 10 μm) in series. The number average molecular weight is also measured by the same method, and the degree of dispersion (weight average molecular weight / number average molecular weight) can be obtained from the number average molecular weight and the weight average molecular weight.

The glass transition temperature (Tg) of the acrylic resin (A) is preferably −100 to 0 ° C., particularly preferably −70 to −20 ° C., and even more preferably −65 to −30 ° C. If the glass transition temperature is too high, the warpage suppression tends to decrease, and if it is too low, the ionic compound (D), which is an antistatic agent described later, tends to move easily and bleed, and the durability tends to decrease.

The glass transition temperature (Tg) is calculated by the following Fox formula.

That is, the glass transition temperature (Tg) of the acrylic resin (A) is the glass transition temperature and the weight fraction when each of the monomers constituting the acrylic resin (A) is homopolymerized by applying it to the Fox formula. It is a value calculated by.
The glass transition temperature when a homopolymer of the monomer constituting the acrylic resin (A) is used is usually measured by a differential scanning calorimeter (DSC), and is usually measured by JIS K7121-1987 or JIS K 6240. It can be measured by a method conforming to.

The viscosity of the acrylic resin (A) is adjusted with a solvent or the like, and the acrylic resin (A) is used as a solution for the pressure-sensitive adhesive composition of the present invention. The viscosity of the acrylic resin (A) solution is preferably 500 to 20000 mPa · s, particularly preferably 1000 to 18000 mPa · s, and even more preferably 2000 to 15000 mPa · s from the viewpoint of ease of handling.
If the viscosity is too high, the fluidity tends to decrease and it tends to be difficult to handle, and if it is too low, the coating tends to be difficult when it is used as an adhesive.

The viscosity of the acrylic resin (A) solution is measured by measuring a resin solution whose temperature has been adjusted to 25 ° C. by a rotational viscosity method using a B-type viscometer.

<Crosslinking agent (B)>
The pressure-sensitive adhesive composition of the present invention contains the cross-linking agent (B) in the acrylic resin (A) in terms of improving the adhesion to the base material and improving the durability of the pressure-sensitive adhesive. Is preferable.

The cross-linking agent (B) reacts with a functional group in the acrylic resin (A) to form a cross-linked structure. For example, an isocyanate-based cross-linking agent, an epoxy-based cross-linking agent, an aziridine-based cross-linking agent, and melamine. Examples thereof include a system cross-linking agent, an aldehyde-based cross-linking agent, an amine-based cross-linking agent, and a metal chelate-based cross-linking agent. Among these, it is preferable to use an isocyanate-based cross-linking agent because it improves the adhesion to the base material and is excellent in the reactivity with the acrylic resin (A).
The above-mentioned cross-linking agent (B) may be used alone or in combination of two or more.

Examples of the isocyanate-based cross-linking agent include a tolylene diisocyanate-based cross-linking agent such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, and a xylylene diisocyanate-based cross-linking agent such as 1,3-xylylene diisocyanate. Diphenylmethane-based cross-linking agents such as diphenylmethane-4,4-diisocyanate, aromatic isocyanate-based cross-linking agents such as naphthalene diisocyanate such as 1,5-naphthalenediocyanate; isophorone diisocyanate, 1,4-cyclohexanediisocyanate, 4,4 Alicyclic isocyanate-based cross-linking agents such as'-dicyclohexylmethane diisocyanate, methylcyclohexanediisocyanate, isopropyridendicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane, norbornandiisocyanate; hexamethylenediisocyanate, trimethylhexa Examples thereof include aliphatic isocyanate-based cross-linking agents such as methylene diisocyanate; and adducts, bullets, and isocyanurates of the above isocyanate compounds.

Among these isocyanate-based cross-linking agents, tolylene diisocyanate-based cross-linking agents are preferable in terms of pot life and durability, and xylylene diisocyanate-based cross-linking agents or isocyanurate skeleton-containing isocyanate-based cross-linking agents are preferable in terms of shortening the aging time. An aromatic ring-free isocyanate-based cross-linking agent is preferable in terms of yellowing resistance. Of these, specifically, tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate and trimethylolpropane adducts, and nucleohydrates are preferable because they have an excellent balance of durability, pot life, and cross-linking rate. ..

Examples of the epoxy-based cross-linking agent include bisphenol A / epichlorohydrin type epoxy resin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, and 1,6-hexanediol diglycidyl ether. , Trimethylol propan triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, diglycerol polyglycidyl ether and the like.

Examples of the aziridine-based cross-linking agent include tetramethylolmethane-tri-β-aziridinyl propionate, trimethylolpropane-tri-β-aziridinyl propionate, and N, N'-diphenylmethane-4,4. ′ -Bis (1-aziridine carboxamide), N, N'-hexamethylene-1,6-bis (1-aziridine carboxamide) and the like can be mentioned.

Examples of the melamine-based cross-linking agent include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resin. ..

Examples of the aldehyde-based cross-linking agent include glyoxal, malondialdehyde, succindialdehyde, maleindialdehyde, glutardaldehyde, formaldehyde, acetaldehyde, and benzaldehyde.

Examples of the amine-based cross-linking agent include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resin, and polyamide.

Examples of the metal chelate-based cross-linking agent include a coordination compound of a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, panadium, chromium, and zirconium with acetylacetone or acetoacetyl ester. And so on.

When such a cross-linking agent (B) is used, its content is preferably 0.005 to 30 parts by weight, particularly preferably 0.01, with respect to 100 parts by weight of the acrylic resin (A). It is 10 parts by weight, more preferably 0.03 to 5 parts by weight, and particularly preferably 0.05 to 3 parts by weight. If the content is too small, the durability tends to decrease, and if it is too large, the stress relaxation property tends to decrease and the substrate tends to warp, or aging for a long time tends to be required.

Further, it is preferable that the pressure-sensitive adhesive composition of the present invention further contains a silane coupling agent (C) as long as the effects of the present invention are not impaired.

<Silane coupling agent (C)>
The silane coupling agent (C) is an organosilicon compound containing at least one reactive functional group and one or more alkoxy groups bonded to a silicon atom in its structure, and is the present invention in that it improves durability. It is preferably contained in the pressure-sensitive adhesive composition of.

Examples of the reactive functional group in the silane coupling agent (C) include an epoxy group, a (meth) acryloyl group, a mercapto group, a hydroxyl group, a carboxy group, an amino group, an amide group, an isocyanate group and the like. Among them, an epoxy group and a mercapto group are preferable, and an epoxy group is particularly preferable, from the viewpoint of excellent durability and reworkability.

The content ratio of the reactive functional group in the silane coupling agent (C) is preferably 3000 g / mol or less, more preferably 1500 g / mol or less, and further preferably 800 g / mol or less. Within the above range, the balance between durability and reworkability tends to be excellent.

The alkoxy group in the silane coupling agent (C) preferably contains an alkoxy group having 1 to 8 carbon atoms from the viewpoint of durability and storage stability, and particularly contains a methoxy group and an ethoxy group. Is particularly preferable.

The silane coupling agent (C) may have an organic functional group other than the reactive functional group and the alkoxy group bonded to the silicon atom, for example, an alkyl group, a phenyl group or the like.

The silane coupling agent (C) preferably has a weight average molecular weight of 500 or more from the viewpoint of reworkability and durability, and more preferably 1000 to 30,000, particularly 1500 to 20000. When the weight average molecular weight is in the above range, the balance between reworkability and durability tends to be excellent.

The weight average molecular weight of the silane coupling agent (C) is the weight average molecular weight converted to the standard polystyrene molecular weight, and can be measured by the following method.
-Device: Gel permeation chromatograph-Detector: Differential refractive index detector RI (manufactured by Tosoh Corporation, RI-8020 type, sensitivity 32)
-Column: TSKgel guardcolum HHR-H (1) (Tosoh, φ6 mm x 4 cm), TSKgel GMHR-N (2) (Tosoh, φ7.8 mm x 30 cm)
-Solvent: tetrahydrofuran (THF)
-Column temperature: 23 ° C
・ Flow velocity: 1.0 mL / min

The reworkability of the silane coupling agent (C) is that it is an oligomer-type organic silicon compound (organosiloxane compound) such as a dimer or a trimer in which a part of the organic silicon compound is hydrolyzed and polycondensed. In terms of durability, some of the mercapto group-containing silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxymethylsilane were hydrolyzed and polycondensed. A cocondensate of a mercapto group-containing oligomeric silane coupling agent or the above mercapto group-containing silane compound with an alkyl group-containing silane compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, or ethyltrimethoxysilane. A mercapto group-containing oligomeric silane coupling agent; γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyl Some epoxy group-containing silane compounds such as dimethoxysilane, methyltri (glycidyl) silane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, and β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane are hydrated. Decomposed and polycondensed epoxy group-containing oligomer-type silane coupling agent; the above epoxy group-containing silane compound and alkyl group-containing silane compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane. An epoxy group-containing oligomer-type silane coupling agent which is a cocondensate of the above; an epoxy group-containing oligomer-type silane coupling agent obtained by ether-modifying a part of these epoxy group-containing oligomer-type silane coupling agents can be mentioned.
These may be used alone or in combination of two or more.

The oligomer-type silane coupling agent preferably has an alkoxy group content of 1 to 60% by weight, particularly preferably 3 to 50% by weight, and further preferably 5 to 45% by weight for durability and rework. It is preferable because it has an excellent balance of sex.

Specific examples of the oligomer-type silane coupling agent include commercially available epoxy group-containing silane coupling agents "X-41-1053", "X-41-1059A", and "X-41-1059A" manufactured by Shin-Etsu Chemical Industry Co., Ltd. Examples thereof include "X-24-9590", "X-24-9589", "X-41-1805", "X-41-1810", and "X-41-1818".

When the silane coupling agent (C) is used, the content thereof is preferably 0.001 to 3 parts by weight, particularly preferably 0.005, with respect to 100 parts by weight of the acrylic resin (A). It is ~ 1 part by weight, more preferably 0.01 to 0.5 part by weight, and particularly preferably 0.015 to 0.3 part by weight.
If the content is too small, the reworkability tends to decrease, and if it is too large, the silane coupling agent (C) tends to bleed and the durability tends to decrease.

When two or more kinds of silane coupling agents (C) are used in combination, it is preferable to use two or more kinds having different weight average molecular weights, particularly those having a weight average molecular weight of 3000 or more and less than 3000. It is preferable to use the same in combination with the above because it is excellent in adhesive strength immediately after bonding, durability in a high temperature and high humidity environment, reworkability and warpage suppression. In this case, the weight blending ratio of the silane coupling agent having a weight average molecular weight of 3000 or more and the silane coupling agent having a weight average molecular weight of less than 3000 [(silane coupling agent having a weight average molecular weight of 3000 or more) / (weight average molecular weight less than 3000). Silane coupling agent)] is usually 99/1 to 1/99, preferably 80/20 to 40/60, and more preferably 70/30 to 50/50.

<Ionic compound (D)>
The pressure-sensitive adhesive composition of the present invention preferably further contains an ionic compound (D) from the viewpoint of measures against static electricity.
The ionic compound (D) is a compound composed of a cation component and an anion component, and is a compound composed of a combination of an organic cation or an inorganic cation as a cation component and an organic anion or an inorganic anion as an anion component. The ionic compound (D) may be used alone or in combination of two or more.

Examples of the organic cation include pyridinium cation, piperidinium cation, pyrrolidinium cation, cation having a pyrrolin skeleton, cation having a pyrrol skeleton, imidazolium cation, tetrahydropyrimidinium cation, dihydropyrimidinium cation, pyrazo. Examples thereof include a rium cation, a pyrazolinium cation, a tetraalkylammonium cation, a trialkylsulfonium cation, and a tetraalkylphosphonium cation.
As the inorganic cation, an alkali metal cation is preferable in terms of antistatic performance, and a lithium cation is particularly preferable.
Among the cation components, organic cations are preferable, nitrogen-containing organic cations are particularly preferable in terms of compatibility with resins, and tetraalkylammonium cations, pyridinium cations, and imidazolium cations are preferable in terms of compatibility with acrylic resin (A). Is preferable.

The anionic component, ^{e.g., Cl -, Br -, I} -, AlCl 4 -, Al 2 Cl 7 -, BF 4 -, PF 6 -, ClO 4 -, NO 3 -, CH 3 COO -, CF 3 COO _{^{-, CH 3 SO 3 -,}} CF 3 SO 3 -, (CF 3 SO 2) 3 C -, AsF 6 -, SbF 6 -, NbF 6 -, TaF 6 -, (C 2 O 4) 2 B -, _{^{SCN -, (CN) 2 N}} -, C 4 F 9 SO 3 -, C 3 F 7 COO -, (CF 3 SO 2) (CF 3 CO) N -, or the following general formula (1) to (4) Those represented by are used.
_{(1) :( C n F 2n} + 1 SO 2) 2 N - ( where, n is an integer of from 1 to 10)
_{(2): CF 2 (C} m F 2m SO 2) 2 N - ( where, m is an integer of from 1 to 10)
_{(3): O 3 S (} CF 2) l SO 3 - ( where, l is an integer of from 1 to 10)
_{(4) :( C p F 2p} + 1 SO 2) N - (C q F 2q + 1 SO 2) ( where, p, q is an integer of from 1 to 10)
Among the above, an anion containing a fluorine atom is particularly preferable, and further, a fluorine-containing sulfonium anion, a fluorine-containing imide anion, and a fluorine-containing sulfonylimide anion have antistatic performance, durability, and compatibility with the acrylic resin (A). It is preferable in terms of points.

As the ionic compound (D) used in the present invention, a nitrogen-containing onium salt is preferable from the viewpoint of compatibility with the acrylic resin (A), and an alkali metal salt is preferable from the viewpoint of excellent heat resistance. The cation component and the anion component constituting the salt are appropriately selected from the combination of the cation component and the anion component and used.

The quaternary ammonium salt is preferable as the ionic compound (D), and specific examples of the quaternary ammonium salt include tributylmethylammonium N, N-bis (trifluoromethanesulfonyl) imide and tetrabutylammonium bis (tri). Fluoromethylsulfonyl) imide, tetrabutylammonium bromide, tetrapentylammonium bromide, tetraoctylammonium bromide, ethyldimethylpropylammonium bis (trifluoromethylsulfonyl) imide, n-butyltrimethylammonium bis (trifluoromethanesulfonyl) imide, methyltrioctyl Ammonium bis (trifluoromethylsulfonyl) imide, tributylmethylammoniummethylsulfate, tributylmethylammoniummethylsulfate, tetrabutylammonium bis (trifluoromethylsulfonyl) imide, tetraethylammonium trifluoromethanesulfonate, tetrabutylammonium benzoate, tetrabutylammonium methane Sulfate, tetrabutylammonium nonafluorobutane sulfonate, tetra-n-butylammonium hexafluorophosphate, tetrabutylammonium trifluoroacetate, tetrahexylammonium tetrafluoroborate, tetrahexylammonium bromide and the like can be mentioned.

From the viewpoint of the balance between antistatic performance and durability, an ionic compound in which the anion component of the ionic compound (D) is a fluorine-containing anion is preferable, and among them, lithium trifluoromethanesulfonate (manufactured by Tokyo Kasei Kogyo Co., Ltd.) ), Lithium N, N-bis (trifluoromethanesulfonyl) imide (manufactured by Sanko Chemical Co., Ltd.), tributylmethylammonium N, N-bis (trifluoromethanesulfonyl) imide (manufactured by 3M) are preferably used, and particularly tributylmethylammonium. N, N-bis (trifluoromethanesulfonyl) imides are preferably used.

Further, when the cation component of the ionic compound (D) is an ammonium-based ionic compound, it is preferably an alkylammonium cation, and the number of carbon atoms in the alkyl chain is excellent in that it has excellent compatibility with the acrylic resin (A). Alkylammonium cations having an alkyl group of 1 to 6 are particularly preferred. On the other hand, when the cation component is an alkali metal salt, it is preferably a lithium cation, a sodium cation, a potassium cation or the like, and a lithium cation is particularly preferable in that it is particularly excellent in moisture and heat resistance.

The melting point of the ionic compound (D) is 0 ° C. or higher, more preferably 10 ° C. to 550 ° C., particularly preferably 20 ° C. to 500 ° C., and even more preferably 25 ° C. to 450 ° C. If the melting point is within such a range, it is difficult to reduce the restraint of the molecular chain of the acrylic polymer by the polymerizable macromonomer (a1) at a high temperature, and the durability is improved.

When the above ionic compound (D) is used, its content is 1 to 20 parts by weight, particularly preferably 1.5 to 15 parts by weight, still more preferably 1.5 parts by weight, based on 100 parts by weight of the acrylic resin (A). 2 to 12 parts by weight.
If the content of the ionic compound (D) is too small, the antistatic performance tends to be low, and the touch panel malfunctions due to static electricity and the display unevenness of the liquid crystal cell tends to occur. If the content is too large, the adhesive layer becomes plastic. Durability tends to decrease due to bleeding or bleeding.

<Other optional ingredients>
Further, in the pressure-sensitive adhesive composition of the present invention, as other optional components, a resin component, an acrylic monomer, a polymerization inhibitor, a corrosion inhibitor, a cross-linking accelerator, a radical generator, etc. Various additives such as peroxides, radical scavengers, ultraviolet absorbers, antioxidants, plasticizers, pigments, stabilizers, fillers, metals, resin particles and the like can be blended. In addition to the above, a small amount of impurities and the like contained in the raw materials for producing the constituent components of the pressure-sensitive adhesive composition may be contained.

When the above other optional component is used, the content thereof is preferably 5 parts by weight or less, particularly preferably 1 part by weight or less, and further preferably 0. It is 5 parts by weight or less. If the content is too large, the compatibility with the acrylic resin (A) tends to decrease, and the durability tends to decrease.

Thus, by mixing the acrylic resin (A), preferably a cross-linking agent (B), a silane coupling agent (C), an ionic compound (D), and if necessary, other optional components, the present invention. The pressure-sensitive adhesive composition can be obtained.

The mixing method is not particularly limited, and various methods such as a method of mixing each component at once, a method of mixing arbitrary components, and then a method of mixing the remaining components collectively or sequentially are adopted. can do.

The pressure-sensitive adhesive composition of the present invention can be made into a pressure-sensitive adhesive by curing (crosslinking), and further, a pressure-sensitive adhesive layer made of such a pressure-sensitive adhesive is laminated on an optical member (optical laminate). An optical member with an adhesive layer can be obtained.
It is preferable that the optical member with the pressure-sensitive adhesive layer is further provided with a release sheet on the surface opposite to the surface of the optical member of the pressure-sensitive adhesive layer.

Examples of the method for manufacturing the optical member with an adhesive layer include the following methods [1] and [2].
[1] A method in which a pressure-sensitive adhesive composition is applied onto an optical member, dried, and then a release sheet is attached, and the treatment is performed by aging at at least one of normal temperature (23 ° C.) and a heated state.
[2] A method in which an adhesive composition is applied onto a release sheet, dried, and then an optical member is attached to the release sheet, and the treatment is performed by aging at at least one of the room temperature and the heated state.
Among these, the method of aging at room temperature by the method of [2] is preferable in that it does not damage the optical member and is excellent in adhesiveness to the optical member.
In the above, the optical member is particularly effective when it is a polarizing plate, but the above method can also be used when forming an adhesive layer on an adherend other than the optical member.

Such an aging treatment is carried out in order to balance the adhesive physical characteristics as the reaction time of the chemical cross-linking of the pressure-sensitive adhesive, and the aging conditions are a temperature of 20 to 70 ° C. and a time of usually 1 to 30 days. Specifically, for example, it may be carried out under conditions such as 23 ° C. for 1 to 20 days, 23 ° C. for 3 to 10 days, and 40 ° C. for 1 to 7 days.

When applying the pressure-sensitive adhesive composition, it is preferable to dilute the pressure-sensitive adhesive composition with a solvent before coating, and the dilution concentration is preferably 5 to 60% by weight, particularly preferably 5 to 60% by weight. It is 10 to 30% by weight.

The solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition, and is, for example, an ester solvent such as methyl acetate, ethyl acetate, methyl acetoacetate, ethyl acetoacetate, acetone, methyl ethyl ketone, and the like. A ketone solvent such as methylisobutylketone, an aromatic solvent such as toluene and xylene, and an alcohol solvent such as methanol, ethanol and propyl alcohol can be used. Among these, ethyl acetate and methyl ethyl ketone are preferably used from the viewpoints of solubility, drying property, price and the like.
These can be used alone or in combination of two or more.

Further, the coating of the pressure-sensitive adhesive composition is carried out by a conventional method such as roll coating, die coating, gravure coating, comma coating and screen printing.

The gel fraction of the pressure-sensitive adhesive layer produced by the above method is preferably 30 to 98% by weight, particularly preferably 35 to 95% by weight, and even more preferably 50% by weight from the viewpoint of durability performance and suppression of decrease in polarization degree. ~ 90% by weight. If the gel fraction is too low, the adhesive layer tends to foam in a high temperature environment, and if it is too high, it tends to float or peel off.

The gel fraction is a measure of the degree of cross-linking (degree of curing), and is calculated by, for example, the following method. That is, the pressure-sensitive adhesive was collected by picking from an pressure-sensitive adhesive film having a pressure-sensitive adhesive layer formed on an optical member, particularly a base material such as a polarizing plate, and the pressure-sensitive adhesive was wrapped in a 200-mesh SUS wire net and adjusted to 23 ° C. By immersing in ethyl for 24 hours, the weight percentage of the insoluble pressure-sensitive adhesive component remaining in the wire net is defined as the gel fraction (%) with respect to the weight of the pressure-sensitive adhesive before immersing in ethyl acetate.

It is preferable that the adhesive layer produced by the above method has a good tack feeling when touched with a finger because it has good wettability when actually applied to the adherend, and thus tends to improve workability. ..

As for the electrical characteristics of the pressure-sensitive adhesive layer obtained by using the pressure-sensitive adhesive composition of the present invention, low surface resistivity is preferable as a countermeasure against static electricity, more preferably 1.0 × 10 ¹⁰ Ω / cm ² or less, particularly preferably. Is 8.0 × 10 ⁹ Ω / cm ² or less, more preferably 5.0 × 10 ⁹ Ω / cm ² or less, and particularly preferably 4.0 × 10 ⁹ Ω / cm ² or less. If the surface resistivity is too high, the adhesive tends to be charged, and when used for liquid crystal display applications, display unevenness due to static electricity tends to occur.

In the present invention, the optical member with an adhesive layer, particularly the polarizing plate with an adhesive layer, is directly or those having a release sheet, the release sheet is peeled off, and then the adhesive layer surface is bonded to a glass substrate. For example, it is used for a liquid crystal display board.

The pressure-sensitive adhesive composition of the present invention exhibits high durability even in a high-temperature environment, and can provide a pressure-sensitive adhesive capable of achieving both reworkability and warpage suppression. A pressure-sensitive adhesive for optical members, particularly a polarizing plate. It is useful as an adhesive for polarizing plates that adheres glass substrates and the like.

Examples of the protective film constituting the polarizing plate include a triacetyl cellulose-based film, an acrylic film, a polyethylene-based film, a polypropylene-based film, a cycloolefin-based film, and the like. However, a polarizing plate laminated using a cycloolefin-based film is particularly preferable because the effect of the present invention can be easily obtained.

Further, by using the above-mentioned adhesive, an image display device such as a liquid crystal display device can be manufactured by laminating a polarizing plate and a liquid crystal cell, and the obtained image display device can be manufactured with high accuracy and durability. Become superior.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the example, "part" and "%" mean the weight standard.

[Polymerizable macromonomer]
Prior to the examples, the following were prepared as polymerizable macromonomers.
The number average molecular weight and the degree of dispersion of the polymerizable macromonomer were measured according to the above-mentioned method.

In addition, when calculating the glass transition temperature, the following values were used for the glass transition temperature when homopolymers of each monomer were used.
-Methyl methacrylate (MMA): 105 ° C
2-Ethylhexyl methacrylate (2EHMA) ・ ・ ・ -10 ℃
・ Lauryl methacrylate / tridecyl methacrylate = 55/45 (SLMA) ・ ・ ・ -64 ℃

(Polymerizable Macromonomer 1)
Acrylic macromonomer which is a copolymer of methyl methacrylate (MMA) and 2-ethylhexyl methacrylate (2EHMA) (manufactured by Mitsubishi Chemical Co., Ltd., MMA: 2EHMA (weight ratio) = 80:20, number average molecular weight 8000, dispersity 1 .83, calculated glass transition temperature 75 ° C)

(Polymerizable macromonomer 2)
Acrylic macromonomer which is a copolymer of methyl methacrylate (MMA) and 2-ethylhexyl methacrylate (2EHMA) (manufactured by Mitsubishi Chemical Co., Ltd., MMA: 2EHMA (weight ratio) = 90:10, number average molecular weight 7100, dispersity 1 .96, calculated glass transition temperature 89 ° C)

(Polymerizable macromonomer 3)
Acrylic macromonomer which is a copolymer of methyl methacrylate (MMA) and lauryl methacrylate / tridecyl methacrylate = 55/45 (SLMA) (manufactured by Mitsubishi Chemical Co., Ltd., MMA: SLMA (weight ratio) = 80:20, number average Molecular weight 5900, dispersion 1.68, calculated glass transition temperature 52 ° C)

(Polymerizable Macromonomer 4)
Acrylic macromonomer containing polymethylmethacrylate as the main component (manufactured by Mitsubishi Chemical Co., Ltd., PMMA = 100%, number average molecular weight 3700, dispersity 1.73, calculated glass transition temperature 105 ° C)

<Acrylic resin>
Next, the acrylic resin (A) or (A') was produced according to the following production method. The composition of each acrylic resin is shown in Table 1 below. The weight average molecular weight, dispersity, and glass transition temperature of the acrylic resin (A) or (A') were measured according to the above-mentioned method.
The viscosity was measured according to the 4.5.3 rotational viscometer method of JIS K5400 (1990).

[Manufacturing of acrylic resin (A-1)]
In a 4-neck round bottom flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet and a thermometer, 2 parts of the above-prepared polymerizable macromonomer 1 (a1) and n-butyl acrylate (a2) 89.3 8 parts of 2-hydroxyethyl acrylate (a3), 0.7 part of acrylic acid (a3), 30 parts of ethyl acetate, 42 parts of acetone, 0.01 part of azobisisobutyronitrile (AIBN) as a polymerization initiator. The reaction was started by raising the internal temperature to the boiling point. Next, 30 parts of an ethyl acetate solution containing 0.04% AIBN was added dropwise and reacted at a reflux temperature for 3.25 hours, then diluted with ethyl acetate to form an acrylic resin (A-1) solution (solid content 24. 9%, viscosity 6760 mPa · s / 25 ° C., weight average molecular weight 1.25 million, dispersion degree 3.18) were obtained.

[Manufacturing of acrylic resin (A-2)]
In the method for producing the acrylic resin (A-1), the same procedure was carried out except that the polymerizable macromonomer 1 (a1) was changed to the polymerizable macromonomer 2 (a1), and the acrylic resin (A-2) solution ( A solid content of 23.4%, a viscosity of 4320 mPa · s / 25 ° C., a weight average molecular weight of 1.22 million, and a dispersity of 3.15) were obtained.

[Manufacturing of acrylic resin (A-3)]
In the method for producing the acrylic resin (A-1), the same procedure was carried out except that the polymerizable macromonomer 1 (a1) was changed to the polymerizable macromonomer 3 (a1), and the acrylic resin (A-3) solution ( A solid content of 24.8%, a viscosity of 5760 mPa · s / 25 ° C., a weight average molecular weight of 1.25 million, and a dispersity of 2.92) were obtained.

[Manufacturing of acrylic resin (A'-1)]
In the method for producing the acrylic resin (A-1), n-butyl acrylate (a2) was changed to 90.3 parts, and the polymerizable macromonomer 1 (a1) was changed to 1 part of the polymerizable macromonomer 4 (a1). Acrylic resin (A'-1) solution (solid content 23.7%, viscosity 4570 mPa · s / 25 ° C., weight average molecular weight 1.25 million, dispersity 2.69) was obtained in the same manner except for the above.

[Manufacturing of acrylic resin (A'-2)]
In the method for producing the acrylic resin (A-1), the amount of n-butyl acrylate (a2) was 91.3 parts, and the same procedure was used except that the polymerizable macromonomer 1 (a1) was not used. A'-2) solution (solid content 20.5%, viscosity 5080 mPa · s / 25 ° C., weight average molecular weight 1.33 million, dispersity 4.30) was obtained.

The monomers used above were manufactured by the following manufacturers.
-N-Butyl acrylate (BA) (manufactured by Mitsubishi Chemical Corporation, Tg-56 ° C)
2-Hydroxyethyl acrylate (HEA) (manufactured by Osaka Organic Chemical Co., Ltd., Tg-15 ° C)
-Acrylic acid (AAc) (manufactured by Mitsubishi Chemical Corporation, Tg 106 ° C)
The Tg is a homopolymer Tg of each monomer.

<Crosslinking agent (B)>
The following were prepared as the cross-linking agent (B).
(B-1): Adduct of tolylene diisocyanate and trimethylolpropane (Tosoh, Coronate L55E)

<Silane coupling agent (C)>
The following were prepared as the silane coupling agent (C).
The weight average molecular weight of the silane coupling agent (C) was measured according to the above method. As for the alkoxy group content, the reactive functional group, the epoxy equivalent or the mercapto equivalent, and the contained alkoxy group, the catalog values were adopted unless otherwise specified.

(C-1): "X-41-1059A": manufactured by Shin-Etsu Chemical Industry Co., Ltd., contained reactive functional group: epoxy group, reactive functional group equivalent: 350 g / mol, contained alkoxy group: methoxy group and ethoxy group, alkoxy Group content: 42%, weight average molecular weight: 2270, dispersibility: 1.86
(C-2): "X-24-9590": manufactured by Shin-Etsu Chemical Industry Co., Ltd., Reactive functional group contained: Epoxide group, Functional group equivalent: 592 g / mol, Alkoxy group contained: Methoxy group, Alkoxy group content: 9 5.5%, weight average molecular weight: 13700, dispersibility: 3.44

<Ionic compound (D)>
The following were prepared as the ionic compound (D).
(D-1): Tributylmethylammonium N, N-bis (trifluoromethanesulfonyl) imide (manufactured by 3M Ltd., FC-4400)

<Examples 1 to 3, Comparative Examples 1 and 2>
The above components were blended as shown in Table 2 below, and the solid content concentration was adjusted to 15% with ethyl acetate to obtain a pressure-sensitive adhesive composition. The gel fraction of each of the obtained pressure-sensitive adhesive compositions was measured by the following method. The results are also shown in Table 2 below. In Table 2, the numerical values in parentheses indicate the compounding portion.

<Gel fraction>
The obtained pressure-sensitive adhesive composition is applied to a polyester-based release sheet (manufactured by Toray Industries, Inc., Therapy WZ) having a thickness of 38 μm so that the thickness after drying is 20 μm, dried at 100 ° C. for 3 minutes, and then a new thickness is obtained. A substrate-less double-sided adhesive sheet was obtained by laminating it on a 38 μm polyester-based release sheet and further aging it in an environment of 23 ° C. × 50% RH for 7 days. After cutting the obtained base material-less double-sided adhesive sheet to a size of 40 mm × 40 mm, one of the release sheets is peeled off, and the adhesive layer side is attached to a SUS mesh sheet (200 mesh) having a size of 50 mm × 100 mm. After the combination, the other release sheet was peeled off, folded back from the center in the longitudinal direction of the SUS mesh sheet to wrap the sample, and then immersed in a sealed container containing 250 g of ethyl acetate for 24 hours. The weight percentage of the insoluble adhesive layer remaining on the SUS mesh sheet with respect to the weight of the adhesive layer before immersion in ethyl acetate was defined as the gel fraction (%).

Using the pressure-sensitive adhesive composition obtained above, a polarizing plate with a pressure-sensitive adhesive layer was prepared according to the following, and the performance was evaluated. The evaluation results are shown in Table 3 below.

[Preparation of polarizing plate with adhesive layer]
The obtained pressure-sensitive adhesive composition was applied to a release sheet (manufactured by Toray Co., Ltd., Therapy WZ) having a thickness of 38 μm so that the thickness after drying was 20 μm, dried at 100 ° C. for 3 minutes, and then triacetyl cellulose (TAC). ) The adhesive layer surface on the opposite side of the release sheet is adhered to the surface of one TAC film of the polarizing plate in which the films are laminated on both sides, and aged for 7 days in an environment of 23 ° C × 50% RH to obtain the adhesive. A layered polarizing plate was obtained [layer structure: release sheet / adhesive layer / TAC-based film 1 / polarizer / TAC-based film 2].
The above-mentioned TAC-based film is a triacetyl-cellulose-based film, and the thickness of the TAC-based film 1 is 40 μm and the thickness of the TAC-based film 2 is 40 μm.
The following evaluation was performed using a polarizing plate with an adhesive layer.

<Durability>
The obtained polarizing plate with an adhesive layer is cut into a size of 165 mm × 97 mm, the release sheet is peeled off, and the adhesive layer surface is pressed against alkali-free glass (Corning, Eagle XG, thickness 1.1 mm) with a 2 kg roller. After two round trips and bonding, an autoclave treatment (0.5 MPa × 50 ° C. × 20 minutes) was performed to prepare a sample for durability test.

[Heat resistance test]
The obtained sample was evaluated as follows for the polarizing plate after being exposed under the condition of heat resistance (85 ° C. × 300 hours).
(Evaluation criteria)
○ ・ ・ ・ No foaming or floating at the edges of the polarizing plate × ・ ・ ・ Foaming or floating at the edges of the polarizing plate

<Adhesive strength>
The obtained polarizing plate with an adhesive layer was cut into a size of 25 mm × 100 mm, the release sheet was peeled off, and the adhesive layer side was attached to non-alkali glass (“Eagle XG” manufactured by Corning Inc., thickness 1.1 mm). After that, autoclave treatment (0.5 MPa × 50 ° C. × 20 minutes) was performed, and after allowing to stand for 24 hours in an atmosphere of 23 ° C. and 50% RH, 90 degree peeling strength (N / 25 mm) at a peeling speed of 300 mm / min. Was measured.

<Reworkability>
The obtained polarizing plate with an adhesive layer was cut into a size of 25 mm × 100 mm, the release sheet was peeled off, and the adhesive layer side was attached to non-alkali glass (“Eagle XG” manufactured by Corning Inc., thickness 1.1 mm). Then, an autoclave treatment (0.5 MPa × 50 ° C. × 20 minutes) was performed, and the mixture was allowed to stand for 24 hours in an atmosphere of 23 ° C. and 50% RH.

(23 ° C x 20 days)
The sample that had been allowed to stand as described above was further allowed to stand for 456 hours in an atmosphere of 23 ° C. and 50% RH, and then the peeling strength (N / 25 mm) of 90 degrees was measured at a peeling speed of 300 mm / min.
(50 ° C x 1 day)
The sample that had been allowed to stand above was further allowed to stand in an atmosphere of 50 ° C. for 24 hours, and then the peeling strength (N / 25 mm) of 90 ° C. was measured at a peeling speed of 300 mm / min in an atmosphere of 23 ° C. and 50% RH. ..

<Warp evaluation>
The obtained polarizing plate with an adhesive layer is cut into a size of 165 mm × 97 mm, the release sheet is peeled off, and the adhesive layer surface is attached to soda glass (manufactured by Nippon Test Panel Co., Ltd., thickness 0.4 mm), and then autoclaved. (0.5 MPa × 50 ° C. × 20 minutes) was carried out to prepare a sample for a polarizing plate warp test.
The obtained sample was exposed under the condition of heat resistance (85 ° C. × 300 hours), then allowed to stand in an atmosphere of 23 ° C. and 50% RH, and after 1 hour, the sample was placed on a flat glass plate and sampled. One side of the short side of the sample was pressed so as to be in close contact with the glass plate, and the distance between the tip of the sample not pressed and the glass plate was measured.

From the above results, in Examples 1 to 3 using an acrylic resin copolymerized with a predetermined polymerizable macromonomer, both reworkability and warpage suppression, which were difficult to achieve at the same time, were good results. Comparative Example 1 in which the polymerizable macromonomer was not used and Comparative Example 2 in which the acrylic resin in which the polymerizable macromonomer by homopolymerization was copolymerized were inferior in warpage suppression as compared with Examples. The result was that the reworkability was further inferior, and it was not possible to achieve both the reworkability and the suppression of warpage.

When the pressure-sensitive adhesive composition of the present invention is used as a pressure-sensitive adhesive for bonding a polarizing plate (protective film) to a metal surface such as a liquid crystal cell (glass plate) or a conductive layer in the manufacture of a liquid crystal display device, Since it has excellent durability even in a high temperature environment, and also has excellent reworkability and warp suppression of the polarizing plate, an adhesive for an optical member for bonding a display and optical components constituting the display, particularly a polarizing plate and a liquid crystal cell. It is useful as an adhesive for a polarizing plate for bonding a glass substrate, a substrate provided with a conductive layer, and the like.

Claims (12)

A pressure-sensitive adhesive composition containing an acrylic resin (A), wherein the acrylic resin (A) is copolymerized with at least two types of alkyl (meth) acrylates and has a glass transition temperature of -40 to 100 ° C. A pressure-sensitive adhesive composition, which is an acrylic resin obtained by polymerizing a polymerization component containing a polymerizable macromonomer (a1). The polymerizable macromonomer (a1) contains a (meth) acrylate (a1-1) having an alkyl group having 1 to 4 carbon atoms and a (meth) acrylate (a1-2) having an alkyl group having 5 to 22 carbon atoms. The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive composition is contained as a copolymerization component. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the polymerizable macromonomer (a1) has a number average molecular weight (Mn) of 1000 to 200,000. Any one of claims 1 to 3, wherein the content ratio of the polymerizable macromonomer (a1) is 0.1 to 20% by weight based on the polymerization component constituting the acrylic resin (A). The pressure-sensitive adhesive composition according to the section. The adhesive according to any one of claims 1 to 4, wherein the acrylic resin (A) is an acrylic resin obtained by further polymerizing a polymerization component containing a functional group-containing monomer (a3). Agent composition. The pressure-sensitive adhesive composition according to claim 5, wherein the functional group-containing monomer (a3) is at least one of a hydroxyl group-containing monomer and a carboxy group-containing monomer. The pressure-sensitive adhesive composition according to any one of claims 1 to 6, further comprising a cross-linking agent (B). The pressure-sensitive adhesive composition according to any one of claims 1 to 7, further comprising a silane coupling agent (C). The pressure-sensitive adhesive composition according to any one of claims 1 to 8, further comprising an ionic compound (D). A pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition according to any one of claims 1 to 9. A pressure-sensitive adhesive for a polarizing plate, which comprises using the pressure-sensitive adhesive according to claim 10. An image display device according to claim 10, wherein a polarizing plate and a liquid crystal cell are bonded together.