JP3317578B2 - Polarizing plate having an adhesive layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a polarizing plate in which a protective layer for covering a polarizing film is provided with an adhesive layer.

[0002]

2. Description of the Related Art A polarizing plate coated on both sides with a protective layer of a cellulose film, for example, a cellulose triacetate film, on a polarizing film, for example, a polyvinyl alcohol film having a polarizing property, is used as a liquid crystal. When applied to the cell surface, it is usual to use a polarizing plate provided with an adhesive layer on the surface of the protective layer. It is not known that the polarizing plate has two pressure-sensitive adhesive layers.

[0003]

The above-mentioned pressure-sensitive adhesives include:
Acrylic resin is widely used because of its excellent adhesiveness and transparency, but when exposed to high temperature or high temperature and high humidity conditions, warpage may occur on the glass plate with the polarizing plate attached, When two plates are used (especially at right angles), problems such as light leakage occur. Such problems can be reduced by lowering the holding power of the pressure-sensitive adhesive layer, but problems such as foaming and peeling of the pressure-sensitive adhesive layer occur.

[0004]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and have found that the pressure-sensitive adhesive layer has two layers, and the gel fraction of the first layer is larger than the gel fraction of the second layer. It has been found that the purpose can be achieved by reducing the size. That is, the present invention provides (1) a polarizing plate having a polarizing film layer, a protective layer and an adhesive layer in this order, the adhesive layer is divided into two layers, and the gel fraction of the adhesive on the protective layer side is the other side. A polarizing plate, which is smaller than the gel fraction of the pressure-sensitive adhesive,
(2) The polarizing plate of (1), wherein both the adhesive on the protective layer side and the adhesive on the other side are acrylic resin-based adhesives, and (3) the gel fraction of the adhesive on the protective layer side is 70% by weight. Or less, and the gel fraction of the adhesive on the other side is 60% by weight or more (1)
Or the polarizing plate of (2).

In the present invention, the pressure-sensitive adhesive layer has two layers, and the gel fraction of the pressure-sensitive adhesive on the protective layer side must be smaller than the gel fraction of the pressure-sensitive adhesive on the other side. The adhesive on the protective layer side can be called a soft segment, and the adhesive on the other side can be called a hard segment. The gel fraction of the soft segment is preferably 70% by weight or less, more preferably 10 to 60% by weight, and still more preferably about 20 to 55% by weight from the viewpoint of warpage and light leakage. The gel fraction of the hard segment is preferably at least 60% by weight, more preferably at least 70% by weight, further preferably about 80 to 95% by weight from the viewpoint of foaming and peeling.

The pressure-sensitive adhesive used in the pressure-sensitive adhesive layer of the present invention is preferably an acrylic resin-based pressure-sensitive adhesive for both the soft segment and the hard segment from the viewpoint of transparency. The acrylic resin is obtained by copolymerizing a polar monomer component with an acrylic acid-based alkyl ester as a main component.
The copolymerization ratio of the polar monomer component is preferably 0.1 to 100 parts by weight of the acrylic acid alkyl ester component.
It is generally 20 parts by weight, more preferably 0.5 to 15 parts by weight, further preferably about 1 to 10% by weight.

As the acrylic acid alkyl ester,
Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, ( Meta)
Alkyl acrylates having an alkyl group having about 1 to 12 carbon atoms, such as octyl acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, undecyl (meth) acrylate, and dodecyl (meth) acrylate And alkyl methacrylate. These may be used in combination of two or more as necessary.

As the polar monomer, those which function as a crosslinking point with a crosslinking agent described later are used. Although there is no particular limitation on its type, generally those having a hydroxyl group or a carboxylic acid group are preferred, for example, acrylic acid, carboxyl group-containing acrylic acid monomers such as methacrylic acid,
Hydroxyl group-containing (meth) acrylate monomers such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate, N, N-dimethylaminoethyl acrylate, Nt And acrylic acid-based polar monomers such as amino group-containing (meth) acrylic acid monomers such as -butylaminoethyl acrylate, and maleic acid. These may be used in combination of two or more as necessary.

The pressure-sensitive adhesive is used in a composition capable of crosslinking an acrylic resin by blending a crosslinking agent. An appropriate crosslinking agent may be used. In general, for example, aliphatic diisocyanates such as hexamethylene diisocyanate and trimethylolpropane adduct of hexamethylene diisocyanate;
Polyisocyanate compounds such as aromatic diisocyanates such as tolylene diisocyanate and tolylene diisocyanate trimethylolpropane adduct; butyl ether;
Melamine compounds such as styrol-melamine and trimethylol-melamine; diamine compounds such as hexamethylenediamine and triethyldiamine; bisphenol A
Epoxy resin compounds such as epichlorohydrin type epoxy resin and polyethylene glycol diglycidyl ether; urea resin compounds; metal salts such as aluminum chloride, ferric chloride, aluminum sulfate, and copper acetate are used. The amount of the crosslinking agent is usually 0.001 to 10 parts by weight, preferably 0.005 to 10 parts by weight per 100 parts by weight of the acrylic resin.
5 parts by weight, more preferably about 0.01 to 3 parts by weight.

The gel fraction of the pressure-sensitive adhesive used in the pressure-sensitive adhesive layer can be adjusted, for example, by controlling the amount of the crosslinking agent. The amount of the crosslinking agent varies depending on the type of the polar monomer component of the acrylic resin, the copolymerization ratio, the type of the crosslinking agent, the production conditions, and the like. Specifically, an acrylic resin having a weight-average molecular weight of 1.5 million (n-butyl acrylate / acrylic acid / 2-hydroxyethyl acrylate = 94.5% by weight / 5% by weight / 0.5% by weight) was prepared by adding In the case of crosslinking with a trimethylolpropane adduct of diisocyanate (1 mol of the latter added to 3 mol of the former), 0.2 to 10 parts by weight of a crosslinking agent per 100 parts by weight of the acrylic resin may cause gelation. An adhesive having a ratio of more than 70% by weight is obtained. When the amount of the crosslinking agent is less than the above amount, an adhesive having a gel fraction of 70% by weight or less can be obtained. In addition, an acrylic resin having a weight average molecular weight of 1.5 million (n-
Butyl acrylate / acrylic acid = 95.0% by weight / 5
% By weight) with a trimethylolpropane adduct of tolylene diisocyanate (1 mol of the latter added to 3 mol of the former), the crosslinking agent is an acrylic resin 1
When 2.0 to 10 parts by weight per 100 parts by weight is used, an adhesive having a gel fraction of more than 70% by weight can be obtained. can get.

The composition and molecular weight of the acrylic resin-based pressure-sensitive adhesive are not particularly limited.
The weight average molecular weight of the acrylic resin-based pressure-sensitive adhesive used for the layer (i) is preferably 1,000,000 or less from the viewpoint of warpage and light leakage. The weight average molecular weight of the acrylic resin pressure-sensitive adhesive used for the hard segment layer (second layer) is preferably 700,000 to 1.5 million from the viewpoint of heat resistance and adhesion.

The polarizing plate of the present invention is obtained by using a polyvinyl alcohol-based polarizing plate film as a base material, providing a protective layer thereon, and then adding an adhesive layer and a release film. As a method of adding an adhesive layer and a release film, a method in which a hard segment layer is provided on a release film, a soft segment layer is provided thereon, and a polarizing film is bonded thereon, or Is usually provided with a soft segment layer, a hard segment layer provided thereon, and a release film laminated thereon. The thickness of the adhesive layer is
Each of the first and second layers is preferably 5 to 100 μm.
m, more preferably about 10 to 50 μm.

[0013]

The present invention will be described more specifically with reference to formulation examples, examples and comparative examples. The gel fraction is obtained by immersing 1 g of the pressure-sensitive adhesive in 100 g of methyl ethyl ketone for 4 days, taking out the dried product, and drying at 110 ° C. for 2 hours. . Gel fraction = (weight after immersion) / (weight before immersion) * 10
0 (% by weight)

Formulation Example 1 Acrylic resin having a weight average molecular weight of 700,000 (resin component: n-
Butyl acrylate / methyl acrylate / 2-hydroxyethyl acrylate = 80% by weight / 18% by weight / 2
100% by weight of trimethylolpropane (1 mol) of tolylene diisocyanate (3 mol)
0.3 part by weight of an adduct was added to obtain a pressure-sensitive adhesive composition. The adhesive composition was applied to a release film with a coater so that the thickness after drying was 25 μm, and dried at 100 ° C. for 3 minutes to obtain an adhesive (A). The gel fraction of the adhesive (A) is 3
It was 0% by weight.

Formulation Example 2 Acrylic resin having a weight average molecular weight of 1.5 million (resin component:
n-butyl acrylate / acrylic acid / 2-hydroxyethyl acrylate = 94.5% by weight / 5% by weight / 5.
1.0 part by weight of trimethylolpropane (1 mol) adduct of tolylene diisocyanate (3 mol) to 100 parts by weight of a copolymer (5% by weight) and 0.5 part by weight of γ-glycidoxypropylmethoxysilane Was added to obtain a pressure-sensitive adhesive composition. The coating and drying were performed in the same manner as in Example 1 to obtain an adhesive (B). The gel fraction of the pressure-sensitive adhesive (B) was 90% by weight.

Example 1 A polyvinyl alcohol polarizing film having a thickness of 25 μm (average degree of polymerization: 1700, average saponification degree: 99.5 mol%, stretched 4 times) was laminated on both sides with a triacetyl cellulose film having a thickness of 80 μm. An adhesive (A) and then an adhesive (B) were laminated on one surface of the polarizing plate, and pressed with a roller to produce a polarizing plate having an adhesive layer. The polarizing plate having the pressure-sensitive adhesive layer was attached to a glass plate and a durability test (90
℃ / 500 hours, 60 ° C 90% RH / 500 hours)
Was done. Table 1 shows the results.

Comparative Examples 1 to 3 Examples except that only one layer of the adhesive (A), only one layer of the adhesive (B), the first layer was the adhesive (B), and the second layer was the adhesive (A) In the same manner as in Example 1, a polarizing plate having an adhesive layer was prepared.
The physical property values measured in the same manner as in the same example are shown in Table 1.

The evaluation method of the durability test is as follows. The polarizing plates of Example 1 and Comparative Examples 1 to 3 having an adhesive layer were cut to a size of 120 * 90 mm with an absorption axis of 45 degrees, and a size of 200 * 100 m was formed on the adhesive surface.
A glass plate having a thickness of 1.1 mm and a thickness of 1.1 mm was stuck together with a laminator so as to prevent air bubbles from entering into a test piece. The test piece was placed on a glass stand and left for 500 hours in a thermostat at 90 ° C. or a thermostat at 60 ° C. and 90% RH, and the following evaluation was performed. Peeling state: Changes in appearance due to peeling were visually observed. Foaming state: Changes in appearance due to peeling were visually observed. Glass warpage: Changes in the appearance of the glass were visually observed. Light Leakage: The test piece was placed in a crossed Nicols state, the transmittance at the measurement positions (A, B) shown in FIG. 1 was measured, and evaluated by the lightness index ratio.

The evaluation criteria are as follows. Peeling state evaluation Peeling less than 0.5 mm ◎ Peeling 0.5 to 1.0 mm △ Peeling more than 1.0 mm × Foaming state No bubbles with a diameter of 20 μm or more are found ◎ A few bubbles with a diameter of 20 to 40 μm are found △ Many bubbles with a diameter of 20 to 40 microns are observed × Glass warpage Glass warpage is less than 0.5 mm ◎ Glass warpage 0.5 to 1.0 mm △ Glass warpage exceeds 1.0 mm × Light leakage Brightness × index ratio (L _B / L _a) is to less than 1.5 ◎ luminosity index ratio 1.5 to 2.0 △ luminosity index ratio exceeds 2.0

[0020]

[Table 1]

[0021]

The polarizing plate of the present invention does not warp, leak light, peel off or foam the adhesive at high temperature, high temperature and high humidity. Utilizing such characteristics, it is used for a liquid crystal display, and is particularly useful for a vehicle, various industrial instruments, display of household electric appliances, and the like.

[Brief description of the drawings]

FIG. 1 shows the measurement positions A and B of the transmittance. Here, the arrow represents the absorption axis of the polarizing plate.

Continuation of front page (56) References JP-A-5-196812 (JP, A) JP-A-5-297220 (JP, A) JP-A-59-111115 (JP, A) JP-A-60-169803 (JP) , A) JP-A-60-207101 (JP, A)

Claims (3)

(57) [Claims] (1) a polarizing film layer, a protective layer and an adhesive layer,
A polarizing plate having a polarizing plate having this order, wherein the pressure-sensitive adhesive layer is divided into two layers, and the gel fraction of the pressure-sensitive adhesive on the protective layer side is smaller than the gel fraction of the pressure-sensitive adhesive on the other side. 2. The polarizing plate according to claim 1, wherein the adhesive on the protective layer side and the adhesive on the other side are both acrylic resin-based adhesives. 3. The gel fraction of the pressure-sensitive adhesive on the protective layer side is 70% by weight.
3. The polarizing plate according to claim 1, wherein the pressure-sensitive adhesive on the other side has a gel fraction of 60% by weight or more. 4.