JP6667441B2 - Adhesive composition and polarizing plate manufactured using the same - Google Patents

Description

The present invention relates to an adhesive composition, and more particularly, to an adhesive composition having improved adhesion and water resistance while maintaining an excellent degree of polarization, and a polarizing plate manufactured using the same.

Polarization used in various image displays such as liquid crystal display (LCD), electroluminescence (EL) display, plasma display (PDP), field emission display (FED), organic light emitting diode (OLED), etc. The plate generally includes a polarizer in which an iodine compound or a dichroic polarizing substance is adsorbed and oriented on a polyvinyl alcohol (PVA) film, and a polarizer protective film is sequentially formed on one surface of the polarizer. The other surface of the polarizer has a multilayer structure in which a polarizer protective film, a pressure-sensitive adhesive layer bonded to a liquid crystal cell, and a release film are sequentially laminated.

Currently, a polarizing plate having a configuration in which a protective film such as triacetyl cellulose (TAC) is bonded to at least one surface of the polarizer via an adhesive layer formed using an aqueous solution of a polyvinyl alcohol-based resin (polyvinyl alcohol-based adhesive). Although generally used, the polarizing plate having such a configuration has a problem that the end faces of the protective film and the polarizer are easily peeled off when used for a long time under wet heat conditions.

Thus, a polarizing plate has been proposed in which a polarizer (polarizing film) and a protective film are joined together using a polyvinyl alcohol-based adhesive, and then heated and dried at a temperature of 90 to 100 ° C. to improve wet heat resistance. However, the problem that the protective film and the end face of the polarizer are easily peeled off when the device is still used for a long time under the condition of wet heat has not been solved.

In order to improve such problems, JP-A-07-134212 discloses an adhesive composition containing a polyvinyl alcohol-based resin, glyoxal, and zinc chloride.

JP-A-07-134212

An object of the present invention is to provide an adhesive composition having improved adhesion and water resistance while maintaining an excellent degree of polarization.

Another object of the present invention is to provide a polarizing plate bonded with the adhesive composition.

1. Acetoacetyl group-modified polyvinyl alcohol resin (A);
A crosslinking agent (B) containing two or more hydroxy or carboxy groups in the molecule; and a water-soluble chelate compound (C),
An adhesive composition for a polarizing plate, wherein the degree of polymerization of the acetoacetyl group-modified polyvinyl alcohol-based resin (A) is 1,000 or less.

2. In the above item 1, the adhesive composition for a polarizing plate, wherein the acetoacetyl group-modified polyvinyl alcohol resin (A) is contained in the adhesive composition at 3 to 9% by weight.

3. In the above item 1, the cross-linking agent (B) containing a bifunctional or higher functional hydroxyl group in the molecule may be 3-methoxy-1,2-propanediol (3-methoxy-1,2-propanediol), 3-ethoxy-1 An adhesive composition for a polarizing plate, which is at least one selected from the group consisting of 2,3-propanediol (3-ethoxy-1,2-propanediol), diethylene glycol (di-ethylene glycol) and glycerol (glycerol).

4. In the above 1 or 2, the cross-linking agent (B) containing a bifunctional or more carboxy group in the molecule is oxalic acid, malonic acid, dimethylmalonic acid, succinic acid, or the like. An adhesive composition for a polarizing plate, which is at least one selected from the group consisting of succinic acid and glutaric acid.

5. In any one of the above items 1 to 4, the cross-linking agent (B) containing a bifunctional or higher functional hydroxy group or carboxy group in the molecule may be added to 100 parts by weight of the acetoacetyl group-modified polyvinyl alcohol resin (A). An adhesive composition for a polarizing plate, which is contained in an amount of 20 to 50 parts by weight.

6. In any one of the above items 1 to 5, the water-soluble chelate compound (C) is at least one selected from the group consisting of zinc chloride, cobalt chloride, magnesium chloride, magnesium acetate, aluminum nitrate, zinc nitrate and zinc sulfate. An adhesive composition for a polarizing plate.

7. 7. The polarizing plate according to any one of 1 to 6, wherein the water-soluble chelate compound (C) is contained in an amount of 2 to 10 parts by weight based on 100 parts by weight of the acetoacetyl group-modified polyvinyl alcohol-based resin (A). Adhesive composition.

8. The adhesive composition for a polarizing plate according to any one of the above items 1 to 7, which does not contain a crosslinking regulator.

9. A polarizing plate, wherein a protective film is bonded to at least one surface of a polarizer with the adhesive composition for a polarizing plate according to any one of the above 1 to 8.

10. An image display device comprising the polarizing plate according to the above item 9.

ADVANTAGE OF THE INVENTION The adhesive composition for polarizing plates of this invention is excellent in adhesive force and water resistance, while showing an excellent degree of polarization even if it does not contain a crosslinking regulator. Thereby, the durability of the polarizing plate can be remarkably improved.

FIG. 1 is a drawing schematically showing a water resistance evaluation test method according to an experimental example.

The present invention comprises an acetoacetyl group-modified polyvinyl alcohol-based resin (A); a crosslinking agent (B) containing a bifunctional or more functional hydroxy or carboxy group in the molecule; and a water-soluble chelate compound (C). The present invention relates to an adhesive composition for a polarizing plate in which the degree of polymerization of the group-modified polyvinyl alcohol-based resin (A) is 1,000 or less, and the adhesive strength and water resistance are improved while maintaining an excellent degree of polarization.

Hereinafter, the present invention will be described in detail.

<Adhesive composition for polarizing plate>

The adhesive composition for a polarizing plate of the present invention includes an acetoacetyl group-modified polyvinyl alcohol-based resin (A); a cross-linking agent (B) containing at least two functional hydroxy or carboxy groups in the molecule; and a water-soluble chelate compound ( C).

Acetoacetyl group-modified polyvinyl alcohol resin (A)

The acetoacetyl group-modified polyvinyl alcohol-based resin contains a functional group having a higher reactivity than a polyvinyl alcohol resin modified such as a carboxy group-modified, a methylol group-modified or an amino group-modified, and has an improved durability. Excellent in terms of surface.

The acetoacetyl group-modified polyvinyl alcohol-based resin (A) can be obtained by reacting a polyvinyl alcohol-based resin with diketene by a known method. Specifically, after dispersing the polyvinyl alcohol-based resin in a solvent such as acetic acid, a method of adding diketene thereto, after previously dissolving the polyvinyl alcohol-based resin in a solvent such as dimethylformamide or dioxane, It can be obtained by a method of adding diketene, a method of bringing diketene gas or liquid diketene into direct contact with a polyvinyl alcohol-based resin, or the like. The acetoacetyl group-modified polyvinyl alcohol-based resin (A) is not particularly limited as long as it has a degree of acetoacetyl group modification of 0.1 mol% or more, preferably 0.1 to 40 mol%, more preferably 1 to 40 mol%. It is preferably 20 mol%, most preferably 2 to 7 mol%. When the degree of modification of the acetoacetyl group is less than 0.1 mol% or when the degree of modification of the acetoacetyl group exceeds 40 mol%, the effect of improving the water resistance may be insignificant.

The saponification degree of the acetoacetyl group-modified polyvinyl alcohol-based resin (A) is not particularly limited, but is preferably 80 mol% or more, and more preferably 85 mol% or more. If the degree of saponification of the polyvinyl alcohol-based resin contained in the adhesive composition is low, sufficient water-solubility is not easily exhibited, and thus the adhesiveness tends to be insufficient.

The degree of polymerization of the acetoacetyl group-modified polyvinyl alcohol-based resin (A) is 1,000 or less, and when the degree of polymerization is 1,000 or less, the reaction rate is slowed, and the stability of liquid preparation is improved.

Examples of commercially available products that can be used include, but are not limited to, Z-100, Z-200, Z-200H, Z-210, Z-220, Z-320 (Nippon Gohsei Chemical Gohsefimer). It is not something to be done. These may be used alone or in combination of two or more.

The acetoacetyl group-modified polyvinyl alcohol-based resin (A) may be contained in the adhesive composition at 3 to 9% by weight. When the weight ratio of the acetoacetyl group-modified polyvinyl alcohol-based resin (A) contained in the adhesive composition is less than 3% by weight, curing may be insufficient and water resistance may be reduced, and may exceed 9% by weight. In such a case, the viscosity may increase and bubbles may be mixed during the bonding process.

Crosslinking agent containing two or more hydroxy or carboxy groups in the molecule (B)

The cross-linking agent (B) containing two or more hydroxy groups or carboxy groups in the molecule of the present invention includes an acetoacetyl group-modified polyvinyl alcohol-based resin (A), a polyvinyl alcohol (PVA) -based polarizer, a cellulose film, and an olefin-based resin. It plays a role of improving the adhesive strength to a protective film such as a film and the water resistance.

Since the crosslinking agent according to the present invention contains two or more hydroxy groups or carboxy groups in the molecule, a condensation reaction between the hydroxy group or carboxy group and the acetoacetyl group contained in the polyvinyl alcohol-based resin occurs. Thus, the adhesive strength and the water resistance were judged to be improved.

Therefore, the adhesive composition for a polarizing plate according to the present invention is excellent in adhesive strength, water resistance and polarization degree even if it does not contain a crosslinking regulator. Examples of the crosslinking regulator are polyvinyl alcohol-based resins having no acetoacetyl group, and examples thereof include polyvinyl alcohol resins and carboxylic acid-modified polyvinyl alcohol resins.

Specific examples of the crosslinking agent (B) having two or more hydroxy groups in the molecule according to the present invention include 3-methoxy-1,2-propanediol, 3-methoxy-1,2-propanediol, and 3-methoxy-1,2-propanediol. Ethoxy-1,2-propanediol (3-ethoxy-1,2-propanediol), diethylene glycol (di-ethylene glycol), glycerol (glycerol), and the like, each of which may be used alone or in combination of two or more. You may.

Specific examples of the crosslinking agent (B) having two or more carboxy groups in the molecule according to the present invention include oxalic acid, malonic acid, dimethylmalonic acid, and succinic acid. Acids (succinic acid), glutaric acid (glutaric acid) and the like may be mentioned, and these may be used alone or in combination of two or more.

The content of the crosslinking agent (B) containing two or more hydroxy groups or carboxy groups in the molecule of the present invention is not particularly limited. For example, 20 to 50 parts by weight per 100 parts by weight of the acetoacetyl group-modified polyvinyl alcohol-based resin (A). Included in parts by weight. When the crosslinking agent is less than 20 parts by weight with respect to 100 parts by weight of the acetoacetyl group-modified polyvinyl alcohol-based resin (A), the water resistance of the adhesive layer is hardly sufficiently exhibited, and when it exceeds 50 parts by weight, There is a problem that the stability of liquid preparation is reduced.

Water-soluble chelate compound (C)

The water-soluble chelate compound (C) contained in the adhesive composition of the present invention has a crosslinking degree between the adhesive layer and a protective film such as a polyvinyl alcohol (PVA) -based polarizer and a cellulose-based film or an olefin-based film. It can play a role of improving the adhesive strength and water resistance by raising it, and a role of improving the optical durability.

Further, the water-soluble chelate compound (C) of the present invention promotes the curing of the crosslinking agent (B) having a bifunctional or more hydroxy or carboxy group in the molecule.

The water-soluble chelate compound (C) may be used without particular limitation as long as it is used in the art. Specific examples include zinc chloride, cobalt chloride, magnesium chloride, and acetic acid. Examples include magnesium, aluminum nitrate, zinc nitrate, and zinc sulfate. Preferably, zinc chloride, zinc nitrate and aluminum nitrate are desirable in that the role of the crosslinking catalyst is excellent. These may be used alone or in combination of two or more.

The content of the water-soluble chelate compound (C) is not particularly limited, but is, for example, 2 to 10 parts by weight based on 100 parts by weight of the acetoacetyl group-modified polyvinyl alcohol resin (A). When the amount of the water-soluble chelate compound (C) is less than 2 parts by weight based on 100 parts by weight of the acetoacetyl group-modified polyvinyl alcohol resin (A), the water resistance of the adhesive layer is hardly sufficiently exhibited, and 10 parts by weight. If it exceeds, there is a problem that the optical characteristics deteriorate.

Additive

If necessary, the adhesive composition for a polarizing plate of the present invention may further include an additive.

The type of the additive is not particularly limited, for example, a silane coupling agent, fine particles, an alcohol for improving diffusibility, a sensitizer, an adhesion promoter, a leveling agent, an ultraviolet absorber, an antioxidant, a dye, a processing aid, Examples include ion trapping agents, antioxidants, tackifiers, fillers, plasticizers, foam inhibitors, antistatic agents, and fragrances. These may be used alone or in combination of two or more.

The content of the additive is not particularly limited, and may be, for example, 0.01 to 3% by weight, preferably 0.5 to 1% by weight based on the total weight of the adhesive composition.

The viscosity at 20 ° C. of the adhesive composition according to the present invention is preferably in the range of 3 to 25 mPa · sec. When the viscosity of the adhesive composition is less than 3 mPa · sec, the water resistance of the polarizing plate cannot be sufficiently exhibited, and when the viscosity is 25 mPa · sec or more, the optical properties of the polarizing plate cannot be improved. There is a problem that characteristics are deteriorated.

The form of the adhesive composition is not particularly limited, but is preferably liquid in order to form a uniform adhesive layer on the surface of the polarizer or the protective film as an adherend. Such a liquid adhesive may be a solution type or a dispersion type of various solvents, a solution type is preferable in consideration of the coatability of the substrate, and a solution using water as a solvent in consideration of the stability. Molds or dispersion types are preferred.

<Polarizing plate and image display device including the same>

The present invention relates to a polarizing plate in which a protective film is bonded on at least one surface of a polarizer with the adhesive composition for a polarizing plate of the present invention.

The polarizer has a dichroic dye adsorbed and oriented on a stretched polyvinyl alcohol-based resin film.

The polyvinyl alcohol-based resin constituting the polarizer is obtained by saponifying a polyvinyl acetate-based resin. Examples of the polyvinyl acetate-based resin include, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate, a copolymer of vinyl acetate with another monomer copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, vinyl ethers, and acrylamide monomers having an ammonium group. Further, the polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of saponification of the polyvinyl alcohol-based resin is usually 85 to 100 mol%, preferably 98 mol% or more. The degree of polymerization of the polyvinyl alcohol-based resin is usually from 1,000 to 10,000, preferably from 1,500 to 5,000.

What formed such a polyvinyl alcohol type resin as a film is used as a raw film of a polarizer. The method for forming the polyvinyl alcohol resin film is not particularly limited, and a known method can be used. The thickness of the raw film is not particularly limited, and may be, for example, 10 to 150 μm.

The polarizer of the present invention comprises a step of continuously uniaxially stretching a polyvinyl alcohol-based film in an aqueous solution, a step of dyeing and adsorbing with a dichroic dye, a step of treating with a boric acid aqueous solution, and a step of washing and drying. Manufactured through

The step of uniaxially stretching the polyvinyl alcohol-based film may be performed before dyeing, may be performed simultaneously with dyeing, or may be performed after dyeing. When performing uniaxial stretching after dyeing, it may be performed before boric acid treatment or may be performed during boric acid treatment. Of course, it is also possible to perform uniaxial stretching in these plural steps. Rolls or hot rolls having different peripheral speeds can be used for uniaxial stretching. The uniaxial stretching may be dry stretching in the air or wet stretching in a state of being swollen with a solvent. The stretching ratio is usually 3 to 8 times.

In the step of dyeing the stretched polyvinyl alcohol-based film with a dichroic dye, for example, a method of immersing the polyvinyl alcohol-based film in an aqueous solution containing a dichroic dye can be used. As the dichroic dye, iodine or a dichroic dye is used. Further, it is preferable that the polyvinyl alcohol-based film be swelled by immersing it in water before dyeing.

When iodine is used as the dichroic dye, a method of dyeing by dipping a polyvinyl alcohol-based film in an aqueous solution for dyeing containing iodine and potassium iodide can be usually used. Usually, the content of iodine in the aqueous solution for dyeing is 0.01 to 1 part by weight with respect to 100 parts by weight of water (distilled water), and the content of potassium iodide is 0.5 to 20 parts by weight with respect to 100 parts by weight of water. Parts by weight. The temperature of the aqueous solution for dyeing is usually 20 to 40 ° C., and the immersion time (dyeing time) is usually 20 to 1,800 seconds.

When a dichroic dye is used as the dichroic dye, a method of immersing a polyvinyl alcohol-based resin film in an aqueous solution containing a water-soluble dichroic dye and dyeing is usually employed. The content of the dichroic dye in the aqueous solution is usually 1 × 10 ⁻⁴ to 10 parts by weight, preferably 1 × 10 ⁻³ to 1 part by weight per 100 parts by weight of water. The aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the aqueous dye solution used for dyeing is usually 20 to 80 ° C., and the immersion time in the aqueous solution is usually 10 to 1,800 seconds.

The step of treating the stained polyvinyl alcohol-based film with boric acid may be performed by immersing the film in a boric acid-containing aqueous solution. Usually, the content of boric acid in the boric acid-containing aqueous solution is 2 to 15 parts by weight, preferably 5 to 12 parts by weight, per 100 parts by weight of water. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide, and the content thereof is usually 0.1 to 15 parts by weight, preferably 5 to 100 parts by weight of water. To 12 parts by weight. The temperature of the boric acid-containing aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C., more preferably 60 to 80 ° C., and the immersion time is usually 60 to 1,200 seconds, preferably 150 to 600 seconds, More preferably, it is 200 to 400 seconds.

After the boric acid treatment, the polyvinyl alcohol-based film is usually washed with water and dried. The water washing treatment can be performed by immersing the boric acid-treated polyvinyl alcohol-based film in water. The temperature of the water for the water washing treatment is usually 5 to 40 ° C., and the immersion time is usually 1 to 120 seconds. A polarizer can be obtained by drying after washing with water. The drying treatment may be usually performed using a hot air dryer or a far-infrared heater. The drying temperature is usually 30 to 100 ° C., preferably 50 to 80 ° C., and the drying time is usually 60 to 600 seconds, preferably 120 to 600 seconds.

The thickness of the polarizer according to the present invention is not particularly limited, but may be, for example, 5 to 40 μm.

The type of the protective film is not particularly limited as long as it is excellent in transparency, mechanical strength, heat stability, moisture shielding property, isotropy, and the like, and examples thereof include an acrylic resin film, a cellulose resin film, and a polyolefin resin. Various transparent resin films including at least one selected from the group consisting of a resin film and a polyester resin film can be used.

Specific examples of the protective film include acrylic resin films such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; polyester resin films such as polyethylene terephthalate, polyethylene isophthalate, polyethylene naphthalate, and polybutylene terephthalate. Cellulose-based resin films such as diacetylcellulose and triacetylcellulose; polyolefin-based resin films such as polyethylene, polypropylene, cyclo- or polyolefin-based having norbornene structure, and ethylene-propylene copolymer; and the like. It is not something to be done.

The thickness of the protective film is not particularly limited, but may be 10 to 200 μm, preferably 10 to 150 μm. When the thickness of the protective film is 10 to 200 μm, when the polarizer protective films are laminated on both surfaces of the polarizer, the respective protective films may have the same or different thicknesses.

The adhesive composition for a polarizing plate according to the present invention may be applied to at least one surface of the polarizer to form an adhesive layer, and the polarizer and the protective film or the adhesive layer are bonded via the adhesive layer. You may.

The thickness of the adhesive layer formed by applying the adhesive composition of the present invention is not particularly limited, but may be usually 0.01 to 10 μm, and preferably 0.1 to 5 μm. Good. If the thickness of the adhesive layer is less than 0.01 μm, the possibility of air bubbles may increase during bonding, and if the thickness of the adhesive layer is more than 10 μm, the cost may increase. .

In order to improve the adhesiveness, the surface of the polarizer and / or the protective film is appropriately subjected to a surface treatment such as a primer treatment, a plasma treatment, a dry treatment such as a corona treatment, and a chemical treatment such as a saponification (alkali) treatment. Is also good. As the saponification (alkali) treatment, a method of dipping in an aqueous solution of an alkali such as sodium hydroxide or potassium hydroxide may be used.

The other surface of the polarizer having the protective film bonded to one surface is appropriately subjected to a surface treatment such as a hard coat treatment, an anti-reflection treatment, an anti-sticking treatment, a treatment for the purpose of diffusion or anti-glare, as necessary. Is also good.

In addition, the other surface of the polarizer having the protective film bonded to one surface, in addition to the above-described surface treatment, a surface treatment layer such as a hard coating layer, an anti-reflection layer, an anti-glare layer, and an anti-static layer, if necessary. May be further laminated, and the optical functional film may be further laminated by an adhesive layer.

The type of the optical functional film is not particularly limited, for example, an optical compensation film in which a liquid crystal compound or a molecular compound thereof is oriented on the surface of the base material, transmits a certain type of polarized light, and polarized light having the opposite property. Reflection-type polarized light separating film that reflects light, retardation film containing polycarbonate resin, retardation film containing cyclic polyolefin resin, anti-glare function additional film having irregularities on the surface, additional film treated with surface anti-reflection treatment, surface And a transflective film having both a reflective function and a transmissive function.

Further, the present invention provides an image display device including the polarizing plate.

The image display device of the present invention may further include a known configuration in the art in addition to the polarizing plate.

Hereinafter, preferred embodiments will be presented for understanding the present invention. However, these embodiments are merely illustrative of the present invention, and do not limit the scope of the appended claims. It is obvious to those skilled in the art that various changes and modifications to the embodiments can be made within the scope of the technical idea, and it is natural that such changes and modifications belong to the appended claims. It is.

Production Example 1. Manufacture of polarizer

A 75 μm-thick polyvinyl alcohol film having an average degree of polymerization of 2,400 and a degree of saponification of 99.9 mol% or more is uniaxially stretched about 5-fold by a dry method, and 60 ° C. water ( (Distilled water) for 1 minute, and then immersed in a 28 ° C. aqueous solution having a weight ratio of iodine / potassium iodide / distilled water of 0.05 / 5/100 for 60 seconds. Then, it is immersed in an aqueous solution of potassium iodide / boric acid / distilled water at a weight ratio of 8.5 / 8.5 / 100 at 72 ° C. for 300 seconds, washed with distilled water at 26 ° C. for 20 seconds, and then washed at 65 ° C. To produce a polarizer having iodine adsorbed and oriented on a PVA-based film.

Production Example 2. Manufacture of protective films

KC8UX (Konica Corporation, T) which is a triacetylcellulose-based film was used after saponification.

Examples and comparative examples

Example 1

(1) Production of adhesive composition

An acetoacetyl group-modified polyvinyl alcohol-based resin having a saponification degree of 99.2 mol% (Gohsenol Z200, Nippon Synthetic Chemical Industry Co., Ltd., average polymerization degree of 1000 or less) is dissolved in water (distilled water), and an adhesive is prepared. An aqueous solution of an acetoacetyl group-modified polyvinyl alcohol resin having a weight ratio of 6% by weight in the composition was obtained.

The acetoacetyl group-modified polyvinyl alcohol-based resin aqueous solution and 3-methoxy-1,2-propanediol serving as a cross-linking agent were added to 100 parts by weight of the acetoacetyl-group-modified polyvinyl alcohol-based resin. 20 parts by weight with respect to 100 parts by weight of an acetoacetyl-modified polyvinyl alcohol-based resin, and zinc chloride (a water-soluble chelate compound) is mixed and adhered to the mixture. An agent composition was produced.

(2) Bonding of polarizer and protective film (production of polarizing plate)

After applying the adhesive composition to both surfaces of the polarizer produced in Production Example 1 so that the dry film thickness becomes 0.1 μm, a cellulose-based protective film (Konica Corporation, KC8UX (trade name), triacetyl cellulose) Film) was bonded using a nip roll. The bonded polarizing plate was dried with a hot air drier at 80 ° C. for 5 minutes to produce a polarizing plate.

Examples 2 to 9 , Comparative Examples 1 and 5 , and Examples 14 and 15

In the same manner as in Example 1, an adhesive composition having the composition and content (parts by weight) shown in Table 1 below was prepared.

Example 10

An adhesive composition was produced under the same conditions as in Example 1 except that the adhesive composition contained 3% by weight of an acetoacetyl group-modified polyvinyl alcohol.

Example 11

An adhesive composition was produced under the same conditions as in Example 1 except that the adhesive composition contained 9% by weight of an acetoacetyl group-modified polyvinyl alcohol.

Example 12

An adhesive composition was produced under the same conditions as in Example 1 except that the adhesive composition contained 2% by weight of an acetoacetyl group-modified polyvinyl alcohol.

Example 13

An adhesive composition was produced under the same conditions as in Example 1 except that the adhesive composition contained 10% by weight of an acetoacetyl group-modified polyvinyl alcohol.

Experimental example

(1) Evaluation of adhesive strength (cutter evaluation)

After leaving the polarizing plates manufactured in the above Examples and Comparative Examples at room temperature for 1 hour, a cutter blade was inserted between the films of the polarizing plate (between the polarizer and the polarizer protective film), and the blade was pushed forward. The method in which the blade was inserted was evaluated according to the following criteria, and the results are shown in Table 2 below.

◎: The cutter blade does not enter between any films

：: When the blade is pushed forward, it stops when the blade enters at least 1 to 2 mm between any one of the films

△: When the blade is pushed forward, it stops when the blade enters 3 to 5 mm between at least one of the films.

X: When the blade is pushed forward, the blade enters without difficulty between at least one of the films

(2) Evaluation of water resistance

After the polarizing plates manufactured in the above Examples and Comparative Examples were left at 23 ° C. and a relative humidity of 55% for 24 hours, a sample of 5 cm × 2 cm with the absorption axis (stretching direction) as a long side was prepared. Thereafter, the dimension of the long side was accurately measured. Here, the sample exhibits a unique color uniformly over the entire surface due to iodine adsorbed on the polarizer (polarizing film).

1A and 1B are diagrams schematically showing a test method for evaluating water resistance. FIG. 1A shows a sample (1) before immersion in hot water, and FIG. 1B shows a sample (1) after immersion in hot water. I have. As shown in FIG. 1 (A), one side of the sample was gripped by a gripper (5), and about 80% of the sample in the longitudinal direction was immersed in a water bath at 60 ° C. and maintained for 4 hours. Thereafter, the sample (1) was taken out of the water tank and the water was wiped off.

The polarizer (polarizing film) (4) of the polarizing plate shrinks by immersion in warm water. The degree of shrinkage of the polarizer (polarizing film) (4) was measured from the end (1a) (the end of the protective film) at the center of the edge of the sample (1). It was evaluated by measuring the distance to the part, and was defined as the contraction length.

Further, as shown in FIG. 1B, the polarizer (polarizing film) (4) located at the center of the polarizing plate is contracted by immersion in warm water, so that the polarizer (polarizing film) is placed between the protective films. Iodine is eluted from the peripheral portion of (4), and a portion (3) where the color is missing occurs at the peripheral portion of the sample (1). The degree of this bleaching was evaluated by measuring the distance from the edge of the shrunk polarizer (polarizing film) (4) at the center of the edge of the sample (1) to the region where the color peculiar to the polarizing plate remained, The length of iodine was removed. The total of the contracted length and the length from which iodine was removed was defined as the total erosion length. The total erosion length is the distance from the end (1a) of the sample (1) to the region where the color peculiar to the polarizing plate remains at the center of the end of the sample (1). It can be determined that the smaller the contraction length, the length from which iodine has been removed, and the total erosion length, the higher the water resistance in the presence of water. And it evaluated in the following four grades according to the total erosion length, and the result was shown in Table 2.

◎: Total erosion length is less than 2 mm

：: Total erosion length is 2 mm or more and less than 3 mm

Δ: Total erosion length is 3 mm or more and less than 5 mm

X: Total erosion length is 5 mm or more

(3) Evaluation of degree of polarization (%)

The polarizing plate manufactured in each of the above Examples and Comparative Examples was cut into a size of 4 cm × 4 cm to prepare a test piece, and the test piece was attached to a measurement holder. Then, an ultraviolet-visible light spectrometer (V-7100, JASCO) and the results are shown in Table 2.

Referring to Table 2 above, it was confirmed that the adhesive composition according to the present invention has excellent adhesive strength and water resistance while maintaining excellent polarization degree.

DESCRIPTION OF SYMBOLS 1 ... Polarizer sample, 2 ... Polarizer protective film, 3 ... Color missing part, 4 ... Polarizer, 5 ... Grip.

Claims (10)

Acetoacetyl group-modified polyvinyl alcohol resin (A);
A crosslinking agent (B) containing two or more hydroxy groups or carboxy groups in the molecule; and
A water-soluble chelate compound (C),
An adhesive composition for a polarizing plate, wherein the degree of polymerization of the acetoacetyl group-modified polyvinyl alcohol-based resin (A) is 1,000 or less.   2. The adhesive composition for a polarizing plate according to claim 1, wherein the acetoacetyl group-modified polyvinyl alcohol-based resin (A) is contained in an amount of 3 to 9% by weight in the adhesive composition.   The said cross-linking agent (B) is at least one selected from the group consisting of 3-methoxy-1,2-propanediol, 3-ethoxy-1,2-propanediol, diethylene glycol, and glycerol. Or the adhesive composition for polarizing plates of 2.   4. The method according to claim 1, wherein the crosslinking agent (B) is at least one selected from the group consisting of oxalic acid, malonic acid, dimethylmalonic acid, succinic acid, and glutaric acid. 5. Adhesive composition for polarizing plate.   The cross-linking agent (B) containing two or more hydroxy groups or carboxy groups in the molecule is contained in an amount of 20 to 50 parts by weight based on 100 parts by weight of the acetoacetyl group-modified polyvinyl alcohol-based resin (A). 5. The adhesive composition for a polarizing plate according to any one of items 4 to 4.   The water-soluble chelate compound (C) is at least one selected from the group consisting of zinc chloride, cobalt chloride, magnesium chloride, magnesium acetate, aluminum nitrate, zinc nitrate and zinc sulfate. The adhesive composition for a polarizing plate according to claim 1.   The polarized light according to any one of claims 1 to 6, wherein the water-soluble chelate compound (C) is contained in an amount of 2 to 10 parts by weight based on 100 parts by weight of the acetoacetyl group-modified polyvinyl alcohol-based resin (A). An adhesive composition for boards.   The adhesive composition for a polarizing plate according to any one of claims 1 to 7, which does not contain a crosslinking regulator.   A polarizing plate, wherein a protective film is bonded to at least one surface of a polarizer with the adhesive composition for a polarizing plate according to claim 1.   An image display device comprising the polarizing plate according to claim 9.