HK1099785B - Water-based adhesive for polarizing element and polarizer obtained with the same - Google Patents

Description

Water-based adhesive for polarizing element and polarizer obtained using the same

Technical Field

The present invention relates to a water-based adhesive for polarizing elements and a polarizer obtained using the same. More particularly, the present invention relates to a water-based adhesive for polarizing elements which is excellent in adhesion of a polarizing element and a protective film and in which adhesion durability particularly in a high-temperature and high-humidity environment is improved, and a polarizer obtained using the adhesive.

Background

Currently, a polarizer is generally manufactured by laminating a protective film such as cellulose acetate film on at least one side of a polarizing element comprising a stretched and oriented film of polyvinyl alcohol (hereinafter abbreviated as "PVA") or its derivative containing iodine or dichroic dye, using an aqueous solution containing a PVA resin as an adhesive.

The polarizer having such a structure has such a drawback that: the polarizing element and the protective film are easily separated from each other when exposed to high temperatures for a long time. In recent years, liquid crystal display devices are used for desktop computers, electronic watches or clocks, personal computers, cellular phones, and instruments for automobiles and machines, and are used or stored under increasingly severe environmental conditions. Therefore, there sometimes arises a problem that: particularly in a high humidity environment, the polarizing element and the protective film are separated from each other, resulting in deterioration of display quality of the liquid crystal display device. In order to improve the strength of the adhesive, there is a method of accelerating the reaction of the adhesive components, and in this case, the usable life in a solution state, so-called "container life", becomes shorter, so that it is necessary to use a two-pack type adhesive. However, in order to improve productivity, a one-pack type adhesive is desirable.

Non-patent document 1 discloses a general method of improving the water resistance of a PVA resin-based adhesive.

Patent document 1 and patent document 2 disclose that an adhesive containing a PVA resin, a resin having a maleic anhydride skeleton in the structure, and a crosslinking agent is used as a wood adhesive.

Patent document 1: JP-A-49-93446

Patent document 2: JP-B-03-7230

Non-patent document 1: "POVAL", page 256-261, written by Nagano, Yamane and Toyoshima and published by Polymer publication Society on 4/1 1981

Disclosure of Invention

Problems to be solved by the invention

An object of the present invention is to provide an adhesive for a polarizing element for providing a polarizer which comprises a polarizing element, particularly a polarizing element containing a boron compound, and a protective film, and which is suppressed in separation between the polarizing element and the protective film in a high-humidity environment, and is excellent in durability. It is another object of the present invention to provide a polarizer obtained by using the adhesive for a polarizing element.

Means for solving the problems

As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved and a one-pack type adhesive having a sufficient pot life can be obtained by using an adhesive containing a PVA resin, a resin having a maleic anhydride skeleton in its structure, and a crosslinking agent as an adhesive for a polarizer. Thus, the present invention has been completed.

That is, the present invention relates to a water-based adhesive for a polarizing element, which contains a polyvinyl alcohol resin, a resin having a maleic anhydride skeleton in its structure, and a crosslinking agent.

The present invention also relates to a polarizer comprising a polarizing element and a protective film bonded to the polarizing element with an adhesive, wherein the adhesive is the above-mentioned water-based adhesive for polarizing elements.

THE ADVANTAGES OF THE PRESENT INVENTION

By bonding the polarizing element and the protective film with the water-based adhesive for polarizing elements of the present invention, the occurrence of separation between the polarizing element and the protective film can be suppressed, and the resulting polarizer can be used and stored in an environment of high temperature and high humidity, which is not possible with a conventional polarizer.

Further, the heat resistance, high temperature and high humidity resistance, and heat and light resistance of the polarizer can be improved by increasing the content of the boron compound in the polarizing element, and the water-based adhesive for polarizing elements of the present invention can give particularly excellent effects on the adhesion between the polarizing element and the protective film, which is deteriorated due to the increase of the boron compound. That is, the water-based adhesive for polarizing elements of the present invention exerts a particularly excellent effect on adhesion between the polarizing element and the protective film even when the content of the boron compound in the polarizing element is increased to about 25 to 40% by weight in terms of boric acid over a content of about 13 to 25% by weight which is generally employed in conventional polarizing elements.

Best mode for carrying out the invention

The water-based binder for a polarizing element of the present invention contains a PVA resin, a resin having a maleic anhydride skeleton in the structure, and a crosslinking agent as essential components.

The PVA resin used in the water-based binder for a polarizing element of the present invention may be a modified PVA resin or a mixture of a PVA resin and a modified PVA resin. As the modified PVA resin, a saponified product of a copolymer of vinyl acetate and an unsaturated carboxylic acid or its derivative, an olefin, a vinyl ether, an unsaturated sulfonate, or the like, or a reaction product of a PVA resin with an aldehyde, a methylol compound, an epoxy compound, an isocyanate, or the like can be used. The modified PVA resin is preferably a modified PVA resin having a carboxyl group, and more preferably a modified PVA resin having an acetoacetyl group.

The average saponification degree of the PVA resin used in the water-based binder for polarizing elements of the present invention is 85 mol% or more, preferably 98 mol% or more. The average polymerization degree of the PVA resin may be optional, and is preferably 500 or more, more preferably 1000-5000.

As the resin having a maleic anhydride skeleton in the structure used in the water-based adhesive for polarizing elements of the present invention, a copolymer of maleic anhydride and α -olefin can be mentioned. By alpha-olefins are meant linear or branched olefins containing a carbon-carbon double bond in the alpha-position, in particular those containing from 2 to 12 carbon atoms, especially those containing from 2 to 8 carbon atoms.

Examples of alpha-olefins that may be used are ethylene, propylene, n-butene, isobutylene, n-pentene, isoprene, 2-methyl-1-butene, n-hexene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 2-ethyl-1-butene, 1, 3-pentadiene, 1, 3-hexadiene, 1, 4-hexadiene, 2, 3-dimethylbutadiene, 2, 4, 4-trimethyl-1-pentene, 2-methyl-1, 3-pentadiene, 2, 5-heptadiene, 1, 3-heptadiene, 2-methyl-1, 3-hexadiene, 1, 3-octadiene, and the like. Among them, particularly preferred are copolymers of isobutylene. As isobutylene, RETURN B.B (a mixture of isobutylene, 1-butene, 2-butene, etc.) can be used. These olefins may be used each alone or in combination of two or more.

The weight average molecular weight of the copolymer of maleic anhydride and isobutylene is preferably 55,000-350,000. If the molecular weight is too high, the viscosity of the binder is too high and coatability is poor. If the molecular weight is too low, the water resistance is insufficient.

The resin having a maleic anhydride skeleton in the structure may contain maleic acid or a salt thereof in the structure in addition to maleic anhydride. The method of introducing maleic acid or a salt thereof into the structure may be amidation of maleic anhydride or copolymerization of maleic anhydride with maleic acid or a derivative thereof.

The resin having a maleic anhydride skeleton in the structure may contain maleimide in addition to maleic anhydride in the structure. The method of introducing maleimide into the structure may be imidization of maleic anhydride or copolymerization of maleic anhydride and maleimide. Examples of maleimides are maleimide; n-substituted alkylmaleimides such as N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-N-butylmaleimide, N-t-butylmaleimide and N-cyclohexylmaleimide; n-substituted alkylphenylmaleimides such as N-methylphenylmaleimide and N-ethylphenylmaleimide; n-alkoxyphenylmaleimides, such as N-methoxyphenylmaleimide and N-ethoxyphenylmaleimide; and their halides, such as N-chlorophenylmaleimide. Among them, maleimide is preferable.

In the resin having a maleic anhydride skeleton in the structure, in the case of those which are easily soluble in water, even water alone may be used as a solvent, but in the case of those which are not easily soluble in water or insoluble in water, they are dissolved in water containing an alkaline substance. The alkaline substance includes, for example: ammonia and ammonia carbonates, phosphates or acetates; organic amines, such as monoethanolamine, diethanolamine, triethanolamine and other alkanolamines, aliphatic amines and aromatic amines; and inorganic salts such as oxides, hydroxides or carbonates of alkaline earth metals, and hydroxides, carbonates, silicates, phosphates and acetates of alkali metals. Among them, preferred are ammonia, carbonates of ammonia, organic amines, oxides, hydroxides or carbonates of alkaline earth metals, and hydroxides or carbonates of alkali metals. These may be used each alone or in combination of two or more.

The crosslinking agent used in the present invention may be those which react with the PVA resin and the resin having a maleic anhydride skeleton in the structure to cause them to crosslink, and is preferably a compound having an epoxy group. Examples of crosslinking agents are: glyoxal, formalin, borax, boric acid, aziridine, dialdehyde starch, melamine resin, polyamide resin, polyethylenimine resin, polyamide epichlorohydrin resin, ketone aldehyde resin, glycine, glycidyl ester, glycidyl ether, ketene dimer, dimethylol urea, ammonium chloride, magnesium chloride, calcium hydroxide, zirconium ammonium carbonate, etc., and preferred are polyglycidyl ethers of polyhydric alcohols and adducts of diamines with glycidyl groups.

In the water-based binder for a polarizing element of the present invention, the weight ratio of the PVA resin to the resin having a maleic anhydride skeleton in the structure is 100/1 to 1000, preferably 100/10 to 1000, more preferably 100/50 to 500. In the adhesive, the weight ratio of the PVA resin and the crosslinking agent is 100/0.5 to 5000, preferably 100/1 to 1000, more preferably 100/5 to 500.

The water-based adhesive for polarizing elements of the present invention can be easily prepared by dissolving a PVA resin, a resin having a maleic anhydride skeleton in the structure, and a crosslinking agent in water or water containing an alkaline substance at the above-mentioned ratio. The concentration including the resin and the crosslinking agent is preferably 2 to 30 wt%, more preferably 2 to 10 wt%.

The polarizer of the present invention comprises a polarizing element and a protective film bonded to each other with a water-based adhesive using the polarizing element of the present invention. The polarizing element used for the polarizer of the present invention is preferably a PVA resin film, and particularly preferably a uniaxially stretched PVA resin film. The PVA resin used for the film is usually produced by saponification of polyvinyl acetate, but the starting material is not necessarily limited to polyvinyl acetate, and may contain a component copolymerizable with vinyl acetate, such as an unsaturated carboxylic acid or its derivative, an olefin, a vinyl ether and an unsaturated sulfonate. The average saponification degree of the PVA resin is suitably 85% or more, preferably 98% or more. The average polymerization degree of the PVA resins used in the present invention may be optional, and is usually 1500 or more, preferably 2300-5000.

The polarizing element used for the polarizer of the present invention is generally prepared by dyeing a PVA resin film in an aqueous solution of iodine or dichroic dye and then uniaxially stretching the film by a wet or dry process. The polarizing element used for the polarizer of the present invention may also be produced by a method of simultaneously performing dyeing and stretching, a method of performing dyeing after stretching, or a method of stretching a PVA resin film prepared by adding a substance having dichroism during the production of the film.

As the dichroic dye, known dyes can be used, and examples thereof are: C.I.direct Yellow 12, C.I.direct Yellow 28, C.I.direct Yellow 44, C.I.direct Orange 26, C.I.direct Orange 39, C.I.direct Orange 107, C.I.direct Red 2, C.I.direct 31, C.I.direct Red 79, C.I.direct Red 81, C.I.direct 247, C.I.direct Green 80, C.I.direct Green 59, and the dyes disclosed in JP-A-59-145255, JP-A-60-156759, JP-A-3-12606, JP-A-11-218610 and JP-A-627-332001. These dyes are generally used in the form of the free acids, alkali metal salts, ammonium salts and amine salts. They may be used each alone, and if necessary, two or more may be used in combination. There is no limitation on the dye used in combination, and those having absorption characteristics in different wavelength ranges and high dichroism are preferable.

In producing the boron-containing polarizing element used for the polarizer of the present invention, for example, a method of immersing the PVA resin film in an aqueous solution containing boric acid before or after dyeing, and a method of immersing the PVA resin film in a dyeing solution containing boric acid to simultaneously perform dyeing can be employed. In the present invention, a method of immersing the PVA resin film in an aqueous solution containing boric acid after dyeing is preferable. When the PVA resin film is stretched, it is preferable to perform uniaxial stretching in an aqueous solution containing boric acid in which the PVA resin film is immersed after dyeing. If the PVA resin film is further immersed in an aqueous solution containing boric acid after uniaxial stretching, the concentration of boric acid can be controlled without changing the optical characteristics obtained by the uniaxial stretching. In this case, the concentration of boric acid in the aqueous solution is preferably 1 to 20% by weight, and the temperature of the solution is preferably 20 to 80 ℃. The boron content in the commercially available polarizer is about 13 to 25 wt% in terms of boric acid concentration, and if it is higher than 25 wt%, the heat resistance and light resistance are improved. However, if the boron content in the polarizing element is too high, the adhesiveness is lowered, and therefore the boron content is preferably 10 to 40 wt% in terms of boric acid concentration. It is preferably 25 to 40 wt% in view of heat resistance and light resistance. As the boron compound, borax or the like can be used. If necessary, a water washing step may be added to the above-mentioned film preparation step.

The polarizer of the present invention is obtained by laminating a protective film excellent in optical transparency and mechanical strength on one side or both sides of the above-described polarizing element by using the adhesive for a polarizing element of the present invention. As the protective film, for example, a cellulose acetate film such as a cellulose diacetate film and a cellulose triacetate film is used, and in addition, an acrylic film, a fluorine-based film such as a tetrafluoroethylene/hexafluoropropylene film, a polyester resin film, a polyolefin resin film, a polycycloolefin resin film and a polyamide resin film may be used. In addition, as the protective film, the above-mentioned resin film whose surface has been pretreated with a material for improving adhesion, such as a PVA resin, may also be used. Further, the protective film may be a film having a function of a flame-retardant film or a viewing angle-enlarging film, such as those having a retardation by themselves or those coated with a liquid crystal compound, or the like. It is also effective to subject the surface of the protective film to saponification treatment using an alkaline substance, corona discharge treatment, glow discharge treatment, electron radiation treatment or high-frequency treatment. The surface of the protective film may also be subjected to pretreatment with a material that improves adhesion to the polarizing element.

A transparent protective layer may be further provided on the surface of the polarizer of the present invention. As the protective layer, for example, an acrylic or silicone hard coat layer, and a urethane protective layer may be mentioned. In addition, in order to further improve the visibility of the liquid crystal display device, an AR (anti-reflection) layer, an LR (low reflection) layer, or an AG (anti-glare) layer may also be provided on the protective layer, each alone or in combination. The AR layer and the LR layer may be formed by vapor deposition or sputtering of a material such as silicon dioxide, titanium dioxide, or magnesium fluoride, or by thinly coating a fluorine-based material. The AG layer may be formed, for example, by dispersing a filler in the hard coat layer. The polarizer of the present invention can be used as an elliptical polarizer by laminating a phase difference plate on the polarizer of the present invention.

The present invention will be explained in more detail by the following examples and test examples, which should not be construed as limiting the present invention. In these examples, "part" means "part by weight" and "%" means "% by weight" unless otherwise specified. The content of the boron compound in the polarizing element was calculated as the amount of boric acid, which was obtained by dissolving the polarizing element in distilled water under heating and performing neutralization titration with sodium hydroxide.

Example 1

50 parts of an aqueous solution containing 5.0% of a PVA resin (having an average degree of polymerization of 2600 and a degree of saponification of 99.4 mol% or more), 50 parts of an aqueous ammonium solution containing 5.0% of a resin having a maleic anhydride skeleton in the structure (trade name: ISOBAN-18, manufactured by Kuraray Co., Ltd.; a copolymer of maleic anhydride and isobutylene having a weight-average molecular weight of 300,000-350,000) and 1.25 parts of polyglycerol polyglycidyl ether (trade name: DENACOL EX-521, manufactured by Nagase Chemtex Co., Ltd.) were mixed to obtain a water-based adhesive for polarizing elements of the present invention. Then, ｃA PVA film having an average degree of polymerization of 4000, ｃA degree of saponification of 99.9 mol% and ｃA thickness of 75 μm was dyed at 45 ℃ for 4 minutes in an aqueous solution containing Natrii sulfas and ｃA dichroic dye in the form of ｃA free acid disclosed in JP-A-2001-33627 and represented by the following formulｃA (1), and then without ｃA drying step, the film was introduced into an aqueous solution at 58 ℃ containing 3 wt% boric acid, and the film was uniaxially stretched 5 times in the aqueous solution. The film was washed by further immersing in a water bath at room temperature, and dried at 70 ℃ for 10 minutes to obtain a polarizing element. The polarizing element and the cellulose triacetate film saponified with an alkaline substance were bonded to each other using the above-obtained water-based adhesive, and dried at 70 ℃ for 5 minutes, and further dried at 100 ℃ for 5 minutes to obtain a polarizer of the present invention. In this example, the boron content in the polarizing element was 16% in terms of boric acid concentration.

[ formula 1]

Example 2

A water-based adhesive for a polarizing element of the invention was obtained in the same manner as in example 1, except that the concentration of the PVA resin in the aqueous solution was 4.0% and the concentration of the resin having a maleic anhydride skeleton in the structure in the aqueous ammonium solution was 4.0%. A polarizer was then obtained in the same manner as in example 1 using the resulting adhesive.

Example 3

67 parts of an aqueous solution containing 5.0% of a PVA resin (having an average degree of polymerization of 2600 and a degree of saponification of 99.4 mol% or more), 33 parts of an aqueous ammonium solution containing 5.0% of a resin having a maleic anhydride skeleton in the structure (trade name: ISOBAN-18, manufactured by Kuraray Co., Ltd.; a copolymer of maleic anhydride and isobutylene having a weight-average molecular weight of 300,000-350,000) and 0.83 part of polyglycerol polyglycidyl ether (trade name: DENACOL EX-521, manufactured by Nagase Chemtex Co., Ltd.) were mixed to obtain a water-based adhesive for polarizing elements of the present invention. A polarizer was then obtained using the resulting adhesive in the same manner as in example 1.

Example 4

17 parts of an aqueous solution containing 5.0% of a PVA resin (having an average degree of polymerization of 2600 and a degree of saponification of 99.4 mol% or more), 83 parts of an aqueous ammonium solution containing 5.0% of a resin having a maleic anhydride skeleton in the structure (trade name: ISOBAN-18, manufactured by Kuraray Co., Ltd.; a copolymer of maleic anhydride and isobutylene having a weight-average molecular weight of 300,000-350,000) and 2.08 parts of polyglycerol polyglycidyl ether (trade name: DENACOL EX-521, manufactured by Nagase Chemtex Co., Ltd.) were mixed to obtain a water-based adhesive for polarizing elements of the present invention. A polarizer was then obtained using the resulting adhesive in the same manner as in example 1.

Example 5

A water-based adhesive for a polarizing element of the present invention was obtained in the same manner as in example 1, except that the amount of the polyglycerol polyglycidyl ether was changed to 0.25 part. A polarizer was then obtained using the resulting adhesive in the same manner as in example 1.

Example 6

A water-based adhesive for a polarizing element of the present invention was obtained in the same manner as in example 1, except that the amount of the polyglycerol polyglycidyl ether was changed to 2.5 parts. A polarizer was then obtained using the resulting adhesive in the same manner as in example 1.

Example 7

A polarizer was obtained using the water-based adhesive for a polarizing element of the present invention in the same manner as in example 1, except that drying after bonding was performed at 70 ℃ for 10 minutes.

Example 8

A water-based adhesive for a polarizing element of the invention was obtained in the same manner as in example 1, except that the PVA resin was changed to a modified PVA resin having an acetoacetyl group (trade name: Z-200H, produced by Nippon Synthetic Chemical Industry co., ltd.). Then, a polarizer was obtained using the obtained adhesive in the same manner as in example 1.

Example 9

A water-based adhesive for a polarizing element of the invention was obtained in the same manner as in example 1, except that 1, 3-bis (N, N-diglycidylaminomethyl) cyclohexane (trade name: TETRAD-C, produced by Mitsubishi Gas Chemical Company, inc.) was used as the crosslinking agent. Then, a polarizer was obtained using the obtained adhesive in the same manner as in example 1.

Example 10

A water-based adhesive for a polarizing element of the present invention was obtained in the same manner as in example 1, except that a copolymer of maleic anhydride and isobutylene (trade name: ISOBAN-04, produced by Kuraray co., ltd.) having a weight average molecular weight of 55,000-65,000 was used as the resin having a maleic anhydride skeleton in the structure. Then, a polarizer was obtained using the obtained adhesive in the same manner as in example 1.

Example 11

The water-based adhesive for a polarizing element of the present invention was obtained in the same manner as in example 1 except that the resin having a maleic anhydride skeleton in the structure used was a resin in which a part of maleic anhydride was maleimide (trade name: ISOBAN-310, produced by Kuraray co., ltd.; a copolymer of maleic anhydride and isobutylene in which a part of maleic anhydride was replaced with maleimide and the weight average molecular weight was 160,000-170,000). Then, a polarizer was obtained using the obtained adhesive in the same manner as in example 1.

Example 12

50 parts of an aqueous solution containing 5.0% of a PVA resin (average degree of polymerization 2600, degree of saponification 99.4 mol% or more), 50 parts of an aqueous solution containing 5.0% of a resin having a structure having maleic anhydride and maleic amic acid skeleton (trade name: ISOBAN-104, manufactured by Kuraray Co., Ltd.; a copolymer of maleic anhydride and isobutylene in which a part of maleic anhydride was replaced by an ammonium salt of maleic amic acid and having a weight average molecular weight of 55,000-65,000) and 1.25 parts of polyglycerol polyglycidyl ether (trade name: DENACOL EX-521, manufactured by Nagase Chemtex Co., Ltd.) were mixed to obtain a water-based adhesive for a polarizing element of the present invention. Then, a PVA film having an average polymerization degree of 4000, a saponification degree of 99.9 mol% and a thickness of 75 μm was dyed at 45 ℃ in an aqueous solution containing the dichroic dye represented by the above formula (1) and mirabilite, and then without a drying step, the film was introduced into an aqueous solution of 58 ℃ containing 3 wt% boric acid, and the film was uniaxially stretched 5 times in the aqueous solution. The film was washed by further immersing in a water bath at room temperature, and dried at 70 ℃ for 10 minutes to obtain a polarizing element. The polarizing element and the cellulose triacetate film saponified with an alkaline substance were bonded to each other using the above-obtained water-based adhesive, and dried at 70 ℃ for 5 minutes, and further dried at 100 ℃ for 5 minutes to obtain a polarizer of the present invention. In this example, the boron content in the polarizing element was 16% in terms of boric acid concentration.

Example 13

50 parts of an aqueous solution containing 5.0% of a PVA resin (having an average degree of polymerization of 2600 and a degree of saponification of 99.4 mol% or more), 50 parts of an aqueous ammonium solution containing 5.0% of a resin having a maleic anhydride skeleton in the structure (trade name: ISOBAN-18, manufactured by Kuraray Co., Ltd.; a copolymer of maleic anhydride and isobutylene having a weight-average molecular weight of 300,000-350,000) and 1.25 parts of polyglycerol polyglycidyl ether (trade name: DENACOL EX-521, manufactured by Nagase Chemtex Co., Ltd.) were mixed to obtain a water-based adhesive for polarizing elements of the present invention. Then, a PVA film having an average polymerization degree of 4000, a saponification degree of 99.9 mol% and a thickness of 75 μm was dyed at 45 ℃ in an aqueous solution containing the dichroic dye represented by the above formula (1) and mirabilite, and then without a drying step, the film was introduced into an aqueous solution of 58 ℃ containing 3 wt% boric acid, and the film was uniaxially stretched 5 times in the aqueous solution. The film was further immersed in an aqueous solution containing 5 wt% boric acid at 55 ℃ for 5 minutes, washed with water, and then dried at 70 ℃ for 10 minutes to obtain a polarizing element. The polarizing element and the cellulose triacetate film saponified with an alkaline substance were bonded to each other using the above-obtained water-based adhesive, and dried at 70 ℃ for 5 minutes, and further dried at 100 ℃ for 5 minutes to obtain a polarizer of the present invention. In this example, the boron content in the polarizing element was 26% in terms of boric acid concentration.

Example 14

Using the adhesive of the present invention obtained in example 9, a polarizer of the present invention was obtained in the same manner as in example 8, except that the film treatment using boric acid after uniaxial stretching in example 9 was performed by immersing the film in an aqueous solution containing 8 wt% boric acid at 40 ℃ for 5 minutes. In this example, the boron concentration in the polarizing element was 29% in terms of boric acid concentration.

Example 15

Using the adhesive of the present invention obtained in example 9, a polarizer of the present invention was obtained in the same manner as in example 9, except that the film treatment using boric acid after uniaxial stretching in example 9 was performed by immersing the film in an aqueous solution containing 8 wt% boric acid at 55 ℃ for 5 minutes. In this example, the boron concentration in the polarizing element was 32% in terms of the boric acid concentration.

Comparative example 1

A PVA film having an average polymerization degree of 4000, a saponification degree of 99.9 mol% and a thickness of 75 μm was dyed at 45 ℃ in an aqueous solution containing a dichroic dye represented by the above formula (1) and mirabilite, and then without a drying step, the film was introduced into an aqueous solution of 58 ℃ containing 3 wt% boric acid, and the film was uniaxially stretched 5 times in the aqueous solution. The film was washed by further immersing the film in a water bath at room temperature, and then dried at 70 ℃ for 10 minutes to obtain a polarizing element. This polarizing element and a cellulose triacetate film saponified with an alkaline substance were bonded to each other using an aqueous solution containing 5% of a PVA resin (average polymerization degree of 2600, saponification degree of 99.4 mol% or more) as a binder, and were dried at 70 ℃ for 10 minutes, and further at 100 ℃ for 10 minutes to obtain a polarizer.

Comparative example 2

50 parts of an aqueous solution containing 5.0% of a PVA resin (average degree of polymerization 2600, degree of saponification 99.4 mol% or more) and 50 parts of an aqueous ammonium solution containing 5.0% of a resin having a maleic anhydride skeleton in the structure (trade name: ISOBAN-18, manufactured by Kuraray Co., Ltd.; copolymer of maleic anhydride and isobutylene having a weight-average molecular weight of 300,000-350,000) were mixed to obtain a water-based adhesive for polarizing elements containing no crosslinking agent. Then, a PVA film having an average polymerization degree of 4000, a saponification degree of 99.9 mol% and a thickness of 75 μm was dyed in an aqueous solution containing a dichroic dye represented by the above formula (1) and mirabilite at 45 ℃, and then, without a drying step, the film was introduced into an aqueous solution containing 3 wt% boric acid at 58 ℃ and uniaxially stretched 5 times in the aqueous solution. The film was washed by further immersing the film in a water bath at room temperature, and then dried at 70 ℃ for 10 minutes to obtain a polarizing element. The polarizing element and a triacetylcellulose film saponified with an alkaline substance were bonded using the adhesive obtained above in the same manner as in comparative example 1 to obtain a polarizer.

Test example 1

The polarizers obtained in examples 1 to 15 and comparative examples 1 to 2 were tested for their adhesion water resistance by immersing them in hot water at 60 ℃ for 120 hours. The results of the water resistance test of the adhesion performed to the polarizer are shown in table 1. In the table, ". smallcircle" indicates no change, and "x" indicates complete separation.

Table 1: results of Water resistance test on polarizer

	Results of Water resistance test	Solid content of resin component	PVA resin/resin having maleic anhydride skeleton in its structure (weight ratio)	Proportion (weight ratio) of the crosslinking agent based on 100 parts of PVA resin	Boric acid concentration in polarizing element
						Example 1	○	5％	100/100	50 portions of	16％
Example 2	○	4％	100/100	50 portions of	16％
						Example 3	○	5％	100/50	25 portions of	16％
Example 4	○	5％	100/500	250 portions of	16％
						Example 5	○	5％	100/100	10 portions of	16％
Example 6	○	5％	100/100	100 portions of	16％
						Example 7	○	5％	100/100	50 portions of	16％
Example 8	○	5％	Modified PVA treeFat/same 100/100 as in example 1	50 portions of	16％
						Example 9	○	5％	100/100	50 parts of glycidyl adduct of diamine	16％
Example 10	○	5％	Resin 100/100 having the same/lower degree of polymerization as in example 1	50 portions of	16％
						Example 11	○	5％	Same/imide-modified resin 100/100 as in example 1	50 portions of	16％
Example 12	○	5％	Maleamic acid-containing resin 100/100 identical to example 1	50 portions of	16％

Example 13	○	5％	100/100	50 portions of	26％
						Example 14	○	4％	100/100	50 portions of	29％
Example 15	○	5％	100/100	50 portions of	32％
						Comparative example 1	×	5％	100/0	0 portion of	16％
Comparative example 2	×	5％	100/100	0 portion of	16％

As shown in table 1, the polarizer using the water-based adhesive for polarizing elements of the present invention was excellent in durability when immersed in hot water at 60 ℃ for 120 hours, regardless of the content of the boron compound in the polarizing element in terms of boric acid.

Example 16

50 parts of an aqueous solution containing 5.0% of a PVA resin (having an average degree of polymerization of 2600 and a degree of saponification of 99.4 mol% or more), 50 parts of an aqueous ammonium solution containing 5.0% of a resin having a maleic anhydride skeleton in the structure (trade name: ISOBAN-18, manufactured by Kuraray Co., Ltd.; a copolymer of maleic anhydride and isobutylene having a weight-average molecular weight of 300,000-350,000) and 1.25 parts of polyglycerol polyglycidyl ether (trade name: DENACOL EX-521, manufactured by Nagase Chemtex Co., Ltd.) were mixed to obtain a water-based adhesive for a polarizing element of the present invention. Then, ｃA PVA film having an average degree of polymerization of 4000, ｃA degree of saponification of 99.9 mol% and ｃA thickness of 75 μm was dyed for 4 minutes in an aqueous solution containing mirabilite, C.I.direct Yellow 28, C.I.direct Orange 39 and ｃA dichroic dye in the form of ｃA free acid disclosed in JP-A-2003-215338 and represented by the following formulｃA (2) at 45 ℃. Then, the film was washed in an aqueous solution containing 2 wt% boric acid at 50 ℃, introduced into an aqueous solution containing 3 wt% boric acid at 57 ℃ without a drying step, and uniaxially stretched 5-fold in the aqueous solution. The film was further washed by immersion in a water bath at room temperature, and dried at 70 ℃ for 10 minutes, to obtain a polarizing element. The polarizing element and the cellulose triacetate film saponified with an alkaline substance were bonded to each other using the adhesive obtained above, and dried at 70 ℃ for 5 minutes and then at 100 ℃ for 5 minutes to obtain a polarizer of the present invention. In this example, the boron content in the polarizing element was 20% in terms of boric acid concentration.

[ formula 2]

Example 17

A water-based adhesive for a polarizing element of the present invention was obtained in the same manner as in example 16, except that a resin having a structure in which maleic anhydride and maleic amide acid skeleton were used (trade name: ISOBAN-104, produced by Kuraray Co., Ltd.; a copolymer of maleic anhydride and isobutylene in which a part of maleic anhydride was replaced by an ammonium salt of maleic amide acid and which had a weight average molecular weight of 55,000-65,000) was used. Then, a polarizer was obtained using the obtained adhesive in the same manner as in example 1.

Example 18

A water-based adhesive for a polarizing element of the present invention was obtained in the same manner as in example 16, except that a resin having a structure in which maleic anhydride and maleic amide acid skeleton were used (trade name: ISOBAN-110, produced by Kuraray Co., Ltd.; a copolymer of maleic anhydride and isobutylene in which a part of maleic anhydride was replaced by an ammonium salt of maleic amide acid and which had a weight average molecular weight of 160,000-170,000). Then, a polarizer was obtained using the obtained adhesive in the same manner as in example 1.

Comparative example 3

A polarizer was obtained in the same manner as in example 16, except that the polarizing element and the cellulose triacetate film saponificated with an alkali substance were bonded to each other using an aqueous solution containing 5% of PVA resin (average polymerization degree 2600, saponification degree 99.4 mol% or more) as a binder.

Test example 2

The solution viscosity of the binders obtained in examples 16 to 18 and comparative example 3 was evaluated by the dropping time of the binder solution using a No. 3 Zahn cup. The adhesion of the polarizers obtained in examples 16 to 18 and comparative example 3 was evaluated by immersing them in hot water at 60 ℃ for 960 hours, and by leaving them in an environment of 60 ℃ and 100% RH for 700 hours. The results are shown in Table 2.

Table 2 solution viscosity of adhesive and results of adhesion test

	Water resistance in hot water at 60 DEG C	Water resistance at 60 ℃ and 100% RH	Solution viscosity of the adhesive	Coatability
					Example 16	○	○	631 seconds	△
Example 17	○	○	44 seconds	◎
					Example 18	○	○	131 seconds	○
Comparative example 3	Separation after x 16 hours	○	55 seconds	◎

As shown in table 2, the polarizer prepared using the water-based adhesive for polarizing elements of the present invention was excellent in the water resistance test performed in hot water at 60 ℃ and the moisture resistance test performed in an environment of 60 ℃ and 100% RH.

Example 19

A PVA film having an average polymerization degree of 2400, a saponification degree of 99.4 mol% and a thickness of 75 μm was dyed in an aqueous solution containing iodine, potassium iodide and boric acid at 45 ℃ for 4 minutes, and then without a drying step, the film was introduced into an aqueous solution containing 3 wt% boric acid at 50 ℃ and uniaxially stretched 5-fold in the aqueous solution. The film was washed by further immersing the film in a water bath at room temperature, and then dried at 70 ℃ for 10 minutes to obtain a polarizing element. Then, a polarizer was obtained using the obtained polarizing element in the same manner as in example 1.

Comparative example 4

A polarizer was obtained in the same manner as in example 19, except that the polarizing element and the cellulose triacetate film saponificated with an alkali substance were bonded to each other using an aqueous solution containing 5% of PVA resin (average polymerization degree 2600, saponification degree 99.4 mol% or more) as a binder.

Test example 3

The polarizers obtained in example 19 and comparative example 4 were immersed in hot water at 60 ℃ for 1 hour, and the adhesiveness of the peripheral portions of these polarizers was evaluated. The results are shown in Table 3.

Table 3 results of adhesion test of peripheral portion of polarizer

	State of edge portion
		Example 19	No separation occurred between the polarizing element and the cellulose triacetate film.
Comparative example 4	A separation of 1mm from the edge occurred between the polarizing element and the cellulose triacetate film, and the polarizing element shrunk.

As shown in table 3, the polarizer prepared using the water-based adhesive for polarizing elements of the present invention was also excellent in adhesiveness at the peripheral portion of the polarizer.

Industrial applicability

The polarizer prepared using the water-based adhesive for polarizing elements of the present invention is excellent in durability, particularly in durability in a high-humidity environment. Therefore, they can be used for display devices used outdoors or under moisture-concentrated conditions. Furthermore, no deterioration of these polarizers occurs at high temperatures and high humidity, for example during transport or storage in tropical or subtropical zones.

Claims (4)

1. A polarizer comprising a polarizing element and a protective film bonded to the polarizing element with an adhesive, wherein the adhesive is a water-based adhesive comprising a polyvinyl alcohol resin, a resin having a maleic anhydride skeleton in the structure, and a crosslinking agent, wherein the resin having a maleic anhydride skeleton in the structure is a copolymer of maleic anhydride and isobutylene having a weight average molecular weight of 55000 to 350000, the weight ratio of the polyvinyl alcohol resin, the resin having a maleic anhydride skeleton in the structure, and the crosslinking agent is 100/(1-1000)/(0.5-5000), and wherein the polarizing element is a polyvinyl alcohol resin film, and the content of boron in the polarizing element is 10-40 wt% in terms of boric acid.

2. A polarizer according to claim 1, wherein the protective film is a cellulose acetate film.

3. The polarizer according to claim 1, wherein the crosslinking agent is a compound having an epoxy group.

4. The polarizer according to claim 1, wherein the polyvinyl alcohol resin is a modified polyvinyl alcohol resin or a mixture of an unmodified polyvinyl alcohol resin and a modified polyvinyl alcohol resin.