JP2009053675A - Adhesive for polarizing plate, polarizing plate and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive for polarizing plates which has excellent adhesive strength, exhibits adequate adhesive force in a short time, and ensures excellent stability of a solution thereof even when a water/alcohol mixed solvent is used. <P>SOLUTION: The adhesive includes a polyvinyl alcohol type resin represented by general formula (1), wherein R<SP>1</SP>-R<SP>3</SP>each independently denotes a hydrogen atom or an alkyl group; X denotes a 4-50C alkylene group; and Y denotes a hydrogen atom or an alkali metal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polarizing plate adhesive that is suitable as an adhesive between a polarizing film and a protective film in the production of a polarizing plate in which a polarizing film and a protective film are bonded to each other. The present invention relates to a polarizing plate obtained using an agent, and a method for producing a polarizing plate using such a polarizing plate adhesive.

Liquid crystal display devices are widely used as image display devices for liquid crystal televisions, computer displays, mobile phones, digital cameras, and the like. Such a liquid crystal display device has a configuration in which polarizing films are disposed on both sides of a glass substrate in which liquid crystal is sealed, and various optical elements such as a phase difference plate are laminated on the glass substrate as necessary.
As the polarizing film, a uniaxially stretched film in which a dichroic material such as iodine is dispersed and adsorbed in a polyvinyl alcohol-based resin (hereinafter, polyvinyl alcohol is abbreviated as PVA) and is crosslinked by a crosslinking agent such as boric acid is widely used. It is used.
This uniaxially stretched film of PVA resin is likely to shrink under high humidity, and usually, a protective film such as triacetyl cellulose is bonded to both sides or one side to supplement moisture resistance and strength, and these are combined to form a polarizing plate. It is used as.

  As an adhesive for adhering the polarizing film and the protective film in such a polarizing plate, an adhesive mainly composed of a PVA resin is used from the viewpoint of affinity for both films. However, the PVA-based resin has high hydrophilicity, and its characteristics may change greatly due to moisture absorption. Even when used as an adhesive for polarizing plates, it cannot withstand the shrinkage of the polarizing film under high humidity, There was a problem in durability, such as peeling off of the protective film and occurrence of white spots.

With respect to the above problems, an adhesive having improved moisture resistance by using a PVA resin containing an acetoacetate group as a PVA adhesive and using a crosslinking agent together, and a polarizing plate using such an adhesive Has been proposed (see, for example, Patent Documents 1 and 2).
JP 2005-189615 A JP 2006-145938 A

In recent years, with an increase in the size of a liquid crystal display device, there is a demand for a polarizing plate in which a polarizing film and a protective film are more firmly bonded.
Furthermore, with the rapid increase in demand for liquid crystal display devices, improvement in productivity has become a major issue. In response to such problems, for example, in the process of laminating a polarizing film and a protective film in the production of a polarizing plate, an adhesive that can be obtained in a short time with sufficient adhesive force to be sent to the next process, and volatilization of the solvent in the adhesive There is a need for an adhesive that has a high speed and can shorten the drying process. For example, with respect to the latter problem, studies have been made to use a low boiling point solvent such as methanol in combination with water as a solvent in the adhesive.

  However, when the present inventors examined in detail the adhesive mainly composed of the acetoacetate group-containing PVA resin described in Patent Documents 1 and 2, it was still in terms of adhesive strength and speed of expression of adhesive force. It turns out that there is room for improvement. In addition, when a water / alcohol mixed solvent is used as the solvent for the adhesives described in Patent Documents 1 and 2, the solubility decreases as the alcohol content increases, and even if the solution once enters a stable state, It is extremely low in properties and may become cloudy with time or may increase in viscosity or gel, and it has been difficult to add alcohol sufficient to improve the volatilization rate.

  That is, the present invention is excellent in adhesive strength as a polarizing plate adhesive used when laminating a polarizing film and a protective film in a polarizing plate, and sufficient adhesive force to be sent to the next step can be obtained in a short time. An object of the present invention is to provide an adhesive for a polarizing plate that is excellent in the stability of a solution even when a water / alcohol mixed solvent is used.

（式中、Ｒ¹、Ｒ²、Ｒ³は、それぞれ独立して水素原子又はアルキル基を示し、Ｘは炭素数が４〜５０のアルキレン基を示し、Ｙは水素原子、またはアルカリ金属を示す） As a result of intensive studies in view of the above circumstances, the present inventor has obtained a polarizing plate containing a PVA resin having a structural unit represented by the general formula (1) as an adhesive for laminating a polarizing film and a protective film. It was found that the object of the present invention can be achieved by using the adhesive for the present invention, and the present invention was completed.

Wherein R ¹ , R ² and R ³ each independently represent a hydrogen atom or an alkyl group, X represents an alkylene group having 4 to 50 carbon atoms, and Y represents a hydrogen atom or an alkali metal. )

In the PVA resin having the structural unit represented by the general formula (1) used in the present invention, the carboxyl group having a high affinity for both the polarizing film and the protective film has an appropriate distance from the PVA main chain. In this case, the degree of freedom is high, and as a result, it is estimated that good adhesive strength can be obtained and sufficient adhesive force can be obtained in a short time. Further, even when various crosslinking agents are used in combination in order to improve the water resistance of the adhesive layer, it is considered that the high degree of freedom of the carboxyl group is effective.
Furthermore, alcohol is a poor solvent for general PVA resins, and even if it is a mixed solvent of water / alcohol, the solubility decreases as the alcohol ratio increases, and even if it becomes a solution once, it becomes cloudy or gels over time However, the PVA resin of the present invention has a characteristic of maintaining a stable solution state even in a water / alcohol mixed solvent having a high alcohol ratio.

Since the adhesive for polarizing plates of this invention is excellent in the adhesive strength of the polarizing film and protective film in a polarizing plate, favorable adhesiveness is obtained over the whole surface also in the case of a large sized polarizing plate.
Moreover, since the adhesive for polarizing plates of the present invention can obtain a sufficient adhesive force in a short time, the process can be shortened, and even when a mixed solvent of water / alcohol is used as a solvent, the adhesive is stable. Since the solution state is maintained, the drying process can be shortened, which is industrially useful.

The description of the constituent requirements described below is an example (representative example) of an embodiment of the present invention, and is not limited to these contents.
Hereinafter, the present invention will be described in detail.

  The present invention relates to an adhesive for polarizing plates, and further relates to a method for manufacturing a polarizing plate using such an adhesive for polarizing plates, and a polarizing plate obtained by such a manufacturing method.

上記一般式（１）において、Ｒ¹、Ｒ²、Ｒ³は、それぞれ独立して水素原子又はアルキル基を示し、Ｘは炭素数が４〜５０のアルキレン基を示し、Ｙは水素原子、またはアルカリ金属を示す。なお、かかるＸの炭素数は、好ましくは６〜３０であり、特に好ましくは６〜２０である。 (PVA resin)
First, the PVA resin used for the polarizing plate adhesive of the present invention will be described.
The PVA-based resin used in the present invention is a PVA-based resin having a structural unit represented by the following general formula (1), and the structure and production method thereof are known, for example, from JP-A-2006-152206 The outline is explained.

In the general formula ^{(1), R 1, R} 2, R 3 is independently a hydrogen atom or an alkyl group, X represents an alkylene group having a carbon number of 4 to 50, Y is a hydrogen atom or, Indicates alkali metal. The number of carbon atoms in X is preferably 6-30, and particularly preferably 6-20.

  The PVA resin used in the present invention is obtained by saponifying a polyvinyl ester resin obtained by copolymerizing a monomer mainly composed of a vinyl ester monomer represented by vinyl acetate, The part other than the structural unit represented by the general formula (1) is composed of a vinyl alcohol structural unit corresponding to the degree of saponification and a slight amount of vinyl acetate structural unit, as in the case of a normal PVA resin.

R ^{1 to} R ³ in the general formula (1) are preferably all hydrogen atoms, but may be substituted with an organic group as long as the resin properties are not significantly impaired. Although not particularly limited, for example, an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, or a tert-butyl group is preferable. And may have a substituent such as a halogen, a hydroxyl group, an ester group, a carboxylic acid group, or a sulfonic acid group.

X in the general formula (1) is an alkylene group having 4 to 50 carbon atoms, and those having 6 to 30 carbon atoms and more preferably 6 to 20 carbon atoms are preferably used. The alkylene group is preferably linear, but may be branched as long as the resin properties are not significantly impaired. If the number of carbon atoms of the alkylene group is too small, sufficient adhesive strength cannot be obtained, or the solubility in a water / alcohol mixed solvent tends to be low. If the number is too large, the adhesive strength decreases or sufficient adhesive strength is obtained. It takes a long time to obtain the water, or the solubility in a water-only solvent or a water / alcohol mixed solvent having a high water content tends to decrease.
Such an alkylene group is usually a hydrocarbon, but a part of the hydrogen may be substituted with a halogen, a hydroxyl group, an ester group, a carboxylic acid group, a sulfonic acid group or the like as long as the resin characteristics are not impaired.

  Content of the structural unit represented by General formula (1) in the PVA-type resin used by this invention is 0.1-20 mol% normally, Especially 0.5-15 mol%, Furthermore, 1-10 Those having mol% are preferably used. If the content of the structural unit represented by the general formula (1) is too small, the adhesive strength tends to be insufficient, or the solubility tends to be insufficient when a water / alcohol solvent is used for the adhesive. is there. Moreover, when there is too much this content, there exists a tendency for water resistance to fall.

  The average degree of polymerization (measured according to JIS K 6726) of the PVA-based resin of the present invention is usually 100 to 4000, preferably 300 to 3000, more preferably 500 to 2000. If the average degree of polymerization is too small, sufficient adhesiveness may not be obtained. On the other hand, if the average degree of polymerization is too large, the viscosity of the adhesive increases, workability decreases, and uniform coating on the substrate is difficult. Tend to be.

  Further, the degree of saponification (measured in accordance with JIS K 6726) of such PVA-based resin is usually 80 mol% or more, particularly 95 mol% or more, more preferably 98 to 99.9 mol%. It is done. If the saponification degree is too low, the water resistance of the adhesive layer tends to be insufficient.

上記一般式（２）において、Ｒ¹、Ｒ²、Ｒ³、Ｘ、は、上記一般式（１）と同様のものが挙げられる。 The method for producing the PVA resin having the structural unit represented by the general formula (1) used in the present invention is not particularly limited. However, the vinyl ester monomer and the compound represented by the following general formula (2) may be used together. A method of saponifying the polymer is preferably used.

In the general formula (2), examples of R ¹ , R ² , R ³ and X include the same as those in the general formula (1).

Moreover, Y in General formula (2) is a hydrogen atom, an alkali metal, or an alkyl group, More preferably, it is a hydrogen atom or an alkali metal. When an ester body in which Y is an alkyl group is used, a transesterification reaction may occur with the hydroxyl group of the PVA main chain in the saponification step during the production of the PVA resin, thereby forming a crosslinked structure.
When Y is an alkyl group, examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, and an octyl group. The ester bond is cleaved during the oxidization reaction to give a corresponding alcohol, and Y becomes a hydrogen atom or an alkali metal in an alkali metal hydroxide used as a saponification catalyst. Accordingly, the alkyl group used as Y is preferably a methyl group that becomes methanol, which is frequently used as a saponification solvent, by-produced alcohol during saponification.

Specific examples of the compound represented by the general formula (2) include undecylenic acid, oleic acid, elaidic acid, cetreic acid, erucic acid, linoleic acid, linolenic acid and the like, and derivatives such as esters and salts thereof. From the viewpoint of easy availability and good copolymerizability, n-1-alkenoic acid in which R ¹ , R ² , and R ³ are hydrogen is preferable, particularly Y is hydrogen and X is —C ₈ H ₁₆ —. Certain undecylenic acids or their alkali metal salts are preferred.

  Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, Examples include vinyl versatate. Of these, vinyl acetate is preferably used from the economical viewpoint.

Further, in the present invention, in addition to the above-described copolymerization component, it is also possible to use a copolymer obtained by copolymerizing other monomers in an amount of about 0.1 to 20 mol% within a range not impairing the object of the present invention. is there.
Other monomers include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, α-octadecene, 3-buten-1-ol, 4-penten-1-ol, 5-hexene- Derivatives such as hydroxy group-containing α-olefins such as 1-ol and 3,4-dihydroxy-1-butene and acylated products thereof, acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, etc. Unsaturated acids, their salts, monoesters or dialkyl esters, nitriles such as acrylonitrile and methacrylonitrile, amides such as diacetone acrylamide, acrylamide and methacrylamide, ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, etc. Olefin sulfonic acids or their salts, al Ruvinyl ethers, dimethylallyl vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinyl ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxolane, glycerol monoallyl ether, 3,4-diacetoxy-1- Examples thereof include vinyl compounds such as butene, substituted vinyl acetates such as isopropenyl acetate and 1-methoxyvinyl acetate, vinylidene chloride, 1,4-diacetoxy-2-butene and vinylene carbonate.

  In the present invention, a mixture of two or more types of PVA resins having different degrees of polymerization, degree of saponification, and content of the structural unit represented by the general formula (1) may be used. Moreover, you may mix and use the PVA-type resin which has a functional group in a side chain different from the PVA-type resin used by this invention in the range which does not impair the objective of this invention.

(Adhesive for polarizing plate)
Next, the polarizing plate adhesive of the present invention will be described.
The polarizing plate adhesive of the present invention is mainly composed of a PVA-based resin having the structural unit represented by the general formula (1), and the content thereof is usually 80% by weight in the total solid content. Above, especially 90% by weight or more. If the content is too small, the adhesive strength may be insufficient.
Although it does not specifically limit as a form of an adhesive agent, In order to form a uniform adhesive bond layer on the surface of the polarizing film or protective film which is a to-be-adhered body, it is preferable to use as a liquid form. Examples of such a liquid adhesive include solutions and dispersions of various solvents, but it is preferably a solution type from the viewpoint of application to a substrate, and usually a solution mainly composed of water from the viewpoint of safety. Preferably used.

Further, after applying the polarizing plate adhesive to the adherend, a drying step is usually provided in order to remove the solvent contained in the adhesive, but for the purpose of shortening the drying step, water is added to the adhesive solution. It is also possible to use a water / alcohol mixed solvent containing an alcohol solvent having a boiling point lower than that of water, that is, a boiling point of 100 ° C. or less, particularly 80 ° C. or less, and further 70 ° C. or less. This is a preferred embodiment.
Specific examples of the alcohol solvent include lower alcohols having 1 to 3 carbon atoms such as methanol, ethanol, n-propanol, and isopropanol, and methanol having the lowest boiling point is preferably used.

  The blending amount of the alcohol solvent is not particularly limited and may be appropriately selected depending on the drying conditions and the type of alcohol used. Usually, the content ratio (weight ratio) of both in the mixed solvent of water and alcohol is used. The range of 99.99 / 0.01 to 20/80, preferably 99/1 to 30/70, particularly 90/10 to 40/60, and more preferably 80/20 to 50/50 is preferably used. If the amount of such alcohol is too large, the viscosity stability of the adhesive solution tends to decrease, and if it is too small, the drying process may not be shortened.

  The solid content concentration of the adhesive solution for polarizing plate cannot be generally described depending on the desired coating amount and the characteristics of the coating apparatus, but is usually 0.5 to 30% by weight, particularly 1 to 20% by weight, Furthermore, the range of 1.5 to 15% is preferably used. If the concentration is too low, drying takes a long time, so that productivity is impaired. On the other hand, if the concentration is too high, the viscosity tends to be high, and uniform coating tends to be difficult.

The adhesive for polarizing plate of the present invention shows a good adhesive strength in the adhesion between the polarizing film and the protective film, and a good adhesive force can be obtained in a short time, further improving the adhesive strength, particularly improving the water-resistant adhesive strength. For this purpose, it is also a preferred embodiment to use various crosslinking agents in combination.
As such a crosslinking agent, those known as crosslinking agents for PVA resins, or compounds having a functional group capable of reacting with a carboxyl group can be used. For example, organic crosslinking agents include formaldehyde, glyoxal, Aldehyde compounds such as glutaraldehyde, urea resin, guanamine resin, methylol group-containing compounds such as methylol melamine, amino resins, water-soluble epoxy resins, glycidyl group-containing compounds such as polyamide polyamine epichlorohydrin, ethylenediamine, hexamethylenediamine, metaxylylenediamine , 1,3-bisaminocyclohexane, amine compounds such as polyoxyalkylene type diamine or polyamine, hydrazides such as adipic acid dihydrazide, carbohydrazide, polyacrylic acid hydrazide Compound, polyisocyanate, isocyanate compounds such as block isocyanate, may be mentioned hydrazine compound, acid anhydride, and the like.
Examples of the inorganic crosslinking agent include boron compounds such as boric acid and borax, chlorohydroxyoxozirconium (“Zircosol ZC-2” manufactured by Daiichi Rare Element Chemical Co., Ltd.), zirconyl nitrate (manufactured by Daiichi Rare Element Chemical Co., Ltd. Zirconium compounds such as Zircozole ZN "), tetraalkoxy titanates, titanium compounds such as water-soluble titanium compounds (" TC-310 "and" TC-400 "manufactured by Matsumoto Pharmaceutical Co., Ltd.), and aluminum compounds such as aluminum sulfate, aluminum chloride and aluminum nitrate And phosphorous compounds such as phosphites and bisphenol A-modified polyphosphoric acid, and silicone compounds having reactive functional groups such as alkoxy groups and glycidyl groups.

  Among them, a glycidyl group-containing compound and a methylol group-containing compound are preferably used from the viewpoint that the reactivity is high and water resistance can be efficiently obtained even with a small amount of addition.

  The amount of such a crosslinking agent is not particularly limited, and may be selected from desired water resistance, but is usually 100 parts by weight or less with respect to 100 parts by weight of the PVA resin, and further 0.1 to 0.1 parts by weight. It is 100 parts by weight, and a range of 0.5 to 50 parts by weight is particularly preferably used. If the amount of such a crosslinking agent is too large, the viscosity stability of the adhesive solution tends to deteriorate.

Further, other resins such as polysaccharides such as starch and cellulose, polyethylene glycol, polyvinyl pyrrolidone, polyoxazoline, water-soluble polyamide, in a range not impairing the object of the present invention, usually 30% by weight or less, particularly 20% by weight or less, Water-soluble resins such as water-soluble polyester, polyacrylamide, and polyethyleneimine, and urethane adhesives and emulsion adhesives can be used in combination.
Similarly, as various additives, antifoaming agents, leveling agents, colorants, dyes, pigments, fluorescent brighteners, pigments, UV absorbers, antioxidants, fillers, plasticizers, antistatic agents, thermal stability Agents, surfactants, desiccants, deodorants, antibacterial agents, preservatives, antifoaming agents, and the like can be included.

(Polarizer)
Next, the polarizing plate of the present invention will be described.
There is no restriction | limiting in particular as a polarizing film used for the polarizing plate of this invention, A well-known thing can be used. For example, (i) A dichroic material such as iodine or a dichroic dye is adsorbed on a vinyl alcohol resin film such as a PVA film, a partially formalized PVA film, or an ethylene-vinyl alcohol resin film. A stretched one (see, for example, JP-A-2001-296427 and JP-A-7-333426), (ii) a birefringent material having liquid crystallinity together with a dichroic material, and a vinyl alcohol resin film (Iii) a uniaxially stretched thermoplastic norbornene resin film containing a dichroic material (for example, see JP-A-2001-356213) .), (Iv) PVA-based resin and ethylene-vinyl alcohol resin are dehydrated or deaceticated and continuously. Introduced polyene structure, a polyene-based film obtained by stretching them (e.g., see JP Patent 2007-17845.), And the like.
Among these, a polarizing film made of a dichroic material such as a PVA film and iodine and uniaxially stretched from the viewpoint of excellent polarization characteristics is preferable.

  The thickness of such a polarizing film is usually 0.1 to 100 μm, particularly 0.5 to 80 μm, and further preferably 1 to 60 μm.

  Such a polarizing film is then laminated with a protective film via an adhesive layer. The thickness of such a protective film is not particularly limited, but usually a thicker one than the polarizing film is used, and it has a function of imparting strength as a base material of the polarizing film, usually 10 to 100 μm, preferably 20 to 80 μm. is there. The material is not particularly limited, and any material that is transparent and excellent in durability is preferable, and known materials can be used. For example, a cellulose ester resin film, a cyclic olefin resin film, (meta ) Acrylic resin film, etc. can be mentioned as suitable ones.

  Typical cellulose ester resins used in such cellulose ester resin films include triacetyl cellulose and diacetyl cellulose, but other lower fatty acid esters of cellulose, cellulose acetate propionate and cellulose acetate. Mixed fatty acid esters such as butyrate can be used. The cellulose ester resin film is subjected to a saponification treatment with an alkaline aqueous solution or the like in order to increase the affinity with the polarizing film or the PVA resin used as the adhesive, but is not limited thereto. is not. Moreover, the thing which apply | coated the antistatic agent on the surface or contained in the film is also used preferably.

Typical examples of the cyclic olefin-based resin used in the above-mentioned cyclic olefin-based resin film include a norbornene-based resin. Examples of the norbornene-based resin include ring-opening (co) polymerization of a norbornene-based monomer. Examples thereof include resins obtained by addition polymerization of norbornene monomers, and resins obtained by addition copolymerization with norbornene monomers and olefin monomers such as ethylene and α-olefin. Specific examples of norbornene-based monomers include dimers such as norbornene and norbornadiene; tricyclics such as dicyclopentadiene and dihydroxypentadiene; heptacyclics such as tetracyclopentadiene; these methyl, ethyl, propyl and butyl Substituents such as alkyl, alkenyl such as vinyl, alkylidene such as ethylidene, aryl such as phenyl, tolyl, and naphthyl; and ester groups, ether groups, cyano groups, halogens, alkoxycarbonyl groups, pyridyl groups, hydroxyl groups, carvone Examples include substituents having groups containing elements other than carbon and hydrogen, such as acid groups, amino groups, hydroxyl-free groups, silyl groups, epoxy groups, acryloyl groups, and methacryloyl groups.
Examples of commercially available cyclic olefin-based resin films include “ARTON” manufactured by JSR, “ZEONOR”, “ZEONEX” manufactured by Nippon Zeon Co., Ltd., “OPTOREZ” manufactured by Hitachi Chemical Co., Ltd., “APEL” manufactured by Mitsui Chemicals, Inc. Can do.

Moreover, as a (meth) acrylic-type resin used for the above-mentioned (meth) acrylic-type resin film, poly (meth) acrylic acid ester, such as polymethyl methacrylate, methyl methacrylate- (meth) acrylic acid copolymer, Methyl methacrylate- (meth) acrylic acid ester copolymer, methyl methacrylate-acrylic acid ester- (meth) acrylic acid copolymer, (meth) acrylic acid methyl-styrene copolymer, alicyclic hydrocarbon group Polymer (for example, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate- (meth) acrylate norbornyl copolymer, etc.), high Tg (meth) obtained by intramolecular crosslinking or intramolecular cyclization reaction Acrylic resins, rubber-acrylic graft type core-shell polymers, and the like can be mentioned.
Examples of such commercially available (meth) acrylic resin films include “Acrypet VRL20A”, “Acrypet IRD-70” manufactured by Mitsubishi Rayon Co., Ltd., “MUX-60” manufactured by UMGABS, and the like.

  In addition to these protective films, polyester resin films such as polyethylene terephthalate and polyethylene naphthalate, polystyrene resin films such as polystyrene and acrylonitrile / styrene copolymers, polyolefin resins such as polypropylene, and polyarylate resin films Water-soluble polyethersulfone resin film, polycarbonate resin film, vinyl chloride resin film, amide resin film such as nylon and aromatic polyamide, (fluorine-containing) polyimide resin film, polyetheretherketone resin film , Polyphenylene sulfide resin films, vinyl alcohol resin films, vinylidene chloride resin films, polyvinyl acetal resin films such as polyvinyl butyral, Riarireto resin film, a polyoxymethylene-based resin films, and the like epoxy resin film. Further, as the protective film, for example, a cured layer such as an acrylic, urethane, acrylic urethane, epoxy, silicone, or other thermosetting type or ultraviolet curing type resin, or a polymer film described in JP-A-2001-343529 ( Specifically, a resin film containing an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer) may be used.

  Among these protective films, cellulose ester-based resin films and cyclic olefin-based resin films are preferably used from the viewpoints of transparency, heat resistance, mechanical strength, durability, etc. Among them, triacetyl cellulose or norbornene-based resins are preferable. Used.

Such a protective film can be subjected to various surface treatments in order to increase the affinity with the polarizing film and the PVA resin used as an adhesive thereof. In addition to the saponification treatment in the base resin film, an easy-adhesion layer or anchor coat layer containing (meth) acrylate latex, styrene latex, polyethyleneimine, polyurethane / polyester copolymer, etc. on the surface of the protective film A surface treatment method using a coupling agent such as a silane coupling agent or a titanium coupling agent, or a method of imparting hydrophilicity to the surface by a corona discharge treatment or an ion assist method (for example, the IRA method of the Micro Engineering Laboratory). And so on. In addition, it is also possible to use together the above-mentioned various surface treatment methods.
In addition, such a protective film can be provided with a hard coat layer on a surface not laminated with the polarizing film, or can be subjected to various treatments such as anti-sticking, anti-reflection, and anti-glare. Furthermore, various optical functional films such as a phase difference plate and a viewing angle widening film can be laminated on a surface that is not laminated with a polarizing film.

The polarizing plate of the present invention is formed by laminating a transparent protective film on at least one surface, preferably both surfaces, of the polarizing film with the polarizing plate adhesive of the present invention. It is formed by uniformly applying an adhesive to a polarizing film and / or a protective film, and bonding them together, followed by pressure bonding and heat drying.
In applying such a polarizing plate adhesive on a polarizing film or a protective film, a roll coater method, an air doctor method, a blade coater method, a spray method, a dipping method, or just before laminating a polarizing film and a protective film, A known method such as pasting the two together after supplying an appropriate amount between the films and pouring them can be used. The coating amount of the aqueous adhesive is usually selected from the range of 0.01 to 10 μm, particularly 0.05 to 5 μm, as the thickness of the adhesive layer after drying. There is a tendency that the force becomes insufficient, and when it is too thick, uniform coating becomes difficult, or thickness unevenness occurs and the appearance tends to deteriorate. For the bonding and pressure bonding, for example, a roll laminator or the like can be used, and the pressure is selected from the range of 0.1 to 10 MPa. The heating and drying conditions are usually 5 to 150 ° C., particularly 30 to 120 ° C., for 10 to 60 minutes, further 30 seconds to 30 minutes, particularly 1 to 20 minutes.

Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the description of the examples unless it exceeds the gist.
In the examples, “parts” and “%” mean weight basis unless otherwise specified.

Example 1
(1) Production of PVA resin In a reaction vessel equipped with a reflux condenser, a dropping funnel and a stirrer, 1000 g of vinyl acetate, 50 g of methanol, undecylenic acid (in the general formula (2), R ¹ , R ² , R ³ are hydrogens, X -C ₈ H ₁₆ -, Y is charged hydrogen) 85.6 g (4 mol%), 0.1 mol% of azobisisobutyronitrile (vs. the charged vinyl acetate monomer) were charged, While stirring, the temperature was raised under a nitrogen stream to carry out polymerization. Two hours after the start of the polymerization, 0.1 mol% of azobisisobutyronitrile (vs. the initial charged vinyl acetate monomer) was further added to continue the polymerization. Thereafter, when the polymerization rate of vinyl acetate reached 62.5%, the polymerization with the polymerization inhibitor was completed. Subsequently, unreacted vinyl acetate monomer was removed out of the system by a method of blowing methanol vapor to obtain a methanol solution of the copolymer.
Next, the solution was diluted with methanol and adjusted to a concentration of 30% and charged into a kneader. While maintaining the solution temperature at 40 ° C., a 2% methanol solution of sodium hydroxide was added to 1 mol unit of vinyl acetate in the copolymer. On the other hand, saponification was carried out by adding an amount of 8 mmol. Saponification progressed as saponification progressed, and finally became particulate. The produced PVA was filtered off, washed well with methanol and dried in a hot air dryer to obtain the desired product.
The saponification degree of the obtained PVA resin was 99 mol% when analyzed by the alkali consumption required for hydrolysis of the residual vinyl acetate unit, and the polymerization degree was analyzed according to JIS K 6726. As a result, it was 1000. The amount of modification of the PVA-based resin (I) was 4 mol% as calculated from NMR measurement.

(2) Preparation of adhesive for polarizing plate 52 parts of 8.65% aqueous solution of PVA resin obtained in (1), 47.5 parts of methanol, and 0.5 part of polyamide polyamine epichlorohydrin as a crosslinking agent Were mixed to prepare an adhesive solution having a solid content concentration of 5% by weight and a water / methanol ratio of 5/5 (weight ratio).

(3) Preparation of sample for evaluation As a substitute for the polarizing film, a biaxially stretched film of PVA (“Boblon” manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., thickness 25 μm) was used, and the adhesive solution obtained in (2) was used for this. Is applied to a coating amount of 0.8 g / m ^2, and a saponified triacetyl cellulose film (thickness 80 μm) is laminated as a protective film, and a laminator (“MRK” manufactured by MC Co., Ltd.) is laminated. -650Y ", lamiroll pressure 0.1 MPa) and dried in a dryer at 70 ° C for 5 minutes to obtain a sample for evaluation. The thickness of the adhesive layer at this time was 0.8 μm.

(4) Evaluation The following evaluation was performed about the adhesive for polarizing plates obtained by (2), and the sample for evaluation obtained by (3). The results are shown in Table 2.
[Stability of adhesive]
The adhesive was stored at room temperature, and the time until it became cloudy or gelled was visually observed and evaluated as follows.
◎ ・ ・ ・ One week or more ○ ・ ・ ・ 5 days or more, less than 7 days △ ・ ・ ・ 3 days or more, less than 5 days × ... less than 3 days [adhesive strength]
After preparing the sample for evaluation, it was stored for 24 hours in an atmosphere of 23 ° C. and 60% RH, cut into a sample width of 25 mm, and subjected to a T-peel test (test speed of 300 mm / min). The same test was conducted 10 points, and the following evaluations were made from the points at which the PVA biaxially stretched film broke. In addition, a material breakage rate means the ratio which the PVA biaxially stretched film fractured | ruptured during intensity | strength measurement here.
◎ ... Material failure rate of 90% or more ○ ... Material failure rate of 80% or more, less than 90% △ ... Material failure rate of 70% or more. Less than 80% x ... Material breakage rate less than 70% [Adhesive strength development time]
After producing the sample for evaluation, it was stored in an atmosphere of 23 ° C. and 60% RH, peeled by hand every certain time, and measured for the time until the material broke, and evaluated as follows.
◎ ... Within 60 minutes ○ ... Over 60 minutes, within 90 minutes △ ... Over 90 minutes, within 120 minutes × ... Over 120 minutes

Example 2
In Example 1, the same as in Example 1 except that the amount of methanol at the time of producing the PVA resin was 200 g, the amount of undecylenic acid used was 42.8 g (2 mol%), and the polymerization rate was 82.2%. A PVA resin having a content of the structural unit represented by the formula (1) of 2 mol%, a polymerization degree of 1100, and a saponification degree of 99 mol% was produced.
Next, a polarizing plate adhesive was obtained in the same manner as in Example 1 except that methylolated melamine was used in place of the polyamide polyamine epichlorohydrin as the cross-linking agent and the water / methanol ratio was 8/2. Evaluated. The results are shown in Table 1.

Example 3
In Example 1, the content of the structural unit represented by the general formula (1) was 4 mol in the same manner as in Example 1 except that the amount of methanol at the time of preparing the PVA-based resin was 750 g and the polymerization rate was 85.6%. %, A polymerization degree of 500, and a saponification degree of 99 mol% were produced.
Subsequently, 47.5 parts of water was blended in place of methanol, and a polarizing plate adhesive was obtained in the same manner as in Example 1 except that the polyamide polyamine epichlorohydrin was not blended, and was similarly evaluated. The results are shown in Table 1.

Comparative Example 1
In Example 1, an acetoacetate group-containing PVA resin (5 mol% acetoacetate group content, polymerization degree 1100, saponification degree 99 mol%) was used as the PVA resin, glyoxal was used as the crosslinking agent, and water A polarizing plate adhesive was obtained in the same manner as in Example 1 except that the ratio of / methanol was set to 8/2, and was similarly evaluated. The results are shown in Table 1.

Comparative Example 2
In Example 1, maleic acid copolymerized PVA resin (maleic acid structural unit content 2 mol%, polymerization degree 1200, saponification degree 99.2 mol%) was used as PVA resin, as in Example 1. Thus, an adhesive for polarizing plate was obtained and evaluated in the same manner. The results are shown in Table 1.

[Table 1]
───────────────────────────────────────
Adhesive stability Adhesive strength Adhesive strength development time ────────────────────────────────────────
Example 1 ◎ ◎ ◎
Example 2 ◎ ◎ ◎
Example 3 ◎ ○ ◎
───────────────────────────────────────
Comparative Example 1 x (gelation) ○ △
Comparative Example 2 × (gelation) × △
───────────────────────────────────────

  Since the polarizing plate adhesive of the present invention is excellent in adhesive strength, the polarizing film and the protective film are hardly peeled off, and a sufficient adhesive force can be obtained in a short time, so that the manufacturing process can be shortened. Furthermore, even when a water / alcohol mixed solvent is used, the drying process after application of the adhesive can be shortened because of excellent stability.

Claims (5)

A polarizing plate adhesive comprising a polyvinyl alcohol resin having a structural unit represented by the general formula (1).

Wherein R ¹ , R ² and R ³ each independently represent a hydrogen atom or an alkyl group, X represents an alkylene group having 4 to 50 carbon atoms, and Y represents a hydrogen atom or an alkali metal. ) The adhesive for polarizing plates according to claim 1, comprising water and an alcohol solvent having a boiling point of 100 ° C or lower. The adhesive for polarizing plates according to claim 1 or 2, comprising at least one crosslinking agent selected from a methylol group-containing compound and a glycidyl group-containing compound. A polarizing plate comprising a protective film bonded to at least one surface of the polarizing film using the polarizing plate adhesive according to claim 1. A method for producing a polarizing plate, comprising: attaching a protective film to at least one surface of a polarizing film using an adhesive containing a polyvinyl alcohol-based resin having a structural unit represented by the following general formula (1).

^{(Wherein, R 1, R 2, R} 3 each independently represent a hydrogen atom or an alkyl group, X represents an alkylene group having a carbon number of 4 to 50, Y represents a hydrogen atom or an alkali metal, )