JP2008281838A - Polarizing plate and adhesive for polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate excellent in water resistance and in discoloration resistance at high temperature and high humidity. <P>SOLUTION: The polarizing plate is obtained by stacking a protective film on at least one surface of a polarizing film by way of an adhesive layer, wherein the adhesive layer contains a reaction product of an acetoacetic ester group-containing polyvinyl alcohol-based resin and an acetal compound having a dialkyl acetal group and one aldehyde group within a molecule. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polarizing plate used in an image display device such as a liquid crystal display device and a polarizing plate adhesive suitable for bonding a polarizing film and a protective film, which is used at the time of manufacturing the polarizing plate.

  Liquid crystal display devices are widely used as image display devices for liquid crystal televisions, personal computers, mobile phones, digital cameras, and the like. The liquid crystal display device has a configuration in which polarizing films are disposed on both sides of a liquid crystal cell in which liquid crystal is sealed in a glass substrate, and various optical elements such as a retardation plate are laminated as necessary. As such a 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. It is used.

Such a uniaxially stretched film of PVA resin tends to shrink under high humidity. Usually, a protective film such as triacetyl cellulose is bonded to both sides or one side to supplement moisture resistance and strength. It is used as.
As an adhesive for adhering a polarizing film and a protective film in such a polarizing plate, an adhesive mainly composed of a PVA resin is widely used from the viewpoint of adhesiveness with a PVA resin film used as a polarizing film. , PVA resin has high hydrophilicity, and its properties may be greatly reduced by moisture absorption. Even in such adhesive applications, the polarizing film and the protective film are peeled off under high humidity, which has problems in durability. there were.

With respect to the above problems, moisture resistance is improved by using a PVA resin containing an acetoacetate group (hereinafter abbreviated as AA-modified PVA resin) as a PVA adhesive and using a crosslinking agent in combination. Adhesives and polarizing plates using such adhesives have been proposed (see, for example, Patent Documents 1 and 2).
JP 2005-189615 A JP 2006-145938 A

In recent years, the application range of liquid crystal display devices has been expanded, and it has become necessary to cope with diversification of use environments. For example, durability under severe environments such as high temperature and high humidity has been demanded.
The adhesive containing the AA-PVA-based resin and the crosslinking agent described in Patent Documents 1 and 2 show excellent water resistance and moisture resistance under normal use conditions, but is obtained using such an adhesive. When the obtained polarizing plate is used for a long time under high temperature and high humidity, slight discoloration is observed, which may cause a problem in a liquid crystal display device in which high performance and high definition are advanced.

  Moreover, although the adhesive agent for polarizing plates containing PVA-type resin is normally used as aqueous solution, the aqueous solution containing AA-ized PVA-type resin and the various crosslinking agents of patent document 2 carries out a crosslinking reaction in water. As it progresses, there is a problem that it gradually increases in viscosity and gels and becomes unusable, or the workability of coating on a polarizing film as a substrate is lowered. Moreover, as described in Patent Document 1, it is possible to lengthen the pot life without reducing water resistance by using methylol melamine as a crosslinking agent and setting the pH of the system to 4.3 or less. Strongly acidic materials are dangerous for workers and are not preferable because they may cause corrosion of metal equipment and decrease durability.

  That is, the present invention is excellent in water resistance and moisture resistance, and is excellent in discoloration resistance under high temperature and high humidity, and used in such a polarizing plate, has excellent viscosity stability, and has a high degree of freedom in pH when used. The object is to provide a high adhesive for polarizing plates.

  As a result of intensive studies in view of the above circumstances, the inventor of the present invention has a polarizing plate in which a protective film is laminated on at least one surface of a polarizing film via an adhesive layer. A polarizing plate containing a reaction product of a polyvinyl alcohol-based resin, an acetal compound having a dialkyl acetal group and one aldehyde group in the molecule, and a PVA resin containing an acetoacetate group and one dialkyl acetal group in the molecule It was found that the object of the present invention was achieved by an adhesive for polarizing plates containing an acetal compound having an aldehyde group, and the present invention was completed.

  The dialkyl acetal group in the acetal compound used in the present invention stably maintains the acetal structure at 5 to 40 ° C. which is the environmental temperature at the time of storage and use of the aqueous adhesive obtained by mixing with the AA-PVA resin. Therefore, it does not react with the acetoacetate group in the AA-PVA-based resin, and such an adhesive is used for bonding the polarizing film and the protective film, and at the time of drying or subsequent heat treatment, for example, at 40 to 200 ° C. The dialkyl acetal group is converted into an aldehyde group by hydrolysis, resulting in a compound having a plurality of aldehyde groups. These aldehyde groups react with acetoacetate groups to crosslink the PVA resin, and the AA-PVA system It is presumed to impart excellent water resistance and moisture resistance to the crosslinked resin.

  Since the polarizing plate of the present invention is excellent in discoloration resistance under high temperature and high humidity, it is suitable for liquid crystal display devices used in various usage environments, and further an adhesive for polarizing plates used for such polarizing plates. Is industrially useful since it has excellent viscosity stability and a high degree of freedom in pH.

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.

  In the present invention, a protective film is laminated on at least one surface of a polarizing film via an adhesive layer containing a reaction product of an AA-PVA-based resin and an acetal compound having a dialkyl acetal group and one aldehyde group in the molecule. The acetoacetate group-containing PVA resin used for the adhesive layer of the polarizing plate and an acetal compound having a dialkyl acetal group and one aldehyde group in the molecule are used. The present invention relates to an adhesive for polarizing plates.

(Polarizer)
First, the polarizing plate of this invention is demonstrated.
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 them, a polarizing film made of a PVA film and a dichroic material such as iodine is preferable. Hereinafter, a polarizing film composed of a PVA film and iodine will be described.
The PVA-based resin used for the PVA-based film is usually produced by saponifying a polyvinyl ester obtained by polymerizing a fatty acid vinyl ester represented by vinyl acetate. For example, unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (ethylene, propylene, n-butene, isobutene, etc.), vinyl ethers. The saponified copolymer may be a copolymer with a component copolymerizable with vinyl acetate such as an unsaturated sulfonate. The degree of saponification of the PVA-based resin is usually 85 to 100 mol%, particularly 90 to 100 mol%, more preferably 95 to 100 mol%. When the degree of saponification is too low, the water resistance tends to be insufficient when forming a polarizing film.

  The average degree of polymerization of the PVA resin may be any, but is usually 1200 to 7000, particularly 1500 to 5000, and more preferably 1600 to 4000. If the average degree of polymerization is too low, it tends to be difficult to stretch the film at the time of forming the polarizing film, and if it is too high, the surface smoothness and transmittance of the film tend to be lowered. In addition, the saponification degree and average polymerization degree of PVA-type resin are measured according to JIS K6726.

A method for producing such a polarizing film is not particularly limited, and a known method may be adopted. A typical example will be described below.
First, a raw film is formed from an aqueous solution of PVA resin. As such a method, a known film forming method can be used, and a solution casting method is usually employed, but a dry / wet film forming method or a gel film forming method can also be carried out. When such a solution casting method is used, the concentration of the PVA-based resin aqueous solution is usually 1 to 50% by weight, and the raw film can be obtained by casting the aqueous solution on a metal roll or the like and drying by heating.

  It is also possible to add various additives to such a PVA-based resin aqueous solution within a range that does not impair the quality of the polarizing plate. Or it is also a preferable embodiment to mix and mix. Examples of such solvents include monohydric alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, and butyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, glycerin, trimethylolpropane, and the like. And polyhydric alcohols, phenols such as phenol and cresol, amines such as ethylenediamine and trimethylenediamine, dimethyl sulfoxide, dimethylacetamide, N-methylpyrrolidone and the like.

  The film thickness of the raw film is usually 30 to 100 μm, preferably 50 to 90 μm. If the film thickness is too thin, stretching tends to be impossible, and if it is too thick, film thickness accuracy tends to decrease.

  Such a raw film is then subjected to a process of uniaxial stretching, adsorption of dichroic material such as iodine or dichroic dye, and cross-linking with a boron compound. In addition, the order of each step is not particularly limited. In particular, it is preferable in terms of productivity to perform uniaxial stretching in at least one of the dichroic material adsorption step and the boron compound treatment step.

  The draw ratio during uniaxial stretching is usually 3.5 to 10 times, and a range of 4.5 to 7 times is particularly preferably selected. At this time, the film may be slightly stretched in the direction perpendicular to the above (stretching to prevent shrinkage in the width direction or more). The temperature conditions during stretching are usually selected from the range of 40 to 130 ° C. The stretching operation is not limited to one stage, and can be performed in multiple stages. Furthermore, the stretching operation can be performed individually at any stage of the manufacturing process. May be finally set within the above range.

  The adsorption of iodine to the PVA stretched film is performed by bringing the film into contact with a liquid containing iodine. As the iodine solution, an iodine-potassium iodide aqueous solution is usually used. In this case, the iodine concentration is 0.1 to 2 g / L, the potassium iodide concentration is 10 to 50 g / L, and potassium iodide / The weight ratio of iodine is preferably 20-100. Moreover, about 30-500 second is practical about time to contact a PVA-type stretched film with a dichroic material solution, and the temperature of a bath has preferable 30-80 degreeC. In addition, as a contact means, arbitrary means, such as immersion, application | coating, and spraying, are applicable.

  The PVA-based stretched film on which iodine is adsorbed is then subjected to a crosslinking treatment with a boron compound. As the boron compound, boric acid and borax are typically used. Such cross-linking treatment is performed by bringing the film obtained above into contact with an aqueous solution of a boron compound or a water-organic solvent mixed solution, and the contact method is typically an immersion method, but a coating method or a spray method. But it is possible. In the case of the immersion method, the concentration is usually selected within the range of 0.5 to 2 mol / L, the bath temperature is usually about 50 to 70 ° C., and the treatment time is usually preferably about 5 to 20 minutes.

  The polarizing film made of PVA film and iodine thus obtained is then laminated with a protective film via an adhesive layer. The thickness of the protective film is usually 10 to 100 μm, preferably 20 to 80 μm, and the material thereof is not particularly limited, and it is preferable if it is transparent and excellent in durability. Suitable examples include cellulose ester resin films, cyclic olefin resin films, (meth) acrylic resin films, and the like.

  Examples of 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 in order to increase the affinity with the polarizing film and the PVA resin used as an adhesive thereof, but is not limited thereto. It is not a thing. Moreover, the thing which apply | coated the antistatic agent on the surface or contained in the film is 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 polyether sulfone resin film, polycarbonate resin film, vinyl chloride resin film, amide resin film such as nylon and aromatic polyamide, (fluorine-containing) polyimide resin film, polyether ether ketone 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. In addition, as a protective film, for example, a cured layer such as an acrylic, urethane, acrylic urethane, epoxy, or silicone thermosetting type or ultraviolet curable 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 can also 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 such that a transparent protective film is bonded to at least one side, preferably both sides, of such a polarizing film via an adhesive layer. The adhesive layer is composed of an AA-PVA-based resin and a molecule. It mainly has a reaction product of an acetal compound having a dialkyl acetal group and one aldehyde group. Such an adhesive layer is usually made by uniformly applying an aqueous adhesive containing an AA-PVA-based resin and an acetal compound having a dialkyl acetal group and one aldehyde group in the molecule to a polarizing film or a protective film, or both. It is formed by applying and bonding the two together, followed by pressure bonding and heat drying.
When coating such a water-based adhesive on a polarizing film or a protective film, a roll coater method, for an air doctor, a blade coater method, a spray method, a dipping method, or just before bonding a polarizing film and a protective film, A known method such as supplying an appropriate amount of an agent (water) solution between the films and pouring the solution and then bonding them together and drying can be used. The coating amount of the aqueous adhesive is usually selected from the range of 1 to 1000 nm, particularly 1 to 500 nm, and more preferably 1 to 300 nm as the thickness of the adhesive layer after drying, and the thickness becomes too thick. Uniform coating tends to be difficult and thickness unevenness tends to occur. Moreover, as heat drying conditions after apply | coating and bonding a water-based adhesive, it is 10-60 minutes normally in 5-150 degreeC, especially 30-120 degreeC, Furthermore, 30 seconds-30 minutes, Especially 1-20 minutes Done on condition.

(AA-modified PVA resin)
Next, the AA-PVA-based resin used in the present invention will be described.
The structure and production method of the AA-PVA-based resin used in the present invention are known, for example, from JP-A-55-094904, JP-A-55-137107, JP-A-57-040508, etc. However, the outline will be described in detail.
Such AA-PVA-based resin is one in which AA groups are introduced into the side chain of the PVA-based resin, and the content of AA groups in the AA-PVA-based resin is usually about 0.1 to 20 mol%, The remaining part consists 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 ordinary PVA resins.

  To obtain such AA-PVA-based resin, a method of reacting a PVA-based resin with diketene, a method of reacting a PVA-based resin with acetoacetate and a transesterification, a saponification of a copolymer of vinyl acetate and vinyl acetoacetate Although it is easy to manufacture and a good quality AA-PVA-based resin can be obtained, it is preferable to manufacture by reacting the PVA-based resin with diketene, which will be described below. It is not limited to.

  As the PVA resin used as a raw material, a saponified product of a vinyl ester monomer polymer or a derivative thereof is generally used. Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, and valeric acid. Examples include vinyl, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate, and vinyl acetate is preferably used from the viewpoint of economy.

Further, a saponified product of a copolymer of a vinyl ester monomer and a monomer copolymerizable with the vinyl ester monomer can be used. Examples of the copolymer monomer include ethylene, propylene, isobutylene, α- Olefins such as octene, α-dodecene, α-octadecene, vinylene carbonates, unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, undecylenic acid, or salts thereof, mono or Dialkyl esters, nitriles such as acrylonitrile and methacrylonitrile, amides such as acrylamide and methacrylamide, olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid and methallyl sulfonic acid or salts thereof, alkyl vinyl ethers, -Acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethyldiallylammonium chloride, dimethylallyl vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinylidene chloride, polyoxyethylene (meth) allyl ether, polyoxypropylene (meth) allyl ether Such as polyoxyalkylene (meth) allyl ether, polyoxyethylene (meth) acrylate, polyoxyalkylene (meth) acrylate such as polyoxypropylene (meth) acrylate, polyoxyethylene (meth) acrylamide, polyoxypropylene (meth) Polyoxyalkylene (meth) acrylamide such as acrylamide, diacetone acrylamide, polyoxyethylene (1- (meth) a Rilamide-1,1-dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, nyl, vinylethylene carbonate, 2,2-dialkyl-4-vinyl-1,3 -Dioxolane, glycerol monoallyl ether, 3,4-diacetoxy-1-butene, 1,4-diacetoxy-2-butene and the like.
The introduction amount of the copolymerization monomer varies depending on the type of the monomer and cannot be generally specified. However, it is usually 20 mol% or less, particularly 10 mol% or less. The compatibility with the agent may decrease.

  The main chain bonding mode of the PVA-based resin is mainly 1,3-bond, but it is also possible to use one in which the content of 1,2-bond, which is a heterogeneous bond, is controlled depending on the polymerization conditions. As a method for controlling the 1,2-bond content, when a high content is obtained, a polymerization solvent having a high boiling point is used or the polymerization temperature is increased by performing pressure polymerization. On the contrary, when a low content is obtained, a chain transfer agent may be used or polymerization may be performed at a low temperature. The content of 1,2-bond is usually 0.6 to 3.5 mol%, particularly 1.3 to 2.5 mol%, more preferably 1.5 to 2.0 mol%. Used.

  The saponification of the obtained polyvinyl acetate resin can be carried out by a known method, but usually it is carried out in the presence of an alkali catalyst or an acid catalyst after dissolving the polyvinyl acetate resin in an alcohol solvent. . As the alcohol solvent, for example, methanol, ethanol, butanol, isopropanol, a mixed solvent of various alcohols such as methanol and methyl acetate, and a mixed solvent of methyl acetate can be used.

As the alkali catalyst, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate and potassium methylate, and alkali catalysts such as alcoholate can be used. As the acid catalyst, an inorganic acid aqueous solution such as hydrochloric acid or sulfuric acid, or an organic acid such as p-toluenesulfonic acid can be used.
Moreover, especially the temperature when performing saponification is although it does not restrict | limit, Usually, it is 10-70 degreeC, and 20-50 degreeC is more preferable.

Next, the PVA resin obtained by saponification of the polyvinyl acetate resin and the diketene are reacted. In this case, the PVA resin and the gaseous or liquid diketene may be directly reacted. An organic acid is adsorbed and occluded in advance in a PVA resin, and then a gaseous or liquid diketene is sprayed and reacted in an inert gas atmosphere, or a mixture of an organic acid and a liquid diketene is sprayed and reacted in a PVA resin. Etc. are used.
As the reaction apparatus for carrying out the above reaction, any apparatus that can be heated and has a stirrer is sufficient. For example, a kneader, a Henschel mixer, a ribbon blender, other various blenders, and a stirring and drying apparatus can be used.

  The acetoacetate group content (degree of acetoacetate esterification, hereinafter abbreviated as AA degree) in the AA-PVA-based resin thus obtained is usually 0.1 to 20 mol%, preferably 0.2 to 15 mol%, especially 0.3 to 10 mol%. If the content is too small, sufficient water resistance may not be obtained, or a sufficient crosslinking rate may not be obtained. Since water solubility may fall or stability of aqueous solution may fall, it is not preferable.

  The AA-PVA-based resin of the present invention preferably has a hydroxyl group average chain length [l (OH)] of usually 10 to 100, particularly 10 to 90, and further 15 to 80. If the hydroxyl chain length is too short or too long, the adhesive strength tends to be insufficient or the water resistance tends to be insufficient.

The hydroxyl group average chain length [l (OH)] is 3- (trimethylsilyl) -2,2,3,3-d ₄ -propionic acid sodium salt (3- (trimethylsilyl) propionic-2, Absorption based on the methylene carbon moiety found in the range of 38-46 ppm in ¹³ C-NMR measurements (solvent: D ₂ O) using 2,3,3-d ₄ -acid sodium salt) [(OH, OH) dyad Absorption = 43-46 ppm absorption with peak top, (OH, OR) dyad absorption = 41-43 ppm absorption with peak top, (OR, OR) dyad absorption = 38-41 ppm It is a value calculated from the following formula.
l (OH) = [2 (OH, OH) + (OH, OR)] / (OH, OR)
(However, the absorption intensity ratios of (OH, OR) and (OH, OH) are all calculated as mole fractions.)
With regard to the hydroxyl group average chain length and the measuring method thereof, “Poval” (Publisher: Kobunshi Shuppankai, page 248, 1981) and Macromolecules, Vol. 10, p532 (1977).

  The method for controlling the hydroxyl group average chain length of the AA-modified PVA resin is not particularly limited, but the dielectric constant at 20 ° C. is 32 or less in the saponification step of polyvinyl acetate during the production of the PVA resin used as a raw material. It is preferable to perform alkali saponification in the presence of such a solvent. A more preferable dielectric constant is 6 to 28, and a particularly preferable dielectric constant is 12 to 25. When the dielectric constant is too high, the block property of the arrangement of the remaining acetic acid groups in the PVA resin is lowered, and the hydroxyl chain length of the AA-PVA resin obtained as a final product tends to be shortened.

  As a solvent having a dielectric constant of 32 or less at 20 ° C., methanol (31.2), methyl acetate / methanol = 1/3 (27.1), methyl acetate / methanol = 1/1 (21.0), methyl acetate / Methanol = 3/1 (13.9), methyl acetate (7.03), isopropyl acetate (6.3), trichlorethylene (3.42), xylene (2.37), toluene (2.38), benzene (2.28), acetone (21.4) and the like. Of these, a mixed solvent of methyl acetate / methanol is preferably used.

  Moreover, the average degree of polymerization (based on JIS K6726) of the AA-PVA-based resin is usually 300 to 4000, preferably 400 to 3500, particularly 500 to 3000. If the average degree of polymerization is too small, sufficient water resistance is achieved. In some cases, a sufficient crosslinking rate cannot be obtained. On the other hand, if it is too large, the viscosity of the adhesive solution becomes too high, and it may be difficult to apply to the adherend.

  Further, the saponification degree of the AA-PVA-based resin of the present invention is usually 80 mol% or more, preferably 85 mol% or more, particularly 90 mol% or more. Decreases, it becomes difficult to obtain a uniform adhesive solution, and the cohesive force as an adhesive tends to decrease.

  In addition, the AA-PVA resin of the present invention includes alkali metal acetate such as sodium acetate mixed or produced as a by-product in the production process (mainly the alkali metal hydroxide used as a saponification catalyst and polyvinyl acetate The organic acid such as acetic acid, and the organic solvent such as methanol and methyl acetate may partially remain.

  In the present invention, a mixture of two or more AA-PVA-based resins having different polymerization degrees, saponification degrees, and AA group contents may be used. Moreover, you may mix and use PVA-type resin different from PVA-type resin used by this invention in the range which does not impair the objective of this invention. Examples of such PVA-based resins include unmodified PVA and modified PVA-based resins copolymerized with the aforementioned various unsaturated monomers.

(Acetal compound)
Next, the acetal compound used in the present invention will be described. Such an acetal compound is made into a solution such as an aqueous solution together with an AA-PVA-based resin, and the dialkylacetal group becomes an aldehyde group upon drying after being applied to an adherend as a liquid adhesive, and the aldehyde group becomes an AA-PVA-based resin. By reacting with the acetoacetate group in the solvent, it is presumed to work as a cross-linking agent for the AA-PVA-based resin.
The acetal compound used in the present invention is a compound having a dialkyl acetal group represented by the following general formula (1) in the molecule and one aldehyde group. In other words, it corresponds to a compound obtained by dialkyl acetalization leaving only one aldehyde group of a compound having a plurality of aldehyde groups in the molecule.

R ¹ and R ² in the dialkyl acetal group represented by the general formula (1) are alkyl groups, which may be either linear or branched, and the number of carbon atoms is usually 1-6. In particular, an alkyl group having 1 to 4 carbon atoms is preferable. If the carbon number is too large, the boiling point of the alcohol represented by R ¹ OH or R ² OH produced as a by-product when the dialkyl acetal group becomes an aldehyde group by hydrolysis or the like increases, It tends to be difficult to remove them sufficiently. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, and the like. Among them, a methyl group is preferably used.
The alkyl groups represented by R ¹ and R ² may be the same or different, but usually the same one is used. In addition, a part of the hydrogen atoms in the alkyl group may be substituted with a halogen, a hydroxyl group, an alkoxy group, an ester group, a carboxylic acid group, a sulfonic acid group, or the like, as long as the effect of the present invention is not significantly impaired.
Moreover, when it has two or more dialkyl acetal groups in a molecule | numerator, those dialkyl acetal groups may be the same or different.

  The number of dialkyl acetal groups in the acetal compound is not particularly limited. However, since it is a hydrophobic group, if it is too much, the water solubility may decrease, and usually 1 to 5, preferably 1 to 3. What is a piece is used.

  In addition, the number of aldehyde groups in the acetal compound is one, and when the number is two or more, the viscosity stability of the adhesive for polarizing plates decreases, which is not preferable. This is because the aldehyde group easily reacts with the AA group in the AA-PVA-based resin at room temperature, but if the number is only one in the molecule, the AA-PVA-based resin is less likely to be cross-linked. When the number is plural, a crosslinked structure is easily formed, and as a result, it is presumed to be for thickening the aqueous solution.

  The chemical structure of the portion other than the dialkyl acetal group and the aldehyde group in the acetal compound used in the present invention is not particularly limited. However, a chemical structure in which the dialkyl acetal group and the aldehyde group are directly bonded, or a linear or branched alkylene group. Those in which both functional groups are bonded are usually used. The molecular weight of the acetal compound is usually from 104 to 300, more preferably from 104 to 200, and particularly preferably from 104 to 150. The smaller the molecular weight, the greater the effect on the added amount, which is preferable. If the molecular weight is too large, the water solubility becomes poor, the amount added to obtain the desired water resistance increases, or sufficient water resistance cannot be obtained.

Specific examples of the acetal compound include dimethoxyethanal (dimethoxyacetaldehyde), diethoxyethanal (diethoxyacetaldehyde), dialkoxyethanal such as di-n-propoxyethanal, dimethoxypropanal (dimethoxypropionaldehyde), Dialkoxypropanal such as diethoxypropanal (diethoxypropionaldehyde), dialkoxybutanal such as dimethoxybutanal, diethoxybutanal, etc. can be mentioned, among them dialkoxyethanal in terms of low molecular weight, In particular, dimethoxyethanal is preferably used.
In addition, “High Link DM” manufactured by Clariant is listed as a commercial product containing such dimethoxyethanal.

  In addition, the manufacturing method of this acetal compound is not specifically limited, What was obtained by the well-known method can be used, For example, dialkoxyethanal which is the most preferable compound for the objective of this application is used. Examples of the production method include a method of continuously reacting glyoxal with methanol, as described in JP-A-H06-234689.

(Adhesive for polarizing plate)
Next, the polarizing plate adhesive of the present invention will be described.
The polarizing plate adhesive of the present invention mainly comprises the AA-PVA-based resin and the acetal compound as described above, and the content ratio is not particularly limited, but is usually AA-PVA-based. A range of 0.1 to 100 parts by weight, further 0.5 to 50 parts by weight, particularly 1 to 20 parts by weight of the acetal compound is suitably used with respect to 100 parts by weight of the resin. The molar ratio (Y / X) of the total amount (Y) of dialkylacetal groups and aldehyde groups to the total amount of AA groups (X) in the AA-PVA-based resin is usually 0.01-100, preferably 0.1 50, especially in the range of 0.3-30. If the content of the acetal compound is too small, the water resistance of the obtained polarizing plate may be insufficient. On the other hand, if the content is too large, the adhesive solution tends to thicken depending on the usage environment, etc. May become shorter.
Further, the form is not particularly limited, but it is preferably in a liquid form in order to form a uniform adhesive layer on the surface of the polarizing film or the protective film as the adherend. Examples of such a liquid adhesive include solutions and dispersions of various solvents, but a solution type is preferable from the viewpoint of application to a substrate, and an aqueous solution is more preferable from the viewpoint of safety. Hereafter, the manufacturing method of adhesive agent aqueous solution is demonstrated.
Such an aqueous solution is (i) a method in which a mixture of an AA-PVA-based resin and an acetal compound is added to water and dissolved, (ii) a method in which an AA-PVA-based resin and an acetal compound are separately dissolved in advance, and (Iii) Although it can be prepared by a method in which an acetal compound is added to an aqueous solution of an AA-PVA-based resin and dissolved, etc., since the acetal compound is often distributed in the market in the form of an aqueous solution, usually (ii) It is desirable to use it for various uses as an aqueous solution of a resin composition by mixing both using a method.

  The concentration when the polarizing plate adhesive of the present invention is used as an aqueous solution cannot be generally specified depending on the desired coating amount and the characteristics of the coating apparatus, but is usually 0.1 to 20% by weight, particularly 0.5 to 0.5%. A range of 10% by weight is preferably used. If the concentration is too low, it takes a long time to dry and the productivity is impaired. Conversely, if the concentration is too high, uniform coating tends to be difficult.

  In addition, such a polarizing plate adhesive aqueous solution can be used in a wide pH range, and viscosity stability and water resistance and discoloration resistance of the obtained polarizing plate are not affected by pH. Such an aqueous adhesive solution can be used in a range of pH 2.5 to 11 at 20 ° C., and is preferably 3 to 10, more preferably 4 to 9. In addition, when such pH is too low, since the case where a container, a coating apparatus, etc. to be used may be corroded, it is necessary to take a rust prevention measure. If the pH is too high, the acetoacetyl group of the AA-PVA-based resin tends to be cleaved by hydrolysis and a good cross-linked structure tends not to be obtained, and the adhesive strength may be reduced.

The adhesive for polarizing plates of the present invention contains an AA-PVA-based resin and an acetal compound as a crosslinking agent, but a crosslinking agent other than the acetal compound can be used in combination.
As such other crosslinking agents, those known as crosslinking agents for AA-PVA-based resins can be used, and examples thereof include aldehyde compounds, methylol compounds, amine compounds, hydrazine compounds, and polyvalent metal compounds. However, from the viewpoint of stability when the aqueous solution is the object of the present invention, the cross-linking agent used together does not react rapidly with the AA group at a room temperature where the cross-linkable functional group is 40 ° C. or lower, and the temperature is raised to a higher temperature. The thing which a crosslinking reaction advances by this is preferable. Examples of the cross-linking agent having such properties include polyvalent metal compounds, compounds in which functional groups are protected, for example, compounds in which all aldehyde groups are acetalized, and compounds in which methylol groups are etherified.

  Specific examples of the polyvalent metal compound include zirconium compounds such as zirconyl chloride, basic zirconyl chloride, zirconyl sulfate, zirconyl nitrate, zirconyl carbonate, ammonium zirconium carbonate, potassium zirconium carbonate and zirconyl acetate.

  Specific examples of the compounds in which all aldehyde groups are acetalized include 1,1,2,2-tetramethoxyethane, 1,1,2,2-tetraethoxyethane, 1,1,3,3- Hydrocarbon compounds having a plurality of acetal groups such as tetramethoxypropane, 1,1,3,3-tetraethoxypropane, 1,1,6,6-tetramethoxyhexane, and bis-1,3- (2,2 -Dimethoxy-1-hydroxyethyl) urea (trade name “Hilink DU”, manufactured by Clariant), bis-1,3- (2,2-dimethoxy-1-hydroxyethyl) -2-imidazolidinone (trade name) “Hilink DMU” (manufactured by Clariant), 1,1 ′, 1 ″-(1,3,5-triazine-2,4,6-triyltriimino) tris [2,2-dimethoxyethanol ] And the like (trade name "High Link DMM" manufactured by Clariant), compound dimethoxyethanal was obtained by adding to the urea or melamine, such as.

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.
Furthermore, various organic solvents having high affinity with water, specifically various alcohols represented by methanol, ethanol, n-propanol and i-propanol, within the range not impairing the object of the present invention. 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. In addition, you may mix | blend any of these after the AA-ized PVA-type resin aqueous solution, the aqueous solution of an acetal compound, or the mixture.

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
A 10% aqueous solution of an AA-PVA-based resin having an average polymerization degree of 1200, a saponification degree of 99.0 mol%, an AA degree of 5.0 mol%, and a hydroxyl group average chain length of 20 and dimethoxyethanal (trade name “HILINK” DM ”(manufactured by Clariant Co., Ltd., 60% aqueous solution) was mixed with 100 parts by weight of AA-modified PVA resin so that dimethoxyethanal was 5 parts by weight in solid content, mixed and stirred, and adhesive for polarizing plate An aqueous solution was obtained. At this time, the molar ratio (Y / X) of the sum (X) of the amount of dimethylacetal groups and the amount of aldehyde groups in dimethoxyethanal to the amount of AA groups (Y) in the AA-PVA-based resin was 1. In addition, pH at 20 degreeC of this aqueous solution was 4.7.
This aqueous solution was cast on a PET film, allowed to stand for 48 hours under conditions of 23 ° C. and 50% RH, and then heat-treated at 70 ° C. for 5 minutes to obtain an adhesive layer film having a thickness of 100 μm.
The water resistance and discoloration resistance of the obtained film were evaluated as follows.

(water resistant)
The obtained film was immersed in hot water at 80 ° C. for 1 hour, and the elution rate (%) of the film was measured. In calculating the dissolution rate (%), the dry weight of the film before immersion in hot water (X ₁ ) and the dry weight of the film after immersion in hot water (X ₂ ) (both in g) were obtained and The elution rate (%) was calculated. The results are shown in Table 1.
Elution rate (%) = [(X ₁ −X ₂ ) / X ₁ ] × 100

(Discoloration resistance)
The obtained film was stored for 1 week under the conditions of 40 ° C. and 90% RH, and the degree of coloring (yellowing) of the film was visually observed and evaluated as follows. The results are shown in Table 1.
○ ・ ・ ・ No coloring is observed △ ・ ・ ・ Slight yellowing is observed × ・ ・ ・ Yellow yellowing is recognized

(Stability of aqueous solution)
The viscosity (a) of the obtained polarizing plate adhesive aqueous solution (7%) at 23 ° C. was measured with a Brookfield viscometer (Brookfield, rotor No. 2, rotation speed 100 rpm), and the aqueous solution was then used. The solution was placed in an atmosphere of 23 ° C., the viscosity of the aqueous solution (b) after 6 days was measured, and the thickening ratio before and after was shown as (b) / (a).

Example 2
In Example 1, the amount of dimethoxyethanal was changed to 1 part by weight (Y / X = 0.2) with respect to 100 parts by weight of AA-PVA-based resin. A plate adhesive aqueous solution was obtained. The pH of this aqueous solution was 4.8. Using this aqueous solution, an adhesive layer film was prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

Example 3
In Example 1, the amount of dimethoxyethanal was changed to 50 parts by weight (Y / X = 10) with respect to 100 parts by weight of AA-PVA-based resin. An aqueous adhesive solution was obtained. The pH of this aqueous solution was 4.6. Using this aqueous solution, an adhesive layer film was prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

Example 4
In Example 1, an AA-PVA-based resin having an average polymerization degree of 1700, a saponification degree of 92 mol%, an AA-degree of conversion of 4 mol%, and a hydroxyl group average chain length of 22 was used as the AA-PVA-based resin. In the same manner, an aqueous polarizing plate adhesive solution was obtained. The pH of such an aqueous solution was 4.3. Using this aqueous solution, an adhesive layer film was prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

Example 5
In Example 1, the amount of dimethoxyethanal was 10 parts by weight (Y / X = 2) with respect to 100 parts by weight of the AA-PVA-based resin. An aqueous adhesive solution was obtained. The pH of this aqueous solution was 4.7. Using this aqueous solution, an adhesive layer film was prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

Example 6
In Example 5, a polarizing plate adhesive was used in the same manner as in Example 5 except that sodium hydroxide was used as a pH adjusting agent with respect to 100 parts by weight of AA-PVA-based resin, and the pH of the aqueous solution was set to 8.1. An aqueous solution was obtained. Using this aqueous solution, an adhesive layer film was prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

Comparative Example 1
In Example 1, an adhesive was used in the same manner as in Example 1 except that instead of dimethoxyethanal, a cyclic acetal compound (trade name “SEKARETZ 755”, manufactured by Omninova), which is a reaction product of glucose and glyoxal, was used. An aqueous solution was obtained. The pH of such an aqueous solution was 4.2. Using this aqueous solution, a film was prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

Comparative Example 2
In Example 1, an aqueous adhesive solution was obtained in the same manner as in Example 1 except that glyoxal was used instead of dimethoxyethanal. The pH of such an aqueous solution was 4.5. Using this aqueous solution, a film was prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

As is apparent from these results, the adhesive for polarizing plates of the present invention is excellent in viscosity stability with almost no increase in viscosity even when stored at 23 ° C. for 6 days.
In addition, the adhesive layer film obtained from such a polarizing plate adhesive is excellent in water resistance, and since it is not colored at all even when stored under high temperature and high humidity, it is extremely excellent in discoloration resistance. . In addition, since the same characteristic is acquired even if pH of adhesive agent aqueous solution changes, it is useful at the point that the freedom degree of pH to use is high.
In this example, the evaluation of water resistance and discoloration resistance is performed on a film having only an adhesive layer, but these results are directly reflected in the characteristics of the polarizing plate containing the adhesive layer. Is.

  The polarizing plate of the present invention is excellent in water resistance, and further excellent in resistance to discoloration under high temperature and high humidity. Therefore, it is extremely suitable for liquid crystal display devices used in a wide variety of applications and various usage environments. . Furthermore, in such a polarizing plate, the adhesive for polarizing plate used for adhesion between the polarizing film and the protective film is industrially useful because it is excellent in viscosity stability when used as an aqueous solution.

Claims (2)

In a polarizing plate in which a protective film is laminated on at least one surface of a polarizing film via an adhesive layer, the adhesive layer comprises an acetoacetate group-containing polyvinyl alcohol resin, a dialkylacetal group and one aldehyde in the molecule A polarizing plate comprising a reaction product with an acetal compound having a group. An adhesive for polarizing plates, comprising an acetoacetate group-containing polyvinyl alcohol resin and an acetal compound having a dialkyl acetal group and one aldehyde group in the molecule.