JP2013125077A - Adhesive for polarizing plate, polarizing plate, manufacturing method of the same, optical film, and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive for a polarizing plate that has excellent thickening stability, and is capable of forming an adhesive layer that has satisfactory water resistance and optical characteristics.SOLUTION: An adhesive for a polarizing plate is used for providing a transparent protective film at least on one side of a polarizer, and contains a polyvinyl alcohol-based resin, a methylol group-containing compound, and an oxyzirconium salt. The content of the methylol group-containing compound and oxyzirconium salt are each less than 10 parts by weight relative to 100 parts by weight of the polyvinyl alcohol-based resin.

Description

  The present invention relates to an adhesive for polarizing plates. Moreover, this invention relates to the polarizing plate using the said adhesive agent for polarizing plates, and its manufacturing method. The polarizing plate can form an image display device such as a liquid crystal display device, an organic EL display device, or a PDP alone or as an optical film obtained by laminating the polarizing plate.

  In a liquid crystal display device, it is indispensable to dispose polarizers on both sides of a glass substrate on which a liquid crystal panel surface is formed because of its image forming method. In general, a polarizer is obtained by dyeing a polyvinyl alcohol film with a dichroic material such as iodine, cross-linking with a cross-linking agent, and forming a film by uniaxial stretching. Since the polarizer is made by stretching, it easily contracts. In addition, since the polyvinyl alcohol film uses a hydrophilic polymer, it is very easily deformed particularly under humidified conditions. Moreover, since the mechanical strength of the film itself is weak, there is a problem that the film is torn. Therefore, a polarizing plate is used in which a transparent protective film such as triacetyl cellulose is bonded to both sides or one side of the polarizer to supplement the strength. The polarizing plate is manufactured by bonding a polarizer and a transparent protective film with an adhesive.

  In recent years, the use of liquid crystal display devices has been expanded, and a wide range of development has been progressing from portable terminals to large-sized TVs for home use, and respective standards have been provided according to each application. Particularly in portable terminal applications, since it is assumed that the user carries around, the demand for durability is very strict. For example, a polarizing plate is required to have water resistance that does not change its characteristics and shape even under humidified conditions that cause condensation.

  As described above, the polarizer is used as a polarizing plate whose strength is reinforced by a transparent protective film. As an adhesive for polarizing plates used for adhesion | attachment of the said polarizer and a transparent protective film, a water-system adhesive agent is preferable, for example, the polyvinyl alcohol-type adhesive agent which mixed the crosslinking agent in the polyvinyl alcohol aqueous solution is used. However, the polyvinyl alcohol-based adhesive may peel off at the interface between the polarizer and the transparent protective film under humidified conditions. This may be because the polyvinyl alcohol resin, which is the main component of the adhesive, is a water-soluble polymer, and the adhesive may be dissolved under the dew condensation condition. In order to solve the above problems, it has been proposed to contain various crosslinking agents. For example, an adhesive for polarizing plates containing a crosslinking agent as a polyvinyl alcohol resin containing an acetoacetyl group and an amino-formaldehyde resin has been proposed (Patent Document 1). In addition, it has been proposed to use an oxyzirconium salt as a crosslinking agent for an adhesive for polarizing plates (Patent Documents 2 and 3).

Japanese Patent No. 4301558 JP 2009-42383 A JP 2009-42384 A

  In Patent Documents 1 to 3, an excessive amount of a crosslinking agent is added to obtain a crosslinking effect. However, when an excessive amount of amino-formaldehyde resin is used as a cross-linking agent, the aqueous solution (adhesive) containing the polyvinyl alcohol-based resin is cross-linked even under room temperature conditions, and is stable because it thickens during work. There is a problem with sex. On the other hand, when an oxyzirconium salt is used as the cross-linking agent, the thickening stability is good, but the oxyzirconium salt is a material having a higher refractive index than that of the polyvinyl alcohol resin, and obtains sufficient water resistance. Therefore, a large amount of addition is necessary. Therefore, an adhesive using an oxyzirconium salt as a crosslinking agent tends to increase the refractive index of the resulting adhesive layer. When the refractive index of the adhesive layer is increased, the difference between the refractive index of the polarizer or the transparent protective film and the refractive index of the adhesive layer is increased, so that there is a problem that the optical characteristics are deteriorated due to interface reflection.

  An object of this invention is to provide the adhesive agent for polarizing plates which can form the adhesive bond layer which has favorable thickening stability and can satisfy water resistance and an optical characteristic.

  Moreover, an object of this invention is to provide the polarizing plate using the said adhesive agent for polarizing plates, and its manufacturing method. Furthermore, an object of the present invention is to provide an optical film in which the polarizing plate is laminated, and to provide an image display device such as a liquid crystal display device using the polarizing plate and the optical film.

  As a result of intensive studies to solve the above problems, the present inventors have found that the object can be achieved by the following polarizing plate adhesive, and have completed the present invention.

That is, the present invention is an adhesive for polarizing plates used for providing a transparent protective film on at least one side of a polarizer,
The polarizing plate adhesive comprises a polyvinyl alcohol resin, a methylol group-containing compound as a first crosslinking agent and an oxyzirconium salt as a second crosslinking agent, and the methylol group-containing compound and oxyzirconium salt are as follows: It is related with the adhesive agent for polarizing plates characterized by mix | blending in the ratio of less than 10 weight part with respect to 100 weight part of polyvinyl alcohol resin, respectively.

  In the adhesive for polarizing plates, the polyvinyl alcohol resin is preferably a polyvinyl alcohol resin containing an acetoacetyl group. An adhesive using a polyvinyl alcohol-based resin containing an acetoacetyl group is preferable in that an adhesive layer having excellent water resistance can be formed.

  In the polarizing plate in which a transparent protective film is provided on at least one surface of the polarizer via an adhesive layer, the adhesive layer is formed of the polarizing plate adhesive. The present invention relates to a polarizing plate.

  In the polarizing plate, the adhesive layer preferably has a refractive index of 1.47 to 1.53.

Further, the present invention provides a method for producing a polarizing plate in which a transparent protective film is provided on at least one surface of a polarizer via an adhesive layer.
The step of applying the polarizing plate adhesive to the surface of the polarizer forming the adhesive layer and / or the surface of the transparent protective film forming the adhesive layer, and bonding the polarizer and the transparent protective film together The manufacturing method of the polarizing plate characterized by including a process.

  The present invention also relates to an optical film in which at least one polarizing plate is laminated.

  Furthermore, this invention relates to the image display apparatus containing the said polarizing plate or the said optical film.

  The adhesive for polarizing plates of the present invention uses a polyvinyl alcohol-based resin, a methylol group-containing compound as a first crosslinking agent, and an oxyzirconium salt as a second crosslinking agent in less than a predetermined amount. The combination of these two kinds of crosslinking agents can satisfy the water resistance. Moreover, the combination of these crosslinking agents can also satisfy the warm water resistance when immersed in warm water.

  In addition, the methylol group-containing compound as the first cross-linking agent progresses quickly under room temperature conditions. However, the adhesive for polarizing plates of the present invention makes the blending amount of the methylol group-containing compound less than a predetermined range and increases the amount. Viscosity stability can be maintained well. Thereby, the pot life of the adhesive agent for polarizing plates is prolonged, a yield improves, and the productivity of a polarizing plate can be improved.

  Further, the oxyzirconium salt as the second cross-linking agent increases the refractive index of the resulting adhesive layer. However, the adhesive for polarizing plate of the present invention has a blending amount of the oxyzirconium salt that is less than a predetermined range, An increase in the refractive index of the adhesive layer is suppressed. As a result, the refractive index of the adhesive layer can be designed closer to the refractive index of the polarizer or the transparent protective film, and the interface reflection of light between the layers of the polarizer or the transparent protective film is less likely to occur. Optical characteristics such as characteristics can be satisfied.

  The polarizing plate adhesive of the present invention contains a polyvinyl alcohol-based resin, a methylol group-containing compound that is a first crosslinking agent, and an oxyzirconium salt that is a second crosslinking agent.

  Examples of the polyvinyl alcohol resin include polyvinyl alcohol resins and polyvinyl alcohol resins having an acetoacetyl group. The polyvinyl alcohol resin having an acetoacetyl group is a polyvinyl alcohol-based adhesive having a highly reactive functional group, and is preferable because the durability of the polarizing plate is improved.

  Polyvinyl alcohol resin is polyvinyl alcohol obtained by saponifying polyvinyl acetate; a derivative thereof; a saponified product of a copolymer of vinyl acetate and a monomer having copolymerizability; Examples thereof include modified polyvinyl alcohols that have been converted into ethers, ethers, grafts, or phosphoric esters. Examples of the monomer include unsaturated carboxylic acids such as (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, (meth) acrylic acid, and esters thereof; α-olefins such as ethylene and propylene, (meth) Examples include allyl sulfonic acid (soda), sulfonic acid soda (monoalkyl malate), disulfonic acid soda alkyl maleate, N-methylol acrylamide, acrylamide alkyl sulfonic acid alkali salt, N-vinyl pyrrolidone, N-vinyl pyrrolidone derivatives and the like. . These polyvinyl alcohol resins can be used singly or in combination of two or more.

  The polyvinyl alcohol-based resin is not particularly limited, but from the viewpoint of adhesiveness, the average degree of polymerization is about 100 to 5000, preferably 1000 to 4000, the average saponification degree is about 85 to 100 mol%, preferably 90 to 100 mol%. It is.

  A polyvinyl alcohol-based resin containing an acetoacetyl group is obtained by reacting a polyvinyl alcohol-based resin with diketene by a known method. For example, a method in which a polyvinyl alcohol resin is dispersed in a solvent such as acetic acid and diketene is added thereto, and a polyvinyl alcohol resin is previously dissolved in a solvent such as dimethylformamide or dioxane, and diketene is added thereto. And the like. Another example is a method in which diketene gas or liquid diketene is brought into direct contact with polyvinyl alcohol.

  The degree of acetoacetyl group modification of the polyvinyl alcohol-based resin containing an acetoacetyl group is not particularly limited as long as it is 0.1 mol% or more. If it is less than 0.1 mol%, the water resistance of the adhesive layer is insufficient and unsuitable. The degree of acetoacetyl group modification is preferably about 0.1 to 40 mol%, more preferably 1 to 20 mol%, and particularly preferably 2 to 7 mol%. When the acetoacetyl group modification degree exceeds 40 mol%, the effect of improving water resistance is small. The degree of acetoacetyl modification is a value measured by NMR.

  Examples of the methylol group-containing compound as the first crosslinking agent include amino-formaldehyde resins such as methylol urea, methylol melamine, alkylated methylol urea, alkylated methylolated melamine, acetoguanamine, and a condensate of benzoguanamine and formaldehyde. Can be mentioned.

  The compounding quantity of a methylol group containing compound is a ratio of less than 10 weight part with respect to 100 weight part of polyvinyl alcohol-type resin. When the blending amount is 10 parts by weight or more, it is not preferable in terms of thickening stability. The blending amount is preferably 9 parts by weight or less, and more preferably 8 parts by weight or less. On the other hand, the blending amount is preferably 1 part by weight or more, and more preferably 2 parts by weight or more from the viewpoint of ensuring water resistance.

The oxyzirconium salt as the first crosslinking agent refers to a compound that can behave as a zirconyl ion (ZrO ²⁺ ) or a complex of these ions. Examples of the oxyzirconium salt include zirconium oxynitrate, zirconium oxyacetate, ammonium oxyacetate, zirconium oxychloride, zirconium oxysulfate, sodium zirconium oxysulfate, zirconium oxycarbonate, potassium potassium oxycarbonate, zirconium ammonium oxycarbonate, oxyoctyl Examples thereof include zirconium acid, zirconium oxystearate, oxyzirconium hydroxide, and zirconium oxychloride. Among these, from the viewpoint of water resistance, zirconium oxynitrate and zirconium oxyacetate are preferable.

  Commercially available products of the oxyzirconium salt include zircozole ZN, zircozol AC-7, zirconium oxychloride, zircozole ZC, zircozol ZC-2, zirconyl sulfate, zircozol ZA, zircozol ZA-30, zircozol ZA-20, zircozole ZK-10. Zirconyl octylate, zirconyl carbonate, zirconium hydroxide, R zirconium hydroxide, NN zirconium hydroxide (all manufactured by Daiichi Rare Element Chemical Co., Ltd.) and the like.

  The amount of the oxyzirconium salt is less than 10 parts by weight based on 100 parts by weight of the polyvinyl alcohol resin. When the blending amount is 10 parts by weight or more, the refractive index of the obtained adhesive layer becomes large, which is not preferable. The blending amount is preferably 9 parts by weight or less, and more preferably 8 parts by weight or less. On the other hand, the blending amount is preferably 1 part by weight or more, and more preferably 2 parts by weight or more from the viewpoint of ensuring water resistance.

  The polarizing plate adhesive of the present invention is a resin solution containing a polyvinyl alcohol-based resin and the cross-linking agent in the above proportions, and is usually used as an aqueous solution. The concentration of the resin solution is not particularly limited, but is preferably from 0.1 to 15% by weight, more preferably from 0.5 to 10% by weight in consideration of coating properties and storage stability. The viscosity of the resin solution is not particularly limited, but is usually in the range of 1 to 50 mPa · s.

  The method for preparing the resin solution that is the polarizing plate adhesive is not particularly limited. Usually, a resin solution is prepared by mixing a polyvinyl alcohol-based resin and a crosslinking agent. In addition, when a polyvinyl alcohol-based resin containing an acetoacetyl group is used as the polyvinyl alcohol-based resin or the amount of the crosslinking agent is large, the use timing of the obtained resin solution, etc. in consideration of the stability of the solution The first and second cross-linking agents may be mixed while considering the above. In addition, the density | concentration of the resin solution which is an adhesive agent for polarizing plates can also be adjusted suitably after preparing a resin solution.

  The polarizing plate adhesive may contain various tackifiers, ultraviolet absorbers, antioxidants, heat stabilizers, hydrolysis stabilizers, and other stabilizers.

  The polarizing plate of the present invention is produced by laminating a transparent protective film and a polarizer using the adhesive. As for the obtained polarizing plate, the transparent protective film is provided in the one side or both sides of the polarizer through the adhesive bond layer formed with the said polarizing plate adhesive.

  Moreover, the polarizing plate of the present invention has the polarizing plate adhesive on the surface of the polarizer forming the adhesive layer and / or the surface of the transparent protective film forming the adhesive layer. It can be obtained by applying and applying a polarizer and a transparent protective film.

  Application | coating of the said adhesive agent may be performed to any of a transparent protective film and a polarizer, and may be performed to both. The application of the adhesive is preferably performed so that the thickness of the adhesive layer after drying is about 10 to 300 nm. The thickness of the adhesive layer is more preferably from 10 to 200 nm, particularly preferably from 20 to 150 nm, from the viewpoint of obtaining a uniform in-plane thickness and obtaining sufficient adhesive strength. When the thickness of the adhesive layer is less than 10 nm, the adhesive strength is not sufficient, and when it exceeds 300 nm, the optical reliability and moisture resistance tend to be lowered.

  The refractive index of the adhesive layer is preferably 1.47 to 1.53. If it is out of the above range, the refractive index of the adhesive layer is too low or too high, and light interface reflection is likely to occur between the polarizer and the adhesive layer and between the transparent protective film and the adhesive layer. Thus, the optical characteristics such as the polarization characteristics of the polarizing plate tend to be lowered.

  The method of adjusting the thickness of the adhesive layer is not particularly limited, and examples thereof include a method of adjusting the solid content concentration of the adhesive solution and an adhesive application device. The method for measuring the thickness of the adhesive layer is not particularly limited, but cross-sectional observation measurement using SEM (Scanning Electron Microscopy) or TEM (Transmission Electron Microscopy) is preferably used. The application operation of the adhesive is not particularly limited, and various means such as a roll method, a spray method, and an immersion method can be employed.

  After applying the adhesive, the polarizer and the transparent protective film are bonded together with a roll laminator or the like. After the bonding, a drying process is performed to form an adhesive layer composed of a coating dry layer. The drying temperature is about 5 to 150 ° C., preferably 30 to 120 ° C., and the drying time is 120 seconds or more, preferably 300 seconds or more.

  The polarizer is not particularly limited, and various types can be used. Examples of the polarizer include hydrophilic polymers such as polyvinyl alcohol film, partially formalized polyvinyl alcohol film, and ethylene / vinyl acetate copolymer partially saponified film, and two colors such as iodine and dichroic dye. And polyene-based oriented films such as those obtained by adsorbing a functional material and uniaxially stretched, polyvinyl alcohol dehydrated products, and polyvinyl chloride dehydrochlorinated products. Among these, a polarizer composed of a polyvinyl alcohol film and a dichroic material such as iodine is preferable. The thickness of these polarizers is not particularly limited, but is generally about 5 to 80 μm.

  A polarizer obtained by dyeing a polyvinyl alcohol film with iodine and uniaxially stretching it can be prepared, for example, by dyeing polyvinyl alcohol in an aqueous solution of iodine and stretching it 3 to 7 times the original length. If necessary, it can be immersed in an aqueous solution of boric acid or potassium iodide. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing. In addition to washing the polyvinyl alcohol film surface with dirt and anti-blocking agents by washing the polyvinyl alcohol film with water, it also has the effect of preventing unevenness such as uneven coloring by swelling the polyvinyl alcohol film. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be dyed with iodine after stretching. The film can be stretched in an aqueous solution of boric acid or potassium iodide or in a water bath.

  The obtained polarizer can be made into the polarizing plate which provided the transparent protective film in the at least single side | surface according to the conventional method. As a material constituting the transparent protective film, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy and the like is used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins, Examples thereof include cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. A transparent protective film is bonded to one side of the polarizer by an adhesive layer. On the other side, as a transparent protective film, (meth) acrylic, urethane-based, acrylurethane-based, epoxy-based, silicone A thermosetting resin such as a system or an ultraviolet curable resin can be used.

  Although the thickness of a transparent protective film can be determined suitably, generally it is about 1-500 micrometers from points, such as workability | operativity, such as intensity | strength and handleability, and thin layer property. 1-300 micrometers is especially preferable, and 5-200 micrometers is more preferable. The transparent protective film is particularly suitable when the thickness is 5 to 150 μm.

  In addition, when providing a transparent protective film on both sides of a polarizer, the protective film which consists of the same polymer material may be used by the front and back, and the protective film which consists of a different polymer material etc. may be used.

  The transparent protective film may be subjected to surface modification treatment before applying the adhesive. Specific examples of the treatment include corona treatment, plasma treatment, primer treatment, and saponification treatment.

  The surface of the transparent protective film to which the polarizer is not adhered may be subjected to a treatment for hard coat treatment, antireflection treatment, sticking prevention, or diffusion or antiglare.

  The polarizing plate of the present invention can be used as an optical film laminated with another optical layer in practical use. The optical layer is not particularly limited. For example, for forming a liquid crystal display device such as a reflection plate, a semi-transmission plate, a retardation plate (including wavelength plates such as 1/2 and 1/4), and a viewing angle compensation film. One or more optical layers that may be used can be used. In particular, a reflective polarizing plate or a semi-transmissive polarizing plate in which a polarizing plate or a semi-transmissive reflecting plate is further laminated on the polarizing plate of the present invention, an elliptical polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on the polarizing plate. A wide viewing angle polarizing plate obtained by further laminating a viewing angle compensation film on a plate or a polarizing plate, or a polarizing plate obtained by further laminating a brightness enhancement film on the polarizing plate is preferable.

  An optical film in which the optical layer is laminated on a polarizing plate can be formed by a method of sequentially laminating separately in the manufacturing process of a liquid crystal display device or the like. There is an advantage that the manufacturing process of a liquid crystal display device or the like can be improved because of excellent stability and assembly work. For the lamination, an appropriate adhesive means such as an adhesive layer can be used. When adhering the polarizing plate and other optical films, their optical axes can be set at an appropriate arrangement angle in accordance with the target retardation characteristics.

  An adhesive layer for adhering to other members such as a liquid crystal cell may be provided on the polarizing plate described above or an optical film in which at least one polarizing plate is laminated. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited. For example, an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is appropriately selected. Can be used. In particular, those having excellent optical transparency such as an acrylic pressure-sensitive adhesive, exhibiting appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and being excellent in weather resistance, heat resistance and the like can be preferably used.

  Attachment of the adhesive layer to one or both sides of the polarizing plate or the optical film can be performed by an appropriate method. For example, a pressure sensitive adhesive solution of about 10 to 40% by weight in which a base polymer or a composition thereof is dissolved or dispersed in a solvent composed of a suitable solvent alone or a mixture such as toluene and ethyl acetate is prepared. A method in which it is directly attached on a polarizing plate or an optical film by an appropriate development method such as a casting method or a coating method, or an adhesive layer is formed on a separator according to the above, and this is applied to a polarizing plate or an optical film. The method of moving up is mentioned.

  The pressure-sensitive adhesive layer can be provided on one side or both sides of a polarizing plate or an optical film as a superimposed layer of different compositions or types. Moreover, when providing in both surfaces, it can also be set as the adhesion layers of a different composition, a kind, thickness, etc. in the front and back of a polarizing plate or an optical film. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 to 500 μm, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  On the exposed surface of the adhesive layer, a separator is temporarily attached and covered for the purpose of preventing contamination until it is put to practical use. Thereby, it can prevent contacting an adhesion layer in the usual handling state. As the separator, except for the above thickness conditions, for example, a suitable thin leaf body such as a plastic film, rubber sheet, paper, cloth, non-woven fabric, net, foam sheet, metal foil, laminate thereof, and the like, silicone type or Appropriate conventional ones such as those coated with an appropriate release agent such as long-chain alkyl, fluorine-based, or molybdenum sulfide can be used.

  In the present invention, the polarizer, the transparent protective film, the optical film, and the like that form the polarizing plate described above, and each layer such as an adhesive layer include, for example, a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, and a cyanoacrylate. It may be a compound having an ultraviolet absorbing ability by a method such as a method of treating with an ultraviolet absorber such as a compound based on nickel or a nickel complex salt compound.

  The polarizing plate or the optical film of the present invention can be preferably used for forming various devices such as a liquid crystal display device. The liquid crystal display device can be formed according to the conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, a polarizing plate or an optical film, and an illumination system as necessary, and incorporating a drive circuit. There is no limitation in particular except the point which uses the polarizing plate or optical film by invention, and it can apply according to the former. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can be used.

  An appropriate liquid crystal display device such as a liquid crystal display device in which a polarizing plate or an optical film is disposed on one side or both sides of a liquid crystal cell, or a backlight or a reflector used in an illumination system can be formed. In that case, the polarizing plate or optical film by this invention can be installed in the one side or both sides of a liquid crystal cell. When providing a polarizing plate or an optical film on both sides, they may be the same or different. Further, when forming a liquid crystal display device, for example, a single layer or a suitable part such as a diffusing plate, an antiglare layer, an antireflection film, a protective plate, a prism array, a lens array sheet, a light diffusing plate, a backlight, etc. Two or more layers can be arranged.

  Examples and the like specifically showing the configuration and effects of the present invention will be described below. In each example, parts and% are based on weight unless otherwise specified.

Example 1
(Polarizer)
A polyvinyl alcohol film having an average polymerization degree of 2400 and a saponification degree of 99.9 mol% and a thickness of 75 μm was immersed in warm water at 30 ° C. for 60 seconds to swell. Next, the film was dyed while being immersed in an aqueous solution of 0.3% concentration of iodine / potassium iodide (weight ratio = 0.5 / 8) and stretched to 3.5 times. Then, it extended | stretched so that the total draw ratio might be 6 times in 65 degreeC borate ester aqueous solution. After extending | stretching, it dried for 3 minutes in 40 degreeC oven, and obtained the polarizer.

(Transparent protective film)
A 80 μm thick triacetyl cellulose (TAC) film was used.

(Preparation of adhesive aqueous solution)
6 parts of methylol melamine as the first crosslinking agent with respect to 100 parts of polyvinyl alcohol resin containing acetoacetyl groups (average polymerization degree: 1200, saponification degree: 98.5 mol%, acetoacetylation degree: 5 mol%) And 5 parts of zirconium oxyacetate as a second cross-linking agent was dissolved in pure water under a temperature condition of 30 ° C. to obtain an aqueous adhesive solution adjusted to a solid content concentration of 4%. The viscosity of the adhesive aqueous solution was 9.6 mPa · s. The pH of the aqueous adhesive solution was in the range of 3.5 to 4.0.

(Creation of polarizing plate)
The adhesive aqueous solution was applied to one side of the transparent protective film so that the thickness of the adhesive layer after drying was 80 nm. Next, a transparent protective film with an adhesive was bonded to both sides of the polarizer under a temperature condition of 23 ° C. with a roll machine, and then dried at 55 ° C. for 6 minutes to prepare a polarizing plate.

Examples 2-5 and Comparative Examples 1-10
In Example 1, an adhesive aqueous solution was prepared in the same manner as in Example 1 except that the type of crosslinking agent and the blending ratio thereof were changed as shown in Table 1. A polarizing plate was prepared in the same manner as in Example 1 using the prepared aqueous adhesive solution.

  The following evaluation was performed about the adhesive agent aqueous solution and polarizing plate obtained by the Example and the comparative example. The results are shown in Table 1.

<Refractive index of adhesive layer>
The prepared adhesive aqueous solution was applied onto the release-treated transparent film with an applicator and dried at 70 ° C. for 10 minutes to form an adhesive layer having a thickness of 5 μm. Thereafter, the adhesive layer was peeled from the transparent film, and the refractive index of the adhesive layer was measured using a prism coupler (Sairon Technology, Inc., SPA-4000).

<Pot life>
Using the rheometer RS1 (manufactured by Haake) and model 222-1267 as a coaxial cylinder, the viscosity of the adjusted aqueous adhesive solution exceeds 50 cps at a liquid temperature and temperature of 23 ° C. Was measured. From the measurement results, the following criteria were evaluated.
○: 8 hours or more.
Δ: 4 hours or more and less than 8 hours.
X: Less than 4 hours.

<Water resistance>
A sample was prepared by cutting the polarizing plate so as to be 50 mm in the absorption axis direction of the polarizer and 25 mm in the direction perpendicular to the absorption axis. The sample was immersed in warm water at 60 ° C., and the amount of peeling (mm) at the end of the sample was measured over time. The amount of peeling (mm) was measured with a caliper. The amount of peeling (mm) after 5 hours is shown in Table 1.

  In Table 1, as the titanium compound, dihydroxybis (ammonium lactate) titanium (Orgachix T-310, manufactured by Matsumoto Kosho) was used. In Comparative Examples 8 and 9, a combination of glyoxal and a titanium compound was used as a cross-linking agent, and the blending amount was controlled in the same manner as in the present invention. However, when glyoxal was used as a cross-linking agent, the thickening progressed quickly and the pot life was satisfied. In the case where a titanium compound is used, an increase in the refractive index cannot be suppressed. In Comparative Example 10, methylol melamine and a titanium compound were combined as a crosslinking agent, and the blending amount was controlled in the same manner as in the present invention. However, the thickening progressed quickly and the pot life could not be satisfied, and the titanium compound was used and the refractive index. Can not be suppressed.

Claims (7)

An adhesive for polarizing plates used to provide a transparent protective film on at least one side of a polarizer,
The polarizing plate adhesive comprises a polyvinyl alcohol resin, a methylol group-containing compound as a first crosslinking agent and an oxyzirconium salt as a second crosslinking agent, and the methylol group-containing compound and oxyzirconium salt are as follows: The adhesive for polarizing plates characterized by mix | blending in the ratio of less than 10 weight part with respect to 100 weight part of polyvinyl alcohol-type resin, respectively.   The adhesive for polarizing plates according to claim 1, wherein the polyvinyl alcohol-based resin contains an acetoacetyl group.   In the polarizing plate in which a transparent protective film is provided on at least one surface of the polarizer via an adhesive layer, the adhesive layer is formed of the polarizing plate adhesive according to claim 1 or 2. A polarizing plate characterized by.   The polarizing plate according to claim 3, wherein the adhesive layer has a refractive index of 1.47 to 1.53. In the method for producing a polarizing plate in which at least one surface of the polarizer is provided with a transparent protective film via an adhesive layer,
The process of apply | coating the adhesive agent for polarizing plates of Claim 1 or 2 to the surface which forms the said adhesive bond layer of a polarizer, and / or the surface which forms the said adhesive bond layer of a transparent protective film, and a polarizer and transparent The manufacturing method of the polarizing plate characterized by including the process of bonding a protective film.   An optical film in which at least one polarizing plate according to claim 3 or 4 is laminated. An image display device comprising the polarizing plate according to claim 3 or 4, or the optical film according to claim 6.