JP2010276673A - Polarizing plate, method for producing the same and adhesive for polarizing plate production - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive for polarizing plate production which has a satisfactory pot life in production and enables to produce a polarizing plate excellent in wet heat resistance and durability; a polarizing plate excellent in wet heat resistance and durability; and a method for producing the same. <P>SOLUTION: In the method for producing the polarizing plate in which a protective film comprising a triacetyl cellulose-based resin is stuck on at least one surface of a polarizing element comprising a polyvinyl alcohol-based resin film through an adhesive layer, the adhesive layer is formed from an adhesive composed of a polyvinyl alcohol-based resin, a crosslinking agent and maleic acid. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an adhesive for polarizing plates, a polarizing plate, and a method for producing the same, and more particularly to adhesion between a polarizing element constituting the polarizing plate and its protective film.

  In recent years, with the increase in demand for liquid crystal display devices, the demand for polarizing plates has also increased. A liquid crystal display device is configured by laminating polarizing plates on both sides or one side of a liquid crystal panel. Such a polarizing plate is generally composed of a polarizing element having polarizing performance and a protective film formed on both sides or one side via an adhesive layer.

  The polarizing element is generally formed by dyeing a polyvinyl alcohol (hereinafter referred to as “PVA”) film with a dichroic dye such as iodine and uniaxially stretching the film. Since the polarizing element formed in this manner is inferior in mechanical strength and moisture resistance, a protective film is attached to and protected on at least one surface thereof. As such a protective film, a triacetyl cellulose (hereinafter referred to as “TAC”) film is often used because it satisfies the required optical transparency.

  For adhesion between the polarizing element and the protective film, it is preferable to use a hydrophilic adhesive because PVA and TAC are both hydrophilic and good adhesiveness can be obtained. As disclosed in Kaihei 7-198945), a PVA-based adhesive is used.

  However, Patent Document 2 (Japanese Patent Laid-Open No. 2005-189615) and the like point out that a sufficient pot life cannot be obtained with a PVA adhesive. The fact that the pot life cannot be obtained means that the adhesive is used for a short period of time, and when such an adhesive with a short pot life is used in the step of bonding the polarizing element and the protective film during the production of the polarizing plate, The problem arises that the productivity of the plate deteriorates. Therefore, Patent Document 2 discloses a technique for adjusting the pH of an adhesive made of an aqueous solution containing an acetoacetyl group-containing PVA resin and a crosslinking agent to 4.3 or less. In paragraph 0030 of Patent Document 2, acetic acid, citric acid, oxalic acid, boric acid, phosphoric acid, formic acid, gluconic acid, nitric acid, hydrochloric acid, and sulfuric acid are disclosed as acids for adjusting the pH. In particular, the use of acetic acid has been proposed.

  However, acetic acid has a problem of promoting the hydrolysis of TAC. That is, in paragraph 0006 of Patent Document 3 (Japanese Patent Laid-Open No. 9-288214), it is described that acetic acid serves as a catalyst to cause hydrolysis of TAC, and possibly to cause a TAC decay phenomenon. Has been.

  With the recent increase in the size of liquid crystal display devices and the diversification of their uses, the polarizing plates used therein are also required to have durability under more severe conditions. Here, with the technique described in Patent Document 2, there arises a problem that the durability of the polarizing plate becomes insufficient even if the problem due to the pot life of the adhesive during production is improved.

JP-A-7-198945 JP 2005-189615 A JP-A-9-288214

  The present invention has been made in view of the above-mentioned problems, and has a pot life sufficient for production, an adhesive for producing a polarizing plate capable of producing a polarizing plate excellent in moist heat resistance and durability, and moisture resistance. It aims at providing the polarizing plate excellent in heat property and durability, and its manufacturing method.

  As a result of intensive studies to solve the above problems, the present inventors have used a maleic acid as an acid to be added to an adhesive for polarizing plates made of PVA resin, so that a sufficient pot life can be obtained in the production of polarizing plates. The present invention was completed by finding that a polarizing plate excellent in wet heat resistance and durability could be produced. Thus, the knowledge that maleic acid imparts good moisture and heat resistance and durability to the protective film of the polarizing element has been obtained by the present inventors.

  That is, the method for producing a polarizing plate of the present invention includes a protective film made of a triacetyl cellulose resin via an adhesive layer on at least one surface of a polarizing element made of a polyvinyl alcohol resin film, as described in claim 1. In the manufacturing method of a polarizing plate in which is bonded, the adhesive layer is formed of an adhesive composed of a polyvinyl alcohol-based resin, a cross-linking agent, and maleic acid. Is the method.

  Moreover, the manufacturing method of the polarizing plate of this invention is a manufacturing method of the polarizing plate of Claim 1 as described in Claim 2, The said adhesive agent is apply | coated to at least one of the said polarizing element and the said protective film. It has a bonding step of bonding the polarizing element and the protective film, and a drying step of performing a drying process in this order.

  Moreover, the manufacturing method of the polarizing plate of this invention is the manufacturing method of the polarizing plate of Claim 1 or Claim 2 as described in Claim 3, WHEREIN: The said adhesive agent is aqueous | water-based adhesive, and pH is set. It is 4.5 or less.

  Moreover, the polarizing plate of this invention is a polarizing plate manufactured by the manufacturing method of the polarizing plate of any one of Claim 1 thru | or 3, as described in Claim 4.

  In the polarizing plate of the present invention, as described in claim 5, a protective film made of a triacetyl cellulose resin is bonded to at least one surface of a polarizing element made of a polyvinyl alcohol resin film via an adhesive layer. The polarizing plate is characterized in that the adhesive layer contains a polyvinyl alcohol resin and maleic acid at least partially crosslinked by a crosslinking agent.

  As described in claim 6, the adhesive for producing a polarizing plate of the present invention has a protective film made of a triacetyl cellulose resin via an adhesive layer on at least one surface of a polarizing element made of a polyvinyl alcohol resin film. An adhesive for producing a polarizing plate for use in producing a bonded polarizing plate, wherein the adhesive layer is composed of a polyvinyl alcohol resin, a crosslinking agent, and maleic acid. It is an agent.

  Moreover, the adhesive for polarizing plate manufacture of this invention is an aqueous adhesive in the adhesive for polarizing plate manufacture of Claim 6, as described in Claim 7, Comprising: pH is 4.5 or less. It is characterized by that.

  According to the present invention, maleic acid is used as an acid to be added to the adhesive for bonding the polarizing element and the protective film, without using acetic acid which adversely affects the moisture and heat resistance and durability of the protective film made of a TAC film. Thus, the heat and humidity resistance and durability of the protective film can be improved, and a polarizing plate with excellent durability can be obtained. Further, since the pH of the adhesive for polarizing plate is adjusted to a predetermined value by maleic acid, a sufficient pot life can be obtained in the production of the polarizing plate, and the productivity of the polarizing plate can be improved. . Furthermore, maleic acid has the advantages that it is easy to handle and has no irritating odor compared to acetic acid or formic acid, and does not pollute the environment air during handling, so that no special ventilation device or the like is required.

It is model sectional drawing of an example of the polarizing plate by this invention.

  The polarizing plate of the present invention comprises a polarizing element having polarizing performance, an adhesive layer formed on at least one surface of the polarizing element, and a protective film bonded to the polarizing element via the adhesive layer. . The adhesive layer and the protective film are preferably formed on both surfaces of the polarizing element, but may be formed only on one surface. An adhesive bond layer is formed using the adhesive agent for polarizing plates of this invention containing PVA-type resin, a crosslinking agent, and maleic acid at least.

  FIG. 1 shows a model cross-sectional view of an example of a polarizing plate according to the present invention. In the figure, reference numeral 10 denotes a polarizing plate having protective films formed on both sides of the polarizing element. The polarizing plate 10 includes a polarizing element 11 and protective films 13a and 13b formed on both surfaces of the polarizing element 11 via adhesive layers 12a and 12b. In this example, the polarizing element 11 is made of a PVA resin formed by being dyed with iodine and stretched, and the film thickness thereof is 30 μm in this example. The protective films 13a and 13b are made of a TAC film, and the film thicknesses are 60 μm in this example. The adhesive layers 12a and 12b are made of a PVA resin that is at least partially crosslinked by a crosslinking agent, and contain maleic acid. Each will be described in detail below.

(adhesive)
The polarizing plate adhesive of the present invention contains at least a PVA-based resin, a crosslinking agent, and maleic acid, and these are mixed at a predetermined concentration to form an aqueous solution.

  The polarizing plate adhesive of the present invention is an appropriate amount of each of these PVA resin powder, crosslinking agent, and maleic acid when used in the step of bonding the polarizing element and the protective film in the polarizing plate production process. Prepared by blending and blending in water.

  As is well known, the PVA resin is generally obtained by saponifying polyvinyl acetate. The degree of saponification is 85 mol% or more, preferably 90 mol% or more, more preferably 95% or more. Moreover, the average degree of polymerization of PVA is 1000-4000, More preferably, it is 1500-3000. As polyvinyl acetate, in addition to vinyl acetate monomer, those obtained by copolymerizing unsaturated carboxylic acid and derivatives thereof, olefins, vinyl ethers, unsaturated sulfonates and the like may be used.

  The PVA resin used in the present invention is preferably a modified PVA resin partially acetoacetylated. Such an acetoacetylated modified PVA can be obtained by a known method, for example, by reacting PVA with diketene.

  Moreover, as modified PVA resin used in the adhesive for polarizing plates of the present invention, instead of forming PVA by acetoacetylation as described above, aldehydes, methylol compounds, epoxy compounds, isocyanates etc. Modified PVA resin obtained by reacting

  Although a well-known thing can be used for a crosslinking agent, it is preferable to use a glyoxal. The blending amount of glioxal is 0.1 to 200, preferably 1 to 100, and more preferably 5 to 60, based on the weight of the modified PVA resin as 100.

  The blending amount of maleic acid is 0.001 to 5, preferably 0.003 to 2, more preferably 0.006 in terms of a weight ratio when the weight of the entire polarizing plate adhesive in aqueous solution is 100. ~ 1. As the maleic acid, maleic anhydride which is an anhydride thereof may be used, or a mixture of maleic acid and maleic anhydride may be used. Maleic anhydride becomes maleic acid when made into an aqueous solution. When using maleic anhydride, it mix | blends so that it may become the said density | concentration when it becomes maleic acid in aqueous solution.

  In the present invention, the pH of the polarizing plate adhesive is adjusted to 4.5 or less, preferably 1 to 4, more preferably 2 to 3. The pH is adjusted by the concentration of maleic acid to be added, but may be further adjusted by adding a base such as sodium hydroxide. By setting the pH within this range, the increase in viscosity over time can be suppressed, and a sufficient pot life, that is, a sufficient expiration date can be obtained, and the productivity of the polarizing plate is good. Moreover, when forming a protective film on both surfaces of a polarizing element, the compounding density | concentration of PVA-type resin of the adhesive agent for polarizing plates of this invention, a glyoxal, and maleic acid is used as that from which pH differs on each surface. May be.

(Polarizing element)
A known polarizing element can be used as the polarizing element of the present invention. The polarizing element is generally formed by using a PVA resin film, dyeing this PVA resin film with a dichroic dye such as iodine, and uniaxially stretching.

  As described above, the PVA resin is generally obtained by saponifying a polyvinyl acetate resin. The degree of saponification is about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% to 100 mol%. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymer. Examples include coalescence. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the PVA resin is 1000 to 10000, preferably 1500 to 5000. This PVA-based resin may be modified, for example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like.

  At the start of the production of the polarizing element, this PVA-based resin is supplied in the form of a film wound on a roll, and the thickness of the PVA-based resin film original at the start of the production (before processing such as stretching) is 20 μm. It is -100 micrometers, Preferably it is 30 micrometers-80 micrometers. Although the width of the film depends on the size of the target polarizing plate, for example, 1500 mm to 4000 mm is practical in production.

  The PVA-based resin film is pulled out from the roll, first subjected to a swelling treatment with a swelling treatment liquid such as water, and then subjected to a solution treatment in the order of a dyeing treatment, a crosslinking treatment and a washing treatment, and then a dyeing treatment step, a crosslinking treatment step, or both. By carrying out uniaxial stretching in the solution of the above step and finally carrying out a drying treatment, the raw material of the polarizing element can be obtained. These steps are generally performed continuously.

  The swelling treatment step is performed for the purpose of removing foreign substances on the surface of the PVA resin film, removing the plasticizer in the film, imparting easy dyeability in the next step, and plasticizing the film. The processing conditions are determined within a range in which these objects can be achieved, and in a range in which problems such as extreme dissolution and devitrification of the film do not occur. For example, it is performed by immersing the film in a swelling treatment solution at about 10 ° C. to 50 ° C., preferably about 20 ° C. to 40 ° C. The immersion time of the film is 30 seconds to 300 seconds, preferably 60 seconds to 240 seconds. In this swelling process, the film swells in the width direction and wrinkles are likely to occur. It is preferable to transport the film while removing the wrinkles. For the purpose of stabilizing the film transport in these baths, the water flow in the bath is controlled by a submerged shower, or an EPC device (Edge Position Control device: a device that detects the end of the film and prevents meandering of the film. ) Etc. are also useful. In this step, since the film swells and expands in the running direction of the film, it is preferable to take measures such as controlling the speed of the transport roll before and after the treatment tank in order to eliminate the slack of the film in the transport direction. In addition, as a swelling treatment liquid to be used, a swelling obtained by adding boric acid, chloride, inorganic acid, inorganic salt, water-soluble organic solvent, alcohol, etc. in the range of 0.01 wt% to 10 wt% in addition to water A processing solution can also be used.

  The dyeing process is performed for the purpose of immersing the film in a dyeing solution and adsorbing and orienting the dichroic dye. The treatment conditions are determined within a range in which these objects can be achieved and within a range in which problems such as extreme dissolution and devitrification of the base film do not occur. There may be one or more dyeing baths. A typical dichroic dye is iodine. In this case, an iodine / potassium iodide aqueous solution is used as the staining solution. The concentration of iodine is preferably such that the amount of iodine is 0.001 to 0.5 and the amount of potassium iodide is 0.1 to 10 with respect to water 100 by weight. The blending amount of potassium iodide is 0.01 to 0.3 and 0.1 to 3.0 / 100. When there are a plurality of dye baths, the concentration may be varied depending on the dye bath.

  Further, instead of potassium iodide, other iodides such as zinc iodide may be used. Furthermore, compounds other than iodide, such as zinc chloride and cobalt chloride, may coexist.

  The temperature of the dyeing solution is 10 ° C to 40 ° C, preferably 20 ° C to 35 ° C, and the immersion time is 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds. Here, when the temperature of the dyeing bath is less than 10 ° C., boric acid is difficult to dissolve when boric acid is added, and when it exceeds 40 ° C., there is a possibility that dissolution of PVA may increase, which is not preferable.

  You may perform a dyeing | staining process, uniaxially stretching in the dyeing bath of this dyeing | staining process process. In performing uniaxial stretching in a dyeing bath, it is necessary to adjust the stretching ratio. For this purpose, for example, it is preferable to provide nip rolls on the inlet side and the outlet side of the dyeing bath so that the rotational speed ratio of both nip rolls can be changed. Moreover, an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar, etc. can be installed in the dyeing bath or at the bath entrance / exit to perform uniaxial stretching. When uniaxial stretching is performed in a plurality of dyeing baths, the stretching ratio may be adjusted independently.

  The crosslinking treatment step is generally performed by immersing the PVA resin film dyed with iodine in an aqueous solution containing boric acid. It is preferable to further contain an iodide in the boric acid-containing aqueous solution. Examples of iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist. Concentrations are, for example, 3 to 10 for boric acid and 1 to 20 for iodide in a weight ratio where the weight of water is 100. The treatment temperature is 45 ° C to 70 ° C, preferably 50 ° C to 65 ° C, and the immersion time is usually about 30 to 600 seconds, preferably 60 to 420 seconds, more preferably 90 to 300 seconds.

  After the crosslinking treatment step, a chemical treatment may be further performed to adjust the optical characteristics. The chemical liquid treatment is performed, for example, by immersing the cross-linked PVA resin film in the chemical liquid, spraying the chemical liquid as a shower, or using both immersion and spraying together. Examples of the chemical solution used here include an aqueous boric acid solution containing zinc chloride and potassium iodide. The temperature of the chemical solution in the chemical treatment is, for example, 20 to 50 ° C., and the immersion time is preferably 2 to 120 seconds.

  The stretching process may be performed in the dyeing process as described above, or may be performed in a crosslinking process and a subsequent chemical process. Moreover, you may provide an extending | stretching process process before and behind these process processes separately. Any one process may be performed, and a plurality of processes, that is, multi-stage stretching may be performed. The overall draw ratio is 4.0 times to 7.0 times, more preferably 5.0 times to 6.5 times. Moreover, the thickness of the PVA-type resin film after extending | stretching is 5 micrometers-50 micrometers, for example, More preferably, they are 20 micrometers-35 micrometers.

  After the crosslinking treatment step or the subsequent chemical treatment step, the PVA resin film is subjected to a water washing treatment before the drying treatment step. In this washing treatment step, treatment with an aqueous zinc chloride solution may be performed in addition to washing with water. Thereafter, a drying process is performed. The drying treatment step is performed in a drying furnace, for example, at a temperature of 30 to 100 ° C. for 60 to 600 seconds. The raw material of the polarizing element which has polarization performance is created by the above process.

  In addition, the manufacturing method of a polarizing element is not limited to the said description, In addition, for example, PVA-type resin film is first uniaxially stretched in the atmosphere or in an inert gas, and thereafter, swelling treatment, dyeing treatment, You may produce by performing a crosslinking process, a water washing process, and a drying process in order. Of course, steps other than those described above may be included as necessary.

(Protective film)
Examples of the protective film include a film made of acetyl cellulose resin such as TAC and diacetyl cellulose, a film made of polyester resin such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate, a film made of polycarbonate resin, and norbornene. And a film made of a cycloolefin resin. Of these transparent protective films, TAC is preferably used.

  The surface of the protective film may be subjected to any surface treatment such as anti-glare treatment, anti-reflection treatment, hard coat treatment, antistatic treatment, and antifouling treatment to form a surface treatment layer. In the surface treatment, these two or more treatments may be performed. These surface treatments are generally applied to the surface opposite to the surface to be bonded to the polarizing element. Either or both of the protective film and its surface protective layer may contain an ultraviolet absorber such as a benzophenone compound or a benzotriazole compound, or a plasticizer such as a phenyl phosphate compound or a phthalate compound. Good.

  The thickness of the protective film is preferably thin from the viewpoint of optical properties, but if it is too thin, the strength is lowered and the processability is poor. The appropriate film thickness is 5 to 200 μm, preferably 10 to 150 μm, and more preferably 20 to 100 μm.

  Depending on the use of the polarizing plate, an optical compensation film having an optically anisotropic layer can also be used as a protective film.

(Adhesion of polarizing element and protective film)
The polarizing element and the protective film thus produced are adhered and laminated using the polarizing plate adhesive according to the present invention described above. When a protective film is laminated on both surfaces of the polarizing element, the bonding process is usually performed by sequentially bonding one surface at a time, but both surfaces may be bonded and bonded simultaneously. In addition, when the polarizing element and the protective film are bonded, in order to improve the adhesion between the polarizing element and the adhesive and between the protective film and the adhesive, one or both of the protective films of the polarizing element is previously corona-treated. Surface treatment such as plasma treatment, ultraviolet irradiation, and primer coating treatment may be performed. Further, the protective film may be saponified.

  When the polarizing element and the protective film are bonded, the adhesive for polarizing plate according to the present invention is prepared as described above, and then applied at a temperature of 15 to 40 ° C. for the adhesive for polarizing plate. The polarizing plate adhesive is usually applied to either the polarizing element or the protective film, but may be applied to both. The temperature of the atmosphere in this bonding step is preferably in the range of 15 to 30 ° C. After application of the adhesive, the polarizing element and the protective film are bonded together.

  After laminating the polarizing element and the protective film, a drying process is performed to remove a solvent such as water contained in the adhesive, and at least a part of the PVA resin in the adhesive is crosslinked by a crosslinking reaction. . Thereby, the applied adhesive is solidified to form an adhesive layer, and the polarizing element and the protective film are firmly bonded. The drying temperature at this time is in the range of 30 to 85 ° C, preferably 45 to 80 ° C. At the time of solvent removal by this drying process, a part of maleic acid is removed, or a part of maleic acid may be changed by a chemical reaction at the time of the drying process. Remains in the adhesive layer formed by the polarizing plate adhesive of the present invention. That is, the adhesive layer of the polarizing plate of the present invention is made of a PVA-based resin that is at least partially crosslinked, and further contains maleic acid. Here, the maleic acid may be maleic anhydride, and maleic acid and maleic anhydride may coexist.

  By the above, the polarizing plate by which the protective film was formed on the both surfaces or single side | surface of the polarizing element through the adhesive bond layer is obtained. The adhesive layer of the polarizing plate of the present invention contains maleic acid. The maleic acid may be maleic anhydride. Maleic acid does not cause a TAC hydrolysis reaction like acetic acid. Therefore, according to this invention, the heat-and-moisture resistance and durability of a protective film become favorable.

  When forming protective films on both surfaces of the polarizing element, the same protective film may be used, but protective films having different materials, compositions, and film thicknesses may be used. In FIG. 1, an example in which a protective layer made of a TAC film is formed on both surfaces is shown as a model. For example, a TAC film is formed on one surface, and a cycloolefin resin such as norbornene is formed on the other surface. A film may be formed. Even when protective films of different materials are formed as described above, the same adhesive for polarizing plates of the present invention may be used for both adhesive layers. By doing in this way, productivity in an adhesion process can be improved. Of course, the present invention is not limited to this, and different adhesives may be used on each surface, and the polarizing plate adhesive according to the present invention may be used at least on the protective layer side made of a TAC-based film. .

  The polarizing plate thus obtained may be coated with an adhesive on one side to form an adhesive layer for later bonding to a liquid crystal panel. Examples of the pressure-sensitive adhesive include acrylic, vinyl alcohol, silicon, polyester, polyurethane, and polyether types. Moreover, the active energy ray polymeric compound may be included.

  It is preferable to provide a curing step after applying the adhesive. This curing step is a step of curing the pressure-sensitive adhesive. In addition, the adhesive layer formed between the polarizing element and the protective film is further cured and stabilized. This curing step is performed under a temperature environment of 15 to 85 ° C, preferably 20 to 50 ° C, more preferably 20 to 30 ° C. The period is, for example, 1 to 90 days. However, if this curing period is long, the productivity is deteriorated, so that it is preferably about 1 to 30 days, and more preferably about 1 to 7 days. The polarizing plate may be cut according to the size of the liquid crystal panel used together. This cutting process may be performed after the polarizing plate is bonded to the liquid crystal panel.

  Examples of the present invention are shown below. In addition, this invention is not limited by these Examples. Polarizers shown in the following examples of the present invention and comparative examples were prepared, and their heat resistance and heat and humidity resistance were evaluated. As the adhesive of the examples, the adhesive for polarizing plate containing maleic acid according to the present invention was prepared and used, and in the comparative example, the adhesive containing acetic acid and formic acid according to Patent Document 2 was used.

  The evaluation was carried out with respect to the optical properties of the polarizing plate with respect to the single hue b value of the single polarizing plate, the single transmittance, and the orthogonal transmittance obtained by superimposing the two polarizing plates so that the polarizing axes are orthogonal to each other. The single hue b value was measured before and after the heat resistance test, and the single transmittance and the single transmittance were measured before and after the wet heat resistance test, and the change was obtained. That is, the smaller this change, the better the heat resistance and moist heat resistance. For these measurements, a spectrophotometer U-3500 manufactured by Hitachi, Ltd. was used. Here, the single transmittance Ys is a value obtained by correcting the visibility according to JIS Z 8701, and the single hue b value is a value obtained by calculating the Lab color space for the C light source according to JIS Z 8730.

<Example 1>
(Preparation of polarizing element)
A 75 μm thick PVA film having an average polymerization degree of 2400 and a saponification degree of 99.9 mol% was immersed in warm water at 25 ° C. for 120 seconds to swell. Next, the PVA film was dyed while immersed in an aqueous solution of 0.6% by weight of iodine / potassium iodide (weight ratio = 2/3) and stretched 2.1 times. Thereafter, the film was stretched in a 55 ° C. boric acid ester aqueous solution so that the total stretching ratio was 5.5 times, washed with water, and dried to produce a polarizing element.

(Preparation of polarizing plate production adhesive)
An aqueous solution A prepared by dissolving a modified PVA resin containing acetoacetyl group (manufactured by Nippon Synthetic Chemical Co., Ltd .: Z-410) in water to a solid content concentration of 3% was prepared. Subsequently, maleic acid was added so that it might become 0.5 weight% with respect to the said aqueous solution A, and the glyoxal was added as a crosslinking agent after that. The addition amount of glioxal was set to 5 by weight when the weight of Z-410 was 100. Sodium hydroxide was added to this aqueous solution to adjust the pH to 2.5 to obtain an adhesive for producing a polarizing plate according to the present invention.

(Preparation of polarizing plate)
The adhesive was applied on one side of a TAC film serving as a protective film so that the thickness of the adhesive layer after drying was 150 nm. Next, after the protective films coated with the above-mentioned adhesive on both surfaces of the polarizing element were bonded together with a roll machine, the polarizing film according to the present invention was obtained by drying at 60 ° C. for 10 minutes.

<Example 2>
As in Example 1, however, the present invention was carried out using an adhesive for producing a polarizing plate prepared by adding maleic acid so as to be 2.0% by weight, not 0.5% by weight with respect to the aqueous solution A. The polarizing plate concerning was obtained.

<Comparative Example 1>
As in Example 1, except that maleic acid was used instead of maleic acid to add 0.5% by weight of acetic acid to the aqueous solution A, a polarizing plate was obtained using an adhesive for producing a polarizing plate.

<Comparative example 2>
As in Example 1, except that maleic acid was used instead of maleic acid and 2.0 wt% of acetic acid was added to the aqueous solution A to obtain a polarizing plate.

<Comparative Example 3>
As in Example 1, however, a polarizing plate was obtained using an adhesive for producing a polarizing plate prepared by adding not formic acid but formic acid to 0.5% by weight of aqueous solution A.

<Comparative example 4>
As in Example 1, however, a polarizing plate was obtained using an adhesive for producing a polarizing plate prepared by adding 2.0% of formic acid to aqueous solution A instead of maleic acid.

(Heat resistance test)
Each of the polarizing plates according to Examples 1 and 2 and Comparative Examples 1 to 4 described above was held in an environmental tester set at 80 ° C. for 500 hours. The single hue b value change Δb was determined from the single hue b value before and after the environmental test of these polarizing plates. The results are shown in Table 1.

  From Table 1, it can be seen that the polarizing plate according to the present invention has a small hue change and excellent heat resistance. Compared with this, the hue change is large in the comparative example, and this suggests the possibility that TAC decomposition occurs in the comparative example. Furthermore, when the formic acid in Comparative Example 3 and Comparative Example 4 was added, the hue change was large even when compared with Comparative Example 1 and Comparative Example 2, which were systems to which the same amount of acetic acid was added. At this time, the polarizing performance of the polarizing plate was also changed, and it was found that formic acid adversely affects not only the decomposition of TAC but also the polarizing element itself.

(Moisture and heat resistance evaluation)
The polarizing plates according to Examples 1 and 2 and Comparative Examples 1 to 4 obtained above were held for 500 hours in an environmental test machine set to 60 ° C. and 90% RH. At this time, the single transmittance Ys and the orthogonal transmittance Tc of the polarizing plate were measured before and after this environmental test, and the single transmittance change ΔYs and the orthogonal transmittance change ΔTc were obtained from these values. It is shown in Table 2.

  From Table 2, it is understood that the polarizing plate using the adhesive containing acetic acid or formic acid shown in the comparative example has both large single transmittance change and orthogonal transmittance change. In particular, when the addition concentrations of acetic acid and formic acid are high as in Comparative Examples 2 and 4, these changes are large, suggesting that TAC decomposition has occurred. According to the follow-up observation, the deterioration in the system to which formic acid was added occurred earlier than the deterioration in the system to which acetic acid was added.

  In contrast to these Comparative Examples 1 to 4, in the polarizing plates using the adhesive according to the present invention of Examples 1 and 2, both the single transmittance change and the orthogonal transmittance change are small. Further, as understood from Example 2, even if the concentration of maleic acid added is increased, no effect is observed. Thus, from these results, it was confirmed that the polarizing plate according to the present invention had good wet heat resistance and durability.

  Moreover, when the pot life at room temperature of the adhesive for producing a polarizing plate according to the present invention used in Example 1 and Example 2 was examined with a digital tachometer viscometer (Visco Basic Plus manufactured by Viscotec Corporation), it was 120 hours. As described above, it was confirmed that 48 hours, which is a pot life required in actual work, was sufficiently satisfied.

10 Polarizing plate 11 with protective films formed on both surfaces of polarizing element Polarizing elements 12a and 12b Adhesive layers 13a and 13b Protective film

Claims (7)

In the method for producing a polarizing plate in which a protective film made of a triacetyl cellulose-based resin is bonded to at least one surface of a polarizing element made of a polyvinyl alcohol-based resin film via an adhesive layer,
The method for producing a polarizing plate, wherein the adhesive layer is formed of an adhesive composed of a polyvinyl alcohol resin, a crosslinking agent, and maleic acid.   It has an adhesive application process for applying the adhesive to at least one of the polarizing element and the protective film, a bonding process for bonding the polarizing element and the protective film, and a drying process for performing a drying process in this order. The manufacturing method of the polarizing plate of Claim 1 characterized by the above-mentioned.   The method for producing a polarizing plate according to claim 1, wherein the adhesive is an aqueous adhesive and has a pH of 4.5 or less.   The polarizing plate manufactured by the manufacturing method of the polarizing plate of any one of Claim 1 thru | or 3. In a polarizing plate in which a protective film made of a triacetyl cellulose-based resin is bonded to at least one surface of a polarizing element made of a polyvinyl alcohol-based resin film via an adhesive layer,
A polarizing plate characterized in that the adhesive layer contains a polyvinyl alcohol resin and maleic acid at least partially crosslinked by a crosslinking agent. In an adhesive for producing a polarizing plate used for producing a polarizing plate in which a protective film made of a triacetyl cellulose-based resin is bonded to at least one surface of a polarizing element made of a polyvinyl alcohol-based resin film via an adhesive layer,
The adhesive for polarizing plate production, wherein the adhesive layer is composed of a polyvinyl alcohol resin, a cross-linking agent, and maleic acid.   It is a water-based adhesive, Comprising: pH is 4.5 or less, The adhesive for polarizing plate manufacture of Claim 6 characterized by the above-mentioned.

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