JP2009237124A - Method of manufacturing polarizing film and its use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a polarizing film by which high-speed processing is achieved while preventing the deviation of film thickness distribution in a width direction of the obtained polarizing film. <P>SOLUTION: In the method of manufacturing the polarizing film, a film of poly(vinyl alcohol) of 2,400 polymerization degree is uniaxially stretched in a dry condition with 1.5 to 2.8 stretching ratio and then uniaxially stretched in a wet condition at least by one of the method either dyeing processing by a dichroic dye or cross-linking processing by immersion in a boric acid-containing aqueous solution. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a polarizing film capable of obtaining a polarizing film excellent in heat resistance with high productivity, and a polarizing plate and an optical laminate using the polarizing film obtained by the production method.

  Conventionally, a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol film has been used. For example, an iodine polarizing film using iodine as a dichroic dye and a dye polarizing film using a dichroic dye as a dichroic dye are known. Such a polarizing film is usually formed into a polarizing plate by attaching a protective film such as triacetyl cellulose to at least one surface, preferably both surfaces, via an adhesive made of an aqueous solution of a polyvinyl alcohol resin.

  As a method for producing a polarizing film, there has been proposed a method in which a film made of polyvinyl alcohol is uniaxially stretched in a dry manner and then dyed and then crosslinked by immersion in a boric acid-containing aqueous solution at 70 to 85 ° C. (See Patent Document 1).

JP-A-8-240715

  However, when the film is stretched dry before the dyeing treatment and the crosslinking treatment as in the manufacturing method described in Patent Document 1 described above, the time required for the reaction at the time of dyeing and crosslinking becomes long, so that high-speed processing is possible. There was a problem that it was difficult and inferior in productivity.

  In order to enable high-speed processing, an unstretched film is subjected to a dyeing treatment and a crosslinking treatment in advance without performing dry stretching, and the stretching of the film is performed simultaneously with the reaction in the liquid when performing these treatments. It is conceivable that it is performed (that is, only wet stretching is performed). In this case, high-speed processing is possible, but on the other hand, rapid shrinkage occurs in the width direction of the film during wet stretching, leading to a phenomenon such as so-called neck-in, resulting in a film thickness distribution in the width direction of the film. There tends to be a bias. Specifically, the film thickness tends to be thicker at the part closer to both ends in the width direction of the film, but such a polarizing film is insufficient in stretching at the part where the film thickness is thick at both ends. Will have the problem of lacking.

  Then, the subject of this invention is providing the manufacturing method of a polarizing film which enables high speed processing, suppressing the bias | inclination of the film thickness distribution in the width direction of the polarizing film obtained.

  The present inventor has intensively studied to solve the above problems. As a result, a polyvinyl alcohol film having a specific degree of polymerization is used as a starting material, and dry stretching is performed in advance at a specific stretching ratio before dyeing, and wet stretching is performed in at least one of dyeing and crosslinking. Therefore, while the reaction in the dyeing process and the crosslinking process is sufficiently advanced in a relatively short time, and also in the wet process, the film is preliminarily stretched in a dry manner, so the neck-in is suppressed and the thickness distribution is uneven. The present inventors have found that a polarizing film with a small amount can be obtained and have completed the present invention.

That is, the present invention has the following configuration.
(1) A film made of polyvinyl alcohol having a polymerization degree of 2400 is uniaxially stretched at a draw ratio of 1.5 to 2.8 times in a dry manner, and then immersed in an aqueous solution containing boric acid and dyeing with a dichroic dye. A method for producing a polarizing film, comprising performing wet uniaxial stretching in at least one of the cross-linking treatments by the method.
(2) The said (1) description which performs the said crosslinking process using the boric-acid containing aqueous solution which contains 5-8 weight part of boric acids with respect to 100 weight part of water, and the temperature is 55 degreeC or more and less than 70 degreeC. Manufacturing method of the polarizing film.
(3) The method for producing a polarizing film according to (1) or (2), wherein a treatment time of the crosslinking treatment is 65 to 150 seconds.
(4) A polarizing plate, wherein a protective film is bonded to at least one surface of the polarizing film produced by the method according to any one of (1) to (3).
(5) A polarizing plate in which a protective film is bonded to at least one surface of the polarizing film produced by the method according to any one of (1) to (3), a retardation film, a brightness enhancement film, and a viewing angle. An optical laminate, wherein at least one selected from the group consisting of an improved film and a transflective film is bonded.

  According to the present invention, there is an effect that high-speed processing can be performed while suppressing the deviation of the film thickness distribution in the width direction of the obtained polarizing film. Thereby, the polarizing film excellent in heat resistance can be obtained with high productivity.

Hereinafter, the present invention will be described in detail.
In the present invention, an unstretched film made of polyvinyl alcohol having a polymerization degree of 2400 (hereinafter also referred to as “polyvinyl alcohol film”) is used as a starting material for producing a polarizing film. The polyvinyl alcohol forming this film is formed by, for example, saponifying a polyvinyl acetate resin, and the degree of saponification is about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99. It is mol%-100 mol%. As the polyvinyl acetate resin, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, vinyl acetate and other monomers copolymerizable therewith (for example, unsaturated carboxylic acids, olefins, vinyl ethers, And unsaturated sulfonic acids and the like (for example, ethylene-vinyl acetate copolymer). These polyvinyl alcohol resins may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes can also be used.

  The thickness of the polyvinyl alcohol film is not particularly limited, but is usually about 20 μm to 100 μm, preferably about 30 μm to 80 μm. The film width is not particularly limited, but about 1500 mm to 4000 mm is practical from an industrial viewpoint.

  In the method for producing a polarizing film of the present invention, first, the polyvinyl alcohol film is uniaxially stretched in a dry manner at a stretch ratio of 1.5 to 2.8 times. When the stretching ratio of the dry stretching is less than 1.5 times, the unevenness of the film thickness distribution in the width direction of the obtained polarizing film becomes large. On the other hand, when it exceeds 2.8 times, the dyeing treatment and the crosslinking treatment are performed. The reaction speed becomes slow and high-speed machining cannot be achieved.

  Uniaxial stretching by a dry method is performed by, for example, a method of compressing and stretching by passing between a pair of known heating rolls, a method of bringing the film into contact with a driving heating roll while applying a backward tension to the film, and orienting it longitudinally uniaxially, etc. be able to. At this time, the temperature of the heating roll is set to a glass transition temperature of polyvinyl alcohol to 160 ° C, preferably 80 to 120 ° C. The uniaxial stretching by the dry method is usually performed in air or an inert gas.

  In the method for producing a polarizing film of the present invention, the polyvinyl alcohol film uniaxially stretched by a dry process is subjected to a swelling treatment as necessary, and then immersed in a dyeing treatment with a dichroic dye and a boric acid-containing aqueous solution. A cross-linking treatment is applied.

  The swelling treatment is performed as necessary for the purpose of removing foreign matter from the film surface, removing the plasticizer in the film, imparting easy dyeability in the dyeing process, and plasticizing the film. The treatment conditions for the swelling treatment may be set as appropriate within a range in which the above-described object can be achieved and a problem such as extreme dissolution or devitrification of the film does not occur. For example, the film may be immersed in a treatment bath containing an aqueous solution of about 20 to 70 ° C., preferably about 30 to 60 ° C., for about 30 to 300 seconds, preferably about 60 to 240 seconds. The aqueous solution used for the swelling treatment may be pure water, and boric acid, chloride, inorganic acid, inorganic salt, water-soluble organic solvent, alcohols and the like in the range of about 0.01 wt% to 10 wt%. It may be an aqueous solution containing.

  In addition, when performing the swelling treatment, problems such as swelling of the film in the width direction and wrinkling of the film are likely to occur, so a widening roll (expander roll), a spiral roll, a crown roll, a cross guider, a bend bar, It is preferable to convey the film while removing the wrinkles of the film with a known widening device such as a tenter clip. In order to stabilize the film transport in the bath, the water flow in the swelling bath is controlled with an underwater shower, or an EPC device (Edge Position Control device: a device that detects the edge of the film and prevents meandering of the film) It is also useful to use these together. In addition, since the film swells and expands in the traveling direction of the film, it is preferable to take measures such as controlling the speed of the transporting roll before and after the treatment tank in order to eliminate sagging of the film in the transporting direction.

  The dyeing treatment with the dichroic dye is performed for the purpose of adsorbing and orienting the dichroic dye on the film. This dyeing | staining process can be performed by immersing a film in dichroic dye containing aqueous solution, and there exist a method using an iodine as a dichroic dye, and a method using a water-soluble dichroic dye.

  When iodine is used as the dichroic dye, for example, iodine / potassium iodide / water (weight ratio) = about 0.003 to 0.2 / at a temperature of about 10 to 45 ° C., preferably about 20 to 35 ° C. What is necessary is just to immerse a film in the dyeing tank which put about 0.1-10 / 100 aqueous solution for about 30-600 second, Preferably it is about 60-300 second. The aqueous solution used here may be an aqueous solution using another iodide (such as zinc iodide) instead of potassium iodide, or an aqueous solution using potassium iodide and another iodide in combination. It may be. Further, for example, an aqueous solution in which a compound other than iodide such as boric acid, zinc chloride, and cobalt chloride coexists can be used. In addition, when using the aqueous solution containing a boric acid, it distinguishes from the below-mentioned bridge | crosslinking process at the point which also contains an iodine. Specifically, when an aqueous solution containing about 0.003 parts by weight or more of iodine is used with respect to 100 parts by weight of water, it is regarded as a dyeing process.

  When a water-soluble dichroic dye is used as the dichroic dye, for example, at a temperature of about 20 to 80 ° C., preferably about 30 to 70 ° C., the dichroic dye / water (weight ratio) = about 0.001 The film may be immersed in a dyeing tank containing a 0.1 / 100 aqueous solution for a period of about 30 to 600 seconds, preferably about 60 to 300 seconds. The aqueous solution used here may contain a dyeing assistant or the like, or may contain, for example, an inorganic salt such as sodium sulfate, a surfactant, or the like. As a dichroic dye, a conventionally well-known thing should just be used and only 1 type may be used and 2 or more types may be used together.

The cross-linking treatment is performed for the purpose of achieving water resistance by immersing a film dyed with a dichroic dye in a boric acid-containing aqueous solution to advance a cross-linking reaction.
The boric acid-containing aqueous solution used for the crosslinking treatment preferably contains 5 to 8 parts by weight of boric acid with respect to 100 parts by weight of water. If the boric acid concentration in the boric acid-containing aqueous solution is less than the above range, crosslinking with boric acid may be insufficient. On the other hand, if it exceeds the above range, boric acid may precipitate on the surface of the roll. There exists a possibility that the heat resistance of the polarizing film produced may fall. In addition, when iodine is used as the dichroic dye, it is preferable to further contain about 1 to 30 parts by weight of iodide in the boric acid-containing aqueous solution. Examples of the iodide used here include potassium iodide and zinc iodide. Furthermore, in the boric acid-containing aqueous solution, if necessary, for example, compounds other than iodide such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, glyoxal, glutaraldehyde, etc. A crosslinking agent may coexist.

  The temperature of the boric acid-containing aqueous solution used for the crosslinking treatment is preferably 55 ° C or higher and lower than 70 ° C. If the temperature of the boric acid-containing aqueous solution is less than 55 ° C, the heat resistance of the polarizing film to be obtained may be reduced. On the other hand, if it is 70 ° C or more, the film may be broken during the crosslinking treatment. .

  In the crosslinking treatment, the film may be usually immersed in a treatment tank containing the boric acid-containing aqueous solution for 65 to 150 seconds. In the present invention, even if the cross-linking treatment time is relatively short as described above, the cross-linking reaction can be sufficiently advanced, so that high speed processing is possible.

  In the method for producing a polarizing film of the present invention, uniaxial stretching is performed in a wet manner in at least one of the dyeing treatment and the crosslinking treatment. Preferably, the wet stretching is performed at least by the crosslinking treatment. In addition, the wet stretching can be performed in any treatment process such as the swelling treatment, a water washing treatment described later, and other immersion treatments. In addition, although extending | stretching by wet may be performed only by one process process, and it may be performed by two or more process processes, it is preferable to perform by several process processes.

The uniaxial stretching by the wet method can be performed by, for example, a method of giving a peripheral speed difference between the nip rolls before and after the treatment bath.
The stretching ratio of the wet stretching performed in the dyeing process and the crosslinking process may be appropriately set so that the final stretch ratio of the film is in a desired range, and is not particularly limited. The film is stretched at a stretch ratio of 1.4 times or more, and the final stretch ratio of the film is preferably 5.0 to 6.0 times. Further, the stretching ratio in the case of performing wet stretching in any processing step other than the dyeing process and the crosslinking process is not particularly limited, and may be appropriately set so that a desired integrated stretching ratio can be finally obtained.

  In each of the treatment steps from the swelling treatment to the water washing treatment described later, in the treatment step in which the film is not wet-stretched, the tension is set so that the tension of the film becomes substantially constant for each treatment step. Control can be performed. The tension of the film in each processing step may be the same or different. In some cases, the tension is inevitably slightly stretched or shrunk by this tension control. In the present invention, such a case is not included in the stretching.

In the method for producing a polarizing film of the present invention, the film subjected to the crosslinking treatment can be subjected to a water washing treatment and / or a drying treatment as necessary.
The water washing treatment is performed, for example, by immersing the crosslinked film in water, spraying water as a shower, or using both immersion and spraying. The temperature of water used for the water washing treatment is usually about 2 to 40 ° C., and the dipping or spraying time is preferably about 2 to 120 seconds.

  The drying treatment may be performed by a known method such as a hot air drying method or a drying method using infrared rays. The drying temperature is usually 40 to 95 ° C., preferably 50 to 80 ° C., and the drying time (residence time in the drying furnace) is usually 50 to 200 seconds, preferably 100 to 190 seconds. Further, the degree of the drying treatment is preferably such that the moisture content of the film after the drying treatment is 15% by weight or less.

In the method for producing a polarizing film of the present invention, treatments other than the treatments described above can be added at any stage as necessary. For example, after the crosslinking treatment, immersion treatment (iodide treatment) with an aqueous iodide solution not containing boric acid may be performed, or immersion treatment (zinc treatment with an aqueous solution containing a zinc compound such as zinc chloride not containing boric acid). ) May be performed.
In general, the polarizing film thus produced preferably has a thickness of about 5 μm to 50 μm.

The polarizing plate of the present invention is obtained by bonding a protective film to at least one surface of the polarizing film obtained by the production method of the present invention described above.
As the protective film, for example, a film made of an acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose, a film made of a polyester resin such as polyethylene terephthalate, polyethylene naphthalate or polybutylene terephthalate, or a film made of a polycarbonate resin And a film made of a cycloolefin resin. Examples of commercially available thermoplastic cycloolefin resins include “Topas” (registered trademark) sold by Ticona of Germany and “Arton” (registered trademark) sold by JSR Co., Ltd. Trademark), “ZEONOR” and “ZEONEX” (all are registered trademarks) sold by Nippon Zeon Co., Ltd., and “APEL” (registered trademark) sold by Mitsui Chemicals, Inc. A film formed of such a cycloolefin-based resin is used as a protective film. For the film formation, a known method such as a solvent casting method or a melt extrusion method is appropriately used. Formed cycloolefin resin films are also commercially available, such as “Essina” and “SCA40” sold by Sekisui Chemical Co., Ltd.

  The protective film may be subjected to surface treatment such as anti-glare treatment, anti-reflection treatment, hard coat treatment, antistatic treatment, and antifouling treatment alone or in combination. The protective film and / or the protective film surface protective layer may have a UV absorber such as a benzophenone compound or a benzotriazole compound, or a plasticizer such as a phenyl phosphate compound or a phthalate compound.

  If the thickness of the protective film is too thin, the strength will decrease and the processability will be inferior. On the other hand, if it is too thick, the transparency will decrease, and the curing time required after lamination will increase. Occurs. Accordingly, the appropriate thickness of the protective film is usually about 5 to 200 μm, preferably about 10 to 150 μm, more preferably about 20 to 100 μm.

  The polarizing film and the protective film are bonded via an adhesive. In order to improve the adhesiveness between the adhesive and the polarizing film and / or protective film, the polarizing film and / or protective film may be subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. A surface treatment may be applied.

  As the adhesive, for example, a water solvent adhesive, an organic solvent adhesive, a hot melt adhesive, a solventless adhesive, or the like is used. Examples of water-based adhesives include polyvinyl alcohol-based resin aqueous solutions and aqueous two-component urethane emulsion adhesives. Examples of organic solvent-based adhesives include two-component urethane adhesives and solventless adhesives. Examples of the agent include a one-component urethane adhesive. When an acetylcellulose-based film whose surface to be bonded to the polarizing film is hydrophilized by saponification or the like is used as a protective film, a polyvinyl alcohol-based resin aqueous solution is suitably used as an adhesive. Polyvinyl alcohol resins used as adhesives include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as other single quantities copolymerizable with vinyl acetate. And vinyl alcohol copolymers obtained by saponifying the copolymer with the polymer, and modified polyvinyl alcohol polymers obtained by partially modifying the hydroxyl groups. For this adhesive, a polyvalent aldehyde, a water-soluble epoxy compound, a melamine compound or the like may be used as an additive.

  The method for laminating the polarizing film and the protective film is not particularly limited. For example, an adhesive is uniformly applied to the surface of the polarizing film or the protective film, and the other film is stacked on the coated surface to roll. The method of pasting by and drying is mentioned. Usually, an adhesive agent is apply | coated at the temperature of about 15-40 degreeC after preparation, and the bonding temperature is the range of about 15-30 degreeC normally. After pasting, a drying treatment is performed to remove a solvent such as water contained in the adhesive, and the drying temperature in this case is usually about 30 to 85 ° C, preferably about 40 to 80 ° C. . Thereafter, the adhesive may be cured by curing for about 1 to 90 days under a temperature environment of about 15 to 85 ° C, preferably about 20 to 50 ° C, more preferably about 35 to 45 ° C. When this curing period is long, productivity deteriorates, so the curing period is about 1 to 30 days, preferably about 1 to 7 days.

  The optical laminate of the present invention is formed by laminating the above polarizing plate and at least one selected from the group consisting of a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film. . Such an optical laminate is a protective film, a function as a retardation film, a function as a brightness enhancement film, a function as a reflection film, a function as a transflective film, a function as a diffusion film, and an optical compensation film. It is also possible to provide an optical function such as

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by this Example.

In addition, the film thickness of the polarizing film obtained by the Example and the comparative example was measured as follows.
<Thickness measurement method>
Using a contact-type film thickness meter (“Digimicro Counter MFC-101” manufactured by Nikon), the film thickness was measured at intervals of 10 mm along the width direction of the polarizing film.

Example 1
An unstretched polyvinyl alcohol film having a polymerization degree of 2400 (“VF-PS # 7500” manufactured by Kuraray Co., Ltd .: a saponification degree of 99.9 mol% or more) was uniaxially stretched by 2.15 times by dry stretching at 110 ° C. The film was then immersed in pure water at 30 ° C. for 55 seconds while maintaining the tension so that the film did not loosen, and the film was sufficiently swollen, and then iodine / potassium iodide / water was 0.028 / 5 / After dyeing by immersing in an aqueous solution at 30 ° C., which is 100 (weight ratio), for 109 seconds, subsequently, at 65 ° C., where potassium iodide / boric acid / water is 10/6/100 (weight ratio). The crosslinking treatment was performed by immersing in an aqueous solution containing boric acid for 78.0 seconds. While the film was swollen and subjected to a dyeing process and a crosslinking process, the film was uniaxially stretched in each immersion solution by wet stretching until the cumulative stretch ratio was 5.27. Then, after washing | cleaning for 16 second with 35 degreeC pure water, it dried for 79 second with 60 degreeC hot air, and obtained the polarizing film. Table 1 shows the maximum value, minimum value, film thickness difference (maximum value-minimum value), and average value of the obtained polarizing film.

(Example 2)
A polarizing film was obtained in the same manner as in Example 1, except that the temperature of the aqueous solution containing boric acid used in the crosslinking treatment was 60 ° C. and the crosslinking treatment conditions were changed so that the film was immersed in the aqueous solution for 97.3 seconds. It was. Table 1 shows the maximum value, minimum value, film thickness difference (maximum value-minimum value), and average value of the obtained polarizing film.

(Comparative Example 1)
It is assumed that uniaxial stretching by dry stretching is not performed, and crosslinking treatment is performed so as to be immersed for 91.1 seconds in a boric acid-containing aqueous solution at 54 ° C. in which potassium iodide / boric acid / water is 12 / 4.8 / 100 (weight ratio). A polarizing film was obtained in the same manner as in Example 1 except that the conditions were changed and the cumulative draw ratio between the swelling of the film and the crosslinking treatment was 5.26 times. Table 1 shows the maximum value, minimum value, film thickness difference (maximum value-minimum value), and average value of the obtained polarizing film.

(Comparative Example 2)
Cross-linking treatment is performed so that uniaxial stretching by dry stretching is not performed, and the substrate is immersed in a boric acid-containing aqueous solution at 54 ° C. in which potassium iodide / boric acid / water is 12 / 4.9 / 100 (weight ratio) for 103.4 seconds. A polarizing film was obtained in the same manner as in Example 1 except that the conditions were changed and the cumulative draw ratio between the swelling of the film and the crosslinking treatment was 5.26 times. Table 1 shows the maximum value, minimum value, film thickness difference (maximum value-minimum value), and average value of the obtained polarizing film.

Polarizing films were prepared using the polarizing films obtained in the above Examples and Comparative Examples, and a heat resistance test was conducted using each of the obtained polarizing plates. The results are shown in Table 1.
That is, first, a polyvinyl alcohol-based adhesive was applied to both surfaces of a polarizing film, and a protective film having a thickness of 80 μm (a triacetyl cellulose film subjected to saponification treatment on the surface) was bonded to both surfaces to produce a polarizing plate. .
Next, the obtained polarizing plate was bonded to soda glass (40 mm × 40 mm, thickness 11 mm) to prepare a test piece, which was subjected to a heat resistance test in which it was heated in an oven at 100 ° C. for 3 hours. The test pieces before and after the heat resistance test were set in an ultraviolet-visible spectrophotometer (“V7100” manufactured by JASCO Corporation), and the UV-visible spectrum of each test piece in the transmission direction and the absorption direction was measured. Then, in accordance with JIS-Z8729, the initial single transmittance (%) and the orthogonal hues (orthogonal a, orthogonal b) before and after the heat resistance test are obtained, and the orthogonal Δ that is the amount of change in the orthogonal hues (orthogonal a, orthogonal b). E was calculated based on the following formula and used as an index of heat resistance. It shows that it is excellent in heat resistance, so that the value of orthogonal (DELTA) E is small.
Orthogonal ΔE = [(orthogonal aII−orthogonal aI) ² + (orthogonal bII−orthogonal bI) ² ] ^0.5
However, orthogonal aI: orthogonal a before the heat resistance test
Orthogonal aII: orthogonal a after the heat resistance test
Orthogonal bI: orthogonal b before heat resistance test
Orthogonal bII: orthogonal b after heat resistance test

  From Table 1, in Examples 1 and 2, the processing time of the crosslinking treatment is equal to or shorter than that of Comparative Examples 1 and 2 in which dry stretching is not performed, and high-speed processing equivalent to that in the case where an unstretched film is stretched by a wet process is achieved. It can be seen that is feasible. In addition, the difference in film thickness of the polarizing films obtained in Comparative Examples 1 and 2 is about 6 μm and the deviation of the film thickness distribution is large, whereas in Examples 1 and 2, this film thickness difference is reduced to about 2 μm. Thus, it is clear that it is possible to suppress the unevenness of the film thickness distribution of the polarizing film obtained even though high-speed processing is possible. Therefore, the polarizing plate using the polarizing film obtained in Examples 1 and 2 shows better heat resistance than the polarizing plate using the polarizing film obtained in Comparative Examples 1 and 2. In terms of optical properties, the polarizing plate using the polarizing film obtained in Examples 1 and 2 exhibits the same performance as the polarizing plate using the polarizing film obtained in conventional Comparative Examples 1 and 2. Confirmed to do.

Claims (5)

  A film made of polyvinyl alcohol having a polymerization degree of 2400 is uniaxially stretched at a draw ratio of 1.5 to 2.8 times in a dry manner, and then is dyed with a dichroic dye and is crosslinked in a boric acid-containing aqueous solution. A method for producing a polarizing film, characterized in that at least one of the above is wet-uniaxially stretched.   The polarizing film according to claim 1, wherein the crosslinking treatment is performed using a boric acid-containing aqueous solution containing 5 to 8 parts by weight of boric acid with respect to 100 parts by weight of water and having a temperature of 55 ° C. or more and less than 70 ° C. Production method.   The manufacturing method of the polarizing film of Claim 1 or 2 whose processing time of the said crosslinking process is 65 to 150 second.   The protective film is bonded by the at least single side | surface of the polarizing film manufactured by the method in any one of Claims 1-3, The polarizing plate characterized by the above-mentioned.   A polarizing plate in which a protective film is bonded to at least one surface of the polarizing film produced by the method according to any one of claims 1 to 3, a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film An optical laminate, wherein at least one selected from the group consisting of films is bonded.