JP2005084506A - Polarizing film and method for producing the same, polarizing plate and optical laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing film with few white spots and no wrinkles, a production method thereof, a polarizing plate and an optical laminate.
SOLUTION: A polyvinyl alcohol film is treated in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment, uniaxial stretching is performed in the boric acid treatment step and / or the preceding step, and at least one after the stretching treatment is performed. It is a polarizing film obtained by relaxing the stretching of the film in the stretching direction by 1 to 5% in one step. A polarizing plate is obtained by pasting a protective film on at least one side of the polarizing film. At least one selected from a phase difference plate, a brightness enhancement film, a viewing angle improvement film, and a transflective plate is bonded to a polarizing plate having a protective film bonded to at least one side to obtain an optical laminate.
[Selection figure] None

Description

  The present invention is a polarizing film with little light leakage (white spots) and no wrinkles and a method for producing the same, a polarizing plate in which a protective film is laminated on at least one side of the polarizing film, a retardation film, a brightness enhancement film, and a viewing angle improvement. The present invention relates to an optical laminate in which either a film or a transflective film is singly or plurally bonded.

  Conventionally, a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol film has been used. That is, an iodine polarizing film using iodine as a dichroic dye, a dye polarizing film using a dichroic dye as a dichroic dye, and the like are known. These polarizing films are usually used as polarizing plates by attaching a protective film such as triacetyl cellulose to one or both sides of the polarizing film via an adhesive made of an aqueous solution of a polyvinyl alcohol resin.

  As a method for producing a polarizing film, for example, in Patent Document 1, after a polyvinyl alcohol film is immersed in water and swollen, it is dyed with the dichroic dye, stretched, and then fixed with iodine to the film. For this purpose, a method is described in which a polyvinyl alcohol film is treated with boric acid, washed with water and then dried.

  Patent Document 2 describes that a dry uniaxially stretched polyvinyl alcohol film is relaxed while being dyed with the dichroic dye-containing aqueous solution, and is further stretched in a boric acid-containing aqueous solution to obtain a polarizing film. Has been.

Thus, the polarizing film obtained is laminated | stacked on the both surfaces or one side, and a protective film is laminated | stacked, and is integrated in a liquid crystal display device as a polarizing plate.
However, when such a liquid crystal display device is used at a high temperature, a so-called “white blank” phenomenon may occur in which light leaks near the midpoint of the four sides around the display screen and appears white. When such white spots occur, the contrast decreases near the midpoints of the four sides around the display screen, and the display quality decreases.

  In order to solve such a problem, Patent Document 3 describes a method for producing a polarizing film in which a boric acid-treated uniaxially stretched polyvinyl alcohol film is washed with water and then dried while applying a predetermined tension. . However, the method described in Patent Document 3 has a problem that wrinkles are generated in the obtained polarizing film.

JP-A-10-153709 JP 2002-182035 A JP 2001-174634 A

  The main problem to be solved by the present invention is to provide a polarizing film having few so-called white spots and a wrinkle-free polarizing film, a manufacturing method thereof, a polarizing plate and an optical laminate.

  As a result of intensive studies to solve the above problems, the present inventors processed a polyvinyl alcohol film in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment, and a boric acid treatment step and / or its treatment. The present invention has found a new fact that a polarizing film with few white spots and wrinkles can be obtained by performing uniaxial stretching in the previous step and further relaxing the stretching of the film in at least one step after the stretching treatment. It came to complete.

  That is, the polarizing film of the present invention is obtained by treating a polyvinyl alcohol film in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment, performing uniaxial stretching in the boric acid treatment step and / or the previous step, and further stretching. In at least one step after the treatment, the stretching of the film is relaxed by 1 to 5% in the stretching direction.

  In the method for producing a polarizing film according to the present invention, a polyvinyl alcohol film is continuously treated in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment, and uniaxial stretching is performed in the boric acid treatment step and / or the previous step. The polarizing film manufacturing method is characterized in that stretching of the film is relaxed by 1 to 5% in the stretching direction in at least one step after the stretching treatment.

  In the present invention, the boric acid treatment step may consist of a plurality of boric acid treatment steps. In that case, the film is stretched in the first boric acid treatment step, and from the next boric acid treatment step. The stretching of the film may be relaxed in at least one of the steps up to the water washing step.

  Moreover, the polarizing plate of the present invention is obtained by bonding a protective film to at least one surface of the polarizing film. This protective film may have any function of a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film. Or even if it is the optical laminated body which bonded at least 1 sort (s) chosen from a phase difference plate, a brightness improvement film, a viewing angle improvement film, and a transflective plate to the said polarizing plate which bonded the protective film on the single side | surface at least. Good.

  According to the present invention, by stretching the film in the stretching direction by 1 to 5% in at least one step after the stretching treatment, there is an effect that the obtained polarizing film has few white spots and no wrinkles. By using the polarizing plate and the optical laminate of the present invention in a liquid crystal display device, a thin and high-quality liquid crystal display can be obtained.

Hereinafter, the present invention will be described in detail.
Examples of the polyvinyl alcohol-based resin that forms the polyvinyl alcohol-based film in the present invention include those obtained by saponifying a polyvinyl acetate-based resin. As a saponification degree, it is 85 mol% or more, Preferably it is 90 mol% or more, More preferably, it is 99 mol%-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 polyvinyl alcohol-based resin is about 1000 to 10,000, preferably about 1500 to 5,000.

These polyvinyl alcohol resins may be modified. For example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like may be used. Usually, as a starting material for producing a polarizing film, an unstretched film of a polyvinyl alcohol-based resin film having a thickness of 20 μm to 100 μm, preferably 30 μm to 80 μm is used. Industrially, the width of the film is practically 1500 mm to 4000 mm.
The thickness of the polyvinyl alcohol polarizing film obtained by treating the unstretched film in the order of swelling, dyeing, water resistance, hue adjustment, washing with water and stretching while stretching is, for example, about 5 to 50 μm.

  The polarizing film of the present invention is a polyvinyl alcohol uniaxially stretched film obtained by adsorbing and orienting a dichroic dye, and there are roughly two production methods as the production method. One is a method in which a polyvinyl alcohol film is uniaxially stretched in air or an inert gas, followed by solution treatment in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment, followed by drying. Secondly, an unstretched polyvinyl alcohol film is treated with an aqueous solution in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment, and uniaxial stretching is performed in a wet manner in the boric acid treatment step and / or the previous step. This is a method of performing drying and finally drying.

In any method, the uniaxial stretching may be performed in one step or in two or more steps, but is preferably performed in a plurality of steps. As a stretching method, a known method can be adopted. For example, stretching between rolls in which stretching is performed with a difference in peripheral speed between two nip rolls for transporting a film, hot roll stretching as described in Japanese Patent No. 2731813 Method and tenter stretching method. The order of the steps is basically as described above, but the number of treatment baths and treatment conditions are not particularly limited, and there is no restriction.
Needless to say, a process not described in the above process can be freely inserted for another purpose. As an example of this process, after boric acid treatment, immersion treatment (iodide treatment) with an aqueous iodide solution not containing boric acid or immersion treatment (zinc treatment) step with an aqueous solution containing zinc chloride not containing boric acid, etc. Can be mentioned.

  The swelling step is performed for the purpose of removing foreign matter from the film surface, removing the plasticizer in the film, imparting easy dyeability in the next step, and plasticizing the film. 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. When the film previously stretched in the gas is swollen, for example, the film is immersed in an aqueous solution at 20 ° C to 70 ° C, preferably 30 ° C to 60 ° C. The immersion time of the film is about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds. In order to swell an unstretched raw film from the beginning, the film is immersed in an aqueous solution of, for example, 10 ° C to 50 ° C, preferably 20 ° C to 40 ° C. The immersion time of the film is about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds.

  In the swelling treatment process, the film is likely to swell in the width direction and wrinkles into the film, so that the film may be spread with a known widening device such as an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar, or a tenter clip. It is preferable to transport the film while removing wrinkles. 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 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 to pure water, the swelling treatment bath used is boric acid (described in JP-A-10-153709), chloride (described in JP-A-06-281816), inorganic acid, inorganic salt, water-soluble An aqueous solution to which an organic solvent, alcohol or the like is added in an amount of 0.01 to 10% by weight can also be used.

  The dyeing step with the dichroic dye is performed for the purpose of adsorbing and orienting the dichroic dye on the film. 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. When iodine is used as the dichroic dye, for example, iodine / KI / water = 0.003 to 0.2 / 0.1 at a temperature of 10 to 45 ° C., preferably 20 to 35 ° C. and in a weight ratio. The immersion treatment is performed at a concentration of 10/100 for 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds. Instead of potassium iodide, other iodides such as zinc iodide may be used. Other iodides may be used in combination with potassium iodide. Further, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc. may coexist. When boric acid is added, it is distinguished from the following boric acid treatment in that it contains iodine. Any dye containing 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water can be regarded as a dyeing tank.

  When a water-soluble dichroic dye is used as the dichroic dye, for example, a temperature of 20 ° C. to 80 ° C., preferably 30 ° C. to 70 ° C., and a weight ratio of dichroic dye / water = 0.001 to 0.00. An immersion treatment is performed at a concentration of 1/100 for 30 seconds to 600 seconds, preferably 60 seconds to 300 seconds. The aqueous solution of the dichroic dye to be used may have a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant or the like. The dichroic dye may be used alone, or two or more dichroic dyes may be used at the same time.

  As described above, the film may be stretched in a dyeing tank. Stretching is performed by a method of giving a peripheral speed difference between the nip rolls before and after the dyeing tank. Similarly to the swelling step, an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar, and the like can be installed in the dyeing bath and / or at the bath entrance / exit.

The boric acid treatment is performed by immersing a polyvinyl alcohol film dyed with a dichroic dye in an aqueous solution containing about 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water. When the dichroic dye is iodine, it is preferable to contain about 1 to 30 parts by weight of iodide.
Examples of iodide include potassium iodide and zinc iodide. Further, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist.
This boric acid treatment is carried out for water resistance, hue adjustment (preventing bluishness, etc.) by crosslinking, and the like. In the case of water resistance by cross-linking, a cross-linking agent such as borax, glyoxal, and glutaraldehyde can be used as necessary in addition to or together with boric acid.
In addition, the boric acid treatment for water resistance may be referred to by names such as water resistance treatment, crosslinking treatment, and immobilization treatment. In addition, boric acid treatment for hue adjustment may be referred to by a name such as complementary color treatment or re-dyeing treatment.

The boric acid treatment is not particularly distinguished depending on the purpose, but is usually performed by appropriately changing the concentrations of boric acid and other additives and the temperature of the treatment bath.
When the raw film is swollen, dyed or treated with boric acid, and the boric acid treatment is aimed at water resistance by crosslinking, about 3 to 10 parts by weight of boric acid and 100% by weight of iodide, iodide Is carried out at a temperature of usually 50 ° C to 70 ° C, preferably 55 ° C to 65 ° C. The immersion time is usually about 30 to 600 seconds, preferably 60 to 420 seconds, and more preferably 90 to 300 seconds.
In addition, when dye | staining and boric-acid-treat the film extended | stretched previously, the temperature of a boric-acid treatment bath is 50 to 85 degreeC normally, Preferably it is 55 to 80 degreeC.

After boric acid treatment for water resistance, boric acid treatment for hue adjustment may be performed. For example, when the dichroic dye is iodine, a boric acid treatment bath containing about 1 to 5 parts by weight of boric acid and about 3 to 30 parts by weight of iodide for 100 parts by weight of water is used for this purpose. It is usually used at a temperature of 10 ° C to 45 ° C. The immersion time is usually about 3 to 300 seconds, preferably 10 to 240 seconds.
The boric acid treatment for adjusting the hue is usually performed at a lower boric acid concentration, a higher iodide concentration, and a lower temperature than the boric acid treatment for water resistance.

These boric acid treatments may be performed in a plurality of steps and are usually performed in 2 to 5 steps. In this case, the aqueous solution composition and temperature of each boric acid treatment tank to be used may be the same or different within the above range. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment may be performed in a plurality of steps, respectively.
In the boric acid treatment process, the film may be stretched in the same manner as in the dyeing process. The final cumulative draw ratio is about 4.5 to 7.0 times, preferably 5.0 to 6.5 times.

  After boric acid treatment, it is washed with water. The water washing treatment is performed, for example, by immersing a polyvinyl alcohol film treated with boric acid for water resistance and / or color tone adjustment in water, spraying water as a shower, or combining immersion and spraying. The temperature of the water in the washing treatment is usually about 2 to 40 ° C., and the immersion time is preferably about 2 to 120 seconds. Drying after washing with water is performed in a drying furnace at a temperature of about 40 to 100 ° C. for about 60 to 600 seconds.

In the present invention, in the step after the stretching treatment, the stretching of the film is relaxed by 1 to 5% in the stretching direction.
When extending | stretching at the dyeing | staining process process, extending | stretching is relieve | moderated by at least 1 process of a subsequent boric-acid process process and a water washing process process. When stretching is completed in the previous process of the dyeing process, stretching is relaxed in at least one of the subsequent processes including the dyeing process and the boric acid process.
When the boric acid treatment step is composed of a plurality of boric acid treatment steps, the film is stretched in the first boric acid treatment step, and the boric acid treatment step after the boric acid treatment step after the boric acid treatment step is performed. Stretching is relaxed in at least one step.
When the above-described iodide treatment or zinc treatment is performed after the boric acid treatment, stretching may be relaxed in these steps.

  Specifically, the stretched polyvinyl alcohol film is relaxed and contracted in a treatment bath. The relaxation rate (that is, the shrinkage rate) is preferably 1 to 5%. If the relaxation rate is less than 1%, there is no effect in reducing the occurrence of white spots. Conversely, if the relaxation rate exceeds 5%, wrinkles are generated in the polyvinyl alcohol film, which may not be used for optical applications. The relaxation may be performed in one step or in a plurality of steps. When performing by several processes, the total relaxation rate before relaxation and after relaxation shall be 1-5%.

A polarizing plate is obtained by bonding a protective film with an adhesive on at least one side of the polarizing film thus produced.
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” (trademark) sold by JSR Co., Ltd. Registered), “ZEONOR” and “ZEONEX” (both registered trademarks) sold by Nippon Zeon Co., Ltd., and “APEL” (trademark registered) sold by Mitsui Chemicals, Inc. A film formed from 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. The formed cycloolefin resin film is also commercially available, for example, “Essina” and “SCA40” sold by Sekisui Chemical Co., Ltd.

  The thickness of the protective film is preferably thin. However, if it is too thin, the strength is lowered and the processability is inferior. On the other hand, if it is too thick, the transparency is lowered and the curing time required after lamination is increased. Problems occur. Therefore, the suitable thickness of a protective film is about 5-200 micrometers, for example, Preferably it is 10-150 micrometers, More preferably, it is 20-100 micrometers.

  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.

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.
Such a protective film may be bonded to one side of the polarizing film or may be bonded to both sides.

  The polarizing film and the protective film are laminated using an adhesive such as a water solvent adhesive, an organic solvent adhesive, a hot melt adhesive, or a solventless adhesive. Examples of aqueous solvent adhesives include aqueous polyvinyl alcohol resins and aqueous two-component urethane emulsion adhesives, and examples of organic solvent adhesives include two-component urethane adhesives as solvent-free adhesives. For example, a one-pack type urethane adhesive may be used. 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 by a roll or the like. The method of pasting and drying is mentioned.

Usually, an adhesive agent is apply | coated at the temperature of 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 at this time is usually in the range of 30 to 85 ° C, preferably 40 to 80 ° C. Thereafter, the adhesive may be cured by curing for about 90 days under a temperature environment of 15 to 85 ° C, preferably 20 to 50 ° C, more preferably 35 to 45 ° C. When this curing period is long, productivity is deteriorated, so the curing period is about 1 to 30 days, preferably 1 to 7 days.
Thus, a polarizing plate in which the protective film is bonded to one side or both sides of the polarizing film through the adhesive layer is obtained.

  In the present invention, the protective film has 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, a function as an optical compensation film, etc. It can also have an optical function. In this case, for example, by laminating an optical functional film such as a retardation film, a brightness enhancement film, a reflection film, a transflective film, a diffusion film, an optical compensation film on the surface of the protective film, it has such a function. In addition, the protective film itself can be given such a function. Further, the protective film itself may have a plurality of functions such as a diffusion film having the function of a brightness enhancement film.

  For example, the protective film is subjected to a stretching process described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, etc., or a process described in Japanese Patent No. 3168850, etc. The function as can be provided. In addition, by forming micropores in the above protective film by a method as described in JP 2002-169025 A or JP 2003-29030 A, two or more layers having different central wavelengths of selective reflection are formed. By superimposing these cholesteric liquid crystal layers, a function as a brightness enhancement film can be imparted. By forming a metal thin film on the above protective film by vapor deposition or sputtering, a function as a reflective film or a transflective film can be imparted. By coating the protective film with a resin solution containing fine particles, a function as a diffusion film can be imparted. Moreover, the function as an optical compensation film can be provided by coating and aligning liquid crystalline compounds, such as a discotic liquid crystalline compound, on said protective film. In addition, using an appropriate adhesive, a brightness enhancement film such as a trade name: DBEF (manufactured by 3M Co., Ltd.), a trade name: a viewing angle improving film such as a WV film (manufactured by Fuji Photo Film Co., Ltd.), a trade name : Commercially available optical functional films such as retardation films such as Sumikalite (registered trademark) (Sumitomo Chemical Co., Ltd.) may be directly bonded to the polarizing film.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

A 75-μm-thick polyvinyl alcohol film (Kurarevinylone VF-PS # 7500, polymerization degree 2,400, saponification degree 99.9 mol% or more) is kept in pure water at 30 ° C. so that the film does not loosen. The film was immersed for about 130 seconds to fully swell the film. Next, the film was immersed in an aqueous solution of iodine / potassium iodide / water in a weight ratio of 0.02 / 1.5 / 100 and dyed to perform uniaxial stretching. Then, uniaxially stretching until the cumulative draw ratio from the original fabric becomes 5.9 times while boric acid treatment is performed by immersing in potassium iodide / boric acid / water in a 60/5 ° C. aqueous solution with a weight ratio of 10/5/100. Went.
Next, the film is stretched in the stretching direction by about 3 in the stretching direction while being immersed in an aqueous solution of potassium iodide / boric acid / water at a weight ratio of 10/3/100 at 40 ° C. for about 30 seconds to perform the second boric acid treatment. % Stretching in the stretching direction (thus, the final stretching ratio is 5.9 × 0.97 = 5.72 times). Finally, it was washed with pure water at 10 ° C. for about 10 seconds and then dried at 60 ° C. for 2 minutes to obtain an iodine-based polarizing film. There was no wrinkle in any process.
A polyvinyl alcohol adhesive is applied to both sides of the polarizing film, and a protective film (a triacetyl cellulose film having a saponified surface, "Fujitac (registered trademark) T80UNL", manufactured by Fuji Photo Film Co., Ltd.), thickness 80 μm] was bonded to both sides and dried at 60 ° C. for 5 minutes to obtain a polarizing plate.
An acrylic pressure-sensitive adhesive was applied to one side of the polarizing plate, and was cut into a rectangle (120 mm × 90 mm) so that its absorption axis was 45 degrees with respect to the long side. The two polarizing plates were bonded to both sides of a transparent glass plate so as to be crossed Nicols, and visually observed. As a result, the portions where the polarizing plates were bonded to both surfaces of the glass plate appeared uniformly black, and no light leakage (white spots) was observed. The glass plate on which the polarizing plate was bonded was allowed to stand for 240 hours under dry heat conditions at 80 ° C. and then visually observed. As a result, light leakage (white spots) near the center of each side of the polarizing plate was relatively small. It was.

Except for not performing the second boric acid treatment, the stretching of the film was relaxed in the stretching direction by about 3% in the stretching direction at the time of washing with water (thus, the final stretching ratio was 5.9 × 0.97 = 5.72 times). In the same manner as in Example 1, an iodine-based polarizing film was obtained. There was no wrinkle in any process.
A protective film was bonded to both surfaces of this polarizing film in the same manner as in Example 1 to obtain a polarizing plate. The polarizing plate was observed for light leakage (white spots) in the same manner as in Example 1, and was the same as in Example 1.

While the second boric acid treatment is performed by immersing in a 60 ° C. aqueous solution of potassium iodide / boric acid / water at a weight ratio of 10/5/100 for about 30 seconds, the film is stretched by about 1% in the stretching direction. Except that the film stretching was relaxed in the stretching direction by about 2% in the stretching direction (thus, the final stretching ratio was 5.9 × 0.99 × 0.98 = 5.72 times). In the same manner as in Example 1, an iodine-based polarizing film was obtained. There was no wrinkle in any process.
A protective film was bonded to both surfaces of this polarizing film in the same manner as in Example 1 to obtain a polarizing plate. The polarizing plate was observed for light leakage (white spots) in the same manner as in Example 1, and was the same as in Example 1.

A 75 μm-thick polyvinyl alcohol film (Kurarayvinilon VF-PS # 7500, polymerization degree 2,400, saponification degree 99.9 mol% or more) was stretched 4.9 times in air using a 125 ° C. hot roll. This dry stretched film was immersed in pure water at 60 ° C. for about 60 seconds while maintaining the tension state so that the film did not loosen, and the film was sufficiently swollen. Next, dyeing treatment was performed by immersing in an aqueous solution of iodine / potassium iodide / water in a weight ratio of 0.05 / 5.0 / 100 at 28 ° C. for about 60 seconds. Tension was maintained so that the film did not relax during dyeing. Then, until the total draw ratio from the original fabric is 5.3 times while the boric acid treatment is performed by immersing in potassium iodide / boric acid / water in a 73 ° C. aqueous solution of 6 / 7.5 / 100 by weight. Uniaxial stretching was performed. Next, without performing the second boric acid treatment, the film was washed with pure water at 10 ° C. for about 10 seconds, and during the washing, the stretching of the film was relaxed in the stretching direction by about 2% (thus, the final draw ratio was 5. 3 × 0.98 = 5.19 times). It dried at 60 degreeC for 2 minute (s), and obtained the iodine type polarizing film. There was no wrinkle in any process.
A protective film was bonded to both surfaces of this polarizing film in the same manner as in Example 1 to obtain a polarizing plate. The polarizing plate was observed for light leakage (white spots) in the same manner as in Example 1, and was the same as in Example 1.
[Comparative Example 1]

A polarizing plate was obtained in the same manner as in Example 1 except that the stretching of the film was not relaxed in the second boric acid treatment step. There was no wrinkle in any process.
When this polarizing plate was bonded to both surfaces of the glass plate in the same manner as in Example 1 and visually observed, the portion where the polarizing plate was bonded to both surfaces of the glass plate appeared uniformly black, and light leakage (white leakage) was Not observed. When the glass plate on which the polarizing plate was bonded was allowed to stand for 240 hours under dry heat conditions at 80 ° C. and then visually observed, light leakage (white spots) near the center of each side of the polarizing plate was found to be in Example 1. It was larger than the polarizing plate of ~ 4.
[Comparative Example 2]

  In the second boric acid treatment step, the film was stretched by 6% in the stretching direction except that the film was wrinkled during the relaxation treatment and used as an optical application. A good polarizing film was not obtained.

Claims (6)

  A polyvinyl alcohol film is processed in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment, uniaxial stretching is performed in the boric acid treatment step and / or the preceding step, and the film is further processed in at least one step after the stretching treatment. A polarizing film obtained by relaxing 1 to 5% of stretching in the stretching direction.   A method for producing a polarizing film in which a polyvinyl alcohol film is continuously treated in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment, and uniaxial stretching is performed in the boric acid treatment step and / or the previous step, A method for producing a polarizing film, wherein stretching of the film is relaxed by 1 to 5% in the stretching direction in at least one step after the stretching treatment.   The boric acid treatment step comprises a plurality of boric acid treatment steps, the film is stretched in the first boric acid treatment step, and at least one of the steps from the next boric acid treatment step to the water washing step. The method for producing a polarizing film according to claim 2, wherein stretching is relaxed.   A polarizing plate comprising a protective film bonded to at least one surface of the polarizing film according to claim 1.   The polarizing plate according to claim 4, wherein the protective film has a function of any one of a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film. An optical laminate comprising the polarizing plate according to claim 4 and at least one selected from a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film.