JP2011110819A - Nip roll for manufacturing polarizing film and method for manufacturing polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nip roll for manufacturing a polarizing film with excellent durability, which inhibits cutting of a polyvinyl alcohol-based film, and to provide a method for manufacturing the polarizing film using this nip roll. <P>SOLUTION: At least the surface of the nip roll is a rubber layer composed mainly of EPDM which contains a carbon black and is vulcanized with a peroxide. The polyvinyl alcohol-based film is subjected to a swelling treatment, a dyeing treatment, a boric acid treatment, a water washing treatment and a drying treatment in that order. In addition, prior to the swelling treatment, dyeing treatment and boric acid treatment among the treatments, and/or during at least one treatment among the swelling treatment, dyeing treatment and boric acid treatment, the polarizing film is manufactured by stretching a film through making a circumferential speed difference between the two nip rolls for conveying the film. The nip roll can be used in this manufacturing method. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nip roll used for wet-stretching a film, and a method for producing a polarizing film using the nip roll, particularly in a process for producing a polarizing film.

  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, a nip roll and a guide roll are used. A polyvinyl alcohol film is immersed in water to swell, then dyed with the dichroic dye, stretched, and then fixed with iodine to the film. For this purpose, a method is known in which a polyvinyl alcohol film is treated with boric acid, washed with water and then dried. At this time, the film is stretched by giving a peripheral speed difference to the nip rolls before and after the treatment bath, the film transport direction is changed by the guide roll, and the film is introduced into and taken out of the treatment liquid (for example, Patent Documents). 1).

  However, in the wet stretching of the polyvinyl alcohol film as described above, there has been a problem that the film has been easily cut. As a cause of such film cutting, in addition to the problem of the film itself, the nip roll used deteriorates due to the influence of iodine, boric acid, potassium iodide, etc. attached to the film for a long time (especially the roll surface is hard) However, in reality, no effective countermeasures have been found.

JP-A-10-170721

  This invention solves the problem of the said prior art example, and provides the manufacturing method of a polarizing film using the nip roll for polarizing film manufacture excellent in the durability which can suppress the cutting | disconnection of a polyvinyl alcohol-type film, and this. This is the issue.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that NBR conventionally used as a material for a nip roll used for stretching adheres to the film over a long period of time in the production process. When using a nip roll containing carbon black and containing EPDM vulcanized with peroxide as a main component, the above-mentioned problems are likely to occur due to the influence of potassium iodide. Thus, the inventors have found that the film can be prevented from being cut, and have completed the present invention.

  That is, the nip roll for producing a polarizing film of the present invention is characterized in that at least the surface is a rubber layer containing carbon black as a main component and containing EPDM vulcanized with a peroxide.

  Moreover, the method for producing a polarizing film according to the present invention comprises treating a polyvinyl alcohol film in the order of swelling treatment, dyeing treatment, boric acid treatment, water washing treatment and drying treatment. Before the acid treatment step and / or during at least one of the swelling treatment, the dyeing treatment and the boric acid treatment, the film is stretched by imparting a difference in peripheral speed between the two nip rolls transporting the film to form the polarizing film. In the manufacturing method, the nip roll is used as a nip roll.

  Since the surface of the nip roll of the present invention is a rubber layer mainly composed of EPDM containing carbon black and vulcanized with peroxide, iodine, boric acid, potassium iodide, etc. adhered to the film over a long period of time. It has excellent durability, and there is little change in weight and friction coefficient, so it is possible to suppress the film from being cut during the polarizing film manufacturing process, and as a result, the productivity and product yield of the polarizing film are also improved. effective.

  The nip roll for producing a polarizing film of the present invention has a rubber layer on its surface, the main component of which is EPDM (ethylene-propylene-diene rubber) vulcanized with a peroxide. As is well known, EPDM introduces a small amount of a third component (diene component) into ethylene-propylene rubber (EPM), which is a copolymer of ethylene and propylene, and double bonds in the main chain. It is a thing with. Examples of the third component include ethylidene norbornene (ENB), 1,4-hexadiene (1,4-HD), dicyclopentadiene (DCP), and the like. EPDM preferably has an iodine value of 5 to 24.

  Examples of peroxides for vulcanizing (crosslinking) EPDM include benzoyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 1,1'-di- -T-butylperoxy-3,3,5-trimethylenecyclohexane, 1,3-di- (t-butylperoxy) -diisopropylbenzene and the like.

The rubber layer in the present invention contains EPDM as a main component and may contain other rubber components. Examples of such other rubber components include, but are not limited to, EPM, butyl rubber, styrene-butadiene rubber, chloroprene rubber, and the like.
In this case, the rubber layer in the present invention should preferably contain 100 to 70% by weight of EPDM. If the blending amount of EPDM is less than 70% by weight, the wear resistance and chemical resistance are lowered. There is a risk.

  Moreover, in this invention, various additives can be mix | blended other than a peroxide. Examples of such additives include reinforcing agents such as carbon black, fillers, paraffinic, naphthenic and aromatic process oils, and vulcanization accelerators such as stearic acid and zinc white. However, it is not limited to these. As the reinforcing agent and filler, an additive having acid resistance such as silica and clay may be added together with carbon black.

After a predetermined amount of such various additives are mixed with a rubber material mainly composed of EPDM and sufficiently kneaded, a rubber layer is coated on the outer peripheral surface of the core metal of the roll by a predetermined extrusion molding or the like. A nip roll is obtained by vulcanization and polishing under pressure. The vulcanization temperature is equal to or higher than the decomposition temperature of the peroxide used.
An adhesive layer may be interposed between the core metal and the rubber layer. The hardness of the adhesive layer is not particularly limited, but is preferably equal to or higher than the rubber hardness of the surface rubber layer in terms of pressure resistance when using a roll and prevention of peeling of the adhesive layer due to chemicals. Examples of the adhesive layer include, but are not particularly limited to, rubber types such as epoxidized rubber that have excellent adhesion to the core metal.

When the obtained nip roll is used in a polarizing film production application, the rubber layer surface hardness (JIS Type A) is preferably 60 to 85 and a tensile strength of 12 to 30 MPa with a rubber hardness meter.
If the rubber hardness of the surface is less than 60, the life and friction resistance of the roll will deteriorate. On the other hand, when the rubber hardness of the surface exceeds 85, the cushioning property is deteriorated, which may adversely affect the film to be processed. The rubber hardness (JIS Type A) of the surface is more preferably 65-80.

  Furthermore, the rubber layer in the present invention has a tensile strength of 12 to 30 MPa, preferably 12 to 20 MPa. If the tensile strength is less than 12 MPa, the wear resistance is poor, a large amount of wear occurs during use, and foreign matter may be mixed. On the other hand, when the tensile strength exceeds 30 MPa, when the surface of the rubber layer is polished, the polishing property is poor and finishing may be difficult.

Rubber layers in the nip rolls of the present invention, the accelerated deterioration test described below, a range weight change of ^{+ 150g / m 2 ~-50g} / m 2, the surface hardness (JIS Type A) changes ± rubber hardness meter It is preferable that the tensile strength is maintained at 70% or more, preferably 80% or more.

The nip roll according to the present invention having such characteristics is placed before and after the treatment bath for stretching the film, and stretching is performed by giving a difference in peripheral speed to these nip rolls.
In addition, you may stretch by installing a nip roll in a processing bath.

Considering the productivity of the nip roll according to the present invention, it is preferable that the surface rubber layer contains EPDM vulcanized with peroxide as a main component and carbon black. That is, since the nip roll usually has a diameter of 300 mm or more and a surface length of 2500 mm or more, in order to produce such a relatively large nip roll, a molding method using a press machine or the like cannot be employed. A rubber sheet is prepared, and the core is coated with rubber by using a method such as so-called ribbon molding, in which the rubber sheet is wound around a core metal or a ribbon-like unvulcanized rubber is extruded. In that case, the joint of the rubber sheet or ribbon occurs, and in some cases, there may be defects in the part, but by vulcanizing with peroxide as described above and containing carbon black It is possible to suppress or prevent the occurrence of defects at the seam.
Here, the carbon black may be 40 to 80 parts by weight with respect to 100 parts by weight of the total amount of the rubber material mainly composed of EPDM forming the rubber layer.

  Next, the manufacturing method of the polarizing film which uses the nip roll concerning this invention is demonstrated. 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 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 subjecting this unstretched film to swelling treatment, dyeing treatment, crosslinking treatment, water washing treatment, and finally drying is about 5 to 50 μm, for example.

  The polarizing film according to the present invention is a polyvinyl alcohol uniaxially stretched film in which a dichroic dye is adsorbed and oriented. As a method for producing the polarizing film, an unstretched polyvinyl alcohol film is swollen with an aqueous solution, dyed, In this method, solution treatment is performed in the order of acid crosslinking treatment and water washing treatment, uniaxial stretching is performed in a wet manner in the boric acid crosslinking treatment step and / or the previous step, and finally drying is performed.

  In the above 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. The stretching method is inter-roll stretching in which stretching is performed with a difference in peripheral speed between two nip rolls that transport the film. Moreover, there is no restriction | limiting in the number of processing baths, processing conditions, etc.

  The swelling treatment step is performed for the purpose of removing foreign matter on 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 the unstretched raw film from the beginning, the film is immersed in an aqueous solution of 10 ° C. to 50 ° C., preferably 20 ° C. to 40 ° C., for example. The immersion time of the film is about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds.

  In the swelling process, problems such as the film swelling in the width direction and wrinkling into the film are likely to occur. 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 wt% to 10 wt% 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. As the dichroic dye, either iodine or a dichroic dye can be used, but iodine is usually used. 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. For example, the case where iodine is used as the dichroic dye will be described as an example. The temperature is 10 ° C. to 45 ° C., preferably 20 ° C. to 35 ° C., and iodine / KI / water = 0.003 to 0 by weight ratio. The immersion treatment is performed at a concentration of 2 / 0.1 to 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 boric acid treatment as the following crosslinking 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.

  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. Further, after the swelling treatment, the polyvinyl alcohol film may be subjected to a wet stretching treatment before the dyeing treatment.

  In the present invention, the boric acid crosslinking treatment is performed by immersing in an aqueous solution containing boric acid as a crosslinking agent. The boric acid crosslinking treatment liquid preferably contains 4 parts by weight or more of boric acid with respect to 100 parts by weight of water, more preferably 4 to 6 parts by weight. Along with boric acid, crosslinking agents such as borax, glyoxal, and glutaraldehyde can also be used. In general, an iodide or the like is used in addition to the crosslinking agent. Examples of iodide include potassium iodide and zinc iodide, and potassium iodide is usually used. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and the like may coexist. A preferable composition of the boric acid crosslinking treatment liquid contains 4 to 6 parts by weight of boric acid with respect to 100 parts by weight of water.

  The treatment conditions using the boric acid crosslinking treatment solution are preferably a treatment temperature of 50 ° C. or more and a treatment time of 50 seconds or less. When the treatment temperature is below 50 ° C., the crosslinking treatment is insufficient and the final optical properties are difficult to obtain. The treatment temperature is usually preferably 60 ° C. or lower. When processing temperature exceeds 60 degreeC, there exists a tendency for the external appearance of a film to be impaired. The treatment time is preferably 50 seconds or less, and the lower limit of the treatment time is usually about 30 seconds.

  After the boric acid crosslinking treatment, the film is washed. This washing treatment is performed, for example, by immersing the polyvinyl alcohol film subjected to the boric acid crosslinking treatment in washing water such as pure water, spraying the washing water as a shower, or using both immersion and spraying. The cleaning process may be performed in multiple stages of two or more stages. In this case, the processing conditions of each stage may be the same or different within the above range.

  In the present invention, uniaxial stretching is performed in at least one step before or during the swelling treatment, dyeing treatment, and boric acid crosslinking treatment step. Or you may add the wet extending process for performing uniaxial stretching between said processes. Uniaxial stretching may be performed in one step, but may be performed in a plurality of steps. Examples of the stretching method include inter-roll stretching in which stretching is performed with a difference in peripheral speed between the two nip rolls that transport the film. In addition, the polyvinyl alcohol film may be uniaxially stretched in advance in a gas such as air or an inert gas before the swelling step. The final cumulative draw ratio is 4.5 to 7.0 times, preferably 5.0 to 6.5 times.

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-based 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.

  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 provided with 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.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, this invention is not limited by these examples.

[Example 1]
“Esprene 501A” (iodine number 12) manufactured by Sumitomo Chemical Co., Ltd. was used as EPDM, dicumyl peroxide was used as the organic peroxide, and a rubber composition was blended according to the following formulation.
EPDM 100 parts by weight Carbon black 50 parts by weight Paraffin oil 5 parts by weight Stearic acid 1 part by weight Zinc white 5 parts by weight Organic peroxide 3 parts by weight The unvulcanized rubber sheet having a thickness of about 1.5 mm was prepared and prepared. The rubber sheet was laminated several times on a metal core which had been previously blasted and coated with an adhesive to cover the rubber. Thus, a rubber roll having a rubber layer with a thickness of 35 mm on the surface was molded. Subsequently, vulcanization was performed at a pressure of 0.5 MPa and a temperature of 160 ° C. for 480 minutes, and after cooling, polishing was performed to obtain a nip roll of Example 1 having a rubber layer with a thickness of 25 mm on the roll surface.

[Comparative Example 1]
Instead of EPDM, NBR (“Nipol DN1042” manufactured by Zeon Corporation) was used as a vulcanizing agent, and a rubber composition was blended according to the following formulation.
NBR 100 parts by weight Carbon black 50 parts by weight Naphthenic process oil 5 parts by weight Stearic acid 1 part by weight Zinc white 5 parts by weight Sulfur 2 parts by weight Vulcanization accelerator (Noxeller DM) 2 parts by weight After sufficiently kneading, it is placed on a calendar machine to prepare and prepare an unvulcanized rubber sheet having a thickness of about 1.5 mm. The surface was previously blasted, and a rubber sheet was laminated several times on the core metal coated with an adhesive to cover the rubber. Thus, a rubber roll having a rubber layer with a thickness of 35 mm on the surface was molded. Subsequently, vulcanization was performed for 480 minutes at a pressure of 0.5 MPa and a temperature of 160 ° C., and after cooling, polishing was performed to obtain a nip roll of Comparative Example 1 having a rubber layer with a thickness of 25 mm on the roll surface.

[Comparative Example 2]
A nip roll of Comparative Example 2 was obtained in the same manner as in Example 1 except that 2.0 parts by weight of sulfur and an appropriate amount of a vulcanization accelerator were blended in place of the organic peroxide.

<Deterioration acceleration test>
Instead of the nip rolls obtained in Example 1 and Comparative Examples 1 and 2, a sample made of a sheet having a thickness of 2 mm was produced under substantially the same conditions as these. Next, each sample was immersed for 4 weeks in an aqueous solution at 70 ° C. containing 7 parts by weight of boric acid, 20 parts by weight of potassium iodide, and 1 mol of iodine, and changes in physical property values before and after immersion were examined. Evaluation items and evaluation methods are as follows.

(1) Weight change The dry weight of the sample before and after immersion was measured to examine the weight change, and evaluated according to the following criteria. It can be seen that the greater the change in weight, the more significant the swelling.
(Criteria for weight change)
A: was + 50 g / m ² or less or -20g / m ² or more.
B: It was +50 to +150 g / m ² or -20 to −50 g / m ² .
C: It was +150 to +350 g / m ² or −50 to −100 g / m ² .
D: + 300g / m was ² or more or -100 g / m ² or less.

(2) Change in hardness The hardness of the sample before and after the immersion was measured with a hardness meter JIS Type A to examine the change in hardness and evaluated according to the following criteria.
(Criteria for hardness change)
A: It was within the range of ± 2.
B: More than ± 2 and within a range of ± 5.
C: Over ± 5 and within the range of ± 15.
D: It was +16 or more or -16 or less.

(3) Tensile strength retention The tensile strength of samples before and after immersion was measured according to JIS K6251 to examine the tensile strength retention, and evaluated according to the following criteria.
(Criteria for maintaining tensile strength)
A: The tensile strength was maintained at 90% or more.
B: The tensile strength was maintained at 80% or more and less than 90%.
C: The tensile strength was maintained at 70% or more and less than 80%.
D: Tensile strength decreased to less than 70%.

表１から、実施例１は全ての項目で比較例１よりも劣化が少なく、しかも過酸化物で架橋した実施例１は、硫黄で架橋した比較例２よりも劣化が少ないことがわかる。 The evaluation results are shown in Table 1. Unless there is a particular problem, each sample is called Example 1 and Comparative Examples 1 and 2 which are the same as the corresponding nip rolls.

From Table 1, it can be seen that Example 1 is less degraded than Comparative Example 1 in all items, and that Example 1 crosslinked with peroxide is less degraded than Comparative Example 2 crosslinked with sulfur.

[Example 2]
(Manufacture of polarizing film)
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, the film was immersed in a boric acid crosslinking treatment liquid having a composition of 5.0 parts by weight of boric acid, 12 parts by weight of potassium iodide, and 100 parts by weight of water at a temperature of 54 ° C. Uniaxial stretching was performed until the cumulative stretching ratio from the original fabric reached 5.9 times. At that time, the nip rolls obtained in Example 1 were respectively installed before and after the boric acid crosslinking treatment tank and uniaxially stretched.
Subsequently, a washing treatment was performed in pure water at 15 ° C. for 9 seconds. Next, it was dried at a temperature of 60 ° C. for 2 minutes to obtain a polarizing film.
Although the polarizing film was continuously produced for 12 weeks using the production process of Example 2, troubles such as film breakage did not occur. On the other hand, when the nip roll of Comparative Example 1 was used, film breakage often occurred during the same period of operation.

<Change in friction coefficient>
In the above-described stretching operation of Example 2, the friction coefficient of each nip roll surface obtained in Example 1 and Comparative Examples 1 and 2 was measured before and after stretching, and the rate of change (decrease rate) was measured. In this case, the static friction coefficient of the nip roll surface before stretching was 0.5 or more.
Evaluation of friction coefficient change was performed according to the following criteria.
A: The rate of change of the coefficient of friction was less than 10% (that is, the coefficient of friction was hardly changed).
B: The change rate of the friction coefficient was 10% or more and less than 20%.
C: The change rate of the coefficient of friction was 20% or more and less than 30%.
D: The rate of change of the friction coefficient was 30% or more (that is, the friction coefficient was greatly reduced).
The evaluation results are shown in Table 2.

Claims (2)

  A nip roll for producing a polarizing film, characterized in that at least the surface is a rubber layer mainly containing EPDM containing carbon black and vulcanized with a peroxide.   A polyvinyl alcohol film is treated in the order of swelling treatment, dyeing treatment, boric acid treatment, water washing treatment and drying treatment, and before the swelling treatment, dyeing treatment and boric acid treatment step, and / or swelling treatment, dyeing. In a method for producing a polarizing film by stretching a film by providing a peripheral speed difference between two nip rolls transporting a film during at least one of the treatment and boric acid treatment, the nip roll according to claim 1. A method for producing a polarizing film, wherein the nip roll is described.