JP4581689B2 - Manufacturing method of polarizing film - Google Patents

Description

The present invention relates to a method of more color unevenness less, to produce a uniform polarization film having a thickness.

  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 at least one surface, preferably both surfaces, with 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).
In recent years, with an increase in the quality of liquid crystal display devices in which a polarizing film is used, there is a demand for a polarizing film having a uniform film thickness with less color unevenness than a polarizing film obtained by a conventional method.
JP-A-10-170721

  The main problem to be solved by the present invention is to provide a method for producing a polarizing film with less color unevenness and a uniform film thickness.

As a result of intensive studies to produce a polarizing film with less color unevenness and a uniform film thickness, the present inventors have made contact with the roll when the film is immersed in a boric acid solution in the boric acid treatment step. When the time from when the film is immersed to when it first comes into contact with the roll in the boric acid solution is set to 0.4 to 1.8 seconds, there is less unevenness in color and the polarization is uniform. The inventors have found that a film can be obtained and have completed the present invention.

That is, in the method for producing a polarizing film of the present invention, a polyvinyl alcohol film is processed in the order of swelling treatment, dyeing treatment, boric acid treatment, water washing treatment and drying treatment, and film transport is performed in at least two treatment steps. In a method for producing a polarizing film by applying a peripheral speed difference between two nip rolls to produce a polarizing film, the film is immersed in a boric acid solution in a non-contact state when the film is immersed in a boric acid solution. The time from the immersion of the film to the first contact with the roll in the boric acid solution is 0.4 to 1.8 seconds.

The time from the immersion of the film to the initial contact with the roll in the boric acid solution is preferably 0.5 seconds or more .
The temperature of the boric acid solution is preferably 50 to 85 ° C.

At least pasted protective film on one surface of the polarizing film obtained as before reporting, Ru can be a polarizing plate. This protective film may have any function of a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film. Further, the polarizing plate stuck a protective film on one side even without low, the phase difference plate, a brightness enhancement film, pasted at least one selected from the viewing angle improving film and the semi-transmissive reflective plate, the optical stack Ru can also be a.

By the method of the present invention, a polarizing film with less color unevenness and a uniform film thickness can be produced, and by using a polarizing plate or an optical laminate produced from this polarizing film for a liquid crystal display device, it is thin. 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. Saponification degree of about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% to 100 mol%. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymer. Examples include coalescence. As the other copolymerizable monomers, for example, unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids and the like. The degree of polymerization of the polyvinyl alcohol-based resin is about 1000 to 10000, preferably about 1500 to 5000.

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 the polarizing film manufacturing, thickness of about 20 m to 100 m, preferably polyvinyl alcohol is used based resin unstretched film fat about 30Myuemu～80myuemu. Industrially, the width of the film is practically about 1500 mm to 4000 mm. The unstretched film is treated in the order of swelling treatment, dyeing treatment, boric acid treatment, and water washing treatment, and finally dried to obtain a polyvinyl alcohol polarizing film having a thickness of, for example , about 5 to 50 μm.

The manufacturing method of a dichroic dye to a polyvinyl alcohol-based uniaxially stretched film adsorbed orientation, there are roughly divided into two methods. One after uniaxial stretching a polyvinyl alcohol film in air or an inert gas, swelling, dyeing treatment, and solution treatment in the order of boration and water washing, a method of performing finally dried, second is The unstretched polyvinyl alcohol film is subjected to solution treatment in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment with an aqueous solution, and then uniaxially stretched in a wet manner in the boric acid treatment step and / or the previous step. This is a method of drying.

In the present invention, in any manner, uniaxial stretching is carried out in multiple 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. Although the order of the basic steps are as above reporting, the number of the treatment bath or, like the constraints have greens process conditions. It goes without saying that also is free to insert the name has steps described above SL process 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 on the film surface, removing the plasticizer in the film, imparting easy dyeability in the next step, and plasticizing the film. Treatment conditions, the range of these objectives can be achieved, and extreme dissolution of the base film, is determined by the malfunction does not occur range such devitrification. When the film previously stretched in gas is swollen, for example, the film is immersed in an aqueous solution of about 20 ° C. to 70 ° C., preferably about 30 ° C. to 60 ° C. Immersion time of the film is about 30 to 300 seconds, preferably a further approximately 60 seconds to 240 second. When the unstretched raw film is swollen from the beginning, the film is immersed in an aqueous solution of, for example, about 10 ° C to 50 ° C, preferably about 20 ° C to 40 ° C. Immersion time of the film is about 30 to 300 seconds, preferably a further approximately 60 seconds to 240 second.

In the swelling treatment step, problems such as swelling of the film in the width direction and wrinkling of the film are likely to occur. Therefore, a known wide roll (expander roll), spiral roll, crown roll, cross guider, bend bar, tenter clip, etc. It is preferable to transport the film while removing the wrinkles of the film with a widening device. In order to stabilize the film transport in the bath, the water flow in the swelling bath is controlled by 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, than even the film in the running direction of the film to swell expanding, sagging such a Kusutame the transport direction of the film, it is preferable to take means such as controlling the speed of the transport rolls before and after the example processing tank . 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 about 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. Treatment conditions, the range of these objectives can be achieved, and extreme dissolution of the base film, is determined by the malfunction does not occur range such devitrification. When iodine is used as the dichroic dye, for example, about 10 ° C. to 45 ° C., preferably at a temperature of about 20 ° C. to 35 ° C., and an iodine / KI / water = about a weight ratio from 0.003 to 0. The immersion treatment is performed at a concentration of 2 / about 0.1 to 10/100 for about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds. Instead of potassium iodide, other iodides such as zinc iodide may be used. In addition, the other iodide but it may also 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 about 0.003 part by weight or more of iodine with respect to 100 parts by weight of water can be regarded as a dyeing tank.

In the case of using a water-soluble dichroic dye as the dichroic dye, for example, about 20 ° C. to 80 ° C., preferably at a temperature of about 30 ° C. to 70 ° C., and a weight ratio dichroic dye / water = about 0 The immersion treatment is performed at a concentration of 0.001 to 0.1100 for about 30 seconds to 600 seconds, preferably about 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 carried out by a method such as to have a peripheral speed difference before and after the nip rolls of dyeing tank. Similarly to the swelling step, a widening roll (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.

Boric acid treatment is carried out by a boric acid aqueous solution having about 1-10 parts by weight containing respect to 100 parts by weight of water, immersing the polyvinyl alcohol-based film dyed with a dichroic dye. When the dichroic dye is iodine, it is preferable to contain about 1 to 30 parts by weight of iodide.
The iodide, potassium iodide, and the like zinc iodide is. Further, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, but it may also be allowed to coexist, such as sodium sulfate.
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 glyoxal or glutaraldehyde can be used in addition to or together with boric acid, if necessary.
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.

This boric acid treatment is performed by appropriately changing the concentrations of boric acid and iodide and the temperature of the treatment bath according to the purpose.
The boric acid treatment for water resistance and the boric acid treatment for hue adjustment are not particularly distinguished, but are carried out under the following conditions.
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 about 50 ° C. to 70 ° C., preferably about 55 ° C. to 65 ° C. The immersion time is usually about 30 to 600 seconds, preferably about 60 to 420 seconds, and more preferably about 90 to 300 seconds.
In addition, when dye | staining and boric-acid treatment the film extended | stretched previously, the temperature of a boric-acid treatment bath is about 50 to 85 degreeC normally, Preferably it is about 55 to 80 degreeC.

After the boric acid treatment for water-resistant, but it may also be made of boric acid treatment for the hue adjustment. 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. And is usually carried out at a temperature of about 10 ° C to 45 ° C. Immersion time usually, about 3 to 300 seconds, preferably about 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 treatment rather it may also be carried out in multiple steps, usually performed are often in 2-5 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 water boration for reduction, the boric acid treatment for hue adjustment but it may also be carried out in a plurality of steps.
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 about 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 water temperature in the water 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 each step after the stretching treatment, tension control may be performed so that the tension of the film becomes substantially constant.
If you exit the stretching in dyeing step, the tension control in subsequent boration step and water washing treatment step. When stretching is completed in the previous process of the dyeing process, tension control is performed in 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 boric acid treatment step from the beginning or the first to the second step, and the next boric acid treatment step after the boric acid treatment step in which the stretching treatment is performed. Tension control is performed in each step from the acid treatment step to the water washing step, or the film is stretched in the boric acid treatment step from the first to the third stage, and the boric acid next to the boric acid treatment step in which the stretching treatment is performed. Although it is preferable to perform tension control in each process from the treatment process to the water washing process, industrially. The film is stretched in the boric acid treatment process from the beginning or the first to the second stage, and tension control is performed in each process from the boric acid treatment process to the water washing process following the boric acid treatment process in which the stretching process was performed. Is more preferable.
When the above-described iodide treatment or zinc treatment is performed after the boric acid treatment, tension control is also performed for these steps.

Tension in each of the process rather than good may be the same, but it may also be different.
The tension to the film in the tension control is not particularly limited, and is appropriately set within a range of about 150 N / m to 2000 N / m, preferably about 600 N / m to 1500 N / m per unit width. When the tension is less than about 150 N / m, the film is likely to be wrinkled. On the other hand, if the tension exceeds about 2000 N / m, problems such as film breakage and shortened life due to bearing wear occur. The tension per unit width is calculated from the film width near the entrance of the process and the tension value of the tension detector.
In addition, when tension control is performed, there are cases where the film is inevitably slightly stretched or shrunk, but in the present invention, this is not included in the stretching process.

In the present invention, when the film is immersed in the boric acid solution in the boric acid treatment step, the film is immersed in a non-contact state in the roll. When it is carried out in contact with the roll, color unevenness occurs and the film thickness in the film width direction becomes non-uniform. The time from when the film is immersed to when it first contacts the roll in the boric acid solution is 0.4 to 5 seconds, preferably 0.5 to 3 seconds. This time is adjusted in consideration of the roll arrangement position and the film transport speed.
If the time until contact with the roll is too short, color unevenness occurs, and the film thickness in the film width direction becomes non-uniform. If it is too long, wrinkles occur and the film thickness becomes non-uniform.
When a protective film is bonded to a polarizing film having uneven color to form a polarizing plate, uneven color is similarly seen, which is not preferable. If a polarizing film having a non-uniform film thickness or wrinkles is used as a polarizing plate, it is not preferred because it tends to break and is inferior in durability.

Rubber rolls, stainless steel polishing rolls and sponge rubber rolls are used as nip rolls and guide rolls used in the present invention, including rolls that first contact in boric acid solution.
The rubber roll is made of NBR or the like and has a hardness of about 60 to 90 degrees, further about 70 to 80 degrees on a JIS Shore C scale measured by a test method of JIS K 6301 , and a surface roughness of JIS B 0601 ( surface roughness) of the roughness of approximately expressed as the mean spacing S of local peaks of the curve 0.1～5S, it is further preferably about 0.5 to 1 S.
The stainless steel polishing roll is made of SUS304, SUS316 or the like, and in order to make the film thickness uniform, the surface roughness is the average distance S between the local peaks of the roughness curve of JIS B 0601 (surface roughness). And a coefficient of dynamic friction of about 0.1 to 0.4, more preferably about 0.15 to 0.35 is preferable. The dynamic friction coefficient in this invention is represented by the value measured in the polyvinyl alcohol-type film and water based on the test method of JISK7125.
The sponge rubber roll has a sponge hardness of about 20 to 60 degrees, further about 25 to 50 degrees on a JIS Shore C scale measured by a test method of JIS K 6301 , and a density of about 0.4 to 0.6 g / cm ³ , or even about 0.42 to 0.57 g / cm ³ , and the surface roughness is about 10 to 30 S expressed by the average interval S between the local peaks of the roughness curve of JIS B 0601 (surface roughness). Further , it is preferably about 15 to 25S.

When the guide roll in the treatment liquid is a widening roll, this is preferably a sponge rubber widening roll. In particular, in the swelling treatment step, it is preferable to use a sponge rubber widening roll. In the swelling treatment step, the polyvinyl alcohol film swells in both the longitudinal and width directions due to absorption of the bath solution, but particularly when the tension is applied without the swelling in the width direction ending, wrinkles and folds are generated on the roll. The use of a sponge rubber widening roll makes it possible to greatly reduce the tension applied to the film due to its light weight, and at the same time, because of the high film gripping force based on its high surface roughness, even a low tension is sufficient. can exert a widening force, and another is the role meandering prevention function of the widening roll also maximize, wrinkles are reduced, Orekomi such is Kunar. The use of the sponge rubber widening roll is not limited to the swelling treatment, and can be used in other treatments.

  A polarizing plate is obtained by bonding a protective film with an adhesive on at least one surface 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” (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 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. Accordingly, a suitable thickness of the protective film is, for example, about 5 to 200 μm, preferably about 10 to 150 μm, more preferably about 20 to 100 μm.

  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, anti-glare treatment, anti-reflection treatment, hard coat treatment, antistatic treatment, surface treatment, such as anti-fouling process but it may also have been subjected alone or in combination. Further, the protective film and / or protective film surface protective layer benzophenone compounds, and ultraviolet absorbers such as benzotriazole compounds, phenyl phosphate compounds, but it may also have a plasticizer such as phthalic acid ester 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. This adhesive, polyvalent aldehydes, water-soluble epoxy compound, but it may also be used as additives, such as melamine compounds.

  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, after made adhesive tone is applied at a temperature of about 15 to 40 ° C., bonding temperature is usually in a range of about 15 to 30 ° C.. 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.
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.

The protection film, functions as a retardation film, a function as a brightness enhancement film, functions as a reflection film, functions as a semi-transmissive reflective film, functions as a diffusion film, etc. functions as an optical compensation film, an optical functional Can also be given. 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.

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, by 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 : Sumika light (registered trademark) (manufactured by Sumitomo Chemical Co., Ltd.) but it may also be pasted directly on the polarizing film commercially available optical functional film of the retardation film, etc., such as.

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

Example 1
A 75 μm-thick polyvinyl alcohol film (Kurarevinylon VF-PS # 7500, polymerization degree 2,400, saponification degree 99.9 mol% or more) is put in pure water at about 30 ° C. so that the film does not loosen. The film was sufficiently swollen by being immersed for about 130 seconds while being kept. Next, uniaxial stretching (total stretching ratio so far: 3.2 times) was performed while dyeing by immersion in an aqueous solution of iodine / potassium iodide / water in a weight ratio of 0.02 / 1.5 / 100. It was. After that, it is immersed in an approximately 55 ° C. aqueous solution of potassium iodide / boric acid / water at a weight ratio of 10/5/100 in a non-contact state with the roll, and the time from the immersion to the contact with the first guide roll is determined. and 1.8 seconds to borated, cumulative stretching ratio from raw makes a uniaxially stretched until 5.9 times. After boric acid treatment, it was washed with pure water at about 10 ° C. for about 10 seconds. After washing with water and drying at about 80 ° C. for 2 minutes, an iodine-based polarizing film having a thickness of about 28 μm was obtained. An NBR rubber roll having a surface roughness of 0.6 S and a rubber hardness (JIS Shore A scale) of 80 degrees was used as the first submerged guide roll in the boric acid treatment tank. Stretching was performed with a difference in peripheral speed between nip rolls arranged before and after the treatment tank.
The obtained polarizing film was not observed color irregularities due to stretching, was a uniform film thickness in the film width direction.

Polyvinyl alcohol-based adhesive was applied to both sides of the obtained polarizing film, and a protective film [Triacetylcellulose film with surface saponification treatment, “Fujitac (registered trademark) T80UNL”, manufactured by Fuji Photo Film Co., Ltd., 80 μm thickness] was bonded to both sides and dried at about 60 ° C. for about 5 minutes to obtain a polarizing plate. There was no uneven color on the polarizing plate.

Example 2
The first contact after immersion in the boric acid solution is an NBR rubber nip roll with a surface roughness of 0.6S and rubber hardness (JIS Shore A scale) of 80 degrees. except for using 0.6 seconds to obtain a polarizing film in the same manner as in example 1.
The obtained polarizing film did not show uneven color due to stretching, and was a film having a uniform film thickness in the film width direction.
A polarizing plate was produced in the same manner as in Example 1 using the obtained polarizing film. There was no uneven color on the polarizing plate.

Example 3
To a first submerged guide rolls boration bath, surface roughness 0.2 S, except that the dynamic friction coefficient is a stainless steel polishing roll is 0.24, the polarizing film in the same manner as in Example 1 Got.
The obtained polarizing film was not observed color irregularities due to stretching, was a uniform film thickness in the film width direction.
A polarizing plate was produced in the same manner as in Example 1 using the obtained polarizing film. There was no uneven color on the polarizing plate.

Example 4
A sponge rubber roll having a sponge hardness of 25 degrees on a JIS Shore C scale, a density of 0.42 g / cm ³ , and a surface roughness of 20S was used as the first submerged guide roll in the boric acid treatment tank. Except for this , a polarizing film was obtained in the same manner as in Example 1.
The obtained polarizing film was not observed color irregularities due to stretching, was a uniform film thickness in the film width direction.
A polarizing plate was produced in the same manner as in Example 1 using the obtained polarizing film. There was no uneven color on the polarizing plate.

Comparative Example 1
Surface roughness 0.6S, except that immersed in rubber hardness (JIS Shore A scale) borate solution while in contact with the NBR rubber nip rolls is 80 degrees, to obtain a polarizing film in the same manner as in Example 1.
The resulting polarizing film showed 12 color irregularities due to stretching. Moreover, it was a film with nonuniform film thickness in the film width direction.

Comparative Example 2
The first contact after immersion in the boric acid solution is an NBR rubber nip roll having a surface roughness of 0.6S and a rubber hardness (JIS Shore A scale) of 80 degrees, and the time from immersion to contact with the nip roll. except that the 0.2 seconds is to obtain a polarizing film in the same manner as in example 1.
In the obtained polarizing film, five color irregularities due to stretching were observed. Moreover, it was a film with nonuniform film thickness in the film width direction.

Claims (2)

A polyvinyl alcohol film is processed in the order of swelling treatment, dyeing treatment, boric acid treatment, water washing treatment, and drying treatment, and a peripheral speed difference is imparted between two nip rolls that transport the film in at least two treatment steps. In the method of producing a polarizing film by stretching the film,
When the film is immersed in the boric acid solution in the boric acid treatment step, the time from when the film is immersed in a non-contact state until the film first contacts the roll in the boric acid solution is 0.4. -A manufacturing method of a polarizing film characterized by being 1.8 seconds. The method for producing a polarizing film according to claim 1 , wherein the temperature of the boric acid solution is 50 to 85 ° C.