JP2006189560A - Method for manufacturing polarizing film, polarizing plate and optical laminate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a polarizing film less liable to crease or break and having good appearance because of few streaks. <P>SOLUTION: In the method for manufacturing the polarizing film by sequentially subjecting a polyvinyl alcohol-based film to swelling, dyeing, boric acid treatment, washing and drying, the drying is carried out in multiple steps while applying tension to the film, the tension is controlled so that tension per unit width of the film in each step of the drying is made substantially constant, tension in the succeeding step is made lower than that in the preceding step, and a drying temperature in the succeeding step is made higher than that in the preceding step. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a polarizing film with less wrinkles and film breakage and less streaking and good appearance, a polarizing plate in which a protective film is laminated on at least one side of the obtained polarizing film, and a retardation film In addition, the present invention relates to an optical laminate in which any one of a brightness enhancement film, a viewing angle improvement film, and a transflective film is bonded alone or in combination.

  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, and the polyvinyl alcohol film is dyed with the dichroic dye, stretched, and then the polyvinyl alcohol film is used to fix iodine to the film. A method of drying after acid treatment, washing with water is known. At this time, tension is applied to the film by giving a peripheral speed difference to the nip roll before and after the treatment bath, the film is stretched, the film transport direction is changed by the guide roll, and the film is introduced into and removed from the treatment liquid. Yes.

Conventionally, the drying process of a film is performed in one step (for example, refer to Patent Document 1 and Patent Document 2). At this time, wrinkles may occur in the film or the film may break. Moreover, when the obtained polarizing film was observed under the reflection of a fluorescent lamp, many streaks were sometimes observed, and the appearance was not always good.
JP-A-10-153709 JP 2001-174634 A

  The main problem to be solved by the present invention is to provide a method for producing a polarizing film having a good appearance with few wrinkles and breakage of the film, less streaks.

  As a result of intensive studies on a method for producing a polarizing film with less wrinkling and film breakage, the present inventors have conducted drying treatment in multiple stages while applying tension to the film, and in each stage of the drying treatment If the tension is controlled so that the tension per unit width of the film is substantially constant, and the subsequent tension is less than or equal to the preceding tension, the film can be produced with less wrinkling and film breakage, and in that case In addition, when the subsequent drying temperature is higher than the previous drying temperature, it has been found that a polarizing film with less streaks and good appearance can be obtained, and the present invention has been completed.

  That is, the method for producing a polarizing film of the present invention is a method for producing a polarizing film by treating a polyvinyl alcohol film in the order of swelling treatment, dyeing treatment, boric acid treatment, water washing treatment and drying treatment. It is characterized by performing in multiple stages while applying tension, controlling the tension so that the tension per unit width of the film in each stage of the drying process is substantially constant, and performing the latter stage tension below the former stage tension. This makes it possible to produce fewer wrinkles and breakage of the film.

  Furthermore, the drying temperature in the latter stage is higher than the drying temperature in the former stage, and this makes it possible to obtain a polarizing film with few streaks and good appearance.

  The drying process is usually performed in two stages, the tension at the former stage is set from the range of 600 to 1500 N / m, the tension at the latter stage is set from the range of 300 to 1200 N / m, and the drying temperature at the former stage is set to 50 to From the range of 90 ° C., the subsequent drying temperature is set from the range of 70 to 100 ° C.

  Furthermore, the polarizing plate of the present invention is obtained by bonding a protective film to at least one surface of the polarizing film obtained as described above. This protective film may have any function of a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film. The optical laminate is obtained by bonding at least one selected from a retardation plate, a brightness enhancement film, a viewing angle improvement film, and a transflective plate to the polarizing plate having a protective film bonded to at least one surface. is there.

  By the method of the present invention, the polarizing film can be produced with less wrinkles and less rupture of the film, and a polarizing film with less streaking and good appearance can be produced. A high-quality liquid crystal display can be obtained by using a polarizing plate and an optical laminate produced from a polarizing film with few streaks and good appearance in a liquid crystal display device.

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. The degree of saponification is about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% to 100 mol%. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymer. Examples include coalescence. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol 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, an unstretched film of a polyvinyl alcohol-based resin film having a thickness of about 20 μm to 100 μm, preferably about 30 μm to 80 μm is used as a starting material for manufacturing a polarizing film. Industrially, the width of the film is practically about 1500 mm to 4000 mm.
The unstretched film is processed 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 μm 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 there are no restrictions on the number of treatment baths or treatment conditions.
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 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. The immersion time of the film is about 30 seconds to 300 seconds, more preferably about 60 seconds to 240 seconds. 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. 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 swelling of the film in the width direction and wrinkling of the film are likely to occur. It is preferable to transport the film while removing wrinkles of the film with an apparatus. 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 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. 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, at a temperature of about 10 ° C. to 45 ° C., preferably about 20 ° C. to 35 ° C., and in a weight ratio, iodine / KI / water = about 0.003 to 0.2 / The immersion treatment is performed at a concentration of 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. 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 about 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, at a temperature of about 20 ° C. to 80 ° C., preferably about 30 ° C. to 70 ° C., and a weight ratio of dichroic dye / water = about 0.001. The immersion treatment is performed at a concentration of about 0.1 / 100 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 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, 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.

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 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 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. And is usually performed at a temperature of about 10 ° C to 45 ° C. The immersion time is 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 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 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.

In each step after the stretching treatment, tension control may be performed so that the tension of the film becomes substantially constant.
When stretching is completed in the dyeing process, tension control is performed in the subsequent boric acid treatment process and the water washing process. 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. It is preferable to perform tension control in each process from the treatment process to the water washing process, but industrially, the film was stretched in the boric acid treatment process from the first or the first to the second stage, and the stretching process was performed. It is more preferable to perform tension control in each step from the boric acid treatment step next to the boric acid treatment step to the water washing step.
When the above-described iodide treatment or zinc treatment is performed after the boric acid treatment, tension control is also performed for these steps.

The tension in each step from the swelling treatment to the water washing treatment may be the same or 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, the drying treatment is performed in multiple stages while applying tension to the film. The tension is controlled so that the tension per unit width of the film in each stage is substantially constant, and the tension in the subsequent stage is less than the tension in the previous stage. That is, when the tension (N / m) per unit width of the film in each stage is N ₁ , N ₂ , N ₃ ... In order from the first stage, N ₁ ≧ N ₂ ≧ N ₃ ≧. N ₁ , N ₂ , N ₃ ... Are set so as to satisfy
As a result, the film can be produced with less wrinkles and less rupture of the film.

Furthermore, in the present invention, the drying temperature in the subsequent stage is higher than the drying temperature in the previous stage. That, T ₁ in order to drying temperature (℃) in each stage from the first stage, T _2, T ₃ when the _{···, T 1 ≦ T 2 ≦} T 3 ≦ ··· to satisfy T ₁ , T ₂ , T ₃ ... Are set.
As a result, a polarizing film with few streaks and good appearance can be obtained.

  The drying process is preferably carried out in a large number of stages by changing the tension little by little, but is naturally limited due to restrictions on equipment and is usually carried out in 2 to 3 stages. When performed in two stages, the tension in the front stage is set from the range of 600 to 1500 N / m, and the tension in the rear stage is set from the range of 300 to 1200 N / m. If the tension is too large, the film will be broken, and if it is too small, wrinkles will increase, which is not preferable.

  Furthermore, at this time, the drying temperature of the former stage is set from the range of 50 to 90 ° C., and the drying temperature of the latter stage is set from the range of 70 to 100 ° C. If the temperature is too high, the film will be ruptured and the optical properties will be lowered. If the temperature is too low, streaks will increase, which is not preferable.

  The drying process time is 60 to 600 seconds, and the drying time in each stage may be the same or different. If the time is too long, the optical properties deteriorate, and if it is too short, the drying becomes insufficient, which is not preferable.

As the nip roll for controlling the tension in the present invention and the guide roll for controlling the film transport direction, a rubber roll, a stainless steel polishing roll and a sponge rubber roll are used.
The rubber roll is made of NBR or the like, and its hardness is about 60 to 90 degrees, preferably about 70 to 80 degrees on the JIS Shore C scale measured by the test method of JIS K 6301, and the surface roughness is JIS B 0601 (surface roughness). It is preferably about 0.1 to 5S, preferably about 0.5 to 1 in terms of the average distance S between the local peaks of the roughness curve.
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, 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.
As the sponge rubber roll, the hardness of the sponge is about 20 to 60 degrees, preferably about 25 to 50 degrees on the JIS Shore C scale measured by the test method of JIS K 6301, and the density is about 0.4 to 0.6 g / cm 3. Preferably, it is about 10-30S, preferably about 15-25S, expressed as an average distance S between local peaks of a roughness curve of about 0.42 to 0.57 g / cm3 and a surface roughness of JIS B 0601 (surface roughness). It is preferable that

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. Accordingly, a suitable thickness of the protective film is, for example, about 5 to 200 μm, preferably about 10 to 150 μm, and 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 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 about 15-40 degreeC after preparation, and the bonding temperature is the range of about 15-30 degreeC normally. After pasting, a drying treatment is performed to remove a solvent such as water contained in the adhesive, and the drying temperature in this case is usually about 30 to 85 ° C, preferably about 40 to 80 ° C. . Thereafter, the adhesive may be cured by curing for about 1 to 90 days under a temperature environment of about 15 to 85 ° C, preferably about 20 to 50 ° C, more preferably about 35 to 45 ° C. When this curing period is long, productivity deteriorates, so the curing period is about 1 to 30 days, preferably about 1 to 7 days.
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 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 above 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, although an Example is shown and this invention is demonstrated further more concretely, this invention is not limited by 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 kept in a 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, uniaxial stretching was performed while immersing in an aqueous solution of iodine / potassium iodide / water at a weight ratio of 0.02 / 1.5 / 100. Then, uniaxial stretching is performed until the cumulative draw ratio from the original fabric reaches 5.9 times while being immersed in a 60 ° C. aqueous solution of potassium iodide / boric acid / water at a weight ratio of 10/5/100 and water-resistant. It was. Furthermore, it was immersed in an aqueous solution of potassium iodide / boric acid / water at a weight ratio of 20/3/100 at 30 ° C. for about 30 seconds, and further washed with pure water at 10 ° C. for about 10 seconds.
Next, the film washed with water was dried at 80 ° C. for 120 seconds while applying a tension of 850 N / m in the first drying process, and subsequently, a tension of 670 N / m was applied to the film in the second drying process. However, the film was dried at 85 ° C. for 180 seconds to obtain a polarizing film.
A polyvinyl alcohol-based adhesive was applied to both surfaces of this polarizing film, and a protective film (a triacetyl cellulose film (thickness: 80 μm) having a saponified surface was bonded to both surfaces to obtain a polarizing plate.
There was little wrinkle generation on the film in the drying step, and no breakage of the film occurred. Moreover, when the obtained polarizing plate was observed under the reflection of a fluorescent lamp, the appearance was good with few streaks.

Comparative Example 1
A polarizing plate was produced in the same manner as in Example 1 except that the tension applied to the film in the first drying treatment was 670 N / m and the tension applied to the film in the second drying treatment was 850 N / m.
There were many wrinkles on the film in the drying process, and the film was broken. Further, when the obtained polarizing plate was observed under the reflection of a fluorescent lamp, there were few streaks.

Comparative Example 2
A polarizing plate was produced in the same manner as in Comparative Example 1 except that the temperature in the first drying treatment was 85 ° C. and the temperature in the second drying treatment was 80 ° C.
There were many wrinkles on the film in the drying process, and the film was broken. Moreover, when the obtained polarizing plate was observed under the reflection of a fluorescent lamp, it had many streaks and poor appearance.

Claims (7)

  In a method for producing a polarizing film by treating a polyvinyl alcohol film in the order of swelling treatment, dyeing treatment, boric acid treatment, water washing treatment and drying treatment, the drying treatment is performed in multiple stages while applying tension to the film, A method for producing a polarizing film, wherein tension is controlled so that the tension per unit width of the film in each stage is substantially constant, and the latter stage tension is less than or equal to the former stage tension.   The method for producing a polarizing film according to claim 1, wherein the drying temperature in the latter stage is higher than the drying temperature in the former stage.   The manufacturing method of the polarizing film of Claim 1 which performs a drying process in 2 steps | paragraphs, and sets and sets the tension | tensile_strength in a back | latter stage from the range of 300-1200 N / m from the range of 600-1500 N / m.   The manufacturing method of the polarizing film of Claim 2 which performs a drying process in 2 steps | paragraphs, and sets the drying temperature of a back | latter stage from the range of 70-100 degreeC from the range of 50-90 degreeC.   The polarizing plate by which a protective film is bonded by the at least single side | surface of the polarizing film manufactured by the method of Claims 1-3.   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.