JP5034600B2 - Manufacturing method of polarizing film - Google Patents

Description

The present invention relates to a method for producing a polarizing film that is produced as a roll-like long product and has little variation in optical characteristics in the width direction . If laminating a transparent protective film on at least one side of the polarizing film obtained by this method, a polarizing plate is Ru can be produced.

  A polarizing film is widely used as a film obtained by adsorbing and orienting a dichroic dye on a polyvinyl alcohol resin film. An iodine polarizing film using iodine as a dichroic dye, a dye polarizing film using a dichroic direct dye as a dichroic dye, and the like are known. These polarizing films are usually used as polarizing plates by laminating a transparent protective film such as triacetyl cellulose via an adhesive made of an aqueous solution of a polyvinyl alcohol resin on one or both surfaces thereof.

  As a method for producing a polarizing film, for example, in JP-A-10-153709 (Patent Document 1), a polyvinyl alcohol resin film is immersed in water to swell, then dyed with iodine, then stretched, A method is described in which boric acid treatment (in other words, water resistance treatment by cross-linking) is performed in order to fix the resin, followed by washing with water and drying. The swelling treatment with water is performed for the purpose of uniformly swelling the film prior to dyeing, shortening the dyeing time, and improving dyeing unevenness. At this time, from the viewpoint of uneven dyeing and the like, in Patent Document 1, boric acid is contained in the swelling treatment bath. Also, in this document 1, after dyeing, the film is immersed in an aqueous solution containing boric acid and stretched, and then further immersed in an aqueous boric acid solution to perform water resistance treatment by crosslinking (referred to as fixing or fixing in this document). Is going.

  JP-A-6-281816 (Patent Document 2) describes that a chloride such as lithium chloride or zinc chloride is added to a swelling treatment bath in order to sufficiently swell the film. JP 2001-141926 A (Patent Document 3) discloses that a polyvinyl alcohol-based resin film is immersed in a water bath to swell in order to reduce dyeing unevenness, and 1.1 to 4 times stretching treatment. After that, it is described that a polarizing film is produced by performing a dyeing treatment and a crosslinking treatment with a dichroic dye.

  Further, JP-A-2005-114990 (Patent Document 4) discloses that treatment is carried out continuously in a bath in the order of swelling treatment, dyeing treatment and boric acid treatment, and at least one of these is uniaxially stretched. When manufacturing a polarizing film, a wet stretching process is provided after the swelling process and before the dyeing process, and in the wet stretching process, the film is uniaxially stretched in a boric acid aqueous solution at a stretching ratio of 1.1 to 3 times. Thus, further improvement in color unevenness is described.

JP-A-10-153709 JP-A-6-281816 JP 2001-141926 A JP 2005-114990 A

  The present inventors have further studied on a method for producing a polarizing film by providing a wet stretching step after the swelling treatment and before the dyeing treatment as shown in Patent Document 4 above. As a result, it has been clarified that the polarizing film obtained by this method is less likely to cause color unevenness, but tends to vary in hue between the central portion and the end portion in the width direction of the roll film. Then, this invention makes it a subject to provide the method of manufacturing the polarizing film and polarizing plate with the optical characteristic in the width direction, especially a high uniformity of a hue.

As a result of intensive studies to solve the above-mentioned problems, the present inventors continuously passed the polyvinyl alcohol-based resin film in the order of the swelling treatment step, the water immersion treatment step, the dyeing treatment step, and the boric acid treatment step. When a polarizing film is produced by uniaxially stretching in both the dyeing process and the boric acid process, the film machine is used in the water immersion process between the swelling process and the dyeing process. The inventors have found a new fact that a polarizing film with high optical uniformity can be obtained by reducing the stretching ratio in the direction as much as possible, and have completed the present invention.

That is, the production method of the polarizing film according to the present invention, a polyvinyl alcohol film, the swelling process, water immersion treatment step, is passed through in the order of the dyeing process and boric acid treatment continuously treated, polarization When manufacturing the film, in the water immersion treatment step, the polyvinyl alcohol-based resin film is treated so as to have a draw ratio of 1 to 1.05 times with respect to the machine direction, and the dyeing treatment step and boric acid are performed. Uniaxial stretching is performed in both of the treatment steps so that the cumulative draw ratio from the swelling treatment step to the boric acid treatment step is 4.5 to 8 times .

In the swelling treatment step, the ratio of the peripheral speed of the outlet side transport roll to the peripheral speed of the inlet side transport roll of the swelling tank for performing the treatment in pure water substantially free of dissolved components is 1.2 to 2. It is done to be doubled. The water immersion treatment step is also performed in pure water substantially free from dissolved components . Water immersion treatment step This is preferably carried out at a temperature of 10 to 50 ° C..

After producing a polarizing film in front Symbol manner, by laminating a transparent protective film on at least one side of the polarizing film obtained, polarizer Ru can be produced. This transparent protective film may have any function of a retardation film, a brightness enhancement film, a viewing angle improvement film, and a transflective film. Or at least 1 sort (s) chosen from a retardation film, a brightness improvement film, a viewing angle improvement film, and a transflective film is pasted on the polarizing plate which pasted a transparent protective film on at least one side, and an optical layered product. It can also be manufactured.

  According to the present invention, a water immersion treatment step is provided between the swelling treatment step and the dyeing treatment step, and in this water immersion treatment step, by reducing the draw ratio with respect to the machine direction of the film, There is an effect that a polarizing film having high optical characteristics in the width direction of the produced film, in particular, high uniformity of hue can be obtained.

Hereinafter, the present invention will be described in detail. In the present invention, the polyvinyl alcohol-based resin film is continuously processed in the order of the swelling treatment step, the water immersion treatment step, the dyeing treatment step, and the boric acid treatment step, and the dyeing treatment step and the boric acid treatment step. Both are uniaxially stretched to produce a polarizing film. In view of the continuous treatment, the polyvinyl alcohol-based resin film is usually supplied in roll form. In FIG. 1, the example of arrangement | positioning of an apparatus suitable for enforcing the manufacturing method of the polarizing film which concerns on this invention was shown typically.

  In the example shown in FIG. 1, the polyvinyl alcohol-based raw film 1 fed out from the raw roll 2 has a swelling tank 3 for performing a swelling treatment, a water immersion tank 4 for carrying out a water immersion treatment, and a dyeing treatment. The dyeing tank 5 and the boric acid tank 6 for performing boric acid treatment are sequentially passed. After leaving the boric acid tank 6, the polyvinyl alcohol-based resin film usually passes through the water washing tank 7, the unreacted boric acid aqueous solution adhering to the previous tank is washed away, and then dried through the drying furnace 8. Thus, the polarizing film 9 can be obtained. Although illustration is omitted, after that, usually, a transparent protective film is bonded to at least one surface of the obtained polarizing film to form a polarizing plate.

[Polyvinyl alcohol resin]
Specifically, the polyvinyl alcohol resin used as the raw material of the polarizing film is a saponified polyvinyl acetate resin. The saponification degree of the polyvinyl alcohol resin is 85 mol% or more, preferably 90 mol% or more, and more preferably 99 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. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, unsaturated amines, and the like. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

  These polyvinyl alcohol-based resins may be modified. For example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and the like modified with aldehydes may be used. Usually, an unstretched film of a polyvinyl alcohol-based resin having a thickness of 20 to 100 μm, preferably 30 to 80 μm is used as the original film of the polarizing film. Industrially, the width of the film is practically about 1,500 to 6,000 mm.

[Manufacture of polarizing film]
The raw fabric film 1 sequentially passes through the swelling tank 3, the water immersion tank 4, the dyeing tank 5, and the boric acid tank 6 and is subjected to each treatment. After leaving the boric acid tank 6, it is washed with water in a water washing tank 7 and finally dried in a drying furnace 8. The thickness of the polyvinyl alcohol polarizing film thus obtained is, for example, about 1 to 50 μm. In addition, although the example which provided the swelling tank 3, the water immersion tank 4, the dyeing tank 5, the boric acid tank 6, and the water washing tank 7 one each was shown in FIG. 1, in each process, it was as needed. A plurality of tanks may be provided.

[Swelling treatment]
The raw film 1 is first subjected to a swelling treatment in a swelling tank 3. This swelling treatment is performed for the purpose of removing foreign matter from the film surface, removing the plasticizer in the film, imparting easy dyeability in a subsequent process, and plasticizing the film. The conditions for the swelling treatment are determined within a range in which these objects can be achieved and in a range in which problems such as extreme dissolution and devitrification of the substrate film do not occur. The swelling treatment is performed by immersing the unstretched raw film in a treatment bath at a temperature of 10 to 50 ° C., preferably 20 to 50 ° C., for example. The swelling treatment time is about 5 to 300 seconds, preferably about 20 to 240 seconds.

In the swelling process, the film swells in the width direction and wrinkles into the film, so problems such as expansion rolls, spiral rolls, crown rolls, cross guiders, bend bars, tenter clips, etc. It is preferable to transport the film while removing the wrinkles. 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, since the film in the running direction of the film to swell expanding, in order to eliminate the slack in the conveying direction of the film, that taken by the hand stage that will control the speed of the transport rolls before and after the Rise Junso 3. Specifically, the ratio of the peripheral speed of the outlet-side transport roll to the peripheral speed of the inlet-side transport roll of the swelling tank 3 (hereinafter sometimes referred to as roll speed ratio) is 1.2 according to the temperature of the treatment bath. It should be in the range of ~ 2 times. Further, if desired, uniaxial stretching can be performed in this step.

The treatment bath used in the swelling tank 3 is pure water, boric acid as described in Patent Document 1 (Japanese Patent Laid-Open No. 10-153709), and Patent Document 2 (Japanese Patent Laid-Open No. 6-281816). is chloride such as, also, other inorganic acids, other inorganic salts, Ru to Rukoto More an aqueous solution water soluble organic solvents, such as alcohols is added in a range of 0.01 to 10 wt% according to . However, in the present invention, in the swelling bath 3, which need use is substantially free of dissolved components deionized water.

[Water immersion treatment]
The polyvinyl alcohol-based resin film after the swelling treatment is drained and then subjected to a water immersion treatment in the water immersion tank 4. This water immersion treatment is carried out in order to adjust the water absorption state in the film width direction and to increase the mechanical properties of the film and further the uniformity of the optical properties of the finally obtained polarizing film. In this step, the film is processed at a draw ratio of 1 to 1.05 times with respect to the machine direction (MD, that is, the running direction of the film). A draw ratio of 1 means that the film does not stretch or shrink in the machine direction. Since a series of steps is performed with a tension that does not loosen the film in the running direction, the draw ratio in this step is not usually less than 1 times, but when the draw ratio exceeds 1.05 times, There exists a tendency for the uniformity of the optical characteristic in the obtained polarizing film to worsen.

The treatment bath used in the water immersion tank 4 is pure water substantially free of dissolved components. When this treatment bath contains a chemical such as boric acid, the uniformity of the film tends to be impaired. Moreover, it is preferable that the temperature of the bath used for this water immersion process is 10-50 degreeC. If the temperature of the treatment bath is lower than 10 ° C, a large-scale cooling facility is required for temperature control, which is uneconomical. Conversely, if it exceeds 50 ° C, the film may be dissolved .

[Dyeing]
After the water immersion treatment, the film is dyed in the dyeing tank 5. The dyeing process with a normal dichroic dye is performed for the purpose of adsorbing the dichroic dye on the film. The processing conditions are determined within a range in which such an object can be achieved, and within a range in which problems such as extreme dissolution and devitrification of the base film do not occur.

  When iodine is used as the dichroic dye, for example, iodine is 0.003 to 0.2 parts by weight and iodine at a temperature of 10 to 50 ° C., preferably 20 to 40 ° C., and 100 parts by weight of water. The dyeing treatment is performed by immersing in an aqueous solution containing 0.1 to 10 parts by weight of potassium halide for 10 to 600 seconds, preferably 30 to 200 seconds. Instead of potassium iodide, other iodides such as zinc iodide may be used. Other iodides may be used in combination with potassium iodide. Furthermore, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc. may coexist. Even when boric acid is added, it is distinguished from the subsequent boric acid treatment in that it contains iodine. Any bath 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 bath.

  On the other hand, when a water-soluble dichroic dye is used as the dichroic dye, the dichroic dye is used at a temperature of, for example, 20 to 80 ° C., preferably 30 to 60 ° C., and 100 parts by weight of water. The dyeing treatment is performed by immersing in an aqueous solution containing 001 to 0.1 parts by weight for 10 to 600 seconds, preferably 20 to 300 seconds. The aqueous solution of the dichroic dye to be used may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. Only one type of dichroic dye may be used, or two or more types of dichroic dyes may be used in combination according to the desired hue.

In the dyeing process, as in the swelling process, an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar, and the like may be appropriately installed in the dyeing bath and / or at the bath entrance / exit. In this dyeing process, to facilities uniaxially stretched in the machine direction at the same time.

[Boric acid treatment]
After the dyeing process, boric acid treatment is performed in the boric acid tank 6. This boric acid treatment is performed by immersing a polyvinyl alcohol-based resin 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 iodine is used as the dichroic dye, the boric acid treatment bath preferably contains about 0.1 to 30 parts by weight of iodide with respect to 100 parts by weight of water in addition to boric acid.

  Examples of iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfite, potassium sulfate, sodium sulfate, etc. may coexist.

  This boric acid treatment is carried out for water resistance and hue adjustment (to prevent bluish ting) by crosslinking. For the purpose of water resistance by cross-linking, a cross-linking agent such as glyoxal or glutaraldehyde can be used together with boric acid as necessary. The boric acid treatment for water resistance is sometimes referred to as water resistance treatment, crosslinking treatment, immobilization treatment, or the like. Further, boric acid treatment is regarded as hue adjustment, and is sometimes referred to as complementary color processing, toning processing, or the like.

  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 preferably carried out under the following conditions.

  When the raw film is sequentially subjected to swelling, water immersion, dyeing, and boric acid treatment, when boric acid treatment aims at water resistance by crosslinking, about 3 parts of boric acid is added to 100 parts by weight of water. An aqueous solution containing 10 to 10 parts by weight and about 1 to 20 parts by weight of iodide is used as a boric acid treatment bath, and is usually performed at a temperature of 50 to 70 ° C, preferably 53 to 65 ° C. The treatment time is usually about 10 to 600 seconds, preferably 20 to 300 seconds, more preferably 20 to 100 seconds.

  After performing boric acid treatment for water resistance, boric acid treatment for hue adjustment may be further performed. For example, when the dichroic dye is iodine, an aqueous solution containing about 1 to 5 parts by weight of boric acid and about 3 to 30 parts by weight of iodide for 100 parts by weight of water is used for this purpose. It is an acid treatment bath and is usually performed at a temperature of about 10 to 45 ° C. The immersion time is usually about 1 to 300 seconds, preferably 2 to 100 seconds. The boric acid treatment for hue adjustment is usually performed at a lower temperature than the boric acid treatment for water resistance.

Therefore, this boric acid treatment may be performed in a plurality of tanks, and usually 1 to 5 tanks are often arranged. When a plurality of tanks are arranged, the film sequentially passes through each tank and the film is subjected to boric acid treatment. When arrange | positioning a some tank, the aqueous solution composition and temperature of each boric-acid processing tank to be used may be the same within the said range, or may differ. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment may be performed in a plurality of tanks, respectively. Also in boration step, similar to the dyeing process, to facilities uniaxially stretched in the machine direction of the film. The final integrated draw ratio ranging from swelling step boration step is from about 4.5 to 8 times, preferably 5-7 times.

[Post-treatment after boric acid treatment]
After the boric acid treatment, a water washing treatment is performed in the water washing tank 7. The water washing treatment is, for example, a method in which a polyvinyl alcohol-based resin film treated with boric acid for water resistance and / or hue adjustment is immersed in water, a method in which water is sprayed as a shower, or a method in which immersion and spraying are used in combination. Etc. The temperature of water in the water washing treatment is usually about 2 to 40 ° C., and the treatment time is usually about 2 to 120 seconds. After washing with water, the film is guided to a drying furnace 8 to dry the film. This drying is performed for about 30 to 600 seconds in a drying furnace 8 maintained at a temperature of about 40 to 100 ° C.

[Uniaxial stretching]
In the present invention, uniaxial stretching is performed in both the dyeing process and the boric acid process . Extending Shin, for example, by a method of attaching a peripheral speed difference to the bath inlet side transport rolls of the transport roll and the tank outlet side of the can be performed. Incidentally, the final cumulative stretching ratio is from about 4.5 to 8 times as described above, and further has good preferable to 5 to 7 times. The cumulative stretching ratio here means how long the reference length in the length direction of the original film is in the film after completion of all stretching treatments, and in the swelling treatment process and water immersion treatment process When the film is stretched, the value including those stretches is obtained. For example, if the portion that was 1 m in the original fabric film is 5 m in all the films after the stretching process, the cumulative stretching ratio at that time is 5 times.

[Production of polarizing plate]
Thus, the manufactured polarizing film can make a polarizing plate by sticking a transparent protective film on the at least single side | surface with an adhesive agent. As the transparent 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 polycarbonate resin Examples thereof include a film and a film made of a cycloolefin resin having a cyclic olefin such as norbornene as a main monomer. Examples of commercially available thermoplastic cycloolefin resins include “Topas” sold by Ticona, Germany, “Arton” sold by JSR, and ZEON Corporation. "Zeonor" and "Zeonex" sold by the company, "Apel" (all trade names) sold by Mitsui Chemicals. When a film formed from such a cycloolefin-based resin is used as a protective film, a known method such as a solvent casting method or a melt extrusion method is appropriately used for film formation. Formed cycloolefin resin films are also commercially available, such as “Essina” and “SCA40” sold by Sekisui Chemical Co., Ltd.

  The thickness of the transparent protective film is preferably thin. However, if it is too thin, the strength is lowered and the processability is inferior. On the other hand, if it is too thick, the transparency is lowered and the curing time required after lamination is increased. Problems occur. Therefore, an appropriate thickness of the protective film is, for example, about 5 to 200 μm, preferably 10 to 150 μm, and more preferably 10 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 transparent protective film may be subjected to surface treatments such as antiglare treatment, antireflection treatment, hard coat treatment, antistatic treatment, and antifouling treatment, either singly or in combination of two or more. 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. The transparent protective film may be bonded to one side of the polarizing film or may be bonded to both sides.

  The polarizing film and the transparent protective film are laminated using an adhesive such as an aqueous solvent adhesive, an organic solvent adhesive, a hot melt adhesive, or a solventless adhesive. Examples of the aqueous solvent-based adhesive include a polyvinyl alcohol-based resin aqueous solution and an aqueous two-component urethane emulsion adhesive, and the organic solvent-based adhesive includes, for example, a two-component urethane adhesive. Examples of the mold adhesive include a one-pack type urethane adhesive and an epoxy adhesive.

  When an acetylcellulose-based film whose surface to be bonded to the polarizing film is hydrophilized by saponification or the like is used as a protective film, a polyvinyl alcohol-based resin aqueous solution is suitably used as an adhesive. Polyvinyl alcohol resins used as adhesives include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as other single quantities copolymerizable with vinyl acetate. And vinyl alcohol copolymers obtained by saponifying the copolymer with the polymer, and modified polyvinyl alcohol polymers obtained by partially modifying the hydroxyl groups. You may mix | blend a polyvalent aldehyde, a water-soluble epoxy compound, a melamine type compound, etc. with this adhesive agent as a crosslinking agent.

  The method for laminating the polarizing film and the transparent 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 overlapped on the coated surface and rolled. The method of pasting and drying by etc. is mentioned.

  Usually, an adhesive agent is apply | coated at the temperature of 15-40 degreeC after preparation, and the bonding temperature is the range of about 15-30 degreeC normally. After pasting, a drying treatment is performed to remove a solvent such as water contained in the adhesive, and the drying temperature at this time is usually in the range of 30 to 100 ° C., preferably 40 to 80 ° C. Thereafter, the adhesive may be cured by curing for about 1 to 90 days under a temperature environment of 15 to 85 ° C, preferably 20 to 50 ° C, more preferably 35 to 45 ° C. When the protective film is an acetylcellulose-based resin, it exhibits sufficient adhesive strength without being subjected to such curing, but a protective film made of other resin is used, and a polarizing film through an aqueous solvent-based adhesive When pasting, it is preferable to apply the curing as described above. When this curing period is long, productivity is deteriorated. Therefore, the curing period is preferably about 1 to 14 days, and more 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 transparent 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, and a function as an optical compensation film. An optical function can be provided. 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, and an optical compensation film on the surface of the transparent protective film, such a function is achieved. In addition, the transparent protective film itself can be provided with such a function. Further, the transparent 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-mentioned transparent protective film is subjected to a stretching treatment described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, etc., or a treatment described in Japanese Patent No. 3168850, etc. A function as a film can be imparted. The retardation characteristics of the retardation film can be appropriately selected, for example, such that the front retardation value is in the range of 5 to 100 nm and the thickness direction retardation value is in the range of 40 to 300 nm. Further, two layers having different center wavelengths of selective reflection are formed in the transparent protective film by forming micropores by a method as described in JP 2002-169025 A or JP 2003-29030 A. By superimposing the above cholesteric liquid crystal layer, a function as a brightness enhancement film can be imparted.

  When a metal thin film is formed on the transparent protective film by vapor deposition or sputtering, a function as a reflective film or a transflective film can be imparted. By coating the transparent 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 transparent protective film. Further, various optical functional films may be directly bonded to the polarizing film using an appropriate adhesive. Examples of commercially available optical functional films include brightness enhancement films such as “DBEF” (trade name) sold by 3M Company (Sumitomo 3M Co., Ltd. in Japan) and Fuji Film Co., Ltd. A viewing angle improving film such as “WV film” (trade name), and a retardation film such as “Sumikalite” (trade name) sold by Sumitomo Chemical Co., Ltd.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not limited by these examples. In the following examples and comparative examples, as shown schematically in FIG. 1, a swelling tank 3, a water immersion layer 4, a dyeing tank 5, a boric acid tank 6, a water washing tank 7, and a drying furnace 8 are sequentially arranged. In addition, various treatments were performed while a long film of polyvinyl alcohol was conveyed by a continuous conveyance device combining a nip roll and a free roll. The raw film 1 includes a polyvinyl alcohol film having a polymerization degree of 2,400, a saponification degree of 99.9 mol% or more, a thickness of 75 μm, and a width of 3,000 mm [“Kuraray Vinylon VF-PS # 7500 manufactured by Kuraray Co., Ltd.” "]" Was used. Stretching was performed with a difference in peripheral speed between the driving nip rolls before and after the treatment tank.

Moreover, the uniformity of the optical characteristics of the obtained polarizing film was evaluated by the b ^* value of the parallel hue. The parallel hue means a hue when natural light is applied in a state where the two polarizing films are overlapped so that the respective absorption axes are the same, and the b ^* value thereof is the parallel spectral transmittance Tp ( λ) is obtained for a continuous wavelength region or at predetermined wavelength intervals, and is calculated according to JIS Z 8729.

The parallel transmittance means the transmittance when natural light is applied in a state where the two polarizing films are overlapped so that the respective absorption axes are the same. Therefore, the parallel spectral transmittance Tp (λ ) Means the transmittance when natural light of wavelength λ is applied in a state where the two polarizing films are overlapped so that the respective absorption axes are the same, this is a value obtained by the method shown below. Is equivalent to That is, linearly polarized light having a wavelength λ is applied to one polarizing film in a direction parallel to the absorption axis, the spectral transmittance k1 (λ) at that time is measured, and then the wavelength λ is perpendicular to the absorption axis. And the spectral transmittance k2 (λ) at that time is measured. The transmittance (parallel spectral transmittance) when the two polarizing films are overlapped so that the respective absorption axes are the same and the natural light of wavelength λ is applied is the transmittance k1 (λ) twice. Since the transmittance {k1 (λ)} ² after passing through the film and the transmittance {k2 (λ)} ² after passing through the film twice at the transmittance k2 (λ) are equal to each other, From these values, the parallel spectral transmittance Tp (λ) at the wavelength λ is obtained by the following equation (I).

Tp (λ) = [{k1 (λ)} ² + {k2 (λ)} ² ] / 2 (I)

These measurements and calculations are performed for continuous wavelength regions or at predetermined wavelength intervals, and b ^{* of the} parallel hue is calculated from the parallel spectral transmittance Tp (λ) at each wavelength λ according to JIS Z 8729. Note that the spectral transmittances k1 (λ) and k2 (λ) and the parallel spectral transmittance Tp (λ) mentioned here are not displayed in%, but are values displayed with 1 being the maximum value. If you want to do that, multiply it by 100.

[Example 1]
First, the film was sufficiently swollen by immersing it in a swelling tank 3 containing pure water at 30 ° C. for about 80 seconds while keeping the tension state of the film so that the original film 1 was not loosened. The roll speed ratio between the inlet and the outlet accompanying the swelling in the swelling tank 3 was 1.2. After draining with a nip roll, it was immersed for about 160 seconds in the water immersion tank 4 containing 30 degreeC pure water. The draw ratio in the machine direction in this tank was 1.04 times. Next, uniaxial stretching was performed at a draw ratio of about 1.5 times while being immersed in the dyeing tank 5 containing an aqueous solution of iodine / potassium iodide / water in a weight ratio of 0.02 / 1.5 / 100. Then, while being immersed in a boric acid tank 6 containing an aqueous solution of potassium iodide / boric acid / water in a weight ratio of 12/5/100 at about 56.5 ° C. for about 130 seconds, the total draw ratio from the original fabric is 5 Uniaxial stretching was performed until it became 3 times. Finally, it was washed with pure water at 9 ° C. for about 16 seconds in the water washing tank 7 and then dried at about 60 ° C. for 160 seconds in the drying furnace 8 to obtain an iodine-based polarizing film.

The obtained polarizing film was to determine the b ^* value of parallel hue in b ^* values and the widthwise end portions of the parallel hue in the width direction central portion. As a result, the difference between the two was 2.1.

  A polarizing plate is obtained by bonding protective films made of triacetyl cellulose to both surfaces of this polarizing film via an adhesive made of an aqueous solution of a polyvinyl alcohol resin. In addition, a protective film made of triacetyl cellulose on one side of the polarizing film, a protective film made of norbornene resin on the other side, and an adhesive made of an aqueous solution of a polyvinyl alcohol resin, respectively, or a solventless type A polarizing plate can also be obtained by pasting through an adhesive.

[Comparative Example 1]
First, the film was sufficiently swollen by immersing it in a swelling tank 3 containing pure water at 30 ° C. for about 50 seconds while keeping the tension of the film so that the original film 1 did not loosen. After draining with a nip roll, it was immersed in a water immersion tank 4 containing 30 ° C. pure water for about 160 seconds, and stretched in this tank at a stretching ratio of 1.20 times in the machine direction. Thereafter, in the same manner as in Example 1, uniaxial stretching in the dyeing tank 5, uniaxial stretching in the boric acid tank 6, washing with water, and drying were performed to obtain a polarizing film.

The obtained polarizing film was to determine the b ^* value of parallel hue in b ^* values and the widthwise end portions of the parallel hue in the width direction central portion. As a result, the difference between the two was 4.9.

  According to the method of the present invention, a polarizing film or a polarizing plate having high uniformity of optical properties in the width direction of a film produced as a roll-like long product can be obtained. The polarizing plate chip cut out from the polarizing plate into various sizes exhibits substantially the same optical characteristics between the individual sheets, and can be effectively applied to various display devices including a liquid crystal display device.

It is a figure which shows typically the example of arrangement | positioning of an apparatus suitable for enforcing the method of this invention.

1 …… Original film of polyvinyl alcohol resin
2 ... Original roll,
3 ... swelling tank,
4 ... Water immersion bath
5 …… Dyeing tank,
6 …… Boric acid tank,
7 …… Washing tank,
8 ... drying oven,
9: Polarizing film.

Claims (3)

A polyvinyl alcohol-based resin film is a method for producing a polarizing film by sequentially passing a polyvinyl alcohol resin film in the order of a swelling treatment step, a water immersion treatment step, a dyeing treatment step, and a boric acid treatment step,
In the swelling treatment step, the ratio of the peripheral speed of the outlet side transport roll to the peripheral speed of the inlet side transport roll of the swelling tank for performing the treatment in pure water substantially free of dissolved components is 1.2 to 2. Do it twice,
In the water immersion treatment step, the polyvinyl alcohol-based resin film is treated so as to have a draw ratio of 1 to 1.05 times with respect to the machine direction in pure water substantially free of dissolved components,
Perform uniaxial stretching in both the dyeing process and the boric acid process,
The cumulative draw ratio from the swelling treatment step to the boric acid treatment step is 4.5 to 8 times,
A method for producing a polarizing film.   The method according to claim 1, wherein the water immersion treatment step is performed at a temperature of 10 to 50 ° C. The method according to claim 1 or 2 integrated stretching ratio from Rise Jun process leading to the boric acid treatment step is made to be 5 to 7 times.

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