KR20080088425A - Manufacturing method of polarizing film and manufacturing method of polarizing plate - Google Patents

Abstract

The swelling treatment step in the swelling tank 3, the water immersion treatment step in the water immersion tank 4, the dyeing treatment step in the dyeing tank 5, and the boric acid bath of the raw film 1 of polyvinyl alcohol-based resin Water immersion when passing through the boric acid treatment step in (6), followed by continuous treatment and uniaxially stretching in one or more of the dye bath (5) and the boric acid bath (6) to produce the polarizing film (9). In tank (4), the polyvinyl alcohol-based resin film is treated so as to have a draw ratio of 1 to 1.05 times of the machine direction. It is preferable that the bath of the water immersion tank 4 is pure water substantially free of a dissolution component. A transparent protective film is bonded to at least one surface of the obtained polarizing film 9, and a polarizing plate is manufactured.

Description

A process for producing a polarizing film and a process for producing a polarizer

This invention relates to the manufacturing method of the polarizing film manufactured as a roll-shaped long object, and the variation of the optical characteristic of the width direction with little, and the manufacturing method of the polarizing plate which laminated | stacked the transparent protective film on at least one surface of the said polarizing film.

The polarizing film is obtained by adsorbing or aligning a dichroic dye to a polyvinyl alcohol-based resin film and is widely used. And the iodine type polarizing film which uses iodine as a dichroic dye, the dye type polarizing film which uses a dichroic direct dye as a dichroic dye, etc. are known. These polarizing films can be normally made into a polarizing plate by bonding transparent protective films, such as triacetyl cellulose, to the one side or both sides through the adhesive agent containing the aqueous solution of polyvinyl alcohol-type resin.

As a manufacturing method of a polarizing film, for example, Unexamined-Japanese-Patent No. 10-153709 (patent document 1) swells a polyvinyl alcohol-type resin film in water, swells, and dyes with iodine, and then extends In addition, a method of boric acid treatment (in other words, water resistance treatment by crosslinking) in order to fix iodine, washing with water, and then drying are described. The swelling treatment with water is performed to uniformly swell the film prior to dyeing, to shorten the dyeing time, to improve dyeing unevenness, and the like. At this time, boron acid is contained in the swelling treatment bath in Patent Literature 1 in view of dyeing unevenness and the like. In addition, in this document 1, after dyeing, the film is immersed in an aqueous solution containing boric acid to be stretched, and then further immersed in an aqueous boric acid solution to thereby carry out a water-resistant treatment by crosslinking (hereinafter referred to as fixation or fixation). Doing.

Japanese Patent Laid-Open No. 6-281816 (Patent Document 2) describes adding chlorides such as lithium chloride and zinc chloride to the swelling treatment bath in order to sufficiently swell the film. In addition, Japanese Unexamined Patent Application Publication No. 2001-141926 (Patent Document 3) discloses that polyvinyl alcohol-based resin films are swelled and swelled in a water bath to reduce dyeing unevenness, and a stretching treatment of 1.1 to 4 times is performed. It is described to manufacture a polarizing film by carrying out the dyeing | staining process and crosslinking process by a dichroic dye after that.

In addition, Japanese Unexamined Patent Publication No. 2005-114990 (Patent Document 4) treats continuously in a bath in order of a swelling process, a dyeing process, and a boric acid process, and also uniaxially stretches in at least one of these polarizing films. To prepare a wet stretching process after the swelling treatment and before the dyeing treatment, and in the wet stretching process, uniaxial stretching is performed at a draw ratio of 1.1 times or more and less than 3 times in an aqueous solution of boric acid, thereby further improving color unevenness. Is described.

[Patent Document 1] Japanese Patent Application Laid-Open No. 10-153709

[Patent Document 2] Japanese Unexamined Patent Publication No. 6-281816

[Patent Document 3] Japanese Unexamined Patent Application Publication No. 2001-141926

[Patent Document 4] Japanese Patent Application Laid-Open No. 2005-114990

The inventors of the present invention have further studied a method for producing a polarizing film by providing a wet stretching step after the swelling treatment and before the dyeing treatment, as disclosed in Patent Document 4. As a result, although the polarization film obtained by this method has little generation | occurrence | production of a color nonuniformity, it turned out that a change tends to change in color in the width direction center part and the edge part of a roll film. Accordingly, an object of the present invention is to provide a method for producing a polarizing film and a polarizing plate having high optical properties in the width direction, in particular, uniformity of color.

MEANS TO SOLVE THE PROBLEM As a result of earnestly researching in order to solve the said subject, the present inventors passed a polyvinyl alcohol-type resin film in a swelling process process, a water immersion process process, a dyeing process process, and a boric acid process process, and processes it continuously, and dyes. When producing a polarizing film by uniaxial stretching in at least one of the treatment step and the boric acid treatment step, in the water immersion treatment step between the swelling treatment step and the dyeing treatment step, the stretching ratio in the machine direction of the film is as long as possible. By making it small, the new fact that a polarizing film with high optical uniformity is obtained was discovered and the present invention was completed.

That is, the manufacturing method of the polarizing film which concerns on this invention passes a polyvinyl alcohol-type resin film in a swelling process process, a water immersion process process, a dyeing process, and a boric acid process in order, and processes it continuously, and a dyeing process and When producing a polarizing film by uniaxial stretching in at least one of the boric acid treatment step, the water immersion treatment step is to process the polyvinyl alcohol-based resin film to have a draw ratio of 1 to 1.05 times the machine direction. will be.

It is preferable to perform the said water immersion treatment process at the temperature of 10-50 degreeC. In addition, it is preferable to perform this water immersion treatment process in the pure water without a dissolving component.

Moreover, after manufacturing a polarizing film by the said method, the manufacturing method of the polarizing plate which concerns on this invention bonds a transparent protective film to at least one surface of the polarizing film obtained. This transparent protective film can be equipped with arbitrary functions of retardation film, a brightness improving film, a viewing angle improvement film, and a semi-transmissive reflective film. Or an optical laminated body can also be manufactured by bonding 1 or more types chosen from retardation film, a brightness improving film, a viewing angle improvement film, and a semi-transmissive film, to the said polarizing plate which bonded the transparent protective film on at least one surface.

According to the present invention, a film produced as a roll-like long object by providing a water immersion treatment step 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. It exhibits the effect that a polarizing film with high optical properties, especially color uniformity, in the width direction of is obtained.

Hereinafter, the present invention will be described in detail. In the present invention, the polyvinyl alcohol-based resin film is continuously processed by passing in the order of the swelling treatment step, the water immersion treatment step, the dyeing treatment step, and the boric acid treatment step, and at least one step of the dyeing treatment step and the boric acid treatment step. It uniaxially stretches to produce a polarizing film. In view of the continuous treatment as described above, the raw film of polyvinyl alcohol-based resin is usually supplied in a roll shape. In FIG. 1, the example of arrangement | positioning of the apparatus suitable for implementing the manufacturing method of the polarizing film which concerns on this invention is shown typically.

In the example shown in FIG. 1, the swelling tank 3 for performing a swelling process, and the water immersion tank 4 for performing a water immersion process, the polyvinyl alcohol-type raw film 1 taken out from the master roll 2 ), A dye bath 5 for dyeing treatment and a boric acid bath 6 for boric acid treatment in turn. The polyvinyl alcohol-based resin film after leaving the boric acid tank (6) is usually passed through a water washing tank (7), whereby the unreacted boric acid aqueous solution attached in the previous tank is washed, and then passed through a drying furnace (8) It is made to dry and the polarizing film 9 is obtained. Although illustration is abbreviate | omitted, a transparent protective film is normally bonded to at least one surface of the polarizing film obtained after that, and it becomes a polarizing plate.

[Polyvinyl Alcohol Resin]

The polyvinyl alcohol-type resin used as the disk of a polarizing film specifically saponifies polyvinyl acetate type resin. The saponification degree of polyvinyl alcohol-type resin is 85 mol% or more, Preferably it is 90 mol% or more, More preferably, it is 99-100 mol%. In addition to polyvinyl acetate which is a homopolymer of vinyl acetate, polyvinyl acetate type resin contains the copolymer of vinyl acetate and the other monomer copolymerizable with this. As another monomer copolymerizable with vinyl acetate, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, unsaturated amines, etc. are mentioned, for example. 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 also be used. Usually, as a raw material of a polarizing film, the unstretched film of polyvinyl alcohol-type resin whose thickness is 20-100 micrometers, Preferably 30-80 micrometers is used.

Industrially, the width of the film is practically about 1,500 to 6,000 mm.

[Production of Polarizing Film]

This raw film 1 passes through the swelling tank 3, the water immersion tank 4, the dyeing tank 5, and the boric acid tank 6 in order, and each treatment is performed. After leaving the boric acid bath 6, it is washed with water in the washing tank 7 and finally dried in the drying furnace 8. The thickness of the polyvinyl alcohol polarizing film obtained in this way is about 1-50 micrometers, for example. In addition, although the example which installed one swelling tank 3, the water immersion tank 4, the dyeing tank 5, the boric acid tank 6, and the washing tank 7 was shown in FIG. 1, it is necessary in each process. According to this, a plurality of tanks can be installed.

[Swelling Treatment]

The raw film 1 is first subjected to a swelling treatment in the swelling tank 3. This swelling treatment is performed for the purpose of removing foreign substances on the surface of the film, removing the plasticizer in the film, imparting dichroism in a subsequent step, plasticizing the film, and the like. The conditions of a swelling process are determined in the range which can achieve these objectives, but does not produce the faults, such as extreme dissolution of a base film, a loss of transparency, and the like. A swelling process is performed by immersing an unstretched raw film in the process bath of 10-50 degreeC, preferably 20-50 degreeC, for example. The swelling treatment time is about 5 to 300 seconds, preferably about 20 to 240 seconds.

In the swelling process, problems such as swelling of the film in the width direction and wrinkles of the film are likely to occur. It is preferable to convey the film, removing the wrinkles. In order to stabilize the conveyance of the film 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 which detects the end of the film and prevents meandering of the film) may be used in combination. useful. In this step, since the film swells and expands also in the traveling direction of the film, in order to eliminate the looseness of the film in the conveying direction, for example, a means such as controlling the speed of the conveying roll before and after the swelling tank 3 is used. It is desirable to take measures. Specifically, the ratio (hereinafter sometimes referred to as roll speed ratio) of the circumferential speed of the outlet-side conveying roll to the circumferential speed of the inlet-side conveying roll of the swelling tank 3 is 1.2 in accordance with the temperature of the treatment bath. It is preferable to set it as about 2 times. In addition, if desired, uniaxial stretching may be performed in this step.

The treatment bath used in the swelling tank 3 is boric acid as described in Patent Document 1 (Japanese Patent Laid-Open No. Hei 10-153709) in addition to pure water, and Patent Document 2 (Japanese Patent Laid-Open No. 6- 6). Chlorides as described in Japanese Patent No. 281816), and other inorganic acids, other inorganic salts, water-soluble organic solvents, alcohols and the like may be added in an amount of 0.01 to 10% by weight. However, in this swelling tank 3, pure water substantially free of dissolving components is preferably used.

[Water immersion treatment]

After dewatering of the polyvinyl alcohol-based resin film after the swelling treatment, a water immersion treatment is performed in the water immersion tank 4. This water immersion treatment is performed in order to adjust the absorption state in a film width direction, and to improve the mechanical property of a film and also the uniformity of the optical characteristic of the finally obtained polarizing film. And in this process, a film is processed by the draw ratio of 1 times or more and 1.05 times or less with respect to a machine direction (MD, ie, the traveling direction of a film). A draw ratio of 1 times means that the film neither stretches nor shrinks with respect to the machine direction.

Since a series of processes are performed by applying tension to the extent that the film does not loosen in the traveling direction, the draw ratio in this step is usually not less than 1 times, but the polarizing film obtained when the draw ratio exceeds 1.05 times There is a tendency for the uniformity of the optical characteristic at to deteriorate.

It is preferable that the temperature of the process bath used by the water immersion tank 4 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. On the contrary, if the temperature exceeds 50 ° C, the film may be dissolved. Moreover, it is preferable that the bath used for this water immersion treatment is pure water substantially free of a dissolution component. When this treatment bath contains a chemical such as boric acid, the uniformity of the film tends to be impaired.

[Dyeing treatment]

After the water immersion treatment, the film is dyed in the dyeing tank 5. The dyeing process by a conventional dichroic dye is performed for the purpose of making a dichroic dye adsorb | suck to a film. The treatment conditions are within the range in which this object can be achieved and are determined in such a range that no defects such as extreme dissolution of the base film, loss of transparency, and the like occur.

When iodine is used as the dichroic dye, for example, at a temperature of 10 to 50 ° C, preferably 20 to 40 ° C, and 0.003 to 0.2 part by weight of iodine and 0.1 to 10 parts of potassium iodide with respect to 100 parts by weight of water A dyeing process is performed by immersing in aqueous solution containing a weight part for 10 to 600 second, Preferably it is 30 to 200 second. Instead of potassium iodide, other iodides such as zinc iodide may be used. Moreover, another iodide can also be used together with potassium iodide. Moreover, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride, etc. can also coexist. Even when boric acid is added, it is distinguished from subsequent boric acid treatment in that it contains iodine. If it is a bath containing 0.003 weight part or more of iodine with respect to 100 weight part of water, it can be considered as a dyeing bath.

On the other hand, in the case of using a water-soluble dichroic dye as the dichroic dye, for example, at a temperature of 20 to 80 ° C, preferably 30 to 60 ° C, 0.001 to 0.1 parts by weight of the dichroic dye with respect to 100 parts by weight of water The dyeing treatment is performed by immersing in an aqueous solution for 10 seconds to 600 seconds, preferably 20 seconds to 300 seconds. The aqueous solution of the dichroic dye to be used may contain a dyeing aid, etc., for example, may contain inorganic salts, such as sodium sulfate, surfactant, etc. Only 1 type may be used for a dichroic dye, and 2 or more types of dichroic dye may be used together according to a desired color.

In the dyeing treatment step, like the swelling treatment step, an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar, and the like may be appropriately installed in the dye bath and / or at the bath entrance and exit. In this dyeing treatment step, uniaxial stretching can be performed simultaneously in the machine direction.

[Boric acid treatment]

After the dyeing treatment, the boric acid treatment is performed in the boric acid bath 6. This boric acid treatment is performed by immersing the polyvinyl alcohol-type resin film dyed by the dichroic dye in the aqueous solution containing about 1-10 weight part of boric acid with respect to 100 weight part 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, zinc iodide, and the like. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfite, potassium sulfate, sodium sulfate, and the like can also coexist.

This boric acid treatment is performed for water resistance by crosslinking, color adjustment (preventing blue color), etc. When it aims at the water resistance by bridge | crosslinking, you may use crosslinking agents, such as glyoxal and glutaraldehyde, with boric acid as needed. Meanwhile, the boric acid treatment for water resistance may be referred to as a water resistance treatment, a crosslinking treatment, an immobilization treatment, or the like. Further, the boric acid treatment may be taken for color adjustment, and may be referred to as complementary color treatment, toning treatment, and the like.

This boric acid treatment is performed by suitably changing the concentration of boric acid and iodide, and the temperature of a process bath according to the objective. The boric acid treatment for water resistance and the boric acid treatment for color adjustment are not particularly distinguished, but are preferably performed under the following conditions.

When the disc film is subjected to swelling, water immersion, dyeing and boric acid treatment in turn, when boric acid treatment is intended for water resistance by crosslinking, about 3 to 10 parts by weight of boric acid and iodide per 100 parts by weight of water An aqueous solution containing about 1 to 20 parts by weight of the aqueous solution 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, and more preferably 20 to 100 seconds.

After the boric acid treatment for water resistance is performed, the boric acid treatment for color 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 is used as a boric acid treatment bath for this purpose. Usually, it is performed at a temperature of about 10 to 45 ° C. Immersion time is about 1 to 300 second normally, Preferably it is 2 to 100 second. Boric acid treatment for color adjustment is usually done at lower temperatures as compared to boric acid treatment for water resistance.

Therefore, this boric acid treatment can also be performed in several tanks, and usually 1-5 tanks are arrange | positioned in many cases. In the case where a plurality of baths are arranged, the films pass through each bath in turn, and the film is subjected to boric acid treatment. When arranging a some tank, the aqueous solution composition and temperature of each boric acid treatment tank to be used may be the same or different within the said range. The boric acid treatment for water resistance and the boric acid treatment for color adjustment can be performed in a plurality of baths, respectively. Also in a boric acid treatment process, uniaxial stretching can be performed in the machine direction of a film similarly to a dyeing process.

The final integrated draw ratio from the swelling treatment process to the boric acid treatment process is about 4.5 to 8 times, preferably 5 to 7 times.

[Post-treatment After Boric Acid Treatment]

After the boric acid treatment, a water washing treatment is performed in the washing tank 7. The water washing treatment is performed by, for example, immersing the boric acid-treated polyvinyl alcohol-based resin film in water, spraying water as a shower or immersing and spraying together for water resistance and / or color adjustment. Is done. The temperature of water in a water washing process is about 2-40 degreeC normally, and a processing time is about 2 to 120 second normally. After washing with water, it is led to the drying furnace 8, and the film is dried. This drying is performed for about 30 to 600 second in the drying furnace 8 maintained at the temperature of about 40-100 degreeC.

[1-axis drawing]

In the present invention, uniaxial stretching is performed in at least one of the above-described dyeing treatment steps and boric acid treatment steps. Although this uniaxial stretching may be performed in one process or in both processes, it is preferable to perform uniaxial stretching in both processes, ie, a dyeing process and a boric acid process. Stretching can be performed, for example by the method of providing a circumferential speed difference to the conveyance roll by the tank entrance side, and the conveyance roll by the tank exit side. On the other hand, the final integrated draw ratio is preferably about 4.5 to 8 times as described above, and more preferably about 5 to 7 times. The integrated draw ratio referred to here means the length of the reference length of the master film in the film after the completion of all the stretching treatments, and the value including these stretchings when stretched in the swelling treatment step or the water immersion treatment step. Becomes For example, if the part which was 1 m in the raw film became 5 m in the film after completion | finish of all extending | stretching processes, the integrated draw ratio at this time will be 5 times.

[Production of Polarizing Plate]

The polarizing film produced in this way can bond a transparent protective film with the adhesive agent on at least one surface, and can be set as a polarizing plate. As the transparent protective film, for example, a film containing an acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose, a film containing a polyester resin such as polyethylene terephthalate or polyethylene naphthalate, polybutylene terephthalate, The film containing polycarbonate resin, the film containing cycloolefin resin which makes cyclic olefins, such as norbornene, the main monomer, etc. are mentioned. Commercially available thermoplastic cycloolefin resins include, for example, "Topas" sold by Ticona, Germany, "Aton" sold by JSR, and Nihon Xeon Co., Ltd. "Zeonor", "Zeonex", and "Apel" (all brand names) sold by Mitsui Chemicals, Inc. are available. When making into a protective film the film formed from such cycloolefin resin, well-known methods, such as the solvent casting method and the melt-extrusion method, are used suitably for film forming. The cycloolefin resin film formed into a film is also marketed, For example, "Esshina", "SCA40", etc. which are sold from Sekisui Kagaku Kogyo Co., Ltd. are mentioned.

The thickness of the transparent protective film is preferably thin, but if too thin, the strength is lowered, resulting in poor workability. On the other hand, if the thickness is too thick, there is a problem that the transparency is reduced or the curing time required after lamination is long. Therefore, the suitable thickness of a protective film is about 5-200 micrometers, for example, Preferably it is 10-150 micrometers, More preferably, it is 10-100 micrometers.

In order to improve the adhesiveness between the adhesive agent and the polarizing film and / or the protective film, the polarizing film and / or the protective film is subjected to surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment and saponification treatment. can do.

Surface treatments such as an antiglare treatment, an antireflection treatment, a hard coating treatment, an antistatic treatment, an antifouling treatment, and the like may be performed on the transparent protective film individually or in combination of two or more kinds. In addition, the protective film and / or protective film surface protective layer may have a ultraviolet absorber, such as a benzophenone type compound and a benzotriazole type compound, a plasticizer, such as a phenyl phosphate type compound and a phthalic acid ester compound. The transparent protective film may be bonded to one side of the polarizing film or may be bonded to both sides.

A polarizing film and a transparent protective film are laminated | stacked using adhesives, such as an aqueous solvent adhesive, an organic solvent adhesive, a hot melt adhesive, and a solventless adhesive. As the aqueous solvent adhesive, for example, an aqueous polyvinyl alcohol resin solution, an aqueous two-component urethane emulsion adhesive, or the like, and as the organic solvent adhesive, for example, a two-component urethane adhesive or the like, is a solvent-free adhesive, for example. A liquid urethane adhesive, an epoxy adhesive, etc. are mentioned, respectively.

When using the acetyl cellulose type film by which the adhesive surface with a polarizing film was hydrophilized by saponification etc. as a protective film, the polyvinyl alcohol-type resin aqueous solution is used suitably as an adhesive agent. As a polyvinyl alcohol-type resin used as an adhesive agent, vinyl obtained by saponifying the copolymer of vinyl acetate and the other monomer copolymerizable with this besides the vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate which is a homopolymer of vinyl acetate. Alcohol-based copolymers, and furthermore, modified polyvinyl alcohol-based polymers in which these hydroxyl groups are partially modified. A polyhydric aldehyde, a water-soluble epoxy compound, a melamine type compound, etc. can be mix | blended with this adhesive agent as a crosslinking agent.

The method of bonding a polarizing film and a transparent protective film is not specifically limited, For example, an adhesive is apply | coated uniformly to the surface of a polarizing film or a protective film, the other film is laminated | stacked on an application surface, and it bonds by a roll etc. and drys The method etc. are mentioned.

Usually, an adhesive agent is apply | coated under the temperature of 15-40 degreeC after manufacture, and joining temperature is the range of about 15-30 degreeC normally. After the bonding, drying treatment is performed to remove solvents such as water contained in the adhesive, but the drying temperature at this time is usually in the range of 30 to 100 ° C, preferably 40 to 80 ° C. Thereafter, the adhesive can be cured by curing for about 1 to 90 days in a temperature environment of 15 to 85 ° C, preferably 20 to 50 ° C, more preferably 35 to 45 ° C. In the case where the protective film is an acetyl cellulose resin, even if such curing is not performed, sufficient adhesive strength is exhibited. However, when the protective film is bonded to the polarizing film through an aqueous solvent adhesive while using a protective film containing other resin, It is preferable to perform the same curing. Since the productivity will worsen when this curing period is long, it is preferable to set it as about 1 to 14 days, and it is more preferable to set it as about 1 to 7 days.

In this way, the polarizing plate by which the protective film was bonded to one side or both sides of a polarizing film through an adhesive bond layer is obtained.

In the present invention, the transparent protective film may have optical functions such as a function as a retardation film, a function as a brightness enhancement film, a function as a reflective film, a function as a semi-transmissive reflective film, a function as a diffusion film, a function as an optical compensation film, and the like. have. In this case, for example, such a function can be provided by laminating an optically functional film such as a retardation film, a brightness enhancement film, a reflection film, a transflective reflection film, a diffusion film, an optical compensation film, and the like on the surface of the transparent protective film. Not only that, but also such a function can be imparted to the transparent protective film itself. In addition, it is possible to have a plurality of functions in the transparent protective film itself, such as a diffusion film having a function of the brightness enhancement film.

For example, the transparent protective film may be subjected to the stretching treatment described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, or the like, or the treatment described in Japanese Patent No. 3168850, or the like, to impart a function as a retardation film. Can be. Retardation characteristics in a retardation film can be suitably selected, for example, a range whose front retardation value is 5-100 nm, thickness direction retardation value 40-300 nm. In addition, two or more layers of collet having different center wavelengths of selective reflection or forming fine pores in the transparent protective film by a method as described in JP-A-2002-169025 or JP-A-2003-29030. By superimposing a steric liquid crystal layer, the function as a brightness improving film can be provided.

When a metal thin film is formed in the said transparent protective film by vapor deposition, sputtering, etc., the function as a reflective film or a semi-transmissive reflective film can be provided. The function as a diffusion film can be provided by coating the resin solution containing microparticles | fine-particles on the said transparent protective film. Moreover, the function as an optical compensation film can be provided by coating and orienting liquid crystal compounds, such as a discotic liquid crystalline compound, on the said transparent protective film. In addition, various optical functional films can be directly bonded to the polarizing film using a suitable adhesive. As a commercial item of an optical functional film, the brightness improvement film like "DBEF" (brand name) sold by 3M company (Sumitomo 3M Co., Ltd. in Japan), for example, "WV film" sold by Fuji Film Co., Ltd. And a retardation film such as "Sumika Light" (trade name) sold by Sumitomo Chemical Co., Ltd.

<Example>

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. The following examples and comparative examples are outlined in Fig. 1, the swelling tank (3), water immersion tank (4), dyeing tank (5), boric acid tank (6), washing tank (7) and drying furnace The apparatus which (8) arrange | positioned in turn is carrying out various processes, conveying the elongate film of polyvinyl alcohol by the continuous conveying apparatus which combined the nip roll and the free roll. As the master film 1, a polyvinyl alcohol film ("Kurare vinylon VF-PS # 7500" manufactured by Kuraray Co., Ltd.) 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 was used. It was. Stretching was performed by giving a peripheral speed difference to the drive nip rolls before and after the treatment tank.

In addition, the uniformity of the optical characteristic of the obtained polarizing film was evaluated by the b ^* value of parallel hue. Parallel color means a color when natural light is exposed in a state where two polarizing films are superimposed so that their absorption axes are the same, and b ^* value thereof is a continuous spectral transmittance Tp (λ) at a wavelength λ. It calculates | requires about one wavelength area or in predetermined | prescribed wavelength space | intervals, and calculates from these in accordance with JIS Z 8729.

Parallel transmittance means transmittance | permeability when natural light is exposed in the state which overlapped two polarizing films so that each absorption axis might become the same, Therefore, parallel spectral transmittance Tp ((lambda)) in arbitrary wavelength (lambda) is 2 The transmittance | permeability when the natural light of wavelength (lambda) was exposed in the state which superposed the long polarizing film so that each absorption axis may become the same, but this becomes equivalent to the value obtained by the method shown below. That is, one piece of polarizing film is subjected to linear polarized light of wavelength λ in the direction parallel to the absorption axis thereof, and the spectral transmittance k1 (λ) at this time is measured, and then linearly polarized light of wavelength λ is applied to the absorption axis and the vertical direction. The spectral transmittance k2 (λ) at this time is measured. And the transmittance | permeability (parallel spectral transmittance) when the natural light of wavelength (lambda) was exposed in the state which overlapped two polarizing films so that each absorption axis might become the same is the transmittance | permeability {after permeating the film twice by the transmittance k1 ((lambda)) { Since the average value of the transmittance {k2 (λ)} ² after passing the film twice at k1 (λ)} ² and the transmittance k2 (λ) is the same, the parallel spectral transmittance Tp (λ) at wavelength λ is determined from these values. Obtained by the following equation (1).

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

These measurements and calculations are performed for successive wavelength ranges or at predetermined wavelength intervals, and the b ^* value of the parallel color is calculated according to JIS Z 8729 from the parallel spectral transmittance Tp (λ) at each wavelength λ. On the other hand, the spectral transmittances k1 (λ) and k2 (λ) and the parallel spectral transmittance Tp (λ) referred to herein are all values which are displayed with 1 as the maximum value instead of the percentage display. Do it.

Example 1

First, the film was sufficiently swelled by being immersed in the swelling tank 3 containing 30 ° C. pure water for about 80 seconds while maintaining the tension state of the film so as not to loosen the original film 1. The roll speed ratio of the inlet and the outlet along the swelling in the swelling tank 3 was 1.2. After dehydrating with a nip roll, it was immersed for about 160 second in the water immersion tank 4 in which 30 degreeC pure water entered. The draw ratio of 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 iodine / potassium iodide / water was immersed in a dye bath 5 containing an aqueous solution of 0.02 / 1.5 / 100 by weight ratio. Thereafter, potassium iodide / boric acid / water was immersed in the boric acid tank 6 containing a 12/5/100 aqueous solution in weight ratio at 56.5 ° C. for about 130 seconds, until the accumulated draw ratio from the disk became 5.3 times. Stretching was performed. Finally, it washed with the pure water of 9 degreeC for about 16 second in the washing tank (7), and after that, it dried for about 160 second at about 60 degreeC in the drying furnace (8), and obtained the iodine type polarizing film.

It was determined for the b ^* value of the color of the parallel in the parallel b ^* color value to the width ends of the central portion in the width direction of the obtained polarizing film. As a result, the difference between them was 2.1.

The polarizing plate is obtained by bonding the protective film containing triacetyl cellulose, respectively, through the adhesive agent containing the aqueous solution of polyvinyl alcohol-type resin on both surfaces of this polarizing film. In addition, a protective film containing triacetyl cellulose on one side of the polarizing film, a protective film containing norbornene-based resin on the other side of the polarizing film, respectively, via an adhesive containing an aqueous solution of polyvinyl alcohol-based resin, or A polarizing plate can also be obtained by bonding through a non-solvent type adhesive agent.

Comparative Example 1

First, the film was sufficiently swelled by being immersed in the swelling tank 3 containing pure water at 30 ° C. for about 50 seconds while maintaining the tension state of the film so as not to loosen the original film 1. After dehydration with a nip roll, it was immersed in the water immersion tank 4 in which 30 degreeC pure water entered for about 160 second, and it extended | stretched by the draw ratio of 1.20 times in this machine direction in this tank. Then, it carried out similarly to Example 1, performed uniaxial stretching in the dyeing tank 5, uniaxial stretching in the boric acid tank 6, water washing, and drying, and obtained the polarizing film.

It was determined for the b ^* value of the color of the parallel in the parallel b ^* color value to the width ends of the central portion in the width direction of the obtained polarizing film. 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 in optical properties in the width direction of a film produced as a roll-shaped long object is obtained. The polarizing plate chip cut | disconnected in various magnitude | sizes from this polarizing plate exhibits substantially the same optical characteristic between each sheet, and can be effectively applied to various display apparatuses, including a liquid crystal display device.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the arrangement | positioning example of the apparatus suitable for implementing the method of this invention.

Explanation of symbols for the main parts of the drawings

1: disc film of polyvinyl alcohol-based resin

2: disc roll

3: swelling tank

4: can immersion tank

5: dyeing tank

6: boric acid bath

7: flush

8: drying furnace

9: polarizing film

Claims (5)

The polyvinyl alcohol-based resin film is continuously processed by passing in the order of the swelling treatment step, the water immersion treatment step, the dyeing treatment step, and the boric acid treatment step, and uniaxially stretched in at least one of the dyeing treatment step and the boric acid treatment step. It is a method of manufacturing a polarizing film, In the said water immersion treatment process, the said polyvinyl alcohol-type resin film is processed so that it may become a draw ratio of 1 times or more and 1.05 times or less with respect to a machine direction. 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, wherein the water immersion treatment step is performed in pure water substantially free of dissolved components. The manufacturing method of the polarizing plate which bonds a transparent protective film to at least one surface of the polarizing film obtained after manufacturing a polarizing film by the method of Claim 1 or 2. The manufacturing method of the polarizing plate which bonds a transparent protective film to at least one surface of the polarizing film obtained after manufacturing a polarizing film by the method of Claim 3.

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