CN101276013A - Manufacturing method of polarizing film and manufacturing method of polarizing plate - Google Patents

Abstract

A method for producing a polarizing film, wherein a raw material film (1) of a polyvinyl alcohol-based resin is sequentially passed through a swelling treatment step in a swelling tank (3), a water immersion treatment step in a water immersion tank (4), The dyeing treatment process in the dyeing tank (5) and the boric acid treatment process in the boric acid tank (6) are continuously processed, and uniaxial drawing is carried out in at least one of the dyeing tank (5) and the boric acid tank (6) When stretching the polarizing film (9), the polyvinyl alcohol-based resin film is treated with respect to the machine direction in a water immersion tank (4) so that the stretching ratio becomes 1 time or more and 1.05 times or less. The bath of the water immersion tank (4) is preferably pure water substantially free of dissolved components. A transparent protective film is pasted on at least one side of the obtained polarizing film (9) to manufacture a polarizing plate.

Description

Manufacturing method of polarizing film and manufacturing method of polarizing plate

technical field

The present invention relates to a method of manufacturing a polarizing film having less unevenness in optical characteristics in the width direction as a roll-shaped elongated object, and a method of manufacturing a polarizing plate in which a transparent protective film is laminated on at least one side of such a polarizing film.

Background technique

Polarizing films are widely used as materials for adsorbing and aligning dichroic dyes on polyvinyl alcohol-based resin films. In addition, iodine-based polarizing films using iodine as a dichroic dye, dye-based polarizing films using a dichroic direct dye as a dichroic dye, and the like are known. These polarizing films are usually bonded with a transparent protective film such as triacetyl cellulose with an adhesive containing a polyvinyl alcohol-based resin aqueous solution on one or both sides to form a polarizing plate.

As a method for producing a polarizing film, for example, JP-A-10-153709 (Patent Document 1) describes that after soaking a polyvinyl alcohol-based resin film in water to swell it, dyeing it with iodine, and then stretching it, in order to The iodine is immobilized, followed by boric acid treatment (in other words, water-resistant treatment by crosslinking), washing with water, and drying. The swelling treatment with water is carried out for the purpose of uniform swelling of the film before dyeing, in order to shorten the dyeing time and improve uneven dyeing. In this case, from the viewpoint of dyeing unevenness, etc., in Patent Document 1, boric acid is contained in the swelling treatment bath. In addition, in this patent document 1, after dyeing, the film is dipped in an aqueous solution containing boric acid to be stretched, and then further immersed in a boric acid aqueous solution to perform water-resistant treatment by crosslinking (referred to as fixation or fixation in this document). .

JP-A-6-281816 (Patent Document 2) describes adding chlorides such as lithium chloride and zinc chloride to a swelling treatment bath in order to sufficiently swell a film. In addition, in JP-A-2001-141926 (Patent Document 3), it is described that in order to reduce uneven dyeing, a polyvinyl alcohol-based resin film is immersed in a water bath to swell it and stretched 1.1 to 4 times. , and then carry out the dyeing treatment with dichroic dye and the method of cross-linking treatment to manufacture polarizing film.

In addition, Japanese Patent Application Laid-Open No. 2005-114990 (Patent Document 4) describes that sequential processing in a bath is performed in the order of swelling treatment, dyeing treatment, and boric acid treatment, and uniaxial stretching is performed in at least one of the steps to produce a polarizer. In the case of a light film, after the swelling treatment and before the dyeing treatment, a wet stretching process is provided. In this 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. Stretching, thereby further improving color unevenness.

[Patent Document 1] Japanese Unexamined Patent Publication No. 10-153709;

[Patent Document 2] Japanese Patent Laid-Open Publication No. 6-281816;

[Patent Document 3] JP-A-2001-141926 Gazette;

[Patent Document 4] JP-A-2005-114990.

Contents of the invention

The inventors of the present invention further studied the method of producing a polarizing film by providing a wet stretching step after the swelling treatment and before the dyeing treatment as shown in the above-mentioned Patent Document 4. As a result, it was found that the polarizing film obtained by this method has less unevenness in color, but unevenness in hue tends to occur in the center and edge portions of the roll film in the width direction. Therefore, the subject of the present invention is to provide a method for producing a polarizing film and a polarizing plate having high optical characteristics in the width direction, especially uniformity in hue.

In order to solve the above-mentioned problems, the inventors of the present invention conducted earnest research, and as a result, it was found that the polyvinyl alcohol-based resin film is sequentially processed through the swelling treatment step, water immersion treatment step, dyeing treatment step, and boric acid treatment step, and in the When performing uniaxial stretching in at least one of the dyeing treatment process and the boric acid treatment process to produce a polarizing film, the mechanical direction of the film should be reduced as much as possible in the water immersion treatment process between the swelling treatment process and the dyeing treatment process. The new fact that a polarizing film with high optical uniformity can be obtained by increasing the elongation magnification has completed the present invention.

That is, the manufacturing method of the polarizing film of the present invention, which makes the polyvinyl alcohol-based resin film sequentially processed through the swelling treatment process, water immersion treatment process, dyeing treatment process and boric acid treatment process, and in the dyeing treatment process and When performing uniaxial stretching to produce a polarizing film in at least one of the boric acid treatment steps, the polyvinyl alcohol-based resin film is treated with respect to the machine direction in the water immersion treatment step so that the stretching ratio becomes 1 time or more and 1.05 times or less.

The aforementioned water immersion treatment step is preferably performed at a temperature of 10 to 50°C. In addition, this water immersion treatment step is preferably performed in pure water substantially free of dissolved components.

In the method for producing a polarizing plate of the present invention, a transparent protective film is attached to at least one side of the obtained polarizing film after the polarizing film is produced by the aforementioned method. The transparent protective film may have any function of retardation film, brightness-enhancing film, viewing angle-improving film, and transflective film. Alternatively, an optical laminate may be produced by bonding at least one film selected from a retardation film, a brightness-enhancing film, a viewing angle-improving film, and a transflective film to the aforementioned polarizer having a transparent protective film attached to at least one side thereof.

According to the present invention, a water immersion treatment step is provided between the swelling treatment step and the dyeing treatment step. In this water immersion treatment step, the stretching ratio to the machine direction of the film is reduced, and the advantages of being manufactured as a roll-shaped long-sized article can be exerted. Optical properties in the width direction of the film, especially the effect of a polarizing film with high uniformity in hue.

Description of drawings

[ Fig. 1 ] is a schematic diagram showing an arrangement example of a preferable apparatus for carrying out the method of the present invention.

Symbol Description

1... The raw material film of polyvinyl alcohol-based resin;

2... Raw material roller;

3...Swelling tank;

4...Water immersion tank;

5... dyeing tank;

6... Boric acid tank;

7...water washing tank;

8...Drying furnace;

9...Polarizing film.

Detailed ways

The present invention will be described in detail below. In the present invention, the polyvinyl alcohol-based resin film is sequentially processed through a swelling treatment process, a water immersion treatment process, a dyeing treatment process, and a boric acid treatment process, and at least one of the dyeing treatment process and the boric acid treatment process is performed. Uniaxial stretching to produce polarizing film. Due to such continuous processing, the raw material film (raw film) of polyvinyl alcohol-based resin is usually provided in the form of a roll. Fig. 1 is a schematic view showing an example of the arrangement of a preferable apparatus for carrying out the method for producing a polarizing film of the present invention.

In the example shown in Fig. 1, the polyvinyl alcohol-based raw material film 1 sent out from the raw material roll (former reel) 2 passes through the swelling tank 3 for swelling treatment, the water for immersion treatment in order. A dipping tank 4, a dyeing tank 5 for dyeing treatment, and a boric acid tank 6 for boric acid treatment. After coming out of the boric acid tank 6, the polyvinyl alcohol-based resin film usually passes through the water washing tank 7 to wash off the unreacted boric acid aqueous solution adhering to the previous tank, and then is dried in the drying oven 8 to obtain the polarizing film 9. Then, usually, a transparent protective film is pasted on at least one side of the obtained polarizing film to form a polarizing plate, which is omitted in the figure.

[polyvinyl alcohol-based resin]

The polyvinyl alcohol-based resin used as the raw material (raw material) of the polarizing film is specifically a resin obtained by saponifying polyvinyl acetate-based resin. The degree of saponification of the polyvinyl alcohol-based resin is 85 mol% or more, preferably 90 mol% or more, more preferably 99 to 100 mol%. Polyvinyl acetate-based resins include copolymers of vinyl acetate and other monomers that can be copolymerized with it, in addition to polyvinyl acetate that is a homopolymer of vinyl acetate. Examples of other monomers that can be copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and unsaturated amines. 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 also be modified, for example, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. may be used. Generally, as a raw material of a polarizing film, an unstretched film of a polyvinyl alcohol-based resin having a thickness of 20 to 100 μm, preferably 30 to 80 μm, is used.

Industrially, the width of the film is about 1,500 to 6,000 mm, which is more practical.

[Manufacture of Polarizing Film]

Such a raw material film 1 passes through the swelling tank 3, the water immersion tank 4, the dyeing tank 5, and the boric acid treatment tank 6 in order, and is respectively treated. After coming out of the boric acid tank 6, the water is washed in the water washing tank 7, and finally dried in the drying furnace 8. The thickness of the polyvinyl alcohol-based polarizing film thus obtained is, for example, about 1 to 50 μm. FIG. 1 shows an example in which one swelling tank 3 , water immersion tank 4 , dyeing tank 5 , boric acid tank 6 , and water washing tank 7 are respectively provided, but a plurality of tanks may be provided in each process as necessary.

[Swelling treatment]

The raw material film 1 is first subjected to swelling treatment in the swelling tank 3 . This swelling treatment is performed for the purposes of removing impurities on the surface of the film, removing plasticizers in the film, imparting easy dyeability in subsequent processes, and plasticizing the film. The swelling treatment conditions are determined within the range that can achieve these purposes and within the range that does not cause adverse conditions such as extreme dissolution and loss of transparency of the raw material film. The swelling treatment is performed by immersing the unstretched raw film in a treatment bath at a temperature of, for example, 10 to 50°C, preferably 20 to 50°C. The swelling treatment time is about 5 to 300 seconds, preferably about 20 to 240 seconds.

In the swelling treatment process, the film is swollen in the width direction, and the film is prone to problems such as wrinkles, so it is preferable to use a widening roll, a spiral roll, a convex roll, a cloth guide, and a bent roll expander (Bend Bar). Known expanding devices such as tenter clips and tenter clips transport the film while eliminating wrinkles of the film. In order to achieve the purpose of stably transporting the film in the bath, spray in water to control the water flow in the swelling bath, or use the EPC device (Edge Position Control) device at the same time; a device that detects the end of the film and prevents the film from swaying left and right ) etc. are feasible. In this step, the film also swells and expands along the advancing direction of the film, so in order to eliminate the slack of the film in the conveying direction, it is preferable to take measures such as controlling the speed of conveying rollers located before and after the swelling tank 3 . Specifically, the ratio of the peripheral speed of the conveying roller on the outlet side of the swelling tank 3 to the peripheral speed of the conveying roller on the inlet side (hereinafter sometimes referred to as the roller speed ratio) is preferably about 1.2 to 2 times depending on the treatment temperature. In addition, if necessary, uniaxial stretching can also be performed in this step.

In the treatment bath used in the swelling tank 3, in addition to pure water, the boric acid described in the aforementioned Patent Document 1 (Japanese Unexamined Patent Publication No. Hei 10-153709), the aforementioned Patent Document 2 ( Chlorides described in Japanese Unexamined Publication No. 6-281816), and aqueous solutions of other inorganic acids, other inorganic salts, water-soluble organic solvents, alcohols, etc. However, it is preferable to use substantially no dissolved components in this swelling tank 3 of pure water.

[Water dipping treatment]

The polyvinyl alcohol-based resin film after the swelling treatment is subjected to water immersion treatment in the water immersion tank 4 after controlling to remove moisture. The water immersion treatment is carried out in order to adjust the water absorption state in the width direction of the film, improve the mechanical properties of the film, and further improve the uniformity of the optical properties of the final polarizing film. And in this process, the film is processed with a stretch ratio of 1 to 1.05 times with respect to the machine direction (MD, that is, the direction in which the film advances). The draw ratio of 1 means that the film neither stretches nor shrinks with respect to the machine direction. A series of processes are performed by applying a tension that does not cause relaxation in the direction of film advancement, so the stretching ratio in this process is usually not lower than 1 time, but if the stretching ratio exceeds 1.05 times, there will be a polarizing film obtained. There is a tendency for the uniformity of optical properties to deteriorate in the medium.

The temperature of the treatment bath used in the water immersion tank 4 is preferably 10 to 50°C. If the temperature of the treatment bath is lower than 10°C, large-scale cooling equipment is required for temperature control, which is uneconomical; on the contrary, if it exceeds 50°C, there is a danger of film dissolution. In addition, the bath used in the water immersion treatment is preferably pure water substantially free of dissolved components. When the treatment bath contains chemicals such as boric acid, the uniformity of the film tends to be impaired.

[coloring processing]

After the water immersion treatment, the film is dyed in the dyeing tank 5 . A usual dyeing treatment using a dichroic dye is performed for the purpose of adsorbing the dichroic dye or the like to a film. The treatment conditions should be determined within the range that can achieve this purpose and within the range that does not cause disadvantages such as extreme dissolution and loss of transparency of the raw material film.

When iodine is used as a dichroic dye, for example, at a temperature of 10 to 50°C, preferably at a temperature of 20 to 40°C, an aqueous solution containing 0.003 to 0.2 parts by weight of iodine and 0.1 to 10 parts by weight of potassium iodide relative to 100 parts by weight of water Dyeing process is carried out by dipping for 10 to 600 seconds, preferably for 30 to 200 seconds. Instead of potassium iodide, other iodides such as zinc iodide and the like can also be used. In addition, other iodides and potassium iodide may be used together. Compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc., may also be present at the same time. When boric acid is added, it is different from the subsequent boric acid treatment in terms of iodine content. As long as it contains 0.003 weight part or more of iodine with respect to 100 weight part of water, it can be regarded as a dyeing bath.

On the other hand, when a water-soluble dichroic dye is used as a dichroic dye, for example, at a temperature of 20 to 80° C., preferably 30 to 60° C., and containing 0.001 to 100 wt. Dyeing treatment is carried out by immersing in 0.1 parts by weight of an aqueous solution for 10 to 600 seconds, preferably 20 to 300 seconds. The aqueous solution of the dichroic dye to be used may further contain dye auxiliaries and the like, for example, inorganic salts such as sodium sulfate, surfactants and the like. One type of dichroic dye may be used alone, or two or more types of dichroic dye may be used in combination depending on the desired hue.

In the dyeing process, as in the swelling process, an expanding roll, a spiral roll, a convex roll, a fabric guide, a bending roll expander, etc. can be appropriately installed in the dyeing bath and/or at the entrance and exit of the bath. In this dyeing treatment step, uniaxial stretching may be performed simultaneously in the machine direction.

[boric acid treatment]

Boric acid treatment is carried out in the boric acid tank 6 after the dyeing treatment. This boric acid treatment is carried out 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 relative to 100 parts by weight of water in addition to boric acid.

Potassium iodide, zinc iodide, etc. are mentioned as an iodide. Compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfite, potassium sulfate, sodium sulfate, etc., may also be present at the same time.

This boric acid treatment is performed to obtain water resistance and hue adjustment (prevention of bluishness) by crosslinking. For the purpose of obtaining water resistance by crosslinking, a crosslinking agent such as glyoxal or glutaraldehyde may be used together with boric acid as needed. The boric acid treatment for water resistance may also be referred to as water resistance treatment, crosslinking treatment, immobilization treatment, or the like. The boric acid treatment can also be interpreted as a treatment for adjusting the hue, which is called complementary color treatment, toning treatment, etc.

This boric acid treatment is performed by appropriately changing the concentration of boric acid and iodide and the temperature of the treatment bath according to the purpose. There is no particular difference between the boric acid treatment for water resistance and the boric acid treatment for hue adjustment, but it is preferable to carry out under the following conditions.

When sequentially performing swelling, water immersion, dyeing, and boric acid treatment on the raw material film, when the purpose is to obtain water resistance through crosslinking, the boric acid treatment contains about 3 to 10 parts by weight of boric acid and iodide relative to 100 parts by weight of water. An aqueous solution of about 1 to 20 parts by weight is used as a boric acid treatment bath, usually at a temperature of 50 to 70°C, preferably at a temperature of 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 boric acid treatment for water resistance, boric acid treatment for hue adjustment may be further performed. For example, when the dichroic dye is iodine, in order to achieve this purpose, an aqueous solution containing about 1 to 5 parts by weight of boric acid and about 3 to 30 parts by weight of iodide relative to 100 parts by weight of water is used as a boric acid treatment bath, usually at 10 It is carried out at a temperature of about 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 generally performed at a lower temperature than the boric acid treatment for water resistance.

This boric acid treatment can be performed in a plurality of tanks, and usually 1 to 5 more tanks are arranged. When a plurality of tanks are arranged, the thin film passes through each tank in order, and the boric acid treatment is performed on the thin film. When a plurality of tanks are arranged, the aqueous solution composition and temperature of the respective boric acid treatment tanks used may be the same or different within the above range. The above-mentioned boric acid treatment for water resistance and boric acid treatment for hue adjustment may be performed in a plurality of tanks, respectively. In the boric acid treatment step, as in the dyeing treatment step, uniaxial stretching may also be performed in the machine direction of the film.

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

[Post-treatment after boric acid treatment]

After the boric acid treatment, water washing treatment is performed in the water washing tank 7 . For water washing treatment, for example, a method of immersing a polyvinyl alcohol-based resin film treated with boric acid for water resistance and/or hue adjustment in water, spraying water in a shower or using a combination of dipping and spraying method etc. The water temperature 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, it is introduced into the drying oven 8 to dry the film. This drying is performed for about 30 to 600 seconds in the drying oven 8 maintained at a temperature of about 40 to 100°C.

[uniaxial stretching]

In the present invention, uniaxial stretching is performed in at least one of the above-mentioned dyeing treatment step and boric acid treatment step. This uniaxial stretching may be performed in one step or in two steps, but it is preferable to perform uniaxial stretching in two steps, that is, a dyeing treatment step and a boric acid treatment step. Stretching can be performed by, for example, a method in which a peripheral speed difference is provided between a conveyor roller on the entrance side of the tank and a conveyor roller on the exit side of the tank. The final cumulative draw ratio is preferably about 4.5 to 8 times, more preferably about 5 to 7 times as described above. The cumulative stretching ratio mentioned here refers to how long the standard length of the raw material film in the longitudinal direction is in the film after all stretching treatments, even when stretching is performed in the swelling treatment process and water immersion treatment process. The value of these stretches. For example, assuming that a portion of 1 m in the raw film becomes 5 m in the film after all the stretching treatments, the cumulative stretching ratio at this time is 5 times.

[Manufacture of polarizer]

The polarizing film produced in this way can be used as a polarizing plate by bonding a transparent protective film to at least one side thereof with an adhesive. As a transparent protective film, for example, films containing acetyl cellulose resins such as triacetyl cellulose and diacetyl cellulose; films containing such as polyethylene terephthalate, polyethylene naphthalate, polyethylene Films of polyester-based resins such as butylene terephthalate; films containing polycarbonate-based resins; films containing cyclic olefin-based resins containing cyclic olefins such as norbornene as main monomers, etc. As commercially available thermoplastic cycloolefin-based resins, for example, "Topas" (Topas) sold by Ticona Corporation of Germany, "Aiton" sold by JSR (KK), and "Topas" sold by Nippon Zeon Co., Ltd.ゼゼオノア" and "ゼオネツクス", "Apel" sold by Mitsui Chemicals Co., Ltd. (all of the above are brand names). When a film made of such a cycloolefin-based resin is used as a protective film, well-known methods such as a solvent casting method and a melt extrusion method are suitable for film formation. There are also commercially available cycloolefin-based resin films, such as "Escina" and "SCA40" sold by SEKISUI CHEMICAL CO., LTD.

The thickness of the transparent protective film is preferably thin, but if it is too thin, the strength will decrease and the workability will be poor; on the other hand, if it is too thick, the transparency will decrease and the aging time required after lamination will become longer. Therefore, the 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 adhesion between the adhesive and the polarizing film and/or protective film, corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, and pre-coating can also be performed on the polarizing film and/or protective film surface treatment, saponification treatment, etc.

For transparent protective films, surface treatments such as anti-glare treatment, anti-reflection treatment, hard-coat treatment, anti-static treatment, and anti-pollution treatment can also be implemented. These surface treatments can be treated individually or in combination of two or more. deal with. In addition, the protective film and/or the surface protective layer of the protective film may also contain ultraviolet absorbers such as benzophenone-based compounds and benzotriazole-based compounds, and plasticizers such as phenyl phosphate-based compounds and phthalate compounds. agent. The transparent protective film can be pasted on one side of the polarizing film, or on both sides.

The polarizing film and the transparent protective film are laminated using adhesives such as water-solvent adhesives, organic solvent-based adhesives, hot-melt adhesives, and solvent-free adhesives. Examples of water-solvent-based adhesives include polyvinyl alcohol-based resin aqueous solutions, water-based two-component urethane emulsion adhesives, and the like; organic solvent-based adhesives include two-component urethane-based emulsion adhesives. Adhesive etc.; As a solventless type adhesive, a one-component type urethane type adhesive, an epoxy type adhesive, etc. are mentioned, for example.

When using an acetylcellulose-based film whose surface to be bonded to the polarizing film has been hydrophilized by saponification or the like as the protective film, it is preferable to use a polyvinyl alcohol-based resin aqueous solution as the binder. The polyvinyl alcohol-based resin used as a binder is not only the vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate homopolymer of vinyl acetate homopolymer, but also vinyl acetate and other monomers that can be copolymerized with it. Vinyl alcohol-based copolymers obtained by saponification of copolymers, and modified polyvinyl alcohol-based polymers whose hydroxyl groups are partially modified. In these binders, polyhydric aldehydes, water-soluble epoxy compounds, melamine-based compounds, and the like may be blended as crosslinking agents.

The bonding method of the polarizing film and the transparent protective film is not particularly limited. For example, an adhesive is uniformly coated on the surface of the polarizing film or the protective film, another film is overlapped on the coated surface, and a roller or the like is used for pasting. combined, and drying methods, etc.

Usually, the adhesive is prepared and applied at a temperature of 15 to 40°C, and the bonding temperature is usually about 15 to 30°C. After lamination, a 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 in the range of 40 to 80°C. Then, it can be aged for about 1-90 days in a temperature environment of 15-85° C., preferably 20-50° C., more preferably 35-45° C., to cure the adhesive. When the protective film is an acetylcellulose-based resin, sufficient adhesive strength can be exhibited even without such aging, but when using a protective film containing other resins and bonding it to the polarizing film with a water-solvent adhesive , it is preferable to carry out aging as described above. If the aging time is long, the production efficiency will be poor, so the aging time is preferably about 1 to 14 days, more preferably about 1 to 7 days.

In this way, a polarizing plate is obtained in which a protective film is bonded to one or both surfaces of the polarizing film via an adhesive layer.

In the present invention, the transparent protective film can have a function as a retardation film, a function as a brightness-enhancing 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, etc. optical function. In this case, for example, by laminating an optically functional film such as a retardation film, a brightness-enhancing film, a reflective film, a semi-transmissive reflective film, a diffusion film, or an optical compensation film on the surface of the transparent protective film, it can be provided with such a function. In addition, it is also possible to make the transparent protective film itself have such a function. In addition, the transparent protective film itself can have various functions, such as a diffusion film that functions as a brightness-enhancing film.

For example, for the above-mentioned transparent protective film, the stretching treatment described in Japanese Patent No. 2841377, Japanese Patent No. 3094113, etc., or the processing described in Japanese Patent No. 3168850, etc., can also be used by these methods It functions as a retardation film. The retardation characteristics in the retardation film, for example, the front retardation value is 5 to 100 nm, the retardation value in the thickness direction is in the range of 40 to 300 nm, etc., and can be appropriately selected. In addition, for the above-mentioned transparent protective film, micropores can also be formed by the methods described in JP-A-2002-169025 and JP-A-2003-29030, or two or more layers with different selective reflection center wavelengths can be laminated. The cholesteric liquid crystal layer can thus function as a brightness-enhancing film.

Forming a metal thin film on the above-mentioned transparent protective film by vapor deposition, sputtering, or the like can impart a function as a reflective film or a semi-transmissive reflective film. By coating the above-mentioned transparent protective film with a resin solution containing fine particles, it is possible to impart a function as a diffusion film. In addition, by coating and aligning a liquid crystal compound such as a discotic liquid crystal compound on the above-mentioned transparent protective film, a function as an optical compensation film can be imparted. It is also possible to directly bond various optical functional films to the polarizing film with an appropriate adhesive. As a commercially available product of an optical functional film, a brightness-enhancing film such as "DBEF" (trade name) sold by 3M Company (in Japan, Sumitomo Triem Co., Ltd.), such as Fuji Film Co., Ltd. A viewing angle-improving film sold by "WV film" (trade name), a retardation film sold by Sumitomo Chemical Co., Ltd. (trade name), and the like.

Example

Below, an Example and a comparative example are shown, and the aspect of this invention is demonstrated more concretely. However, the present invention is not limited to these examples. In the following examples and comparative examples, as shown in the schematic diagram in FIG. 1 , a long film of polyvinyl alcohol is conveyed to a swelling tank 3 and a water immersion tank 4 in order by a continuous conveying device combining nip rollers and guide rollers. , dyeing tank 5, boric acid tank 6, washing tank 7 and drying oven 8 devices while performing various treatments. As the raw material film 1, a polyvinyl alcohol film with a degree of polymerization of 2,400, a degree of saponification of 99.9 mol % or more, a thickness of 75 μm, and a width of 3,000 mm ["Kurare Vinilon VF-PS #7500" manufactured by Kuraray Co., Ltd.] was used. Stretching is carried out by making the driving nip rollers before and after the treatment tank have a peripheral speed difference.

The uniformity of optical properties of the obtained polarizing film was evaluated by the parallel hue b ^* value. Parallel hue refers to the hue when natural ^light is irradiated in the state where two polarizing films are overlapped and their respective absorption axes are the same. The spectral transmittance Tp(λ) is then calculated according to JIS Z 8729.

Parallel transmittance refers to the transmittance when two polarizing films are overlapped and their absorption axes are the same when irradiated with natural light. Therefore, the parallel split transmittance Tp(λ) at a certain wavelength λ The transmittance when irradiated with natural light of wavelength λ in the state where two polarizing films are overlapped and the respective absorption axes are the same is equivalent to the value obtained by the method shown below. That is, a polarizing film is irradiated with linearly polarized light of wavelength λ in a direction parallel to its absorption axis, the spectral transmittance k1(λ) at this time is measured, and then irradiated with a straight line of wavelength λ in a direction perpendicular to the absorption axis. polarized light, and measure the spectral transmittance k2(λ) at this time. When two polarizing films are overlapped and their absorption axes are the same, the transmittance (parallel spectral transmittance) when irradiated with natural light of wavelength λ and the transmittance {k1 (λ)} ² and the average value of the transmittance {k2(λ)} ² after transmitting the film twice with the transmittance k2(λ) are equal, so use these values to calculate the wavelength at the wavelength λ according to the following calculation formula (I). Parallel spectral transmittance Tp(λ).

Tp(λ)＝[{k1(λ)} ² +{k2(λ)} ² ]/2(I)

These measurements and calculations are carried out in the continuous wavelength region or at predetermined wavelength intervals, and the parallel spectral transmittance Tp(λ) at each wavelength λ is used to calculate the parallel hue b ^* in accordance with JIS Z 8729. The spectral transmittance k1( λ) and k2(λ) as well as the parallel spectral transmittance Tp(λ) are not expressed in %, they are all expressed with 1 as the maximum value, when expressed in %, it can be enlarged 100 times.

[Example 1]

Firstly, the raw material film 1 is dipped for about 80 seconds in the swelling tank 3 filled with pure water at 30° C. in a tensioned state without slack in the film, so that the film is fully swollen. While swelling in the swelling tank 3, the roll speed ratio between the entrance and the exit is 1.2. After controlling the moisture with nip rolls, it was dipped for about 160 seconds in the water immersion tank 4 filled with pure water at 30°C. The draw ratio in the machine direction in this tank was 1.04 times. Next, uniaxial stretching was carried out at a draw ratio of about 1.5 times while dipping 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, uniaxial stretching is carried out while immersing 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 56.5° C. for 130 seconds, so that the cumulative stretching ratio of the raw material Reached 5.3 times. Finally, it was washed with pure water at 9° C. for about 16 seconds in the washing tank 7 , and then dried at about 60° C. for 160 seconds in the drying oven 8 to obtain an iodine-based polarizing film.

For the obtained polarizing film, the parallel hue b ^* value at the central portion in the width direction and the parallel hue b ^* value at the end portions in the width direction were determined, and the difference between them was 2.1.

A polarizing plate was obtained by bonding protective films containing triacetyl cellulose to both surfaces of the polarizing film via an adhesive containing a polyvinyl alcohol-based resin aqueous solution. In addition, a protective film containing triacetyl cellulose is pasted on one side of the above-mentioned polarizing film through an adhesive containing a polyvinyl alcohol-based resin aqueous solution or a non-solvent type adhesive, and a protective film containing norbornene is pasted on the other side. A resin-based protective film can also be used to obtain a polarizer.

[Comparative example 1]

Firstly, the raw material film 1 is dipped for about 50 seconds in the swelling tank 3 filled with pure water at 30° C. in a tensioned state where the film does not sag, so that the film is fully swollen. After controlling the moisture with nip rollers, it was dipped for about 160 seconds in a water immersion tank 4 filled with pure water at 30° C., and stretched in the machine direction at a draw ratio of 1.20 times in the tank. Then, the same operation as in Example 1 was carried out, uniaxially stretched in the dyeing tank 5, uniaxially stretched in the boric acid tank 6, washed with water and dried to obtain a polarizing film.

For the obtained polarizing film, the parallel hue b ^* value at the central portion in the width direction and the parallel hue b ^* value at the end portions in the width direction were determined, and the difference between them was 4.9.

Industrial applicability

According to the method of the present invention, it is possible to obtain a polarizing film or a polarizing plate having high uniformity in optical properties in the width direction of the film produced as a roll-shaped elongated article. Cutting the polarizing plate into small polarizing plates of various sizes exhibits substantially the same optical characteristics between the plates, and can be effectively used in various display devices including liquid crystal display devices.

Claims (5)

1. the manufacture method of polarized light film, it is that the polyvinyl alcohol resin film is handled continuously by swelling treatment process, water retting treatment process, dyeing treatment process and boric acid treatment process in order, and carry out the method that uniaxial tension is made polarized light film at least one operation in dyeing treatment process and boric acid treatment process, wherein

In aforementioned water retting treatment process, handle aforementioned polyvinyl alcohol resin film, make stretching ratio reach more than 1 times and below 1.05 times with respect to operating direction.

2. method according to claim 1, wherein, aforementioned water retting treatment process is carried out under 10～50 ℃ temperature.

3. method according to claim 1 and 2, wherein, aforementioned water retting treatment process is carried out in the pure water that does not have solvent components basically.

4. the manufacture method of polarized light piece, it is after making polarized light film with claim 1 or 2 method described in any, at the one side at least of the gained polarized light film transparent protective film of fitting.

5. the manufacture method of polarized light piece, it is after described method is made polarized light film with claim 3, at the one side at least of the gained polarized light film transparent protective film of fitting.

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