JP2002131548A - Method for producing polarizing film, polarizing plate and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polarizing film in which irregular color and a shift of an absorption axis occur hardly as a method for producing a polarizing film by applying tension to a polyvinyl alcohol film while holding both ends of the film to stretch the film, to provide a polarizing plate obtained in a high yield ratio from a polarizing film with little irregular color produced by the method and to provide a liquid crystal display using the polarizing plate. SOLUTION: In the method for producing a polarizing film, a crosslinking component is incorporated into a continuously supplied polyvinyl alcohol film, tension is applied to the film in an atmosphere at 30-80 deg.C and 70-99% RH while holding both ends of the film by holding means to stretch the film by 2.0-8.0 times and the stretched film is dried while keeping a width change within ±5%. Dyeing is carried out before supply or after drying.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polarizing film by stretching a polyvinyl alcohol-based film in the width direction and adsorbing and orienting a dichroic substance. Further, the present invention relates to a polarizing plate using a polarizing film manufactured by using the method, and a liquid crystal display device using the polarizing plate.

[0002]

2. Description of the Related Art A polarizing plate is a liquid crystal display (hereinafter referred to as "LC").
D)), the demand is rapidly increasing. Generally, a polarizing plate is obtained by laminating a protective film on both sides or one side of a polarizing layer having a polarizing ability via an adhesive layer. As the polarizing layer, polyvinyl alcohol (hereinafter referred to as "P
VA ") is mainly used, and the PVA film is stretched uniaxially and then dyed with iodine or a dichroic dye, or reversely dyed and stretched, and further polarized by crosslinking with a boron compound. A film is formed, and a protective film is pasted and used as a polarizing plate. In general,
A method is employed in which iodine is adsorbed in a liquid phase and then drawn in a liquid by a roll method. In addition, dry stretching under high temperature,
A method of subjecting a film to staining while keeping the film under tension is also used. Normally, since the film is stretched uniaxially in the longitudinal direction, the absorption axis of the polarizing film is substantially parallel to the longitudinal direction.

In the conventional LCD, the transmission axis of the polarizing plate is arranged at an angle of 45 ° with respect to the vertical or horizontal direction of the screen. Had to be punched in a 45 ° direction. However, when punching in the 45 ° direction, a portion that cannot be used eventually occurs near both ends of the roll, and especially in a large-sized polarizing plate,
There was a problem that the yield was small. Further, there is a problem that it is difficult to reuse the material of the polarizing plate after lamination, resulting in an increase in waste.

[0004]

In order to solve this problem, the present inventors have disclosed in Japanese Patent Application No. 2000-208713 the absorption axis inclined at 45 ° in the longitudinal direction with good productivity using a tenter stretching machine or the like. A method for manufacturing a polarizing film with is proposed. That is, the locus L1 of the holding means from the substantial holding start point at one end of the film to the substantial holding release point.
And the locus L2 of the holding means from the substantial holding start point to the substantial holding release point at the other end of the film and the distance W between the two substantial holding release points satisfy the following equation (2). Stretching, Formula (2) | L2-L1 |> 0.4W or (i) 1.1 to 2 at least in the film width direction
(Ii) the longitudinal movement speed difference of the holding device at both ends of the film is set to 1% or less, and (iii) the film traveling direction and the substantial stretching of the film at the exit of the step of holding both ends of the film. It has been proposed that the oblique orientation with respect to the longitudinal direction can be achieved by bending the film advancing direction while holding both ends of the film so that the angle between the directions is inclined by 20 to 70 °.

However, when a polarizing film is manufactured by this stretching method, it is very difficult to install a so-called tenter device in a liquid, and stretching must be performed in a gas phase. When a wet membrane that has been previously dyed with iodine is stretched in dry air,
The drying unevenness causes color unevenness and lowers the display quality of the LCD. Also, if you try to use for dyeing after the tenter withdrawal,
It is necessary to once release from the holding means and release from tension,
In conventional dry stretching, a misalignment occurs in the oblique orientation, and a desired orientation cannot be obtained.

An object of the present invention is to provide a method for producing a polarizing film by applying a tension while holding both ends of a polyvinyl alcohol-based film to produce a polarizing film, in which a color unevenness and a deviation of an absorption axis are hardly caused. Is to do. Another object of the present invention is to provide a polarizing plate which can be obtained at a high yield from a polarizing film having less color unevenness manufactured by the manufacturing method. Still another object of the present invention is to provide a liquid crystal display device using the polarizing plate.

[0007]

Means for Solving the Problems The inventors of the present invention have intensively studied means for achieving the above objects, and as a result, have found a method for producing a polarizing film with less color unevenness and less absorption axis deviation. That is,
According to the present invention, a method for producing a polarizing film having the following constitution, a polarizing plate,
And a liquid crystal display device, and the above object of the present invention is achieved. 1. The polyvinyl alcohol-based film continuously supplied contains a crosslinking component, and while holding both ends by holding means, a tension is applied in an atmosphere of 30 ° C to 80 ° C and 70 to 99% RH to 2.0 to A method for producing a polarizing film, comprising: stretching after stretching 8.0 times, drying while keeping the width change within ± 5%, and then subjecting the film detached from the holding means to dyeing. 2. A continuously supplied polyvinyl alcohol-based film is dyed and contains a cross-linking component, and tension is applied under an atmosphere of 30 to 80 ° C. and 70 to 99% RH while holding both ends by holding means. A method for producing a polarizing film, comprising: stretching the film at a ratio of 2.0 to 8.0 times, and drying the film while keeping the width change within ± 5%. 3. 3. The method for producing a polarizing film according to the above item 2, wherein the dyeing is performed with a solution of a substance containing iodine and iodine ions. 4. 4. The method for producing a polarizing film according to any one of the above items 1 to 3, wherein the film moisture at the time when the film is detached from the holding means is 10% or less. 5. The method for producing a polarizing film according to any one of the above items 1 to 4, wherein the drying temperature after stretching is 60 to 130 ° C. 6. The method for producing a polarizing film according to any one of the above items 1 to 5, wherein the orientation direction of the film immediately after detachment from the holding means forms an angle of 40 to 50 ° with respect to the film transport direction. 7. 7. A polarizing plate, wherein at least one surface of the polarizing film produced by the method according to any one of 1 to 6 above is protected by a transparent film. 8. The polarizing plate of the above item 7 was placed on both sides of the liquid crystal cell.
A liquid crystal display device used for at least one of the polarizing plates.

[0008]

Embodiments of the present invention will be described below in detail. A first feature of the present invention is that a polyvinyl alcohol-based film (hereinafter, also referred to as a “PVA-based film”) contains a crosslinking component, and is stretched in a high humidity atmosphere, whereby unevenness of polyiodide ion generation due to drying unevenness is obtained.
Alternatively, it suppresses the degree of crystallinity and degree of orientation unevenness due to unevenness in drying. The second feature of the present invention is that the wet film is dried while keeping the width almost constant, and at the same time, the cross-linking is advanced, thereby increasing the strength of the stretched film and separating from the stretching means. The purpose of the present invention is to suppress the displacement of the orientation axis due to swelling due to moisture in the tension and dyeing steps.

An example of a method for manufacturing a polarizing film according to the present invention will be schematically described with reference to FIG. FIG.
It is a schematic diagram of an example of a tenter equipment which manufactures a polarizing film with a 5 ° absorption axis inclined. (A) is a step of introducing a raw film, (b) is a step of stretching in the width direction, and (c) is a step of sending the stretched film to the next step. The PVA-based film 11 is
It is introduced from the direction of (a) and bites into the tenter stretching machine. After biting, the solution of the crosslinking agent is applied by the application means 12 in the step (a), and is uniaxially stretched in the width direction in the step (b). The atmosphere during stretching is 30 ° C to 80 ° C, 70 to 9
It needs to be 9% RH. Here, after the film is bent in the direction of film advance in order to incline the orientation axis, the film is dried in step (c) while keeping the width substantially constant, and after removing volatile components sufficiently, it is released in the direction (b). After the release, the stretched and crosslinked film is immersed in a dyeing solution in the dyeing tank 15, adsorbs dichroic substances such as iodine and dichroic dyes, and becomes a polarizing film.

Another example of the method for producing a polarizing film of the present invention will be schematically described with reference to FIG. FIG. 2 is a schematic view of an example of a so-called ordinary widthwise uniaxial stretching type tenter stretching machine. The PVA-based film 21 is dyed in a dichroic substance dyeing tank 22, coated with a crosslinking agent solution by a coating means 23, and bitten into a tenter stretching machine. (B) 30 ° C to 80 ° C in the step,
After being uniaxially stretched in the width direction under an atmosphere of 70 to 99% RH, the film is dried while keeping the width substantially constant in the step (c). Becomes

In any case, in the drying in the step (c), the width change needs to be maintained at ± 5%, and ± 3%, in order to suppress the deviation of the alignment axis due to uneven crosslinking. More preferred. If the change in width is too large, a knicks or break is likely to occur in the polarizing film during curing. The drying temperature is preferably from 60 to 130 ° C., and this temperature is appropriately changed depending on the type of the dichroic substance to be adsorbed and whether the adsorption step is before or after the stretching step. The lower temperature side is preferable when iodine or the like having a high sublimation property is adsorbed before the stretching step, and when dyeing is performed after the stretching step, or even before the stretching step, when a dichroic substance having a low sublimation property is used. Is preferably on the higher temperature side to promote the dura. The moisture in the film at the time when the film is separated from the holding means is preferably 10% or less, and is preferably 5% or less.
% Is more preferable. If the amount of water at the time of separation is too large, the film is deformed due to the line tension after separation, and the film tends to shift in the absorption axis direction.

In the examples of FIGS. 1 and 2, the steps (a) and (b) can be clearly separated, but there is no need to clearly separate the steps (a) and (b). The stretching can be started immediately after the stretching.

The means for applying the crosslinking agent to the PVA-based film is not particularly limited, and any method such as immersion, application, and spraying of the film in a liquid can be used.
Particularly, a dipping method and a coating method are preferable. As a coating means, a roll coater, a die coater, a bar coater, a slide coater,
Any commonly known means such as a curtain coater can be used. Further, a method in which cloth, cotton, a porous material, or the like impregnated with the solution is brought into contact with the film is also preferable. As the cross-linking agent, those described in U.S. Pat. No. 2,328,979 can be used, but boric acid and borax are practically preferably used. Also, zinc, cobalt, zirconium, iron,
Metal salts such as nickel and manganese can also be used together. The application of the cross-linking agent may be performed before biting into the stretching machine, or may be performed after biting, and in the step (b) of the example of FIGS. It may be performed in any of the steps up to the end.

In the present invention, as shown in FIG. 1, the orientation direction of the film immediately after being released from the holding means is at an angle of 40 to 50 ° with respect to the film transport direction.
The greatest effect is exhibited when combined with the stretching method described in Japanese Patent No. 713. When the orientation axis is inclined with respect to the longitudinal direction of the film, line tension, swelling of the dyeing solution, and the like are likely to affect the angle of the orientation axis, but this is prevented by the method of the present invention. it can.

A PVA-based film serving as a raw material of a polarizing film is usually a saponified polyvinyl acetate. Examples of the PVA-based film include unsaturated carboxylic acids, unsaturated sulfonic acids, olefins, and the like.
A component copolymerizable with vinyl acetate, such as vinyl ethers, may be contained. Further, a modified PVA containing an acetoacetyl group, a sulfonic acid group, a carboxyl group, an oxyalkylene group, or the like can also be used. Although the saponification degree of PVA is not particularly limited, solubility, polarization, heat resistance,
80 to 100 mol% is preferable from the viewpoint of moisture resistance and the like,
90-100 mol% is particularly preferred. The degree of polymerization of PVA is not particularly limited, but is preferably 800 to 10000, and is preferably 1 to 10,000 in view of film strength, heat resistance, moisture resistance, stretchability, and the like.
000 to 5000 are particularly preferred. Further, the syndiotacticity of PVA is not particularly limited, and can take any value depending on the purpose. The thickness of the film before stretching is not particularly limited, but is preferably 1 μm to 1 mm from the viewpoint of stability of film retention and uniformity of stretching.
~ 200 µm is particularly preferred.

The stretching is preferably performed three times or more, and
5 times or more is more preferable. The thickness of the film after stretching is not particularly limited, but from the viewpoint of handleability, durability, and economy, it is 5 to 5.
100 μm is preferable, and 10 to 40 μm is more preferable.

As a dyeing method, a solution of a dichroic substance is added to P
Any means such as a method of dipping a VA-based film, a method of applying or spraying a dichroic substance solution on the film, and the like are possible. In addition, not only the above-described liquid-phase adsorption but also a gas-phase adsorption can be performed as needed. Dyeing may be performed in the stretching step, before or after the stretching step, or in both steps, and it is also possible to mix a dichroic substance in advance when casting the PVA-based film.

As the dichroic substance, iodine is preferably used. Iodine may be used alone, but is more preferably used together with an iodide such as potassium iodide. It is also preferable to dye with a dichroic dye. Specific examples of dichroic dyes include, for example, dye compounds such as azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes, and anthraquinone dyes. I can give it.
Water-soluble ones are preferred, but not limited thereto. Further, it is preferable that a hydrophilic substituent such as a sulfonic acid group, an amino group, or a hydroxyl group is introduced into these dichroic dyes.

Representative dichroic dyes include, for example, C.I. Eye. direct. Yellow 12, sea. Eye. direct. Orange 39, sea. Eye. direct. Orange 72, sea. Eye. direct. Red
28, sea. Eye. direct. Red 39, sea.
Eye. direct. Red 79, Sea. Eye. direct. Red 81, sea. Eye. direct. Red
83, Sea. Eye. direct. Red 89, sea. Eye. direct. Violet 48, C.I. Eye. direct. Blue 67, Sea. Eye. direct. Blue 90, Sea. Eye. direct. Green 59, sea. Eye. Acid. Red 37 and the like, and further described in JP-A-1-161202 and JP-A-1-1-1.
No. 72906, JP-A-1-172907, JP-A-1-172907
183602, JP-A-1-248105, JP-A-1
And the dyes described in JP-A-265205 and JP-A-7-261024. In particular, C. Eye. direct. Red 28 (Congo Red) has long been known as preferred for this application. These dichroic dyes are used as a free acid or a salt of an alkali metal salt, an ammonium salt or an amine. By mixing two or more of these dichroic dyes, polarizers having various hues can be manufactured. As a polarizing element or a polarizing plate, a compound (dye) exhibiting black when the polarizing axes are orthogonal to each other or a compound in which various dichroic dyes are blended so as to exhibit black are preferable because they have excellent single-plate transmittance and polarization ratio.

The polarizing film produced by the present invention can be used as a polarizing plate by attaching a protective film to both sides or one side. The type of the protective film is not particularly limited,
Cellulose acylates such as cellulose acetate and cellulose acetate butyrate, polycarbonate, polyolefin, polystyrene, polyester and the like can be used. The protective film of the polarizing plate is required to have physical properties such as transparency, appropriate moisture permeability, low birefringence, and appropriate rigidity, and when viewed comprehensively, cellulose acylates are preferable, and cellulose acetate is particularly preferable.

As for the physical properties of the protective film, physical properties according to the intended use are required. Typical preferable physical properties for use in a normal transmission type LCD are shown below. The thickness is preferably 5 to 500 μm from the viewpoint of handleability and durability, and is preferably 20 to 20 μm.
0 μm is more preferable, and 20 to 100 μm is particularly preferable. The retardation value is 0 at 632.8 nm.
150 nm is preferable, 0 to 20 nm is more preferable,
0-5 nm is particularly preferred. It is preferable that the slow axis of the protective film be substantially parallel or orthogonal to the absorption axis of the polarizing film from the viewpoint of avoiding linear polarization from being made elliptical. However, when the protective film is provided with a function of changing the polarization property such as a retardation plate, the present invention is not limited thereto, and the absorption axis of the polarizing plate and the slow axis of the protective film can have any angle. The visible light transmittance is preferably at least 60%, particularly preferably at least 90%.
The dimensional decrease after treatment at 90 ° C. for 120 hours is 0.3 to 0.0
It is preferably 1%, particularly preferably 0.15 to 0.01%. The tensile strength value of the film by a tensile test is preferably 50 to 1000 MPa,
-300 MPa is particularly preferred. The moisture permeability of the film is
100 to 800 g / m ² · day is preferred, and 300 to
Particularly preferred is 600 g / m ² · day. Of course, the protective film of the present invention is not limited to the above values.

The polymerization degree (average viscosity) of cellulose acetate, which is particularly preferably used for the protective film, is 200 to 700.
Are preferable, and those having 250 to 550 are particularly preferable. Cellulose as a raw material for cellulose acetate includes cotton linter and wood pulp. Cellulose acetate obtained from any of the raw material celluloses may be used, or may be used as a mixture.

The cellulose acetate film is usually produced by a solvent casting method. In the solvent casting method, a concentrated solution (hereinafter, referred to as a dope) is prepared by dissolving cellulose acetate and various additives in a solvent, and then casting the solution on an endless support such as a drum or a band, and evaporating the solvent. That is, a film is formed. The casting and drying methods in the solvent casting method are described in U.S. Pat. Nos. 2,336,310 and 23,676.
No. 03, No. 2492078, No. 2492977, No. 2492978, No. 2607704, No. 27390
Nos. 69 and 2739070, British Patent 640731
Nos. 736892 and JP-B-45-455.
No. 4, No. 49-5614, JP-A-60-176834.
And JP-A-60-203430 and JP-A-62-115035.

Examples of organic solvents for dissolving cellulose acetate include hydrocarbons (eg, benzene, toluene), halogenated hydrocarbons (eg, methylene chloride, chlorobenzene), alcohols (eg, methanol, ethanol, diethylene glycol), ketones (Eg, acetone), esters (eg, ethyl acetate, propyl acetate) and ethers (eg, tetrahydrofuran, methyl cellosolve) and the like. Of these, halogenated hydrocarbons having 1 to 7 carbon atoms are preferably used, and methylene chloride is most preferably used. From the viewpoint of physical properties such as solubility of cellulose acetate, peeling property from a support, mechanical strength of a film, and optical properties, it is possible to mix one or several alcohols having 1 to 5 carbon atoms in addition to methylene chloride. preferable. The alcohol content is 2% based on the whole solvent.
It is preferably from 25 to 25% by weight, more preferably from 5 to 20% by weight. Specific examples of alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol and the like.
-Butanol or a mixture thereof is preferably used.

In addition to cellulose acetate, components that become solids after drying include plasticizers, ultraviolet absorbers, inorganic fine particles, heat stabilizers such as salts of alkaline earth metals such as calcium and magnesium, and antistatic agents. An agent, a flame retardant, a lubricant, an oil agent, a release accelerator from a support, a hydrolysis inhibitor, and the like can be optionally included.

Examples of preferably added plasticizers include:
Triphenyl phosphate, biphenyl diphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, tributyl phosphate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, diethyl hexyl phthalate, triacetin, ethyl phthalyl ethyl glycolate And trimethyl trimellitate. Particularly, triphenyl phosphate, biphenyl diphenyl phosphate, diethyl phthalate, ethyl phthalyl ethyl glycolate, and trimethyl trimellitate are preferred. These plasticizers may be used alone, or
More than one species may be used in combination. The amount of the plasticizer added is preferably 5 to 30% by weight based on cellulose acetate, and particularly preferably 8 to 30% by weight.
It is preferably at most 16% by weight.

Any kind of ultraviolet absorber can be selected according to the purpose. Salicylic acid ester-based, benzophenone-based, benzotriazole-based, benzoate-based, cyanoacrylate-based, nickel complex-based absorbers and the like are used. Benzophenone and benzotriazole are particularly preferred.

The inorganic fine particles to be added to cellulose acetate include silica, kaolin, talc, diatomaceous earth,
Quartz, calcium carbonate, barium sulfate, titanium oxide, alumina and the like can be arbitrarily used according to the purpose.
The number average particle size of the dispersed particles is preferably from 0.01 to 100 μm, particularly preferably from 0.1 to 10 μm.

As the release accelerator from the support, a surfactant is effective and is not particularly limited, such as phosphoric acid type, sulfonic acid type, carboxylic acid type, nonionic type and cationic type.
These are described, for example, in JP-A-61-243837.

When the above cellulose acetate film is used as a protective film, hydrophilicity is imparted to the film surface by means of saponification, corona treatment, flame treatment, glow discharge treatment or the like in order to enhance the adhesion to the PVA-based resin. Is preferred. Alternatively, a hydrophilic resin may be dispersed in a solvent having an affinity for cellulose acetate, and a thin layer may be applied. Among the above means, saponification treatment is particularly preferable because the flatness and physical properties of the film are not impaired. The saponification treatment is performed by immersing the film in an aqueous alkaline solution such as caustic soda. After the treatment, it is preferable to neutralize with a low-concentration acid and sufficiently wash with water in order to remove excess alkali.

On the surface of the protective film of the polarizing plate of the present invention, a liquid crystal display for compensating a viewing angle of an LCD described in JP-A-4-229828, JP-A-6-75115 and JP-A-8-50206 is disclosed. Optically anisotropic layer, antiglare layer or antireflection layer for improving display visibility, or layer having PS wave separation function by anisotropic scattering or anisotropic optical interference for improving LCD brightness (polymer (Dispersed liquid crystal layer, cholesteric liquid crystal layer, etc.), hard coat layer to enhance the scratch resistance of the polarizing plate, gas barrier layer to suppress the diffusion of moisture and oxygen, easily adhesive layer to increase the adhesion to the polarizing film or adhesive or adhesive An arbitrary functional layer such as a layer imparting slipperiness can be provided. The functional layer may be provided on the polarizing film side or on the opposite surface to the polarizing film, and can be appropriately selected according to the purpose.

Various functional films can be directly bonded to one or both surfaces as a protective film on the polarizing film of the present invention. Examples of the functional film include a retardation film such as a λ / 4 plate and a λ / 2 plate, a light diffusion film, a plastic cell having a conductive layer provided on the surface opposite to the polarizing plate, anisotropic scattering and anisotropic optical interference. Examples include a brightness enhancement film having a function, a reflector, and a reflector having a semi-transmissive function.

As the protective film for the polarizing plate, one or a plurality of the above-mentioned preferred protective films can be laminated. The same protective film may be attached to both sides of the polarizing film,
A protective film having different functions and physical properties may be bonded to both surfaces. In addition, since the above-mentioned protective film is bonded only to one surface and the liquid crystal cell is directly bonded to the other surface, it is also possible to directly provide an adhesive layer and not bond the protective film. In this case, it is preferable to provide a peelable separator film outside the adhesive.

The adhesive for adhering the protective film and the polarizing film is not particularly limited, and any known adhesive such as PVA, modified PVA, urethane, and acrylic can be used. The thickness of the adhesive layer is preferably from 0.01 to 20 μm, more preferably from 0.1 to 10 μm.

The polarizing plate of the present invention preferably has a higher transmittance from the viewpoint of enhancing the contrast of the liquid crystal display device.
The higher the degree of polarization, the better. Transmittance is preferably 30%
Or more, more preferably 40% or more. The degree of polarization is preferably at least 95.0%, more preferably at least 99%, particularly preferably at least 99.9%.

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples.

[0037]

EXAMPLES In each of the examples, the characteristics of the polarizing plate were measured as follows. (Transmittance) The transmittance was measured using a Shimadzu spectrophotometer UV-3100PC, and the spectral transmittance τ was determined every 10 nm.
The transmittance T (%) was calculated from (λ) according to the following equation.

[0038]

(Equation 1)

In the formula, P (λ) is a spectral distribution of a standard light D65 light source according to JIS Z8720. y (λ) is J
It is a color matching function based on a 2-degree visual field X, Y, Z system according to ISZ8701.

(Degree of Polarization) The degree of polarization P (%) is calculated by the following equation.

[0041]

(Equation 2)

Here, Tp is the transmittance (%) when the absorption axes of the two polarizing plates are superposed in parallel in a sample obtained by superposing the two polarizing plates, and Tc is the absorption of the two polarizing plates. This is the transmittance (%) when the axes are superimposed orthogonally.

Example 1 A PVA film having a thickness of 75 μm was introduced into a tenter stretching machine shown in FIG. 1, and an aqueous solution of boric acid 60 g / l was applied at 45 ° C. using a die coater. The film was stretched 5.3 times in the width direction in an atmosphere of 50 ° C. and 95% RH, bent, and dried and fixed with hot air at 110 ° C. while keeping the width change constant (± 0%). The water content when the film was released was 2%. The film after detachment is immersed in a solution of 0.1 g / l of iodine, 6 g / l of potassium iodide, and 50 g / l of boric acid, and is immersed in a dyeing solution so that the transmittance of the polarizing plate becomes approximately 42%. Was adjusted and dyed to prepare a polarizing film. On both surfaces of this polarizing film, Fujitac TD80UF manufactured by Fuji Photo Film Co., Ltd. (cellulose acetate film, film thickness: 80 μm, retardation: 3.5 nm, tensile strength in the longitudinal direction: 170 MPa, width direction: 145 MPa, dimension decrease after processing at 90 ° C. for 120 hours 0) .1
3%, transparency 92.5%) with 1.5N NaO at 60 ° C.
H solution for 180 seconds, saponification treatment, water washing and neutralization treatment, and PVA (Kuraray PVA117H) 4
It was pasted through a weight% aqueous solution and dried to obtain a polarizing plate. The absorption axis of the polarizing plate was inclined by 45 ° with respect to the longitudinal direction. When the obtained polarizing plate was observed through transmission with Sharksten light, no color unevenness was observed.

Example 2 A PVA film having a thickness of 75 μm was coated with 0.1 g / l of iodine.
It is immersed in an aqueous solution (staining solution) of potassium iodide 6 g / l, stained, dried once, and then boric acid 60 g is coated with a bar coater.
/ L of a 45 ° C aqueous solution was applied and introduced into a tenter stretching machine in the form of FIG. 4.7 in an atmosphere of 40 ° C. and 95% RH
The film was stretched twice in the width direction, then dried and fixed with 70 ° C. hot air while keeping the width change constant (± 0%), and then separated to form a polarizing film. The moisture content of the polarizing film upon detachment was 3%.
A protective film was attached to both surfaces of the separated polarizing film in the same manner as in Example 1, and further dried to obtain a polarizing plate. The immersion time in the staining solution was adjusted so that the transmittance of the polarizing plate was approximately 42%. The absorption axis of the polarizing plate was perpendicular to the longitudinal direction. When the obtained polarizing plate was observed through transmission with Sharksten light, no color unevenness was observed.

Example 3 A polarizing plate was manufactured in the same manner as in Example 1 except that the drying temperature was 30 ° C. The film moisture at the time of separation is 16%
Met. When the obtained polarizing plate was observed by transmission with Sharksten light, no color unevenness was observed, but a partial shift of the absorption axis occurred, and light leakage was observed in a crossed Nicols state.

Comparative Example 1 A polarizing film and a polarizing plate were produced in the same manner as in Example 2 except that the stretching atmosphere was changed to 50 ° C. and 20% RH.
When the obtained polarizing plate was observed through transmission with Sharksten light, very strong color unevenness was confirmed.

Table 1 shows the results of Examples 1, 2, and 3 and Comparative Example 1.

[0048]

[Table 1]

Example 4 The polarizing plates of Examples 1 and 2 were replaced with a polarizing plate on the backlight side of a liquid crystal display, and the display quality was observed.
Excellent brightness and visibility were shown.

[0050]

The method for producing a polarizing film according to the present invention is a method of stretching by applying tension while holding both ends of a PVA-based film, and stretching under a high humidity condition and keeping the width almost constant. The wetted film is dried in the immersed state, and at the same time, the crosslinking proceeds, so that the obtained polarizing film has less color unevenness and deviation of the absorption axis. Since the polarizing film obtained by the manufacturing method of the present invention has little color unevenness and deviation of the absorption axis as described above, a liquid crystal display device in which a polarizing plate using this polarizing film is arranged in a liquid crystal cell has excellent brightness and visibility. Shows sex. In one embodiment of the method for producing a polarizing film of the present invention, the orientation direction of the film immediately after detachment from the holding means is 40 to 90 with respect to the film transport direction.
Since the polarizing film has an angle of 50 °, the obtained polarizing film has an absorption axis of 40 to 50 ° with respect to the longitudinal direction, and a polarizing plate with a high yield can be obtained from a multilayer film in which a protective film is provided on this polarizing film. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view of a tenter facility for producing a polarizing film having an absorption axis inclined at 45 ° to the longitudinal direction used in the production method of the present invention.

FIG. 2 is a schematic view of a normal widthwise uniaxial stretching type tenter stretching machine used in the production method of the present invention.

[Explanation of symbols]

 (A) Film introduction direction (b) Film transport direction to the next step (a) Step of introducing a film (b) Step of stretching a film (c) Step of sending a stretched film to the next step 11 PVA-based film 12 Coating means 13, 14 Locus of left and right film holding means 15 Staining solution tank 16, 17 Coating boundary of crosslinking component solution 21 PVA-based film 22 Staining solution tank 23 Coating means 24, 25 Locus of left and right film holding means 26, 27 Coating of crosslinking component solution boundary

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29K 105: 24 B29K 105: 24 B29L 7:00 B29L 7:00 11:00 11:00 C08L 29:04 C08L 29:04 F term (reference) 2H049 BA02 BA27 BB43 BC01 BC03 BC22 2H091 FA08X FA08Z FB02 FB12 FC01 FC22 GA16 LA12 4F073 AA05 AA15 BA17 BB01 EA02 GA01 HA05 4F210 AA19 AG01 AH73 AM26 AR06 QA02 QC03 QD13

Claims (8)

[Claims] 1. A continuous supply of a polyvinyl alcohol-based film containing a crosslinking component, tension applied to the film at 30 ° C. to 80 ° C. and an atmosphere of 70% to 99% RH while holding both ends by holding means. A method for producing a polarizing film, comprising stretching the film to 2.0 to 8.0 times, drying the film while keeping the width change within ± 5%, and then subjecting the film detached from the holding means to dyeing. 2. A continuously supplied polyvinyl alcohol-based film is dyed and contains a crosslinking component, and is held at 30 ° C. to 80 ° C. and 70 to 9 while holding both ends by holding means.
A method for producing a polarizing film, comprising: applying a tension in an atmosphere of 9% RH, stretching the film 2.0 to 8.0 times, and then drying the film while keeping the width change within ± 5%. 3. The method for producing a polarizing film according to claim 2, wherein the dyeing is performed with a solution of a substance containing iodine and iodine ions. 4. The method for producing a polarizing film according to claim 1, wherein the film moisture at the time when the film is detached from the holding means is 10% or less. 5. The method for producing a polarizing film according to claim 1, wherein the drying temperature after stretching is 60 to 130 ° C. 6. The polarizing film according to claim 1, wherein the orientation direction of the film immediately after being released from the holding means is at an angle of 40 to 50 ° with respect to the film transport direction. Method. 7. A polarizing plate, wherein at least one side of a polarizing film produced by the method according to claim 1 is protected by a transparent film. 8. A liquid crystal display device wherein the polarizing plate according to claim 7 is used for at least one of two polarizing plates arranged on both sides of a liquid crystal cell.