JP5300160B2 - Manufacturing method of polarizing film - Google Patents

Abstract

This manufacturing method for a polarizing film, in which at least a swelling treatment, a dyeing treatment, a crosslinking treatment, a stretching treatment, and a cleaning treatment are carried out on a polyvinyl alcohol film, is characterized in that during at least one of the treatments subsequent to the crosslinking treatment, a water-soluble antioxidant is added to the treatment liquid so as to satisfy the following formula (1): 0.0005<=A×B<=0.03 (1) (in the formula, A represents the concentration (mol/L) of the water-soluble antioxidant in the treatment bath, and B represents the reductive power of the water-soluble antioxidant in the reduction of iodine to iodine ions). This manufacturing method makes it possible to provide a polarizing film having high contrast and excellent polarizing capabilities for preventing the occurrence of light leakage in the short wavelength region.

Description

  The present invention relates to a method for producing a polarizing film. The present invention also relates to a polarizing plate using the polarizing film. The polarizing film and the polarizing plate can be used alone or as an optical film laminated thereon to form an image display device such as a flat panel display such as a liquid crystal display device or an organic EL display device.

  Conventionally, as a polarizing film used for a liquid crystal display device or the like, an absorption dichroic polarizing film formed by uniaxially stretching a polyvinyl alcohol film dyed with iodine or a dichroic dye has been widely used. . Further, the polarizing film is used as a polarizing plate supplemented with strength by sticking a transparent protective film such as saponified triacetyl cellulose on both sides or one side.

  Particularly in recent years, with the increase in size of liquid crystal display devices, diversity of applications, improvement of functions, and improvement of luminance, improvement of optical properties of polarizing plates used in liquid crystal display devices has been demanded. Development of a polarizing plate having a high degree of polarization, that is, a high contrast is required.

  For example, in Patent Document 1, for the purpose of improving polarization performance, a polyvinyl alcohol film is swollen with swelling water, heated and humidified with high humidity and low temperature warm air, and then dyed with a dye solution of a dichroic dye. There has been proposed a method for producing a polarizing film, which comprises drawing weakly in a drawing solution and then drawing strongly.

  However, the polarizing film obtained by the above production method is not satisfactory with respect to contrast, and there is a problem that light leakage tends to occur in a short wavelength region.

JP 2007-199509 A

  An object of this invention is to provide the manufacturing method of the polarizing film which is excellent in the polarization characteristic which is high contrast and can prevent generation | occurrence | production of the light leak in a short wavelength range.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the object can be achieved by the following method for producing a polarizing film, and have completed the present invention.

That is, the present invention provides a polarizing film manufacturing method in which at least a swelling treatment, a dyeing treatment, a crosslinking treatment, a stretching treatment, and a washing treatment are performed on a polyvinyl alcohol film.
In at least 1 process after the said dyeing | staining process, it is related with the manufacturing method of the polarizing film characterized by including a water-soluble antioxidant in a process liquid so that following formula (1) may be satisfy | filled.
0.0005 ≦ A × B ≦ 0.03 (1)
[In the above formula, A is the concentration (mol / L) of the water-soluble antioxidant in the treatment bath, and B is the reducing power of the water-soluble antioxidant that reduces iodine to iodine ions. ]

The optical properties of the polarizing film, I ₃ by the amorphous portion of iodine and polyvinyl alcohol (PVA) molecule ^- expression by aligning to form a complex, and stretching the complex was formed region ^- complex and I ₅ To do.

  Generally, an iodine complex in a polarizing film absorbs light in the visible light region and exhibits polarization characteristics. As a method for suppressing light leakage of the polarizing film, it is conceivable to increase the amount of iodine complex in the polarizing film. However, if the PVA film is treated with a high concentration dye bath to increase the amount of iodine complex, the iodine complex increases in the PVA molecule, and there is an excess of iodine that is not complexed. In particular, the light transmittance of the polarizing film tends to decrease.

As described above, the present inventors adsorbed excessively on the PVA molecules by adding a water-soluble antioxidant so as to satisfy the formula (1) in the treatment liquid in at least one treatment after the crosslinking treatment. It has been found that iodine can be selectively removed. As a result, a high-contrast polarizing film can be obtained. Further, by reduction effect of the water-soluble antioxidant, excessively adsorbed iodine iodide ion in PVA molecule ^- is reduced to, I ₃ (I) ^- complexes and I ₅ ^- for iodide ion to form a complex is increased, consequently I ₃ ^- complex and I ₅ ^- complex can suppress light leakage in the short wavelength region of the polarizing film increases.

“A × B” in the above formula (1) is an index indicating the reducing ability to reduce iodine to iodine ion (I ⁻ ). When A × B is less than 0.0005, iodine excessively adsorbed on the PVA molecules cannot be sufficiently removed, so that the contrast of the polarizing film cannot be improved. On the other hand, when A × B exceeds 0.03, the iodine complex in the PVA film is broken and the polarization characteristics cannot be secured, and the PVA film is in a decolored state, so that the optical characteristics as a polarization film can be obtained. Disappear.

  The water-soluble antioxidant is preferably at least one selected from the group consisting of ascorbic acid, sodium erythorbate, thiosulfate, and sulfite.

  The polarizing film obtained by the manufacturing method has a feature that it has high contrast and light leakage hardly occurs in a short wavelength region.

  The present invention also relates to a polarizing plate in which a transparent protective film is laminated on at least one surface of the polarizing film.

  The present invention also relates to an optical film in which at least one of the polarizing film or the polarizing plate is laminated.

  Furthermore, this invention relates to the image display apparatus containing the said optical film.

  With the production method of the present invention, the polarizing film has a high contrast that achieves both high transmittance and a high degree of polarization, and has a feature that light leakage hardly occurs in a short wavelength region. By using the polarizing film, the display contrast of the liquid crystal display device is improved.

  As a polyvinyl alcohol film (hereinafter referred to as “PVA film”) which is a raw material of the polarizing film, a known film can be used without any particular limitation. Usually, a PVA film having a thickness of about 10 to 300 μm is used. Preferably it is 20-100 micrometers.

  As the PVA film, for example, a polyvinyl alcohol film conventionally used for a polarizer is preferably used. Examples of the material for the PVA film include polyvinyl alcohol and derivatives thereof. Derivatives of polyvinyl alcohol include polyvinyl formal, polyvinyl acetal and the like, olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid and alkyl esters thereof, acrylamide and the like. Can be given. The degree of polymerization of polyvinyl alcohol is preferably about 100 to 10,000, and more preferably 1,000 to 10,000. A saponification degree of about 80 to 100 mol% is generally used.

  In addition to the above, PVA films include hydrophilic polymer films such as partially saponified ethylene / vinyl acetate copolymers, polyene-based oriented films such as dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride. can give.

  You may add additives, such as a plasticizer and surfactant, in a PVA film. Examples of the plasticizer include polyols and condensates thereof, and examples thereof include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. The amount of the plasticizer used is not particularly limited, but is preferably 20% by weight or less in the PVA film.

  The polarizing film of the present invention is produced by subjecting the PVA film to at least swelling treatment, dyeing treatment, crosslinking treatment, stretching treatment and washing treatment.

  The swelling process is performed before the dyeing process. In addition to washing the surface of the PVA film and the anti-blocking agent by the swelling treatment, swelling of the PVA film also has an effect of preventing unevenness such as uneven coloring.

  The swelling treatment is usually performed by immersing the film in a treatment liquid. As the treatment liquid, water, distilled water, or pure water is usually used. If the main component is water, the treatment liquid may contain a small amount of an iodide compound, a surfactant, an additive such as boric acid, alcohol, and the like. Moreover, when making the said processing liquid contain the iodide compound, the density | concentration of the iodide compound is about 0.1 to 10 weight%, Preferably it is 0.2 to 5 weight%.

  The treatment temperature in the swelling treatment is usually preferably adjusted to about 20 to 45 ° C, more preferably 25 to 40 ° C. If there is swelling unevenness, the portion becomes uneven dyeing in the dyeing process, so that swelling unevenness is not generated. The immersion time is usually about 10 to 300 seconds, preferably 20 to 240 seconds.

  The swelling treatment may be performed together with the stretching treatment. In that case, it is preferable to stretch the film 1.2 to 4 times the original length, and more preferably 1.6 to 3 times.

  The dyeing treatment is usually performed by immersing the film in a dyeing solution. As the staining solution, an iodine solution is generally used. As the iodine aqueous solution used as the iodine solution, an aqueous solution containing iodine ions with, for example, potassium iodide or the like as iodine and a dissolution aid is used. Other aids such as iodides such as lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide and titanium iodide. Can be used. The iodine concentration is about 0.01 to 0.5% by weight, preferably 0.02 to 0.4% by weight, and the potassium iodide concentration is about 0.01 to 10% by weight, preferably 0.02 to 8% by weight. %. In iodine staining, the temperature of the iodine solution is usually about 20 to 50 ° C., preferably 25 to 40 ° C. The immersion time is usually about 10 to 300 seconds, preferably 20 to 240 seconds.

  In the crosslinking treatment, a boron compound is usually used as a crosslinking agent. The crosslinking treatment may be performed together with the stretching treatment. The crosslinking treatment can be performed multiple times. Examples of the boron compound include boric acid and borax. The boron compound is generally used in the form of an aqueous solution or a water-organic solvent mixed solution. Usually, an aqueous boric acid solution is used. The boric acid concentration of the boric acid aqueous solution is about 0.1 to 13% by weight, preferably 2 to 13% by weight. The boric acid aqueous solution or the like can contain an iodide compound such as potassium iodide. When the iodide compound is contained in the boric acid aqueous solution, the iodide compound concentration is about 0.1 to 10% by weight, preferably 0.2 to 5% by weight.

  The crosslinking treatment can be performed by immersing the dyed PVA film in an aqueous boric acid solution or the like. In addition, it can be performed by applying or spraying a boric acid aqueous solution or the like to the film. The processing temperature in a crosslinking process is 25 degreeC or more normally, Preferably it is 30-85 degreeC, More preferably, it is 30-60 degreeC. The treatment time is usually 10 to 800 seconds, preferably 30 to 500 seconds.

  The stretching treatment is usually performed by uniaxial stretching. This stretching process can be performed together with the dyeing process and the crosslinking process. As the stretching method, either a wet stretching method or a dry stretching method can be adopted, but it is preferable to use a wet stretching method. As the wet stretching method, for example, stretching is generally performed in a solution in a swelling process or after a dyeing process. Further, the stretching treatment can be performed after the crosslinking treatment or together with the crosslinking treatment. On the other hand, in the case of dry stretching, examples of the stretching means include an inter-roll stretching method, a heated roll stretching method, and a compression stretching method. The stretching process can be performed in multiple stages.

  An iodide compound such as potassium iodide can be contained in the treatment liquid used in the wet stretching method. When the treatment solution contains an iodide compound, the iodide compound concentration is preferably about 0.1 to 10% by weight, more preferably 0.2 to 5% by weight. The treatment temperature in the wet stretching method is usually 25 ° C. or higher, preferably 30 to 85 ° C., more preferably 50 to 70 ° C. The immersion time is usually about 10 to 800 seconds, preferably about 30 to 500 seconds.

  Although the draw ratio can be appropriately set according to the purpose, the total draw ratio is about 2 to 9 times, preferably 4.5 to 6.8 times, more preferably 5 to 6.5 times. The total stretching ratio refers to a cumulative stretching ratio including stretching in those steps when stretching is involved in a swelling process described later other than the stretching process.

  The washing treatment can be performed by washing with water, distilled water, pure water or the like, for example. The water washing treatment is usually performed by immersing the film in a water washing bath. The washing treatment can be performed by immersing in an aqueous solution containing an iodide such as potassium iodide. For example, the aqueous solution preferably has a potassium iodide concentration of about 0.5 to 10% by weight, more preferably 1 to 8% by weight. The temperature of the cleaning liquid in the cleaning treatment is usually 5 to 50 ° C, preferably 10 to 45 ° C, more preferably 15 to 40 ° C. The immersion time is usually 1 to 300 seconds, preferably 10 to 240 seconds. The cleaning with the aqueous solution can be performed in combination with water cleaning, and can be performed before or after the water cleaning.

  In addition to the above treatment, an insolubilization treatment may be performed. The insolubilization treatment is performed by immersing the PVA film in an aqueous boric acid solution. By performing the insolubilization treatment, water resistance can be imparted to the PVA film. The concentration of boric acid is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The temperature of the boric acid aqueous solution is preferably 20 to 50 ° C. The insolubilization treatment is usually performed before the swelling treatment or simultaneously with the swelling treatment, before the dyeing treatment, or before the crosslinking treatment.

In the production method of the present invention, in at least one treatment after the dyeing treatment, a water-soluble antioxidant is contained in the treatment liquid so as to satisfy the following formula (1).
0.0005 ≦ A × B ≦ 0.03 (1)
[In the above formula, A is the concentration (mol / L) of the water-soluble antioxidant in the treatment bath, and B is the reducing power of the water-soluble antioxidant that reduces iodine to iodine ions. ]

  “A × B” is preferably 0.0008 to 0.025, more preferably 0.0015 to 0.02. The calculation method of the reducing power of the water-soluble antioxidant is as described in the examples.

  Examples of the water-soluble antioxidant include ascorbic acid, erythorbic acid, chlorogenic acid, citric acid, rosmarinic acid, salts thereof, thiosulfate, and sulfite, and these can be used alone. Or two or more of them may be used in combination. Examples of the salt include alkali metal salts such as sodium salt and potassium salt. In particular, ascorbic acid, sodium erythorbate, or thiosulfate is preferably used from the viewpoint of stability in aqueous solution (sustainability of reducing power).

  The water-soluble antioxidant is contained in at least one of the baths used for at least one treatment after the dyeing treatment, or separately in a treatment liquid containing the water-soluble antioxidant. Let Usually, the swelling treatment is first applied. Next, for example, when a dyeing process is performed, a water-soluble antioxidant can be contained in a crosslinking process, a stretching process, a cleaning process, or a separate water-soluble antioxidant process.

  In addition, the said dyeing | staining process, bridge | crosslinking process, and extending | stretching process can be performed by the batch process which performs a some process simultaneously. In the case where a batch process in which a plurality of processes are performed simultaneously is performed, a water-soluble antioxidant can be contained in the bath used for the batch process. Moreover, when each process of the said dyeing | staining process, bridge | crosslinking process, and extending | stretching process is a multistage process, a water-soluble antioxidant can be contained in at least 1 process of the said multistage process.

  Thereafter, the film may be dried. In the drying treatment, the drying time and the drying temperature are appropriately set according to the moisture content required for the obtained polarizer (film). The drying temperature is usually controlled in the range of 20 to 150 ° C, preferably 40 to 100 ° C.

  The polarizing film produced by the above method can be a polarizing plate provided with a transparent protective film on at least one side thereof according to a conventional method. The transparent protective film can be provided as a coating layer made of a polymer or a laminate layer of the film. As the transparent polymer or film material for forming the transparent protective film, an appropriate transparent material can be used, but a material excellent in transparency, mechanical strength, thermal stability, moisture barrier property and the like is preferably used. Examples of the material for forming the transparent protective film include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as cellulose diacetate and cellulose triacetate, acrylic polymers such as polymethyl methacrylate, polystyrene, acrylonitrile, Examples thereof include styrene polymers such as styrene copolymers (AS resins), polycarbonate polymers, and the like. In addition, polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or the above Polymer blends and the like are also examples of polymers that form the transparent protective film. The transparent protective film can also be formed as a cured layer of thermosetting or ultraviolet curable resin such as acrylic, urethane, acrylurethane, epoxy, and silicone.

  Moreover, the polymer film described in JP-A-2001-343529 (WO01 / 37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) a substitution in the side chain And / or a resin composition containing a thermoplastic resin having unsubstituted phenyl and a nitrile group. A specific example is a film of a resin composition containing an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film made of a mixed extruded product of the resin composition or the like can be used. Since these films have a small phase difference and a small photoelastic coefficient, problems such as unevenness due to the distortion of the polarizing plate can be eliminated, and since the moisture permeability is small, the humidification durability is excellent.

  Although the thickness of a transparent protective film can be determined suitably, generally it is about 1-500 micrometers from points, such as workability | operativity, such as intensity | strength and handleability, and thin layer property. 1-300 micrometers is especially preferable, and 5-200 micrometers is more preferable.

  Moreover, it is preferable that a transparent protective film has as little color as possible. Therefore, Rth = (nx−nz) · d (where nx is the refractive index in the slow axis direction in the film plane, nz is the refractive index in the film thickness direction, and d is the film thickness). A transparent protective film having a direction retardation value of −90 nm to +75 nm is preferably used. By using a film having a thickness direction retardation value (Rth) of −90 nm to +75 nm, the coloring (optical coloring) of the polarizing plate caused by the protective film can be almost eliminated. The thickness direction retardation value (Rth) is more preferably −80 nm to +60 nm, and particularly preferably −70 nm to +45 nm.

  As the protective film, a triacetyl cellulose film, a norbornene-based film, a cycloolefin-based film, and an acrylic resin film are preferable from the viewpoints of polarization characteristics and durability. A triacetyl cellulose film is particularly preferable. In addition, when providing a protective film on both sides of a polarizing film, the protective film which consists of the same polymer material may be used by the front and back, and the protective film which consists of a different polymer material etc. may be used.

  The surface of the transparent protective film to which the polarizing film is not adhered may be subjected to a treatment for the purpose of hard coat layer, antireflection treatment, sticking prevention, diffusion or antiglare.

  The antireflection layer, the antisticking layer, the diffusion layer, the antiglare layer, and the like can be provided on the transparent protective film itself, or can be provided as a separate optical layer from the transparent protective film.

  An adhesive is used for the adhesion treatment between the polarizing film and the transparent protective film. Examples of the adhesive include isocyanate adhesives, polyvinyl alcohol adhesives, gelatin adhesives, vinyl latexes, and water-based polyesters. As the adhesive, an adhesive made of an aqueous solution is usually used.

  The polarizing plate of this invention is manufactured by bonding the said transparent protective film and a polarizing film using the said adhesive agent. Application | coating of an adhesive agent may be performed to any of a transparent protective film and a polarizing film, and may be performed to both. After the bonding, a drying process is performed to form an adhesive layer composed of a coating dry layer. Bonding of the polarizing film and the transparent protective film can be performed with a roll laminator or the like. The thickness of the adhesive layer is not particularly limited, but is usually about 0.1 to 5 μm.

  The polarizing plate of the present invention can be used as an optical film laminated with another optical layer in practical use. The optical layer is not particularly limited. For example, for forming a liquid crystal display device such as a reflection plate, a semi-transmission plate, a retardation plate (including wavelength plates such as 1/2 and 1/4), and a viewing angle compensation film. One or more optical layers that may be used can be used. In particular, a reflective polarizing plate or a semi-transmissive polarizing plate in which a polarizing plate or a semi-transmissive reflecting plate is further laminated on the polarizing plate of the present invention, an elliptical polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on the polarizing plate. A wide viewing angle polarizing plate obtained by further laminating a viewing angle compensation film on a plate or a polarizing plate, or a polarizing plate obtained by further laminating a brightness enhancement film on the polarizing plate is preferable.

  The polarizing plate or the optical film of the present invention can be preferably used for forming various devices such as a liquid crystal display device. The liquid crystal display device can be formed according to the conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, a polarizing plate or an optical film, and an illumination system as necessary, and incorporating a drive circuit. There is no limitation in particular except the point which uses the polarizing plate or optical film by invention, and it can apply according to the former. As the liquid crystal cell, any type such as a TN type, an STN type, or a π type can be used.

  Examples and the like specifically showing the configuration and effects of the present invention will be described below. In each example, parts and% are based on weight unless otherwise specified.

(Measurement of reducing power of water-soluble antioxidants)
By the oxidation-reduction reaction, the reducing power of the water-soluble antioxidant was measured by the following volumetric titration method.
1-2 ml of a 0.5% aqueous starch solution (manufactured by Kishida Chemical Co., Ltd., for titration) was added to a 0.1% aqueous iodine solution (25 ml) and colored black. A water-soluble antioxidant aqueous solution having a molar concentration of 0.01 mol / L was dropped into the colored iodine aqueous solution using a burette, and the titration amount (ml) when the color of the aqueous solution became colorless was determined as reducing power. B.

Example 1
While stretching a 75 μm-thick PVA film (trade name: VF-PS # 7500, manufactured by Kuraray Co., Ltd.) for 1 minute in 30 ° C. pure water (swelling bath), the draw ratio is 2 with respect to the original length. The film was stretched in the flow direction so as to be doubled. Thereafter, the PVA film was immersed in an iodine aqueous solution (dye bath) at 30 ° C. containing 0.045% iodine and 0.315% potassium iodide for 30 seconds, and the draw ratio was 3 with respect to the original length while dyeing. The film was stretched in the flow direction so as to be 3 times. Next, the film was stretched in the flow direction so that the stretch ratio was 3.6 times the original length while being immersed in an aqueous solution containing 3% boric acid and 3% potassium iodide for 30 seconds. . Thereafter, the film was immersed in a 60 ° C. aqueous solution (crosslinking bath) containing 4% boric acid, 5% potassium iodide and 0.0000662 mol / L ascorbic acid for 60 seconds, and the draw ratio with respect to the original length was The film was stretched in the flow direction so as to be 6.0 times. Thereafter, the film was immersed in a 30 ° C. aqueous solution (cleaning bath) containing 3% potassium iodide for 10 seconds for cleaning. Finally, the film was drained and dried for 4 minutes in an oven at 60 ° C. while maintaining tension to produce a polarizing film.

Examples 2-9, Comparative Examples 1-6
A polarizing film was produced in the same manner as in Example 1 except that the type and concentration of the water-soluble antioxidant and the treatment bath to which the water-soluble antioxidant was added were changed as shown in Table 1.

(Evaluation)
About the polarizing film obtained by the Example and the comparative example, the following optical characteristic was evaluated. The results are shown in Table 1.

(Measurement of single transmittance and degree of polarization)
The spectral transmittance of the polarizing film at a wavelength of 380 to 780 nm was measured using a spectrophotometer with an integrating sphere (trade name: V7100, manufactured by JASCO Corporation). The transmittance for each linearly polarized light was measured with 100% of the completely polarized light obtained through the Grantera-prism polarizing film. The Y value in the C light source 2 ° field of view was calculated from the measured spectral transmittance according to the CIE1931 Yxy color system. These were designated as single transmittance (Ts (Y)), parallel transmittance (Tp (Y)), and orthogonal transmittance (Tc (Y)).

The degree of polarization (P) was calculated by {(parallel transmittance−orthogonal transmittance) / (parallel transmittance + orthogonal transmittance)} ^1/2 × 100 (%).

[Evaluation of dichroic ratio]
The dichroic ratio was calculated by substituting the single transmittance (Ts (Y)) and the degree of polarization (P) obtained by the above measurement into the following formula.

  Dichroic ratio = log [Ts (Y) /91.6× {1- (P / 100)}] / log [Ts (Y) /91.6× {1+ (P / 100)}]

[Evaluation of contrast]
The spectral transmittance of the polarizing film at a wavelength of 410 nm was measured using a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation, trade name: V7100). The transmittance for each linearly polarized light was measured with 100% of the completely polarized light obtained through the Grantera-prism polarizing film. The contrast (Cr _{410 nm} ) at a wavelength of 410 nm was calculated by substituting the values of parallel transmittance (Tp _{410 nm} ) at a wavelength of 410 nm and orthogonal transmittance (Tc _{410 nm} ) at a wavelength of 410 nm into the following equation. Note that these transmittances are Y values obtained by correcting the visibility with a two-degree field of view (C light source) of JIS Z 8701.
Cr _410nm = Tp _410nm / Tc _410nm

  The polarizing film and the polarizing plate of the present invention can form an image display device such as a flat panel display such as a liquid crystal display device or an organic EL display device as an optical film obtained by laminating the polarizing film or the polarizing plate.

Claims (1)

In the method for producing a polarizing film, the polyvinyl alcohol film is subjected to at least swelling treatment, dyeing treatment, crosslinking treatment, stretching treatment and washing treatment.
The polarizing film does not contain an aluminosilicate polymer, and
In at least one treatment after the dyeing treatment, at least one water-soluble antioxidant selected from the group consisting of ascorbic acid, sodium erythorbate, and sulfite is included in the treatment liquid so as to satisfy the following formula (1): The manufacturing method of the polarizing film characterized by the above-mentioned.
0.0062 ≦ A × B ≦ 0.02 (1)
[In the above formula, A is the concentration (mol / L) of the water-soluble antioxidant in the treatment bath, and B is the reducing power of the water-soluble antioxidant that reduces iodine to iodine ions. ]