JP2018135426A - Polyvinyl alcohol film and method for producing the same, and polarization film prepared therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol film that makes it possible to obtain a polarization film having a high limit stretching rate and excellent polarization performance.SOLUTION: A PVA film has: a degree of saponification of 99 mol% or more; a peak top molecular weight in a molecular weight distribution obtained by gel permeation chromatography, of 160,000-5,000,000; and the content of components with a molecular weight 1,000-50,000 in the molecular weight distribution, of 17-40 mass%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a polyvinyl alcohol film having a high limit draw ratio and a method for producing the same. Moreover, it is related with the polarizing film excellent in polarizing performance, and its manufacturing method.

  A polarizing plate having a light transmission and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal having a light switching function. A polarizing plate is generally a cellulose triacetate (TAC) film on both surfaces of a polarizing film produced by swelling a polyvinyl alcohol (hereinafter sometimes abbreviated as “PVA”) film and then uniaxially stretching and dyeing. It is manufactured by bonding the protective film.

  In recent years, in order to improve the image quality of LCDs such as liquid crystal televisions, liquid crystal projectors, word processor displays, personal computer displays, OA equipment terminal displays, aircraft and automobile instrument panel displays, the polarization performance of polarizing films has been required to improve. Yes.

  As a method for improving the performance of the polarizing film, a method using a high polymerization degree PVA can be mentioned. In Patent Document 1, an aqueous solution in which 70 parts of PVA having an average degree of polymerization of 3800 and a degree of saponification of 99.5 mol% and 30 parts of PVA having an average degree of polymerization of 1100 and a degree of saponification of 99.7 mol% are cast and dried. A polarizing film obtained by dyeing and stretching the obtained PVA film after obtaining the PVA film is described. However, the PVA film of the original fabric described in Patent Document 1 has a low limit stretch ratio and is insufficient in productivity. Furthermore, the polarizing performance of the polarizing film obtained using the PVA film was still insufficient.

JP-A-4-204802

  This invention is made | formed in order to solve the said subject, and it aims at providing the polyvinyl-alcohol film which can obtain the polarizing film with a high limit stretch ratio and excellent polarization performance, and its manufacturing method. Moreover, it aims at providing the polarizing film obtained using such a polyvinyl alcohol film, and its manufacturing method.

  The above problem is that the saponification degree is 99 mol% or more, and the peak top molecular weight of the molecular weight distribution determined by gel permeation chromatography (hereinafter sometimes abbreviated as “GPC”) is 160,000 to 5,000. And a PVA film having a molecular weight distribution of 1,000 to 50,000 in the molecular weight distribution of 17 to 40% by mass.

  A polarizing film containing a dichroic dye in the PVA film and having a polarization degree of 99.9% or more is a preferred embodiment of the present invention.

  The said subject is the manufacturing method of the said PVA film formed into a film after mixing PVA (A) with a viscosity average polymerization degree of 2,000-20,000, and PVA (B) with a viscosity average polymerization degree of 200-1,000. It is also solved by providing. At this time, the mass ratio (B / A) of PVA (B) to PVA (A) is preferably 8/92 to 40/60. The manufacturing method of the polarizing film which dye | stains and uniaxially stretches with respect to the PVA film manufactured by the said method is also a suitable embodiment of this invention.

  The polarizing film obtained using the PVA film of the present invention has high polarizing performance. Moreover, since the PVA film has a high limit drawing ratio, the area of the obtained polarizing film increases. Therefore, by using the PVA film of the present invention as the raw material of the polarizing film, a polarizing film having excellent polarizing performance can be produced with high productivity.

It is the figure which showed the molecular weight distribution of the PVA film in Example 1 and Comparative Example 1. It is the figure which plotted the mass swelling degree and limit stretch ratio of the PVA film of Examples 1-3 and Comparative Examples 1-3.

  The PVA film of the present invention has a saponification degree of 99 mol% or more, a peak top molecular weight of molecular weight distribution determined by GPC measurement of 160,000 to 5,000,000, and a molecular weight of 1,000 in the molecular weight distribution. It is a film of PVA whose content of the component of -50,000 is 17-40 mass%.

  In the present invention, a GPC apparatus having a differential refractive index detector is used for GPC measurement of a PVA film. HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) or the like is used as a solvent used for dissolving the eluent and the PVA film. In addition, a salt such as sodium trifluoroacetate may be added to HFIP in order to suppress the adsorption of the sample to the GPC column filler. By performing GPC measurement on the solution in which the PVA film is dissolved, a chromatogram in which the values measured by the differential refractive index detector are plotted against the elution time is obtained. By using a calibration curve obtained by measuring standard polymethyl methacrylate (PMMA), the molecular weight distribution in terms of PMMA of PVA constituting the PVA film can be obtained by converting the elution time at this time into molecular weight. Specifically, the GPC measurement method and the molecular weight distribution calculation method described in Examples described later can be employed. When the peak of PVA and the peak of other components other than PVA in the PVA film overlap, GPC measurement is performed after removing the other components in the PVA film in advance.

  The peak top molecular weight in the molecular weight distribution of the PVA film of the present invention thus obtained needs to be 160,000 to 5,000,000. In the present invention, the molecular weight at the peak position in the molecular weight distribution is defined as the peak top molecular weight. When there are a plurality of peaks in the molecular weight distribution, the molecular weight at the peak having the highest peak height is defined as the peak top molecular weight. When the peak top molecular weight is less than 160,000, when a polarizing film is produced using a PVA film, the polarizing performance of the obtained polarizing film becomes insufficient and the mechanical properties of the PVA film are insufficient. become. The peak top molecular weight is preferably 180,000 or more. On the other hand, when the peak top molecular weight exceeds 5,000,000, the limit draw ratio of the PVA film is lowered, and thus the productivity is lowered when a polarizing film is produced using the PVA film. The peak top molecular weight is preferably 2,000,000 or less, more preferably 1,000,000 or less, further preferably 500,000 or less, and particularly preferably 300,000 or less.

  The content of components having a molecular weight of 1,000 to 50,000 in the molecular weight distribution of the PVA film of the present invention needs to be 17 to 40% by mass. When the content of the component having a molecular weight of 1,000 to 50,000 in the molecular weight distribution is in such a range, the limiting draw ratio of the PVA film is improved, and the polarizing performance of the polarizing film obtained using the PVA film Will improve. As will be described later, as a raw material of the PVA film, a molecular weight of 1 by a method using PVA (B) having a viscosity average polymerization degree of 200 to 1,000 together with PVA (A) having a viscosity average polymerization degree of 2,000 to 20,000 A PVA film having a content of components in the range of 1,000 to 50,000 can be obtained. The content of components having a molecular weight of 1,000 to 50,000 in the molecular weight distribution of the PVA film is determined from the peak area in the molecular weight distribution.

  When the content of the component having a molecular weight of 1,000 to 50,000 in the molecular weight distribution of the PVA film is less than 17% by mass, the polarizing performance of the polarizing film obtained when the polarizing film is produced using the PVA film Becomes insufficient. Furthermore, since the limit draw ratio of a PVA film falls, productivity falls when manufacturing a polarizing film using a PVA film. The content of the component is preferably 18% by mass or more. From the viewpoint of obtaining a PVA film having an extremely high limit drawing ratio, the content of the component is preferably 20% by mass or more, and more preferably 25% by mass or more. On the other hand, when the content of the component exceeds 40% by mass, when the polarizing film is produced using the PVA film, the polarizing property of the obtained polarizing film becomes insufficient, and the mechanical properties of the PVA film Becomes insufficient. The content of the component is preferably 35% by mass or less. When producing a polarizing film using a PVA film, the content of the component is preferably 25% by mass or less from the viewpoint of obtaining a polarizing film having extremely high polarizing performance.

  It is preferable that ratio (Mw / Mn) of the weight average molecular weight Mw with respect to the number average molecular weight Mn calculated | required from the said molecular weight distribution of the PVA film of this invention is 3.5-15. When the ratio (Mw / Mn) is less than 3.5, when a polarizing film is produced using a PVA film, the polarizing performance of the obtained polarizing film may be insufficient. Moreover, when the limit draw ratio of a PVA film falls and a polarizing film is manufactured using a PVA film, there exists a possibility that productivity may fall. On the other hand, when the ratio (Mw / Mn) exceeds 15, the polarizing film obtained may have insufficient polarizing performance. Moreover, when the limit draw ratio of a PVA film falls and a polarizing film is manufactured using a PVA film, there exists a possibility that productivity may fall. The ratio (Mw / Mn) is more preferably 10 or less, and still more preferably 8 or less.

  The saponification degree of the PVA film of the present invention needs to be 99 mol% or more. When the saponification degree is less than 99 mol%, the water resistance of the PVA film becomes insufficient. In the present invention, the degree of saponification refers to the vinyl alcohol relative to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units that can be converted to vinyl alcohol units by saponification of the PVA constituting the PVA film. It refers to the ratio of the number of moles of units (mol%). The degree of saponification can be measured according to the description of JIS K6726-1994 using a PVA film as a sample.

  In the present invention, PVA used for the production of PVA film is vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, It can be produced by a method of saponifying a polyvinyl ester obtained by polymerizing one or more vinyl esters such as propenyl. Of the vinyl esters, vinyl acetate is preferable from the viewpoint of productivity.

  The polyvinyl ester is preferably obtained using only vinyl ester as a monomer. Two or more vinyl esters may be used at this time, but one is preferable. As long as the effects of the present invention are not impaired, the polyvinyl ester may be a copolymer of one or two or more vinyl esters and other monomers copolymerizable therewith. .

  Examples of the other monomer copolymerizable with the vinyl ester include α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (meth) acrylic acid or a salt thereof; ) Methyl acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, (meth ) (Meth) acrylic acid esters such as t-butyl acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylamide; N-methyl (meth) ) Acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylic (Meth) acrylamide propanesulfonic acid or a salt thereof, (meth) acrylamidepropyldimethylamine or a salt thereof, (meth) acrylamide derivatives such as N-methylol (meth) acrylamide or a derivative thereof; N-vinylformamide, N-vinyl N-vinylamides such as acetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. Vinyl ether; Vinyl cyanide such as (meth) acrylonitrile; Vinyl halide such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; Acetic acid Allyl compounds such as allyl and allyl chloride; maleic acid or its salt, ester or acid anhydride; itaconic acid or its salt, ester or acid anhydride; vinylsilyl compound such as vinyltrimethoxysilane; unsaturated sulfonic acid or its salt, etc. Can be mentioned. The polyvinyl ester can have one or more structural units derived from the other monomers.

  The proportion of structural units derived from other monomers in the polyvinyl ester is preferably 15 mol% or less, preferably 10 mol% or less, based on the number of moles of all structural units constituting the polyvinyl ester. More preferred is 5 mol% or less.

  As long as the effect of the present invention is not impaired, the PVA may be modified with one or two or more types of graft copolymerizable monomers. At this time, graft copolymerization can be performed on the polyvinyl ester or PVA. Examples of the graft copolymerizable monomer include an unsaturated carboxylic acid or a derivative thereof; an unsaturated sulfonic acid or a derivative thereof; and an α-olefin having 2 to 30 carbon atoms. The proportion of structural units derived from the graft copolymerizable monomer in the polyvinyl ester or PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester or PVA. The PVA used in the present invention is preferably not graft copolymerized.

  A part of the hydroxyl group of the PVA may be cross-linked or may not be cross-linked. The PVA may have a hydroxyl group partially reacted with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure or may not form an acetal structure.

  The PVA film of the present invention may contain a plasticizer. When the PVA film contains a plasticizer, the handleability and stretchability are improved. A polyhydric alcohol is preferably used as the plasticizer, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. The PVA film can contain one or more of these plasticizers. Among these, glycerin is preferable from the viewpoint of further improving the stretchability of the PVA film.

  The content of the plasticizer in the PVA film is preferably 3 to 20 parts by mass, more preferably 5 to 17 parts by mass, and further preferably 7 to 14 parts by mass with respect to 100 parts by mass of PVA. preferable. When the content of the plasticizer in the PVA film is 3 parts by mass or more with respect to 100 parts by mass of PVA, the stretchability of the PVA film is further improved. On the other hand, when the content of the plasticizer in the PVA film is 20 parts by mass or less with respect to 100 parts by mass of PVA, the plasticizer bleeds out on the surface of the PVA film and the handling property of the PVA film is reduced. be able to.

  The PVA content in the PVA film is preferably in the range of 50 to 100% by mass, more preferably in the range of 80 to 100% by mass, and in the range of 85 to 100% by mass. Is more preferable.

  In addition, when producing a PVA film using a film-forming stock solution described later, the film-forming property is improved and the occurrence of uneven thickness of the film is suppressed, and when a metal roll or belt is used for film-forming, From the viewpoint that the PVA film can be easily peeled from these, it is preferable to contain a surfactant in the film-forming stock solution. When a PVA film is produced using a film-forming stock solution containing a surfactant, a surfactant may be contained in the obtained PVA film. The type of the surfactant is not particularly limited, but anionic surfactants and nonionic surfactants are preferable, and anionic surfactants are more preferable from the viewpoint of easily peeling the PVA film from a metal roll or belt. These surfactants can be used alone or in combination of two or more.

  Suitable examples of the anionic surfactant include carboxylic acid types such as potassium laurate; sulfate ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecylbenzene sulfonate.

  Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; polyoxyethylene laurylamino Alkylamine type such as ether; alkylamide type such as polyoxyethylene lauric acid amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; polyoxy An allyl phenyl ether type such as alkylene allyl phenyl ether is preferred.

  0.01-0.5 mass part is preferable with respect to 100 mass parts of PVA, and, as for content of surfactant in the film-forming stock solution, 0.02-0.3 mass part is more preferable. When the content of the surfactant is 0.01 parts by mass or more, the film forming property and the peelability can be improved. On the other hand, when the content of the surfactant is 0.5 parts by mass or less, it is possible to suppress the surfactant from bleeding out on the surface of the PVA film, causing blocking, thereby reducing the handleability. The content of the surfactant in the PVA film is preferably in the range described above as the content of the surfactant in the film forming stock solution.

  The PVA film may be composed only of PVA, or may be composed only of PVA and a plasticizer and / or a surfactant. Moreover, you may contain other components other than PVA, a plasticizer, and surfactant, such as antioxidant, an antifreezing agent, a pH adjuster, a masking agent, a coloring inhibitor, and an oil agent as needed.

  Although the manufacturing method of the said PVA film is not specifically limited, It forms into a film after mixing PVA (A) with a viscosity average polymerization degree of 2,000-20,000, and PVA (B) with a viscosity average polymerization degree of 200-1,000. Is preferred. Usually, when a PVA having a viscosity average polymerization degree of 1,000 or less is used, a polarizing film having sufficient polarization performance cannot be obtained, and thus such a low polymerization degree PVA is not used as a raw material for the polarizing film. . On the other hand, as a result of intensive studies by the present inventors, by using PVA (B) having a low viscosity average polymerization degree together with PVA (A), a polarizing film having a high limit draw ratio and excellent polarization performance can be obtained. It has been found that a PVA film can be obtained.

  When the viscosity average polymerization degree of PVA (A) is less than 2,000, the mechanical properties of the resulting PVA film may be insufficient. On the other hand, when the viscosity average degree of polymerization of PVA (A) exceeds 20,000, it becomes difficult to handle and the productivity may be lowered. The viscosity average polymerization degree of PVA (A) is more preferably 10,000 or less, and further preferably 8,000 or less. From the viewpoint of further improving the limit draw ratio of the PVA film, the viscosity average polymerization degree of PVA (A) is preferably 6,000 or less, more preferably 4,000 or less, and particularly preferably 3,000 or less. The degree of saponification of PVA (A) is preferably 99 mol% or more.

  When the viscosity average degree of polymerization of PVA (B) is less than 200, when the PVA film is immersed in water, the PVA is likely to be eluted, which may cause a problem when a polarizing film is produced. On the other hand, when the viscosity average degree of polymerization of PVA (B) exceeds 1,000, the effect of improving the limit draw ratio of the PVA film may not be obtained. The viscosity average polymerization degree of PVA (B) is more preferably 700 or less, and further preferably 400 or less. The degree of saponification of PVA (B) is preferably 99 mol% or more. The viscosity average polymerization degree and saponification degree of PVA (A) and PVA (B) can be measured according to the description of JIS K6726-1994.

  It is preferable to mix them so that the mass ratio (B / A) of PVA (B) to PVA (A) is 8/92 to 40/60. From the viewpoint of obtaining a PVA film having an extremely high limit stretching ratio, the mass ratio (B / A) is more preferably 20/80 or more. On the other hand, when producing a polarizing film using a PVA film, the mass ratio (B / A) is more preferably 20/80 or less from the viewpoint of obtaining a polarizing film having extremely high polarizing performance.

  The film forming method of the PVA film is not particularly limited, but a cast film forming method, an extrusion film forming method, a wet film forming method, a gel film forming method, etc. are preferable from the point that a film having a uniform thickness and width is obtained. A membrane method and an extrusion film forming method are more preferable. Among these film forming methods, the extrusion film forming method is particularly preferable because a PVA film having a uniform thickness and width and good physical properties can be obtained. These film forming methods may be used alone or in combination of two or more.

  As a film-forming stock solution used for production of a PVA film, PVA (A), PVA (B), a film-forming stock solution in which a plasticizer, a surfactant, and other components are dissolved in a liquid medium as required, or PVA (A ), PVA (B), and optionally, a plasticizer, a surfactant, other components, and a liquid medium, and can be produced using a film-forming stock solution in which PVA (A) and PVA (B) are melted. . It is preferable that each component in the film-forming stock solution is uniformly mixed.

  Examples of the liquid medium used for the film-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylol. Propane, ethylenediamine, and diethylenetriamine can be mentioned, and one or more of these can be used. Among these, water is preferable from the viewpoint of low environmental load and recoverability.

  The volatile fraction of the film-forming stock solution (the content ratio of volatile components such as a liquid medium removed by volatilization or evaporation during film formation in the film-forming stock solution) varies depending on the film-forming method, the film-forming conditions, etc. Mass% is preferred. When the volatile fraction of the film-forming stock solution is 50% by mass or more, the viscosity of the film-forming stock solution does not become too high, and filtration and defoaming are smoothly performed during preparation of the film-forming stock solution, and there are few foreign matters and defects. Film production is facilitated. On the other hand, when the volatile fraction of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and the production of an industrial PVA film becomes easy. The PVA film obtained by film formation can be subjected to drying or heat treatment as necessary.

  Although there is no limitation in particular in the shape of a PVA film, Since a polarizing film can be manufactured continuously with sufficient productivity, it is preferable that it is a long PVA film. The length of the PVA film is not particularly limited, and can be set as appropriate according to the application of the polarizing film to be produced. For example, the length can be 5 to 20,000 m. Although the width | variety of the said PVA film is not specifically limited, Since the wide polarizing film is calculated | required in recent years, it is preferable that it is 50 cm or more, It is more preferable that it is 2 m or more, It is further more preferable that it is 4 m or more. Although it is not particularly limited to the upper limit of the width of the PVA film, if it is too wide, it tends to be difficult to stretch uniformly when a polarizing film is produced with a practically used apparatus. The width is preferably 7 m or less.

  The thickness of the PVA film is not particularly limited, but is usually 1 to 100 μm, preferably 5 to 75 μm, and particularly preferably 10 to 60 μm. When the thickness is too thin, there is a tendency that stretching breakage is likely to occur during the uniaxial stretching process for producing the polarizing film. Moreover, when the said thickness is too thick, there exists a tendency for a stretch spot to generate | occur | produce at the time of the uniaxial stretching process for manufacturing a polarizing film. The PVA film is preferably a single layer film, but may be a laminate in which a PVA layer and another layer such as a thermoplastic resin film are laminated. In the case of a laminate, the thickness of the PVA layer is preferably in the above range.

  A polarizing film containing a dichroic dye in the PVA film thus obtained and having a polarization degree of 99.9% or more is a preferred embodiment of the present invention. The polarizing film obtained using the PVA film of the present invention has high polarizing performance. Moreover, since the PVA film has a high limit drawing ratio, the area of the obtained polarizing film increases. Therefore, by using the PVA film of the present invention as the raw material of the polarizing film, a polarizing film having excellent polarizing performance can be produced with high productivity.

  Although the manufacturing method of the said polarizing film is not specifically limited, The method of dyeing | staining and uniaxial stretching with respect to the PVA film obtained by the said method is preferable, and swelling, dyeing | staining, and uniaxial are performed with respect to the PVA film obtained by the said method. A method of stretching is more preferable. In addition to these steps, it is also preferable to further perform crosslinking, fixing treatment, drying, heat treatment, etc. on the PVA film. The order in particular of each process is not restrict | limited, One or two or more processes can also be performed simultaneously. Also, one or more of each step can be performed twice or more. Each process will be specifically described below.

  The swelling step for the PVA can be performed by immersing the PVA film in water. The temperature of water at this time is preferably within the range of 20 to 40 ° C, more preferably within the range of 22 to 38 ° C, and even more preferably within the range of 25 to 35 ° C. Moreover, as time to immerse in water, it is preferable to exist in the range for 0.1 to 5 minutes, and it is more preferable to be in the range for 0.5 to 3 minutes. In addition, the water at the time of immersing in water is not limited to pure water, The aqueous solution in which various components melt | dissolved may be sufficient, and the mixture of water and a water-soluble organic solvent may be sufficient.

  The degree of swelling of the PVA film is preferably in the range of 160 to 240% by mass, more preferably in the range of 170 to 230% by mass, and particularly preferably in the range of 180 to 220% by mass. . When the degree of swelling is 160% or more, crystallization of PVA can be prevented from proceeding extremely, and the film can be stably stretched to a higher magnification. On the other hand, when the degree of swelling is 240% by mass or less, dissolution of PVA during stretching is suppressed, and stretching can be performed even under higher temperature conditions. In the present invention, the swelling degree of the PVA film is a value obtained by dividing the mass when the PVA film is immersed in distilled water at 30 ° C. for 30 minutes by the mass after drying at 105 ° C. for 16 hours. Means the percentage.

  The dyeing | staining process with respect to the said PVA can be performed by making a dichroic dye contact with a PVA film. As the dichroic dye, an iodine dye is generally used. The dyeing treatment may be performed before the uniaxial stretching step described later or after the uniaxial stretching step, but the former is preferable. The dyeing process is generally performed by immersing the PVA film in a solution (particularly an aqueous solution) containing iodine-potassium iodide as a dyeing bath. In the present invention, such a dyeing method is suitably employed. The The iodine concentration in the dyeing bath is preferably in the range of 0.01 to 0.5% by mass, and the potassium iodide concentration is preferably in the range of 0.01 to 10% by mass. Moreover, it is preferable that the temperature of a dyeing bath shall be 20-50 degreeC, especially 25-40 degreeC. The time for immersing the PVA film in the dyeing bath is preferably in the range of 0.1 to 10 minutes, and more preferably in the range of 0.2 to 5 minutes.

  The crosslinking step for the PVA film can be performed by immersing the PVA film in an aqueous solution containing a crosslinking agent. Thereby, it is possible to more effectively prevent PVA from eluting into water when wet-stretching at a high temperature. From this viewpoint, the crosslinking step is preferably performed before the uniaxial stretching step. Moreover, when performing the said dyeing process, it is preferable to perform a bridge | crosslinking process after a dyeing process. As said crosslinking agent, 1 type, or 2 or more types of boron compounds, such as boric acid salts, such as boric acid and borax, can be used. The concentration of the crosslinking agent in the aqueous solution containing the crosslinking agent is preferably in the range of 1 to 15% by mass, and more preferably in the range of 2 to 7% by mass. Sufficient stretchability can be maintained when the concentration of the crosslinking agent is in the range of 1 to 15% by mass. The aqueous solution containing a crosslinking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the crosslinking agent is preferably in the range of 20 to 50 ° C, particularly in the range of 25 to 40 ° C. It can bridge | crosslink efficiently by making the said temperature into the range of 20-50 degreeC.

  Apart from the uniaxial stretching step described later, the PVA film may be uniaxially stretched during each step or between the steps described above. By performing such stretching (pre-stretching), wrinkles can be prevented from entering the PVA film. Based on the original length of the original PVA film before stretching, the total stretching ratio of pre-stretching (the ratio obtained by multiplying the stretching ratios in each step) is 4 based on the polarization performance in the case of producing a polarizing film. It is preferable that it is less than 2 times. The draw ratio in the swelling process is preferably 1.05 to 3 times, the draw ratio in the dyeing process is preferably 3 times or less, and the draw ratio in the crosslinking process is preferably 2 times or less.

  The uniaxial stretching process for the PVA film can be performed by uniaxially stretching the PVA film using a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid, or can be carried out in the dyeing bath described above or in a fixing treatment bath described later. In the case of the dry stretching method, the stretching may be performed at room temperature, may be performed while heating, or may be performed in the air using a PVA film after water absorption. Among these, the wet stretching method is preferable, and uniaxial stretching is more preferable in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 6.0% by mass, more preferably in the range of 1.0 to 5.0% by mass, It is particularly preferable that the content be in the range of -4.5% by mass. Moreover, the boric acid aqueous solution may contain potassium iodide, and the concentration is preferably in the range of 0.01 to 10% by mass.

  The stretching temperature in the uniaxial stretching step is preferably within a range of 30 to 90 ° C, more preferably within a range of 40 to 80 ° C, and particularly preferably within a range of 50 to 70 ° C. From the viewpoint that the shrinkage force in the stretching direction of the polarizing film to be obtained is greatly reduced and the dimensional stability is further improved, a wet stretching method is used at such a stretching temperature (liquid temperature). Uniaxial stretching is particularly preferred.

  From the viewpoint of polarizing performance when a polarizing film is produced, the draw ratio in the drawing step is preferably 1.2 times or more, more preferably 1.5 times or more, and 2 times or more. Is more preferable. Moreover, the total draw ratio including the draw ratio of the above-mentioned pre-stretch (the ratio obtained by multiplying the stretch ratio in each step) is 6.5 times or more based on the original length of the original PVA film before stretching. Preferably there is. The PVA film of the present invention has a high limit draw ratio. And the polarizing film obtained using the said PVA film has high polarizing performance. Therefore, by stretching the PVA film of the present invention at such a high magnification, a polarizing film having excellent polarization performance can be produced with high productivity. The upper limit of the total stretch ratio is not particularly limited, but the total stretch ratio is preferably 8 times or less in order to prevent stretching.

  The direction of uniaxial stretching in the case of uniaxially stretching a long PVA film is not particularly limited, and uniaxial stretching in the long direction and lateral uniaxial stretching in the width direction can be employed. In the case of producing a polarizing film, uniaxial stretching in the longitudinal direction is preferable from the viewpoint of obtaining a film having excellent polarizing performance. Uniaxial stretching in the longitudinal direction can be performed by changing the peripheral speed between the rolls using a stretching apparatus including a plurality of rolls parallel to each other. On the other hand, lateral uniaxial stretching can be performed using a tenter type stretching machine.

  In the case of producing a polarizing film, it is preferable to perform a fixing treatment step on the PVA film after the stretching step. Thereby, adsorption of the dichroic dye (iodine dye etc.) with respect to a PVA film becomes strong. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more of boron compounds such as boric acid and borax can be used. Moreover, you may add an iodine compound and a metal compound in a fixed treatment bath as needed. The concentration of the boron compound in the fixed treatment bath is preferably 0.5 to 15% by mass. By setting it as such a range, adsorption | suction of a dichroic dye can be strengthened more. The temperature of the fixing treatment bath is preferably 15 to 60 ° C.

  It is preferable to perform the drying process with respect to the said PVA film at 30-150 degreeC, especially 50-130 degreeC. When the moisture content of the polarizing film becomes 10% or less by drying, tension may be applied to the polarizing film and heat treatment may be performed at 80 to 140 ° C. for about 1 to 15 minutes.

  The polarizing film thus obtained is used as a polarizing plate by attaching a protective film that is optically transparent and has high mechanical strength to both sides or one side. As the protective film, a cellulose triacetate (TAC) film, an acetic acid / cellulose butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Examples of the adhesive used at this time include PVA-based adhesives and urethane-based adhesives, among which PVA-based adhesives are suitable.

  The polarizing plate obtained as described above can be used as a component of an LCD after being coated with an acrylic adhesive or the like and then bonded to a glass substrate. At the same time, it may be bonded to a retardation film, a viewing angle improving film, a brightness improving film, or the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited at all by the following examples. In the following examples, each characteristic was evaluated by the following method.

[Measurement of molecular weight distribution of PVA film]
A PVA film was measured by gel permeation chromatography (GPC) under the following conditions to obtain a chromatogram. Using a calibration curve obtained by measuring standard polymethyl methacrylate, the elution time at this time was converted to molecular weight to obtain a molecular weight distribution in terms of polymethyl methacrylate of the PVA film.
GPC device: manufactured by Tosoh Corporation, HLC-8320
Detector: Differential refractive index detector Column: Two TSKgel GMHHR-H made by Tosoh Corporation were connected in series.
Eluent: A solvent in which 20 mmol / L sodium trifluoroacetate was added to HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) was used.
Eluent flow rate: 0.20 ml / min Column temperature: 40 ° C
Calibration curve: Calibration curves were prepared using 12 types of standard polymethylmethacrylates with different molecular weights.

[Measurement of mass swelling degree of PVA film]
A film of 5 cm × 10 cm cut out from the PVA film obtained in each of the following examples was immersed in 1 L of 30 ° C. pure water for 30 minutes and then taken out. After the moisture on the film surface was wiped off with filter paper, the film mass W1 (G) was measured. Next, the film was dried in a hot air dryer at 105 ° C. for 16 hours, and then the film mass W2 (g) was measured. Using the obtained W1 and W2, the mass swelling degree was calculated by the following formula (1).
Mass swelling rate (%) = (W1 / W2) × 100 (1)

[Measurement of limit draw ratio]
A sample was taken from the PVA film to a size of MD 100 mm × TD 50 mm, and a marked line having a length of 50 mm was written in the center of the sample. Attach four samples with marked lines to the stretching jig, and uniaxially in the length direction (MD) to 2.2 times the original length while the samples are immersed in water at a temperature of 30 ° C for 1 minute. Drawing (first stage drawing) was performed. The sample was then immersed in a dyeing bath at a temperature of 30 ° C. containing 0.03% by mass of iodine and 3.0% by mass of potassium iodide for 3.2 minutes, 3.2 times the original length. The film was uniaxially stretched in the length direction (MD) (second-stage stretching). The sample was then immersed in a crosslinking bath containing 30% by weight of boric acid and 3.0% by weight of potassium iodide at a temperature of 30 ° C. for 2 minutes while maintaining the original length of 3.6. Uniaxial stretching (third-stage stretching) was performed in the length direction (MD) up to twice. Further, the sample was uniaxially stretched (fourth stage stretching) while being immersed in a stretching bath at a temperature of 55 ° C. containing 4.0% by mass of boric acid and 5.0% by mass of potassium iodide, When two of the four sheets were cut, they were removed from the stretching bath. The marked line lengths of two uncut samples were measured, the marked line length after stretching was divided by the marked line length before stretching (50 mm), and this was defined as the limit stretching ratio at a stretching temperature of 55 ° C. did. In addition, the limit stretching ratio at a stretching temperature of 60 ° C. was also evaluated in the same manner as described above except that the temperature of the stretching bath was changed to 60 ° C.

[Polarization performance of polarizing film]
(A) Measurement of transmittance Ts Two square samples having a length direction of 2 cm and a width direction of 2 cm were collected from the polarizing film obtained in the following examples, and a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation " V7100 "), and in accordance with JIS Z8722: 2009 (object color measurement method), the visibility of the visible light region of the C light source and 2 ° field of view is corrected, and one sample is measured in the length direction. The light transmittance when tilted by 45 ° and the light transmittance when tilted by −45 ° were measured, and an average value Ts1 (%) thereof was obtained. Similarly, for the other sample, the light transmittance when tilted by 45 ° and the light transmittance when tilted by −45 ° were measured, and an average value Ts2 (%) thereof was obtained. Ts1 and Ts2 were averaged by the following formula (2) to obtain the transmittance Ts (%) of the polarizing film.
Ts = (Ts1 + Ts2) / 2 (2)

(B) Measurement of degree of polarization V Light transmittance T‖ (%) and length when two samples collected by measuring the transmittance Ts are stacked so that their length directions are parallel to each other. The light transmittance T ⊥ (%) when stacked so that the vertical directions are orthogonal to each other is measured in the same manner as in the case of “(a) Measurement of transmittance Ts”, and the degree of polarization is calculated by the following equation (3). V (%) was determined.
V = {(T‖−T⊥) / (T‖ + T⊥)} 1/2 × 100

[Example 1]
(1) Production of PVA film 90 parts by mass of a high degree of polymerization PVA having a viscosity average degree of polymerization of 2,400 (saponification degree 99.9 mol%), and a low degree of polymerization PVA10 having a viscosity average degree of polymerization 300 (saponification degree 99.0 mol%) Cast a film-forming stock solution consisting of 10 parts by mass of glycerin as a plasticizer, 0.1 part by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant and 90% by mass of water onto a metal drum at 80 ° C. The film was dried until the volatile content (water content) became 5% by mass to obtain a long unheat-treated film having a thickness of 30 μm, a length of 1.5 m, and a width of 30 cm. Next, this unheated film was heat-treated at a temperature of 113 ° C. for 10 minutes to produce a PVA film having a mass swelling degree of 198%. The obtained film was subjected to GPC measurement to obtain a molecular weight distribution of the PVA film. The molecular weight distribution at this time is shown in FIG. The molecular weight peak top molecular weight (Mp) calculated | required from the said molecular weight distribution was 204,000, and the ratio of the component (low molecular weight component) of molecular weight 1,000-50,000 was 21.5 mass%. Moreover, the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the PVA film were determined from the molecular weight distribution. Furthermore, about the obtained PVA film, the limit draw ratio was evaluated in both 55 degreeC and 60 degreeC extending | stretching baths. These results are shown in Table 1.

(2) Production of polarizing film (stretching bath is 55 ° C)
The polarizing film was manufactured by performing the swelling process, the dyeing process, the bridge | crosslinking process, the extending | stretching process, the fixing process process, and the drying process with respect to the PVA film obtained by (1) as follows. Four rectangular films having a length direction of 100 mm and a width direction of 50 mm collected from the PVA film were attached to a stretching jig and immersed in water at a temperature of 30 ° C. for 1 minute. The film was uniaxially stretched in the length direction (MD) twice (first-stage stretching). The film was then immersed in a dyeing bath at a temperature of 30 ° C. containing 0.03% by mass of iodine and 3.0% by mass of potassium iodide at a concentration of 3.2% of the original length. The film was uniaxially stretched in the length direction (MD) (second-stage stretching). Then, while the film was immersed in a crosslinking bath containing 30% by weight of boric acid and 3.0% by weight of potassium iodide at a temperature of 30 ° C. for 2 minutes, the film had an original length of 3.6. Uniaxial stretching (third-stage stretching) was performed in the length direction (MD) up to twice. Further, the film was uniaxially stretched (fourth stage stretching) while immersed in a stretching bath at a temperature of 55 ° C. containing 4.0% by mass of boric acid and 5.0% by mass of potassium iodide. When two of the four sheets were cut, they were removed from the stretching bath. Thereafter, the film was washed by dipping for 5 seconds in a fixed treatment bath at a temperature of 22 ° C. containing boric acid at a concentration of 1.5% by mass and potassium iodide at a concentration of 5% by mass, followed by drying at 60 ° C. A polarizing film having a thickness of 13 μm was produced by drying for 240 seconds using a machine. In the step of uniaxial stretching in the dyeing bath, the polarizing film was produced by finely adjusting the iodine concentration so that the transmittance Ts was 44.0%. As a result, the polarization degree V of the obtained polarizing film was 99.980%. It had good optical performance.

(3) Production of polarizing film (stretching bath is 60 ° C.)
A polarizing film having a thickness of 12 μm was produced by the same method as “(2) Production of polarizing film (stretching bath was 55 ° C.)” except that the temperature of the stretching bath was 60 ° C. As a result of manufacturing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.985%, and the optical film had good optical performance.
[Example 2]

(1) Production of PVA film An unheat-treated film was obtained in the same manner as in Example 1 except that the low polymerization degree PVA was changed to one having a viscosity average polymerization degree of 500 (saponification degree of 99.0 mol%). Next, this unheated film was heat-treated at a temperature of 110 ° C. for 10 minutes to produce a PVA film having a mass swelling degree of 201%. The obtained film was subjected to GPC measurement to obtain a molecular weight distribution of the PVA film. The peak top molecular weight calculated | required from the said molecular weight distribution was 205,000, and the ratio of the component of molecular weight 1,000-50,000 was 19.4 mass%. Moreover, the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the PVA film were determined from the molecular weight distribution. Furthermore, the limit draw ratio was evaluated about the obtained PVA film. These results are shown in Table 1.

(2) Production of polarizing film (stretching bath is 55 ° C)
A polarizing film having a thickness of 13 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 55 ° C.). As a result of producing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.980%, which was favorable.

(3) Production of polarizing film (stretching bath is 60 ° C.)
A polarizing film having a thickness of 12 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 60 ° C.). As a result of manufacturing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.985%, which was favorable.
[Example 3]

(1) Production of PVA Film An unheated film was obtained in the same manner as in Example 1 except that the high polymerization degree PVA was 70 parts by mass and the low polymerization degree PVA was 30 parts by mass. Next, this unheated film was heat-treated at a temperature of 130 ° C. for 10 minutes to produce a PVA film having a mass swelling degree of 200%. The obtained film was subjected to GPC measurement to obtain a molecular weight distribution of the PVA film. The peak top molecular weight calculated | required from the said molecular weight distribution was 202,000, and the ratio of the component of molecular weight 1,000-50,000 was 30.0 mass%. From the molecular weight distribution, the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the PVA film were determined. Furthermore, the limit draw ratio was evaluated about the obtained PVA film. These results are shown in Table 1.

(2) Production of polarizing film (stretching bath is 55 ° C)
A polarizing film having a thickness of 13 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 55 ° C.). As a result of producing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.965%.

(3) Production of polarizing film (stretching bath is 60 ° C.)
A polarizing film having a thickness of 12 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 60 ° C.). As a result of manufacturing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.981%.
[Comparative Example 1]

(1) Production of PVA film An unheat-treated film was obtained in the same manner as in Example 1 except that the high polymerization degree PVA was 100 parts by mass and the low polymerization degree PVA was not used. Next, this unheated film was heat-treated at a temperature of 108 ° C. for 10 minutes to produce a PVA film having a mass swelling degree of 203%. The obtained film was subjected to GPC measurement to obtain a molecular weight distribution of the PVA film. The molecular weight distribution at this time is shown in FIG. The peak top molecular weight calculated | required from the said molecular weight distribution was 206,000, and the ratio of the component of molecular weight 1,000-50,000 was 15.2 mass%. Moreover, the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the PVA film were determined from the molecular weight distribution. Furthermore, the limit draw ratio was evaluated about the obtained PVA film. These results are shown in Table 1.

(2) Production of polarizing film (stretching bath is 55 ° C)
A polarizing film having a thickness of 14 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 55 ° C.). As a result of producing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.965%.

(3) Production of polarizing film (stretching bath is 60 ° C.)
A polarizing film having a thickness of 13 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 60 ° C.). As a result of manufacturing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.981%.
[Comparative Example 2]

(1) Production of PVA film A PVA film was produced in the same manner as in Comparative Example 1 except that the unheated film was heat treated at a temperature of 111 ° C, and a PVA film having a mass swelling degree of 197% was obtained. About the obtained PVA film, the limit draw ratio was evaluated. The results are shown in Table 1.

(2) Production of polarizing film (stretching bath is 55 ° C)
A polarizing film having a thickness of 14 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 55 ° C.). As a result of producing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.965%.

(3) Production of polarizing film (stretching bath is 60 ° C.)
A polarizing film having a thickness of 13 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 60 ° C.). As a result of manufacturing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.981%.
[Comparative Example 3]

(1) Production of PVA film A PVA film was produced in the same manner as in Comparative Example 1 except that an unheated film was heat treated at a temperature of 114 ° C to obtain a PVA film having a mass swelling degree of 191%. About the obtained PVA film, the limit draw ratio was evaluated. The results are shown in Table 1.

(2) Production of polarizing film (stretching bath is 55 ° C)
A polarizing film having a thickness of 14 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 55 ° C.). As a result of producing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.965%.

(3) Production of polarizing film (stretching bath is 60 ° C.)
A polarizing film having a thickness of 13 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 60 ° C.). As a result of manufacturing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.981%.
[Comparative Example 4]

(1) Production of PVA film An unheat-treated film was obtained in the same manner as in Example 1 except that the low polymerization degree PVA was changed to one having a viscosity average polymerization degree of 1,100 (saponification degree 99.0 mol%). Next, this unheated film was heat-treated at a temperature of 109 ° C. for 10 minutes to produce a PVA film having a mass swelling degree of 200%. The obtained film was subjected to GPC measurement to obtain a molecular weight distribution of the PVA film. The peak top molecular weight calculated | required from the said molecular weight distribution was 206,000, and the ratio of the component of molecular weight 1,000-50,000 was 16.0 mass%. Moreover, the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the PVA film were determined from the molecular weight distribution. Furthermore, the limit draw ratio was evaluated about the obtained PVA film. These results are shown in Table 1.

(2) Production of polarizing film (stretching bath is 55 ° C)
A polarizing film having a thickness of 14 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 55 ° C.). As a result of producing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.965%.

(3) Production of polarizing film (stretching bath is 60 ° C.)
A polarizing film having a thickness of 13 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 60 ° C.). As a result of manufacturing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.981%.

[Comparative Example 5]
(1) Production of PVA film 70 parts by mass of PVA having a viscosity average polymerization degree of 3,800 (saponification degree 99.9 mol%) and low polymerization having a viscosity average polymerization degree of 1,100 (saponification degree 99.0 mol%) A non-heat-treated film was obtained in the same manner as in Example 1 except that 30 parts by mass of PVA was used. Next, this unheated film was heat-treated at a temperature of 105 ° C. for 10 minutes to produce a PVA film having a mass swelling degree of 199%. The obtained film was subjected to GPC measurement to obtain a molecular weight distribution of the PVA film. The peak top molecular weight calculated | required from the said molecular weight distribution was 235,000, and the ratio of the component of molecular weight 1,000-50,000 was 15.0 mass%. Moreover, the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the PVA film were determined from the molecular weight distribution. Furthermore, the limit draw ratio was evaluated about the obtained PVA film. These results are shown in Table 1.

(2) Production of polarizing film (stretching bath is 55 ° C)
A polarizing film having a thickness of 14 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 55 ° C.). As a result of producing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.980%.

(3) Production of polarizing film (stretching bath is 60 ° C.)
A polarizing film having a thickness of 13 μm was produced in the same manner as in the production of the polarizing film of Example 1 (stretching bath was 60 ° C.). As a result of producing the polarizing film so that the transmittance Ts was 44.0%, the polarization degree V of the obtained polarizing film was 99.985%.

  FIG. 2 is a diagram in which the mass swelling degree and the stretching limit stretching ratio (stretching temperature 55 ° C.) of the PVA films of Examples 1 to 3 and Comparative Examples 1 to 3 are plotted. The PVA films of Comparative Examples 1 to 3 have different mass swelling degrees. Even if the degree of mass swelling was increased, the stretch limit stretch ratio was only slightly improved. On the other hand, compared with these PVA films, the PVA films of the present invention (Examples 1 to 3) having a predetermined molecular weight distribution had remarkably high stretch limit stretch ratios. Thus, the area of the polarizing film obtained increases by manufacturing a polarizing film using the PVA film of this invention which has a high limit stretch ratio for an original fabric. Furthermore, by producing a polarizing film using the PVA film of the present invention, the film can be stretched at a high magnification, so that the orientation of the dichroic material is increased and the polarizing performance is improved. The polarizing film obtained by using the PVA film of the present invention makes the best use of the above characteristics, such as a liquid crystal television, a liquid crystal projector, a display for a word processor, a display for a personal computer, an OA equipment terminal display, a display for an instrument panel of an aircraft or an automobile, etc. Used for displays, filters, sunglasses, window glass, anti-glare films for various lights, various sensors, etc.

Claims (5)

  The saponification degree is 99 mol% or more, the peak top molecular weight of the molecular weight distribution determined by gel permeation chromatography measurement is 160,000 to 5,000,000, and the molecular weight in the molecular weight distribution is 1,000 to 50,000. The polyvinyl alcohol film whose content of 000 component is 17-40 mass%.   The dichroic pigment | dye contains in the polyvinyl alcohol film of Claim 1, and the polarizing film whose polarization degree is 99.9% or more.   The polyvinyl alcohol film according to claim 1, wherein the polyvinyl alcohol film (A) having a viscosity average polymerization degree of 2,000 to 20,000 and the polyvinyl alcohol (B) having a viscosity average polymerization degree of 200 to 1,000 are mixed and then formed into a film. Manufacturing method.   The method for producing a polyvinyl alcohol film according to claim 3, wherein a mass ratio (B / A) of the polyvinyl alcohol (B) to the polyvinyl alcohol (A) is 8/92 to 40/60.   The manufacturing method of the polarizing film which dye | stains and uniaxially stretches with respect to the polyvinyl alcohol film manufactured by the method of Claim 3 or 4.

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