JP2021059612A - Polyvinyl alcohol film and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a polyvinyl alcohol film which can suppress the occurrence of swelling wrinkles at the initial stage of stretching when producing a polarizing film and can produce a polarizing film having a small shrinkage force at the time of heating and excellent polarization performance. I will provide a. SOLUTION: The degree of swelling (A) is 150 to 185%, the softening point (B) is 60 to 68 ° C., and the relaxation obtained by pulse NMR measurement in a 3 mass% heavy aqueous borate solution at 60 ° C. The crystal component amount (a1) calculated from the curve is 2 to 10%, the ratio (a2 / a1) of the bound amorphous component amount (a2) to the crystal component amount (a1) is 2 to 6, and the thickness. A polyvinyl alcohol film having a size of 10 to 50 μm is used. [Selection diagram] Fig. 2

Description

The present invention relates to a polyvinyl alcohol film suitable as a raw film for producing a polarizing film, a method for producing the same, and a method for producing a polarizing film using the same.

A polarizing plate having a function of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. LCDs are widely used in small devices such as calculators and watches, laptop computers, LCD monitors, LCD color projectors, LCD TVs, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors. .. Among the fields of application of these LCDs, liquid crystal televisions and liquid crystal monitors are becoming larger and thinner, and as the glass used is made thinner, the polarizing plate is also required to be thinner from the viewpoint of shrinkage stress.

As a polarizing plate, a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be abbreviated as "PVA") is dyed, uniaxially stretched, and if necessary, further fixed with a boron compound or the like to form a polarizing film. After production, it is produced by laminating a protective film such as a cellulose triacetate (TAC) film on the surface of the polarizing film. Therefore, in order to achieve a thinner polarizing plate, it is required to manufacture a thin polarizing film using a thinner PVA film. The specific thickness of the PVA film is required to be 60 μm or less, further 50 μm or less.

However, when a thin polarizing film is produced using a conventionally known polyvinyl alcohol film, warpage of the polarizing plate due to shrinkage of the polarizing film has been a problem. In order to reduce the warp of the polarizing plate, a method of lowering the degree of polymerization of the polyvinyl alcohol resin, which is the material of the polarizing film, has been proposed. However, when a polarizing film is made of the resin, the orientation of PVA is caused by stretching. The problem was that the polarization performance was lowered without sufficient progress.

Patent Document 1 describes a PVA film composed of PVA having a degree of polymerization of 5100 to 10000 and having a degree of swelling and retardation showing values in a specific range, and is used as a raw material for a polarizing film having good polarization performance. It is also stated that. However, when a polarizing film is produced using PVA having a high degree of polymerization in this way, there is a problem that the stretching tension at the time of stretching becomes high and the shrinkage force of the polarizing film becomes large.

Further, in order to reduce the shrinkage force, it is possible to reduce the film thickness of the polyvinyl alcohol film used for stretching, but when a film having a thin film thickness is produced by a conventionally known method, swelling wrinkles occur at the initial stage of stretching. There was a problem.

According to Patent Document 2, a PVA film having a swelling degree of 250% or more is subjected to a wet heat treatment for 200 seconds or more under the conditions of a temperature of 55 to 100 ° C. and a relative humidity of 80% RH or more, whereby the swelling degree is 190 to 230%. A method for producing a PVA film is described. However, when a polarizing film is produced using the PVA film thus obtained, wrinkles due to swelling are likely to occur at the initial stage of the stretching operation, and the degree of polarization of the obtained polarizing film is insufficient.

Patent Document 3 describes a PVA film having a swelling degree of 110% or more and less than 190%, a softening point of 60 ° C. or more and 68 ° C. or less, and a thickness of 50 μm or less, and the PVA film is stretched at the time of stretching. It is said that it is hard to cut. Such a PVA film is produced by contacting a film-formed film with a gas having a temperature of 70 ° C. or higher and 100 ° C. or lower and a relative humidity of 60% or higher and 100% or lower for a short time. However, when a polarizing film is manufactured using such a PVA film, the polarizing performance becomes insufficient.

WO2010 / 071094 WO2014 / 050697 WO2016 / 167238

The present invention has been made to solve the above problems, and it is possible to suppress the occurrence of swelling wrinkles at the initial stage of stretching when producing a polarizing film, and the shrinkage force at the time of heating is small and the polarizing performance is small. It is an object of the present invention to provide a polyvinyl alcohol film capable of producing an excellent polarizing film. Another object of the present invention is to provide a method for producing the polyvinyl alcohol film. Another object of the present invention is to provide a method for producing a polarizing film using the polyvinyl alcohol film.

The above-mentioned problems are relaxation obtained by pulse NMR measurement in a 3 mass% borate heavy solution at 60 ° C., where the swelling degree (A) is 150 to 185% and the softening point (B) is 60 to 68 ° C. The crystal component amount (a1) calculated from the curve is 2 to 10%, the ratio (a2 / a1) of the bound amorphous component amount (a2) to the crystal component amount (a1) is 2 to 6, and the thickness is It is solved by providing a polyvinyl alcohol film having a size of 10 to 50 μm. At this time, it is preferable that the degree of swelling (A) and the softening point (B) satisfy the following formula (1).
450 ≦ A + 5B ≦ 520 (1)

Further, the above-mentioned problem is to form a polyvinyl alcohol film by casting an aqueous solution of polyvinyl alcohol having a degree of polymerization of 2600 to 6000 on a roll or a belt heated to 50 to 100 ° C., and obtain a polyvinyl alcohol film. The method for producing a polyvinyl alcohol film, which comprises drying until the water content reaches 1 to 20% by mass, and then performing a wet heat treatment for 3 to 300 minutes in an atmosphere having a temperature of 50 to 100 ° C. and a relative humidity of 60 to 100%. It is also solved by providing.

Further, the above problem is also solved by providing a method for producing a polarizing film, which comprises a step of dyeing the polyvinyl alcohol film with a dichroic dye and a step of stretching the polyvinyl alcohol film.

By using the polyvinyl alcohol film of the present invention as a raw material, it is possible to suppress the occurrence of swelling wrinkles at the initial stage of stretching when producing a polarizing film. Further, the polarizing film produced by using the polyvinyl alcohol film of the present invention has a small shrinkage force at the time of heating and is excellent in polarizing performance.

It is a figure which showed the lower frame 1 and the upper frame 2 for the measurement of a softening point (B). It is a graph which plotted the softening point (B) with respect to the swelling degree (A) of the PVA film obtained in an Example and a comparative example.

The polyvinyl alcohol film of the present invention has a swelling degree (A) of 150 to 185%, a softening point (B) of 60 to 68 ° C., and pulse NMR measurement in a 3 mass% boric acid heavy aqueous solution at 60 ° C. The amount of crystal component (a1) calculated from the relaxation curve obtained in 1) is 2 to 10%, and the ratio (a2 / a1) of the amount of bound amorphous component (a2) to the amount of crystal component (a1) is 2 to 6. The thickness is 10 to 50 μm. Hereinafter, these configurations will be described in detail.

The swelling degree (A) of the PVA film of the present invention is 150 to 185%. The degree of swelling (A) is an index showing the water retention capacity when the PVA film is immersed in water, and the mass of the PVA film after being immersed in water at 30 ° C. for 30 minutes is dried at 105 ° C. for 16 hours after immersion. It can be obtained as a percentage by dividing by the mass later. Specifically, it can be measured according to the method described in the later examples. If the degree of swelling (A) is too low, a sufficient plasticizing effect of water cannot be obtained, the stretching tension becomes high, and fractures occur frequently. The degree of swelling (A) is preferably 155% or more, and more preferably 160% or more. On the other hand, if the degree of swelling (A) is too high, swelling wrinkles occur during stretching, which is not preferable from the viewpoint of process passability and spots. The degree of swelling (A) is preferably 180% or less.

The softening point (B) of the PVA film of the present invention is 60 to 68 ° C. The softening point (B) is an index indicating the heat resistance and water resistance of the PVA film, and is used as the hot water breaking temperature when the PVA film is immersed in pure water at 30 ° C. and then heated at a heating rate of 5 ° C./min. It is something that can be sought. Specifically, it can be measured according to the method described in the later examples. If the softening point (B) is too low, wrinkles are generated during stretching, which is not preferable from the viewpoint of process passability. The softening point (B) is preferably 62 ° C. or higher, and more preferably 63 ° C. or higher. On the other hand, if the softening point (B) is too high, the stress during stretching becomes high and the shrinkage force of the polarizing film becomes large, which is not preferable. The softening point (B) is preferably 67 ° C. or lower, and more preferably 66 ° C. or lower.

The PVA film of the present invention has a crystal component amount (a1) of 2 to 10%, which is calculated from a relaxation curve obtained by pulse NMR measurement in a 3 mass% borate heavy aqueous solution at 60 ° C., and is a bound non-crystal. The ratio (a2 / a1) of the component amount (a2) to the crystal component amount (a1) is 2 to 6.

Here, pulsed NMR, unlike high-resolution NMR, as commonly used in such determination of the structure of the organic compound, it is possible to measure each relaxation time of the ^{1 H} nuclei associated with molecular mobility of the system, It is an analytical method that can determine the abundance ratio of each motor component in the system by utilizing its high quantification. In the present invention, the crystalline component amount in the PVA film (a1), bound amorphous component amount (a2) and Upon obtaining the amorphous component amount ^{(a3), 1} H spin - using spin relaxation time _{T 2.} Specifically, _{A 1} to A _{10 are all positive values so that the T 2} transition curve obtained in the measurement of the spin-spin relaxation time T ₂ ^{of 1} H approximately applies to the following equation (2). To ask. At this time, the relaxation time corresponding to each of _{A 1} to A _{10 is set to c 1 to} c ₁₀ . The fitting is performed using the linear least squares method. Of the obtained values, the component amounts having a relaxation time of 0.003, 0.01, and 0.03 ms, that is, A ₁ + A ₂ + A _3, are defined as the crystal component amount (a1), and the relaxation time is 0. 05 and components of 0.1 ms, i.e. _a 4 + _{a 5} above bound amorphous component amount (a2) is defined to be relaxation time 0.3,0.5,0.8,1 and 3ms ingredient amounts, That is, A ₆ + A ₇ + A ₈ + A ₉ + A ₁₀ was defined as the amount of amorphous component (a3). The total of (a1), (a2) and (a3) is 100%. As specific conditions for pulse NMR measurement, each condition described later in the examples can be adopted. Table 1 shows the sorting of components by relaxation time.

In the pulse NMR measurement, the PVA film to be measured is immersed in a 3 mass% boric acid heavy aqueous solution at 60 ° C. for 30 minutes in advance. Then, the above-mentioned component ratio can be obtained by obtaining the ratios of the crystal component amount (a1), the bound amorphous component amount (a2) and the amorphous component amount (a3) after immersion. Since the PVA film after immersion can be used for pulse NMR measurement as it is, it is preferable to immerse the PVA film in a heavy aqueous solution of boric acid in an NMR tube or the like. As a specific immersion method and conditions, the method described later in the examples can be adopted. By immersing in a heavy aqueous solution of boric acid and cross-linking with boric acid, the amounts of the above components related to the effects of the present invention such as polarization performance can be obtained.

In the PVA film of the present invention, the amount of crystal component (a1) calculated from the transition curve obtained by pulse NMR measurement is 2 to 10%. If the amount of crystal component (a1) is too small, the film may be cut when stretched in water. The amount of crystal component (a1) is preferably 4% or more, and more preferably 5% or more. On the other hand, if the amount of the crystal component (a1) is too large, the shrinkage force when the obtained polarizing film is heated becomes large. The amount of crystal component (a1) is preferably 9.5% or less, and more preferably 9% or less.

The PVA film of the present invention has a ratio (a2 / a1) of the amount of bound amorphous component (a2) to the amount of crystal component (a1) calculated from the relaxation curve obtained by pulse NMR measurement of 2 to 6. When the ratio (a2 / a1) is less than 2, the polarization performance of the obtained polarizing film deteriorates. The ratio (a2 / a1) is preferably 2.3 or more, and more preferably 2.5 or more. On the other hand, when the ratio (a2 / a1) exceeds 6, the shrinkage force at the time of drying becomes too high. The ratio (a2 / a1) is preferably 5 or less, and more preferably 4 or less.

The polyvinyl alcohol film of the present invention preferably satisfies the following formula (1) in terms of swelling degree (A) and softening point (B). As described above, the degree of swelling (A) is an index showing the water retention capacity when the PVA film is immersed in water, and when it is large, it is easily stretched in water with low stress. Further, the softening point (B) is an index indicating the heat resistance and water resistance of the PVA film, and if it is large, the stress during stretching becomes high. Therefore, the balance of both values is important for proper stretching with low stress. By evaluating a large number of samples, it was found that the effect of the change in the softening point (B) on the stretchability is about 5 times that of the change in the degree of swelling (A). did.
450 ≦ A + 5B ≦ 520 (1)

By including the value of A + 5B of the PVA film in a specific range, it is possible to suppress the occurrence of swelling wrinkles at the initial stage of stretching when producing a polarizing film, and to obtain a polarizing film having a small shrinkage force during heating. Can be compatible with each other. A + 5B is preferably 520 or less, more preferably 515 or less, and even more preferably 510 or less. On the other hand, A + 5B is preferably 450 or more, more preferably 460 or more, and further preferably 470 or more.

Examples of the PVA constituting the PVA film of the present invention include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versaticate, vinyl laurate, vinyl stearate, vinyl benzoate, and isoacetate. Examples thereof include those obtained by saponifying a polyvinyl ester obtained by polymerizing one or more vinyl esters such as propenyl. Among the above vinyl esters, vinyl acetate is preferable from the viewpoints of ease of production, availability, cost and the like of PVA.

The above-mentioned polyvinyl ester is preferably obtained by using only one kind or two or more kinds of vinyl esters as a monomer, and more preferably one obtained by using only one kind of vinyl ester as a monomer. However, it may be a copolymer of one kind or two or more kinds of vinyl esters and another monomer copolymerizable therewith, as long as the effect of the present invention is not impaired.

Other monomers copolymerizable with the above vinyl ester include, for example, α-olefin having 2 to 30 carbon atoms such as ethylene, propylene, 1-butyl, 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, ( (Meta) acrylate esters such as t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylamide, N-methyl ( Meta) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide propanesulfonic acid or a salt thereof, (meth) acrylamidepropyldimethylamine or a salt thereof, (Meta) acrylamide derivatives such as N-methylol (meth) acrylamide or derivatives thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methylvinyl ether, ethylvinyl ether, n-propylvinyl ether, i -Vinyl ethers such as propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanide such as (meth) acrylonitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, fluoride Vinyl halides such as vinylidene; allyl compounds such as allyl acetate and allyl chloride; maleic acid or salts thereof, esters or acid anhydrides; itaconic acid or salts thereof, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; Unsaturated sulfonic acid and the like can be mentioned. The above polyvinyl ester can have a structural unit derived from one or more of the other monomers described above.

The ratio of the structural units derived from the other monomers to the polyvinyl ester is preferably 15 mol% or less, preferably 10 mol%, based on the number of moles of all the structural units constituting the polyvinyl ester. It is more preferably less than or equal to 5 mol% or less.

Ethylene is suitable as the other monomer. Copolymerization of ethylene may improve the polarization performance of the obtained polarizing film. The content of ethylene units in PVA is preferably 0.5 to 8 mol%. The content of ethylene units is more preferably 1 mol% or more, still more preferably 1.5 mol% or more. On the other hand, the content of ethylene units is more preferably 5 mol% or less.

In particular, when the other monomer described above is a monomer that may promote the water solubility of the obtained PVA, such as (meth) acrylic acid, unsaturated sulfonic acid, etc., the obtained PVA In order to prevent PVA from dissolving when the film is used as a raw film for producing a polarizing film, the proportion of structural units derived from these monomers in the polyvinyl ester is the total of all the structural units constituting the polyvinyl ester. Based on the number of moles of the structural unit, it is preferably 5 mol% or less, and more preferably 3 mol% or less.

The above-mentioned polyvinyl alcohol may be modified with one or more kinds of graft-copolymerizable monomers as long as the effect of the present invention is not impaired. Examples of the graft copolymerizable monomer include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms. The proportion of structural units derived from the graft copolymerizable monomer in polyvinyl alcohol is preferably 5 mol% or less based on the number of moles of all structural units constituting polyvinyl alcohol.

The above-mentioned PVA may or may not have a part of its hydroxyl group crosslinked. Further, in the above-mentioned PVA, a part of its hydroxyl group may react with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure, or may not react with these compounds to form an acetal structure. You may.

The degree of polymerization of PVA is preferably in the range of 1500 to 6000. If the degree of polymerization is less than 1500, the durability of the obtained polarizing film tends to decrease. The degree of polymerization is more preferably 1800 or more, and even more preferably 2600 or more. On the other hand, when the degree of polymerization exceeds 6000, the production cost tends to increase and the process passability during film formation tends to deteriorate. The degree of polymerization is more preferably 5000 or less, and even more preferably 4500 or less. The degree of polymerization of PVA referred to in the present specification means the average degree of polymerization measured according to the description of JIS K6726-1994.

The saponification degree of the PVA is preferably 98 mol% or more, more preferably 98.5 mol% or more, and further preferably 99 mol% or more from the viewpoint of water resistance of the polarizing film. .. If the degree of saponification is less than 98 mol%, the water resistance of the obtained polarizing film tends to deteriorate. The degree of saponification of PVA in the present specification refers to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units possessed by PVA that can be converted into vinyl alcohol units by saponification. The ratio (mol%) of the number of moles of vinyl alcohol units. The degree of saponification can be measured according to the description of JIS K6726-1994.

The PVA film of the present invention preferably contains a plasticizer. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. One or more of these plasticizers can be included. Among these, glycerin is preferable from the viewpoint of improving stretchability.

The content of the plasticizer in the PVA film of the present invention is preferably in the range of 1 to 20 parts by mass with respect to 100 parts by mass of PVA contained therein. When the content of the plasticizer is 1 part by mass or more, the stretchability of the PVA film can be further improved. The content is more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more. On the other hand, when the amount of the plasticizer is 20 parts by mass or less, it is possible to prevent the PVA film from becoming too flexible and the handleability from being lowered. The content is more preferably 17 parts by mass or less, and further preferably 15 parts by mass or less.

If necessary, the PVA film of the present invention may further contain components such as an antioxidant, an antioxidant, a pH adjuster, a concealing agent, an antioxidant, an oil agent, and a surfactant described later.

The shape of the PVA film of the present invention is not particularly limited, but a long film is preferable. As a result, a more uniform polyvinyl alcohol film can be continuously and easily produced, and the polarizing film can be continuously used even when the polarizing film is produced by using the polyvinyl alcohol film. The length of the long film (length in the length direction) is not particularly limited and can be appropriately set according to the intended use, for example, in the range of 5 to 30,000 m.

The width of the PVA film of the present invention is not particularly limited and can be appropriately set according to the use of the PVA film and the polarizing film produced from the PVA film. However, in recent years, the screen size of liquid crystal televisions and liquid crystal monitors has been increasing. From this point of view, if the width of the PVA film is 3 m or more, more preferably 4 m or more, it is suitable for these applications. On the other hand, if the width of the PVA film is too large, it tends to be difficult to uniformly perform uniaxial stretching itself when producing a polarizing film with a practical device, so the width of the polyvinyl alcohol film is 7 m or less. Is preferable.

The thickness of the PVA film of the present invention is 10 to 50 μm. It is necessary to be 50 μm or less from the viewpoint that a thin polarizing film can be obtained, the shrinkage force of the polarizing film and the polarizing plate using the polarizing film is reduced, and the thin glass to be laminated is prevented from warping. It is preferably 40 μm or less, more preferably 30 μm or less, and particularly preferably 25 μm or less. On the other hand, when the thickness of the PVA film is 10 μm or more, the handleability at the time of producing the polarizing film is improved.

Examples of the liquid medium used for preparing 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 the like. Examples thereof include trimethylolpropane, ethylenediamine and diethylenetriamine, and one or more of these can be used. Of these, water is preferably used from the viewpoint of environmental load and recoverability.

The volatile fraction (moisture content) of the film-forming stock solution varies depending on the film-forming method, film-forming conditions, etc., but is generally 50 to 95% by mass. If the volatile content of the membrane-forming stock solution is too low, the viscosity of the membrane-forming stock solution becomes too high, making it difficult to filter and defoam when preparing the membrane-forming stock solution, making it difficult to produce a polyvinyl alcohol film with few foreign substances and defects. Tends to be. The volatile fraction is preferably 55% by mass or more, and more preferably 60% by mass or more. On the other hand, if the volatile fraction of the film-forming stock solution is too high, the concentration of the film-forming stock solution becomes too low, and it tends to be difficult to form an industrial polyvinyl alcohol film. The volatile fraction is preferably 90% by mass or less, and more preferably 85% by mass or less.

In addition, the film-forming stock solution preferably contains a surfactant. By containing a surfactant, the film-forming property is improved and the occurrence of thickness unevenness of the polyvinyl alcohol film is suppressed, and the polyvinyl alcohol film can be easily peeled off from the roll or belt used for film-forming. Become. When a polyvinyl alcohol film is produced from a film-forming stock solution containing a surfactant, the polyvinyl alcohol film contains the surfactant. The type of the above-mentioned surfactant is not particularly limited, but an anionic surfactant or a nonionic surfactant is preferable from the viewpoint of peelability from a roll, a belt or the like.

As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfate ester type such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and a sulfonic acid type such as dodecylbenzene sulfonate are suitable.

Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether; an alkylphenyl ether type such as polyoxyethylene octylphenyl ether; an alkyl ester type such as polyoxyethylene laurate; and 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 oleic acid diethanolamide; Polyoxyalkylene allylphenyl ether and the like The allylphenyl ether type of the above is suitable.

These surfactants may be used alone or in combination of two or more.

When the film-forming stock solution contains a surfactant, the content thereof is preferably in the range of 0.01 to 0.5 parts by mass with respect to 100 parts by mass of PVA. When the content of the surfactant is less than 0.01 parts by mass with respect to 100 parts by mass of PVA, the effect of improving the film-forming property and the peelability due to the addition of the surfactant is less likely to appear. The content of the surfactant is more preferably 0.02 parts by mass or more, and further preferably 0.05 parts by mass or more. On the other hand, if it exceeds 0.5 parts by mass with respect to 100 parts by mass of PVA, the surfactant may bleed out to the surface of the PVA film and cause blocking, resulting in poor handleability. The content of the surfactant is more preferably 0.3 parts by mass or less, and further preferably 0.2 parts by mass or less.

As a film-forming method for forming a PVA film using the above-mentioned film-forming stock solution, for example, a wet film-forming method, a gel film-forming method, a casting film-forming method, an extrusion film-forming method, or the like can be adopted. it can. In addition, a method based on a combination of these can also be adopted. Among the above film-forming methods, the casting film-forming method or the extrusion film-forming method is preferably adopted because a PVA film having a uniform thickness and width and good physical characteristics can be obtained.

The specific film-forming method is not particularly limited, but a T-shaped slit die, a hopper plate, an I-die, a lip coater die, or the like is used to rotate the film-forming stock solution on the peripheral surface of a heated roll or belt. It is uniformly discharged, and the volatile components are evaporated from one surface of the film discharged onto the roll or belt and dried to obtain a PVA film, or one or more after being dried in this way. Examples thereof include a method of further drying on the peripheral surface of the rotating roll of the PVA film, or passing through a hot air drying device to further dry the PVA film.

The surface temperature of the roll or belt used for film formation can be, for example, 50 to 100 ° C. By setting the surface temperature to 50 ° C. or higher, water can be removed with high productivity. The surface temperature is more preferably 60 ° C. or higher, further preferably 65 ° C. or higher, and particularly preferably 70 ° C. or higher. On the other hand, by setting the surface temperature to 100 ° C. or lower, it is possible to suppress the occurrence of surface unevenness due to rapid evaporation of water. The surface temperature is more preferably 95 ° C. or lower, and even more preferably 90 ° C. or lower. It is preferable to form a PVA film by casting it on a roll or belt heated to the above temperature range.

It is preferable to dry the PVA film obtained by forming the film until the water content reaches 1 to 20% by mass from the viewpoint of productivity and process passability. The drying method is not particularly limited, but it is preferable to dry by releasing moisture from one side on the roll or belt. Further, after peeling from the roll, heat treatment may be performed with another roll or hot air. The water content is more preferably 2% by mass or more. On the other hand, the water content is more preferably 15% by mass or less.

It is preferable that the PVA film dried to a moisture content of 1 to 20% by mass is subjected to a wet heat treatment for 3 to 300 minutes in an atmosphere having a temperature of 50 to 100 ° C. and a relative humidity of 60 to 100%. Hereinafter, the conditions of the wet heat treatment will be described in detail.

The temperature during the wet heat treatment is preferably 50 to 100 ° C. By performing a wet heat treatment at a temperature within such a range, a PVA film satisfying the constitution of the present invention can be produced with high productivity. The temperature is more preferably 55 ° C. or higher. On the other hand, the temperature is more preferably 90 ° C. or lower, further preferably 80 ° C. or lower, and particularly preferably 75 ° C. or lower.

The relative humidity of the atmosphere during the wet heat treatment is preferably 60% or more. By performing a wet heat treatment at a humidity of 60% or more, the degree of swelling of the obtained PVA film can be efficiently increased. The humidity is more preferably 70% or more, and even more preferably 80% or more. On the other hand, when the wet heat treatment is performed in an environment where water vapor is saturated (relative humidity 100%), water droplets may adhere to the film, so the humidity is preferably 98% or less, more preferably 95%. It is as follows.

The time of the wet heat treatment is preferably 3 to 300 minutes. By performing such a time-humidity heat treatment, a PVA film satisfying the constitution of the present invention can be produced with high productivity. The time is more preferably 7 minutes or more, further preferably 13 minutes or more, and particularly preferably 16 minutes or more. On the other hand, the time is more preferably 200 minutes or less, and even more preferably 100 minutes or less.

By the above-mentioned production method, the swelling degree (A) is 150 to 185%, the softening point (B) is 60 to 68 ° C., and the pulse NMR measurement in a 3 mass% boric acid heavy aqueous solution at 60 ° C. The amount of crystal component (a1) calculated from the relaxation curve obtained in 1) is 2 to 10%, and the ratio (a2 / a1) of the amount of bound amorphous component (a2) to the amount of crystal component (a1) is 2 to 6. PVA film can be obtained. Then, a polyvinyl alcohol film capable of suppressing the occurrence of swelling wrinkles at the initial stage of stretching when producing a polarizing film, and producing a polarizing film having a small shrinkage force at the time of heating and excellent polarization performance can be produced. Can be provided.

In order to improve the runnability at the time of winding, the PVA film may be dried with hot air at 40 ° C. to 60 ° C. after the moist heat step. However, if the hot air temperature in this step exceeds 70 ° C., the softening point (B) of the PVA film rises, which is not preferable.

The use of the PVA film of the present invention is not particularly limited, but the PVA film of the present invention has no swelling wrinkles at the initial stage of stretching and can be stably stretched, so that it can be used as a raw film for producing a polarizing film. It is desirable to use it.

The method for producing a polarizing film using the PVA film of the present invention as a raw film is not particularly limited, and any conventionally adopted method may be adopted. Examples of such a method include a method of dyeing and uniaxially stretching the PVA film of the present invention, and specifically, swelling, dyeing, uniaxially stretching, and optionally the PVA film of the present invention. Further, a method of performing fixing treatment, drying, heat treatment and the like can be mentioned. In this case, the order of each treatment such as swelling, staining, uniaxial stretching, and fixing treatment is not particularly limited, and one or more treatments can be performed at the same time. It is also possible to perform one or more of each process twice or more.

The swelling can be performed by immersing the PVA film in water. The temperature of the water when immersed in water is preferably in the range of 20 to 40 ° C, more preferably in the range of 22 to 38 ° C, and preferably in the range of 25 to 35 ° C. More preferred. The time for immersion in water is, for example, preferably in the range of 0.1 to 5 minutes, and more preferably in the range of 0.5 to 3 minutes. The water when immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and an aqueous medium.

The dyeing is preferably performed using iodine, and the dyeing time may be any stage before uniaxial stretching, during uniaxial stretching, and after uniaxial stretching. Dyeing is generally performed by immersing a PVA film in a solution containing iodine-potassium iodide (particularly an aqueous solution) as a dyeing bath, and such a dyeing method is also preferably adopted in the present invention. .. The concentration of iodine in the dyeing bath is preferably in the range of 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably in the range of 0.01 to 10% by mass. The temperature of the dyeing bath is preferably 20 to 50 ° C, particularly preferably 25 to 40 ° C.

The uniaxial stretching may be performed by either 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, in the above-mentioned dyeing bath or in the fixing treatment bath described later. Further, in the case of the dry stretching method, it can be carried out 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, and 1.5. It is particularly preferably in the range of ~ 4.0% by mass. Further, the boric acid aqueous solution may contain potassium iodide, and the concentration thereof is preferably in the range of 0.01 to 10% by mass.

The stretching temperature in uniaxial stretching is preferably in the range of 30 to 90 ° C, more preferably in the range of 40 to 80 ° C, and particularly preferably in the range of 50 to 70 ° C. Further, the stretching ratio in uniaxial stretching is preferably 5 times or more, more preferably 5.5 times or more, and particularly preferably 6 times or more, from the viewpoint of the polarization performance of the obtained polarizing film. The upper limit of the draw ratio is not particularly limited, but the draw ratio is preferably 8 times or less.

In the production of the polarizing film, it is preferable to carry out a fixing treatment in order to strengthen the adsorption of the dye (iodine or the like) on the PVA film. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing one or more kinds of boron compounds such as boric acid and borax can be used. Further, if necessary, an iodine compound or a metal compound may be added to the fixing treatment bath. The concentration of the boron compound in the fixing treatment bath is generally preferably about 2 to 15% by mass, particularly preferably about 3 to 10% by mass. The temperature of the fixing treatment bath is preferably 15 to 60 ° C, particularly preferably 25 to 40 ° C.

Drying is preferably carried out at 30 to 150 ° C., particularly 50 to 130 ° C. When the moisture content of the polarizing film becomes 10% or less due to drying, tension is applied to the polarizing film and heat treatment is performed at about 80 to 120 ° C. for about 1 to 5 minutes. You can get the film.

The polarizing film obtained as described above has a small shrinkage force during heating and is excellent in polarizing performance. The degree of polarization of the polarizing film is preferably 99% or more, more preferably 99.5% or more, further preferably 99.9% or more, and particularly preferably 99.95% or more. preferable.

The obtained polarizing film is usually used as a polarizing plate by laminating a protective film that is optically transparent and has mechanical strength on both sides or one side thereof. As the protective film, a cellulose triacetate (TAC) film, a cellulose acetate / butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Further, examples of the adhesive for bonding include PVA-based adhesives and urethane-based adhesives, and among them, PVA-based adhesives are preferable.

The polarizing plate obtained as described above can be used as a component of an LCD by being coated with an adhesive such as acrylic 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.

The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples. The measurement methods adopted in the following examples, comparative examples and reference examples are shown below.

(1) Measurement of swelling degree (A) A rectangular sample of 10 cm in the width direction and 20 cm in the length direction is cut out from the PVA film to be measured, and this sample is further stripped with a width of 2 to 3 mm and a length of 20 cm. It was cut into a shape. Then, all of these strip-shaped samples were immersed as they were in 1,000 g of distilled water at 30 ° C. After immersion for 30 minutes, the strip-shaped sample is taken out and centrifuged at 3,000 rpm for 5 minutes using a centrifuge (KOKUSAN XEM-KL-5886), and the mass after dehydration is "N" (all of the strip-shaped sample). Total) was measured. Subsequently, the strip-shaped sample was dried in a dryer at 105 ° C. for 16 hours, and then the mass "M" (the total of all the strip-shaped samples) was measured, and the degree of swelling (A) was calculated by the following formula (i). Was calculated.
Swelling degree (A) (%) = 100 x N / M (i)

(2) Measurement of softening point (B) A square sample of 3 cm in the width direction and 3 cm in the length direction is cut out from the PVA film to be measured, and the metal lower frame 1 and upper frame 2 as shown in FIG. I sandwiched it between. The PVA film sandwiched between the two frames was fixed to a jig that could be maintained horizontally at a predetermined height. In addition, a glass beaker having a volume of 1 L containing 800 mL of pure water was prepared. A 3.5 g iron ball was placed on the PVA film in the center of the opening of the upper frame 2 and slowly submerged in the water in the beaker. After immersion in water, the temperature of the water was raised at a rate of 5 ° C./min. The water temperature when the PVA film was torn and the iron ball blocked the light of the lamp 5 mm below was defined as the softening point (B) of the PVA film.

(3) Evaluation of swelling wrinkles A sample of 5 cm in the width direction and 10 cm in the length direction is cut out from the PVA film to be measured, and a stretching jig is used to stretch the sample uniaxially in the length direction so that the chuck distance is 5 cm. It was sandwiched between the two and immersed in distilled water at 30 ° C. Immediately after immersion, uniaxial stretching was performed in the length direction for 30 seconds at a stretching rate of 25 mm / min (50% / min). Immediately after stretching, the PVA film was pulled up from the water bath at a speed of 50 mm / sec, and the wrinkles on the film surface at that time were visually observed from a position 1 m away from the front of the film under illumination of 500 lux with a fluorescent lamp. The case where there were no wrinkles on the film surface was designated as A, the case where one or two wrinkles were observed was designated as B, and the case where three or more wrinkles were observed was designated as C.

(4) Amount of crystal component (a1) and amount of bound amorphous component (a2) in PVA film
A sample (100 mg) obtained from the PVA film obtained in the following Example or Comparative Example was shredded to a size of about 5 mm × 5 mm and then put into an NMR tube together with 1 mL of heavy water. The NMR tube was immersed in a constant temperature bath at 60 ° C. 30 minutes, using a pulsed NMR (Bruker BioSpin Co., Ltd. "minispec mq20 WVT"), spin of the ¹ H samples - measuring the spin relaxation time _{T 2} did. The measurement conditions are as follows.
-Pulse sequence: Solid-Echo method (90x-τ-90y)
-RF pulse width: 8.2 μs
・ Pulse interval: 1 μs
・ Pulse repetition time: 1s
・ Measurement temperature: 60 ° C
・ Dummy shot: 4 times

_{The T 2} relaxation curve obtained by the above measurement is sorted into components for each relaxation time based on Table 1 and fitted to the following equation (2) by the linear minimum square method, and the amount of crystal components in which all are positive values. (A1), the amount of bound amorphous component (a2) and the amount of amorphous component (a3) were determined, and the ratio (a2 / a1) of the amount of crystal component (a1) and the amount of bound amorphous component (a2) was calculated.

(5) Measurement of Shrinkage Force of Polarizing Film The shrinkage force was measured using an autograph "AG-X" with a constant temperature bath manufactured by Shimadzu Corporation and a video-type extensometer "TR ViewX120S". A polarizing film whose humidity was adjusted at 20 ° C./20% RH for 18 hours was used for the measurement. After the constant temperature bath of the autograph "AG-X" was set to 20 ° C, a polarizing film (length direction 15 cm, width direction 1.5 cm) was attached to the chuck (chuck interval 5 cm), and at the same time as the tension was started, the temperature was constant to 80 ° C. The temperature rise of the tank was started. The polarizing film was pulled at a speed of 1 mm / min, the tension was stopped when the tension reached 2N, and the tension was measured up to 4 hours later in that state. At this time, since the distance between the chucks changes due to thermal expansion, a marked line sticker is attached to the chuck, and the distance between the chucks is increased by the amount of movement of the marked line sticker attached to the chuck using the video type extensometer "TR ViewX120S". Was measured so that it could be corrected. For the contraction force, a value calculated by subtracting 2N, which is a hold tension, from the tension after 4 hours was used.

(6) Evaluation of polarization performance of polarizing film (measurement of transmittance Ts)
Two samples of 2 cm in the length direction and 1.5 cm in the width direction of the polarizing film were collected from the central portion of the polarizing film obtained in the following Example or Comparative Example, and a spectrophotometer with an integrating sphere (JASCO Corporation). Using "V7100" manufactured by Co., Ltd.), the visibility of the visible light region of the C light source and 2 ° field is corrected in accordance with JIS Z 8722 (measurement method of object color), and the length of one sample is lengthened. The light transmittance when tilted by + 45 ° with respect to the direction and the light transmittance when tilted by −45 ° were measured, and their average value Ts1 (%) was obtained. In the same manner for the other sample, the light transmittance when tilted by + 45 ° and the light transmittance when tilted by −45 ° were measured, and their average value Ts2 (%) was obtained. Ts1 and Ts2 were averaged according to the following formula (ii) to obtain the transmittance Ts (%) of the polarizing film.
Ts = (Ts1 + Ts2) / 2 (ii)

(7) Evaluation of polarization performance of polarizing film (measurement of degree of polarization V)
When two samples collected by the above-mentioned measurement of transmittance Ts are overlapped so that their length directions are parallel to each other, the light transmittance T‖ (%) and the length direction are orthogonal to each other. The light transmittance T⊥ (%) of the above was measured in the same manner as in the case of the above “(1) Measurement of transmittance Ts”, and the degree of polarization V (%) was obtained by the following formula (iii).
V = {(T‖-T⊥) / (T‖ + T⊥)} ^1/2 x 100 (iii)

[Example 1]
The ethylene-modified polyvinyl alcohol used in this example (ethylene unit content 2.5 mol%, saponification degree 99.3 mol%, degree of polymerization 2800) is ethylene obtained by copolymerizing ethylene and vinyl acetate. It was obtained by saponifying modified polyvinyl acetate. A membrane-forming stock solution having a volatile content of 66% by mass was prepared, consisting of 100 parts by mass of the ethylene-modified PVA, 10 parts by mass of glycerin as a plasticizer, 0.1 parts by mass of polyoxyethylene lauryl ether sodium sulfate as a surfactant, and water. The obtained membrane-forming stock solution was cast on a metal drum at 80 ° C., dried until the volatile content (moisture content) reached 10% by mass, and then heat-treated with a heat treatment roll at 105 ° C. for 1 minute. The volatile content (moisture content) of the film after the heat treatment was 3% by mass. Then, the film was subjected to a moist heat treatment for 30 minutes in a constant temperature and humidity chamber at 60 ° C. and a relative humidity of 90%, and then dried at room temperature until the water content reached 8% by mass to obtain a PVA film. Tables 2 and 3 show the production conditions and evaluation results of the PVA film. The swelling degree (A) of this PVA film was 165%, the softening point (B) was 66.0 ° C., and the film thickness was 20 μm. The amount of crystal component (a1) at 60 ° C. in a 3 mass% boric acid heavy aqueous solution of this film was 8.6%, (a2) was 23.0%, and (a3) was 68.4%, and the ratio (a2) was / A1) was 2.68. The result of the swelling wrinkle evaluation was A. The evaluation results of the obtained polarizing film are shown in Table 3.

A polarizing film was prepared using the PVA film obtained as described above as a raw material. After stretching 2.0 times to MD in pure water at 30 ° C, the total stretching ratio becomes 2.36 times in a dyeing solution at 32 ° C containing 0.03% by mass of iodine and 3% by mass of potassium iodide. Then, in a cross-linking tank at 32 ° C. containing 2.6% by mass of boric acid, the mixture was stretched so that the total stretching ratio was 2.6 times, and further 2.8% by mass of boric acid and potassium iodide were added. Was stretched in a stretching tank at 57 ° C. containing 5.0% by mass until the total stretching ratio became 6.0 times. Subsequently, it was immersed in a washing tank containing 1.5% by mass of boric acid and 4.8% by mass of potassium iodide for 4 seconds, and dried in a drying oven at 70 ° C. for 4 minutes. When the transmittance of the polarizing film thus produced was 44.0%, the degree of polarization was 99.97%, and the shrinkage force of this polarizing film was 8.7N.

[Example 2]
It consists of 100 parts by mass of unmodified polyvinyl alcohol (degree of polymerization 4000, saponification degree 99.95 mol%), 10 parts by mass of glycerin as a plasticizer, 0.1 parts by mass of polyoxyethylene lauryl ether sodium sulfate as a surfactant, and water. A film-forming stock solution having a volatile content of 66% by mass was prepared. The obtained membrane-forming stock solution was cast on a metal drum at 80 ° C. and dried until the water content reached 10% by mass. After that, the film was subjected to a wet heat treatment under the same conditions as in Example 1 without heat treatment, and then dried at room temperature until the water content reached 8% by mass to obtain a PVA film. Tables 2 and 3 show the production conditions and evaluation results of the PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 1]
The same film-forming stock solution as in Example 1 was cast on a metal drum at 80 ° C. and dried until the water content reached 5% by mass. Then, heat treatment was carried out for 10 minutes in a hot air dryer at 145 ° C. to obtain a PVA film. The water content of the film after the heat treatment was 3% by mass. Tables 2 and 3 show the production conditions and evaluation results of the PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 2]
The same film-forming stock solution as in Example 2 was poured on a metal drum at 80 ° C. and dried until the water content reached 5% by mass. Then, heat treatment was carried out for 3 minutes in a hot air dryer at 115 ° C. to obtain a PVA film. The water content of the film after the heat treatment was 3% by mass. Tables 2 and 3 show the production conditions and evaluation results of the PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 3]
The same film-forming stock solution as in Example 1 was cast on a metal drum at 80 ° C., dried until the water content reached 5% by mass, and heat-treated on a heat treatment roll at 115 ° C. for 1 minute to obtain a PVA film. The water content of the film after the heat treatment was 3% by mass. Tables 2 and 3 show the production conditions and evaluation results of the PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 4]
The same film-forming stock solution as in Example 2 was cast on a metal drum at 80 ° C., dried until the water content reached 10% by mass, and heat-treated with a heat treatment roll at 95 ° C. for 1 minute to obtain a PVA film. The water content of the film after the heat treatment was 5% by mass. Tables 2 and 3 show the production conditions and evaluation results of the PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 5]
Volatile component consisting of 100 parts by mass of polyvinyl alcohol (degree of polymerization 1700, degree of saponification 99.95 mol%), 10 parts by mass of glycerin as a plasticizer, 0.1 parts by mass of polyoxyethylene lauryl ether sodium sulfate as a surfactant, and water. A film-forming stock solution having a rate of 66% by mass was cast on a metal drum at 80 ° C. and dried until the water content reached 10% by mass. Then, the heat treatment was performed for 3 minutes in a hot air dryer at 125 ° C. to obtain a PVA film. The water content of the film after the heat treatment was 3% by mass. Tables 2 and 3 show the production conditions and evaluation results of the PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 6]
The same film-forming stock solution as in Comparative Example 5 was cast on a metal drum at 80 ° C. and dried until the water content reached 10% by mass. Then, the heat treatment was performed for 3 minutes in a hot air dryer at 140 ° C. to obtain a PVA film. The water content of the film after the heat treatment was 3% by mass. Tables 2 and 3 show the production conditions and evaluation results of the PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 7]
The same film-forming stock solution as in Comparative Example 5 was cast on a metal drum at 80 ° C. and dried until the water content reached 10% by mass. Then, heat treatment was carried out for 3 minutes in a hot air dryer at 108 ° C. to obtain a PVA film. The water content of the film after the heat treatment was 4% by mass. Tables 2 and 3 show the production conditions and evaluation results of the PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 8]
The same film-forming stock solution as in Example 2 was poured on a metal drum at 80 ° C. and dried until the water content reached 10% by mass. Then, heat treatment was carried out for 10 minutes in a hot air dryer at 80 ° C. to obtain a PVA film. The water content of the film after the heat treatment was 5% by mass. Tables 2 and 3 show the production conditions and evaluation results of the PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 9]
Volatile component consisting of 100 parts by mass of polyvinyl alcohol (degree of polymerization 2400, degree of saponification 99.95 mol%), 10 parts by mass of glycerin as a plasticizer, 0.1 parts by mass of polyoxyethylene lauryl ether sodium sulfate as a surfactant, and water. A film-forming stock solution having a rate of 66% by mass was cast on a metal drum at 80 ° C. and dried until the water content reached 5% by mass. Then, without heat-treating the film, it is subjected to a wet heat treatment for 50 minutes in a constant temperature and humidity chamber at 60 ° C. and a relative humidity of 90%, and then dried at room temperature until the moisture content reaches 8% by mass to obtain a PVA film. Obtained. Tables 2 and 3 show the production conditions and evaluation results of the obtained PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 10]
The same film-forming stock solution as in Comparative Example 9 was cast on a metal drum at 80 ° C. and dried until the water content reached 5% by mass. Then, without heat-treating the film, it is subjected to a wet heat treatment in a constant temperature and humidity chamber at 80 ° C. and a relative humidity of 90% for 6.5 minutes, and then dried at room temperature until the moisture content reaches 8% by mass and PVA. I got a film. Tables 2 and 3 show the production conditions and evaluation results of the obtained PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 11]
The same film-forming stock solution as in Comparative Example 9 was cast on a metal drum at 95 ° C. and dried until the water content reached 10% by mass to obtain a PVA film. Then, without heat-treating the film, it is subjected to a wet heat treatment for 5 minutes in a constant temperature and humidity chamber at 80 ° C. and a relative humidity of 90%, and then dried at room temperature until the moisture content reaches 8% by mass to obtain a PVA film. Obtained. Tables 2 and 3 show the production conditions and evaluation results of the obtained PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

[Comparative Example 12]
The same film-forming stock solution as in Comparative Example 9 was cast on a metal drum at 95 ° C. and dried until the water content reached 10% by mass to obtain a PVA film. Then, without heat-treating the film, it is subjected to a wet heat treatment for 3 minutes in a constant temperature and humidity chamber at 85 ° C. and a relative humidity of 90%, and then dried at room temperature until the moisture content reaches 8% by mass to obtain a PVA film. Obtained. Tables 2 and 3 show the production conditions and evaluation results of the obtained PVA film. Next, using the obtained PVA film as a raw material, a polarizing film was prepared in the same manner as in Example 1. The evaluation results of the obtained polarizing film are shown in Table 3.

1 Lower frame 2 Upper frame

Claims (4)

The degree of swelling (A) is 150 to 185%, the softening point (B) is 60 to 68 ° C., and it is calculated from the relaxation curve obtained by pulse NMR measurement in a 3 mass% heavy aqueous borate solution at 60 ° C. The crystal component amount (a1) is 2 to 10%, the ratio (a2 / a1) of the bound amorphous component amount (a2) to the crystal component amount (a1) is 2 to 6, and the thickness is 10 to 10. A polyvinyl alcohol film having a thickness of 50 μm. The polyvinyl alcohol film according to claim 1, wherein the degree of swelling (A) and the softening point (B) satisfy the following formula (1).
450 ≦ A + 5B ≦ 520 (1) An aqueous solution of polyvinyl alcohol having a degree of polymerization of 2600 to 6000 was cast on a roll or belt heated to 50 to 100 ° C. to form a polyvinyl alcohol film, and the obtained polyvinyl alcohol film had a water content of 1 to 1. The polyvinyl alcohol film according to claim 1 or 2, which is dried to 20% by mass and then subjected to a wet heat treatment for 3 to 300 minutes in an atmosphere having a temperature of 50 to 100 ° C. and a relative humidity of 60 to 100%. Production method. A method for producing a polarizing film, comprising a step of dyeing the polyvinyl alcohol film according to claim 1 or 2 with a dichroic dye and a step of stretching.

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