JP6816638B2 - Manufacturing method of polyvinyl alcohol film, polyvinyl alcohol film, and polarizing film - Google Patents

Description

The present invention relates to a method for producing a polyvinyl alcohol-based film, more specifically, a method for producing a polyvinyl alcohol-based film having a low haze and no defects by a continuous casting method, a polyvinyl alcohol-based film obtained by the production method, and the polyvinyl. The present invention relates to a polarizing film manufactured using an alcohol-based film as a raw material.

Conventionally, a polyvinyl alcohol-based film is prepared by dissolving a polyvinyl alcohol-based resin in a solvent such as water to prepare a stock solution for film formation, and then the stock solution is used as a cast type such as a cast drum (drum type roll) or a cast belt. It is manufactured by casting to form a film (continuous casting method), peeling from the cast mold, and then drying using a metal heating roll or the like. The polyvinyl alcohol-based film thus obtained is used for many purposes as a film having excellent transparency and dyeability, and one of the useful uses is a polarizing film. Such a polarizing film is used as a basic component of a liquid crystal display, and in recent years, its use has been expanded to devices requiring high quality and high reliability.

Under these circumstances, with the increase in definition and brightness of liquid crystal screens, there is a need for a polyvinyl alcohol-based film that is more transparent than conventional products and has few defects. When the haze of the polyvinyl alcohol-based film is large, the transparency is lowered and the light transmittance of the obtained polarizing film is lowered, which hinders the brightness and definition of the display. Further, when the polyvinyl alcohol-based film has many defects, the display defects of the polarizing film also increase, and it becomes difficult to manufacture a high-quality display. The haze in the present invention is an index of transparency, and is the total value of the external haze caused by light scattering on the film surface and the internal haze caused by light scattering inside the film. Further, the defects in the present invention are mainly spot-like defects due to foreign matter, surface-like defects due to dirt, and optical defects such as unevenness and streaks.

In order to produce a polyvinyl alcohol-based film with low haze and few defects, the cast surface must be smooth and clean. Generally, the cast surface is subjected to metal plating such as chrome plating in order to ensure surface smoothness. However, even if the cast type is initially smooth, organic substances adhere to the film when the production of the film is repeated, so that the surface roughness increases and the defects also increase. Such organic substances are mainly decomposition products of polyvinyl alcohol-based resins and decomposition products of additives.

As a method for improving the surface smoothness and thickness accuracy of a polyvinyl alcohol-based film, for example, a method of forming a film on a metal surface (cast type surface) having a surface roughness of 3S or less has been proposed (for example, Patent Document 1). (See.) Further, a method of forming a fluororesin film on the surface of the cast mold to improve the peelability has been proposed (see, for example, Patent Document 2). Further, a method of applying a polyoxyethylene alkylamine to a cast mold has been proposed (see, for example, Patent Document 3).

Japanese Unexamined Patent Publication No. 2001-315138 Japanese Unexamined Patent Publication No. 2006-305924 Japanese Unexamined Patent Publication No. 51-1905

However, in the technique disclosed in Patent Document 1, although a smooth and flat film can be obtained at the start of use of the cast mold, organic substances adhere to the surface of the cast mold after repeated production, and the surface roughness and external haze of the film increase. However, there was a tendency for defects to increase. In addition, the ductility of the undiluted solution for film formation to the cast mold is lowered, and the film is lifted from the surface of the cast mold, making it difficult to transport the film to the next process.

The technique disclosed in Patent Document 2 can reduce the adhesion of organic substances at the start of use of the cast mold, but when the cast mold is repeatedly heated / cooled, the fluorine-based resin film on the surface is peeled off and the film is peeled off from the cast mold. As the property deteriorated, the defects of the film tended to increase.

In the technique disclosed in Patent Document 3, the peelability of the film can be improved by applying polyoxyethylene alkylamine to the cast surface, but the polyvinyl alcohol-based film at that time was narrow in width and short in length, and is currently used. It was not possible to meet the demands for a width of 4 m or more and a length of 4 km or more, and further improvements were required in terms of optical performance such as haze and phase difference, and quality such as the number of defects.

In order to eliminate such problems, at the manufacturing site of polyvinyl alcohol-based films, the production is stopped and the surface of the cast mold is manually cleaned, or if the problems are not solved by cleaning, large-scale repairs are performed. The reality is that there is. These cleanings and repairs require a great deal of labor as the cast type becomes larger in size, which causes a great decrease in the productivity of the polyvinyl alcohol-based film.

Further, if the entire surface of the cast mold is not physically and / or chemically stable, not only the aqueous solution of the polyvinyl alcohol-based resin cannot be uniformly cast, but also it becomes difficult to stably peel off the film. Such a defect is particularly remarkable in the case of a thin film, and has caused breakage and wrinkles of the film. Further, non-uniform casting and peeling induced uneven film thickness and uneven retardation of the polyvinyl alcohol-based film.

Usually, an additive such as a surfactant is added to the aqueous solution of the polyvinyl alcohol-based resin in order to stabilize the ductility and the peelability. However, as described above, such a surfactant and its decomposition products cause an increase in haze and defects of the polyvinyl alcohol-based film, and it is necessary to reduce the blending amount as much as possible.

Therefore, the present invention provides a method for producing a polyvinyl alcohol-based film, which can obtain a polyvinyl alcohol-based film having a low haze and few defects without particularly performing cleaning or repair of a cast type under such a background. Is the purpose.

However, as a result of diligent research in view of such circumstances, the present inventors have obtained a hydrophilic treatment on the cast surface using a surfactant when producing a polyvinyl alcohol-based film by the continuous casting method. We have found that a polyvinyl alcohol-based film having low haze and few defects can be obtained, and completed the present invention.

That is, the gist of the present invention is a method for producing a polyvinyl alcohol-based film in which an aqueous solution of a polyvinyl alcohol-based resin is continuously cast in a cast mold to form a film, and the obtained film is peeled from the cast mold and then dried. The present invention relates to a method for producing a polyvinyl alcohol-based film, wherein the cast-type surface before casting is continuously hydrophilized with a surfactant and the contact angle with water is 5 to 50 °. Is.

The present invention also provides a polyvinyl alcohol-based film obtained by using the above-mentioned production method, and a polarizing film made by using the polyvinyl alcohol-based film.

By using the method for producing a polyvinyl alcohol-based film of the present invention, a polyvinyl alcohol-based film having low haze and few defects can be efficiently obtained, and further, a high-quality polarizing film can be obtained by using the polyvinyl alcohol-based film. is there.

FIG. 1 is an explanatory view showing a method of applying a surfactant solution in which a non-woven fabric for coating impregnated with the surfactant solution is brought into contact with the surface of a rotating cast drum. FIG. 2 is an explanatory view showing a method of applying a surfactant solution in which one non-woven fabric for application is slid in the width direction of a cast drum. FIG. 3 is an explanatory view showing a method of applying a surfactant solution using a roll-type cleaning device. FIG. 4 is an explanatory diagram showing a method of wiping off a surfactant solution that brings a dry non-woven fabric or sponge into contact with the surface of a rotating cast drum. FIG. 5 is an explanatory view showing a method of applying a high-concentration surfactant solution only to the end portion in the width direction of the cast drum.

The present invention is a method for producing a polyvinyl alcohol-based film in which an aqueous solution of a polyvinyl alcohol-based resin is continuously cast in a cast mold to form a film, and the obtained film is peeled from the cast mold and then dried. The cast-type surface before stretching is continuously hydrophilized with a surfactant, and the contact angle with water is 5 to 50 °.

As the polyvinyl alcohol-based resin of the present invention, an unmodified polyvinyl alcohol-based resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) of vinyl acetate and a copolymerizable component can also be used. .. Examples of the component copolymerizable with vinyl acetate include unsaturated carboxylic acids (including, for example, salts, esters, amides, and nitriles) and olefins having 2 to 30 carbon atoms (for example, ethylene, propylene, and n-butene). , Isobutene, etc.), vinyl ethers, unsaturated sulfonates, etc. Further, a modified polyvinyl alcohol-based resin obtained by chemically modifying the hydroxyl group after saponification can also be used.

Further, as the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can also be used. The polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain is, for example, (i) a method for saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (ii) acetate. A method for saponifying and decarbonizing a copolymer of vinyl and vinyl ethylene carbonate, (iii) saponifying and decarbonating a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane. It can be obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glycerin monoallyl ether, or the like.

The weight average molecular weight of the polyvinyl alcohol-based resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and even more preferably 120,000 to 260,000. If the weight average molecular weight is too small, it tends to be difficult to obtain sufficient optical performance when the polyvinyl alcohol-based resin is used as an optical film, and if it is too large, stretching becomes difficult when the polyvinyl alcohol-based resin film is used as a polarizing film. , Industrial production tends to be difficult. The weight average molecular weight of the polyvinyl alcohol-based resin is the weight average molecular weight measured by the GPC-MALS method.

The average degree of saponification of the polyvinyl alcohol-based resin is preferably 97 to 100 mol%, particularly preferably 98 to 100 mol%, and further preferably 99 to 100 mol%. If the degree of saponification is too low, it tends to be difficult to obtain sufficient optical performance when a polyvinyl alcohol-based resin is used as an optical film.
Here, the average degree of saponification in the present invention is measured according to JIS K 6726.

As the polyvinyl alcohol-based resin used in the present invention, two or more kinds having different modified species, modified amounts, weight average molecular weight, average saponification degree and the like may be used in combination.

In the present invention, it is preferable that the polyvinyl alcohol-based resin is washed with water and dehydrated using a centrifuge or the like to obtain a polyvinyl alcohol-based resin wet cake having a water content of 50% by weight or less. If the water content is too high, it tends to be difficult to obtain the desired aqueous solution concentration.
The polyvinyl alcohol-based resin wet cake is dissolved in warm water or hot water to prepare a polyvinyl alcohol-based resin aqueous solution.

The method for preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited, and for example, it may be prepared using a heated multi-screw extruder, or in a melting can provided with a vertical circulation flow generation type stirring blade. It is also possible to add the above-mentioned polyvinyl alcohol-based resin wet cake and blow steam into the can to dissolve and prepare an aqueous solution having a desired concentration.

The concentration of the polyvinyl alcohol-based resin aqueous solution thus obtained is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and even more preferably 20 to 50% by weight. If the concentration of the aqueous solution is too low, the drying load becomes large and the production capacity tends to decrease, and if it is too high, the viscosity tends to be too high and uniform dissolution tends to be impossible.

In addition to the polyvinyl alcohol-based resin, the polyvinyl alcohol-based resin aqueous solution includes commonly used plastics such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, and trimethylolpropane, if necessary. Agents and nonionic, anionic and / or cationic surfactants may be blended.

Examples of the nonionic surfactant include polyoxyethylene hexyl ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene dodecyl ether, and polyoxyethylene. Poly such as tetradecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene octadecyl ether, polyoxyethylene eicosyl ether, polyoxyethylene oleyl ether, coconut oil reduced alcohol ethylene oxide adduct, and beef fat reduced alcohol ethylene oxide adduct. Oxyethylene alkyl ether, caproic acid mono or diethanolamide, capricate mono or diethanolamide, capric acid mono or diethanolamide, laurate mono or diethanolamide, palmitate mono or diethanolamide, stearate mono or diethanolamide, oleic acid mono Alternatively, diethanolamide, coconut oil fatty acid mono or diethanolamide, or higher fatty acids alkanolamides such as propanolamide and butanolamide in place of these ethanolamides, caproic acid amides, capric acid amides, capric acid amides, lauric acid amides, palmitins. Higher fatty acid amides such as acid amides, stearic acid amides, and oleic acid amides, hydroxyethyl laurylamine, polyoxyethylene hexylamine, polyoxyethylene heptylamine, polyoxyethylene octylamine, polyoxyethylene nonylamine, and polyoxyethylene decylamine. , Polyoxyethylene dodecylamine, polyoxyethylene tetradecylamine, polyoxyethylene hexadecylamine, polyoxyethylene octadecylamine, polyoxyethylene oleylamine, polyoxyethylene oleylamine, polyoxyethylene alkylamine, polyoxyethylene capron, etc. Polyoxyethylene higher grades such as acid amide, polyoxyethylene capric acid amide, polyoxyethylene capric acid amide, polyoxyethylene laurate amide, polyoxyethylene palmitate amide, polyoxyethylene stearate amide, and polyoxyethylene oleic acid amide. Fatty acid amide, dimethyllaurylamine oxide, dimethylstearyloxide, dihydroxyethyllaurylamine Amine oxides such as oxides can be mentioned.

Examples of the anionic surfactant include sodium hexyl sulfate, sodium heptyl sulfate, sodium octyl sulfate, sodium nonyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate, sodium tetradecyl sulfate, and sodium hexadecyl sulfate, as sulfate ester salt types. Sodium octadecyl sulfate, sodium eicosyl sulfate, or alkyl sulfates such as potassium salts, calcium salts, ammonium salts, etc., sodium polyoxyethylene hexyl ether sulfate, sodium polyoxyethylene heptyl ether sulfate, sodium polyoxyethylene octyl ether sulfate, Polyoxyethylene nonyl ether sulfate sodium, polyoxyethylene decyl ether sulfate sodium, polyoxyethylene dodecyl ether sulfate sodium, polyoxyethylene tetradecyl ether sulfate sodium, polyoxyethylene hexadecyl ether sulfate sodium, polyoxyethylene octadecyl ether sulfate sodium, Polyoxyethylene eicosyl ether sodium sulfate, or polyoxyethylene alkyl ether sulfates such as potassium salts and ammonium salts thereof, polyoxyethylene hexylphenyl ether sulfate sodium sulfate, polyoxyethylene heptylphenyl ether sulfate sodium sulfate, polyoxyethylene octylphenyl Sodium ether sulfate, sodium polyoxyethylene nonylphenyl ether sulfate, sodium polyoxyethylene decylphenyl ether sulfate, sodium polyoxyethylene dodecylphenyl ether sulfate, sodium polyoxyethylene tetradecylphenyl ether sulfate, sodium polyoxyethylene hexadecylphenyl ether sulfate , Polyoxyethylene octadecylphenyl ether sulfate sodium, polyoxyethylene eicosylphenyl ether sulfate sodium, or polyoxyethylene alkylphenyl ether sulfates such as potassium salts and ammonium salts thereof, caproic acid ethanolamide sodium sulfate, capricate ethanolamide Sodium sulfate, sodium capricate ethanolamide sulfate, sodium laurate ethanolamide sulfate, sodium palmitate ethanolamide sulfate, sodium stearate ethanolamide sulfate, sodium oleate ethanolamide sulfate or these moss Rium salts, and higher fatty acid alkanolamide sulfates such as propanolamide and butanolamide, sulfated oils, higher alcohols ethoxysulfate, and monoglyculfate can be used instead of these ethanolamides. In addition to the above sulfate ester salt type, fatty acid soap, N-acylamino acid and salts thereof, polyoxyethylene alkyl ester carboxylate, carboxylate type such as acylated peptide, alkylbenzene sulfonate, alkylnaphthalene sulfonate, etc. , Naphthalene sulfonic acid salt formalin polycondensate, melamine sulfonic acid salt formalin condensate, dialkyl sulfosuccinic acid ester salt, alkyl sulfosuccinate disalt, polyoxyethylene alkyl sulfosuccinic disalt, alkyl sulfoacetate, α-olefin sulfone Sulfonate type such as acid salt, N-acylmethyl taurine salt, dimethyl-5-sulfoisophthalate sodium salt, polyoxyethylene alkyl ether phosphate, polyoxyethylene alkyl phenyl ether phosphate, alkyl phosphate, etc. The phosphate ester salt type of the above can also be mentioned.

Examples of the cationic surfactant include laurylamine hydrochloride, lauryltrimethylammonium chloride, and laurylpyridinium chloride.

The above-mentioned surfactant may be used alone or in combination of two or more.

The blending amount of the surfactant is preferably 10 to 100,000 ppm, particularly preferably 100 to 10,000 ppm, based on the polyvinyl alcohol-based resin. If the blending amount is too small, the peelability of the film from the cast mold tends to decrease, and if it is too large, the haze of the film tends to increase.

Examples of the cast type used in the present invention include a cast drum (drum type roll), a cast belt, and a resin film. In each case, the aqueous solution of the polyvinyl alcohol-based resin cast on the surface is dried while rotating to continuously form a film. Among these, a cast drum and a cast belt are preferable in terms of surface smoothness of the polyvinyl alcohol-based film, and a cast drum is particularly preferable in terms of productivity.

As the cast drum, it is preferable that the surface of stainless steel (SUS) containing iron as a main component is metal-plated to prevent scratches. Examples of the metal plating include chrome plating, nickel plating, zinc plating, and the like, and these are used as a single layer or two or more layers laminated. Among these, it is preferable that the outermost surface is chrome-plated from the viewpoint of easy smoothing of the cast type surface and durability.

The surface roughness Ra of the cast drum used in the present invention is preferably 30 nm or less, particularly preferably 1 to 25 nm, and further preferably 5 to 20 nm. If the surface roughness Ra of the cast drum is too large, the surface roughness of the polyvinyl alcohol-based film tends to increase.

A polyvinyl alcohol-based film is produced by casting a polyvinyl alcohol-based resin aqueous solution on such a cast mold and drying it. For example, when a cast drum is used as the cast mold, it is produced by the following steps.
(A) A step of continuously hydrophilizing the surface of a rotating cast drum with a surfactant.
(B) A step of discharging and casting an aqueous solution of a polyvinyl alcohol-based resin from a T-type slit die on the surface of a hydrophilic cast drum.
(C) A step of drying a polyvinyl alcohol-based resin aqueous solution on the surface of a cast drum to form a film.
(D) A step of peeling the film from the surface of the cast drum.
(E) A step of further drying the peeled film and heat-treating it if necessary.

The present invention is characterized in that the surface of the cast mold is continuously hydrophilized with a surfactant, but as a matter of course, the hydrophilic treatment is performed at a position where the surface of the cast mold is exposed. It is done. That is, when the cast drum is used, it is performed after the film is peeled off in the step (D) and before the aqueous solution of the polyvinyl alcohol-based resin is cast in the step (B). At such a position, it is preferable to make the entire width of the rotating cast drum hydrophilic from the viewpoint of work efficiency. Even when the cast mold is a cast belt or a resin film, hydrophilicity may be continuously performed over the entire width of the transferred mold at such a position.

Hereinafter, the hydrophilic treatment of the present invention will be specifically described. The hydrophilization treatment preferably involves drying an aqueous solution of a surfactant and / or an alcohol solution of a surfactant (hereinafter, collectively referred to as "surfactant solution") on the surface of a cast drum. It is done by. For example, it is done by applying a surfactant solution over the entire width of the cast drum and drying the solvent.

Examples of the surfactant include the above-mentioned surfactants. Among these, nonionic surfactants are preferable in terms of chemical stability, and amide-based nonionic surfactants are particularly preferable in terms of solubility. It is an activator.
As such an amide-based nonionic surfactant,
Caproic acid mono or diethanolamide, caprylic acid mono or diethanolamide, caproic acid mono or diethanolamide, lauric acid mono or diethanolamide, palmitic acid mono or diethanolamide, stearic acid mono or diethanolamide, oleic acid mono or diethanolamide, and Oleic acid fatty acid mono or diethanolamide, or higher fatty acid alkanolamides such as propanolamide and butanolamide in place of these ethanolamides;
Higher fatty acid amides such as caproic acid amide, caprylic acid amide, capric acid amide, lauric acid amide, palmitate amide, stearic acid amide, and oleic acid amide;
Polyoxyethylene caproic acid amide, polyoxyethylene caproic acid amide, polyoxyethylene caproic acid amide, polyoxyethylene laurate amide, polyoxyethylene palmitate amide, polyoxyethylene stearate amide, polyoxyethylene oleic acid amide, etc. Polyoxyethylene higher fatty acid amide;
And so on.

Among these, an amide-based nonionic surfactant having a molecular weight of 200 to 500 is preferable in terms of excellent hydrophilicity efficiency, and a higher fatty acid alkanolamide is particularly preferable, and a higher fatty acid alkanolamide is more preferable in terms of stability. Lauric acid mono or diethanolamide is excellent in treatment workability.

The above-mentioned surfactant may be used alone or in combination of two or more.

The blending amount of the surfactant is preferably 0.1 to 10% by weight, more preferably 0.2 to 5% by weight, and particularly preferably 0.3 to 3% by weight based on the total amount of the surfactant solution. There is% by weight. If the blending amount is too small, the hydrophilicity of the cast drum surface tends to be insufficient, and if it is too large, the haze of the film tends to increase.

When an alcohol solution of a surfactant is used in the present invention, the alcohol used is preferably an alcohol having 1 to 6 carbon atoms which may contain an ether bond, for example, methanol, methoxymethanol, dimethoxymethanol, ethoxymethanol. , Methoxyethoxymethanol, n-propoxymethanol, iso-propoxymethanol, ethoxyethoxyethanol, methoxypropoxymethanol, n-butoxymethanol, iso-butoxymethanol, t-butoxymethanol, ethoxy-n-propoxymethanol, ethoxy-iso-propoxy Methanol, pentoxyethanol, ethanol, 2-methoxyethanol, 1,1-dimethoxyethanol, 2,2-dimethoxyethanol, 1,2-dimethoxyethanol, 1-ethoxyethanol, 2-ethoxyethanol, 1-methoxy-2-ethoxy Ethanol, 1-ethoxy-2-methoxyethanol, 1,1-diethoxyethanol, 1,2-diethoxyethanol, 2,2-diethoxyethanol, 1-n-propoxyethanol, 1-iso-propoxyethanol, 2- n-propoxyethanol, 2-iso-propoxyethanol, 1-methoxy-2-n-propoxyethanol, 1-methoxy-2-iso-propoxyethanol, 2-methoxy-1-n-propoxyethanol, 2-methoxy-1 -Iso-propoxyethanol, 1-n-butoxyethanol, 1-iso-butoxyethanol, 1-t-butoxyethanol, 2-n-butoxyethanol, 2-iso-butoxyethanol, 2-t-butoxyethanol, 1- Propanol, 2-methoxypropanol, 3-methoxypropanol, 1,1-dimethoxypropanol, 1,2-dimethoxypropanol, 2,2-dimethoxypropanol, 1,3-dimethoxypropanol, 2,3-dimethoxypropanol, 3,3 -Dimethoxypropanol, 1-ethoxypropanol, 2-ethoxypropanol, 3-ethoxypropanol, 1-ethoxy-1-methoxypropanol, 2-ethoxy-2-methoxypropanol, 3-ethoxy-3-methoxypropanol, 1-ethoxy-2 -Methanol, 2-ethoxy-1-methoxypropanol, 1-ethoxy-3-methoxypropanol, 3-ethoxy-1-methoxypropanol , 2-propanol, 1-methoxy-2-propanol, 1,1-dimethoxy-2-propanol, 1,2-dimethoxy-2-propanol, 1-ethoxy-2-propanol, 2-ethoxy-2-propanol, 1-methoxy 1-ethoxy-2-propanol, 1-methoxy-2-ethoxy-2-propanol, 1-n-propoxy2-propanol, 1-iso-propoxy2-propanol, 2-n-propoxy2-propanol, 2-iso- Propoxy 2-propanol, 1-butanol, 1-methyl-1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 4-methyl-1-butanol, 1-methoxy-1-butanol, 1 -Methyl-1-methoxy-1-butanol, 2-methyl-1-methoxy-1-butanol, 3-methyl-1-methoxy-1-butanol, 3-methyl-1-methoxy-1-butanol, 4-methyl -1-methoxy-1-butanol, 2-methoxy-1-butanol, 1-methyl-2-methoxy-1-butanol, 2-methyl-2-methoxy-1-butanol, 3-methyl-2-methoxy-1 -Butanol, 4-methyl-2-methoxy-1-butanol, 3-methoxy-1-butanol, 1-methyl-3-methoxy-1-butanol, 3-methyl-3-methoxy-1-butanol, 4-methyl -3-methoxy-1-butanol, 4-methoxy-1-butanol, 1-methyl-4-methoxy-1-butanol, 2-methyl-4-methoxy-1-butanol, 3-methyl-4-methoxy-1 -Butanol, 4-methyl-4-methoxy-1-butanol, 1-ethoxy-1-butanol, 2-ethoxy-1-butanol, 3-ethoxy-1-butanol, 4-ethoxy-1-butanol, 1,1 -Dimethoxy-1-butanol, 1,2-dimethoxy-1-butanol, 1,3-dimethoxy-1-butanol, 1,4-dimethoxy-1-butanol, 2-butanol, 1-methoxy-2-butanol, 2 −methoxy-2-butanol, 3-methoxy-2-butanol, 4-methoxy-2-butanol, 1-ethoxy-2-butanol, 2-ethoxy-2-butanol, 3-ethoxy-2-butanol, 4-ethoxy -2-butanol, iso-butanol, 1-methoxy-iso-butanol, 2-methoxy-iso-butanol, 3-methoxy-iso-butano , 1,1-dimethoxy-t-butanol, 3,3-dimethoxy-iso-butanol, 3,3'-dimethoxy-iso-butanol, 1,2-dimethoxy-iso-butanol, 1,3-dimethoxy- iso-butanol, 2,3-dimethoxy-iso-butanol, 1-ethoxy-iso-butanol, 2-ethoxy-iso-butanol, 3-ethoxy-iso-butanol, t-butanol, 2-methoxy-t-butanol, 2,2-Dimethoxy-t-butanol, 2,2'-dimethoxy-t-butanol, 2-ethoxy-t-butanol, 1-pentanol, 1-methyl-1-pentanol, 2-methyl-1-pen Tanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, 1-methoxy-1-pentanol, 2-methoxy-1-pentanol, 3-methoxy-1-pentanol, 4-methoxy -1-Pentanol, 5-methoxy-1-pentanol, 2-pentanol, 1-methoxy-2-pentanol, 2-methoxy-2-pentanol, 3-methoxy-2-pentanol, 4-methoxy -2-Pentanol, 3-pentanol, 1-methoxy-3-pentanol, 2-methoxy-3-pentanol, 3-methoxy-3-pentanol, 1-hexanol, 2-hexanol, 3-hexanol, Cyclopropanol, cyclobutanol, cyclopropyl methanol, cyclopentanol, 1-cyclopropyl-1-ethanol, 2-cyclopropyl-1-ethanol, cyclobutyl methanol, cyclohexanol, 1-cyclopropyl propanol, 2-cyclopropyl propanol , 3-Cyclopropylpropanol, 1-cyclobutyl ethanol, 2-cyclobutyl ethanol, cyclopentyl methanol, di (cyclopropyl) methanol and the like. Among these, those having a boiling point of 50 to 200 ° C. are preferable, particularly preferably those having a boiling point of 60 to 190 ° C., and more preferably those having a boiling point of 70 to 180 ° C. in terms of dryness.

The alcohol used in the present invention may contain water or an ether compound (excluding the above alcohol) as an auxiliary component in order to control safety and coatability. The blending ratio of the auxiliary component is preferably less than 50% by weight of the total alcohol.

Examples of the ether compound include ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol dipropyl ether, propylene glycol dibutyl ether, and diethylene glycol dimethyl ether. Diethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol dipropyl ether, triethylene glycol dibutyl ether, trimethylene glycol dimethyl ether, trimethylene glycol diethyl ether, trimethylene Examples thereof include glycol dipropyl ether and trimethylene glycol dibutyl ether. Among these, those having a boiling point of 50 to 200 ° C. are preferable, and those having a boiling point of 100 to 190 ° C. are particularly preferable, in terms of dryness.

The method of applying the surfactant solution is not particularly limited, and a method of contacting a non-woven fabric, a sponge, and / or a brush impregnated with the surfactant solution with the surface of a rotating cast drum, a method of contacting the surface of the cast drum with the surfactant solution, and the surface of the cast drum. In the present invention, a non-woven fabric, a sponge, and / or a brush impregnated with a surfactant solution is brought into contact with the surface of a rotating cast drum in that it can be uniformly applied. Is preferable, and particularly preferably, it is a method of bringing a non-woven fabric impregnated with a surfactant solution into contact with the surface of a rotating cast drum (see FIG. 1).

The non-woven fabric used in the present invention is not particularly limited, and examples thereof include nylon-based non-woven fabrics, polyester-based non-woven fabrics, and polyolefin-based non-woven fabrics. Among these, nylon-based non-woven fabric and polyester-based non-woven fabric are preferable, and polyester-based non-woven fabric is particularly preferable, and polyester-based non-woven fabric made of polyethylene terephthalate fiber is more preferable, and polyester-based non-woven fabric is particularly preferable, because the coating efficiency of the surfactant is excellent. It is a polyester-based non-woven fabric composed of terephthalate fibers and nylon fibers.

The sponge used in the present invention is not particularly limited, and examples of the sponge include polyvinyl alcohol sponge, urethane sponge, polyethylene sponge, silicon sponge, melamine sponge, and rubber sponge. Of these, polyvinyl alcohol sponge is preferable because it does not damage the surface of the cast drum. Further, in terms of impregnation property of the surfactant solution, a sponge having a density of 1 to 100 kg / m ³ is preferable.

After use, the non-woven fabric, sponge, and / or brush can be washed with a solvent such as water or alcohol, dried if necessary, and reused.

The method of impregnating the non-woven fabric, sponge, and / or brush with the surfactant solution is not particularly limited, and is continuous or intermittent from the spray nozzle or slit die to the extent that the non-woven fabric, sponge, and / or brush does not dry. It should be supplied to. If desired, the surfactant solution may be applied once to a medium such as a coating roll and then transferred to a non-woven fabric, sponge, and / or brush.

To bring the non-woven fabric, sponge, and / or brush into contact with the surface of the rotating cast drum, the non-woven fabric, sponge, and / or brush may be pressed with a pressing jig such as a blade, pad, or roll. The degree of pressing is not particularly limited, but is preferably 0.01 N or more, particularly preferably 0.1 to 100 N, and further preferably 1 to 10 N in that it also cleans the cast drum surface at the same time as coating. When pressed excessively, the load on the cast drum becomes large, which tends to hinder the smooth rotation of the cast drum.

To apply the surfactant solution to the entire width of the cast drum, for example, when using a non-woven fabric, apply with a non-woven fabric that matches the width of the cast drum, or divide the width of the cast drum into several parts and apply with multiple non-woven fabrics. Examples thereof include a method in which one or more non-woven fabrics are slid in the width direction of the cast drum and applied. Among these, a method in which one piece of non-woven fabric is applied while sliding in the width direction of the cast drum is preferable from the viewpoint of application efficiency and simplicity of the apparatus (see FIG. 2). An excessively long non-woven fabric tends to cause meandering and loosening of the cloth, and tends to cause uneven coating. This method is the same when using a sponge or a brush.

A preferred embodiment of the present invention includes a method using a roll-type coating device (see FIG. 3). Specifically, a dry and clean non-woven fabric is unwound from a roll (unwinding roll) on which the non-woven fabric is wound, and while the non-woven fabric is in contact with a cast drum, it is wiped off and a surfactant solution is applied, and then the non-woven fabric is applied. Is a method of winding a roll (winding roll). The direction of transfer of the non-woven fabric on the cast drum is preferably opposite in the direction of rotation of the cast drum in terms of coating efficiency. For coating, for example, the surfactant solution is spray-coated from a spray nozzle onto a coating roll installed at an intermediate point where the non-woven fabric comes into contact, and the coating roll and the non-woven fabric are brought into contact with each other to transfer the surfactant solution to the non-woven fabric. , The non-woven fabric is made by contacting the surface of the cast drum. By such a method, it is possible to always apply and wipe with a clean non-woven fabric, and a polyvinyl alcohol-based film having less defects can be obtained.

The coating temperature of the surfactant solution may be the same as the surface temperature of the cast drum during the production of the polyvinyl alcohol-based film, and is preferably 50 to 100 ° C., particularly preferably 55 to 98 ° C. More preferably, it is 60 to 97 ° C. If the coating temperature is too low, the drying property tends to decrease, and conversely, if the coating temperature is too high, uniform coating tends to be difficult. In order to keep the coating temperature constant, the surfactant solution used for coating or the non-woven fabric may be heated to such a temperature range. In general, the surface temperature of the cast drum in the step (B) is 50 to 100 ° C. for drying the aqueous solution of the polyvinyl alcohol-based resin.

The coating speed of the surfactant solution may be the same as the rotation speed of the cast drum during the production of the polyvinyl alcohol-based film, and is preferably 1 to 50 m / min, particularly preferably 10 to 40 m / min. Minutes, more preferably 15-30 m / min. If the coating speed is too slow, the productivity tends to decrease, and conversely, if the coating speed is too fast, the coating efficiency tends to decrease. In general, the rotation speed of the cast drum in the step (B) is 5 to 50 m / min in consideration of productivity and drying speed.

A plurality of the above-mentioned coating methods can be combined, and the surfactant solution can be applied in a plurality of times, or different surfactant solutions can be applied in the first and second times.

In addition, a cleaning device may be attached in order to remove foreign substances and impurities before applying the surfactant solution. Examples of such a cleaning device include a device having a blade for scraping foreign matter and an ultraviolet cleaning device.

The applied surfactant solution is dried by the casting of the polyvinyl alcohol-based resin aqueous solution in the above-mentioned step (B). Drying is controlled by the selection of solvent, the temperature of the cast drum, etc., but if necessary, the excess surfactant solution after application can be wiped off, or warm air can be blown onto the surface of the cast drum to accelerate drying. May be good.

Examples of the method of wiping off the surfactant solution include a method of bringing a dry non-woven fabric or sponge into contact with the surface of a rotating cast drum (see FIG. 4). Such wiping is required when the surfactant solution is excessively applied to the cast drum surface. The excess surfactant solution does not dry by the casting of the polyvinyl alcohol-based resin aqueous solution in the above-mentioned step (B), which not only makes the ductility and peelability non-uniform, but also increases the haze of the polyvinyl alcohol-based film. Further, it causes uneven film thickness and uneven phase difference. As a matter of course, wiping off all the surfactant molecules present on the surface of the cast drum needs to be avoided because the hydrophilization treatment of the present invention is wasted.

As one embodiment of the present invention, only the widthwise end of the cast drum may be hydrophilized, or a high-concentration surfactant solution may be applied only to such an end (see FIG. 5). ). Since the thin film tends to break from such an end portion, it is possible to avoid the breakage by improving the peelability of the end portion by the hydrophilic treatment.

Thus, the hydrophilization treatment of the above-mentioned step (A) is completed. Up to this point, the method of hydrophilic treatment has been described by taking a cast drum as an example of the cast type, but when a cast belt or a resin film is used as the cast type, the hydrophilic treatment can be performed by the same method.

In the present invention, the contact angle of the hydrophilized cast surface with water needs to be 5 to 50 °, preferably 8 to 30 °, and particularly preferably 10 to 20 °.
If the contact angle is less than 5 °, the peelability of the film from the cast mold is lowered and the object of the present invention cannot be achieved. On the contrary, if it exceeds 50 °, the polyvinyl alcohol system to the cast mold is used. The ductility of the aqueous resin solution is reduced, and the object of the present invention cannot be achieved.
As described above, the polyvinyl alcohol-based resin aqueous solution usually contains a surfactant in order to stabilize the ductility and peelability, and the surfactant increases the haze and defects of the film. .. However, by performing the hydrophilic treatment of the present invention, the amount of the surfactant compounded in the polyvinyl alcohol-based resin aqueous solution can be reduced, and the above-mentioned problems can be solved.

Further, the contact angle contact is preferably 10 ° or less, particularly preferably 7 ° or less, and further preferably 5 ° or less. If the contact angle is too large, the ductility of the polyvinyl alcohol-based resin aqueous solution to the cast mold and the peelability of the film from the cast mold tend to be unstable. The contact angle contact includes in-plane contact on the entire surface of the cast mold that has been hydrophilized, and also includes fluctuations over time. The time-dependent fluctuation means, for example, the difference in contact angle between immediately after the treatment and several seconds after the treatment.

The hydrophilic cast-type surface preferably has an adhesive strength of 0.1 to 3.5 N / 10 mm, particularly preferably 0, when the following adhesive tape peeling test is performed according to JIS Z0237. .5-3.2N / 10mm, more preferably 1-3N / 10mm. If the adhesive strength is too low, the transferability of the cast mold surface tends to decrease, and conversely, if it is too high, the peelability of the film from the cast mold tends to decrease.
(Adhesive tape peeling test)
Test conditions: Peeling angle 90 °, Peeling speed 300 mm / min, Test environment: 23 ° C 50% RH
Adhesive tape: Nichiban CT-24 (adhesive tape for cross-cut test / grid test, width 24 mm)

Since the above JIS standard is a test method for adhesive tape, a washed SUS304 steel plate is used as a test plate (attachment base material) for testing. However, in the present invention, the adhesive tape is cast at a constant level. The mold (paste base material) is tested. As a matter of course, cleaning the cast-type surface after the hydrophilic treatment does not result in a test, so cleaning is not performed in the present invention.

Further, the contact of the adhesive force is preferably 1 N / 10 mm or less, particularly preferably 0.7 N / 10 mm or less, and further preferably 0.5 N / 10 mm or less. If the pressure of the adhesive force is too large, the ductility of the polyvinyl alcohol-based resin aqueous solution to the cast mold and the peelability of the film from the cast mold tend to be unstable.

The surface of the cast mold for which the hydrophilization treatment has been completed proceeds to the step (B) and is used for producing a polyvinyl alcohol-based film.

Hereinafter, steps (B) to (E) will be described by taking the case where a cast drum is used as the cast type as an example.
The step (B) is a step of discharging and casting a polyvinyl alcohol-based resin aqueous solution from the T-type slit die on the surface of the hydrophilic cast drum.

First, the polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include static defoaming and defoaming with a multi-screw extruder having a vent. As the multi-screw extruder having a vent, a twin-screw extruder having a vent is usually used.

After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution is introduced into the T-shaped slit die in a fixed amount, cast on a cast mold that has been hydrophilized, and formed by a casting method.

The temperature of the aqueous solution at the outlet of the T-shaped slit die is preferably 80 to 100 ° C, particularly preferably 85 to 99 ° C. If the temperature of the aqueous solution is too low, it tends to cause poor flow, and if it is too high, it tends to foam.

The viscosity of the aqueous solution of the polyvinyl alcohol-based resin is preferably 50 to 200 Pa · s at the time of discharge, and particularly preferably 70 to 150 Pa · s. If the viscosity of the aqueous solution is too low, the flow tends to be poor, and if it is too high, casting becomes difficult.

The discharge rate of the aqueous solution discharged from the T-shaped slit die to the cast drum is preferably 0.1 to 5 m / min, particularly preferably 0.2 to 4 m / min, and even more preferably 0.3 to 3 m / min. Minutes. If the discharge rate is too slow, the productivity tends to decrease, and if it is too fast, the flow tends to be difficult.

The diameter of the cast drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, and even more preferably 2.8 to 4 m. If the diameter is too small, the drying length tends to be insufficient and the speed tends to be low, and if it is too large, the transportability tends to decrease.

The width of the cast drum is preferably 4 m or more, particularly preferably 4.5 m or more, and further preferably 5 m or more. If the width of the cast drum is too small, productivity tends to decrease.

Next, the step (C) will be described.
The step (C) is a step of drying an aqueous solution of a polyvinyl alcohol-based resin on the surface of the cast drum to form a film.

The surface temperature of the cast drum is preferably 50 to 100 ° C, particularly preferably 60 to 97 ° C. If the surface temperature is too low, drying tends to be poor, and if it is too high, the aqueous solution tends to foam.

The rotation speed of the cast drum is preferably 1 to 50 m / min, particularly preferably 2 to 40 m / min, and even more preferably 3 to 35 m / min. If the rotation speed is too slow, the productivity tends to decrease, and if it is too fast, the drying tends to be insufficient.

Next, the step (D) will be described.
The step (D) is a step of peeling the film from the surface of the cast drum.

The dried film is stripped from the surface of the cast drum and transferred to a thermal roll and finally to a take-up roll. In the present invention, the stress at the time of peeling the film from the cast drum (peeling stress) is important. The peeling stress is preferably 0.01 N / 10 mm or less, and particularly preferably 0.001 to 0.005 N / 10 mm. If the peel stress is too large, the film tends to break easily, and conversely, if the peel stress is too low, the peeling does not stabilize and the film tends to have phase difference unevenness.

As a method for controlling the peeling stress, when the composition of the polyvinyl alcohol-based resin aqueous solution is the same, in addition to the hydrophilicity of the cast drum surface of the present invention, control of the water content of the film at the time of peeling can be mentioned. In the present invention, the water content is preferably 5 to 25% by weight, particularly preferably 7 to 23% by weight, still more preferably 9 to 22% by weight, and particularly preferably 10 to 20% by weight.

Next, the step (E) will be described.
The step (E) is a step of further drying the peeled film and heat-treating it if necessary.

The peeled film is further dried by alternately passing the front surface and the back surface of the film through a plurality of heat rolls. The surface temperature of the heat roll is not particularly limited, but is usually 40 to 150 ° C. If the surface temperature is too low, the final polyvinyl alcohol-based film will be poorly dried, and if it is too high, it will be too dry and will tend to cause poor appearance such as swelling.

After drying with a hot roll, the film may be heat treated. When the heat treatment is performed, the temperature is preferably 70 to 150 ° C, particularly preferably 80 to 140 ° C. If the heat treatment temperature is too low, the water resistance of the polyvinyl alcohol-based film tends to be insufficient, and if it is too high, the stretchability during the production of the polarizing film tends to decrease. Examples of such a heat treatment method include a method of blowing hot air on both sides of the film using a floating dryer and a method of irradiating both sides of the film with near infrared rays using an infrared lamp.

The raw fabric of the polyvinyl alcohol-based film that has been dried and heat-treated as necessary is wound into a roll to form a product. The width of the product may be adjusted by slitting both ends of the film before winding.

The width of the polyvinyl alcohol-based film of the present invention is preferably 4 m or more in terms of widening the polarizing film, particularly preferably 4.5 m or more, and further preferably 4.5 to 6 m in terms of avoiding fracture. is there.

The length of the polyvinyl alcohol-based film of the present invention is preferably 4 km or more from the viewpoint of increasing the area of the polarizing film, particularly preferably 5 km or more, and further preferably 5 to 50 km from the viewpoint of transport weight.

The thickness of the polyvinyl alcohol-based film of the present invention is preferably 50 μm or less, particularly preferably 30 μm or less, and more preferably 5 to 30 μm from the viewpoint of avoiding fracture, from the viewpoint of thinning the polarizing film.

The haze of the polyvinyl alcohol-based film of the present invention is preferably 0.5% or less, particularly preferably 0.3% or less, still more preferably 0.2% or less, and particularly preferably 0.2% or less in terms of the light transmittance of the polarizing film. Is 0.1% or less.

The surface roughness Rz of the polyvinyl alcohol-based film of the present invention is preferably 0.3 μm or less, particularly preferably 0.2 μm or less, and further preferably 0.1 μm or less.
If the surface roughness Rz is too large, the degree of polarization of the polarizing film tends to decrease.

The polyvinyl alcohol-based film of the present invention has a height of 1 μm or more, preferably 3 or less in 1 mm ² (including punctate and linear), particularly preferably 2 or less, still more preferably 1. Less than or equal to. If the number of such defects is too large, the optical defects of the polarizing film tend to increase.

Such a polyvinyl alcohol-based film has low haze and few defects, and is therefore preferably used as a raw material for a polarizing film.
Hereinafter, a method for producing a polarizing film obtained by using the polyvinyl alcohol-based film of the present invention will be described.

The polarizing film of the present invention is produced by unwinding the polyvinyl alcohol-based film from a roll, transferring it in the horizontal direction, and performing steps such as swelling, dyeing, boric acid cross-linking, stretching, washing, and drying.

The swelling step is performed before the dyeing step. In addition to being able to clean the dirt on the surface of the polyvinyl alcohol-based film by the swelling step, there is also an effect of preventing uneven dyeing by swelling the polyvinyl alcohol-based film. In the swelling step, water is usually used as the treatment liquid. If the main component of the treatment liquid is water, it may contain a small amount of an iodide compound, an additive such as a surfactant, alcohol and the like. The temperature of the swelling bath is usually about 10 to 45 ° C., and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

The dyeing step is performed by contacting the film with a liquid containing iodine or a dichroic dye. Usually, an aqueous solution of iodine-potassium iodide is used, and an iodine concentration of 0.1 to 2 g / L and a potassium iodide concentration of 1 to 100 g / L are suitable. It is practical that the dyeing time is about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 ° C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the water solvent.

The boric acid cross-linking step is carried out using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixed solution at a concentration of about 10 to 100 g / L, and it is preferable that potassium iodide coexists in the solution from the viewpoint of stabilizing the polarization performance. The temperature at the time of treatment is preferably about 30 to 70 ° C., the treatment time is preferably about 0.1 to 20 minutes, and if necessary, a stretching operation may be performed during the treatment.

In the stretching step, it is preferable to stretch 3 to 10 times, preferably 3.5 to 6 times in the uniaxial direction. At this time, a slight stretching (stretching to the extent of preventing shrinkage in the width direction or more) may be performed in the direction perpendicular to the stretching direction. The temperature at the time of stretching is preferably 30 to 170 ° C. Further, the stretching ratio may be finally set in the above range, and the stretching operation may be performed not only in one step but also in any range of the manufacturing process.

The washing step is performed by immersing the polyvinyl alcohol-based film in, for example, an aqueous solution of iodide such as water or potassium iodide, and precipitates generated on the surface of the film can be removed. When an aqueous potassium iodide solution is used, the potassium iodide concentration may be about 1 to 80 g / L. The temperature during the cleaning treatment is usually 5 to 50 ° C, preferably 10 to 45 ° C. The treatment time is usually 1 to 300 seconds, preferably 10 to 240 seconds. The washing with water and the washing with an aqueous potassium iodide solution may be performed in an appropriate combination.

The drying step may be carried out in the air at 40 to 80 ° C. for 1 to 10 minutes.

The degree of polarization of the polarizing film thus obtained is preferably 99.5% or more, particularly preferably 99.8% or more. If the degree of polarization is too low, the contrast in the liquid crystal display tends to decrease. The degree of polarization is generally the light transmittance (H ₁₁ ) measured at wavelength λ and the two polarized light in a state where two polarizing films are superposed so that their orientation directions are the same. It is calculated according to the following formula from the light transmittance (H ₁ ) measured at the wavelength λ in a state where the films are superposed so that the orientation directions are orthogonal to each other.
[(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

Further, the simple substance transmittance of the polarizing film of the present invention is preferably 43% or more. If the single transmittance is too low, it tends to be impossible to achieve high brightness of the liquid crystal display.
The single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

The polarizing film thus obtained can also be used as a polarizing plate by laminating and adhering an optically isotropic polymer film or sheet as a protective film on one or both sides thereof. Examples of the protective film include films such as cellulose triacetate, cellulose diacetate, polycarbonate, polymethylmethacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether sulfone, polyarylene ester, poly-4-methylpentene, and polyphenylene oxide. Or you can give a sheet.
Further, for the purpose of thinning the polarizing film, instead of the protective film, a curable resin such as urethane resin, acrylic resin, urea resin is applied to one or both sides of the protective film, and the polarizing film is cured to form a polarizing plate. You can also do it.

The polarizing film or polarizing plate made of the polyvinyl alcohol-based film of the present invention has excellent polarization performance, and is a portable information terminal, a personal computer, a television, a projector, a signage, an electronic desk computer, an electronic clock, a word processor, an electronic paper, a game machine. , Video, camera, photo album, thermometer, audio, liquid crystal display device such as automobile and mechanical instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable display, display element (CRT, LCD, organic EL, electronic paper) Etc.), preferably used for anti-reflection layers, optical communication equipment, medical equipment, building materials, toys, etc.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.
In the example, "part" and "%" mean a weight standard.
Measure each physical property as follows.

<Measurement conditions>
(1) Contact angle (°)
Using a "portable contact angle meter PCA-1" manufactured by Kyowa Interface Science Co., Ltd., 2 μl of water droplets created from an injection needle are dropped onto the cast drum surface, and the liquid shape after 1 second is measured, and the θ / 2 method is used. Calculated in. The measurement atmosphere is 23 ° C. and 50% RH. Such measurements were performed at 10 points on the cast surface, and the average value was defined as the contact angle (°), and the difference between the maximum value and the minimum value was defined as the contact angle deflection (°).

(2) Adhesive strength (N / 10 mm)
According to JIS Z0237, the adhesive tape peeling test was performed at 10 points on the cast surface, and the average value was taken as the adhesive strength (N / 10 mm). The test conditions are as follows.
Test conditions: Peeling angle 90 °, peeling speed 300 mm / min Test environment: 23 ° C 50% RH
Adhesive tape: Nichiban CT-24 (adhesive tape for cross-cut test / grid test, width 24 mm)

(3) Peelability During film formation, the peeling state of the film from the cast drum was visually observed, and the peelability was evaluated according to the following criteria.
(Evaluation criteria)
○ ・ ・ ・ Peeled cleanly over the entire length △ ・ ・ ・ Although it was peeled off, a part of the film adhered × ・ ・ ・ Breakage occurred without peeling

(4) Haze (%)
Ten test pieces of 50 mm × 50 mm were cut out from the end portion (position 100 m from the end) of the obtained polyvinyl alcohol-based film, measured using a haze meter NDH-2000 manufactured by Nippon Denshoku Co., Ltd., and the average value of the ten sheets was calculated. The haze (%) was used.

(5) Surface roughness Rz (μm)
Ten test pieces of 50 mm × 50 mm were cut out from the end portion (position 100 m from the end) of the obtained polyvinyl alcohol-based film, and a laser focus microscope VK-9700 (measurement length: 1 mm, objective lens: 20) manufactured by KEYENCE CORPORATION was cut out. The surface in contact with the cast mold was measured using (times), and the average value of 10 sheets was taken as the surface roughness Rz (μm).

(6) Disadvantages (pieces / mm ² )
A 50 mm × 50 mm test piece was cut out one by one from the tip (100 m from the tip), the center, and the end (100 m from the end) of the obtained polyvinyl alcohol-based film, and laser focus manufactured by KEYENCE CORPORATION. Using a microscope VK-9700 (objective lens: 10x), the number of defects (dots) with a height or depth of 1 μm or more existing in 1 mm × 1 mm (area 1 mm ² ) of the surface in contact with the cast mold. The maximum value among the three sheets was defined as the number of defects (pieces / mm ² ).

(7) Phase difference unevenness A test piece having a length of 30 cm and a width of 30 cm was cut out from the end portion (position 100 m from the end) of the obtained polyvinyl alcohol-based film, and two polarizing plates in a cross Nicol state (single transmittance 43). The in-plane phase difference was observed in transmission mode using a light box with a surface illuminance of 14,000 lux in a dark room with an angle of 45 ° between (5.5%, degree of polarization 99.9%), and the following criteria were used. Evaluated in.
(Evaluation criteria)
○ ・ ・ ・ The shade could not be confirmed.
× ・ ・ ・ The shade was confirmed.

(8) Polarization degree (%), single transmittance (%)
From the obtained polarizing film, a strip sample of 50 mm in the stretching direction × 1 m in the width direction was cut out in 100 m increments, and using Otsuka Electronics Co., Ltd .: RETS-1100A, the degree of polarization and the single transmittance over the entire width at a pitch of 10 mm in the width direction. Was measured, and the degree of polarization (%) and the single transmittance (%) of the obtained polarizing film were used.

(9) Display defects (pieces / m ² )
A test piece having a length of 1 m and a width of 1 m was cut out from the end portion (position 100 m from the end) of the obtained polarizing film, and visually inspected in an environment of 15,000 lp, and the number of display defects (pieces / m ² ) of 100 μm or more. ) Was measured.

<Example 1>
(Hydrophilic treatment of cast drum)
First, on a cast drum (diameter 3 m, width 5.5 m, surface chrome plating, surface roughness Ra 11 nm, initial contact angle 92 °), width 5.5 m, length (contact length) 10 cm, thickness 0.5 mm. A polyester-based non-woven fabric (65% polyethylene terephthalate fiber / 35% nylon fiber) was installed (see FIG. 1). The installation position is 1 m upstream from the discharge position of the polyvinyl alcohol-based resin aqueous solution, and 0.5 m downstream from the film peeling position.
Next, the polyester-based non-woven fabric was brought into contact with the entire width of the cast drum using a pressing blade (width 5.5 m, manufactured by Teflon (registered trademark)) to prepare an aqueous solution of a surfactant, laurate diethanolamide (molecular weight 287). An aqueous solution (surfactant concentration 1% by weight) in which 1 kg is dissolved in 99 kg of water is supplied and impregnated into the entire polyester-based non-woven fabric from a plurality of spray nozzles installed at 0.1 kg / min, and cast rotating at 20 m / min. It was applied to the surface of the drum (surface temperature 80 ° C.).
When the surface of the cast drum was visually observed, the applied aqueous solution dried quickly, and no defects such as turbidity were observed on the surface. The contact angle on the surface of the cast drum was measured and found to be 10 °, confirming that it had been hydrophilized.

(Manufacturing of polyvinyl alcohol film)
Add 1,000 kg of polyvinyl alcohol resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 2,000 kg of water, 100 kg of glycerin as a plasticizer, and 0.6 kg of sodium dodecyl sulfate as a surfactant, and stir. While raising the temperature to 150 ° C., the concentration was adjusted to a resin concentration of 25% to obtain a uniformly dissolved polyvinyl alcohol-based resin aqueous solution.
Next, the polyvinyl alcohol-based resin aqueous solution is supplied to a twin-screw extruder having a vent to defoam, and then the aqueous solution temperature is set to 95 ° C., and after the hydrophilization treatment of rotating at 20 m / min from a T-type slit die. A film was formed by continuously ejecting and casting on the surface of the cast drum. When the ductility was visually confirmed, it was good.
Subsequently, the film (moisture content 18%) obtained by drying on the cast drum was peeled off from the cast drum. When the peelability was visually confirmed, it was good and no breakage occurred. After the film is peeled off, the surface of the cast drum is again hydrophilized, and while rotating, it moves to the lower part of the T-shaped slit die and is used for film formation.
Finally, the peeled film was further dried using a hot roll, and then wound up to obtain a roll of a polyvinyl alcohol-based film (width 5 m, thickness 30 μm, length 5 km). Visual observation of the cast drum surface was continued until the end of film production, but no defects such as turbidity occurred. The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 2.

(Manufacturing of polarizing film)
The obtained polyvinyl alcohol-based film was unwound from a roll and stretched 1.7 times while being immersed in a water tank having a water temperature of 25 ° C. Next, it was stretched 1.6 times while being immersed in an aqueous solution of iodine 0.5 g / L and potassium iodide 30 g / L at 28 ° C., and then boric acid 40 g / L and potassium iodide 30 g / L were composed. It was immersed in an aqueous solution (55 ° C.) and simultaneously subjected to boric acid treatment while being uniaxially stretched 2.1 times. Then, it was washed with an aqueous solution of potassium iodide and dried to obtain a polarizing film having a total draw ratio of 5.8 times. The characteristics of the obtained polarizing film are shown in Table 2.

<Example 2>
In Example 1, instead of the polyester-based non-woven fabric having a width of 5.5 m, a length (contact length) of 10 cm, and a thickness of 0.5 mm, a plate having a width of 0.9 m, a length (contact length) of 10 cm, and a thickness of 1 mm is used. The cast drum was hydrophilized in the same manner as in Example 1 except that 6 polyvinyl alcohol sponges (PVA sponges manufactured by Aion Co., Ltd.) were used to obtain a polyvinyl alcohol film and a polarizing film. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are as shown in Table 2.

<Example 3>
In Example 1, 1 kg of lauric acid diethanolamide (molecular weight 287) was added to 99 k of water.
Examples except that an aqueous solution (concentration 0.1% by weight) in which 0.1 kg of laurate diethanolamide (molecular weight 287) was dissolved in 99.9 kg of water was used instead of the aqueous solution (concentration 1% by weight) dissolved in g. The cast drum was hydrophilized in the same manner as in No. 1 to obtain a polyvinyl alcohol-based film and a polarizing film. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are as shown in Table 2.

<Example 4>
In Example 1, 1 kg of diethanolamide laurate (molecular weight 287) was added to 99 kg of 2-propanol (boiling point 82 ° C.) in place of an aqueous solution (concentration 1% by weight) in which 1 kg of diethanolamide laurate (molecular weight 287) was dissolved in 99 kg of water. The cast drum was hydrophilized in the same manner as in Example 1 except that an alcohol solution dissolved in 1 (concentration: 1% by weight) was used to obtain a polyvinyl alcohol-based film and a polarizing film. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are as shown in Table 2.

<Example 5>
In Example 1, 1 kg of lauric acid diethanolamide (molecular weight 287) was 1 kg of 1-hexanol (boiling point 157 ° C.) 99 kg instead of an aqueous solution (concentration 1% by weight) in which 1 kg of laurate diethanolamide (molecular weight 287) was dissolved in 99 kg of water. The cast drum was hydrophilized in the same manner as in Example 1 except that an alcohol solution dissolved in 1 (concentration: 1% by weight) was used to obtain a polyvinyl alcohol-based film and a polarizing film. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are as shown in Table 2.

<Example 6>
In Example 1, 1 kg of sodium dodecylsulfonate (molecular weight 272) was added to 1-hexanol (boiling point of 157 ° C.) in place of an aqueous solution (concentration: 1% by weight) in which 1 kg of laurate diethanolamide (molecular weight 287) was dissolved in 99 kg of water. The cast drum was hydrophilized in the same manner as in Example 1 except that an alcohol solution dissolved in 99 kg (concentration: 1% by weight) was used to obtain a polyvinyl alcohol-based film and a polarizing film. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are as shown in Table 2.

<Example 7>
A polyvinyl alcohol-based film was produced in the same manner as in Example 1 except that 0.6 kg of sodium dodecyl sulfate was not used in Example 1 to obtain a polyvinyl alcohol-based film and a polarizing film. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are as shown in Table 2.

<Example 8>
In Example 1, a polyvinyl alcohol-based film and a polarizing film were obtained in the same manner as in Example 1 except that the hydrophilic treatment of the cast drum was changed to the following method. The characteristics of the obtained polyvinyl alcohol-based film and polarizing film are as shown in Table 2.
(Hydrophilic treatment of cast drum)
A roll-type coating device was installed at a position where the surface of the cast drum was exposed (see FIG. 3). A dry polyester non-woven fabric (65% polyethylene terephthalate fiber / 35% nylon fiber) having a width of 1 m, a length of 1 km, and a thickness of 0.5 mm is unwound from the unwinding roll at 2 mm / sec and brought into contact with the cast drum (contact length). 10 cm), the polyester-based non-woven fabric is impregnated with an aqueous solution (concentration: 1% by weight) in which 1 kg of laurate diethanolamide (molecular weight 287) is dissolved in 99 kg of water through a coating roll placed at the contact intermediate point. The non-woven fabric was applied while sliding in the width direction of the cast drum at 20 cm / sec (see FIG. 2), and the applied polyester-based non-woven fabric was wound on a winding roll.
The surfactant solution was supplied to the coating roll at 0.02 kg / min using a spray nozzle.

<Comparative example 1>
In Example 1, a polyvinyl alcohol-based film was produced in the same manner as in Example 1 except that the surface of the cast drum was not hydrophilized. The contact angle of the cast drum surface before production was measured and found to be 92 °. Further, when the chrome-plated surface of the cast drum was visually observed during the film formation, it was confirmed that the white turbidity increased as the production progressed and the surface of the cast drum became dirty. Further, the production was discontinued because a part of the film did not peel off from the surface of the cast drum at the end of the production. The characteristics of the obtained polyvinyl alcohol-based film (length 4 km) are as shown in Table 2. Further, using the obtained polyvinyl alcohol-based film, a polarizing film was obtained in the same manner as in Example 1. The characteristics of the obtained polarizing film are as shown in Table 2.

<Comparative example 2>
In Example 1, an attempt was made to produce a polyvinyl alcohol-based film in the same manner as in Example 1 except that the surface of the cast drum was not hydrophilized and 0.6 kg of sodium dodecyl sulfate was not used. It was difficult to peel off the film from the film, and the film broke during the production, so the production was discontinued.

<Comparative example 3>
In Example 1, instead of an aqueous solution (concentration 1% by weight) in which 1 kg of laurate diethanolamide (molecular weight 287) was dissolved in 99 kg of water, an aqueous solution in which 1 kg of heptaoxyethylene laurylamine (molecular weight 494) was dissolved in 99 kg of water (concentration 1% by weight). A polyvinyl alcohol-based film was produced by hydrophilizing the cast drum in the same manner as in Example 1 except that a concentration of 1% by weight was used, but a part of the film did not peel off from the surface of the cast drum at the end of production. Therefore, production was discontinued. The characteristics of the obtained polyvinyl alcohol-based film (length 4 km) are as shown in Table 2. Further, using the obtained polyvinyl alcohol-based film, a polarizing film was obtained in the same manner as in Example 1. The characteristics of the obtained polarizing film are as shown in Table 2.

In Examples 1 to 8, since the cast type was subjected to the hydrophilic treatment of the present invention, the peelability of the film was good, and the obtained polyvinyl alcohol-based film had a small haze and surface roughness, and had drawbacks. On the other hand, in Comparative Example 1, since the cast type was not subjected to the hydrophilic treatment of the present invention, the peelability of the film was inferior, and the obtained polyvinyl alcohol-based film had a large haze and surface roughness, which was a drawback. In many cases, uneven phase difference was also confirmed. Further, in Comparative Example 1, white turbidity occurs on the surface of the cast drum during film formation of the film, and cleaning or repair is required.
Further, in Example 7, although the undiluted solution for film formation did not contain a surfactant, the cast type was subjected to the hydrophilic treatment of the present invention, so that good peelability could be obtained. On the other hand, in Comparative Example 2, since the cast mold was not subjected to the hydrophilic treatment of the present invention, the peelability of the film was poor and the film was broken during production. Therefore, the cast mold of the present invention was made hydrophilic. It can be seen that the treatment is effective in reducing the amount of surfactant.
Further, in Comparative Example 3, since the selection of the surfactant is not appropriate, the contact angle of the cast type is outside the range of the present invention, and the obtained polyvinyl alcohol-based film has a large haze and surface roughness, and has drawbacks. You can see that there are many.
Then, it can be seen that the polarization characteristics and qualities of the polarizing film obtained from each polyvinyl alcohol-based film are superior to those of the comparative examples in the examples.

Claims (7)

A method for producing a polyvinyl alcohol-based film in which an aqueous solution of a polyvinyl alcohol-based resin is continuously cast in a cast mold to form a film, and the obtained film is peeled from the cast mold and then dried. Casting before casting. A method for producing a polyvinyl alcohol-based film, wherein the mold surface is continuously hydrophilized with a surfactant and the contact angle with water is 5 to 50 °. Against casting mold surface, according to JIS Z0237, claim 1, adhesive strength at the time of performing the following adhesive tape peel test, characterized by using a cast type which becomes 0.1~3.5N / 10mm method for producing a polyvinyl alcohol film of the serial placement.
(Adhesive tape peeling test)
Test conditions: Peeling angle 90 °, peeling speed 300 mm / min Test environment: 23 ° C 50% RH
Adhesive tape: Nichiban CT-24 (adhesive tape for cross-cut test / grid test, width 24 mm) The method for producing a polyvinyl alcohol-based film according to claim 1 or 2 , wherein the surfactant is an amide-based nonionic surfactant. The method for producing a polyvinyl alcohol-based film according to claim 3 , wherein the amide-based nonionic surfactant is an amide-based nonionic surfactant having a molecular weight of 200 to 500. The claim is characterized in that the hydrophilization treatment is carried out by a method in which an aqueous solution of a surfactant and / or an alcohol solution of a surfactant is applied over the entire width of the cast mold and wiped and / or dried on the surface of the cast mold. Item 4. The method for producing a polyvinyl alcohol-based film according to any one of Items 1 to 4 . The method for producing a polyvinyl alcohol-based film according to claim 5 , wherein the concentration of the surfactant in the aqueous solution of the surfactant and / or the alcohol solution of the surfactant is 0.1 to 10% by weight. The method for producing a polyvinyl alcohol-based film according to any one of claims 1 to 6 , wherein the cast mold is a cast drum having a chrome-plated surface.

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