JP4968669B2 - Polyvinyl alcohol film for polarizing film and polarizing film and polarizing plate using the same - Google Patents

Description

  The present invention relates to a polyvinyl alcohol film for a polarizing film, more specifically, a polyvinyl alcohol film for a polarizing film for producing a polarizing film having excellent polarizing performance over the entire visible light range without being uniaxially stretched at a high magnification, And a polarizing film and a polarizing plate using the same.

  Conventionally, a polyvinyl alcohol film is prepared by dissolving a polyvinyl alcohol resin in a solvent such as water to prepare a stock solution, then forming a film by a solution casting method (casting method), and drying using a metal heating roll or the like. It is manufactured by doing. The polyvinyl alcohol film thus obtained is used for many applications as a film having excellent transparency, and one of its useful applications 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 a device requiring high quality and high reliability.

In general, a polarizing film is a film in which a polyvinyl alcohol film is dyed with a dichroic dye and uniaxially stretched in a boron compound or before and after the process, so that the dichroic dye is oriented and polarizing performance is exhibited. It is.
Under such circumstances, with the increase in brightness and definition of screens of liquid crystal televisions and the like, there is a demand for a polarizing film that is further superior in optical properties than conventional products.

  In response to such demands, as a polarizing film obtained by improving the polyvinyl alcohol resin, for example, a polarizing film using a polyvinyl alcohol resin having a high degree of polymerization (see, for example, Patent Document 1) or a main chain. A polarizing film (for example, refer to Patent Document 2), which is based on a uniaxially stretched film made of a polyvinyl alcohol-based polymer in which the amount of 1,2-glycol bonded directly to is 1.8 mol% or more, is cationic. Polarizing film made of a polyvinyl alcohol film comprising a vinyl alcohol polymer containing 0.01 to 20 mol% of a group-containing unit and 0.5 to 24 mol% of an α-olefin unit having 4 or less carbon atoms ( For example, see Patent Document 3).

JP-A-1-105204 JP-A-8-136728 JP 2003-248123 A

  However, in the technique disclosed in Patent Document 1, the optical performance as a polarizing film is improved by increasing the polymerization degree of the polyvinyl alcohol resin. However, when the polymerization degree of the polyvinyl alcohol resin increases, There was a problem that the tension of the equipment became higher, the load on the equipment became larger than usual, and new equipment was required.

  Further, in the disclosed techniques of Patent Documents 2 and 3, in order to further improve the polarization performance as the polarizing film, it is necessary to perform high-stretching. However, if the stretching ratio is increased, the neck-in in the width direction of the film is increased. (Shrinkage in the width direction of the film) occurred, and the yield in the film width direction was reduced.

  That is, if a polyvinyl alcohol-based film that can obtain a polarizing film having excellent polarization performance without requiring high-stretching can be provided, the problem of stretching equipment is reduced, which is very effective.

  In view of this, the present invention provides a polyvinyl alcohol film for a polarizing film for producing a uniform polarizing film having excellent polarization performance over the entire visible light range without being uniaxially stretched at a high magnification. It is intended.

  However, as a result of intensive studies by the present inventors to solve the above-mentioned problems, by including a crosslinking agent in the polyvinyl alcohol film in advance, the polarizing performance is excellent even without uniaxial stretching at a high magnification. It was found that a uniform polarizing film could be obtained, and the present invention was completed.

That is, the gist of the present invention is a polyvinyl alcohol film formed by forming a resin composition containing a polyvinyl alcohol resin (A) and a crosslinking agent (B), and has an equilibrium swelling degree in water at 20 ° C. The present invention was completed by finding that a polyvinyl alcohol film for a polarizing film having a content of 150 to 300% meets the above purpose.

  In addition, the total light transmittance of the film in the present invention is preferably 90 to 95% from the viewpoint of the transmittance and the degree of polarization when the polarizing film is formed, and the average crystallinity of the film by X-ray diffraction method It is preferable that it is 40 to 60% from the point of the water resistance at the time of polarizing film manufacture.

  In the present invention, it is preferable to further contain a polyhydric alcohol (C) and a surfactant (D) in view of mechanical strength, suitability for slitting, and blocking resistance of the film.

  In the present invention, the film width is preferably 2 m or more, and the film thickness is preferably 30 to 70 μm.

  In the present invention, a polarizing film comprising the polyvinyl alcohol film for the polarizing film, and a polarizing plate comprising a protective film on at least one surface of the polarizing film are also provided.

  The polyvinyl alcohol film for polarizing film of the present invention can produce a polarizing film having excellent polarizing performance over the entire visible light range without being uniaxially stretched at a high magnification, and is used for polarized sunglasses, liquid crystal display devices, etc. It is very useful as a film raw film.

The polyvinyl alcohol film for a polarizing film of the present invention is a polyvinyl alcohol film formed by forming a resin composition containing a polyvinyl alcohol resin (A) and a cross-linking agent (B). It is a polyvinyl alcohol film for a polarizing film having an equilibrium swelling degree of 150 to 300%. Conventionally, a polyvinyl alcohol film has been used as a raw film for a polarizing film, but there has been no polyvinyl alcohol film containing a crosslinking agent.

  The polyvinyl alcohol film for a polarizing film of the present invention is obtained by forming a resin composition containing a polyvinyl alcohol resin (A) and a crosslinking agent (B) by a casting method.

  As the polyvinyl alcohol-based resin (A), usually a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is used, but the polyvinyl alcohol-based film of the present invention is not necessarily limited thereto. However, a resin obtained by saponifying a copolymer of vinyl acetate and a component copolymerizable with a small amount of vinyl acetate can also be used. Examples of components copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (ethylene, propylene, n-butene, isobutene, etc.). , Vinyl ethers, unsaturated sulfonates and the like.

  Further, as the polyvinyl alcohol resin, it is also preferable to use a polyvinyl alcohol resin having a 1,2-glycol bond in the side chain, and the polyvinyl alcohol resin having a 1,2-glycol bond in the side chain is, for example, ( A) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (a) a method of saponifying and decarboxylating a copolymer of vinyl acetate and vinyl ethylene carbonate, A method of saponifying and deketalizing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane, and (d) a copolymer of vinyl acetate and glycerol monoallyl ether. It is obtained by a saponification method or the like.

  The weight average molecular weight of the polyvinyl alcohol-based resin (A) is preferably 120,000 to 300,000, more preferably 140000 to 260000, and further preferably 160000 to 200000. If the weight average molecular weight is too small, sufficient optical performance tends not to be obtained when the polyvinyl alcohol resin is used as a polarizing film, and if too large, stretching tends to be difficult when the film is used as a polarizing film. Yes, industrial production is difficult and undesirable. In addition, the weight average molecular weight of polyvinyl alcohol-type resin is a weight average molecular weight measured by GPC-LALLS method.

  The average saponification degree of the polyvinyl alcohol resin is preferably 90 mol% or more, more preferably 98 to 100 mol%, and still more preferably 99 to 100 mol%. When the average saponification degree is too small, there is a tendency that sufficient optical performance cannot be obtained when a polyvinyl alcohol-based resin is used as a polarizing film. Here, the saponification degree in the present invention is obtained by analyzing the alkali consumption required for hydrolysis of residual vinyl acetate.

  Further, the viscosity of a 4% by weight aqueous solution of the polyvinyl alcohol resin (A) at 20 ° C. is usually 8 to 400 mPa · s, particularly 40 to 300 mPa · s, more preferably 50 to 270 mPa · s, and 4 wt% If the% aqueous solution viscosity is too low, the stretchability at the time of preparing the polarizing film tends to be insufficient, and if it is too high, the flatness and transmittance of the film tend to be lowered.

  The cross-linking agent (B) used in the present invention is not particularly limited as long as it can take a cross-linked structure with the polyvinyl alcohol-based resin. Among them, boron compounds such as borax, boric acid, borate, etc. In particular, boric acid and borax are preferable.

  About content of this crosslinking agent (B), Preferably it is 0.5-15 weight part with respect to 100 weight part of polyvinyl alcohol-type resin (A), Especially 1-10 weight part, Furthermore, 1-8. Part by weight is preferred. When there is too little content of a crosslinking agent (B), the effect of this invention will be difficult to acquire, and when too much, it exists in the tendency for a film to break easily at the time of a slit.

  Thus, in the present invention, a polyvinyl alcohol-based film is prepared by containing the polyvinyl alcohol-based resin (A) and the crosslinking agent (B), but preferably further contains a polyhydric alcohol (C) and a surfactant (D). It is preferable to make it from the point of peelability at the time of film forming and blocking resistance.

  The polyhydric alcohol (C) used in the present invention effectively contributes to stretchability when producing a polarizing film. For example, ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, Examples include triethylene glycol, tetraethylene glycol, trimethylolpropane, and polyethylene glycol having a polymerization degree of 300 or less. These polyhydric alcohols can be used alone or in combination of two or more. Among them, particularly preferred are glycerin alone, or a combination of glycerin and diglycerin or glycerin and trimethylolpropane.

  As content of this polyhydric alcohol (C), it is preferable that it is 1-20 weight part normally with respect to 100 weight part of polyvinyl alcohol-type resin (A), 3-15 weight part especially, Furthermore, 7 It is preferably ˜13 parts by weight. If the content of the polyhydric alcohol (C) is too small, the stretchability tends to be reduced when the polarizing film is formed, and if it is too large, the temporal stability of the polyvinyl alcohol film for the polarizing film tends to be lowered.

  In addition, the surfactant (D) used in the present invention functions to suppress film surface smoothness and adhesion between films when wound into a roll when a polyvinyl alcohol film for a polarizing film is formed. For example, anionic surfactants and nonionic surfactants can be used alone or in combination of two or more, but in particular, an anionic surfactant and a nonionic surfactant can be used in combination. It is preferable in terms of transparency of the film.

Examples of such anionic surfactants include:
(1) aliphatic alkyl sulfonates,
(2) alkyl sulfate ester salt,
(3) polyoxyethylene alkyl ether sulfate,
(4) polyoxyethylene alkylphenyl ether sulfate,
(5) higher fatty acid alkanolamide sulfate and the like.

(1) Specific examples of the aliphatic alkyl sulfonate include, for example, sodium hexyl sulfonate, sodium heptyl sulfonate, sodium octyl sulfonate, sodium nonyl sulfonate, sodium decyl sulfonate, sodium dodecyl sulfonate, tetradecyl sulfone. And sodium dodecyl sulfonate, sodium tetradecyl sulfonate, sodium hexadecyl sulfonate, sodium hexadecyl sulfonate, sodium octadecyl sulfonate, sodium octadecyl sulfonate, sodium alkyldecyl sulfonate A sodium sulfonate, a mixture of a secondary alkyl sodium sulfonate having 10 to 18 carbon atoms, or the like is used. The counter cation of the aliphatic alkyl sulfonate is not particularly limited, and examples thereof include Na ⁺ , Ca ²⁺ , NH ₄ ⁺ , or a mixture thereof, and among these, Na ⁺ is particularly preferable.

(2) Specific examples of the alkyl sulfate ester salt include, for example, sodium hexyl sulfate, sodium heptyl sulfate, sodium octyl sulfate, sodium nonyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, and sodium octadecyl sulfate. , Sodium eicosyl sulfate, alkali metal salts such as potassium salts thereof, alkaline earth metal salts such as calcium salts, and organic amine salts such as ammonium salts, preferably sodium dodecyl sulfate, sodium octadecyl sulfate, etc. Is done. Further, the counter cation is not particularly limited, and Na ⁺ , Ca ²⁺ , NH ₄ ⁺ , or a mixture thereof may be mentioned, and among these, Na ⁺ is particularly preferable.

(3) Specific examples of polyoxyethylene alkyl ether sulfate include, for example, sodium polyoxyethylene hexyl ether sulfate, sodium polyoxyethylene heptyl ether sulfate, sodium polyoxyethylene octyl ether sulfate, sodium 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 sulfate Or organic amine salts such as alkali metal salts and ammonium salts of these potassium salts. , Preferably polyoxyethylene dodecyl ether sulfate or the like is used. Further, the counter cation is not particularly limited, and Na ⁺ , Ca ²⁺ , NH ₄ ⁺ , or a mixture thereof may be mentioned, and among these, Na ⁺ is particularly preferable.

(4) Specific examples of polyoxyethylene alkyl phenyl ether sulfate include, for example, sodium polyoxyethylene hexyl phenyl ether sulfate, sodium polyoxyethylene heptyl phenyl ether sulfate, sodium polyoxyethylene octyl phenyl ether sulfate, polyoxyethylene nonyl Sodium phenyl ether sulfate, sodium polyoxyethylene decyl phenyl ether sulfate, sodium polyoxyethylene dodecyl phenyl ether sulfate, sodium polyoxyethylene tetradecyl phenyl ether sulfate, sodium polyoxyethylene hexadecyl phenyl ether sulfate, polyoxyethylene octadecyl phenyl ether sulfate Sodium, sodium polyoxyethylene eicosyl phenyl ether sulfate , Or alkali metal salts such as the potassium salts, and organic amine salts such as ammonium salts, the use of polyoxyethylene nonylphenyl ether sulfate is preferable. Further, the counter cation is not particularly limited, and Na ⁺ , Ca ²⁺ , NH ₄ ⁺ , or a mixture thereof may be mentioned, and among these, Na ⁺ is particularly preferable.

(5) Specific examples of the higher fatty acid alkanolamide sulfate include, for example, sodium caproic acid ethanolamide sulfate, sodium caprylic acid ethanolamide sulfate, sodium capric acid ethanolamide sulfate, sodium lauric acid ethanolamide sulfate, and palmitic acid ethanolamide sulfate. Sodium, stearic acid ethanolamide sodium sulfate, oleic acid ethanolamide or potassium salts thereof, and propanolamide and butanolamide instead of these ethanolamides may be mentioned. Further, the counter cation is not particularly limited, and Na ⁺ , Ca ²⁺ , NH ₄ ⁺ , or a mixture thereof may be mentioned, and among these, Na ⁺ is particularly preferable.

  In addition to the anionic surfactants (1) to (5) above, sulfate ester salts such as sulfated oil, higher alcohol ethoxy sulfate, monoglyculate, fatty acid soap, N-acyl amino acid and salts thereof , Carboxylate types such as polyoxyethylene alkyl ester carboxylates and acylated peptides, alkylbenzene sulfonates, alkyl naphthalene sulfonates, salt formalin polycondensates of naphthalene sulfonic acid, salt formalin condensates of melamine sulfonic acid, Dialkyl sulfosuccinic acid ester salt, sulfosuccinic acid alkyl di-salt, polyoxyethylene alkyl sulfosuccinic acid di-salt, alkyl sulfoacetate, α-olefin sulfonate, N-acylmethyl taurate, dimethyl-5-sulfoisophthalate sodium salt, etc. Sulfonate It can polyoxyethylene alkyl ether phosphates, polyoxyethylene alkyl phenyl ether phosphates, also be used an anionic surfactant phosphate ester salt type such as alkyl phosphates.

On the other hand, as a nonionic surfactant, for example,
(6) General formula R—O (C ₂ H ₄ O) _n H
(Here, R is an alkyl group or an alkenyl group, and its carbon number is 6-22, preferably 8-18. These may be a single alkyl group or a mixed alkyl group. (Also, an alkyl group having an alkyl distribution obtained from palm oil, palm oil, palm kernel oil, beef tallow, etc. can be used.)
A polyoxyethylene alkyl ether represented by

(7) General formula R—X—O (C ₂ H ₄ O) _n H
(Here, R is an alkyl group or an alkenyl group, and its carbon number is 6-22, preferably 8-18. These may be a single alkyl group or a mixed alkyl group. It is also possible to use an alkyl group having an alkyl distribution obtained from palm oil, palm oil, palm kernel oil, beef tallow, etc. X is a phenylene group, n is 1 to 20, preferably 2 to 10. Is shown.)
A polyoxyethylene alkylphenyl ether represented by

(8) General formula RCONH-R'-OH or RCON- (R'-OH) ₂
(Here, R is an alkyl group or an alkenyl group, and its carbon number is 6-22, preferably 8-18. These may be a single alkyl group or a mixed alkyl group. It is also possible to use an alkyl group having an alkyl distribution obtained from palm oil, palm oil, palm kernel oil, beef tallow, etc. R ′ is —C ₂ H ₄ —, —C ₃ H ₆ —, — C ₄ H ₈ - is either).
A higher fatty acid mono- or dialkanolamide represented by

(9) General formula RCONH ₂
(Here, R is an alkyl group or an alkenyl group, and its carbon number is 6-22, preferably 8-18. These may be a single alkyl group or a mixed alkyl group. (Also, an alkyl group having an alkyl distribution obtained from palm oil, palm oil, palm kernel oil, beef tallow, etc. can be used.)
A higher fatty acid amide represented by

(10) In formula _{RNH (C 2 H 4 O)} x H or _{H (C 2 H 4 O)} y N (R) (C 2 H 4 O) x H
(Here, R is an alkyl group, and its carbon number is 6-22, preferably 8-18. These may be a single alkyl group or a mixed alkyl group. An alkyl group having an alkyl distribution obtained from palm oil, palm oil, palm kernel oil, beef tallow, etc. can also be used.x and y represent an integer of 1 to 30, preferably 3 to 15.)
A polyoxyethylene alkylamine represented by

(11) Polyoxyethylene higher fatty acid amide (12) Amine oxide and the like.

(6) Specific examples of polyoxyethylene alkyl ether include, for example, polyoxyethylene hexyl ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene dodecyl Examples include ether, polyoxyethylene tetradecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene octadecyl ether, polyoxyethylene oleyl ether, and polyoxyethylene eicosyl ether. In particular, polyoxyethylene dodecyl ether, polyoxyethylene octadecyl ether, and the like are preferable.

(7) Specific examples of polyoxyethylene alkyl phenyl ether include, for example, polyoxyethylene hexyl phenyl ether, polyoxyethylene heptyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, polyoxyethylene decyl phenyl Examples include ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene tetradecyl phenyl ether, polyoxyethylene hexadecyl phenyl ether, polyoxyethylene octadecyl phenyl ether, polyoxyethylene eicosyl phenyl ether, and the like. In particular, polyoxyethylene nonylphenyl ether is suitable.

(8) Specific examples of higher fatty acid mono- or dialkanolamide include, for example, caproic acid mono- or diethanolamide, caprylic acid mono- or diethanolamide, capric acid mono- or diethanolamide, lauric acid mono- or diethanolamide, palmitic acid mono- or Diethanolamide, stearic acid mono- or diethanolamide, oleic acid mono- or diethanolamide, coconut oil fatty acid mono- or diethanolamide, or propanolamide or butanolamide instead of these ethanolamides may be mentioned. Among these, alkyldiethanolamide is preferable, and specifically, lauric acid diethanolamide and palm oil fatty acid diethanolamide are preferably used. In particular, the diethanolamide and diethanolamine [NH- (C ₂ The use of a mixture of adducts with (H ₄ OH) ₂ ] (1: 2 molar form) is advantageous in terms of water solubility.

(9) Specific examples of higher fatty acid amides include, for example, caproic acid amide, caprylic acid amide, capric acid amide, lauric acid amide, palmitic acid amide, stearic acid amide, oleic acid amide, etc., among them palmitic acid amide Stearic acid amide is preferred.

(10) Specific examples of polyoxyethylene alkylamine include, for example, polyoxyethylene hexylamine, polyoxyethylene heptylamine, polyoxyethylene octylamine, polyoxyethylene nonylamine, polyoxyethylene decylamine, polyoxyethylene dodecyl Examples include amine, polyoxyethylene tetradecylamine, polyoxyethylene hexadecylamine, polyoxyethylene octadecylamine, polyoxyethyleneeicosylamine, and among them, polyoxyethylene dodecylamine is preferable.

(11) Specific examples of the polyoxyethylene higher fatty acid amide include, for example, polyoxyethylene caproic acid amide, polyoxyethylene caprylic acid amide, polyoxyethylene capric acid amide, polyoxyethylene lauric acid amide, polyoxyethylene myristic acid. Examples include amides, polyoxyethylene palmitic acid amides, polyoxyethylene stearic acid amides, polyoxyethylene oleic acid amides, among which polyoxyethylene lauric acid amides and polyoxyethylene stearic acid amides are suitable.

(12) Specific examples of amine oxides include, for example, dimethyl lauryl amine oxide, dimethyl stearyl oxide, dihydroxyethyl lauryl amine oxide, etc. Among them, dimethyl lauryl amine oxide is preferable.

  In addition to the nonionic surfactants of (6) to (12) above, ethylene oxide derivatives of alkylphenol formalin condensate, polyoxyethylene polyoxypropylene block polymer, polyoxyethylene glycerin fatty acid ester, polyoxyethylene castor Oil and hydrogenated castor oil, polyoxyethylene sorbitan fatty acid ester, ether ester type nonionic surfactant such as polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, sorbitan fatty acid ester, fatty acid monoglyceride, propylene glycol fatty acid ester, sucrose fatty acid ester Ester type surfactants such as can also be used in combination.

  As content of this surfactant (D), it is preferable that it is 0.01-1 weight part normally with respect to 100 weight part of polyvinyl alcohol-type resin (A), Especially 0.02-0.5. It is preferable that the amount is 0.03 to 0.2 parts by weight. If the content of the surfactant (D) is too small, it is difficult to obtain an anti-blocking effect, and if it is too much, the transparency of the film tends to be lowered.

  Moreover, when using together an anionic surfactant and a nonionic surfactant, an anionic surfactant is 0.01-1 weight part normally with respect to 100 weight part of polyvinyl alcohol-type resin (A), In particular, it is preferable to use 0.02 to 0.2 parts by weight, more preferably 0.03 to 0.1 parts by weight, and the nonionic surfactant is usually 0.01 to 1 part by weight, particularly 0.02 parts. It is preferable to use -0.2 weight part, Furthermore, 0.03-0.1 weight part is used. If the amount of the anionic surfactant is too small, the dispersibility of the dye at the time of forming the polarizing film tends to decrease and the number of dyeing spots tends to increase. If the amount is too large, foaming occurs when the polyvinyl alcohol resin is dissolved, and bubbles are mixed in the film. The anti-blocking effect tends to be difficult to obtain if the amount of the nonionic surfactant is too small, and the transparency and flatness of the film tend to be lowered if the amount is too large.

  In the present invention, it is also useful to add an antioxidant in order to prevent yellowing of the film. Examples of the antioxidant include phenolic antioxidants, and 2,6-di- T-butyl-p-cresol, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,4'-butylidenebis (3-methyl-6-t-butylphenol) and the like are preferable. The antioxidant is usually used in a range of about 2 to 100 ppm with respect to the polyvinyl alcohol resin.

  Thus, in the present invention, a polyvinyl alcohol film is formed using the polyvinyl alcohol resin (A) and the crosslinking agent (B), preferably a polyhydric alcohol (C) and a surfactant (D). is there.

  The polyvinyl alcohol film of the present invention needs to have an equilibrium swelling degree of 150 to 300% in water at 20 ° C. If the equilibrium swelling degree is less than the lower limit value, the adsorption ability of the dichroic dye is lowered. If the upper limit is exceeded, the degree of polarization when the polarizing film is formed decreases, and the object of the present invention cannot be achieved. A preferable range of the equilibrium swelling degree is 170 to 270%, and a more preferable range is 180 to 260%.

  Here, the degree of equilibrium swelling is the degree of water absorption when the polyvinyl alcohol film is immersed in water and reaches equilibrium, and is determined as follows.

That is, a 10 cm × 10 cm film piece was immersed in a constant temperature water bath at 20 ° C. for 15 minutes to swell, then the surface adhering water was gently wiped off with a filter paper to obtain the weight of the film after immersion. Time drying is performed, and the weight at this time is obtained by the following formula as the weight of the film after drying.
Equilibrium swelling degree = (weight of film after immersion / weight of film after drying) × 100

The polyvinyl alcohol film of the present invention preferably has a total light transmittance of 90 to 95% in terms of transmittance and degree of polarization when used as a polarizing film, particularly 91 to 94%. Is preferably 92 to 93%. If the total light transmittance is too low, the transmittance and degree of polarization of the polarizing film tend to decrease, and if it is too high, the production cost of the film tends to increase.
Here, the total light transmittance of the film is measured according to JIS K7361-1.

  Furthermore, the polyvinyl alcohol film of the present invention usually preferably has an average crystallinity of 40 to 60% according to the X-ray diffraction method from the viewpoint of productivity and water resistance of the polarizing film, particularly 40 to 40%. 55%, more preferably 40 to 50% is preferable. If the average crystallinity is too low, cooling is required in the water swelling process, which is a polarizing film manufacturing process, and if it is too high, the adsorption ability of the dichroic dye tends to decrease rapidly.

Here, the average crystallinity (Xc) of the polyvinyl alcohol-based film (average crystallinity of the entire region in the depth direction of the film) is a value obtained by the following formula.
Xc = Sc / (Sc + Sa)
Here, Sc and Sa decompose the curve obtained by removing the blank curve measured in the absence of the sample from the diffraction X-ray intensity curve of the corresponding sample into a crystal part (Sc) and an amorphous part (Sa), It is the area of the chart corresponding to each. Although there is no restriction | limiting in the X-ray-analysis apparatus used for a measurement, the present inventors used Rigaku Denki Co., Ltd. "X-ray-diffraction apparatus RINT1200V".

Next, the manufacturing method of the polyvinyl alcohol-type film of this invention is demonstrated concretely.
In the present invention, an aqueous solution of a polyvinyl alcohol resin composition is prepared using a polyvinyl alcohol resin (A) and a crosslinking agent (B), preferably a polyhydric alcohol (C) and a surfactant (D), A polyvinyl alcohol film is produced by casting the aqueous solution on a drum-type roll or an endless belt, preferably a drum-type roll, and forming and drying the film.

  In the production method of the present invention, first, the polyvinyl alcohol resin powder is washed to remove sodium acetate usually contained in the resin. In the washing, washing with methanol or water is performed, but the method of washing with methanol requires solvent recovery, so that the washing method with water is more preferable.

  Next, the water-containing polyvinyl alcohol resin wet cake after washing is dissolved to prepare a polyvinyl alcohol resin aqueous solution. When the water-containing polyvinyl alcohol resin wet cake is dissolved in water as it is, a desired high-concentration aqueous solution is obtained. Therefore, it is preferable to perform dehydration once. The dehydration method is not particularly limited, but a method using centrifugal force is common.

  By the washing and dehydration, it is usually preferable to obtain a wet polyvinyl alcohol resin wet cake having a water content of 50% by weight or less, preferably 30 to 45% by weight. If the water content is too high, it tends to be difficult to obtain a desired aqueous solution concentration.

  Next, an aqueous solution of the polyvinyl alcohol-based resin composition used for forming a polyvinyl alcohol-based film is prepared by adding water, a water-containing polyvinyl alcohol-based resin wet cake after dehydration, a crosslinking agent (B), and a polyhydric alcohol in a dissolution tank. It is prepared by charging (C), surfactant (D), etc., heating, stirring and dissolving. In the production method of the present invention, it is particularly preferable from the viewpoint of solubility that water-containing polyvinyl alcohol resin wet cake is dissolved by blowing water vapor in a dissolution tank equipped with a vertical circulation flow generation type stirring blade.

  When water vapor is blown into a dissolving tank equipped with a vertical circulation flow generation type stirring blade to dissolve the water-containing polyvinyl alcohol resin wet cake, water vapor is blown, and the resin temperature is usually 40 to 80 ° C., preferably 45 to 45 ° C. When the temperature reaches 70 ° C., it is preferable that stirring is started from the viewpoint of uniform dissolution. If the resin temperature is too low, the load on the motor tends to increase. If the resin temperature is too high, the polyvinyl alcohol resin tends to be hardened and cannot be uniformly dissolved. Furthermore, it is also preferable from the viewpoint that uniform melting can be achieved by blowing water vapor and pressurizing the inside of the can when the resin temperature is usually 90 to 100 ° C, preferably 95 to 100 ° C. If the resin temperature is too low, undissolved products tend to be formed. Then, when the resin temperature reaches 130 to 150 ° C., the blowing of water vapor is finished, and stirring is continued for 0.5 to 3 hours to perform dissolution. After dissolution, the concentration is adjusted so that the desired concentration is obtained.

  The concentration of the aqueous solution of the polyvinyl alcohol-based resin composition thus obtained is usually preferably 10 to 50% by weight, more preferably 15 to 40% by weight, and particularly preferably 20 to 30% by weight. If the concentration of the aqueous solution is too low, the drying load increases and the production capacity is inferior. If the concentration is too high, the viscosity becomes too high and uniform dissolution tends to be impossible.

  Next, the obtained aqueous solution of the polyvinyl alcohol-based resin composition is defoamed. Examples of the defoaming method include stationary defoaming and defoaming with a multi-screw extruder. In the production method of the present invention, from the viewpoint of productivity, there is a method of defoaming using a multi-screw extruder. preferable.

  After the defoaming process, the aqueous solution of the polyvinyl alcohol-based resin composition discharged from the multi-screw extruder is introduced into a T-type slit die by a certain amount, and cast onto a drum-type roll or an endless belt, The film is formed and dried. As the T-type slit die, a T-type slit die having an elongated rectangle is usually used. The resin temperature at the exit of the T-shaped slit die is usually preferably 80 to 100 ° C, more preferably 85 to 98 ° C. If the resin temperature at the exit of the T-type slit die is too low, there is a tendency to cause poor flow, and if it is too high, there is a tendency to foam.

The casting is performed with a drum-type roll or an endless belt, but it is preferably performed with a drum-type roll in terms of widening, lengthening, film thickness uniformity, and the like.
In casting a film with a drum-type roll, for example, the rotation speed of the drum is usually preferably 5 to 30 m / min, particularly preferably 6 to 20 m / min. The surface temperature of the drum-type roll is usually preferably 70 to 99 ° C, more preferably 75 to 97 ° C. If the surface temperature of the drum-type roll is too low, drying tends to be poor, and if it is too high, foaming tends to occur.

  The diameter of the drum roll is preferably 2000 to 5000 mm, more preferably 2400 to 4500 mm, and particularly preferably 2800 to 4000 mm. If the diameter of the drum-type roll is too short, the drying length tends to be insufficient and the speed does not appear. If it is too long, the production tends to be difficult. The width of the drum roll is preferably 1000 to 5000 mm, more preferably 2000 to 4500 mm, and particularly preferably 3000 to 4300 mm. If the width of the drum-type roll is too short, the productivity tends to be inferior, and if it is too long, the transportability tends to be inferior.

  Drying of the polyvinyl alcohol film formed by the drum type roll is performed by alternately passing the front and back surfaces of the film through a plurality of drying rolls. Although the surface temperature of a drying roll is not specifically limited, Usually, it is preferable that it is 60-100 degreeC, Furthermore, it is 65-90 degreeC. If the surface temperature is too low, drying tends to be poor, and if it is too high, it tends to dry too much, leading to poor appearance.

The diameter of the drying roll is preferably 100 to 1000 mm, more preferably 150 to 900 mm, and particularly preferably 200 to 800 mm. If the diameter of the drying roll is too short, an enormous number of drying rolls tend to be required, and if it is too long, film conveyance tends to become unstable. The number of drying rolls is usually 2 to 30.
In the present invention, it is preferable to perform heat treatment after drying.

As for the heat treatment, (1) a method of adjusting a temperature of 60 to 180 ° C. and passing a roll having a diameter of 0.2 to 2 m (usually 1 to 30), the surface of which is hard chrome plated or mirror-finished, Examples include a method using a floating dryer (length: 2 to 30 m, temperature 80 to 180 ° C.).
If necessary, humidity may be adjusted after the heat treatment.

  In general, the polyvinyl alcohol film of the present invention preferably has a film width of 2 m or more, a film length of 3000 m or more, and a film thickness of 10 to 200 μm. The width of the film is preferably 2.5 m or more, more preferably 3 to 6 m, and further preferably 3 to 5 m. When the width is too short, the productivity in manufacturing the polarizing film tends to be inferior. The length of the film is preferably 4000 m or more, more preferably 4500 m or more, and further preferably 5000 m or more. If the length of the film is too short, the productivity in manufacturing the polarizing film tends to be inferior. The thickness of the film is preferably 30 to 70 μm, more preferably 35 to 65 μm, still more preferably 40 to 60 μm, and particularly preferably 45 to 55 μm. If the thickness of the film is too short, stretching tends to be difficult, and if it is too long, it is difficult to reduce the thickness of the polarizing film.

The polyvinyl alcohol film of the present invention thus obtained is used as a raw film for a polarizing film.

  Hereinafter, the manufacturing method of the polarizing film of this invention using the polyvinyl alcohol-type film for polarizing films of this invention is demonstrated.

  The polarizing film of the present invention is produced through processes such as normal dyeing, stretching, boric acid crosslinking and heat treatment. As a method for producing a polarizing film, a polyvinyl alcohol film is stretched and immersed in a solution of iodine or dichroic dye and dyed, and then treated with a boron compound. After stretching and dyeing are performed simultaneously, a boron compound is treated. There are a method, a method of dyeing with iodine or a dichroic dye and stretching, and then a method of treating with a boron compound, a method of dyeing and then stretching in a solution of a boron compound, etc., which can be appropriately selected and used. As described above, the polyvinyl alcohol film (unstretched film) may be stretched and dyed, and further subjected to boron compound treatment separately or simultaneously, but during at least one of the dyeing step and the boron compound treatment step. It is desirable from the viewpoint of productivity to carry out uniaxial stretching.

  Stretching is usually 3 to 10 times, preferably 3.5 to 7 times in a uniaxial direction, but in the present invention, the polyvinyl alcohol film contains a crosslinking agent (B). It does not need to be stretched at a high magnification such as a stretching ratio of 7 times or more, and it has excellent polarization performance and becomes a uniform polarizing film. That is, in this invention, it is effective in the range of especially 4-6 times among the said draw ratios. In the case of such uniaxial stretching, there may be a slight stretching (stretching to prevent shrinkage in the width direction or more) in the direction perpendicular to the stretching direction.

  The temperature at the time of stretching is usually preferably selected from 20 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be performed not only in one stage but also in any stage of the manufacturing process.

  The film is dyed by bringing the film into contact with a liquid containing iodine or a dichroic dye. Usually, an iodine-potassium iodide aqueous solution is used, the iodine concentration is 0.1 to 2 g / L, the potassium iodide concentration is 10 to 50 g / L, and the potassium iodide / iodine weight ratio is 20 to 100. Is appropriate. The dyeing time is practically 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 aqueous solvent. As the contact means, any means such as dipping, coating, spraying and the like can be applied.

  The dyed film is then treated with a boron compound. As the boron compound, boric acid and borax are practical. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 0.3 to 2 mol / L, and it is practically desirable that a small amount of potassium iodide coexists in the solution. The treatment method is preferably an immersion method, but of course, an application method and a spray method can also be carried out. The temperature during the treatment is usually preferably about 20 to 60 ° C., and the treatment time is usually preferably about 3 to 20 minutes, and if necessary, the stretching operation may be performed during the treatment.

  The polarizing film of the present invention thus obtained can be used as a polarizing plate by laminating and bonding an optically isotropic polymer film or sheet as a protective film on one or both surfaces thereof. As a protective film used for the polarizing plate of the present invention, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, cyclo type Or a film or sheet of norbornene-based polyolefin or the like can be mentioned.

  For the purpose of reducing the thickness of the polarizing film, instead of the protective film, a curable resin such as a urethane resin, an acrylic resin, or a urea resin may be applied and laminated on one or both surfaces.

  A polarizing film (including at least one surface laminated with a protective film or a curable resin) has a transparent pressure-sensitive adhesive layer formed on a surface of the polarizing film as required by a generally known method. In some cases, it may be put to practical use. Examples of pressure-sensitive adhesive layers include acrylic acid esters such as butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, and α- such as acrylic acid, maleic acid, itaconic acid, methacrylic acid, and crotonic acid. Since the main component is a copolymer with a monoolefin carboxylic acid (including those added with vinyl monomers such as acrylonitrile, vinyl acetate, and styrene), the polarizing properties of the polarizing film are not impaired. Although it is particularly preferable, the present invention is not limited to this, and any pressure-sensitive adhesive having transparency can be used. For example, polyvinyl ether or rubber may be used.

  The polarizing film of the present invention includes an electronic desk calculator, an electronic clock, a word processor, a personal computer, a liquid crystal television, a portable information terminal, a liquid crystal display device such as an instrument for automobiles and machinery, sunglasses, eye protection glasses, stereoscopic glasses, a display element. (CRT, LCD, etc.) For reflection reduction layers, medical equipment, building materials, toys and the like.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to a following example, unless the summary is exceeded.
In the examples, “parts” and “%” mean weight basis unless otherwise specified.

Each physical property was performed as follows.
(1) Average Saponification Degree of Polyvinyl Alcohol Resin The analysis was performed based on alkali consumption required for hydrolysis of residual vinyl acetate units.

(2) Viscosity of 4% aqueous solution of polyvinyl alcohol resin The water temperature was adjusted to 20 ° C. and measured with a Heppler viscometer.

(3) Equilibrium swelling degree (%) of polyvinyl alcohol film
After a 10 cm × 10 cm film piece is immersed for 15 minutes in a constant temperature water bath at 20 ° C. and swollen, the adhering water on the surface is gently wiped off with a filter paper to obtain the film weight after immersion, and then dried at 105 ° C. for 2 hours. The weight at this time was taken as the weight of the film after drying, and was calculated according to the following formula.
Equilibrium swelling degree = (weight of film after immersion / weight of film after drying) × 100

(4) Total light transmittance of polyvinyl alcohol film (%)
It measured based on JISK7361-1.

(5) Average crystallinity (%) of polyvinyl alcohol film
The average crystallinity (Xc) of the polyvinyl alcohol film (the average crystallinity in the entire region in the depth direction of the film) is a value determined by the following formula.
Xc = Sc / (Sc + Sa)

  Here, Sc and Sa decompose the curve obtained by removing the blank curve measured in the absence of the sample from the diffraction X-ray intensity curve of the corresponding sample into a crystal part (Sc) and an amorphous part (Sa), It is the area of the chart corresponding to each. A diffraction X-ray intensity curve is obtained by irradiating a non-orientated sample by rotating a CuKα1 ray at a wavelength of 0.15405 nm by a graphite monochromator at 40 KV and 50 mA in a plane perpendicular to the incident X-ray by 76 revolutions per minute. An X-ray diffractometer RAD-γC (using a copper counter cathode) having a diffraction angle of 2θ = 5 to 35 deg was used.

(6) Optical properties of polarizing plate Using a high-speed multi-wavelength birefringence measuring apparatus (“RETS-2000” manufactured by Otsuka Electronics Co., Ltd.), the polarization degree and transmittance of the obtained polarizing plate at wavelengths of 460 nm, 540 nm, and 640 nm. And the dichroic ratio was measured.

Example 1
Into a 500 L tank, 200 kg of 5 ° C. water was added, and while stirring, 42 kg of a 4% aqueous solution viscosity at 20 ° C. of 68 mPa · s and an average saponification degree of 99.8 mol% of 42 kg were added. Stirring was continued for a minute. Then, after draining water, 20 kg of water was further added and stirred for 15 minutes. The obtained slurry was dehydrated to obtain a polyvinyl alcohol resin (A) wet cake having a water content of 40%.

  70 kg (42 kg of resin content) of the obtained polyvinyl alcohol resin (A) wet cake was put in a dissolution tank, and 1.7 kg of boric acid (100 parts of polyvinyl alcohol resin (A) as a crosslinking agent (B) was added to boric acid. 4 parts), 4.2 kg of glycerin as the polyhydric alcohol (C), 21 g of sodium dodecylsulfonate, 8 g of polyoxyethylene dodecylamine and 10 kg of water as the surfactant (D) were added, and water vapor was blown from the bottom of the tank. Stirring was performed when the internal resin temperature reached 50 ° C., and when the internal resin temperature reached 100 ° C., the system was pressurized. After the temperature was raised to 150 ° C., water vapor injection was stopped (water vapor injection). The total amount is 75 kg). After stirring for 30 minutes and uniformly dissolving, an aqueous solution of a polyvinyl alcohol-based resin composition having a concentration of 23% was obtained by adjusting the concentration.

Next, the aqueous solution (liquid temperature 147 degreeC) of the polyvinyl alcohol-type resin composition was supplied to the twin-screw extruder, and it defoamed. An aqueous solution of the defoamed polyvinyl alcohol resin composition was cast on a cast drum from a T-shaped slit die (straight manifold die) to form a film. The conditions for such casting film formation are as follows.
Drum type roll diameter (R1): 3200 mm, width: 4.3 m, rotation speed: 8 m / min, surface temperature: 90 ° C.,
Resin temperature at T-type slit die outlet: 95 ° C

Drying was performed while the front and back surfaces of the obtained film were alternately passed through a drying roll under the following conditions.
Drying roll diameter (R2): 320 mm, width: 4.3 m, number (n): 10, rotational speed: 8 m / min,
Surface temperature: 80 ° C

A polyvinyl alcohol film for a polarizing film having a width of 3000 mm, a thickness of 50 μm, and a length of 4000 m is continuously heat-treated at 140 ° C. by a floating dryer (length: 18.5 m) that blows hot air from both sides of the film. Got. Table 1 shows each physical property value of the obtained polyvinyl alcohol film for polarizing film.

  Using the polyvinyl alcohol film for polarizing film of the present invention obtained above, a polarizing film and further a polarizing plate were obtained in the following manner, and optical characteristics were evaluated.

  The obtained polyvinyl alcohol film for polarizing film was stretched 1.5 times while being immersed in a water bath having a water temperature of 20 ° C. Next, it was stretched 1.3 times while being immersed for 240 seconds in a dyeing tank (20 ° C.) consisting of 0.2 g / L of iodine and 15 g / L of potassium iodide, and further 50 g / L of boric acid and 30 g of potassium iodide. The sample was immersed in a boric acid treatment tank (50 ° C.) having a composition of / L and simultaneously subjected to boric acid treatment for 5 minutes while being uniaxially stretched 2.5 times (total draw ratio was 4.9 times). Then, it dried and obtained the polarizing film.

  Next, using a polyvinyl alcohol-based aqueous solution as an adhesive on both surfaces of the obtained polarizing film, a 80 μm thick triacetyl cellulose film was bonded and dried at 50 ° C. to obtain a polarizing plate. About this polarizing plate, the polarization degree and the light transmittance were measured. The measurement results are shown in Table 2. As shown in Table 2, a material having very high polarization performance over the entire visible light range was obtained.

Example 2
In Example 1, the same procedure was performed except that the polyvinyl alcohol resin (A) was changed to a polyvinyl alcohol resin (A) having a 4% aqueous solution viscosity of 113 mPa · s and an average saponification degree of 99.4 mol%. A polyvinyl alcohol film (width 3 m, thickness 50 μm, length 4000 m) was obtained. Table 1 shows each physical property value of the obtained polyvinyl alcohol film for polarizing film.

  About the obtained polyvinyl-alcohol-type film for polarizing films, it carried out similarly to Example 1, and obtained the polarizing film and the polarizing plate, and measured the polarization degree and the light transmittance. The measurement results are shown in Table 2. As shown in Table 2, a material having very high polarization performance over the entire visible light range was obtained.

Example 3
In Example 1, it carried out similarly except having changed the boric acid as a crosslinking agent (B) into 2.5 kg (6 parts of boric acid with respect to 100 parts of polyvinyl alcohol resin (A)). Width 3 m, thickness 50 μm, and length 4000 m). Table 1 shows each physical property value of the obtained polyvinyl alcohol film for polarizing film.

  About the obtained polyvinyl-alcohol-type film for polarizing films, it carried out similarly to Example 1, and obtained the polarizing film and the polarizing plate, and measured the polarization degree and the light transmittance. The measurement results are shown in Table 2. As shown in Table 2, a material having very high polarization performance over the entire visible light range was obtained.

Comparative Example 1
In Example 1, it carried out similarly except not having mix | blended the boric acid as a crosslinking agent (B), and obtained the polyvinyl alcohol-type film (Width 3m, thickness 50micrometer, length 4000m). Table 1 shows each physical property value of the obtained polyvinyl alcohol film for polarizing film.
About the obtained polyvinyl alcohol-type film, it carried out similarly to Example 1, and obtained the polarizing film and the polarizing plate, and measured the polarization degree and the light transmittance. The measurement results are shown in Table 2. As shown in Table 2, the dichroic ratio at 460 nm was low, and the polarization performance as in Examples was not obtained.

Comparative Example 2
In Example 1, a polarizing film was produced using the produced polyvinyl alcohol film (width 3 m, thickness 50 μm, length 4000 m) except that boric acid as a crosslinking agent (B) was not blended. In doing so, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1 except that the draw ratio during boric acid treatment was changed to 3.2 times (total draw ratio was 6.2 times).
About the obtained polarizing plate, it carried out similarly to Example 1, and measured the polarization degree and the light transmittance. The measurement results are shown in Table 2. As shown in Table 2, the dichroic ratio at 460 nm was low, and the polarization performance as in Examples was not obtained.

Comparative Example 3
In Example 1, except that boric acid as a crosslinking agent (B) was 0.4 kg (1 part of boric acid with respect to 100 parts of polyvinyl alcohol resin (A)), and the heat treatment temperature was changed to 170 ° C. with a floating dryer. Was carried out in the same manner to obtain a polyvinyl alcohol film (width 3 m, thickness 50 μm, length 4000 m). Table 1 shows each physical property value of the obtained polyvinyl alcohol film for polarizing film.
With respect to the obtained polyvinyl alcohol film for polarizing film, an attempt was made to obtain a polarizing film in the same manner as in Example 1, but the film was broken during stretching in the boric acid treatment bath. The polarizing plate was obtained by reducing the magnification from 5 times to 2.4 times, and the degree of polarization and light transmittance were measured.

Comparative Example 4
In Example 1, 0.2 kg of boric acid as a crosslinking agent (B) (0.5 part of boric acid with respect to 100 parts of polyvinyl alcohol resin (A)), and the heat treatment temperature was changed to 90 ° C. by a floating dryer. A polyvinyl alcohol film (width 3 m, thickness 50 μm, length 4000 m) was obtained in the same manner. Table 1 shows each physical property value of the obtained polyvinyl alcohol film for polarizing film.
About the obtained polyvinyl alcohol-type film, it carried out similarly to Example 1, and obtained the polarizing film and the polarizing plate, and measured the polarization degree and the light transmittance. The measurement results are shown in Table 2.

The polyvinyl alcohol film for a polarizing film of the present invention is a polyvinyl alcohol film formed by forming a resin composition containing a polyvinyl alcohol resin (A) and a cross-linking agent (B). Since the film has an equilibrium swelling degree of 150 to 300%, it has an effect of obtaining a uniform polarizing film having excellent polarization performance over the entire visible light range without being uniaxially stretched at a high magnification. Electronic watches, word processors, personal computers, personal digital assistants, liquid crystal display devices such as automobile and machinery instruments, sunglasses, eye protection glasses, stereoscopic glasses, reflection reduction layers for display elements (CRT, LCD, etc.), medical equipment, It is very useful as an original film for polarizing films used for building materials and toys.

Claims (13)

It is a polyvinyl alcohol film formed by forming a resin composition containing a polyvinyl alcohol resin (A) and a crosslinking agent (B), and the equilibrium swelling degree in water at 20 ° C. is 150 to 300%. A polyvinyl alcohol film for a polarizing film, which is characterized.   The polyvinyl alcohol film for a polarizing film according to claim 1, wherein the total light transmittance of the film is 90 to 95%.   The polyvinyl alcohol film for a polarizing film according to claim 1 or 2, wherein the film has an average crystallinity of 40 to 60% by X-ray diffraction.   The polyvinyl alcohol film for a polarizing film according to any one of claims 1 to 3, wherein the average saponification degree of the polyvinyl alcohol resin (A) is 90 mol% or more.   The polyvinyl alcohol film for a polarizing film according to any one of claims 1 to 4, wherein the polyvinyl alcohol resin (A) has a 4 wt% aqueous solution viscosity at 20 ° C of 8 to 400 mPa · s.   Content of a crosslinking agent (B) is 0.5-15 weight part with respect to 100 weight part of polyvinyl alcohol-type resin (A), The polyvinyl for polarizing films in any one of Claims 1-5 characterized by the above-mentioned. Alcohol film.   Furthermore, the polyhydric alcohol (C) and surfactant (D) are contained, The polyvinyl alcohol-type film for polarizing films in any one of Claims 1-6 characterized by the above-mentioned.   The polyvinyl alcohol film for polarizing film according to any one of claims 1 to 7, wherein the film width is 2 m or more.   The thickness of a film is 30-70 micrometers, The polyvinyl-alcohol-type film for polarizing films in any one of Claims 1-8 characterized by the above-mentioned.   The polyvinyl alcohol film for a polarizing film according to any one of claims 1 to 9, which is substantially an unstretched film.   The polyvinyl alcohol film for a polarizing film according to any one of claims 1 to 10, which is used for an original film of a polarizing film.   A polarizing film obtained by subjecting the polyvinyl alcohol-based film for polarizing film according to claim 1 to dyeing, uniaxial stretching, and crosslinking treatment. A polarizing plate comprising a protective film provided on at least one surface of the polarizing film according to claim 12.