JPH03287630A - Production of polyvinyl alcohol film and production of polarizing film - Google Patents

Abstract

PURPOSE:To obtain a PVA film free from discoloration and lowering in the degree of polymerization at an advantageous cost by forming a film from a PVA polymer obtained by saponifying a vinyl ester polymer in a specified solvent. CONSTITUTION:The purpose film is obtained by forming a film from a polyvinyl alcohol(PVA) polymer solution obtained by saponifying a vinyl ester polymer in at least one solvent selected from among dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, a 1-10C diamine compound and a 1-10C triamine compound. It is desirable in respect of film strength and processability that the average degree of polymerization of the PVA polymer is 1,500 or above, desirably 4,000 or above, and it is desirable in respect of processability such as film formation and drawing that it is 50,000 or below.

Description

[Detailed Description of the Invention] A. The present invention relates to a method for producing a polyvinyl alcohol film and a method for producing a polarizing film using the obtained polyvinyl alcohol film (hereinafter, polyvinyl alcohol may be abbreviated as PVA). be).

More specifically, the polyvinyl ester polymer is selected from dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, a diamine compound having 1 to 10 carbon atoms, and a triamine compound having 1 to 10 carbon atoms. By directly forming a film from a PVA polymer solution obtained by saponification in a solvent containing a seed solvent as a film forming stock solution, the decrease in the degree of polymerization of the PVA polymer is small, and it is easy to process. is PVA
A method for producing a PVA-based film that is advantageous in terms of performance and cost by eliminating the dissolution step of the PVA-based polymer, and the PVA-based film is advantageous in performance and cost.
The present invention relates to a method for producing a polarizing film using a VA polymer film. Here, the average degree of polymerization of the polyvinyl ester polymer is the polyvinyl acetate obtained by saponifying the polyvinyl ester polymer to a degree of saponification of 99.0 mol% or higher and then re-acetating it in acetone at a temperature of 3.
It is expressed as a viscosity average degree of polymerization determined from the intrinsic viscosity [η] measured at 0° C. using the following formula.

P = ([η] It has the following characteristics: good resistance to oil and organic chemicals, excellent barrier properties against gases such as oxygen, no dust in the air due to low electrostatic charge, and low pollution when incinerated. Therefore, it is mainly used for packaging materials and materials for polarizing films.In recent years, since high-strength polyethylene fibers have been developed from gel spinning and ultra-stretching of ultra-high molecular weight polyethylene, high-polymerized PVA has been used as an application. High-strength PVA fibers, high-strength, high-modulus biaxially oriented PVA films and their manufacturing methods were disclosed in Japanese Patent Application Laid-Open No. 61-2.
83526, and a highly durable PVA polarizing film and manufacturing method are known from Japanese Patent Application No. 1-105204 and others.

However, when the present inventors investigated these methods, it was found that when both the degree of polymerization and the degree of saponification of PVA become high, it is difficult to uniformly dissolve the PVA in a solvent.
It has been found that the degree of polymerization of PVA decreases when it is dissolved under harsh conditions, and thus it is desired to obtain a film with satisfactory performance. This phenomenon became more pronounced as the degree of polymerization of PVA increased.

If the polymerization degree of PVA is high and a poor solvent that causes gelation is used, the solubility of PVA will decrease,
P if stirring at a high point for a long time to ensure uniform melting.
The problem arises that color decomposition of VA occurs.

Even when PVA is heated and dissolved using dimethyl sulfoxide, which is said to be a good solvent for PVA, the degree of polymerization is high.
In addition, in the case of PVA with a high degree of saponification, it is necessary to make the dissolution conditions severe, and the degree of polymerization of PVA is greatly reduced. In particular, it is known that the degree of polymerization of PVA in dimethyl sulfoxide solution is greatly reduced by heating etc. (for example, Koubunshi Kagaku 16゜217, (1959)), and when it is made into a film, it may be colored or have reduced strength. often impairs its physical properties.

When a film is formed from a PVA solution dissolved in this way, a satisfactory PVA film cannot be obtained, perhaps because defects occur in the film structure, or because the polymerization degree of high polymerization degree PVA decreases or coloring occurs. There wasn't. Also, the PVA
The polarizing film Bi produced using the film had sufficient polarizing properties and had a low λ'5.

C Problems to be Solved by the Invention As mentioned above < The PVA polymer used in the production of PVA film has a high degree of saponification of 99 mol% or more, so the powder state of the PVA polymer has high crystallinity. However, the purpose of the present invention is to eliminate this process of dissolving PVA-based polymers, and to solve the problem of solubility in organic solvents.
The object of the present invention is to provide a method for producing PVA-based films and polarizing films that eliminates coloring of PVA-based polymers and decreases in the degree of polymerization that occur during the dissolution process, and is further advantageous in terms of cost.

The present inventors used conventional PVA-based polymers for filtering D.
As a result of intensive studies to solve the above-mentioned drawbacks when producing a polyvinyl ester film, we found that the polyvinyl ester polymer was mixed with dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, N-methylpyrrolidone, a diamine compound having 1 to 10 carbon atoms, and a diamine compound having 1 to 10 carbon atoms. A PVA-based polymer can be produced by forming a film using a polyvinyl alcohol-based polymer solution obtained by saponifying the polyvinyl alcohol-based polymer solution as a film-forming stock solution in a solvent mainly consisting of at least IN solvent selected from ~10 triamine compounds. PV
PV is advantageous in terms of cost since the dissolution process of A-based polymer can be omitted.
The present invention was completed by discovering a method for producing an A-based film and a polarizing film.

The contents of the present invention will be explained in more detail below.

The polyvinyl ester polymer of the present invention is produced from vinyl ester by bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization, but any polymerization method can be used without any limitations.

Examples of such polyvinyl ester polymers include vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl persate. Among these, vinyl acetate polymers are particularly preferred.

Furthermore, a copolymer obtained by copolymerizing a monomer copolymerizable with the vinyl ester monomers mentioned above may also be used, and this may be used within the scope of the invention. Such units include, for example, ethylene, propylene, l
- Olefins such as butene and isobutyne, acrylic acid and its salts, methyl acrylate, ethyl acrylate, n-propyl acrylate, amount of acrylic acid - propyl, n-butyl acrylate, acrylic ill! (-butyl, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, acrylic esters such as octadecyl acrylate, methacrylic acid and its salts, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-methacrylate
Methacrylic acid esters such as butyl, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, acrylamide, n-methylacrylamide, N-ethylacrylamide, N, Methylacrylamide, diacetone acrylamide, acrylamide pro? Cinsulfonic acid and its salts, acrylamide propyldimethylamine and its salts, other quaternary salts, acrylamide derivatives such as N-methylolacrylamide and its derivatives, methacrylamide, N-methylacrylamide, N-ethylmethacrylamide, methacrylamide Propanesulfonic acid and its salts, methacrylamide propyldimethylamine and its salts or quaternary salts thereof, methacrylamide derivatives such as N-methylolacrylamide and its derivatives, methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, 1-propyl vinyl ether, Vinyl ethers such as n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, nitriles such as acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, etc. Vinyl halides, allyl compounds such as allyl acetate and allyl chloride, maleic acid and its salts and esters, itaconic acid and its salts or esters, vinyl silyl compounds such as vinyl trimethoxine, isopropenyl acetate, etc. Can be mentioned.

The average degree of polymerization of the polyvinyl ester polymer is not particularly limited, but from the viewpoint of film strength and processing characteristics, it is preferably 1,500 or more, particularly preferably 4,000 or more, and is suitable for processing such as film formation and stretching. 5 in terms of characteristics
It is less than oooo.

The solvent used in the present invention is selected from diamine compounds having 1 to 10 carbon atoms such as methylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, ethylenediamine, and propylene diamine, and triamine compounds having 1 to 10 carbon atoms such as diethylenetriamine. At least one type of solvent can be used as the main solvent, and among these, dimethyl sulfoxide is particularly preferred. The solvent can be used alone, but it is not necessarily necessary to use the solvent alone. Alcohols, glycols, such as methanol, ethanol, propanol, ethylene glycol, propylene glycol, glycerin, diethylene glycol, etc. Water, acetic acid,
Alternatively, methyl acetate or the like may be used as a mixed solvent.

The solvent used in the present invention must be able to dissolve the polyvinyl ester polymer and also completely dissolve the PVA polymer produced after saponification.

It is necessary that the solvent dissolves both the polyvinyl ester polymer and the PVA polymer, but if a large amount of methanol, which is a non-solvent for the PVA polymer, is used in saponification or after saponification, cloudiness may occur. or PV
Although the A-based polymer may precipitate and separate, these solvents can also be used if a homogeneous and transparent solution can be obtained by distilling off these non-solvents after saponification. Further, other solvents other than those mentioned above may be used in combination within a range that does not impair the effects of the present invention, and there are no particular limitations on the N type of the solvent or the mixing ratio.

For the saponification reaction, a conventional method is used in which a polyvinyl ester polymer is saponified in the above-mentioned solvent by transesterification reaction and/or direct saponification reaction using an alkali catalyst or an acid catalyst. As saponification catalysts, sodium hydroxide, potassium hydroxide, amines, alkali metal alcolades, alkali metal carbonates, and alkali metal bicarbonate salts are preferably used. This is particularly preferred since the degree of polymerization decreases little during coalescence.

In addition, special care must be taken to avoid discoloration of the PVA polymer generated during the saponification reaction and a decrease in the degree of polymerization.To do this, sufficient deoxidation is performed and a radical scavenger such as hydroquinone or hydroquinone ether is added to the reaction system. It is desirable to add it to

The saponification degree of the obtained PVA-based polymer is not particularly limited, but is at least 85 mol% or more, preferably 95 mol%.
More preferably, it is more than 98 mol%.

Next, a film is formed from the PVA polymer solution.

The PVA-based polymer solution after saponification can be used as it is as a film-forming material.In addition, the PVA-based polymer solution in which acetic acid, methyl acetate, and other solvents by-produced during the saponification reaction are separated by operations such as vacuum distillation. A polymer solution may be used as a film-forming stock solution.

Examples of film forming methods include casting from the PVA polymer solution and dry film forming by extrusion into air or an inert gas such as nitrogen. In addition, the PVA
Wet film formation can also be carried out by extruding a polymer solution into a poor solvent. It is also possible to perform wet film forming in which the PVA polymer solution is once extruded into air or an inert gas such as nitrogen to form a liquid film, and then introduced into a coagulating liquid to form a film. To explain this wet film formation in more detail, a liquid film of the PVA polymer solution is formed in an atmosphere, and then this liquid film is cooled and solidified using a cold W medium such as decalin, paraffin, trichloroethylene, or carbon tetrachloride. After gelation, a film can also be formed by introducing the gel into a solvent-removal solution and removing the solvent. Furthermore, it is of course possible to introduce the liquid film into a cooling space such as a freezing room, cool it, solidify it, and gel it, then remove the solvent and form a film. The coagulant is compatible with the solvent of the PVA polymer solution and is a poor solvent for the PVA polymer, such as alcohols such as methanol, ethanol, propatool, acetone, and benzene. ,toluene,
For marco, a mixed solvent of these, the PVA-based polymer, and a one-part solvent and an aqueous inorganic salt solution are used. The liquid film of the PVA-based polymer solution is usually adjusted at -30 to 120°C, although it varies depending on the solvent of the PVA-based polymer solution.

Solvent removal from the formed film is generally carried out by extraction with chemicals and/or drying. The stretching method of the present invention employs wet stretching in an aqueous or organic solvent bath, dry heat stretching in an inert gas atmosphere, or a combination of both before or after the solvent is completely removed. be done. The stretching temperature varies depending on the stretching conditions, but is usually between 10°C and 250°C. At a stretching temperature of 250° C. or higher, the molecular chains are removed, the stretching ratio decreases to 7 ni, and color decomposition occurs, leading to a decrease in film strength. Stretching ratio: i It is necessary to set it to at least 3@ or more. If the stretching ratio is less than 3@, sufficient C film strength and processability will not be exhibited. Further, during dry heat stretching, it is preferable to carry out the operation in an inert gas. The film thickness after stretching is not particularly limited, but is preferably 5 to 100 μm, and 10 to 100 μm.
~40 μm (particularly preferred).

Further, a polarizing film using the PVA film produced as described above is produced, for example, by the following method.

The thus prepared PVA film (hereinafter abbreviated as original film) is subjected to adsorption of dichroic substances such as iodine and dyes and uniaxial stretching. There is no problem whether the suction operation and the stretching operation are performed simultaneously or separately, and the order thereof is arbitrary. In addition, boron compounds such as boric acid or borax are sometimes added to strengthen the adsorption of dichroic substances onto the raw film, but this is not possible even if it is carried out simultaneously with adsorption and stretching. It is optional to perform this at any time before or after the e operation.

Adsorption of a dichroic substance onto a raw film is usually carried out by immersing the raw film in a liquid containing the dichroic substance, but there are no particular restrictions on the operating conditions or method. Usually, when using iodine, an iodine-potassium iodide aqueous solution is used, and when using a dye, an aqueous dye solution is used.

As the dichroic substance used in the polarizing film of the present invention, in addition to iodine, so-called dichroic dyes may be used alone or in combination. For example, black17 is a typical example.
．． 19.154; brotn44.106.195°210, 223; red2.23.28.31.37
．． 39.79.81°24 (1,242,247; b
luel, 15.22. '1B, 90.9B.

151, 168.202.236.249.270;
violet9.1251, 98: greenl,
85; yellow8.12.44.86.87;
orange2ε, 39.1 (IS, 107, etc.) If the amount of the dichroic substance in the film is too small, the optical properties of the polarizing film cannot be exhibited, and if it is too large, the optical properties and water resistance are , 001 is usually used for polyvinyl alcohol-based polymers because it is a factor that reduces heat resistance.
Adjust to a range from weight% to 111%.

If the PVA film is to be used as a polarizing film, it is preferable to use a PVA film with a reduced stretching ratio due to caulking, and after adsorbing the dichroic substance, the total stretching ratio is 3 times. It is preferable to stretch the film so as to achieve the above.

After the adsorption and stretching have been carried out, the original film is dried and heat treated under a fixed length in air or a nitrogen stream.

The polarizing film of the present invention thus obtained can be used alone, or it can be used by laminating an optically transparent and mechanically strong protective film on one side. It can also be used. As the protective film, cellulose acetate film, acrylic film, polyester film, etc. are usually used.

Although the present invention has been described in detail above, particularly preferred embodiments of the present invention are as follows.

(a) The average degree of polymerization of the polyvinyl ester polymer is 40
3. The method for producing a polyvinyl alcohol film according to claim 2, wherein the polyvinyl alcohol film is 0.00 or more.

Dan-Niritaka! Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not intended to be limited in any way by the above.

In addition, "%" and "parts" in the examples refer to "% by weight" and "parts by weight", respectively, unless otherwise specified.

Note that the transmittance and polarization degree were measured using a spectrophotometer. The transmittance was measured in accordance with JIS-Z-117f)1, and the degree of polarization was calculated using the formula below.

Here, T and T are transmittances measured by stacking two polarizing films so that their stretching axes are parallel and perpendicular to each other. A polarizing film is usually used with a protective film laminated thereon, but in the following Examples and Comparative Examples, measurements were made on the polarizing film alone after the protective film was peeled off.

Example 1 Vinyl acetate was subjected to suspension polymerization at 15°C by a conventional method, followed by deliquification,
After washing and drying, polyvinyl acetate was obtained. The polyvinyl acetate was saponified to 99.0 mol% or more of saponified K in a conventional manner, and 0.1 part of the PVA was added to a mixed solution of 8 parts of acetic anhydride and 2 parts of pyridine, with occasional stirring, at a temperature of 105°C for 20 minutes. The average degree of polymerization determined from the intrinsic viscosity [η] of polyvinyl acetate obtained by repeating acetylation for several hours and repeated reprecipitation purification in acetone-ether and acetone-water systems was 9500. there were. Next, in a 500-volume glass reaction vessel equipped with a stirrer and a cooling tube, 20 parts of the above polyvinyl acetate and 1 part of dimethyl sulfoxide were added.
80 parts and 37 parts of methanol were charged, polyvinyl acetate was dissolved with stirring, nitrogen was bubbled through the system to remove oxygen, and then oxygen was removed with nitrogen separately. A 5% solution of potassium carbonate in dimethyl sulfoxide was prepared by adding 10 parts of potassium carbonate in dimethyl sulfoxide. 30 minutes at a temperature of 60°C. Thirty minutes after the addition of potassium carbonate as a saponification catalyst, IN-acetic acid was added to stop the reaction. The reaction solution was homogeneous and transparent before saponification, during the saponification reaction, and during the saponification reaction. A portion of this solution was taken out and purified by reprecipitation using a water-acetone system, followed by further Soxhlet extraction with acetone for 24 hours, followed by drying at a temperature of 60° C. to obtain PVA as a white powder. The degree of saponification of the obtained PVA was measured and was 99.
．． It was 7 mol%. Next, the average degree of polymerization of PVA was measured by the following method.

0.1 part of the PVA was mixed with 1128 parts of anhydrous vinegar and 2 parts of pyridine at a temperature of 105°C for 20 minutes with occasional stirring.
The intrinsic viscosity of the obtained polyvinyl acetate was measured at 30°C in acetone by repeating acetylation for several hours and repeating reprecipitation purification in acetone-ether and acetone-water systems [η
The average degree of polymerization determined from the sample was 93oO.

Low-boiling fractions such as methanol and methyl acetate were distilled off from this reaction solution under reduced pressure to obtain a membrane-forming stock solution. The concentration of PVA was 5.2%. The solution was cast onto a polyethylene terephthalate film, immersed in a methanol coagulation bath to form a film, and then introduced into a methanol extraction bath to remove dimethyl sulfoxide from the solution. Next, a transparent PVA film with a thickness of 20I711 was obtained by naturally drying it at room temperature, uniaxially stretching it 8 times at 150°C, and heat-setting it at 19f)'C in a nitrogen gas atmosphere for 3 minutes under constant length. Obtained.

Example 2 300IIll equipped with stirrer and cooling pipe! Into a glass reaction vessel, 20 parts of the polyvinyl acetate used in Example 1,
Weigh out 250 parts of dimethyl sulfoxide, 37 parts of methanol, and 0.02 alK of hydroquinone,
After dissolving the polyvinyl acetate with stirring, the dimethyl sulfoxide solution of polyvinyl acetate was heated to a saponification temperature of 6.
The temperature was set at 0°C.

Next, 3 parts of a separately prepared methanol solution of sodium hydroxide with a concentration of 10% was added to the reaction vessel at 60°C, and the temperature was increased to 60°C.
A saponification reaction was carried out for 30 minutes. 30 minutes after adding a 10% methanol solution of sodium hydroxide, IN-
The reaction was stopped by adding 20 parts of acetic acid.

A portion of this solution was taken out, and after repeating reprecipitation purification in a water-acetone system, it was further purified thoroughly by acetone Soxhlet, and then dried at a temperature of 60°C to form a white powder of P.
Got a VA. When the degree of saponification was measured, it was 99.5 mol%. 0.1 part of the PVA was re-acetified in a mixture of 8 parts of acetic anhydride and 2 parts of pyridine at 105°C for 20 hours with occasional stirring, and then reprecipitated in an acetone-ether and acetone-water system to obtain a polyamide resin. The intrinsic viscosity of vinyl acetate was measured in acetone at 30° C. [The average degree of polymerization determined from η was 9200.

This reaction solution was used as a film-forming stock solution in the same manner as in Example 1 to obtain a transparent PVA-based film with a thickness of 19 μm.

The stretching ratio was 8 times.

Example 3 Example! The transparent film with a thickness of 20 μm obtained in
．． 2g/L Potassium iodide 50g/L was immersed in an aqueous solution at 30°C for 2 minutes. Then, in an aqueous solution containing boric acid 60g/+2 and potassium iodide 30g/L, it was immersed at room temperature. After performing boric acid treatment for 5 minutes, it was dried under hot air at 40°C under a fixed length to obtain a polarizing film with a thickness of 20 μm.The transmittance of the obtained polarizing film was 47.4%. , the degree of polarization was 99.9%.

Comparative Example 1 The polyvinyl acetate obtained by polymerization in Example 1 was dissolved in methanol, and a methanol solution of sodium hydroxide with a concentration of 10% was added to the methanol solution at a temperature of 40°C. Example of 0 or less when λ conversion reaction is performed!
The saponification degree and average degree of polymerization of PVA were measured by the same method as 99.7 mol% and 95%, respectively.
It was 00.

The obtained PVA was dissolved in dimethyl sulfoxide at a concentration of 5.2%.
The mixture was melted at a temperature of 95° C. for 6 hours so that the temperature was as follows.

After dissolution, an apparently fine-transparent liquid was obtained, but it was colored brown. When a portion of this solution was sampled and the degree of polymerization of PVA after dissolution was measured, it was found to have decreased to 6,200.

A PVA film having a thickness of 18 μI was obtained by performing film formation 1 according to the method of Example 1, drying, stretching and heat setting. The film was colored yellow.

Comparative Example 2 Using the PVA film obtained in Comparative Example 1, a polarizing film with a thickness of 18 μm was obtained in the same manner as in Example 3.

The resulting polarizing film had a transmittance of 38.6% and a degree of polarization of 96.5%.

Example 4 Vinyl acetate was heated in a 10% methanol system at a temperature of 4 using a conventional method.
After solution polymerization at 0°C and stopping the polymerization at a polymerization rate of 24%,
Remove unreacted vinyl acetate with methanol vapor and reduce the concentration to 2.
A methanol paste of 2% polyvinyl acetate was obtained. The viscosity average degree of polymerization of this polyvinyl acetate was measured in the same manner as in Example 1 and found to be 4,500.

In the glass reaction vessel used in Example 1, 180 parts of hedimethylformamide and 178 parts of methanol paste of polyvinyl acetate having a concentration of 22% were mixed to obtain a homogeneous solution. After distilling off 881iiK of methanol from this solution under reduced pressure, the solution was replaced with nitrogen and 0.38 g of sodium methylate was added. The saponification reaction was carried out at a temperature of 60°C, but as the saponification proceeded, the entire system became thicker and gelled, so the temperature of the system was lowered to 95°C while distilling methanol off.
A clear and homogeneous PVA solution was obtained. Example by taking a part of this solution! P by the same method as
When the degree of saponification and average degree of polymerization of VA were measured, the degree of saponification was 99.6 mol % and the average degree of polymerization was 4500, and the degree of polymerization decreased and the IT color was C due to dissolution and saponification.

The PVA solution was used as a film-forming stock solution, and the solution was cast onto a polyethylene terephthalate film, immersed in a bath containing 71 parts of methanol and 30 parts of dimethylformamide at a temperature of 1°C to form a film, and then introduced into a methanol extraction bath. , dimethylformamide was removed. Next, after evaporating methanol with hot air at a temperature of 60°C, 1
By uniaxially stretching 7 times at 50℃ and further heat setting at 190℃ for 3 minutes under constant length in a nitrogen gas atmosphere, the thickness was 18μ.
A transparent film of m was obtained.

Example 5 Using the transparent film with a thickness of 18μ obtained in Example 4,
A polarizing film was obtained in the same manner as in Example 3.

The resulting polarizing film had a transmittance of 47.6% and a degree of polarization of 99.9 mol%.

Comparative Example 3 The methanol paste of polyvinyl acetate obtained in Example 4 was subjected to ordinary alkaline saponification, and the degree of saponification was 99.6.
A PVA powder having a mol% and viscosity average degree of polymerization of 4500 was obtained.

This PVA powder was dissolved in dimethylformamide to a concentration of l.
In order to prepare a 0% solution, the mixture was stirred and heated at a temperature of 95° C. for 6 hours, but since it did not dissolve, it took a total of 16 hours to obtain a membrane forming stock solution. The average degree of polymerization of PVA after dissolution had decreased to 2,700. A PVA film was prepared according to the method of Example 4, and a yellow colored film with a thickness of 20 μm was obtained.

Compared to Example 4, a decrease in the degree of polymerization and coloration were observed.

Comparative Example 4 Using the PVA film obtained in Comparative Example 3, a polarizing film with a thickness of 20 μm was obtained in the same manner as in Example 3.

The obtained polarizing film had a transmittance of 38.0% and a degree of polarization of 95.6%, which was a significant decrease in performance compared to Example 5.

As is clear from the above examples, the present invention uses polyvinyl ester polymers such as dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, N-methylpyrrolidone, diamine compounds having 1 to 10 carbon atoms, and carbon number 1~1
By forming a film using a PVA-based polymer solution obtained by saponification in a solvent mainly containing at least one solvent selected from triamine compounds of It is possible to provide a manufacturing method that can stably and easily produce PVA-based films and polarizing films on an industrial scale, with little reduction in the degree of polymerization and coloring caused by dissolving PVA.

Conventionally, in the case of high polymerization degree PVA with an average degree of polymerization of 4000 or more, there were various problems in uniformly dissolving it in a solvent to prepare a membrane forming stock solution, and there were problems with dissolution temperature, time, and stirring, as well as PVA-based PVA. Although the physical properties of the polymer decreased significantly,
According to the present invention, the process of dissolving the PVA-based polymer in a solvent can be eliminated, and the deterioration in physical properties of films and polarizing films can be minimized, and the various expenses required for this dissolution process can be greatly reduced, making it advantageous in terms of cost. reactor.

Claims (5)

[Claims] (1) Dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide,
A polyvinyl alcohol polymer obtained by saponification in a solvent mainly consisting of at least one solvent selected from N-methylpyrrolidone, a diamine compound having 1 to 10 carbon atoms, and a triamine compound having 1 to 10 carbon atoms. A method for producing a polyvinyl alcohol film, the method comprising forming a film from a solution. (2) The average degree of polymerization of the polyvinyl ester polymer is 15
00 or more, the method for producing a polyvinyl alcohol film according to claim 1. (3) The method for producing a polyvinyl alcohol film according to claim 1 or 2, wherein the saponification conditions include adding an alkali metal carbonate as a saponification catalyst after deoxidizing the solution of the polyvinyl ester polymer. (4) Claim 1 or 2, characterized in that the polyvinyl ester polymer is saponified by adding a radical scavenger.
The method for producing the polyvinyl alcohol film described above. (5) A method for producing a polarizing film, comprising using a polyvinyl alcohol film obtained by the production method according to any one of claims 1 to 4.