JPH03287631A - 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 saponifying a polyvinyl ester in the polymerization solution from which unreacted vinyl ester is removed by contact with a solvent and forming the saponificate into a film. CONSTITUTION:A vinyl ester polymer solution is obtained by bringing a polymerization solution obtained by polymerizing a vinyl ester and containing unreacted vinyl ester into contact with at least one solvent selected from among dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, a 1-10C diamine compound and a 1-10C triamine compound, thereby removing unreacted vinyl ester from the solution. The purpose film is obtained by forming a film from the vinyl alcohol polymer obtained by saponifying the vinyl ester polymer in this solution.

Description

[Detailed Description of the Invention] The present invention A is a method for producing a polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) film, mainly a polyvinyl ester polymer used as a thick film forming solution for a polyvinyl alcohol polymer film. The present invention relates to a method for producing a solution layer, a method for producing a polyhinyl alcohol polymer solution, and a method for producing a t-divalent optical film using the obtained film.

B. Conventional technology: Conventional PVA films not only have excellent optical properties such as transparency and gloss, but also have good oil resistance and organic chemical resistance, and excellent gas barrier properties against oxygen and other gases. It is mainly used for packaging materials and polarizing film materials because it has characteristics such as low electrostatic chargeability so that dust in the air is not electrodeposited, and low pollution when incinerated. In addition, in recent years, since high-strength polyethylene fibers have been developed from gel spinning and ultra-stretching of ultra-high molecular weight polyethylene, high-strength PVA fibers using high polymerization degree PVA, high-strength polyethylene fibers, etc.
A two-wheel stretched PVA film with a high elastic modulus and a method for producing the same are disclosed in JP-A-61-283526, and a highly durable PVA polarizing film and a method for producing the same are disclosed in Japanese Patent Application No. 1-103204.

However, the present inventors investigated these methods and found that when both the degree of polymerization and the degree of saponification of PVA are high, it is difficult to uniformly dissolve the PVA in a solvent, and it is difficult to dissolve PVA under harsh conditions. It has been found that the degree of polymerization of PVA decreases, and as a result, a film with satisfactory performance cannot be obtained. This phenomenon became more pronounced as the degree of polymerization of PVA increased.

In addition, if a poor solvent that has a high degree of polymerization and causes gelation is used, the solubility of PVA will decrease, and if stirred for a long time at high temperature to uniformly dissolve, PVA will be colored and decomposed. A problem arises.

Furthermore, even when dissolving PVA by heating using dimethyl sulfoxide, which is said to be a good solvent for PVA, in the case of PVA with a high degree of polymerization and a high degree of saponification, it is necessary to make the dissolution conditions harsher, which may cause a decrease in the degree of polymerization of PVA. big. In particular, it is known that the degree of polymerization of PVA in a dimethyl sulfoxide solution decreases significantly due to excessive heating (for example, Koubunshi Kagaku 16.21? (1959)), and when it is made into a film, it may suffer from discoloration or a decrease in strength. This often impairs the physical properties of the film.

When a film is formed from PVA fukai dissolved in this way, a satisfactory PVA film may be produced, perhaps due to defects in the film structure or due to a decrease in the degree of polymerization or coloring of the high polymerization degree PVA. It's not a good idea.

Another problem is that although there is no particular restriction on the degree of polymerization of the PVA polymer required to produce PVA-based film, it is particularly important to PVA polymers larger than 8000 require the use of many solvents and complicated solvent recovery and purification processes in the manufacturing process, resulting in very high costs and making industrial use difficult. When the polyvinyl sultyl polymer and PVA polymer used in the present invention are used in solution in the saponification process or film forming process, the concentration is as high as 20% considering process passability, and furthermore, the average degree of polymerization is 4000. In the above cases, the concentration will be around 10%, especially if the average degree of polymerization is 8,000 or more, the concentration will be less than 8%, and the amount of solvent used will need to be 5 times to 131 kg or more than the polymer used in these cases. Furthermore, during the recovery and purification process, unreacted vinyl ester contained in the polymerization reaction solution,
Because the boiling points of methanol, methyl acetate, water, acetic acid, and aldehydes are in a relatively narrow range, it is necessary to use a multi-stage distillation column and a large reflux ratio, which leads to high costs. .

C Problems to be Solved by the Invention The purpose of the present invention is to eliminate the dissolution process of PVA-based polymers, eliminate the discoloration and decrease in the degree of polymerization of PVA-based polymers that occur during the dissolution process, and create PVA-based polymers that are more cost-effective. The present invention provides a method for producing a polarizing film and a polarizing film.

In order to solve the Df1 problem, the present inventors developed PVA using a conventional PVA-based polymer.
In order to solve the above-mentioned drawbacks when producing a system film, we conducted extensive studies and found that a polymerization reaction solution containing unreacted vinyl ester obtained by polymerizing vinyl ester was mixed with dimethyl sulfoxide, dimethyl formamide, and dimethyl. Acetamide, N-methylpyrrolidone, carbon number 1~
R selected from 10 diamine compounds and triamine compounds having 1 to 10 carbon atoms are brought into contact with at least one solvent, and unreacted vinyl ester is removed to obtain a polyhinyl ester polymer solution. By forming a film from a PVA polymer solution obtained by saponifying a polyvinyl ester polymer in a solution, PVA
The present invention has been completed by discovering a method for producing a PVA film and a polarizing film that is less likely to cause a decrease in the degree of polymerization or discoloration of the polymer and is advantageous in terms of cost.

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

Vinyl esters used in the present invention include monomers 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 is particularly preferred.

In addition, monomers that can be copolymerized with the vinyl ester monomers described above may be copolymerized within a range that does not impair the spirit of the present invention. Examples of such monomer units include ethylene, propylene, 1-butene, isobutyne, Olefins such as acrylic acid and its salts, methyl acrylate, ethyl acrylate, n-propyl acrylate, propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, acrylic Acrylic acid esters such as 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate, methacrylic acid and its salts, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate , i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, methacrylic acid esters such as octadecyl methacrylate, acrylamide, n-methylacrylamide, N-ethylacrylamide, N, N- Acrylamide derivatives such as dimethylacrylamide, diacetone acrylamide, acrylamide propane sulfonic acid and its salts, acrylamide bropylene methylamine and its salts, quaternary salts thereof, N-methylolacrylamide and its derivatives, methacrylamide, Methacrylamide derivatives such as N-methylacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine class salts, N-methylolacrylamide and its derivatives, methylhinyl ether,
Ethyl vinyl ether, n-propyl vinyl ether,
Vinyl ethers such as i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodenruvinyl ether, stearyl vinyl ether, nitriles such as acrylonitrile and methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl fluoride , halides such as vinylidene fluoride, allyl compounds such as allyl acetate and allyl chloride,
Examples of maleic acid and its salts include its esters, itaconic acid and its salts or its esters, vinyl trimethoquinone compounds and the like, and isopropenyl acetate.

The vinyl ester of the present invention can be polymerized by bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization. Furthermore, in order to obtain a PVA film with a high degree of polymerization, it is necessary to polymerize the vinyl ester at a low temperature. Industrially, other polymerization methods except emulsion polymerization require polymerization at low temperatures and very slow polymerization rates.
Emulsion polymerization is particularly preferred.

When carrying out suspension polymerization or emulsion polymerization at a temperature below 0°C, it is necessary to use a freezing point depressant, but considering the post-polymerization process, dimethyl sulfoxide or dimethylacetamide can be used as an organic solvent for the freezing point depressant. Although it can be advantageous, it is not limited to these.

Next, in order to remove unreacted vinyl esters contained in the obtained polymerization reaction solution, the solvents to be brought into contact with the polymerization reaction solution include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylenediamine, bromine, etc. A solvent based on a solution of at least one selected from diamine compounds such as birenamine and triamine compounds such as butiethylenetriamine can be used, and among these, dimethyl sulfoxide is particularly preferred. Various methods can be used for contacting the polymerization reaction solution with the above solvent. For example, a method in which the polymerization reaction solution after polymerization is poured into the solvent to make it a homogeneous solvent and then unreacted vinyl ester is removed by heating, or a method in which the polymerization reaction solution is continuously fed to a distillation column and further vaporized from the solvent and/or heated. The solvent is also continuously fed in the same way to remove unreacted vinyl ester, methanol, water, and other relatively low-boiling point solvents contained in the polymerization reaction solution, while a solution of the polyvinyl ester polymer in the solvent is fed from the bottom of the column. A method is taken to obtain it. The content of unreacted vinyl ester in the obtained polyvinyl ester polymer solution is preferably reduced to 0.5% or less, and more preferably 0.1% or less. The solvent after removal is dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, carbon number 1-1
It is essential that at least one solvent is selected from diamine compounds with a carbon number of 0 and triamine compounds with a carbon number of 1 to 1O, but it does not necessarily have to be the solvent alone, and methanol, ethanol, propatool, etc. , alcohols or glycols such as ethylene glycol, propylene glycol, glycerin or diethylene glycol, or in some cases, water, acetic acid, or methyl acetate 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 as a substitute.

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 as a saponification agent or as a saponification agent, Cloudy 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 completion of the sonication.

There are no particular limitations on the types and mixing ratio of other solvents that can be used in combination with the solvent used in the present invention.

In addition, when producing a highly polymerized PVA-based polymer, low-temperature emulsion polymerization is preferably used. When preparing a polyvinyl ester polymer solution, the emulsifier used in emulsion polymerization may be mixed into the polyvinyl ester polymer solution, but it may be mixed as long as it does not interfere with the gist of the present invention. . This emulsifier is used not only in the polyvinyl ester polymer solution, but also in each solution in the saponification process, in the film forming stock solution, in the film forming process, and in each solution during the polarizing film manufacturing process (even if there are three, it is necessary to improve the process passability and PVA film production). C may be mixed in as long as it has a large adverse effect on the physical properties of C.

The nano-oxidation reaction is carried out using dimethyl sulfate of polyvinyl ester, dimethylformamide, dimethylacetamide, N
- C9 selected from methylpyrrolidone, diamine compounds having 1 to IO carbon atoms, and triamine compounds having 1 to 10 carbon atoms;
In at least one solvent, an alkaline catalyst or an acid catalyst may be used for the transesterification reaction and/or for saponification by a direct saponification reaction. Sodium hydroxide, potassium hydroxide, amines, alcolades of alkali metals, alkali metal carbonates, and alkali metal hydrogen carbonates are preferably used as saponification catalysts, and among them, alkali metal carbonates and PVA systems for saponification are used. This is particularly preferred because the degree of polymerization of the polymer decreases to a small extent. In addition, special care must be taken to prevent discoloration of the PVA polymer generated during the saponification reaction and a decrease in the degree of polymerization, but in order to do so, it is necessary to sufficiently deoxidize and scavenge radicals such as hydroquinone and hydroquinone monomethyl ether. It is desirable to add the agent into the saponification reaction system. The degree of saponification of the obtained PVA-based polymer is not particularly limited, but is at least 85 mol% or more, preferably 95 mol% or more, and more preferably 98 mol% or more. In addition, the average degree of polymerization of the PVA-based polymer is not particularly limited, and from the viewpoint of film strength and processing characteristics, it is preferably 1500 or more, particularly 400.
It is more preferably 0 or more, and 50,000 or less from the viewpoint of processing characteristics such as film formation and stretching.

Here, the average degree of polymerization of the PVA-based polymer is 3% in acetone for polyvinyl acetate obtained by reacetylating the PVA-based polymer.
It is expressed as a viscosity average degree of polymerization determined from the intrinsic viscosity measured at 0° C. using the following formula.

p = ([η] Wet film formation by extrusion into a film, tf! medium, - Dry-wet film formation in which a film is formed by extrusion in air or an inert gas such as nitrogen, and then introduced into a coagulation liquid to form a film. To explain wet-dry film formation in more detail, a broken film of the PVA solution is formed in an atmosphere,
Next, this liquid film is cooled and solidified using a cooling medium such as decalin, paraffin, trichloroethylene, or carbon tetrachloride.
After gelation, it can be introduced into a solvent-removal solution to remove the solvent and form a film.

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, and 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;
Examples include alcohols such as methanol, ethanol, propatool, and butanol, mixed solvents of acetone, benzene, toluene, and the like with the solvent for the PVA polymer solution, aqueous inorganic salt solutions, and caustic soda water solutions. However, the present invention is not limited thereto.

The liquid film of the above-mentioned PVA-based polymer solution varies depending on the solvent of the PVA-based polymer solution, but is usually -30 to 120°C.
It is adjusted accordingly.

The solvent is generally removed from the formed film by extraction with a chemical and/or drying. In the stretching process of the present invention, before and after the solvent is completely removed, an aqueous solution is used (72). 1 is wet stretching in a solvent-based bath;
Dry stretching in an inert gas or atmosphere, or a combination of the two can be used. The stretching temperature varies depending on the stretching conditions, but is usually between 10'C and 250C. At a stretching temperature of 250°C or less, the molecular chains are stripped, resulting in a decrease in the stretching ratio, and color decomposition occurs, resulting in a decrease in film strength.

The stretching ratio needs to be at least 3 times or more. If the stretching ratio is less than 3 times, sufficient film strength and processing characteristics will not be exhibited. It is also preferred that the dry heat stretching be carried out in an inert gas atmosphere. The film thickness after stretching is not particularly limited, but is preferably 5 to 100 μm, and 10 to 100 μm.
404 m is particularly preferred.

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

Adjusted? A dichroic substance such as iodine or a dye is adsorbed onto a t ts P VA film (hereinafter referred to as a raw film), and a spreading operation is performed in any order.

Is it possible to add boron compounds such as boric acid or borax to strengthen the adsorption of dichroic substances to the dichroic film? It can be carried out at any time before or after the 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. When using iodine, an aqueous iodine-potassium iodide 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.
．． 19154; brown44.1 (161952
10,223: red2.23.28.31.37.
39.79.81240, 242.247; blue
l, 15.22.7B, 90.9g.

151, 16L 202.236.249.270;
violet9.1251.98; green
l, 85: yellow8.12.44.86
87; orange26.39.108.107 and the like. 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, it will deteriorate the optical properties, water resistance, and heat resistance. Therefore, polyvinyl alcohol is usually used. For system polymers, 0
．． It is adjusted to a range of 0.01% to 1% by weight.

When using the PVA-based film as a polarizing film, it is preferable to use a PVA-based film with a reduced stretching ratio in advance, and after adsorbing the dichroic substance, it is stretched so that the total stretching ratio is 3 times or more. It is preferable to do so.

The raw film that has been adsorbed and stretched is subjected to a dry heat treatment in air or a nitrogen stream under a fixed length.

The polarizing film of the present invention thus obtained can be used alone, or can be used by laminating an optically transparent and mechanically strong protective film on both or one side. You can use it. As the protective film, a cellulose acetate film, an acrylic film, a 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) Claim 2, which is vinyl ester polymerization or emulsion polymerization.
The method for producing the polyvinyl alcohol film described above.

(b) The average degree of polymerization of the polyvinyl alcohol polymer is 4
000 or more, the method for producing a polyvinyl alcohol film according to embodiment (a).

The present invention will be explained in more detail with reference to Examples below.
The present invention is not limited to these in any way.

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-8701, and the degree of polarization was calculated using the formula below.

Here, T1 and T2 are transmittances measured by stacking two polarizing films so that their stretching axes are parallel and orthogonal to each other. Polarizing films are usually used laminated with a protective film, but in the following Examples and Comparative Examples, the polarizing film alone without a protective film was measured.

Example 1 Into a reactor equipped with a stirrer, a thermometer, a nitrogen introduction tube, and a cooling tube, 200 parts of ion-exchanged water, 200 parts of vinyl acetate, and polyoxyethylene [P OE (40)] nonylphenyl ether (Nonipol 400, Weighed out 6 parts of Sanyo Chemical (Aji), 0.0120 parts of Fe504-7H*O, 0.2 DB of Rongalit, and 0.040 parts of 2-mercaptoethanol, and boiled them for 30 minutes.
Cool to 5°C while introducing nitrogen, adjust with separately degassed ion exchange water, and add 0.060% hydrogen peroxide solution to 1.
．． Polymerization was started while uniformly and continuously adding the solution at 0 parts/hr. Furthermore, separately degassed ion exchange water/methanol = 3/
+ (weight ratio) was adjusted by mixing and melting, and 0.8 parts/hr of 2-mercaptoethanol soluble acid was uniformly and continuously added at 0.8 parts/hr. During the polymerization, the system was blown with nitrogen gas to prevent nitrogen from entering the system, and emulsion polymerization was carried out for 5 hours until the polymerization rate was 60.
Polymerization was stopped at % r2.

The average degree of polymerization of polyvinyl acetate was 8,000. 100 parts of the emulsion after polymerization was poured into 170 parts of dimethyl sulfokid (hereinafter abbreviated as DMSO) and dissolved by stirring. The dissolved paste was continuously fed into a vacuum distillation column, and at the same time, 180 m of DMS◯ vapor was continuously fed. The pressure in the middle of the column is 2TomHgSA
The temperature is 82℃ and f2. Unreacted vinyl acetate and water are distilled off from the top of the column, resulting in 100% DMS of polyvinyl acetate.
An O solution was obtained from the bottom of the column. This DMSO solution of polyvinyl acetate was a homogeneous, transparent, viscous solution.

Next, 200 parts of this DM SO solution of polyvinyl acetate was placed in a reactor equipped with a stirrer and a heating jacket, and 31 parts of methanol was added and stirred until dissolved. After removing oxygen from the melon and raising the temperature to 60°C, 8.5ff of a methanol solution of carbon potassium from which oxygen had been removed by nitrogen bubbling was added, and the temperature was raised to 60°C.
The saponification reaction was carried out for 30 minutes. The saponification reaction was stopped by adding acetic acid. After saponification, the reaction system was heated to 90° C., and low-boiling fractions such as methanol and methyl acetate were distilled off to obtain a membrane-forming stock solution. The PVA concentration of the stock solution was 6.0%. The reaction solution before saponification of the DMSO solution of polyvinyl acetate, during the saponification reaction, the saponification agent, and even the film forming stock solution was uniform and transparent. A portion of the membrane forming stock solution was taken out, and after repeated reprecipitation purification using a water-acetone system, Soxhlet extraction was performed using acetone for 24 hours, and then dried at a temperature of 60°C to obtain white powder PVA. The degree of saponification was measured and found to be 99.7 mol%. 0.1 part of the PVA was stirred from time to time in a mixed solution of 8 parts of acetic anhydride and 2 parts of pyridine, and then acetylated again at a temperature of 105°C for 20 hours, and then reprecipitation purification was repeated in an acetone-ether and acetone-water system. r2.

The intrinsic viscosity of polyvinyl acetate was measured in acetone at a temperature of 30°C [calculated from η, the average degree of polymerization was 7800
No decrease in the degree of polymerization was observed during the process including these saponification reactions. The solution is cast onto a polyethylene terephthalate film, immersed in a methanol coagulation bath to form a film, and then introduced into a methanol extraction bath,
Dimethyl sulfoxide was removed from the solution. Then,
A transparent PVA-based film with a thickness of 20 μm was obtained by naturally drying at room temperature, uniaxially stretching 8 times at 150° C., and further heat-setting at 190° C. for 3 minutes under constant length in a nitrogen gas atmosphere.

Example 2 The transparent film with a thickness of 20 μm obtained in Example 1 was treated with 0 iodine.
．． 2 g/(!, potassium iodide 50 g/l!) was immersed in an aqueous solution at 30°C for 2 minutes. Then, boric acid 60 g/(!, potassium iodide 30 g/l! After performing boric acid treatment for 5 minutes at
A polarizing film of m was obtained. The resulting polarizing film had a transmittance of 47.4% and a degree of polarization of 99.9%.

Comparative Example 1 Polyvinyl acetate emulsion 100 polymerized in Example 1
The mixture was homogeneously dissolved in 220 parts of methanol, poured continuously into a purging tower, and unreacted vinyl acetate was removed by blowing methanol vapor from the bottom of the tower from a to obtain a methanol solution of polyvinyl acetate. At this time, the amount of methanol that was poured from the bottom of the column was 212 parts. The composition of this methanol solution of polyvinyl acetate was 7.0% polyvinyl acetate, 6.8% water, 9.8% DMSO, 0.35% emulsifier, and 76% methanol. Water in this methanol solution of polyvinyl acetate could not be completely distilled off. In order to reduce this moisture content to 2%, it is calculated that approximately three times the amount of blown methanol is required.

Saponification was carried out at 40°C with a molar ratio of O1 using a methanol solution of 10% caustic soda, but since the degree of saponification did not exceed 99.2 mol%, after crushing and deliquing, methanol was newly added to make a slurry of about 15%. Then, a methanol solution of caustic soda was added at a molar ratio of 0.03, and the mixture was resaponified at a temperature of 40°C for 5 hours. The saponification degree of the obtained PVA and the average polymerization degree of the polyvinyl acetate used as a resaponification substitute were 99 and 8, respectively.
% and 7900 Teatsu f2. This PVA was dried in a dry air dryer at 105°C to obtain a white PVA powder.

In this way, it is necessary to use a very large amount of solvent and to recover and purify the solvent, resulting in a very high cost.

Next, this PVA was dissolved in DMSO at a concentration of 5% while stirring at a temperature of 95° C. for 16 hours, resulting in a brownish color, and the average degree of polymerization of the PVA after dissolution was significantly lowered to 5,400.

This solution was subjected to film formation, drying, stretching, and island fixation in the same manner as in Example 1 to obtain a PVA film with a thickness of 19 μm. The film was colored yellow.

Comparative Example 2 Using the PVA film obtained in Comparative Example 1, a polarizing film with a thickness of 19 μm was obtained in the same manner as in Example 2.

The obtained polarizing film had a transmittance of 39.5% and a degree of polarization of 95.5%, which was a significant decrease in performance compared to Example 2.

Example 3 100 parts of vinyl acetate was charged into the polymerization tank used in Example 1, and after the atmosphere was sufficiently replaced with nitrogen, an azo initiator (trade name: V-70) manufactured by Wako Tsumugi Co., Ltd. was added at 0.0014 FfJ. Bulk polymerization was carried out at a temperature of 40° C. for 4.5 hours, and the polymerization was stopped at a polymerization rate of 23.9%. Thereafter, dimethylformamide (hereinafter abbreviated as DMF) vapor was simultaneously blown into the vacuum distillation column in the same manner as in Example 1, and unreacted vinyl acetate was expelled. A solution was obtained. Immediately after polymerization and DMF
The viscosity average degree of polymerization of polyvinyl acetate in solution is 7.
There was no decrease in the degree of polymerization at 400 and 7300. 100 parts of this DMF solution of polyvinyl acetate and 20 parts of methanol were charged into the reaction vessel used in Example 1, and after sufficiently purging with nitrogen while stirring the stall, 0.35 parts of sodium methylate and 0.0 parts of hydroquinone monomethyl ether were added.
．． A saponification reaction was carried out at a temperature of 60°C.

As the saponification progressed, the entire system became thicker and a little gelled, so the temperature of the system was lowered to the point where methanol was distilled off:)95
After raising the temperature to °C, a clear and homogeneous PVA solution was obtained. A part of this solution was sampled and the saponification degree and average polymerization degree were measured by the same method as in Example 1.
There was no decrease in the degree of polymerization or coloration due to the saponification reaction. The concentration of this PVA in DMF solution was 7.8%.

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 70 parts of methanol and 30 parts of dimethylformamide at a temperature of 10°C to form a film, and then introduced into a methanol extraction bath. Then, dimethylformamide was removed from the solution.

Next, after evaporating methanol with hot air at a temperature of 60°C, it was uniaxially stretched 7 times at 150°C, and further heat-set at 190°C for 3 minutes in a nitrogen gas atmosphere under a fixed length to obtain a thickness of 1.
A transparent film of 8 μm was obtained.

Example 4 100 parts of vinyl acetate and D
After charging 100 parts of MSO and thoroughly purging with nitrogen, a starting column (trade name V2O) manufactured by Wako Tsumugi Co., Ltd. was heated to 0.32N.
After charging, solution acid polymerization was carried out at a temperature of 30°C for 4 hours, and the polymerization was stopped at a polymerization rate of 48%. Thereafter, unreacted vinyl acetate was removed by the same method as in Example 1, and 2
A 0% DMSOm solution was obtained.

The solution was saponified in the same manner as in Example 1 to obtain a transparent and uniform solution of PVA in DM SO having a concentration of 100%. Immediately after polymerization, the average degree of polymerization of polyvinyl acetate and substitute PVA in the DM SO solution was 450, respectively.
There was no decrease in the degree of polymerization at 0.4500 and 4400.

This PVA DM SO solution was used as a film forming stock solution in the same manner as in Example 1 to obtain a transparent PVA film with a thickness of 20 μm. The stretching ratio was 7 times.

Comparative Example 3 Polyvinyl acetate polymerized in Example 3 was treated in the same manner as in Comparative Example 1 to remove unreacted vinyl acetate, saponification, re-saponification,
After drying, a white PVA powder was obtained. Obtained P
The degree of saponification and average degree of polymerization of VA were 997 mol% and 7300, respectively.

Dissolve this PVA powder in DMF and i! 1tf7.5
% solution was prepared by stirring and thickening at a temperature of 95°C for 6 hours, and it took a total of 16 hours to obtain a film-forming stock solution. After dissolution, the average degree of polymerization of PVA decreased to 4900, which was L1. Example 3 When a PVA film was prepared according to method G, it had a thickness of 20 μm.
The film was colored yellow and obtained. Compared to Example 3, the degree of polymerization was reduced and the coloring was improved.

As is clear from the above examples, the present invention does not require isolation of polyvinyl ester polymers or PVA polymers from polymerization to film formation, and a solution mainly consisting of the solvent used in the present invention. By consistently using f co-processing, the decrease in the degree of polymerization of PVA-based polymers is small, and it is possible to significantly reduce the amount of solvent and utilities used in the process, making it safe and easy on an industrial scale. The purpose of this invention is to provide a manufacturing method capable of producing a PVA-based film and a polarizing film.

Claims (5)

[Claims] (1) A polymerization reaction solution containing unreacted vinyl ester obtained by polymerizing vinyl ester is mixed with dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, a diamine compound having 1 to 10 carbon atoms, and a diamine compound having 1 to 10 carbon atoms. A polyvinyl ester polymer solution is obtained by contacting with at least one solvent selected from 1 to 10 triamine compounds and removing unreacted vinyl ester, and then saponifying the polyvinyl ester polymer in the solution. A method for producing a polyvinyl alcohol film, which comprises forming a film from a polyvinyl alcohol polymer solution obtained by. (2) The method for producing a polyvinyl alcohol film according to claim 1, wherein the vinyl ester is polymerized by bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization. (3) The average degree of polymerization of the polyvinyl alcohol polymer is 1
The method for producing a polyvinyl alcohol film according to claim 1 or 2, wherein the polyvinyl alcohol film has a molecular weight of 500 or more. (4) The polyvinyl alcohol according to any one of claims 1 to 3, wherein the saponification conditions include adding an alkali metal carbonate as a saponification catalyst after deoxidizing the solution of the polyvinyl ester polymer. Production method for film. (5) A method for producing a polarizing film, which uses a polyvinyl alcohol film obtained by the method according to any one of claims 1 to 4.