JPH1192575A - Preparation of membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preparation method of a membrane composed of a new PVA which has such characteristics of a membrane made of a conventional PVA as high tenacity, transparency and oil resistance as well as excellent heat resistance, water resistance and heat resistance on wetting. SOLUTION: While manufacturing a membrane made of a polyvinyl alcohol polymer, a radical generating agent in an amt. of 0.05-5 mole % and a radical crosslinking auxiliary in an amt. of 0.05-5 mole % are added or adhered to the repeating unit of the polyvinyl alcohol polymer, followed by a thermal treatment to crosslink solid polymer. A desirable polyvinyl alcohol polymer has an average mol.wt. of >=1,000 and a degree of saponification of >=70 mole %.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high strength, heat resistant,
The present invention relates to a method for producing a film made of a polyvinyl alcohol-based polymer having excellent water resistance, moist heat resistance and durability.

[0002]

2. Description of the Related Art A polyvinyl alcohol film has extremely excellent properties such as mechanical and mechanical properties, transparency, oxygen barrier properties, cryogenic electrical insulation and oil resistance, and is therefore used in the form of films, membranes and sheets. It has been awarded as a packaging material for fiber products, a gas barrier material, various membrane filters, separation membranes, electrical insulation materials, optical films such as polarizing film substrates, and oil-resistant belt materials.

However, in recent years, the above materials and applications have been required to maintain performance under severer conditions than before, especially under high temperature and high humidity. At present, a film using a conventional polyvinyl alcohol-based polymer, which has a problem at the time of absorbing moisture, cannot be completely used. On the other hand, it is known that by cross-linking a film made of a polyvinyl alcohol-based polymer with formaldehyde, butyraldehyde, or glyoxal alone or in a mixture, the water resistance and wet heat resistance of such a film can be improved. The effect was not always enough.

Conventionally, when acetalizing a film made of a polyvinyl alcohol-based polymer (hereinafter abbreviated as PVA), a method of treating the film entirely in an aqueous acid solution has been adopted. However, the present inventors have found that in this method, a strong acid such as hydrochloric acid or sulfuric acid is required in order for the acetalization reaction to proceed sufficiently, and that the temperature also needs to be 50 ° C. or higher. It became clear. Treatment under such conditions is nothing less than treatment in a good solvent for PVA, and it is inevitable that the film swells during the treatment, and PVA itself partially dissolves. I was afraid. These phenomena have the effect of disturbing the molecular orientation of PVA and lowering the crystallinity, and as a result, there has been a problem in that the mechanical and mechanical strength inherent to the film made of PVA is reduced.

[0005] Further, a film made of PVA is usually cast from a solution of the polymer, a dry film forming method (extrusion into an inert gas such as air or nitrogen), a wet film forming method (PV).
A is extruded into a poor solvent), a dry-wet film formation method, or the like. The above-mentioned acid treatment step is usually performed after film formation. However, if the acid used for acetalization remains, it causes coloring and strength reduction of the film made of PVA. Therefore, a sufficient neutralization and water washing step is actually required. However, there is a problem that the cost of the process is increased.

[0006]

Under these circumstances, the present invention has greatly improved the water resistance and wet heat resistance without impairing the mechanical and mechanical properties inherent in PVA and without requiring complicated steps. It is intended to provide a method for producing a film.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, when producing a film made of a polyvinyl alcohol-based polymer, the repeating unit of the polyvinyl alcohol-based polymer was used. 0.05-5 mol%
After containing or attaching 0.05 to 5 mol% of a radical crosslinking agent and a radical cross-linking assistant, and then cross-linking the polymer by heat treatment. I came to.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the contents of the present invention will be described in more detail. PVA constituting the membrane of the present invention is a conventional PVA.
It is obtained by saponification of polyvinyl acetate or a copolymer thereof, which is a method for producing VA. Also, by decomposition of homopolymers or copolymers of vinyl ether such as vinyl pivalate, vinyl formate such as vinyl formate, bulky vinyl ester or highly polar vinyl ester, or t-butyl vinyl ether, trimethylsilyl vinyl ether or benzyl vinyl ether. can get.

Here, the comonomer unit in the case of a copolymer is divided into a unit that produces a vinyl alcohol unit by saponification or decomposition and a unit other than the unit.

The latter comonomer unit is copolymerized mainly for the purpose of modification, and is used within a range not to impair the purpose of the present invention. Examples of such a unit include olefins such as ethylene, propylene, 1-butene, and isobutene, acrylic acid and its salts, methyl acrylate, ethyl acrylate, n-propyl acrylate,
Acrylates such as i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, methacrylic acid and salts thereof, 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 Methacrylic esters such as octadecyl, acrylamide,
N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts and quaternary salts, N-methylolacrylamide and its derivatives, etc. Acrylamide derivative, methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N, N-dimethylmethacrylamide, diacetone methacrylamide, methacrylamidopropanesulfonic acid and salts thereof, methacrylamidopropyldimethylamine and salts thereof And quaternary salts, methacrylamide derivatives such as N-methylol methacrylamide and derivatives thereof, methyl vinyl ether, ethyl vinyl ether, n
Vinyl ethers such as -propyl vinyl ether, i-propyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, benzyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether;
Nitriles such as acrylonitrile and methacrylonitrile; vinyl chlorides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts and esters; itaconic acid And salts and esters thereof, vinylsilyl compounds such as vinyltrimethoxysilane, and isopropenyl acetate.

The degree of saponification of PVA is usually preferably at least 70 mol%. In particular, when heat resistance, water resistance and oil resistance are required, the saponification degree is preferably 90 to 99.99 mol%. Here, the degree of saponification represents the ratio of vinyl alcohol units after saponification to units that can be converted to vinyl alcohol units by saponification in a homopolymer or copolymer of vinyl acetate, and the residue is a vinyl acetate unit. It is.

[0012] The degree of polymerization of PVA also affects the performance of the membrane of the present invention. The degree of polymerization is appropriately selected depending on the use of the film, but from the viewpoint of film strength and processing characteristics, is 500 or more, preferably 1
000 or more, more preferably 2000 or more, and 30,000 or less from the viewpoint of processing characteristics such as film formation and stretching.

The membrane made of PVA produced by the present invention is not particularly limited in shape and transparency, and is a general term for so-called ordinary films, membranes and sheets. The thickness of the film is not particularly limited and is appropriately selected depending on the use of the film to be used, but is preferably in the range of 10 to 200 μm. The PVA film manufacturing method of the present invention using PVA as described above can be performed by a cast film forming method from a solution or a dry film forming method (such as in air or nitrogen) depending on the required film thickness, film use, and purpose. Extrusion into active air), a wet film formation method (extrusion of the PVA into a poor solvent), a dry-wet film formation method, and the like.

As the solvent used at this time, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, ethylene glycol, glycerin, water, hexafluoroisopropanol and the like are used alone or in combination. In addition, an aqueous solution of an inorganic salt such as lithium chloride and calcium chloride can be used alone or as a mixture with the organic solvent. However, when the radical generator and the crosslinking assistant of the present invention are mixed and added to the solvent, a solvent that causes the radical generator or the crosslinking assistant to aggregate or separate is not desirable, and a solvent that uniformly disperses or dissolves the solvent is preferable. Further, if the acidity or alkalinity in the polymer solution is high, the radical generator and the radical crosslinking assistant may react with the PVA-based polymer in the solution, which is not preferable. In this regard, water, dimethyl sulfoxide, a mixture of dimethyl sulfoxide and water, glycerin, ethylene glycol, and the like are preferably used.

The concentration of PVA at the time of film formation varies depending on the film formation method, but is usually 1 to 50% by weight, and the temperature is usually in the range of room temperature to 250 ° C.

The PVA membrane of the present invention may contain anything other than the above-mentioned PVA without impairing the gist of the present invention. For example, ordinary PVA, other polymers, plasticizers such as glycerin, etc. And inorganic compounds such as clay, silica and calcium carbonate. If necessary, dyes and pigments for coloring, and stabilizers such as antioxidants and ultraviolet absorbers may be added.

A feature of the present invention is that, when a film made of PVA is produced, a radical generator is added to the inside or surface of the PVA from 0.05 mol% to 5 mol% based on the repeating unit of the PVA.
After adding or adhering 0.05 to 5 mol% of the radical crosslinking assistant to the repeating unit of PVA, the polymer is cross-linked by heat treatment.

The radical generator that can be used in the present invention is not particularly limited as long as it is a compound that generates a radical by heat. Specifically, isobutyl peroxide, α, α'-bis (neodecanyl peroxy) Diisopropylbenzene, cumyl peroxyneodecanate, di-n-propylperoxydicarbonate, diisopropylperoxydicarbonate, 1,1,3,3
-Tetramethylbutylperoxyneodecanate, bis (4-t-butylcyclohexyl) peroxydicarbonate, 1-cyclohexyl-1-methylethylperoxyneodecanate, di-2-ethoxyethylperoxydicarbonate, di (2-ethylhexyl) Peroxy) dicarbonate, t-hexylperoxyneodecanate, dimethoxybutylperoxydicarbonate,
Di (3-methyl-3-methoxybutylperoxy) dicarbonate, t-butylperoxyneodecanate,
2,4-dichlorobenzoyl peroxide, t-hexylperoxypivalate, t-butylperoxypivalate, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, lauryl peroxide, stearoyl peroxide, 1,1,3 , 3-tetramethylbutylperoxy-2-ethylhexanoate, succinic peroxide, 2,5-dimethyl-
2,5-di (2-ethylhexanoylperoxy) hexane, 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2 -Ethylhexanoate, m-toluoyl peroxide, benzoyl peroxide, t-butylperoxyisobutyrate, di-t-butylperoxy-2-methylcyclohexane, 1,1-bis (t-hexylperoxy) -3,3 , 5-trimethylcyclohexane, 1,
1-bis (t-hexylperoxy) cyclohexane,
1,1-bis (t-butylperoxy) -3,3,5-
Trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, 2,2-bis (4,4-
Di-t-butylperoxycyclohexyl) propane,
1,1-bis (t-butylperoxy) cyclododecane, t-hexylperoxyisopropyl monocarbonate, t-butylperoxymaleic acid, t-butylperoxy-3,5,5-trimethylhexanoate, t
-Butyl peroxylaurate, 2,5-dimethyl-
2,5-di (m-toluoylperoxy) hexane, t
-Butyl peroxyisopropyl monocarbonate, t
-Butylperoxy-2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2,5-
Dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, 2,2-bis (t-butylperoxy) butane, t-butylperoxybenzoate, n-butyl-4,4-bis (t- Butylperoxy) valerate, dibutylperoxyisoisophthalate, α, α′-bis (t-butylperoxy) diisopropylbenzene, dicumyl peroxide,
2,5-dimethyl-2,5-di (t-butylperoxy) hexane, t-butylcumyl peroxide, di-t
-Butyl peroxide, p-menthane hydroperoxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, diisopropylbenzene hydroperoxide, t-butyltrimethylsilyl peroxide, 1,1,3,3- Tetramethylbutyl hydroperoxide, cumene hydroperoxide, t-hexyl hydroperoxide, t-butyl hydroperoxide, 2,
Organic peroxides such as 3-dimethyl-2,3-diphenylbutane are exemplified. Among these compounds, when the decomposition temperature of the organic peroxide is higher than the decomposition temperature of PVA, the PVA is severely deteriorated by the heat treatment for driving the crosslinking reaction, and the mechanical strength of the film is reduced. From the above viewpoint, 1,1-bis (t-butylperoxy) cyclohexane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-bis (t
-Butylperoxy) cyclododecane, t-hexylperoxyisopropyl monocarbonate, t-butylperoxymaleic acid, t-butylperoxy-3,5,
5-trimethylhexanoate, t-butylperoxylaurate, 2,5-dimethyl-2,5-di (m-toluoylperoxy) hexane, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-
2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, 2,2-bis (t-butylperoxy) butane, t- Butyl peroxybenzoate, n-
Butyl-4,4-bis (t-butylperoxy) valerate, dibutylperoxyisoisophthalate, α,
α'-bis (t-butylperoxy) diisopropylbenzene, dicumyl peroxide, 2,5-dimethyl-
2,5-di (t-butylperoxy) hexane, t-butylcumyl peroxide, di-t-butyl peroxide, p-menthane hydroperoxide, 2,5-dimethyl-2,5-di (t-butylperoxy) Hexin-
3, diisopropylbenzene hydroperoxide, t-
Butyltrimethylsilyl peroxide, 1,1,3,3
Organic peroxides such as -tetramethylbutyl hydroperoxide, cumene hydroperoxide, t-hexyl hydroperoxide are preferred. These compounds may be used alone or in combination of two or more.

Next, the radical crosslinking assistant that can be used in the present invention is not particularly limited as long as it is a compound generally used for radical crosslinking of an olefin resin. For example, it has two or more ethylenically unsaturated bonds. A compound or a quinone dioxime compound, more specifically,
p-benzoquinone, p-benzoquinone dioxime, P,
Quinone or quinone dioxime compounds such as P'-dibenzoyldiquinone dioxime; polyfunctional maleimide compounds such as N, N'-m-phenylenedimaleimide and N, N '-(4,4-methylenediphenylene) dimaleimide; Polyfunctional methacrylate compounds such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, allyl methacrylate; diallyl fumarate, diallyl phthalate, tetraallyl oxyethane ,
Triallyl cyanurate, triallyl isocyanurate, ethylene glycol diallyl ether, diethylene glycol diallyl ether, polyethylene glycol diallyl ether, trimethylolpropane triallyl ether, pentaerythritol triallyl ether,
Polyfunctional allyl compounds such as pentaerythritol tetraallyl ether; polyfunctional vinyl compounds such as divinylbenzene and divinylpyridine; isoprene, 1,3-butadiene, 1,4-pentadiene, 1,5-hexadiene,
1,6-peptadiene, 1,7-octadiene, 1,7
-Octadien-3-ol, 1,8-nonanediene,
Polyene compounds such as polyisoprene and polybutadiene;
And compounds such as thiourea. Among these, quinone or a quinone dioxime compound, thiourea, or the like is preferable from the viewpoints of stability under high temperature and moist heat and reactivity with PVA, and specifically, p-benzoquinone and p-benzoquinone dioxime. , P, P'-dibenzoyldiquinone dioxime, thiourea and the like are particularly preferred crosslinking assistants. These compounds may be used alone or in combination of two or more.

Among the combinations of these radical generators and crosslinking assistants, the combinations in which the crosslinking reaction was observed more efficiently include organic peroxides and quinone or quinone dioxime compounds; organic peroxides and thiourea. There are, for example, combinations of diisopropylbenzene hydroperoxide and p-benzoquinone; diisopropylbenzene hydroperoxide and thiourea; cumene hydroperoxide and p-benzoquinone; cumene hydroperoxide and thiourea.

The application of the radical generator and the radical crosslinking aid used in the present invention may be performed at any stage of the PVA film production process. Also, even if a radical generator and a radical crosslinking aid are applied in the same step,
It may be applied sequentially in different steps. Specifically, a method of dissolving or dispersing in a solvent used at the time of film formation and including it in the PVA, and when a poor solvent is used at the time of film formation, a radical generator and / or
Alternatively, a method of dissolving or dispersing a radical crosslinking aid, a method of applying a radical generator and / or a radical crosslinking aid dissolved or dispersed in an appropriate solvent or water to the surface of the formed film, and the like, may be mentioned. Can be Among them, a method of dissolving or dispersing in a solvent used at the time of film formation and incorporating it into the PVA, or a method of using a poor solvent at the time of film formation, a radical generator and / or The method of dissolving or dispersing the radical crosslinking aid is preferable in that the radical generator and the radical crosslinking aid can be uniformly and sufficiently contained in the film, and the amounts can be easily controlled.

The content or amount of the radical generator in the present invention is appropriately selected depending on the purpose of use of the membrane.
Mol%, more preferably 0.1 to 1 mol%. If the content or the amount of adhesion is less than 0.05 mol%, the amount of radicals generated during the heat treatment is small, so that the moist heat resistance is insufficient. If it exceeds 5 mol%, the mechanical and mechanical properties inherent in the PVA film are excellent. The properties, transparency, oil resistance and the like are lowered, which is not preferable. The content or the attached amount can be controlled by changing the amount of the radical generator in the solvent containing the radical generator or the poor solvent.

The content or amount of the radical crosslinking aid in the present invention is appropriately selected depending on the purpose of use of the membrane.
The content is 5 to 5 mol%, and more preferably 0.1 to 1 mol%. If the content or the amount of adhesion is less than 0.05 mol%, the amount as a cross-linking assistant is insufficient, so that the wet heat resistance is insufficient. If it exceeds 5 mol%, the mechanical and mechanical properties inherent in the PVA film are excellent. The properties, transparency, oil resistance and the like are lowered, which is not preferable. The content or the attached amount can be controlled by changing the amount of the radical crosslinking aid in the solvent containing the radical crosslinking aid or the poor solvent.

Next, by subjecting the radical generator contained or attached to the PVA film to thermal decomposition by applying an appropriate heat treatment, radicals are generated and the crosslinking reaction proceeds. As a mechanism of the crosslinking method, radicals generated by the thermal decomposition of the radical generator are first converted to PV
The tertiary hydrogen of A is extracted. Here, before PVA from which the tertiary hydrogen has been extracted is beta-cleaved, the PVA molecular chain is not broken by attacking the coexisting radical crosslinking assistant, and the radical is chemically bonded to the PVA. Left inside. This radical is a radical generated on another polyvinyl alcohol molecular chain, or
It is presumed that a cross-linking structure is formed by a coupling reaction with a radical in the cross-linking aid chemically bonded to A.

The temperature in the heat treatment step is 200 ° C. or higher, preferably 230 ° C. or higher. Since the decomposition of polyvinyl alcohol occurs, the upper limit of the heat treatment temperature is 260 ° C.
It is. The heat treatment may be performed at the same time as the drying of the film or the dry heat drawing step. In the dry heat drawing step, the thermal decomposition of the radical generator is not sufficient, or the crosslinking aid and P
If the reaction with VA has not progressed sufficiently, a heat treatment step following the dry heat drawing step can be added. The upper limit heating temperature at this time is 260 ° C. because decomposition of polyvinyl alcohol is not preferable.

[0026]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to the examples.
The various physical property values in the present invention are defined by the following methods. 1) Viscosity average polymerization degree of PVA The viscosity average polymerization degree PA was calculated based on JIS K-6726.

2) Content of Radical Generator and Radical Crosslinking Aid in Polyvinyl Alcohol Film The film before the heat treatment containing the radical generator and the radical crosslinking aid is dissolved in dimethyl sulfoxide at 50 to 140 ° C. By proton NMR, C of PVA
The peak area ratio of the radical generator and the radical crosslinking assistant to the H ₂ group peak was calculated, and the content of PVA with respect to the repeating unit was determined from a calibration curve prepared in advance.

3) Dissolution amount of membrane in hot water Approximately 100 milligrams of the finally obtained PVA membrane (thickness: about 20 micrometers) was precisely evaluated in a test tube, and distilled water 1
After adding 0 ml, the tube was sealed and heat-treated (121 ° C., 2 ° C.) in an autoclave (manufactured by Yamato Scientific, SP22).
Time). The PVA in the test tube was separated by filtration, washed with distilled water and dried (120 ° C., 10 hours or more), and the dissolution rate was determined.

Examples 1 to 12 Polyvinyl alcohol having a degree of polymerization of 1700 and a degree of saponification of 99.5 mol% was dissolved in dimethyl sulfoxide to obtain a 20% by weight solution. The solution was cast on a glass plate and poured into a methanol bath ( (0 ° C.) to form a film. Further, the film was thoroughly washed in methanol to remove all dimethyl sulfoxide in the film. Finally, diisopropylbenzene hydroperoxide (concentration: 0.1 mol / liter) was used as a radical generator.
And various radical crosslinking assistants (concentration 0.2
(Mol / liter) in a methanol bath at room temperature for 30 minutes to contain a radical generator and a radical crosslinking assistant inside and on the surface of the film, and then dry in a hot air drier (50 ° C., 30 ° C.). Minute). Next, the obtained film was subjected to a heat treatment at 230 ° C. for 10 minutes under a nitrogen stream. Table 1 shows the content of each compound in the dried membrane and the elution rate of the finally obtained membrane.

Examples 13 to 24 Except that cumene hydroperoxide was added as a radical generator at a concentration of 0.1 mol / liter to the last methanol bath, film formation was performed in the same manner as in Examples 1 to 12. Drying and heat treatment were performed. Table 1 also shows the content of each compound in the dried membrane and the elution rate of the finally obtained membrane.

[0031]

[Table 1]

Comparative Examples 1 to 12 Except that the radical generator was not added to the last methanol bath, the film formation, drying and drying were performed in the same manner as in Examples 1 to 12.
Heat treatment was performed. Table 2 also shows the content of each compound in the dried membrane and the elution rate of the finally obtained membrane.

Comparative Example 13 Film formation, drying and heat treatment were carried out in the same manner as in Examples 1 to 12, except that the radical generator and the radical crosslinking assistant were not added to the final methanol extraction bath. Table 2 also shows the content of each compound in the dried membrane and the elution rate of the finally obtained membrane.

Comparative Examples 14 to 23 Example 1 was repeated except that the various radical generators shown in Table 1 were added at a concentration of 0.1 mol / liter to the final methanol extraction bath, and no radical crosslinking aid was added. Film forming, drying, and heat treatment were performed in the same manner as in Nos. 1 to 12. Table 2 also shows the content of each compound in the dried membrane and the elution rate of the finally obtained membrane.

[0035]

[Table 2]

Examples 25 to 29, Comparative Examples 24 to 29 Cumene hydroperoxide was added as a radical generator at the concentration shown in Table 2 to the final methanol extraction bath, and p-benzoquinone was used as a radical crosslinking assistant. At the concentrations shown in Table 1. Other than that, film formation, drying, and heat treatment were performed in the same manner as in Examples 1 to 12. Table 3 shows the content of each compound in the dried membrane and the elution rate of the finally obtained membrane.

[Table 3]

[0037]

As is apparent from the above examples, the film obtained by the production method of the present invention is particularly excellent in water resistance and wet heat resistance as compared with the conventional PVA film. The PVA membrane obtained by the production method of the present invention is used for various packaging materials, gas barrier materials, optical films such as polarizing film base materials and filter base materials, and various separation films utilizing the above characteristics. Value is extremely high.

Claims (2)

[Claims] When producing a film comprising a polyvinyl alcohol polymer, 0.05 to 5 mol% of a radical generator and 0.05 to 5 mol% of a repeating unit of the polyvinyl alcohol polymer are used. A method for producing a film, characterized in that the polymer is crosslinked by heat treatment after containing or attaching a radical crosslinking aid. 2. The method according to claim 1, wherein the polyvinyl alcohol-based polymer has an average degree of polymerization of 1000 or more and a degree of saponification of 70 mol% or more.