JPS6044334B2 - Method for manufacturing hydrophilic membrane - Google Patents

Description

Detailed Description of the Invention The present invention relates to a new method for producing a hydrophilic membrane obtained by introducing a sulfone group into an ethylene copolymer, and in particular to a method for producing a hydrophilic membrane with significantly improved permselectivity. This invention relates to a new manufacturing method.

Hydrophilic membranes with ion exchange properties, in which ion exchange groups such as sulfone groups are introduced into polymer resin films, are attracting attention for various uses as functional polymer membranes with various unique permselective properties.

For example, (1) separation and recovery of solutes using diffusion dialysis based on differences in solute concentration, (2) solute separation and recovery technology using electrodialysis using electrical energy, and (3) oxidation-reduction using electrode reactions that occur following electrodialysis. Product manufacturing technology, (4)
Separation techniques such as reverse osmosis and pervaporation, and (5) techniques for use as polymer electrolytes in fuel cell diaphragms, etc. have been studied and some have been put into practical use. In these technical fields, hydrophilic membranes with ion exchange properties are characterized by selective permeability between ions such as ions of opposite signs and ions of the same sign, selective permeability between neutral molecules and ions, and selective permeability between neutral molecules. The selective permeability function for each purpose, such as the selective permeability, is utilized.

Previously, it was already known that a hydrophilic membrane with ion-exchange properties, in which sulfone groups were introduced almost uniformly throughout the interior, could be obtained from an ethylene copolymer film in a short period of time.
It is known from Japanese Patent Publication No. 51-41035, Japanese Patent Publication No. 52-29988, and US Patent No. 392,533.

Similarly, a hydrophilic membrane having ion exchange properties can be obtained from a film made of a resin composition containing an ethylene copolymer and a thermoplastic resin that is relatively inert to the sulfonating agent. , known from US Pat. No. 3,925,33.

Also, Japanese Patent Application No. 1098, No. 1098, Japanese Patent Application No. 114, No. 1983.
No. 684, Patent Application No. 15798-1980, Patent Application No. 1984-9
No. 65(1) proposes a hydrophilic membrane that is an improved hydrophilic membrane obtained by introducing a sulfone group into a conventionally known ethylene copolymer, and a method for producing a hydrophilic membrane. Such a hydrophilic membrane has excellent ion exchange performance and low electrical resistance in an electrolytic solution, as well as (1) excellent barrier properties against organic substances; (2)
It has excellent permselectivity such as excellent barrier properties against anions, and also has practical properties such as (3) being able to handle it in a dry state with almost no change in membrane performance, and (4) being flexible. It has the potential to be applied to a wide variety of fields such as ion exchange membranes, electrolytic separation membranes, dialysis membranes, various battery diaphragms, and separation membranes. The present inventors have arrived at the present invention as a result of extensive studies aimed at further improving the selective permselectivity of a hydrophilic membrane obtained by incorporating a sulfone group into the above-mentioned dry tyrene-based copolymer.

To explain the purpose of the present invention in more detail, the purpose of the present invention is to have low electrical resistance in an electrolytic solution and improve various permselective properties, and in particular, to improve barrier properties against organic substances. There is a particular thing.

To explain the present invention, the method for producing a hydrophilic membrane of the present invention includes 97 to 82 mol% of ethylene and 3 to 18 mol% of ethylene.
0H2-5 [in the formula, R1=H, -CH3, R2=-0C0R3, -COOR4, (where R3=C1 to C, a hydrocarbon group, R4=H, a Cl to C6 hydrocarbon group, an alkali metal and A resin composition containing at least one type of ethylene copolymer selected from ethylene copolymers with a monomer having the structure (ions that can form salts with other carboxylic acid groups) A film made of or a composite film having the film on at least one surface is reacted with a sulfonating agent so that the electrical resistance in dilute sulfuric acid is 0.
01 to 5 Ω·d, and then heat-treated in a state in which at least a part of the sulfone groups of the hydrophilic membrane are -SO3H.

A hydrophilic membrane produced by such a production method has significantly improved permselectivity compared to a hydrophilic membrane obtained by introducing a sulfone group into a conventional ethylene copolymer. To explain in more detail the method for producing the hydrophilic membrane of the present invention, the present invention involves forming a resin composition containing at least one type of ethylene copolymer into a single film or a composite film using a conventionally known film forming method. After forming into a film or the like, if the resin composition contains a plasticizer, the resin composition is subjected to a sulfonation reaction while extracting the plasticizer with a sulfonating agent, or is sulfonated. At least a portion of the plasticizer is extracted with a solvent before sulfonation and
Electrical resistance in dilute sulfuric acid is 0.01-5Ω・d1
Preferably, it is a hydrophilic membrane of 0.05 to 1 Ω·d, and then at least a part of the sulfone groups of the hydrophilic membrane is -SO3
This is a method for producing a hydrophilic membrane with improved selectivity, characterized by carrying out heat treatment in an H state.

And, the ethylene copolymer referred to in the present invention is 97-
82 mol% ethylene and 318 mol% CH2=C
[In the formula, R1=H, -CH3, R2=-0C0R3,
-COOR4, (where R3=C1 to C5 hydrocarbon group,
Ethylene-based copolymerization with a monomer having a structure of R4 = H, Cl to C6 hydrocarbon groups, alkali metals, other metal ions, etc., as well as ions that can form salts with carboxylic acid groups) Within this range, a hydrophilic film having an electrical resistance in dilute sulfuric acid of 0.01 to 5 Ω·d can be obtained with good productivity and high quality.

In the present invention, the ions that can form salts with other carboxylic acid groups include, for example, Mg2+, Ca2+
, Zn2+, etc., trivalent metal ions such as Ae3+, and cations that can form salts with -COO groups such as NFI4+.

Furthermore, in the present invention, the ethylene copolymer composition refers to a composition made of at least one type of ethylene copolymer, a composition in which a relatively inert thermoplastic resin is added to a sulfonating agent, and a composition composed of a relatively inert thermoplastic resin added to the sulfonating agent. A plasticizer that is compatible with the resin component and can be extracted from the film and/or hydrophilic membrane using a solvent and/or a sulfonating agent is mixed therein.

In addition, a film made of an ethylene copolymer composition refers to a single film or a multilayer film formed by molding the ethylene copolymer composition using a normal film molding method, or a single film or a multilayer film formed from the ethylene copolymer composition. It is a composite film made by combining one or more reinforcing materials such as , woven fabric, non-woven fabric, and microporous membrane.

The thermoplastic resin that is relatively inert to the sulfonating agent referred to in the present invention has a significantly slower sulfonation reaction than the above-mentioned ethylene copolymer. There are no particular limitations, but materials that can be easily mixed and dispersed using ordinary plastic processing methods are good because they are easy to produce and produce films with uniform quality, such as low-density polyethylene, Polyolefin resins such as medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, and polybutene-1 are suitable.

Further, in the present invention, the blending ratio of the thermoplastic resin in the ethylene resin composition containing the thermoplastic resin is preferably at most 85% by weight of the total resin components, and more preferably 7% by weight. A hydrophilic film having particularly excellent oxidation resistance and low electrical resistance in an electrolytic solution can be obtained with good productivity when the amount is 15% by weight or more.

In addition, the plasticizer that is compatible with and extractable from the resin component is a plasticizer that is uniformly dispersed in an amount of at least 5 parts by weight per 1 part by weight of the resin component in the melted state of the resin component. However, a thin film can be formed by melt molding, and under the extraction conditions of the plasticizer, a solvent or a sulfonating agent that hardly dissolves the resin component is used before, during or after the reaction. Any material that can be extracted from the film or membrane may be used.

Examples of plasticizers include phthalate esters represented by diethyl flutaate and dioctyl phthalate, as well as linear dibasic acid esters, phosphate esters, epoxy plasticizers, and polyesters. Plasticizers, chlorinated products such as chlorinated paraffin, chlorinated fatty acid esters, etc., which are normally used as plasticizers for plastics, or
At least one additive is selected from various other additives that meet the above requirements and have a plasticizing effect and/or a swelling effect.

The amount of plasticizer added is preferably as large as possible because the time required for sulfonation is shortened, but usually, in order to stably form a thin film, it is necessary to add at most 10 parts of the resin component. 20 parts by weight of plasticizer is suitable, preferably 10 to 100 parts by weight.

In addition, the woven fabric referred to in the present invention is a woven fabric obtained from inorganic or polymeric fibers by weaving methods such as plain weaving, oblique weaving, satin weaving, leno weaving, etc. The number of fibers may be appropriately selected depending on the purpose within a range in which the texture of the fabric does not collapse to an extreme degree during adhesion with the resin composition and/or during handling.

Furthermore, the fiber material is not particularly limited as long as it is relatively inert to the sulfonating agent and does not change significantly either physically or chemically during the heat treatment of the present invention. However, it is necessary to select it appropriately depending on the purpose and use. For example, polyethylene, polypropylene, and fluororesin fibers are preferred because they are relatively inert to sulfonating agents and other chemicals, and have relatively excellent heat resistance. In addition, non-woven fabrics and microporous membranes are similar to woven fabrics, and should be within the range that does not lose their shape extremely during adhesion with the resin composition and/or handling, and should have excellent chemical resistance and heat resistance. The material, thickness, effective conductive area, etc. may be selected as appropriate depending on the purpose.

In the method for producing a hydrophilic membrane according to the present invention, the method for molding the film made of the ethylene copolymer composition includes a molding method performed in ordinary plastic processing, for example, for a single film, compression molding, Flat films or tubular films are produced by extrusion molding, casting, etc., and for multilayer films, various single films are created individually, and then multilayered by compression molding, etc., in the desired combination, or by coextrusion. It is possible to create a multilayer film using a method.

In addition, composite films reinforced with one or more types of reinforcing materials such as woven fabrics, non-woven fabrics, and microporous membranes can be made by forming a single film and then compression molding the reinforcing material and the film or passing it between hot rolls. The reinforcing material may be composited by a method such as extrusion lamination, applying a solution or latex to the reinforcing material, etc., and is not particularly limited, and may be appropriately selected depending on the purpose. In order to introduce sulfone groups into the above-mentioned film, in the case of a film made of a resin composition to which a plasticizer has been added, a solvent is appropriately selected depending on the type of plasticizer used, and most of the resin components from the film are dissolved. After extracting only the plasticizer without extracting the plasticizer, or after containing the plasticizer without extracting it, use fuming sulfuric acid alone, sulfur trioxide, chlorosulfonic acid, etc. diluted with a solvent as necessary, or sulfur trioxide. It is preferable to sulfonate with a complex compound.

The temperature of the sulfonation reaction is suitably 60° C. or less and the reaction time is suitably within 2 hours; if the reaction exceeds these conditions, undesirable side reactions are likely to occur.

Then, by appropriately selecting the type and concentration of the sulfonating agent according to the film thickness, composition, type and presence of reinforcing material, and electrical resistance in the desired electrolyte within these conditions, A sulfone group is introduced so that the film becomes a hydrophilic film with an electrical resistance of 0.01 to 5 Ω·d.

Then, the hydrophilic membrane obtained by the above method is heat-treated in a state in which at least a part of the sulfone groups bonded to the hydrophilic membrane is -SO3H, thereby achieving the desired hydrophilic membrane with excellent permselectivity. membrane can be obtained.

Comparing the hydrophilic membranes obtained by the conventional method and the method of the present invention, which have the same electrical resistance in the electrolytic solution, the hydrophilic membrane obtained by the method of the present invention has a selective permselectivity, especially for ions against organic substances. This means that the permselectivity is significantly superior.

In the present invention, the electrical resistance in dilute sulfuric acid before heat treatment is preferably 0.01 to 5 Ω·d, particularly 0.05 Ω·d.
~1Ω·d is suitable. When the resistance in dilute sulfuric acid exceeds 5Ω・d, the effect of heat treatment is small, and when the resistance is less than 0.01Ω・d, it is difficult to handle the film during heat treatment.
0.01~5Ω・d1 described above, preferably 0.05~
1Ω・CTI is desirable.

In addition, in order to heat-treat the hydrophilic film, it is necessary that at least a part of the sulfone groups bonded to the hydrophilic group be in the -SO3H state, for example, all of the sulfone groups are in the -SO3H state. In the state of metal salt, the effect of heat treatment is difficult to expect. In addition, the heat treatment temperature was 5
The temperature range is preferably 0 to 250°C, especially 100 to 200°C.
C is preferred.

At temperatures below 50°C, the processing time becomes significantly longer;
If the temperature exceeds 0℃, on the other hand, it is necessary to control the temperature extremely short. Therefore, the above-mentioned temperature conditions of 50 to 250℃, preferably 100 to 200℃, are essential for quality stability and productivity. It is suitable from the viewpoint of

In addition, the time required for heat treatment depends on the heat treatment method (conduction heating method, radiation heating method, convection heating method, etc.), the thickness and composition of the hydrophilic film, the type and presence of reinforcing material, before and after heat treatment. It is determined appropriately depending on the electrical resistance in the electrolyte of the hydrophilic membrane, etc., but it is usually preferable to heat it in the range of 3 to 6 particles for reasons such as quality stability and productivity. In addition, in the production method of the present invention, heat treatment after sulfonation includes 1. After sulfonation treatment, the sulfonating agent is washed with sulfuric acid, water, etc., and then heat treatment is performed.
After the sulfonation treatment, the sulfonation agent is washed with sulfuric acid, water, etc., dried, and then heat treated. It is desirable to carry out a method such as processing in the order of washing with water etc., then drying, converting at least part of the sulfonate into -SO3H groups with acid, and then heat treatment. It can be selected as appropriate depending on the ester group content of the ethylene copolymer and the heat treatment method.

Further, the heat treatment method of the present invention includes the above-described heat transfer heating method,
It goes without saying that either the radiation heating method or the convection heating method can be used, and the method may be selected as appropriate depending on the method for treating the hydrophilic film before the heat treatment. The reason why the hydrophilic membrane obtained by the production method of the present invention has significantly superior permselectivity compared to the hydrophilic membrane obtained by the conventional method is currently unclear, but the present invention They estimate that this is due to the following reasons.

By introducing a considerable amount of sulfone groups into a film containing an ethylene copolymer, an electroporous hydrophilic film with low electrical resistance in an electrolytic solution can be obtained.
It is conventionally known.

The above hydrophilic membrane is -0H1 or -COO
Because it has M and -SO3M groups (M=H1 ions that can form salts with alkali metals or other carboxylic acid groups and sulfonic acid groups), water, hydrophilic substances, and cations easily permeate, and conversely, lipophilic substances It also has selective permeability that makes it difficult for large anions to pass through. and,
In the present invention, by heat-treating a hydrophilic film having -SO3H groups, the -SO3H groups undergo some chemical change, resulting in partial hydrophobization and/or partial crosslinking of the hydrophilic film. It is presumed that this improves the selective permselectivity of the membrane.

For example, to describe the case where the selective permeability of hydrophilic substances is improved, the above-mentioned partial hydrophobization and/or partial cross-linking can be applied to substances with different hydrophilic strengths or different molecular or ion sizes. It is surmised that the influence was different, and that the selective permselectivity of the hydrophilic membrane obtained by the conventional method was expressed to a greater extent.

As a result, the hydrophilic membrane obtained by the method of the present invention can be used for all the various uses of hydrophilic membranes obtained by conventional methods, such as electrolytic separation membranes, dialysis membranes, various separation membranes, battery diaphragms, and This enables efficient use in polymer electrolyte membranes for fuel cells, etc.

In carrying out the present invention, it is practically convenient to carry out the above-mentioned heat treatment, then neutralize with an alkaline chemical or the like, wash thoroughly with water and dry before handling. Furthermore, it goes without saying that in order to carry out the present invention under the above conditions, it is possible to process the film in any other desired manner, for example, in other shapes than a continuous film, such as a tube shape, a bag shape, a hollow fiber shape, and the like.

In addition, for the purpose of improving oxidation resistance, chemical resistance, etc., before or after heat treatment, three-dimensional crosslinking before sulfonation or chemical treatment after sulfonation (Japanese Patent Application No. 56-1579
It is also possible to implement a method such as (see No. 8). Hereinafter, in Examples and Comparative Examples, the permselectivity of the hydrophilic membrane obtained by the method of the present invention will be evaluated using methanol, which has high hydrophilicity and has a relatively small molecular size (normally, water with a high electrical resistance in the electrolytic solution). The present invention will be explained in further detail by describing the improvement of the barrier properties of the hydrophilic membranes (which easily permeate hydrophilic membranes).

Throughout this specification, the measurement conditions and test methods for each physical property value are as follows.

(1) Electrical resistance (Ω・CIL) specific gravity in dilute sulfuric acid is 1.2
Measuring device (JIS) filled with dilute sulfuric acid (At23°C)
C23l3), set the sample on the
When a DC constant current of mA/CTl is applied, the voltage drop due to the sample is measured, and the value calculated from the following formula is used as the electrical resistance in dilute sulfuric acid.

[Before measurement, immerse the sample in dilute sulfuric acid with a specific gravity of 1.2 (At23°C) for at least 24 hours] R = Electrical resistance of the sample in dilute sulfuric acid (Ω・CTl) V1 = When the sample is not set Voltage drop (■) V2 = Voltage drop when sample is set (■) (2) Permeability coefficient of methanol Dilute sulfuric acid (A) with a specific gravity of 1.2 (At23°C) and dilute sulfuric acid (A) with a specific gravity of 1.2 (At23°C) The solution (B), which is a mixture of dilute sulfuric acid and 4V01% methanol in C), is brought into contact with the sample through the sample, and the liquid (B) is separated from the solution (A) at a temperature of 23°C.
This is the value obtained by measuring the amount of methanol permeated into the liquid and calculating the methanol permeation coefficient according to a conventional method.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 4 A copolymer of 94.2 mol% ethylene and 5.8 mol% methyl methacrylate was saponified (saponification degree = 60 mol%) and neutralized (neutralization degree = 30 mol%). %) -COO
20% by weight of high-density polyethylene (density = 0.955 Da/D,
Approximately 3 powders of MI=7) were kneaded at 190°C in a kneader, and then 4 parts by weight were mixed with 100 parts by weight of the resin mixture.
Liquid paraffin (manufactured by Kokusan Kagaku Co., Ltd.) was added to the weighing section, and the mixture was further kneaded at 190°C for about 3 times.

Next, the resin composition was thermoplasticized in an extruder at a temperature of 180°C, extruded through a circular die, and rapidly cooled with water at a temperature of 20°C from the surroundings to a thickness of 40 μm.
A thick film was obtained. Then, the above film was immersed in 1,1,1-trichloroethane at room temperature for about 1 minute to extract liquid paraffin, and then placed in fuming sulfuric acid containing 12% free sulfur trioxide and treated at 35°C for 7 minutes. , concentrated sulfuric acid, diluted sulfuric acid, and water in this order, neutralized with an aqueous potassium hydroxide solution, washed with water, and dried to obtain a hydrophilic membrane.

The electrical resistance of this hydrophilic membrane in dilute sulfuric acid is 0.15Ω・c
It was ai. Next, this hydrophilic membrane was treated with a 1N aqueous hydrochloric acid solution to convert most of the -SO3K groups into -SO3H groups, washed with distilled water, and then dried at room temperature.

Next, this hydrophilic membrane was dried in a hot air dryer at 150°C.
Heat treatment was performed while changing the treatment time.

As shown in Table 1, the result was a hydrophilic membrane with extremely excellent methanol barrier properties despite having low electrical resistance in dilute sulfuric acid. Comparative Examples 1 to 4 Examples 1 to 4 were prepared by variously changing the sulfonation conditions of Example 1.
A hydrophilic membrane having almost the same electrical resistance in dilute sulfuric acid as in Example 4 was prepared, and the methanol barrier property was measured. It was inferior.

(The hydrophilic membranes of Comparative Examples 1 to 4 were not subjected to the heat treatment performed in Examples 1 to 4.) Examples 5 to 7 92.3 mol% of ethylene and 7.7 mol of this acrylic ester For 4 mass% of copolymer (MI=2) with
High density polyethylene (density = 0.965y/C4, M
I=13) 60% by weight was melt-kneaded in a kneader in the same manner as in Example 1, and then 66.7 parts by weight of liquid paraffin was added to 100 parts by weight of the resin mixture and further melt-kneaded.

Next, the resin composition was extrusion-molded using an extruder equipped with a circular die to obtain a film having an original thickness of 30 μm.

After extracting the plasticizer in the same manner as in Example 1, the powder was sulfonated at a temperature of 35°C, followed by washing in the order of concentrated sulfuric acid, diluted sulfuric acid, and water, followed by hydroxylation. After treatment with an aqueous potassium solution, the membrane was washed with water and dried to obtain a hydrophilic membrane.

The electrical resistance of this hydrophilic membrane in dilute sulfuric acid is 0.50Ω・d
It was hot. Next, this hydrophilic membrane was treated with an aqueous hydrochloric acid solution as in Example 1 to change most of the -SO3K groups to -SO3H groups, washed with distilled water, and then dried at room temperature.

Next, this hydrophilic membrane was dried in a hot air dryer at 150'C.
Heat treatment was performed while changing the treatment time.

As shown in Table 3, the membrane was hydrophilic and had excellent methanol barrier properties despite having a low electrical resistance in dilute sulfuric acid. Comparative Examples 5 to 7 Examples 5 to 7 were prepared by variously changing the sulfonation conditions of Example 5.
A hydrophilic membrane having almost the same electrical resistance in dilute sulfuric acid as in Example 7 was prepared, and the methanol barrier property was measured. It was inferior.

(The hydrophilic membranes of Comparative Examples 5 to 7 were not subjected to the heat treatment performed in Examples 5 to 7.) Examples 8 to 12 The electrical resistance in dilute sulfuric acid was 0.1
A hydrophilic film of Ω·Cd was heat-treated under the conditions shown in Table 5, and as a result, a hydrophilic film with excellent methanol barrier properties was obtained.

These hydrophilic membranes had significantly superior permselectivity compared to hydrophilic membranes obtained by conventional methods having the same electrical resistance in dilute sulfuric acid. Examples 13 to 16 A 40 pm thick film (Examples 13 and 14) made of a copolymer of 92.9 mol% ethylene and 7.1 mol% vinyl acetate (MI=2.5) and Example 1 A 40 μm thick film made of the ethylene copolymer used in
Examples 15 and 16) were sulfonated by a conventionally known method, and most of the sulfone groups were in the state of -SO3H,
As a result of heat treatment performed under the conditions shown in Table 6, the resulting hydrophilic membrane had significantly superior methanol barrier properties compared to hydrophilic membranes obtained by conventional methods.

Example 17 The composition ratios of the ethylene copolymer and high-density polyethylene used in Example 5 were changed to 8% by weight and 20% by weight, respectively, and 43 parts by weight was added to 10 parts by weight of the resin component. Dioctyl phthalate was added to the resin mixture to form a 50 μm thick film.

The above film was irradiated with an electron beam with a gel fraction of 8=15.
Polypropylene woven fabric after cross-linking by irradiation to achieve
50 denier yarn (multifilament) - 50 mesh weave] was sandwiched between two of the films 12
Pressure bonding was carried out at a temperature of 0°C. After cooling, the composite film was immersed in 1,1,1-trichloroethane for 3 minutes,
Liquid paraffin was extracted, dried at room temperature, and then sulfonated to produce a hydrophilic membrane with an electrical resistance of 0.2 Ω·d in dilute sulfuric acid. Most of the sulfone groups are heated at 150°C for 3 minutes in the state of -SO3H,
A hydrophilic membrane having an electrical resistance of 0.63 Ω in dilute sulfuric acid and a methanol permeability coefficient of 4.8×10 −4 C7 rL/Min was obtained.

This hydrophilic membrane has the following characteristics compared to hydrophilic membranes obtained by conventional methods:
It was extremely excellent in permselectivity. 1 Gel fraction (%) Value obtained by dissolving the resin in boiling p-xylene and calculating the proportion of the undissolved portion using the following formula Weight of only the resin portion that does not contain plasticizer, inorganic filler, etc. Examples 18 A 40 μm thick film was made from the ethylene copolymer used in Example 1.

In addition, on the other hand, dioctyl phthalate, anhydrous finely divided silicic acid, and powdered high-density polyethylene (density = 0.950y/Cd
．． ．． A microporous membrane having a thickness of 200 pm was molded from the resin composition obtained from MI=1) by a conventionally known method.

Next, the microporous membrane was sandwiched between the two thin films and bonded under pressure at a temperature of 1100C.

Next, the above composite film was heated to 100% by tenter method.
After stretching 3 x 3 times at a temperature of 150°C, it was subjected to sulfonation treatment to form a hydrophilic film with an electrical resistance of 0.18Ω・d in dilute sulfuric acid. When heat treated for 3 minutes under the temperature conditions of
A hydrophilic membrane of 5.1×10 −4 cm/min was obtained.

This hydrophilic membrane has the following characteristics compared to hydrophilic membranes obtained by conventional methods:
It was found that the permselectivity was significantly superior.

Comparative Example 8 As a result of heat treatment for 1 hour and 3 hours at a temperature of 200°C in a state where all the sulfone groups of the hydrophilic membrane prepared in Example 8 before heat treatment were in the -SO3K state, the electrical resistance in dilute sulfuric acid was slightly increased, but the methanol permeability coefficient remained almost unchanged, and the permselectivity was not improved.

Claims (1)

[Claims] 1 97-82 mol% ethylene and 3-18 mol% ▲
There are mathematical formulas, chemical formulas, tables, etc. ▼ [In the formula, R_1=H, -
CH_3, R_2=-OCOR_3, -COOR_4,
(However, R_8 = hydrocarbon group of C_1 to C_5, R_4 =
At least one type of ethylene copolymer selected from ethylene copolymers with monomers having a structure of [H, C_1 to C_6 hydrocarbon groups, alkali metals, and other ions that can form salts with carboxylic acid groups]] A film made of a resin composition containing at least an ethylene copolymer or a composite film having at least one layer of the film is reacted with a sulfonating agent, and the electrical resistance in dilute sulfuric acid is 0.01 to 5 Ω·c.
1. A method for producing a hydrophilic membrane, which comprises forming a hydrophilic membrane of m^2 and then heat-treating the hydrophilic membrane in a state where at least a part of the sulfone groups is -SO_3H. 2 Electrical resistance in dilute sulfuric acid is 0.05 to 1Ω・cm^2
A method for producing a hydrophilic membrane according to claim 1. 3. The method for producing a hydrophilic membrane according to claim 1 or 2, characterized in that the heat treatment is carried out under a temperature condition of 50 to 250°C. 4. The resin composition contains at least one of the ethylene copolymers.
4. A method for producing a hydrophilic membrane according to any one of claims 1 to 3, which contains a thermoplastic resin and other thermoplastic resins. 5. Any one of claims 1 to 4, wherein the composite film comprises a film made of the resin composition and one or more reinforcing materials selected from woven fabrics, nonwoven fabrics, and microporous membranes. A method for producing a hydrophilic membrane as described in section. 6 A patent claim in which the film made of the resin composition is a film made of a mixture of a resin component containing at least one type of the ethylene copolymer and a plasticizer that is compatible with and extractable from the resin component. The method for producing a hydrophilic membrane according to any one of items 1 to 5 above.