JPH0352778B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an ion exchange membrane, and more particularly to a novel method for producing an ion exchange membrane, which comprises employing a specific base material and a specific polymerization method.

Ion exchange membranes, such as cation exchange membranes with cation exchange groups such as sulfonic acid groups and carboxylic acid groups, or anion exchange membranes with anion exchange groups such as quaternary ammonium groups, are used in various electrolytic diaphragms, electrical A wide range of applications have been proposed, including dialysis membranes, diffusion dialysis membranes, fuel cell diaphragms, and various waste liquid treatment membranes. Therefore, in the case of a practical ion exchange membrane,
Mainly from the viewpoint of mechanical strength, it is generally considered desirable to support the ion exchange resin in the form of a membrane on the base material. As a method for supporting an ion exchange resin on a base material in the form of a membrane, a method is known in which a base material such as cloth is lined with an ion exchange membrane using a hot press method and laminated like embedding. Various methods have been proposed in the past, in which the polymer is impregnated onto a substrate, polymerized, and subjected to an ion-exchange group introduction reaction if necessary, either as it is or after partial polymerization if necessary.

In the method for manufacturing an ion exchange membrane, which comprises impregnating and supporting a polymerizable monomer on a base material, polymerizing the monomer, and performing an ion exchange group introduction reaction if necessary, depending on the type of base material, The affinity with the ion exchange resin is low, and therefore the resulting ion exchange membrane may have insufficient mechanical strength and electrochemical properties. In particular, when the base material is made of olefin polymers such as polyethylene and polypropylene, or fluorinated olefin polymers such as tetrafluoroethylene, trifluorochloroethylene, and vinylidene fluoride, heat resistance, chemical resistance, etc. Although an ion exchange membrane excellent in this respect can be expected, conventional polymerization methods encounter the above-mentioned problems. For the purpose of solving such problems, Japanese Patent Publication No. 57-30136, Japanese Patent Publication No. 59-14047,
As described in US Pat. No. 4,414,090, etc., a method has been proposed in which a polymerizable monomer is graft-polymerized onto a base material by employing ionizing radiation irradiation as a polymerization means.

However, as pointed out in the above-mentioned Japanese Patent Publication No. 57-30136, when using the ionizing radiation irradiation polymerization method, many In this case, the base material itself deteriorates, and as a result, it is difficult to obtain an ion exchange membrane with sufficient mechanical strength. In Japanese Patent Publication No. 57-30136, a method is employed in which a 3 to 80% by weight graft polymerized layer is formed on a base material, and an ion exchange resin is supported through this polymerized layer.

In addition, Special Publication No. 8857 and Special Publication No. 56-8857
Publication No. 34014 describes an ion exchange membrane based on polypropylene fibers or cloth.
This method employs a pre-irradiation method under specific conditions or a short-time low-temperature co-irradiation method based on the discovery of a unique phenomenon in polypropylene related to radiation graft polymerization. Special Publication No. 56-8857 and Special Publication No. 1988
The ion exchange membrane obtained by the method described in Publication No. 34014 has excellent mechanical strength and chemical properties because the base material and the membrane forming layer are firmly bonded substantially through graft polymerization. It is said to have long-term stable properties.

According to the research of the present inventor, in the method of employing a base material made of a fluorinated olefin polymer, impregnating the base material with a polymerizable monomer and polymerizing it, heating in the presence of a polymerization initiator is not possible. It has been found that when polymerization is used, the resulting ion exchange membrane becomes extremely fragile. That is, styrene, divinylbenzene,
When a polymerizable monomer such as chloromethylstyrene is impregnated and supported, heated and polymerized, and the resulting film is subjected to sulfonation or quaternary ammonium formation, the base material and the generated ion exchange resin may come into contact with each other during the reaction process or handling. The problem is that it peels off easily and, furthermore, the ion exchange resin produced is brittle, so cracks and micro-cracks easily occur. In addition, when the ionizing radiation irradiation polymerization method is adopted in order to overcome the above-mentioned difficulties in thermal polymerization, if all the impregnated and supported polymerizable monomers are polymerized under the irradiation of ionizing radiation, the substrate itself will deteriorate. Ultimately, an ion exchange membrane with sufficient mechanical strength cannot be obtained.

The present invention was completed based on the recognition of the above problems, and is an ion exchange method in which a base material is impregnated and supported with a polymerizable monomer, the monomer is polymerized, and if necessary, an ion exchange group introduction reaction is performed. In the method for producing a membrane, a material made of a fluorinated olefin polymer is used as a base material, and the polymerizable monomer impregnated and supported on the base material is partially polymerized by irradiation with ionizing radiation in the first stage, and then in the second stage. The present invention provides a novel method for producing an ion exchange membrane, characterized in that the remainder of the membrane is polymerized by heating in the presence of a polymerization initiator.

In the present invention, the polymerizable monomer impregnated and carried on a specific base material is partially polymerized by irradiation with ionizing radiation in the first stage, and then the remaining part is polymerized by the action of a polymerization initiator in the second stage without irradiation with ionizing radiation. It is important to polymerize by heating. When only one of the ionizing radiation irradiation polymerization method and the heating polymerization method is used, the resulting polymer may be firmly bonded to the base material due to deterioration of the base material or brittleness or peeling of the formed film-forming resin layer. It is difficult to obtain ion exchange membranes with sufficient mechanical strength.

Accordingly, in the present invention, a wide range of conventionally known or well-known polymerizable monomers can be employed. A desired polymerizable monomer can be selected and employed depending on the type of the intended ion exchange membrane or whether or not an ion exchange group introduction reaction is necessary. A preferred specific example is a polymerizable monomer mixture containing styrene, chloromethylstyrene and divinylbenzene as essential components. In particular, the use of styrene and chloromethylstyrene is disadvantageous if one of them is not used in order to form a strong ion exchange membrane with the resulting polymer firmly bonded to a specific base material. Therefore, it is a preferred embodiment of the present invention. In the present invention, by employing a specific base material and a specific polymerization method, the difficulty that the base material and the film-forming resin layer easily peel off can be solved, or the film-forming resin layer itself can be made strong and easy to use. Problems such as the occurrence of cracks and microcracks are also eliminated.

The preferred polymerizable monomer mixture described above is 10-80% styrene, 10-80% chloromethylstyrene, 1-25% divinylbenzene, based on the total weight of styrene, chloromethylstyrene and divinylbenzene.
It is preferable to contain. The preferred range of this content differs slightly depending on the type of ion exchange membrane intended, but for example, if the purpose is a cation exchange membrane, it is preferable to use styrene at the higher end of the above range, or for an anion exchange membrane. When the purpose is a membrane, it is possible to select chloromethylstyrene from the larger end of the above range. In any case, if too much divinylbenzene is used, it will increase the electrical resistance of the resulting ion exchange membrane, and if it is too small, it will be disadvantageous to achieve mechanical strength, but it is usually possible within the above range. It is preferable to use as little as possible, especially divinylbenzene5.
Approximately 15% is suitable. If chloromethylstyrene is used in too large a quantity, the resin layer will swell and collapse when used as an anion exchange membrane, and the resistance will be high when used as a cation exchange membrane. Also, if too little chloromethylstyrene is used, the resistance will be high if the purpose is an anion exchange membrane, and the resin layer will swell and collapse if the purpose is a cation exchange membrane. do. Therefore, preferably 20-65%
The degree is selected. Furthermore, for the same reason, styrene is preferably selected to have a content of about 20 to 65%.

Furthermore, in the present invention, it is important to use a fluorinated olefin polymer as the base material. Adoption of such a base material is advantageous from the viewpoint of heat resistance and chemical resistance of the intended ion exchange membrane. As the base material, a film-like base material can be adopted as long as it is made of the above-mentioned materials, but normally, a thin film-like porous base material such as a woven fabric such as cloth or net, a non-woven fabric, or a porous film is suitable. will be adopted. Although the reason for this is not necessarily clear, the adoption of a specific polymerization method improves the affinity or reactivity of the polymerizable monomer with the material of the base material, and improves the affinity and reactivity of the polymerizable monomer with the material of the film forming layer produced as a result of the polymerization reaction. An ion exchange membrane that is firmly bonded to the base material can be obtained. The base material is usually employed in the form of a thin film having a thickness of about 5 to 500 microns, preferably about 20 to 300 microns. In the case of porous base materials, the porosity is 90% or less, especially 80%, mainly from the viewpoint of mechanical strength.
% or less. In addition, porosity is (1 - apparent specific gravity of base material ÷ true specific gravity of base material) ×
100, and the apparent specific gravity indicates the specific gravity taking into consideration the space occupied by the base material, and the true specific gravity indicates the specific gravity of the material itself of the base material.

In the present invention, various examples of the fluorinated olefin polymer constituting the base material include polymers or copolymers such as tetrafluoroethylene, trifluorochloroethylene, vinylidene fluoride, and hexafluoropropylene. , specifically polytetrafluoroethylene,
Polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene chloride copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer Examples include merging. In particular, from the viewpoint of effects related to the adoption of the above specific polymerization means, ethylene-tetrafluoroethylene copolymers, ethylene-tetrafluoroethylene chloride copolymers, propylene-tetrafluoroethylene copolymers, etc. An olefin-fluorinated olefin copolymer such as a fluorinated olefin copolymer can be suitably employed.

In the present invention, the polymerizable monomer mixture is impregnated and supported on the above-mentioned specific base material and polymerized, but there is no particular reason to limit the polymerization conditions. However, it is usually preferable to employ polymerization conditions that allow graft polymerization with the base material to occur. For example, a method may be employed in which the base material is pretreated by irradiation with ionizing radiation, or a simultaneous irradiation method may be employed in which the base material impregnated and supported with a polymerizable monomer is irradiated with ionizing radiation for polymerization. In the present invention, as described above, the polymerizable monomer impregnated and supported on the base material is partially polymerized by irradiation with ionizing radiation in the first stage, and heated in the presence of a polymerization initiator in the latter stage (irradiation with ionizing radiation). A polymerization method in which the remainder is polymerized (without polymerization) can be preferably employed.

Therefore, when the polymerizable monomer mixture is partially polymerized by irradiation with ionizing radiation such as gamma rays or electron beams, the conversion rate of the polymerization reaction is about 80% or less, preferably 10 to 70%, especially about 30% or more. It is desirable to select If irradiation conditions that excessively increase the polymerization reaction conversion rate at this stage are adopted, the base material itself will deteriorate due to ionizing radiation, and as a result, it will be difficult to obtain an ion exchange membrane with sufficient mechanical strength. Become. Then, residual polymerization is carried out by heating in the presence of a polymerization initiator such as benzoyl peroxide without irradiation with ionizing radiation. In a normal polymerization operation, a method is adopted in which a polymerizable monomer mixture to which a polymerization initiator is added is impregnated onto a base material, and a first step of polymerization is performed by irradiation with ionizing radiation, followed by a second step of heating polymerization.

As the ionizing radiation, gamma rays from Co-60 or Cs-127 sources, or electron beams from an electron beam accelerator are preferably used, with a dose rate of 10 ² to 10 ⁸ rad/sec,
Preferably, the irradiation rate is 10 ⁵ to ^{10 7} rad/sec. The irradiation dose is selected so as to obtain the above-mentioned polymerization reaction conversion rate, and the irradiation temperature and irradiation time are similarly selected. Usually below 60℃, preferably 10~
0.5 to 48 hours, preferably 1 to 48 hours at a temperature of about 40℃
By irradiating for about 20 hours, the desired polymerization reaction conversion can be achieved at an irradiation dose of 0.5 to 10 Megarads, preferably 1.5 to 8 Megarads. In addition, there is no particular reason to limit the conditions for the thermal polymerization in the latter stage, but it is usually heated to a temperature above which the added polymerization initiator can act actively, and the remaining thermal polymerization is carried out to complete the polymerization. . For example, when a polymerization initiator such as benzoyl peroxide is used,
It is desirable to carry out heating polymerization at 150°C, preferably about 80-120°C for 0.5-12 hours. By using a polymerization initiator that is active at low temperatures, it is possible to lower the heating temperature and shorten the polymerization time.

In the present invention, the polymerizable monomer mixture includes polymerizable monomers other than the above three preferred components, such as acrylic acid, methacrylic acid, hydroxyacrylate, hydroxymethacrylate, vinylpyridine, alkyl-substituted vinylpyridine, acrylonitrile, butadiene, isoprene, and vinyltoluene. , ethylvinylbenzene, etc. may also be added, and an appropriate organic solvent such as tetrahydrofuran, benzene, etc. may be used as a solution. Furthermore, before the polymerizable monomer mixture is impregnated and supported on the base material, it is partially polymerized in advance,
Alternatively, it is also possible to use a material blended with polystyrene, nitrile-butadiene rubber, or the like.

When a base material is impregnated with a polymerizable monomer mixture and polymerized, the monomer is impregnated between polyester films, glass plates, aluminum foils, etc. that are inert to the polymerization reaction and can be peeled off after the polymerization reaction is completed. The method of sandwiching the base materials can be suitably employed in the present invention. For example, it is preferable to sandwich the base material impregnated and supported with the polymerizable monomer mixture between polyester films such as polyethylene terephthalate film to carry out the above-mentioned first and second stage polymerization, and also to conduct the polymerization between the base material impregnated with the monomer and the polyester film. It is also possible to laminate the films and subject them to the polymerization operation as a roll with the substrate side facing inside. Thus, when heating polymerization is performed subsequent to the first-stage polymerization by ionizing radiation irradiation, it is also possible to carry out the heating polymerization in warm water. Furthermore, when impregnating and supporting a polymerizable monomer mixture on a base material, it is also effective to use a reduced pressure operation.

In the present invention, the polymer impregnated and supported on a base material and polymerized, in the case of a suitable three-component mixture, is subjected to an ion exchange group introduction reaction to form an ion exchange membrane. It is also possible to form an ion exchange membrane directly by blending an ion exchange group-containing compound with the polymerizable monomer mixture. Usually, after the above-mentioned first-stage and second-stage polymerization reactions are completed, cation exchange groups or anion exchange groups are introduced by conventionally known or well-known means to produce the desired ion exchange membrane. For example, a method of introducing a sulfonic acid type cation exchange group using a sulfonating agent such as concentrated sulfuric acid or chlorosulfonic acid, or a method of aminating a chloromethyl group with a tertiary amine to introduce a quaternary ammonium type anion exchange group. Methods and the like may be exemplified.

The ion exchange membrane obtained by the method of the present invention is
By using a specific base material, it has superior heat resistance and chemical resistance compared to conventional ion exchange membranes, and by using a specific polymerization method, it has sufficient mechanical strength to firmly bond the membrane forming layer and base material. It can be made into an ion exchange membrane with strength. Naturally, electrical properties such as effective resistance, transference number, ion selectivity, etc. can be adjusted as appropriate. Therefore, the ion exchange membrane of the present invention can be used in a wide range of applications that have been proposed for conventional cation exchange membranes and anion exchange membranes, and its applications will further expand by taking advantage of the above-mentioned excellent properties and advantages. in particular,
Examples of uses include diaphragms for fuel cells, diaphragms for various electrolysis, diaphragms for redox batteries, membranes for acid recovery and concentration, membranes for alkali recovery and concentration, membranes for high-temperature electrodialysis, membranes for high-temperature diffusion dialysis, and membranes for double decomposition.

Examples of the present invention will be described in more detail below, but the present invention is not limited by such explanations, and appropriate additions and changes may be made without departing from the purpose and spirit of the present invention. It goes without saying that this is possible. Note that the proportions in the examples indicate weight proportions unless otherwise specified. Further, various physical properties of the ion exchange membrane were measured as follows.

Effective resistance: sandwiching a membrane between two-chamber cells,
Fill both chambers with 0.5N NaCl solution at 1000c/s
Measure the resistance of the entire cell using an AC bridge, then remove the membrane and measure the resistance of only the solution. The total resistance R of the membrane is determined from the difference between both resistances, and the effective resistance Rm is obtained using the following formula.

Rm=R・S (Ω−cm ² ) S: membrane area Transference number: sandwich the membrane between two-chamber cells,
Fill both chambers with a solution of 0.5NKCl/2.5NKCl and measure the electromotive force between the two solutions using an agaric electrode to determine the transference number.

Strength (bursting strength): Using a Schieren bursting strength tester, pressure is applied through a thin rubber membrane using glycerin as a pressure medium, and the maximum pressure at which the membrane bursts is measured.

Example 1 A cloth woven from an ethylene-tetrafluoroethylene copolymer (thickness 145 μ, weight 81.3 g/m ² ) was used as a base material, and this base material was coated with 8% divinylbenzene, 49% styrene, and chloride. A syrup with a composition of 43% methylstyrene is impregnated with 2% benzoyl peroxide, and the impregnated cloth is sandwiched and fixed between two polyester films and two glass plates. Furthermore, radiation polymerization was performed by irradiating cobalt-60 with 3 megarads of gamma rays at room temperature, and then at 90°C.
Heat polymerization in warm water for 6 hours to form a polymer film. This polymerized membrane is sulfonated in 98% concentrated sulfuric acid at 60°C for 16 hours to obtain a cation exchange membrane.

The performance of the completed cation exchange membrane is determined by its effective resistance.
17Ω−cm ² (in 0.5NKCl), thickness 152μ, transference number 87%,
The bursting strength was 5 kg/cm ² or more.

Example 2 Divinylbenzene 11 was added to the same base material as in Example 1.
%, styrene 28%, and chloromethylstyrene 61% was impregnated with 2% benzoyl peroxide, and a polymer film was obtained in the same manner as in Example 1. This polymerized film was coated with 1N trimethylamine.
Amination treatment is performed at 60°C for 16 hours to obtain an anion exchange membrane.

The performance of the completed anion exchange membrane is as follows: effective resistance 6.8Ω-cm ² , thickness 174μ, transference number 85%, and bursting strength 5.
It was more than Kg/ ^cm2 .

Comparative Example 1 A syrup with a composition of 9% divinylbenzene, 43% styrene, and 48% chloromethylstyrene was added with 2% benzoyl peroxide, and the same ethylene-tetrafluoroethylene copolymer thread as in Example 1 was prepared. A woven cloth was impregnated with the solution, fixed in the same manner as in Example 1, and heated and polymerized in warm water at 90° C. for 12 hours to form a polymer film. Using this polymer film, the same procedure as in Example 1 was carried out.
Sulfonated with 98% concentrated sulfuric acid to create a cation exchange membrane.
In the same manner as in Example 2, it was aminated with 1N trimethylamine to obtain an anion exchange membrane. Although polymerized membranes were obtained that were indistinguishable from Examples 1 and 2 at first glance, when an ion exchange membrane was obtained by introducing an exchange group, the resin layer and base material of each membrane peeled off.

Comparative Example 2 A syrup having the same composition as Comparative Example 1 was added to Example 1.
It was impregnated into a cloth woven with threads of the same ethylene-tetrafluoroethylene copolymer and fixed. When this film was irradiated with cobalt-60 radiation until polymerization was completed (approximately 8 megarads) to form a polymer film, the resulting polymer film became brittle and collapsed.

Claims (1)

[Scope of Claims] 1. A method for producing an ion exchange membrane comprising impregnating and supporting a polymerizable monomer on a base material, polymerizing the monomer, and performing an ion exchange group introduction reaction if necessary, in which a fluorinated base material is used. Using an olefin polymer, the polymerizable monomer impregnated and supported on the base material is partially polymerized by irradiation with ionizing radiation in the first stage, and the remaining part is polymerized by heating in the presence of a polymerization initiator in the second stage. A method for producing an ion exchange membrane, characterized by: 2. The manufacturing method according to claim 1, wherein the conversion rate of the polymerization reaction of the polymerizable monomer in the first stage by irradiation with ionizing radiation is 80% or less.