JPH0352777B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an ion exchange membrane, and more particularly, to a novel method of manufacturing an ion exchange membrane, which comprises employing a combinatorial mixture of a specific base material and a specific polymerizable monomer. Regarding the manufacturing 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 and laminated in a manner similar to embedding. Alternatively, various methods have been proposed in the past, in which, after partially polymerizing if necessary, the polymer is impregnated and supported on a base material, polymerized, and if necessary, an ion exchange group introduction reaction is performed.

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.

According to the research of the present inventor, styrene, chloromethylstyrene, divinylbenzene, etc. have been known as polymerizable monomers used in the production of ion exchange membranes, but olefinic polymers and fluorinated It has been newly discovered that when a base material made of an olefin polymer is used, there are the following problems. That is, as in the above-mentioned Japanese Patent Publication No. 57-30136, the base material is subjected to a specific pretreatment such as irradiation with ionizing radiation, and then impregnated with a specific monomer solution to be grafted and polymerized; is impregnated with a specific monomer solution and polymerized by irradiation with ionizing radiation to form a specific polymer layer grafted with 3 to 80% by weight on the base material, and the ion exchange resin is applied through this polymer layer. It is said that it is necessary to adopt measures such as support. In addition, based on the discovery of a unique phenomenon of polypropylene related to radiation graft polymerization, there are
As in Publication No. 34014, it is said that it is necessary to adopt a pre-irradiation method under specific conditions or a short-time low temperature co-irradiation method. Therefore, in the production of cation exchange membranes using styrene and divinylbenzene or the production of anion exchange membranes using chloromethylstyrene and divinylbenzene, there are cases where the base material deteriorates or the membrane forming layer peels off. However, by adopting these three components as essential components, an ion exchange membrane with sufficient mechanical strength can be obtained smoothly and advantageously. This is what we discovered.

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, an olefin polymer and/or a fluorinated olefin polymer is used as the base material, and the three components of the polymerizable monomers are styrene, chloromethylstyrene, and divinylbenzene as essential components. The present invention provides a novel method for producing an ion exchange membrane characterized by using a mixture of:

In the present invention, it is important to impregnate and support a mixture on a base material and polymerize it, which has three essential components: styrene, chloromethylstyrene, and divinylbenzene. In particular, if either styrene or chloromethylstyrene is not used, it will be difficult to produce an ion exchange membrane with the resulting polymer firmly bonded to the base material. In the case of adopting a component system, there are problems in that the base material and the film-forming resin layer easily separate from each other, or the film-forming resin layer itself is extremely fragile and easily generates cracks and micro-cracks.

In the present invention, the polymerizable monomer mixture impregnated and supported on the substrate includes 10 to 80% styrene, 10 to 80% chloromethylstyrene, based on the total weight of styrene, chloromethylstyrene, and divinylbenzene.
Preferably it contains 1 to 25% divinylbenzene. 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, too much divinylbenzene will increase the electrical resistance of the resulting ion exchange membrane, and too little amount will cause
Although it is disadvantageous to achieving mechanical strength, it is usually preferable to adopt the lowest possible value within the above range.
In particular, about 5 to 15% divinylbenzene is suitable. If chloromethylstyrene is used in too large a quantity, the flexibility of the resin layer will decrease and cracks will easily occur, and if the purpose is an anion exchange membrane, the resin layer will swell and collapse; If the purpose is to achieve this, the problem arises that the resistance is high. If the amount of chloromethylstyrene is too small, the bond between the base material and the resin layer will be weak and it will be easy to peel off, and if the purpose is an anion exchange membrane, the resistance will be high. When intended as an exchange membrane, the resin layer swells and collapses. 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%.

Therefore, in the present invention, it is important to employ as the base material an olefin polymer and/or a fluorinated olefin polymer.
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 polymerizable monomer mixture containing three specific components as essential components improves the affinity or reactivity for the above-mentioned base material, and improves the film produced as a result of the polymerization reaction. An ion exchange membrane in which the forming layer polymer and the base material are firmly bonded can be obtained. The thickness of the base material is usually 5~
It is employed in the form of a thin film of about 500 microns, preferably about 20 to 300 microns. In the case of a porous base material, the porosity is preferably 90% or less, particularly 80% or less, mainly from the viewpoint of mechanical strength. 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.

Examples of olefin-based polymers include homopolymers of olefins such as ethylene, propylene, butene, and methylpentene, mutual copolymers of these olefins, and copolymers of olefins with other monomers. Examples include high-density polyethylene, low-density polyethylene, and polypropylene. In addition, various examples of fluorinated olefin polymers include polymers or copolymers such as tetrafluoroethylene, trifluorochloroethylene, vinylidene fluoride, and hexafluoropropylene.
Specifically, polytetrafluoroethylene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, ethylene-trifluorochloroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer , propylene-tetrafluoroethylene copolymers, and the like.

In the present invention, a specific 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 method. However, it is usually preferable to employ a polymerization method that causes graft polymerization with the base material. 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 a preferred embodiment of the present invention, 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 second stage. A polymerization method in which the remaining portion is polymerized (without irradiation) can be preferably employed.

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 80% or less, preferably 5 to 50%, particularly 10 to 40%. It is desirable to select the degree. 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 5 Megarads. 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-mentioned three essential components, such as acrylic acid, methacrylic acid, hydroxyacrylate, hydroxymethacrylate, vinylpyridine, alkyl-substituted vinylpyridine, acrylonitrile, butadiene, isoprene, vinyltoluene, It is also possible to add ethylvinylbenzene, etc., and it may be used as a solution in an appropriate organic solvent such as tetrahydrofuran or benzene. 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 impregnating and carrying a polymerizable monomer mixture on a base material and polymerizing it, 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 substrate and polymerized is subjected to an ion exchange group introduction reaction in the case of an essential three-component mixture 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. Method of creating a polymeric membrane capable of cyclization reaction
A cyclization reaction is performed using AlCl ₃ and SnCl ₄ as catalysts to form a crosslinked structure, and then SnCl ₄ is added to chloromethyl ether.
Examples include a method in which the membrane is chloromethylated and quaternary aminated to form an anion exchange membrane.

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 polymerizable monomer mixture, the membrane forming layer and base material are strongly bonded. It can be an ion exchange membrane with mechanical 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. Specifically, applications 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. may be exemplified.

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 Polypropylene cloth (thickness 112μ, weight 44.2g/
m ² ) base material with 10% divinylbenzene and styrene.
A syrup with a composition of 48% chloromethylstyrene and 42% chloromethylstyrene is impregnated with 2% benzoyl peroxide, and this is fixed between two polyester films and two glass plates. Furthermore, radiation polymerization is performed by irradiating 3 megarads of cobalt-60 gamma rays at room temperature, and then heat polymerization is performed in warm water at 90°C for 6 hours to create 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 effective resistance 4.43Ω-cm ² , thickness 184μ, transference number 85.
%, and the bursting strength was 5 kg/cm ² or more.

Example 2 A syrup composition of 11% divinylbenzene, 28% styrene, and 61% chloromethylstyrene was used, and the same base material as in Example 1 was impregnated with 2% benzoyl peroxide. Example 1
Make a polymeric membrane using the same method as above. This polymer film is 1N
An anion exchange membrane is obtained by amination using trimethylamine at 60°C for 16 hours.

The performance of the completed anion exchange membrane is as follows: effective resistance 2.7Ω-cm ² , thickness 168μ, transference number 93%, and burst strength 3.
It was more than Kg/ ^cm2 .

Example 3 A base material of cloth (thickness 145μ, weight 81.3g/m ² ) woven from ethylene-tetrafluoroethylene copolymer,
A syrup with a composition of 8% divinylbenzene, 49% styrene, and 43% chloromethylstyrene is impregnated with 2% benzoyl peroxide, and this is fixed between two polyester films and two glass plates. . Furthermore, radiation polymerization is performed by irradiating 3 megarads of cobalt-60 gamma rays at room temperature, and then heat polymerization is performed in warm water at 90°C for 6 hours to form a polymer film. This polymerized membrane was treated with 98% concentrated sulfuric acid at 60°C.
A cation exchange membrane is obtained by sulfonation treatment for 16 hours. The performance of the completed cation exchange membrane is effective resistance 17Ω-cm ² , thickness 152μ, transference number 87%, and burst strength 5.
It was more than Kg/ ^cm2 .

Example 4 A syrup composition of 11% divinylbenzene, 28% styrene, and 61% chloromethylstyrene was used, to which 2% benzoyl peroxide was added, and the same base material as in Example 3 was impregnated. A polymeric membrane was prepared in the same manner as in Example 3. This polymer film
An anion exchange membrane is obtained by amination treatment using 1N trimethylamine at 60°C for 16 hours.

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 The same polypropylene cloth base material as in Example 1 was impregnated with a syrup containing 8% divinylbenzene and 92% styrene with the addition of 2% benzoyl peroxide, and this was coated with two polyester films. Secure it between two glass plates. Furthermore, radiation polymerization is performed by irradiating 3 megarads of cobalt-60 gamma rays at room temperature, and then heat polymerization is performed in warm water at 90°C for 6 hours to form a polymer film. This polymer film is 98
% concentrated sulfuric acid at 60°C for 16 hours to obtain a cation exchange membrane. The resulting cation exchange membrane swelled significantly due to water content, became approximately twice the size of the polymer membrane, and completely collapsed.

Comparative Example 2 A polypropylene cloth base material similar to that of Example 1 was coated with syrup having a composition of 8% divinylbenzene and 92% chloromethylstyrene, and 2% benzoyl peroxide.
The material is impregnated with the added material and fixed between two polyester films and two glass plates.
Furthermore, radiation polymerization is performed by irradiating 3 megarads of cobalt-60 gamma rays at room temperature, and then heat polymerization is performed in warm water at 90°C for 6 hours to form a polymer film. This polymerized film was treated with 1N trimethylamine at 60°C.
Amination treatment is performed for 16 hours to obtain an anion exchange membrane. Although the resulting anion exchange membrane showed little dimensional change due to swelling due to water content, the resin layer completely peeled off from the base material and could not be used as an ion exchange membrane.

Claims (1)

[Claims] 1. Styrene 10 to 80% based on the total weight of styrene, chloromethylstyrene, and divinylbenzene in the base material.
%, 10 to 80% of chloromethylstyrene, and 1 to 25% of divinylbenzene are impregnated and supported, partially polymerized by irradiation with ionizing radiation in the first stage, and the remaining part polymerized by heating in the presence of a polymerization initiator in the second stage. A method for manufacturing an ion exchange membrane. 2.Claim 1, wherein the polymerization reaction conversion rate of the polymerizable monomer in the first stage by irradiation with ionizing radiation is 80% or less.
the method of.