JP5196236B2 - Cation exchange membrane and method for producing the same - Google Patents

Description

  The present invention relates to a cation exchange membrane used for salt production and a method for producing the same.

  An electrodialysis tank using positive and anion exchange membranes is used in the seawater concentration step in the ion exchange membrane salt production method. An ion exchange membrane used for an electrodialysis tank needs to improve the concentration performance without increasing the electrical resistance of the membrane in order to reduce the production cost of salt.

  A number of methods for producing an ion exchange membrane for salt production have been proposed (see, for example, Patent Documents 1 to 3). Among them, a monomer having a functional group into which an ion exchange group can be introduced, and a crosslinking agent. In addition, a method in which a mixture containing a polymerization initiator as a main component is applied to a woven fabric made of polyvinyl chloride and polymerized, and then ion exchange groups are introduced as necessary is widely known.

However, it has been difficult to improve the concentration performance of the ion exchange membrane obtained by this method without increasing the electrical resistance of the membrane.
In order to solve such problems, a method of obtaining an ion exchange membrane by impregnating and supporting a polymerizable monomer on a polypropylene fiber substrate or the like and then graft polymerizing with ionizing radiation, or a polymerizable monomer on a polyolefin substrate or the like A method has been proposed in which a polymer is impregnated and supported, and then partially polymerized with ionizing radiation, followed by heating in the presence of a polymerization initiator to complete the polymerization and obtain an ion exchange membrane (for example, a patent) References 4-6).

However, none of the methods yielded satisfactory results in terms of membrane concentration performance.
Japanese Examined Patent Publication No. 39-27861 Japanese Patent Publication No.40-28951 Japanese Patent Publication No. 44-19253 JP-A-51-52489 JP 60-238327 A Japanese Patent Application Laid-Open No. 06-271687

  This invention is made | formed in view of such a subject, Compared with the membrane currently used about the cation exchange membrane used for salt production, it improves a concentration performance, without increasing an electrical resistance. It is for the purpose.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors filled a polystyrene-based copolymer into the pores of a porous substrate made of polyethylene or the like, and then irradiated with ionizing radiation. The present inventors have found that a cation exchange membrane into which a sulfonic acid group has been introduced improves the concentration performance without increasing the electric resistance as compared with a conventionally used cation exchange membrane for salt production. More specifically, a monomer such as styrene and divinylbenzene is filled in the pores of a porous substrate made of ultrahigh molecular weight polyethylene, thermally polymerized, irradiated with an electron beam, and then sulfonate groups are formed. The present inventors have found that the introduced cation exchange membrane improves the concentration performance without increasing the electric resistance as compared with a conventionally used cation exchange membrane for salt production.

That is, the present invention has achieved the above object by adopting the following configuration.
(1) Ri polyolefin Tona, average pore diameter in the pores of the porous film-like substrate is 0.005～5Myuemu, was charged with copolymer has at least a copolymer component of styrene and divinylbenzene after, ionizing radiation and a porous film-like substrate and the copolymer is chemically bonded by irradiating, after the, salt production for cation exchange membrane, which comprises introducing a sulfonic acid group.
(2) in the pores, is filled with a polymerizable mixture containing scan styrene and divinyl benzene, performs thermal polymerization, after irradiation with ionizing radiation, and introducing a sulfonic acid group wherein the ( A cation exchange membrane for salt production as described in 1).
(3) The salt-forming cation exchange membrane according to (1) or (2), wherein the polyolefin is polyethylene.
(4) The salt-forming cation exchange membrane according to (1) or (2), wherein the polyolefin is ultrahigh molecular weight polyethylene.
(5) The copolymer further includes a polymerizable monomer capable of introducing a sulfonic acid group, and is treated with a compound capable of imparting a sulfonic acid group after irradiation with ionizing radiation after thermal polymerization. The cation exchange membrane for salt production according to any one of (2) to (4), characterized in that it is characterized in that
(6) The salt-forming cation exchange membrane according to any one of (2) to (4), wherein the copolymer further contains a polymerizable monomer having a sulfonic acid group.

(7) Ri polyolefin Tona, the average pore size of the pores of the porous film-like substrate is 0.005～5Myuemu, by filling a polymerizable mixture containing scan styrene and divinylbenzene, a thermal polymerization after Tsu row, by irradiating the ionizing radiation of a porous film base material and the copolymer is chemically bonded, after them, the salt manufacturing a cation exchange membrane, which comprises introducing a sulfonic acid group Production method.
(8) The method for producing a cation exchange membrane for salt production according to (7), wherein the ionizing radiation is an electron beam.
(9) The method for producing a cation exchange membrane for salt production as described in (8) above, wherein the electron beam dose is 50 to 1000 kGy.

As is clear from the above, the gist of the present invention resides in the following (1) to (3).
(1) Ri polyolefin Tona, in the pores of the porous film-like substrate average pore size of 0.005～5Myuemu, after filling the copolymer has at least a copolymer component of styrene and divinylbenzene and a porous substrate and a copolymer is chemically bonded by irradiating the ionizing radiation, after its, salt production for cation exchange membrane, which comprises introducing a sulfonic acid group.
(2) in the pores, is filled with a polymerizable mixture containing scan styrene and divinyl benzene, performs thermal polymerization, after irradiation with ionizing radiation, and introducing a sulfonic acid group wherein the ( A cation exchange membrane for salt production as described in 1).
(3) Ri polyolefin Tona, the average pore size of the pores of the porous film-like substrate is 0.005～5Myuemu, by filling a polymerizable mixture containing scan styrene and divinylbenzene, a thermal polymerization after Tsu line, and a porous substrate and a copolymer is chemically bonded by irradiating the ionizing radiation, after its manufacturing method of salt production for the cation exchange membrane and introducing a sulfonic acid group.

  According to the present invention, a cation exchange membrane with improved concentration performance can be provided without increasing the electrical resistance as compared with the cation exchange membrane currently used for salt production, which can contribute to reduction in salt production cost.

The method for producing a cation exchange membrane of the present invention generally comprises a polymerizable monomer having a functional group capable of introducing a cation exchange group into a pore of a porous substrate made of polyolefin, a crosslinkable monomer. After filling the polymerizable mixture containing the body, performing thermal polymerization, irradiating the porous substrate filled with the obtained copolymer with ionizing radiation, if necessary using chlorosulfonic acid or the like It is characterized by introducing a sulfonic acid group.
More specifically, a monomer such as styrene and divinylbenzene is filled in the pores of a porous substrate made of polyethylene or ultrahigh molecular weight polyethylene, and thermal polymerization is performed. A sulfonic acid group is introduced into the copolymer after irradiating the filled porous substrate with an electron beam.

Hereinafter, embodiments of the present invention will be described in detail.
In the present invention, the polyolefin is a polymer of an organic compound having a double bond in the molecule. Specifically, polymers of aliphatic olefins such as polyethylene, polypropylene, polybutylene and polybutadiene, polymers of aromatic olefins such as polystyrene, poly α-methylstyrene and polydivinylbenzene, polymethyl methacrylate, polyvinyl acetate, Polymers of oxygen-containing olefins such as polyvinyl alcohol, polymers of nitrogen-containing olefins such as polyacrylonitrile and poly-N-vinylpyrrolidone, halogen-containing olefins such as polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, and polytetrafluoroethylene And the like. These polyolefins may be used alone or a plurality of polyolefins may be mixed. Moreover, the copolymer of 2 or more types of said olefins, or a graft copolymer may be sufficient. It may have a crosslinked structure by copolymerization with a compound having two or more double bonds, electron beam irradiation, plasma irradiation, ultraviolet irradiation, chemical reaction, or the like. Among them, polyethylene is preferable from the viewpoint of chemical stability and cost, and ultrahigh molecular weight polyethylene having a molecular weight of 1,000,000 or more is particularly preferable. In the present invention, the polyolefin may contain various additives such as an antioxidant, an ultraviolet absorber, and an antistatic agent as long as the desired characteristics are not impaired.

The porous substrate in the present invention is a film-like material having an average pore diameter of 0.001 to 50 μm, a thickness of 1 to 300 μm, and a porosity of 1 to 95%. The average pore diameter of the porous substrate is preferably 0.005 to 5 μm, and particularly preferably 0.01 to 2 μm. The thickness of the porous substrate is preferably 5 to 200 μm, particularly preferably 10 to 150 μm. The porosity of the porous substrate is preferably 10 to 90%, particularly preferably 20 to 80%. The porosity here means the apparent density ρa (g / cm ³ ) based on the weight and thickness per unit area of the porous substrate, and the polyolefin constituting the porous substrate (in the case where an additive is included) The value calculated from the true density ρt (g / cm ³ ) of the product including the additive by the following formula.
Porosity (%) = (1−ρa / ρt) × 100

In the present invention, as a method for producing a porous substrate, a wide range of conventional methods can be used without any limitation. For example, a melted polymer is made into a sheet, a laminated lamella structure is formed by heat treatment, and the crystal opening is separated by uniaxial stretching, or the polymer and solvent are heated and melted into a sheet for microphase separation. And a phase separation method in which the solvent is extracted and removed uniaxially or biaxially.
As a porous base material concerning this invention, Asahi Kasei Chemicals Co., Ltd. Hypore (product name), Tonen Chemical Nasu Co., Ltd. cetilla (product name), etc. are mentioned, for example.

  In the present invention, the copolymer means a polymer having two or more monomers as constituent units. For example, a copolymer produced by addition polymerization of a compound having a double bond such as styrene and chloromethylstyrene, a copolymer produced by polycondensation such as a reaction between a dicarboxylic acid and a dialcohol, Examples thereof include a copolymer produced by polyaddition as in the reaction of diisocyanate and dialcohol. Moreover, what has a crosslinked structure like the copolymer of styrene and divinylbenzene is also contained.

  In the present invention, the copolymer contains at least a copolymer component of styrene and divinylbenzene, but other copolymer components are not particularly limited as long as they copolymerize with styrene and divinylbenzene. For example, styrene monomers such as chloromethyl styrene, α-methyl styrene, vinyl toluene, p-methoxy styrene, p-ethyl styrene, m-ethyl styrene, o-ethyl styrene, methyl acrylate, methyl methacrylate, acrylamide Acrylic acid or methacrylic acid monomers such as acrylonitrile, aromatic dienes such as divinyltoluene, divinylnaphthalene, 1,2-bis (vinylphenyl) ethane, aromatic polyenes such as trivinylbenzene, ethylene glycol di Examples thereof include acrylic acid dienes such as methacrylate and N, N-methylenebisacrylamide, and acrylic acid polyenes such as pentaerythritol triacrylate.

  In the present invention, as a method of filling the copolymer in the pores of the porous substrate, a wide range of conventional methods can be used without any limitation. For example, after immersing a porous substrate in a copolymer solution, a method of removing the solvent, a polymerizable mixture containing a polymerizable monomer and a crosslinkable monomer is filled in the pores of the porous substrate Then, there are a method of polymerizing by light irradiation, a method of performing thermal polymerization by filling a polymerizable mixture containing a polymerizable monomer and a crosslinkable monomer into the pores of a porous substrate. Among these, a method of performing thermal polymerization by filling a polymerizable mixture containing a polymerizable monomer and a crosslinkable monomer into the pores of a porous substrate is particularly preferable. In addition, as a method of filling a polymerizable mixture containing a polymerizable monomer and a crosslinkable monomer into the pores of the porous substrate, a polymerization monomer and a polymerization containing a crosslinkable monomer can be used. A method of immersing the porous substrate in a porous mixture or a solution thereof is preferred.

  In the present invention, ionizing radiation means a particle beam or electromagnetic wave moving at a high speed having a property of causing an ionizing action when passing through a substance. Specifically, α rays, β rays, γ rays are used. X-rays, proton beams, electron beams, neutron beams, ultraviolet rays, and the like, and γ rays and electron beams are particularly preferable.

  When an electron beam is used for ionizing radiation, the irradiation dose is preferably 1 to 3000 kGy, and particularly preferably 50 to 1000 kGy. When the irradiation amount is too small, the improvement of the concentration performance of the salt-forming cation exchange membrane is small, and when the irradiation amount is too large, the salt-forming cation exchange membrane becomes brittle and the mechanical strength is lowered. The temperature at the time of irradiation is −10 to 130 ° C., preferably 10 to 50 ° C. Although the atmosphere at the time of irradiation can be in air, it is preferably performed in an atmosphere of an inert gas such as nitrogen, helium, argon, or under vacuum in order to prevent an oxidation reaction.

  In addition, after irradiating the porous substrate filled with the copolymer with an electron beam, the radical remaining in the porous substrate or the copolymer is eliminated to complete the reaction. is there. The temperature of the heat treatment is 30 to 180 ° C., preferably 50 to 130 ° C., and the heating time is 5 seconds to 3 days, preferably 30 minutes to 1 day. The heat treatment can be performed in the air, but it is preferable to perform the heat treatment in an atmosphere of an inert gas such as nitrogen, helium, argon, or the like in order to prevent an oxidation reaction.

  It is not always clear what kind of reaction occurs by irradiating a porous substrate made of polyolefin filled with a copolymer containing at least a copolymer of styrene and divinylbenzene with ionizing radiation. It is considered that radicals are generated in the porous base material and the copolymer by irradiating radiation, and chemical coupling occurs between the porous base material and the copolymer when they are coupled. As a result, it is estimated that the adhesion between the porous substrate and the copolymer is improved, and the concentration performance is improved when a sulfonic acid group is introduced to form a cation exchange membrane for salt production.

  As a method for introducing a sulfonic acid group into a copolymer filled in a porous substrate after irradiating with ionizing radiation, a method conventionally used as a method for producing a cation exchange membrane for a salt can be applied without limitation. . For example, a method of copolymerizing a polymerizable mixture containing styrene and divinylbenzene and sulfonating with a sulfonating agent such as concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid, sulfur trioxide, and sulfuryl chloride, and having an aromatic ring A method in which a monomer is copolymerized with a polymerizable mixture containing styrene and divinylbenzene, and an aromatic ring is sulfonated with a sulfonating agent such as concentrated sulfuric acid, and a monomer of a sulfonic acid derivative is converted into styrene and divinylbenzene. A method of introducing a sulfonic acid group by copolymerization with a polymerizable mixture containing, such as hydrolysis, copolymerizing a monomer having an epoxy group with a polymerizable mixture containing styrene and divinylbenzene, sodium sulfite, etc. Of introducing a sulfonic acid group by reaction with styrene, a polymerizable mixture containing a monomer having a sulfonic acid group and styrene and divinylbenzene And a method of co-polymerization. Among them, a method of copolymerizing a polymerizable mixture containing styrene and divinylbenzene and sulfonating with a sulfonating agent such as concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid, sulfur trioxide, and sulfuryl chloride is particularly suitable. is there.

  Sulfonation with a sulfonating agent such as concentrated sulfuric acid can be carried out with only a sulfonating agent, but it is effective to use a solvent such as 1,2-dichloroethane, trichloroethylene, tetrachloroethylene, methylene chloride, chloroform, carbon tetrachloride. is there. The temperature for sulfonation is -20 to 100 ° C, preferably 0 to 80 ° C.

  In the present invention, the polymerizable mixture refers to a mixture of a polymerizable monomer, a crosslinkable monomer, rubber, a linear polymer substance, a plasticizer, a polymerization initiator, and the like.

In the present invention, the polymerizable monomer having a functional group capable of introducing a sulfonic acid group is a polymerizable monomer having a functional group that can easily introduce a sulfonic acid group or a sulfonic acid group. Specifically, the monomers listed below are listed.
(1) A monomer having an aromatic ring into which a sulfonic acid group is easily introduced. For example, styrene, chloromethyl styrene, α-methyl styrene, vinyl toluene, p-methoxy styrene, p-ethyl styrene, m-ethyl styrene, o-ethyl styrene and the like.
(2) A monomer of a sulfonic acid derivative that easily introduces a sulfonic acid group. For example, ethyl vinyl sulfonate, methyl allyl sulfonate, ethyl p-styrene sulfonate, methyl 2-acrylamido-2-methylpropane sulfonate, and the like.
(3) A monomer having an epoxy group that easily introduces a sulfonic acid group. For example, glycidyl methacrylate, epoxy styrene, butadiene monoxide and the like.
(4) A monomer having a sulfonic acid group. For example, vinyl sulfonic acid, sodium vinyl sulfonate, allyl sulfonic acid, sodium allyl sulfonate, p-styrene sulfonic acid, sodium p-styrene sulfonate, 2-acrylamido-2-methylpropane sulfonic acid, 2-acrylamide-2- Sodium methylpropane sulfonate and the like.

  In the present invention, the crosslinkable monomer can be used without particular limitation as long as it has at least two double bonds in the molecule. For example, aromatic dienes such as divinylbenzene, divinyltoluene, divinylnaphthalene, 1,2-bis (vinylphenyl) ethane, aromatic polyenes such as trivinylbenzene, ethylene glycol dimethacrylate, N, N-methylenebisacrylamide And acrylic acid-based polyenes such as pentaerythritol triacrylate and tetramethylolmethane tetraacrylate, and the like. Divinylbenzene is particularly preferable.

  In order to impart flexibility to the synthesized cation exchange membrane, it is also effective to add an elastic body such as rubber to the polymerizable mixture. As the rubber, those conventionally used for ion-exchange membranes for salt production can be used without any limitation. For example, nitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), natural rubber, ethylene propylene rubber, butyl rubber, chloroprene rubber, acrylic rubber, hydrogenated nitrile butadiene rubber, epichlorohydrin rubber, chlorosulfonated polyethylene, chlorinated polyethylene Norbornene rubber or the like can be used, and these can be used alone or in admixture of two or more. Among them, NBR and SBR are particularly preferable.

  In addition, in order to impart flexibility to the synthesized cation exchange membrane, for example, polyvinyl chloride fine powder, polyethylene fine powder, polypropylene fine powder, etc. may be added to the polymerizable mixture as a linear polymer substance. It is effective and can be used alone or in admixture of two or more. For the same purpose, it is also effective to add dioctyl phthalate, di-2-ethylhexyl phthalate, dibutyl phthalate, tributyl phosphate or aliphatic acid, alcohol ester of aromatic acid, etc. as a plasticizer to the polymerizable mixture. is there.

  In the following description and examples, all parts are parts by weight. The amount of rubber, linear polymer material and plasticizer added to the polymerizable mixture containing styrene and divinylbenzene is not particularly limited, but the polymerizable monomer containing styrene and divinylbenzene and the crosslinkable monomer are not limited. When the total amount of the polymer is 100 parts, the rubber is preferably 50 parts or less, the linear polymer substance is preferably 30 parts or less, the plasticizer is preferably 50 parts or less, particularly the rubber is 30 parts or less, and the linear polymer substance is 20 parts or less. The plasticizer is preferably 30 parts or less.

  In the present invention, a wide variety of conventional methods can be used for thermal polymerization without any limitation. It is possible to polymerize only by heating without using a polymerization initiator, but after immersing the porous substrate in a polymerizable mixture containing styrene and divinylbenzene to which a polymerization initiator has been added, A method of sandwiching a glass plate and a polyester film and heating in a dryer is preferable.

  Although the polymerization initiator used for thermal polymerization is not particularly limited, azobisisobutyronitrile (AIBN), 1,1′-azobiscyclohexane-1-carbonitrile, dimethyl-2,2′-azobis (2- Azo polymerization initiators such as methylpropionate) and 2,2′-azobis (2,4-dimethylvaleronitrile), benzoyl peroxide (BPO), t-butyl peroxybenzoate, dilauryl peroxide, di-peroxide Peroxide polymerization initiators such as t-butyl and disuccinic peroxide can be used, and AIBN and BPO are particularly preferable.

  Specific examples of thermal polymerization are shown below. The porous substrate is immersed for 3 seconds to 12 hours at room temperature in a polymerizable mixture in which 80 parts of styrene, 20 parts of divinylbenzene, 5 parts of NBR and 1 part of AIBN are mixed. After a predetermined time, the porous substrate is taken out, sandwiched between a glass plate and a polyester film, and placed in a dryer. The temperature of thermal polymerization is 30 to 120 ° C., preferably 50 to 100 ° C., and is maintained for 3 to 24 hours.

As a next step, ionizing radiation is irradiated to a porous substrate filled with a copolymer of styrene and divinylbenzene in the pores. Specific examples in the case of irradiating an electron beam as ionizing radiation are shown below.
After inserting a porous base material filled with a copolymer of styrene and divinylbenzene into pores into an oxygen-impermeable polyethylene bag, the inside of the bag is purged with nitrogen, and the bag is heat sealed and closed. Next, the bag containing this substrate is irradiated with an electron beam at 50 to 1000 kGy at room temperature in a nitrogen atmosphere. After the electron beam irradiation, heat treatment is performed at 50 to 130 ° C. for 30 minutes to 1 day with the porous substrate filled with a copolymer of styrene and divinylbenzene or the like in the bag. After the heat treatment, the porous substrate in which pores are filled with a copolymer of styrene and divinylbenzene or the like is taken out from the bag, and sulfonic acid groups are introduced.

  Introducing sulfonic acid groups into the copolymer of styrene and divinylbenzene filled in the pores of the porous substrate can be used without any limitation by a wide range of conventional methods. Is shown below.

  A porous substrate filled with pores of a copolymer of styrene and divinylbenzene in a 1,2-dichloroethane solution having a chlorosulfonic acid concentration of 1 to 50% by weight is immersed at 0 to 80 ° C. for 1 to 72 hours. And react. After reacting for a predetermined time, the membrane is thoroughly washed with water. Thereafter, the membrane is hydrolyzed by being immersed in an aqueous sodium hydroxide solution having a concentration of 1 to 10% by weight for 1 to 24 hours, and then the membrane is sufficiently washed with water.

  Hereinafter, the cation exchange membrane of the present invention and the production method thereof will be described in more detail based on examples. In addition, this invention is not limited to this Example.

Example 1
A glass container containing 75 parts of styrene, 25 parts of divinylbenzene (55% divinylbenzene (isomer mixture) (product name)) manufactured by Wako Pure Chemical Industries, Ltd. (product name)), and 1 part of AIBN, is made of ultrahigh molecular weight polyethylene. A base material, Tonen Chemical Nasu Co., Ltd. Cetilla E30MMS (film thickness 31 μm, pore diameter 0.051 μm, porosity 38%) was immersed for 3 hours. After soaking, Setilla E30MMS was taken out, sandwiched between a glass plate and a polyester film, placed in a dryer, and subjected to thermal polymerization at 60 ° C. for 16 hours and at 90 ° C. for 3 hours.

  After inserting Cetilla E30MMS filled with the copolymer by thermal polymerization into the polyflex bag Hiryu (product name) manufactured by Asahi Kasei Packs Co., Ltd., which is an oxygen-impermeable polyethylene bag, the inside of the bag is purged with nitrogen. After the oxygen was removed, it was heat sealed and closed. Next, using an electron beam irradiation device Iwasaki Electric Co., Ltd. Electrocurtain EC250 / 30 / 90L (product name), the electron beam was placed at 25 ° C. with an acceleration voltage of 250 keV at 100 kGy in a bag containing Setilla E30MMS filled with this copolymer. Irradiated. Next, heat treatment was performed at 60 ° C. for 19 hours without opening the bag, and then the SETILA E30MMS irradiated with an electron beam was taken out from the bag.

  Next, after immersing Cetilla E30MMS irradiated with an electron beam in a 1,2-dichloroethane solution having a chlorosulfonic acid concentration of 10% by weight at room temperature for 24 hours, the membrane was sufficiently washed with water. Thereafter, it was immersed in an aqueous solution of sodium hydroxide having a concentration of 10% by weight for 24 hours. The obtained cation exchange membrane was thoroughly washed with water and stored in 0.5N-NaCl aqueous solution.

(Concentration test)
Further, the cation exchange membrane and a commercially available anion exchange membrane (Asahi Glass Co., Ltd. ASA) were mounted on a small electrodialysis apparatus (membrane area 8 cm ² ), and a concentration test was performed at 25 ° C. A 0.5N-NaCl aqueous solution was used as the feed solution under the concentration conditions of a desalting chamber flow rate of 6 cm / s and a current density of 3 A / dm ² .

(Other examples, comparative examples)
The cation exchange membrane synthesized by changing only the electron beam irradiation amount from Example 1 was used in Examples 2 to 4, the cation exchange membrane synthesized without irradiating the electron beam was Comparative Example 1, and the cation exchange for current salt production. Membranes (Asahi Glass Co., Ltd. CSO) used as membranes were set as Comparative Examples 2 and 3, and together with Example 1, the physical properties of the porous substrate used for the synthesis of the cation exchange membrane are shown in Table 1, The polymerization conditions are shown in Table 2, and the electron beam irradiation conditions and the membrane characteristics of the obtained cation exchange membrane are shown in Table 3. In Table 2, chloromethylstyrene is abbreviated as “CMS” and divinylbenzene as “DVB”.

In addition, a cation exchange membrane synthesized by changing the porous substrate, polymerizable monomer, rubber, electron beam irradiation amount or heat treatment conditions, etc. in the same manner as in Examples 5 to 15 was irradiated with an electron beam. The cation exchange membranes synthesized without comparison were designated as Comparative Examples 4 to 7, the physical properties of the porous substrate used for the synthesis of the cation exchange membranes were shown in Table 1, the thermal polymerization conditions were shown in Table 2, the electron beam irradiation conditions and the obtained results. Table 3 shows the membrane characteristics of the obtained cation exchange membrane. As chloromethylstyrene, AGC Seimi Chemical Co., Ltd. chloromethylstyrene CMS-P (product name) was used. The membrane resistance is measured by mounting the cation exchange membrane on a membrane resistance measurement cell (membrane area 1.8 cm ² ), filling both sides of the membrane with 0.5N-NaCl aqueous solution, and using a milliohm meter at 25 ° C. and a frequency of 1 kHz. Then, the cation exchange membrane was removed, and the electrical resistance of the blank was measured under the same conditions. The difference between the two was taken as the membrane resistance. The brine concentration was determined by measuring the Cl concentration of the concentrated NaCl aqueous solution obtained in the concentration test.

As a result of the concentration test, the relationship between membrane resistance and brine concentration is shown in FIGS. The solid line shown in FIG. 1 is a straight line showing a concentration performance equivalent to that of a commercially available ion exchange membrane, and the broken line is a straight line drawn through Comparative Example 1 without changing the slope of the solid line. Similarly, the solid line shown in FIGS. 2 to 5 is also a straight line showing the concentration performance equivalent to that of the commercially available ion exchange membrane, and the broken line is also Comparative Example 4 without changing the slope of the straight line showing the concentration performance equivalent to that of the commercially available ion exchange membrane. It is a straight line drawn so as to pass through 7. The membrane performance shown above the broken line can be said to be high concentration performance as compared with the comparative example (membrane not irradiated with electron beam).
As shown in Table 3 and FIGS. 1 to 5, all the membranes synthesized according to the present invention have higher concentration performance than commercially available ion exchange membranes, and higher concentration performance than membranes that do not irradiate electron beams. Indicated.

  The cation exchange membrane for salt production of the present invention can improve the concentration performance without increasing the electrical resistance and can be stably operated over a long period of time, compared with a conventionally used membrane. It can contribute to the reduction.

It is a graph showing the relationship between the membrane resistance of the cation exchange membrane in Examples 1-4 of this invention, and Comparative Examples 1-3, and a brine concentration. It is a graph showing the relationship between the membrane resistance of the cation exchange membrane and brine concentration in Example 5 and Comparative Example 4 of the present invention. It is a graph showing the relationship between the membrane resistance of the cation exchange membrane in Examples 6-9 of this invention, and the comparative example 5, and brine concentration. It is a graph showing the relationship between the membrane resistance of the cation exchange membrane in Examples 10-11 of this invention, and the comparative example 6, and brine concentration. It is a graph showing the relationship between the membrane resistance of the cation exchange membrane in Examples 12-15 of this invention, and the comparative example 7, and brine concentration.

Claims (9)

Ri polyolefin Tona, the average pore size of the pores of the porous film-like substrate is 0.005～5Myuemu, after filling the copolymer has at least a copolymer component of styrene and divinylbenzene, ionizing a porous film-like substrate and the copolymer is chemically bonded by irradiating the radiation, its after, salt production for cation exchange membrane, which comprises introducing a sulfonic acid group. The pores are filled with the polymerizable mixture containing the scan styrene and divinyl benzene, performs thermal polymerization, after irradiation with ionizing radiation, according to claim 1, characterized in that introducing a sulfonic acid group Cation exchange membrane for salt production.   The cation exchange membrane for salt production according to claim 1 or 2, wherein the polyolefin is polyethylene.   The cation exchange membrane for salt production according to claim 1 or 2, wherein the polyolefin is ultra high molecular weight polyethylene. The polymerizable mixture further contains a polymerizable monomer capable of introducing a sulfonic acid group, and is treated with a compound capable of imparting a sulfonic acid group after irradiation with ionizing radiation after thermal polymerization. The cation exchange membrane for salt production according to any one of claims 2 to 4. The cation exchange membrane for salt production according to any one of claims 2 to 4, wherein the polymerizable mixture further contains a polymerizable monomer having a sulfonic acid group . Ri polyolefin Tona, average pore diameter in the pores of the porous film-like substrate is 0.005～5Myuemu, by filling a polymerizable mixture containing scan styrene and divinylbenzene, the thermal polymerization was Tsu line after, ionizing radiation and a porous film-like substrate and the copolymer is chemically bonded by irradiating, after the method of salt production for the cation exchange membrane and introducing a sulfonic acid group. 8. The method for producing a cation exchange membrane for salt production according to claim 7, wherein the ionizing radiation is an electron beam. The method for producing a cation exchange membrane for salt production according to claim 8, wherein the irradiation amount of the electron beam is 50 to 1000 kGy.

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