Anion exchange membrane and method for producing the same

Abstract

To provide an anion exchange membrane which enhances adhesion between a polyolefin-based woven fabric and an anion exchange resin, and can achieve low electric resistance and high strength.SOLUTION: An anion exchange membrane has a base material composed of a polyolefin-based woven fabric and an anion exchange resin, and has an electric resistance measured at 25°C using salt solution of 0.5 M of 1.0 Ωcm2 or more and 2.5 Ωcm2 or less, a burst strength of 0.7 MPa or more and 1.2 MPa or less, and a water permeation amount measured using pressurized water of 0.1 MPa of 300 ml / (m2 hr) or less, in which a thickness of the base material is 90 μm or more and 160 μm or less, and an opening ratio of the base material is 35% or more and 55% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an anion exchange membrane and a method for producing the same.

Background Art

[0002] An ion exchange membrane has a structure in which an ion exchange resin is held on a specific base material. When a membrane is formed of the ion exchange resin alone, it has low strength and a large morphological change due to swelling that occurs when it is immersed in a liquid, so it is not suitable for practical use. For this reason, an ion exchange resin is held on a base material that has a predetermined strength, does not undergo a morphological change due to swelling, and does not impair the ion exchange ability peculiar to the ion exchange resin, and is used as an ion exchange membrane.

[0003] In the ion exchange membrane as described above, conventionally, a woven fabric made of polyvinyl chloride has been widely used as the base material. However, an ion exchange membrane having a polyvinyl chloride base material has disadvantages such as low heat resistance and chemical resistance. Therefore, recently, ion exchange membranes having polyolefins such as polyethylene and polypropylene as base materials have been widely studied.

[0004] By the way, an ion exchange membrane having a polyolefin as a base material has extremely high heat resistance and chemical resistance compared to one having a polyvinyl chloride as a base material. However, the adhesiveness between the polyolefin base material and the ion exchange resin is poor. Along with this, when swelling and drying (shrinkage) are repeated, peeling between the ion exchange resin and the base material easily occurs. As a result, there is a problem that the function as a diaphragm deteriorates, the water permeability increases, and the current efficiency decreases. Furthermore, the low adhesiveness between the polyolefin base material and the ion exchange resin naturally leads to low durability.

[0005] As a means for improving the adhesion between a polyolefin substrate and an ion exchange resin, methods such as irradiating the surface of the polyolefin substrate with electron beams or subjecting it to corona treatment are usually considered. However, such methods not only require large-scale equipment but also have the problem of impairing the strength of the polyolefin substrate, making it difficult to put into practical use. Also, when applying and polymerizing a monomer, which is a precursor of the ion exchange resin, to the polyolefin substrate, by setting the polymerization temperature slightly higher than the melting point of the polyolefin, a part of the polyolefin is melted to enhance the adhesion to the ion exchange resin. However, since the strength of the polyolefin substrate decreases due to melting, it becomes necessary to increase the substrate thickness to enhance the substrate strength. In this case, the electrical resistance of the ion exchange membrane increases by the increased thickness, and the adhesion also decreases over time. For this reason, various means for improving adhesion have been proposed.

[0006] For example, Patent Document 1 proposes an ion exchange membrane using a woven fabric made of multifilaments composed of polyethylene having a weight average molecular weight of 10 5 or more (so-called ultra-high molecular weight polyethylene) as a substrate. In such an ion exchange membrane, not only is the strength and the like improved by the multifilaments of ultra-high molecular weight polyethylene, but also the contact area between the ion exchange resin and the substrate is increased, so that the adhesion between the two is enhanced.

[0007] In addition, Patent Document 2 proposes a method for manufacturing an ion exchange membrane in which a monomer paste for forming an ion exchange precursor resin containing polyethylene fine particles with a particle size of 10 μm or less is applied to a cloth-like substrate made of polyethylene, polymerization is carried out at a temperature higher than the melting point of the polyethylene fine particles, and an ion exchange group is introduced into the ion exchange resin precursor thus formed. According to this method, since the polyethylene fine particles act as a thickening agent, an appropriate viscosity and drawability are imparted to the monomer paste, and it becomes possible to uniformly adhere it to the cloth-like substrate made of polyethylene. Further, in the obtained ion exchange membrane, a sea-island structure composed of polyethylene distributed in a sea-like manner and an ion exchange resin distributed in an island-like manner is formed, and the polyethylene continuously connected in a sea-like manner is thermally fused to the cloth-like substrate made of polyethylene. Therefore, even if the substrate is a woven fabric formed from monofilaments, the adhesiveness with the ion exchange resin is improved.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, in Patent Document 1, ultra-high molecular weight polyethylene is a special polymer that is difficult to mold normally, so it is extremely expensive, and moreover, its multifilament woven fabric is extremely difficult to obtain. Therefore, a method that can improve the adhesiveness even with a monofilament woven fabric that is easy to obtain and inexpensive is required.

[0010] In Patent Document 2, polymerization at a high temperature (105 degrees in the examples) is required to melt the polyethylene-based cloth-like substrate, resulting in a problem of reduced mechanical strength of the obtained ion exchange membrane. Furthermore, even if high adhesiveness is once obtained, for example, when the ion exchange resin repeatedly swells and shrinks, a gap is formed between the substrate and the ion exchange resin, increasing the water permeability, resulting in low current efficiency, and further improvement in adhesiveness is required.

[0011] The present invention has been made in view of such points, and an object thereof is to provide an anion exchange membrane that enhances the adhesion between a polyolefin-based woven fabric and an anion exchange resin and achieves both low electrical resistance and high strength.

Means for Solving the Problems

[0012] The anion exchange membrane according to the present invention includes a substrate made of a polyolefin-based woven fabric and an anion exchange resin, and has an electrical resistance measured using 0.5 M saline at 25°C of 1.0 Ω·cm 2 or more and 2.5 Ω·cm 2 or less, a bursting strength of 0.7 MPa or more and 1.2 MPa or less, a water permeability measured using 0.1 MPa pressurized water of 300 ml / (m 2 ·hr) or less, the thickness of the substrate is 90 μm or more and 160 μm or less, and the aperture ratio of the substrate is 35% or more and 55% or less.

[0013] The substrate may be made of a polyethylene-based woven fabric.

[0014] The substrate may be made of a polyolefin monofilament woven fabric.

[0015] Using a two-compartment cell with the configuration of anode (Pt plate) (1.0 mol / L sulfuric acid aqueous solution) / anion exchange membrane / (0.25 mol / L sulfuric acid aqueous solution) cathode (Pt plate) as an electrolytic cell, after energizing for 1 hour under the condition of a current density of 10 A / dm 2 at a liquid temperature of 25°C, the current efficiency measured for sulfate ions may be 40% or more.

[0016] The anion exchange resin may contain a modified styrene-based thermoplastic resin elastomer modified by a polar group.

[0017] The anion exchange resin may be a polystyrene-based anion exchange resin.

[0018] The anion exchange resin may have a crosslinked structure.

[0019] The method for producing an anion exchange membrane according to the present invention includes a monomer component containing a functional group capable of introducing an anion exchange group or a monomer having an anion exchange group and a crosslinkable monomer, and a polymerizable composition for forming an anion exchange resin containing a polymerization initiator, which is a base material made of a polyolefin-based woven fabric having a thickness of 90 μm or more and 160 μm or less and an aperture ratio of 35% or more and 55% or less. Impregnation to be impregnated into the gap step, and after the Impregnation step, copolymerizing the monomer component at 40°C or more and less than 80°C.

[0020] The base material may be made of a polyethylene-based woven fabric.

[0021] The polymerizable composition for forming an anion exchange resin may contain the polymerization initiator having a decomposition temperature of 90°C or less for obtaining a half-life of 10 hours.

[0022] The functional group capable of introducing an anion exchange group or the monomer having an anion exchange group may be a styrene-based monomer having a functional group capable of introducing an anion exchange group or an anion exchange group.

Advantages of the Invention

[0023] The anion exchange membrane according to the present invention has a base material thickness of 90 μm or more and 160 μm or less, an aperture ratio of the base material of 35% or more and 55% or less, keeps the electrical resistance as a membrane low, and has high strength.

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present invention will be described in detail. The following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its applications, or its uses.

[0025] As described in the section of the background art and the problems to be solved by the invention, when manufacturing an anion exchange membrane using an inexpensive polyolefin-based woven fabric as a base material, it is difficult to maintain high strength of the anion exchange membrane, lower the electrical resistance, and further sufficiently increase the adhesion between the polyolefin-based woven fabric and the anion exchange resin. However, the inventors of the present application have conducted various studies and arrived at the present invention.

[0026] (Embodiment 1) The anion exchange membrane according to Embodiment 1 includes a base material made of a polyolefin-based woven fabric and an anion exchange resin, and has an electrical resistance measured using 0.5 M saline at 25°C of 1.0 Ω·cm 2 or more and 2.5 Ω·cm 2 or less, a bursting strength of 0.7 MPa or more and 1.2 MPa or less, a water permeability measured using 0.1 MPa pressurized water of 300 ml / (m 2 ·hr) or less, the thickness of the base material is 90 μm or more and 160 μm or less, and the aperture ratio of the base material is 35% or more and 55% or less.

[0027] The anion exchange membrane of Embodiment 1 having the above properties has an electrical resistance of 1.0 Ω·cm 2 or more and 2.5 Ω·cm 2 or less, which is a small value within the range, so that electrodialysis and the like can be efficiently carried out. The electrical resistance is preferably in the range of 1.3 Ω·cm 2 or more and 2.3 Ω·cm 2 or less.

[0028] The bursting strength of the anion exchange membrane of the present embodiment is more preferably in the range of 0.8 MPa or more and 1.1 MPa or less. Further, the anion exchange membrane of the present embodiment has a water permeability measured using 0.1 MPa pressurized water of 300 ml / (m 2Since it has a small value of, for example, 50 ml / (m·hr) or less, it is excellent in anion selectivity and concentration performance. The water permeation rate is more preferably 50 ml / (m 2 ·hr) or less. The lower limit of the water permeation rate is 0 ml / (m 2 ·hr).

[0029] The method for measuring the electric resistance is as follows. An anion exchange membrane is sandwiched in a two-compartment cell having platinum black electrodes, 0.5 mol / L - NaCl aqueous solution is filled on both sides of the anion exchange membrane, and the resistance between the electrodes at 25°C is measured by an AC bridge (frequency: 1000 cycles / second). The electric resistance = membrane resistance (Ω·cm 2 ) is obtained from the difference between the resistance between the electrodes with the anion exchange membrane installed and the resistance between the electrodes without the anion exchange membrane. The anion exchange membrane used for this measurement was previously equilibrated in 0.5 mol / L - NaCl aqueous solution.

[0030] The method for measuring the bursting strength is as follows. The anion exchange membrane was immersed in 0.5 mol / L - NaCl aqueous solution for 4 hours or more and thoroughly washed with ion-exchanged water. Then, without drying the membrane, the bursting strength was measured in accordance with JIS - P8112 using a Mullen bursting tester (manufactured by Toyo Seiki).

[0031] The method for measuring the water permeation rate is as follows. An ion exchange membrane was sandwiched in a cylindrical cell, 50 ml of water was put on the upper part, and when a pressure of 0.1 MPa was applied from above, the amount of water Wpw permeating through the ion exchange membrane in 1 hour was measured, and the water permeation rate was calculated according to the following formula. At this time, the effective area of the membrane is 12.6 cm 2 . This measurement was carried out at 25°C.

[0032] Water permeation rate (ml / (m 2 ×hr)) = Wpw / (S×t) In the formula, S is the effective area of the membrane (m 2 ), and t is the test time (hour).

[0033] The method for measuring the aperture ratio of the equipment is as follows. It was calculated according to the following formula from the wire diameter (μm) and the mesh number of the threads constituting the base material.

[0034] Open area ratio (%) = (mesh opening) 2 / (mesh opening + wire diameter) 2 In the formula, the mesh opening (μm) is represented by 25400 / number of meshes - wire diameter (μm), and the number of meshes is the number of yarns per inch. The value 25400 is because 1 inch corresponds to 25400 μm.

[0035] Also, in the anion exchange membrane according to this embodiment, a two-compartment cell having a configuration of anode (Pt plate) (1.0 mol / L sulfuric acid aqueous solution) / anion exchange membrane / (0.25 mol / L sulfuric acid aqueous solution) cathode (Pt plate) is used as an electrolytic cell, and the current density is 10 A / dm at a liquid temperature of 25°C 2 After energizing for 1 hour under the conditions, it is preferable that the current efficiency measured for sulfate ions is 40% or more.

[0036] <Polyolefin woven fabric> Examples of polyolefins include homopolymers of α-olefins such as ethylene, propylene, 1-butene, and 4-methyl-1-pentene, or random or block copolymers thereof. Specifically, low-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, and poly-4-methyl-1-pentene can be mentioned. Among them, low-density polyethylene, high-density polyethylene, and polypropylene are preferable, and polyethylene-based polymers such as low-density polyethylene and high-density polyethylene are most preferable in terms of easy availability and chemical resistance.

[0037] The polyolefin-based substrate may have any form such as woven fabric, non-woven fabric, porous film, etc., but woven fabric is preferred from the viewpoint of strength. The opening ratio of the woven fabric needs to be 35% or more and 55% or less. When the opening ratio of the woven fabric becomes small, the electrical resistance increases. Conversely, when the opening ratio increases, the bursting strength decreases, and the adhesion between the polyolefin-based substrate and the anion exchange resin decreases, resulting in deteriorated water permeability. When the opening ratio is 35% or more and 55% or less, an anion exchange membrane excellent in both electrical resistance and adhesion can be obtained. More preferably, the opening ratio is 40% or more and 50% or less.

[0038] The single yarn of the woven fabric can be either multifilament or monofilament, but monofilament is preferred from the viewpoint of adhesion. Also, in terms of balancing strength and membrane resistance, the thickness of the polyolefin-based woven fabric needs to be 90 μm or more and 160 μm or less, and more preferably 95 μm or more and 140 μm or less. The linear diameter of the single yarn is preferably 1 to 70 denier (10 to 100 μm).

[0039] <Anion exchange resin> The anion exchange resin forming the anion exchange membrane is a known one, for example, one in which an anion exchange group is introduced into a resin forming a skeleton. Examples of the resin forming the skeleton include polymers obtained by polymerizing monomers having an ethylenically unsaturated double bond such as vinyl-based, styrene-based, and acrylic-based, and their copolymer polymers, and hydrocarbon-based resins such as polymers containing an aromatic ring in the main chain such as polysulfone, polyphenylene sulfide, polyether ketone, polyether ether ketone, polyether imide, polyphenylene oxide, polyether sulfone, and polybenzimidazole. Among them, styrene-based anion exchange resins mainly composed of styrene-based monomers are preferred as the resin forming the skeleton.

[0040] It is preferable that these anion exchange resins have a crosslinked structure because it densifies the resin and enhances swelling suppression properties and membrane strength, etc. The crosslinked structure may be an ionic crosslink, but a covalent crosslink is preferred.

[0041] Further, the anion exchange group is not particularly limited as long as it is a reactive group that can carry a positive charge in an aqueous solution. For example, examples of the anion exchange group include primary to tertiary amino groups, quaternary ammonium groups, pyridyl groups, imidazole groups, quaternary pyridinium groups, etc. Generally, quaternary ammonium groups and quaternary pyridinium groups, which are strongly basic groups, are preferred.

[0042] <Manufacture of Anion Exchange Membrane> The anion exchange membrane according to this embodiment is manufactured as follows.

[0043] A polymerizable composition is prepared by mixing a monomer having an anion exchange group, a crosslinkable monomer, a polymerization initiator, and other polymerization-curable components for forming an anion exchange resin. The polymerizable composition is immersed in a polyolefin woven fabric as a base material to fill the voids of the woven fabric, and then the polymerizable composition is polymerized and cured to produce an anion exchange resin. Thereby, the target anion exchange membrane can be obtained.

[0044] The polymerization and curing temperature is set to a temperature lower than the melting point of the polyolefin woven fabric so as not to reduce the strength of the base material. Although it depends on the type of polyolefin and the polymerization-curable component and the polymerization and curing time, the upper limit of the polymerization and curing temperature is preferably 40°C or more lower than the melting point of the polyolefin constituting the base material. Specifically, the polymerization and curing temperature is preferably 40°C or more and less than 80°C, more preferably 55°C or more and less than 77°C. If polymerization is carried out at an excessively low temperature, voids may occur at the interface between the polyolefin woven fabric and the anion exchange resin, leading to a decrease in current efficiency. On the other hand, if the temperature is excessively high, a part of the polyolefin may dissolve, resulting in a decrease in the strength of the obtained anion exchange membrane.

[0045] The monomer having an anion-exchange group in the condensation-curing component may be one conventionally used for producing an anion-exchange resin. For example, aromatic ammonium-based monomers such as vinylbenzyltrimethylammonium and vinylbenzyltriethylammonium, (meth)acrylic acid derivative-based monomers having a quaternary ammonium group such as 2-(meth)acryloyloxyethyltrimethylammonium chloride and 2-(meth)acryloyloxyethyltriethylammonium chloride, nitrogen-containing heterocyclic monomers such as vinylpyridine and vinylimidazole, and their salts and esters can be mentioned. These monomers may be used alone or in combination of two or more that are copolymerizable with each other. Also, the crosslinkable monomer is used to densify the anion-exchange resin and enhance swelling suppression properties, membrane strength, etc., and is not particularly limited. For example, divinyl compounds such as divinylbenzene, divinylsulfone, butadiene, chloroprene, divinylbiphenyl, trivinylbenzenes, divinylnaphthalene, diallylamine, and divinylpyridine can be mentioned, among which divinylbenzene is preferred. Such a crosslinkable monomer is generally preferably contained in an amount of 0.1 to 50% by mass, more preferably 1 to 40% by mass, based on the total monomer components in the polymerizable composition for forming the anion-exchange resin.

[0046] Furthermore, in addition to the monomer having an anion-exchange group and the crosslinkable monomer described above, other monomers copolymerizable with these monomers may be added as necessary. Examples of other monomers include styrene, chloromethylstyrene, acrylonitrile, methylstyrene, ethylvinylbenzene, acrolein, methyl vinyl ketone, vinylbiphenyl, etc. The blending amount of other monomers varies depending on the purpose of addition, but generally, it is preferably blended in an amount of 0.1 to 60% by mass based on the total monomer components in the polymerizable composition for forming the anion-exchange resin. Particularly when imparting flexibility, it is preferably blended in an amount of 1 to 50% by mass, particularly 5 to 40% by mass.

[0047] As the polymerization initiator, conventionally known ones can be used without particular limitation, but the decomposition temperature for obtaining a half-life of 10 hours is preferably 90 ° C or lower, more preferably 80 ° C or lower. Specifically, 1,1-bis(t-hexylperoxy)cyclohexane, dibenzoyl peroxide, t-butyl peroxy-2-ethylhexanoate, t-hexyl peroxy-2-ethylhexanoate, 2,5-2,5-di(2-ethylhexanoylperoxy)hexane, disuccinic acid peroxide, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, dilauroyl peroxide, di(3,3,5-trimethylhexanoyl) peroxide, t-butyl peroxybivalate, t-hexyl peroxybivalate, t-butyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, di(2-ethylhexyl) peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate and other organic peroxides are used. The polymerization initiator is preferably blended in an amount of 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, based on 100 parts by mass of the monomer component contained in the polymerizable composition for forming an anion exchange resin.

[0048] The above polymerizable composition may further contain an additive made of a thermoplastic resin. Specifically, examples of the thermoplastic resin include polyolefins such as polyethylene and polypropylene and their modified products, styrene-butadiene copolymers and their hydrogenated products and modified products, polyacrylonitriles, butadiene-acrylonitrile copolymers and their hydrogenated products and modified products, styrene-ethylene-butadiene copolymers and their hydrogenated products and modified products, styrene-isoprene copolymers and their hydrogenated products and modified products, chlorinated polyethylene, polyvinyl chloride, etc. Among these, it is preferable to add a thermoplastic resin that is an elastomer, and a styrenic thermoplastic resin elastomer is particularly preferable. Among the styrenic thermoplastic resin elastomers, those modified with a polar group are most preferable. Here, the thermoplastic resin preferably has a tensile elastic modulus of 0.01 MPa or more, more preferably 0.1 MPa or more and 1000 MPa or less as measured according to ISO527. The blending amount of the thermoplastic resin is not particularly limited, but is preferably 0.5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the monomer component contained in the polymerizable composition for forming the anion exchange resin.

[0049] The styrenic thermoplastic resin elastomer is a thermoplastic elastic resin composed of a copolymer of a monomer unit derived from an aliphatic hydrocarbon-based monomer and a monomer unit based on a styrenic monomer. The styrenic thermoplastic resin elastomer has a high affinity of the styrenic monomer unit portion with an anion exchange resin (especially a polystyrene-based anion exchange resin), and a high affinity of the aliphatic hydrocarbon-based monomer unit portion with a polyolefin-based substrate, so it functions to improve the adhesion between the anion exchange resin and the polyolefin-based substrate. The modified styrenic thermoplastic resin elastomer has a higher polarity than the unmodified one and better adhesion with the ion exchange resin.

[0050] Such styrenic thermoplastic elastomers may be styrene-ethylene-butylene copolymers, styrene-ethylene-propylene copolymers, etc., but usually, copolymers of styrene and conjugated diolefins such as butadiene and isoprene are preferably used because of their ease of polymerization.

[0051] Examples of the polar group include a hydroxy group, an alkoxy group, a carbonyl group, an epoxy group, a carboxy group, an acidic group, an ester group, an amide group, an acid anhydride group, an amino group, a halogen group, etc. Among them, an acidic group or an acid anhydride group is preferred because of their polarity and affinity for the anion exchange group. The acidic group is not particularly limited, such as a sulfo group, a phospho group, a carboxy group, etc., but a carboxy group is preferred. On the other hand, the acid anhydride group is preferably a group obtained by anhydrating the above carboxy group. Specifically, in the case of a cyclic acid anhydride group, a maleic anhydride group, a phthalic anhydride group, a succinic anhydride group, a glutaric anhydride group, etc. can be mentioned, and in the case of an acyclic acid anhydride group, an acetic anhydride group, a propionic anhydride group, a benzoic anhydride group, etc. can be mentioned. The most preferred group for modification is a maleic anhydride group. The amount of modification of the polar group with respect to the styrenic thermoplastic elastomer is not particularly limited, but is preferably 0.1 to 20% by mass, more preferably 0.2 to 10% by mass, and still more preferably 0.2 to 5% by mass based on the polymer.

[0052] Further, the above polymerizable composition may further contain a thickener, known additives, etc., if necessary.

[0053] Examples of the thickener include polyolefin powders with an average particle shape of 10 μm or less, saturated aliphatic hydrocarbon polymers such as ethylene-propylene copolymers and polybutylene, and styrenic polymers such as styrene-butadiene copolymers. By using such a thickener, the viscosity can be adjusted to a range that can effectively prevent dripping during the film-forming operation.

[0054] Furthermore, examples of the additive include plasticizers such as dioctyl phthalate, dibutyl phthalate, tributyl phosphate, tributyl acetyl citrate, or alcohol esters of fatty acids and aromatic acids, and hydrochloric acid scavengers such as styrene oxide and ethylene glycol diglycidyl ether. The blending amount of the additive varies depending on the purpose of addition, but it is preferably blended in an amount of 0.1 to 50 parts by mass, particularly 0.5 to 30 parts by mass, based on 100 parts by mass of the monomer component contained in the polymerizable composition for forming the anion exchange resin.

[0055] There is no particular limitation on the method for impregnating the voids of the base material, which is a polyolefin-based woven fabric, with such a polymerizable composition. For example, it is carried out by immersing the polyolefin-based base material in a tank filled with the aforementioned polymerizable composition. Of course, instead of immersion, the polymerizable composition can also be impregnated by methods such as spray coating or coating using a doctor blade.

[0056] As described above, the polymerizable composition impregnated into the polyolefin-based woven fabric is heated, copolymerized, and cured in a polymerization apparatus such as a heating oven.

[0057] In this polymerization step, generally, a method is adopted in which a polyolefin-based woven fabric filled with a polymerizable composition is sandwiched between films such as polyester and heated from room temperature under pressure. The pressure is generally about 0.1 to 1.0 MPa and is applied by an inert gas such as nitrogen or by pressing with a roll or the like. By this pressurization, polymerization is carried out in a state where the excess polymerizable composition present at the outer interface of the polyolefin-based woven fabric is pushed into the voids of the polyolefin-based woven fabric, and the generation of resin accumulation and the like can be effectively prevented.

[0058] Other polymerization conditions depend on factors such as the type of the polymerization curable component, etc., and may be appropriately selected and determined from known conditions. As described above, the polymerization temperature is set to a temperature significantly lower than the melting point of the polyolefin-based woven fabric (specifically, 40°C or higher and lower than 80°C), and the polymerization time also varies depending on the polymerization temperature, etc., but generally it is about 3 to 20 hours. By the completion of the polymerization curing, an anion exchange membrane supported on the polyolefin-based woven fabric can be obtained.

[0059] Also, in this embodiment, instead of the polymerization curable component for forming the anion exchange resin, an anion exchange membrane can also be formed by using a polymerization curable component for forming an anion exchange resin precursor having a reactive group into which an anion exchange group can be introduced. Specifically, instead of the monomer having the anion exchange group, a monomer having a reactive group into which an anion exchange group can be introduced is blended into the polymerizable composition to produce an anion exchange membrane precursor. Also in this case, an anion exchange membrane precursor may be prepared in the same manner as in the case of blending a monomer having an anion exchange group, except that the anion exchange group introduction step described later is added.

[0060] The monomer having a reactive group into which an anion exchange group can be introduced may be one conventionally used for manufacturing an anion exchange resin. For example, vinyl pyridine, methyl vinyl pyridine, ethyl vinyl pyridine, vinyl pyrrolidone, vinyl carbazole, vinyl imidazole, amino styrene, alkyl amino styrene, dialkyl amino styrene, trialkyl amino styrene, chloromethyl styrene, acrylamide, acrylamide, oxime, styrene, vinyl toluene, etc. are suitable. These monomers may be used alone or in combination of two or more that are copolymerizable with each other.

[0061] In addition to the monomer having a reactive group into which an anion exchange group can be introduced and the crosslinkable monomer, other monomers can be used as needed. Examples of other monomers include acrylonitrile, acrolein, methyl vinyl ketone, etc.

[0062] The anionic exchange group introduction step is carried out after polymerizing and curing the polymerizable composition to obtain a film of the anionic exchange resin precursor resin. In such a step, in order to introduce a primary to tertiary amino group, a quaternary ammonium group, a pyridyl group, an imidazole group, a quaternary pyridinium group, etc., a primary to tertiary amine or the like is allowed to act on the obtained precursor resin as an anionic exchange group introducing agent, or an anionic exchange group is introduced by performing treatments such as alkylation or amination. Thereby, the target anionic exchange membrane can be obtained.

[0063] Further, in the present embodiment, instead of using the above-described polymerizable composition for forming an anionic exchange resin or a polymerizable composition for forming an anionic exchange resin precursor resin, a solution of an anionic exchange group-containing polymer obtained by dissolving an anionic exchange group-containing polymer in a solvent can also be filled into the voids of a polyolefin-based woven fabric.

[0064] The thickness of the anionic exchange membrane produced as described above is preferably in the range of 100 to 300 μm. If this thickness is too thin, the strength of the anionic exchange membrane may significantly decrease. If the thickness is excessively thick, there may be inconveniences such as an increase in electrical resistance.

[0065] The bursting strength of the anionic exchange membrane is adjusted according to the thickness, but is in the range of 0.7 MPa or more and 1.2 MPa or less, by adjusting the filament diameter and thickness of the polyolefin-based woven fabric, the blending amount of the crosslinkable monomer in the polymerization curable component, and the like.

[0066] In the anionic exchange membrane according to the present embodiment, a polyolefin-based woven fabric is used as a base material, the electrical resistance is 1.0 Ω·cm 2 or more and 2.5 Ω·cm 2 or less, the bursting strength is 0.7 MPa or more and 1.2 MPa or less, and the water permeation amount measured using 0.1 MPa pressurized water is 300 ml / (m 2·hr) or less. That is, the anion exchange membrane according to this embodiment uses a thin polyolefin woven fabric with a large aperture ratio as a base material, has a sufficiently large bursting strength, a small electrical resistance, and also has the property of a small water permeation amount which is an index of the adhesion between the anion exchange resin and the base material. A small water permeation amount means that the amount of gaps generated during the manufacturing process of this anion exchange membrane and when a certain pressure is applied during water permeation measurement is small. Therefore, it indicates that the anion exchange resin is firmly adhered to the polyolefin woven fabric. For this reason, in the anion exchange membrane of this embodiment, the base material and the anion exchanger filled in the voids of the base material are firmly adhered, and as a result, it has excellent durability, a small electrical resistance, and a high current efficiency when used for electrodialysis or the like. When copolymerizing the anion exchange resin from a monomer, the copolymerization is carried out at a temperature lower than the melting point of the polyolefin which is the base material, so the polyolefin woven fabric has not suffered a decrease in strength due to copolymerization.

[0067] The anion exchange membrane of the present invention having such properties can be usefully utilized in many fields such as an electrodialysis membrane used in the desalination process in the salt production and food fields, an electrolyte membrane of a fuel cell, and a diffusion dialysis membrane used for acid recovery from an acid containing metal ions generated in the steel industry and the like.

[0068] (Example) Examples and comparative examples are shown below. Various properties of the polyolefin woven fabric and the anion exchange membrane were measured by the following methods.

[0069] 1. Aperture ratio of polyolefin woven fabric It was calculated from the yarn diameter (μm) and the mesh number of the yarns constituting the polyolefin woven fabric according to the following formula.

[0070] Aperture ratio (%) = (mesh opening) 2 / (mesh opening + yarn diameter) 2 (1) In formula (1), Mesh opening (μm) = 25400 / mesh number - yarn diameter (μm) Mesh number = number of yarns per inch (average value) It becomes

[0071] 2. Water Permeation Rate of Anion Exchange Membrane An anion exchange membrane was sandwiched in a cylindrical cell, 50 ml of water was placed on top, and when a pressure of 0.1 MPa was applied from above, the amount of water Wpw that permeated through the ion exchange membrane in one hour was measured, and the water permeation rate was calculated according to the following formula. At this time, the effective area of the membrane was 12.6 cm 2 is.

[0072] Water permeation rate (ml / (m 2 ×hour)) = Wpw / (S × t) (2) In formula (2), S: Effective area of the membrane (m 2 ) t: Test time

[0073] 3. Anion Exchange Capacity and Water Content The anion exchange membrane is immersed in a 1 mol / L - HCl aqueous solution for 10 hours or more. Then, the counter ion is replaced from chloride ion to nitrate ion with a 1 mol / L - NaNO 3 aqueous solution, and the released chloride ions are quantified using a silver nitrate aqueous solution with a potentiometric titrator (AT - 710, manufactured by Kyoto Electronics Industry Co., Ltd.) (Amol).

[0074] Next, the same anion exchange membrane was immersed in a 1 mol / L - NaCl aqueous solution for 4 hours or more and thoroughly washed with ion - exchanged water. Then, the surface moisture was wiped off with tissue paper, and the mass of the membrane when wet (Wg) was measured. Further, it was dried under reduced pressure at 60 °C for 5 hours to measure the weight when dry (Dg). Based on the above measured values, the anion exchange capacity and water content of the anion exchange membrane were determined by the following formulas.

[0075] Anion exchange capacity [meq / g - dry mass] = A × 1000 / D Water content [%] = 100 × (W - D) / D

[0076] 4. Thickness of Anion Exchange Membrane After immersing the anion exchange membrane in a 0.5 mol / L - NaCl solution for 4 hours or more, the moisture on the surface of the membrane was wiped off with tissue paper and measured using a micrometer (MED - 25PJ, manufactured by Mitutoyo Corporation).

[0077] 5. Electrical Resistance of Anion Exchange Membrane An anion exchange membrane was sandwiched in a two - compartment cell having platinum black electrodes, and both sides of the anion exchange membrane were filled with a 0.5 mol / L - NaCl aqueous solution. The resistance between the electrodes at 25°C was measured using an alternating current bridge (frequency 1000 cycles / second), and the electrical resistance (Ω·cm 2 ) was determined from the difference between the resistance between the electrodes and the resistance between the electrodes when the ion exchange membrane was not installed. The anion exchange membrane used in the above measurement was one that had been equilibrated in a 0.5 mol / L - NaCl aqueous solution in advance.

[0078] 6. Current Efficiency of Anion Exchange Membrane A two - compartment cell having the following configuration was used. Anode (Pt plate) (1.0 mol / L - sulfuric acid aqueous solution) / Anion exchange membrane / (0.25 mol / L - sulfuric acid aqueous solution)Cathode (Pt plate) After passing an electric current at a current density of 10 A / dm 2 for 1 hour at a liquid temperature of 25°C, the solution on the cathode side was recovered. The sulfuric acid concentrations of the recovered solution and the initial solution were quantified using a potentiometric titration apparatus (AT - 710, manufactured by Kyoto Electronics Industry Co., Ltd.) with an aqueous sodium hydroxide solution, and the current efficiency was calculated using the following formula.

[0079] Current efficiency (%)=(CB - CS) / (I×t / F)×100 In the above formula, CB: Concentration of the initial solution CS: Concentration of the solution recovered after passing the current I: Current value (A) t: Electrolysis time (sec) F: Faraday constant (96500 C / mol) is as follows.

[0080] 7. Tensile Strength at Break of Anion Exchange Membrane The anion exchange membrane was immersed in a 0.5 mol / L aqueous NaCl solution for 4 hours or more and thoroughly washed with ion-exchanged water. Then, without drying the membrane, the bursting strength was measured in accordance with JIS-P8112 using a Mullen bursting tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.).

[0081] <Example 1> A mixture with the following formulation was prepared.

[0082] Styrene (St) 16.6 parts by mass Divinylbenzene (DVB) (purity 57%, the rest is ethylvinylbenzene) 16.8 parts by mass p-Chloromethylstyrene (CMS) 66.6 parts by mass Tributyl acetylcitrate (ATBC) 25.0 parts by mass Styrene oxide (StO) 3.4 parts by mass t-Butyl peroxy-2-ethylhexanoate (BPE) (trade name: Perbutyl O, manufactured by NOF Corporation) 3.3 parts by mass To this mixture, 20.7 parts by mass of a hydrogenated styrene-butadiene triblock copolymer modified with maleic anhydride (trade name: Tough Tech M1913, manufactured by Asahi Kasei Corporation) having a polystyrene content of 30% by weight was added, and the mixture was stirred at 40 °C for 20 hours to obtain a uniform polymerizable composition.

[0083] Next, the following high-density polyethylene monofilament woven fabric (PE30D-100) was prepared.

[0084] High-density polyethylene monofilament woven fabric (PE30D-100); Warp: 100 mesh - wire diameter 68 μm (30 denier) Weft: 100 mesh - wire diameter 68 μm (30 denier) Thickness: 128 μm Open area ratio: 54% The polymerizable composition obtained above was applied onto the above high-density polyethylene monofilament woven fabric (PE30D-100), and both sides were coated using a polyester film as a release material, followed by polymerization at 70 °C for 5 hours.

[0085] Next, the obtained film-like polymer was immersed in methanol for 20 hours to remove the plasticizer and polymerization residues. Then, an amination reaction was carried out at 30 °C for 16 hours using an aqueous solution of 5 wt% trimethylamine and 25 wt% acetone to obtain an anion exchange membrane. The properties of the obtained anion exchange membrane are as follows and are shown in Table 2. The composition of the anion exchange membrane is shown in Table 1.

[0086] Thickness: 159 μm Ion exchange capacity: 2.0 meq / g - dry mass Water content: 34% Electrical resistance: 1.7 Ω·cm 2 Water permeation rate: 0 ml / (m 2 ·hour) Current efficiency: 44% Breaking strength: 0.89 MPa <Example 2> As a polyolefin-based monofilament substrate, the following polyethylene woven fabric (PE33D-100) was prepared.

[0087] High-density polyethylene monofilament woven fabric (PE33D-100); Warp: 100 mesh - wire diameter 76 μm (33 denier) Weft: 100 mesh - wire diameter 76 μm (33 denier) Thickness: 132 μm Open area ratio: 49% An anion exchange membrane of the present invention was obtained in the same manner as in Example 1 except that the above polyethylene woven fabric (PE33D-100) was used. The membrane properties of the obtained anion exchange membrane are shown in Table 2.

[0088] <Example 3> As a polyolefin-based monofilament substrate, the following polyethylene woven fabric (PE33D-120) was prepared.

[0089] High-density polyethylene monofilament woven fabric (PE33D-120); Warp: 120 mesh - wire diameter 76 μm (33 denier) Horizontal thread: 120 mesh - wire diameter 76 μm (33 denier) Thickness: 132 μm Open area ratio: 41% An anion exchange membrane of the present invention was obtained in the same manner as in Example 1, except that the above-mentioned polyethylene woven fabric (PE33D - 120) was used. The membrane properties of the obtained anion exchange membrane are shown in Table 2.

[0090] <Example 4> As a polyolefin monofilament substrate, the following polyethylene woven fabric (PE33D - 130) was prepared.

[0091] High - density polyethylene monofilament woven fabric (PE33D - 130); Longitudinal thread: 130 mesh - wire diameter 76 μm (33 denier) Horizontal thread: 130 mesh - wire diameter 76 μm (33 denier) Thickness: 132 μm Open area ratio: 37% An anion exchange membrane of the present invention was obtained in the same manner as in Example 1, except that the above-mentioned polyethylene woven fabric (PE33D - 130) was used. The membrane properties of the obtained anion exchange membrane are shown in Table 2.

[0092] <Example 5> As a polyolefin monofilament substrate, the following polypropylene woven fabric (PP30D - 100) was prepared.

[0093] High - density polypropylene monofilament woven fabric (PP30D - 100); Longitudinal thread: 100 mesh - wire diameter 68 μm (30 denier) Horizontal thread: 100 mesh - wire diameter 68 μm (30 denier) Thickness: 128 μm Open area ratio: 54% An anion exchange membrane of the present invention was obtained in the same manner as in Example 1, except that the above-mentioned polypropylene woven fabric (PP30D - 100) was used. The membrane properties of the obtained anion exchange membrane are shown in Table 2.

[0094] <Comparative Example 1> As a polyolefin monofilament base material, the following polyethylene woven fabric (PE33D-80) was prepared.

[0095] High-density polyethylene monofilament woven fabric (PE33D-80); Warp: 80 mesh - wire diameter 76 μm (33 denier) Weft: 80 mesh - wire diameter 76 μm (33 denier) Thickness: 130 μm Open area ratio: 58% An anion exchange membrane of the present invention was obtained in the same manner as in Example 1 except that the above polyethylene woven fabric (PE33D-80) was used. The membrane properties of the obtained anion exchange membrane are shown in Table 2.

[0096] In Comparative Example 1, the water permeation rate was significantly deteriorated compared with the example. From this, it was confirmed that when the open area ratio of the base material is too large, the adhesion between the resin and the base material deteriorates.

[0097] <Comparative Example 2> As a polyolefin monofilament base material, the following polyethylene woven fabric (PE200) was prepared.

[0098] High-density polyethylene monofilament woven fabric (PE200); Warp: 156 mesh - wire diameter 86 μm (50 denier) Weft: 100 mesh - wire diameter 86 μm (50 denier) Thickness: 185 μm Open area ratio: 32% An anion exchange membrane of the present invention was obtained in the same manner as in Example 1 except that the above polyethylene woven fabric (PE200) was used. The membrane properties of the obtained anion exchange membrane are shown in Table 2.

[0099] In Comparative Example 2, the resistance was deteriorated compared with the example. From this, it was confirmed that when the open area ratio of the base material is too small, a preferable low-resistance membrane cannot be obtained.

[0100] <Comparative Example 3> As a polyolefin-based monofilament substrate, the following polyethylene woven fabric (PE120) was prepared.

[0101] High-density polyethylene monofilament woven fabric (PE120); Warp: 96 mesh - wire diameter 106 μm (62 denier) Weft: 76 mesh - wire diameter 122 μm (71 denier) Thickness: 260 μm Open area ratio: 38% An anion exchange membrane of the present invention was obtained in the same manner as in Example 1 except that the above polyethylene woven fabric (PE120) was used. The membrane properties of the obtained anion exchange membrane are shown in Table 2.

[0102] In Comparative Example 3, the resistance is deteriorated compared with the Example. From this, it was confirmed that when the substrate is too thick, a preferable low-resistance membrane cannot be obtained.

[0103] <Comparative Example 4> An anion exchange membrane of the present invention was obtained in the same manner as in Example 3 except that the polymerization temperature was set to 105°C. The membrane properties of the obtained anion exchange membrane are shown in Table 2.

[0104] In Comparative Example 4, the bursting strength is deteriorated compared with the Example. From this, it was confirmed that when the polymerization temperature is too high, a preferable high-strength membrane cannot be obtained.

[0105]

Table 1

[0106]

Table 2

[0107] (Other Embodiments) The above embodiments are examples of the invention of the present application, and the invention of the present application is not limited to these examples. Well-known techniques, conventional techniques, or known techniques may be combined with or partially replaced in these examples. Further, modified inventions that can be easily conceived by those skilled in the art are also included in the invention of the present application.

Claims

1. An anion exchange membrane comprising a base material made of a polyolefin woven fabric and an anion exchange resin, The electrical resistance measured using 0.5 M saline solution at 25°C is 1.0 Ω·cm ２ or more and 2.5 Ω·cm ２ or less, and having a bursting strength of 0.8 MPa or more and 1.1 MPa or less, The water permeability measured using pressurized water at 0.1 MPa is 300 ml / (m ２ ·hr) or less, wherein the thickness of the base material is 90 μm or more and 160 μm or less, and the aperture ratio of the base material is 35% or more and 55% or less. Anion exchange membrane.

2. The anion exchange membrane according to claim 1, wherein the base material is made of a polyethylene woven fabric.

3. The anion exchange membrane according to claim 1 or 2, wherein the base material is made of a monofilament woven fabric of polyolefin.

4. A two-compartment cell with the structure of anode (Pt plate) (1.0 mol / L sulfuric acid aqueous solution) / anion exchange membrane / (0.25 mol / L sulfuric acid aqueous solution) cathode (Pt plate) is used as the electrolytic cell. After electrolyzing for 1 hour under the conditions of a liquid temperature of 25 °C and a current density of 10 A / dm ２ The anion exchange membrane according to any one of claims 1 to 3, wherein the current efficiency measured for sulfate ions is 40% or more after energization for 1 hour under the above conditions.

5. The anion exchange membrane according to any one of claims 1 to 4, wherein the anion exchange resin contains a modified styrene-based thermoplastic resin elastomer modified by a polar group.

6. The anion exchange membrane according to any one of claims 1 to 5, wherein the anion exchange resin is a polystyrene-based anion exchange resin.

7. The anion exchange membrane according to any one of claims 1 to 6, wherein the anion exchange resin has a crosslinked structure.

8. An impregnation step of impregnating a void of a base material made of a polyolefin woven fabric having a thickness of 90 μm or more and 160 μm or less and an aperture ratio of 35% or more and 55% or less with a polymerizable composition for forming an anion exchange resin containing a monomer component containing a functional group capable of introducing an anion exchange group or a monomer having an anion exchange group and a crosslinkable monomer, and a polymerization initiator, and a step of copolymerizing the monomer component at 55°C or more and less than 77°C for a polymerization time of 3 to 20 hours after the impregnation step A method for producing an anion exchange membrane.

9. The method for producing an anion exchange membrane according to claim 8, wherein the base material is made of a polyethylene woven fabric.

10. The method for producing an anion exchange membrane according to claim 8 or 9, wherein the polymerizable composition for forming the anion exchange resin contains the polymerization initiator having a decomposition temperature of 90°C or less for obtaining a half-life of 10 hours.

11. The method for producing an anion exchange membrane according to any one of claims 8 to 10, wherein the functional group capable of introducing an anion exchange group or the monomer having an anion exchange group is a styrene-based monomer having a functional group capable of introducing an anion exchange group or an anion exchange group.

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