JPH08269217A - Bipolar membrane - Google Patents

Abstract

PURPOSE: To obtain a bipolar membrane possessing good mechanical strengths and showing a low water dissociation voltage and a high current efficiency at a high current density. CONSTITUTION: This bipolar membrane consists of at least two layers, wherein the first layer contains fine metal oxide particles and contains ion exchange groups entirely consisting of anion exchange groups, the fine metal oxide particles have a specific surface area of 5-250m<2> /g and a mean particle diameter of 0.5-10μm, the anion exchange capacity of the matrix polymer constituting the first layer is 2-4.5meq/g resin, and the second layer is made of a polymer having cation exchange groups.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bipolar membrane used for decomposing water to produce hydrogen ions and hydroxide ions and producing an acid or a base from a neutral salt.

[0002]

2. Description of the Related Art Proposals concerning bipolar films are described in V. J.
Frilete (J. Phys. Chem. 60, 4
35 (1956)), it has been done a lot over the past 30 years. For example, one in which an anion exchange membrane and a cation exchange membrane are joined with an ion exchange adhesive (Japanese Patent Publication No. 34-3961), an anion exchange membrane and a cation exchange membrane are fine powder of a strongly basic anion exchange resin, or a strong acidity. Of the paste-type mixture of the cation exchange resin and the thermoplastic resin, and press-bonded (Japanese Patent Publication No. 35-14).
No. 531), a mixture of a partially polymerized vinyl pyridine and an epoxy resin was applied to a cation exchange membrane, and irradiation was performed during curing (Japanese Patent Publication No. 38-166).
No. 38) and the like. However, these bipolar membranes have a defect that the water dissociation voltage of the membrane is high even though the current density is low.

Further, one side of a single sheet is provided with anion permeability or cation permeability, and from the other side,
A bipolar membrane (Japanese Patent Publication No. Sho 60-31860) having ion permeability of the opposite charge, a polymer membrane having a functional group suitable for introducing an ion exchange group is covered with a coating film, and the integral body is subjected to sulfonation treatment. After that, after peeling off the coating film, a method for producing a bipolar membrane in which an anion-exchange group is introduced on the peeled surface (Japanese Patent Publication No. 14251/1989).
No. gazette). However, these are not industrially useful because it is difficult to control the reaction at the time of introducing an exchange group, it may be difficult to produce a membrane on a large industrial scale, and high current efficiency may not be obtained.

On the other hand, a laminated structure useful for the production of a bipolar film, which is a bipolar film comprising an interface layer (intermediate layer) in which a matrix polymer and an ion-exchange resin dispersed therein have opposite charges (Japanese Patent Laid-Open No. 60-210638). However, the voltage of water dissociation of the membrane is relatively low, but it is still not sufficient. Furthermore, a bipolar membrane comprising an interface layer (intermediate layer) containing fine cation exchange resin particles dispersed in a matrix polymer containing a quaternary amine group and a non-quaternary amine group (Japanese Patent Publication No. 1-502673).
Gazette and U.S. Pat. No. 4,766,161). This shows a low water dissociation voltage, but it is difficult to use a very fine ion exchange resin, and it is difficult to control the gelation and drying process during the formation of the anion layer, and the production is not easy. Further, since the polymer is obtained by dissolving the polymer in a solvent, casting and drying, it has drawbacks such as difficulty in production and poor mechanical strength as compared with the one obtained by bulk polymerization.

Further, there is one using an inorganic material for the purpose of lowering the high electric resistance of the bipolar film. A bipolar membrane in which an anion exchange membrane or a cation exchange membrane is immersed in a cation aqueous solution in an oxidized state, treated with an alkaline aqueous solution, and then heated and pressurized to join the two membranes (Japanese Patent Publication No. 3-50).
5894), a bipolar membrane in which a polymer film of a cation exchange group is formed on the surface of an anion exchange membrane in which heavy metal ions are present in the membrane (JP-A-4-63292), and the cation exchange membrane is impregnated with iron. A material having a surface coated with a post-anion exchange resin (Japanese Patent Laid-Open No. 4-2285).
No. 91). Membranes utilizing these inorganic substances have a structure of an anion exchange membrane and a cation exchange membrane and do not have an intermediate layer structure, and although the effect of introducing inorganic substances is obtained, the water dissociation voltage of the bipolar membrane is sufficiently low. There was a drawback that you could not get.

Further, an inorganic ion exchanger is allowed to exist at the interface between an anion exchange membrane and a cation exchange membrane (Japanese Patent Laid-Open No. 6-
172557, JP-A-6-172558,
JP-A-6-263896, European Patent EP0600
470). The one using such an inorganic ion exchanger is more stable than the one treated with the alkaline aqueous solution by immersing it in the cation aqueous solution in the above-mentioned oxidation state,
There is a problem that the known inorganic ion exchanger itself used is easily dissolved under the condition of strong acid and strong alkaline, and the dialysis performance of the bipolar membrane is insufficient.

[0007]

SUMMARY OF THE INVENTION The present invention provides a bipolar membrane having good mechanical strength, low water dissociation voltage at high current density, and high current efficiency.

[0008]

That is, according to the present invention, in a bipolar film having at least two layers, the first layer contains fine particles of a metal oxide and has only an anion exchange group as an ion exchange group, particles of the metal oxide oxide, (1) a specific surface area of 5m ² / g~250m ² / g,
(2) The average particle diameter is 0.5 μm to 10 μm, and the anion exchange capacity of the matrix polymer forming the first layer is 2 meq / g to 4.5 meq per unit weight of the resin.
/ G, and the second layer is made of a polymer having a cation exchange group.
The fine particles of the metal oxide are preferably fine particles containing at least one oxide selected from the IVA group such as titanium, zirconium and hafnium.

Although the effect of the present invention is not clear, by having a first layer containing fine particles of a metal oxide in a matrix polymer having only anion exchange groups, a water dissociation field is formed in this layer. It is thought to be because it is done.
Here, the first layer is a layer in which fine particles 3 of a metal oxide not coated with an ion exchange resin are dispersed and present in a matrix polymer 4 as shown by 1 in FIG. It is arranged in close contact with the cation exchange resin layer. Further, as shown in FIG. 2, it may be between both the anion exchange resin layer and the cation exchange resin layer and may be in contact with both of them. The second layer is a cation exchange resin layer as shown by 2 in FIG. The third layer is the layer shown by 5 in FIG. 2 and is an anion exchange resin layer having the same charge as the matrix polymer of the first layer. The thickness of the bipolar film as shown in FIGS. 1 and 2 is 1 μm to 1 mm.

The metal oxide as referred to in the present invention is, for example, a metal salt, a metal hydroxide or the like which is acid and alkali resistant by heat treatment such as firing, and specific examples thereof include those of group IVA such as titanium oxide and zirconium oxide. Metal oxides are preferred. Sintered oxides are preferable because they are advantageous in terms of strength and chemical resistance. In addition, two or more kinds of these oxides may be contained, and further, other component elements may be contained. The metal oxide as referred to in the present invention is different from a hydrous oxide or an acidic salt type inorganic ion exchanger having ion exchange characteristics. Hydrous oxide and acidic salt type inorganic ion exchangers are not stable under the conditions of strong acid and strong alkali,
It is not preferable because the dialysis performance of the bipolar membrane is lacking in stability.

The shape of the metal oxide fine particles in the present invention is preferably such that the primary particle size is small and the specific surface area is large. The primary particle diameter is 0.02 μm to 0.5 μm, and these fine particles are usually agglomerated and compared with the primary particle diameter,
The aggregated particles have a larger average particle size. The average particle size of the agglomerated particles during handling is 0.5 μm to 10 μm.
Fine particles of μm are preferred. If the average particle size is too large, it is difficult to obtain a uniform particle when forming the first layer, and the voltage of water dissociation tends to increase. If it is too small, the handling becomes very complicated and there is a problem in application on an industrial scale. The matrix polymer referred to in the present invention is a polymer containing an anion exchange resin forming the first layer, and has a continuous and uniform structure. The present invention provides that water dissociation becomes efficient due to the structure of the first layer composed of the fine particles of the above-mentioned metal oxide dispersed in the matrix polymer, and that the first layer itself has an anion exchange group contained in the matrix polymer. Thereby becomes a bipolar film having a novel structure that also acts as an anion layer.

The dissociation of water in the first layer of the bipolar membrane referred to in the present invention is caused by the surface of the metal oxide fine particles in the first layer, the surface of the anion exchange resin in the matrix polymer, their interface, or the second layer. It is not clear whether this is the bonding interface between the cation layer and the anion exchange resin portion of the first layer. However, when the water dissociation performance is affected by the distance between the surface of the metal oxide particles and the anion-exchange groups of the matrix polymer surrounding them, the positional relationship, the density of the exchange groups, and the water molecules that hydrate to a fixed charge. Considered, the design of the internal structure of the first layer is extremely important.

The metal oxide fine particles are dispersed in the matrix polymer to form a kind of mosaic structure, and the dissociated hydrogen ions and hydroxide ions do not recombine,
It is possible to reach the cation layer and the anion layer, respectively. The dialysis voltage of the bipolar membrane having the structure as in the present invention is mainly determined by the structure of the first layer, which is the field of water dissociation, and the type of metal oxide fine particles,
It is considered to be influenced by the morphology and the dispersion structure of the fine particles of the metal oxide in the matrix polymer.

Furthermore, in the present invention, it has been found that the first layer alone exhibits the ion selective permeability of the anion-exchange group possessed by the matrix polymer, and can play the role of the anion layer. Therefore, the bipolar film can be formed only by joining the cation layer, which is the second layer, to the first layer. The surface area (specific surface area) per unit weight of the metal oxide fine particles is preferably large, and is preferably 5 m ² / g or more because the water dissociation voltage can be lowered. However, because of its strength and structural restrictions, its specific surface area is fixed, so there is a limit in this respect. Further, those having a pore structure can be used, but it is necessary to ensure a sufficient contact interface between the surface of the metal oxide and the matrix polymer, and as the average pore diameter, the matrix polymer is in the pores. It must be large enough to fit in. Normal,
Those having an average pore diameter of 5 nm or more are preferably used.

From the above, the maximum value of the specific surface area is 2
It becomes 50 m ² / g. Such metal oxide fine particles are commercially available and can be easily obtained. The fine particles of the metal oxide have a specific surface area and an average particle diameter within a certain preferred range, so that the acid and the base can be separated with a low water dissociation voltage. Even if the metal oxide fine particles are replaced with simple metal oxides having different specific surface areas and average particle diameters, the low water dissociation voltage as in the present invention cannot be achieved at all.

The matrix polymer includes quaternized polyvinyl pyridine, quaternized polyvinyl imidazole, quaternized polyvinyl benzyl chloride, a copolymer of these with divinyl benzene, and a fluorine-containing anion exchange resin. The ion exchange capacity of the matrix polymer is 2.0 meq / unit weight of resin.
g to 4.5 meq / g is required. If the exchange capacity is too low, the hydrolytic voltage becomes high, which is not preferable. On the contrary, it is preferable that the exchange capacity is high, but the upper limit is restricted by the additives and the monomers to be copolymerized.

As the matrix polymer of the first layer,
A crosslinked structure is preferred from the viewpoints of electric resistance, dimensional stability and mechanical strength of the film. The crosslinked structure is preferably three-dimensionally crosslinked, and a crosslinking agent having two or more vinyl groups as a monomer forming a matrix polymer is preferably used. Examples of the cross-linking agent here include m-, p-, o-,
Examples thereof include polyvinyl compounds such as divinylbenzene, divinylsulfone, butadiene, chloroprene, trivinylbenzenes, divinylnaphthalene and trivinylnaphthalene. In addition, polyamine crosslinking can be used as another crosslinking agent. Diamine or polyamine can be used as the amine crosslinking agent.

The polyamine crosslinking agent referred to here is
N, N-dimethylpropanediamine, N, N, N ',
N'-tetramethylhexanediamine and the like. In addition, in these matrix polymers, elasticity increase,
An additional substance such as a plasticizer or a linear polymer may be contained as necessary for improving the adhesiveness or increasing the viscosity. Regarding the degree of crosslinking of the matrix polymer, it is preferable that a crosslinking agent such as divinylbenzene is contained in an amount of 1 part to 20 parts, preferably 5 parts to 15 parts, relative to the other monomers. To increase the mechanical strength, it is preferable to add a crosslinking agent,
Addition of 20 parts or more may cause inconvenience such as increase in water dissociation voltage.

Further, the weight composition ratio between the fine particles of the metal oxide and the matrix polymer becomes brittle when the composition ratio of the matrix polymer is small, and the electric resistance is deteriorated. The range of this is preferably 1: 1.5 to 1: 7. If the amount of the metal oxide fine particles is too large, cracks or strength reduction may occur when the first layer is formed, and if the amount is too small, disadvantages such as an increase in water dissociation voltage may occur.
This composition ratio has an optimum range depending on the form of the metal oxide, and the above range is preferable. The cation layer, which is the second layer, is a cation exchange resin containing polystyrene sulfonic acid, a cation exchange resin containing perfluorosulfonic acid resin, or the like, and may optionally include three-dimensional crosslinking with divinylbenzene or the like. Moreover, you may contain additional substances, such as a plasticizer and a linear polymer, as needed.
A woven fabric of polyvinyl chloride or polypropylene may be used as the reinforcing fabric for increasing the mechanical strength. Other, net,
A reinforcing material such as cloth or a microporous film may be used.

As the method for producing the bipolar membrane of the present invention, the first layer is formed of a matrix polymer having an anion exchange group in which fine particles of metal oxide are dispersed, and the cation exchange resin layer is formed as a second layer. For the adhesion, a cation-exchangeable adhesive may be used, and a cation-exchange membrane may be adhered or heat-pressure fused. Alternatively, a resin containing a cation exchange group may be dissolved in a solvent, coated on the surface of the first layer, dried and then adhered. Further, as the second layer, a three-dimensionally crosslinked one can be used. For example, a method of polymerizing a mixed monomer of styrene and dibenenylbenzene on the first layer and introducing an exchange group with sulfuric acid or the like, or a styrene sulfone containing a sulfone group hydrophobized with amine hydrochloride or the like on the first layer. A method of polymerizing a mixed monomer of an acid monomer and divinylbenzene is used.

In the present invention, the third layer may be formed if necessary in order to improve the current efficiency and the chemical durability. In this case, an anion exchange resin layer is formed in close contact with the first layer opposite to the second layer. Therefore, the polymer of the third layer is basically an anion exchange resin layer having the same charge as the first layer. As the method for forming the third layer, an adhesive method such as a casting method is used as in the case of forming the second layer. As described above, the inventors of the present invention have earnestly studied and have obtained a bipolar film having the following three advantages. That is, the first characteristic is that the fine particles of the metal oxide have a specific surface area and an average particle diameter within a certain range, and the fine particles of the metal oxide are dispersed in the first layer, so that the high current density and low water To show the dissociation voltage.

A second feature of the present invention is that the first layer allows the matrix polymer to be utilized as the anion layer,
Since only the first layer and the second layer can exhibit high performance as a bipolar film, it is very advantageous in manufacturing. The third feature of the present invention is that since the first layer for water dissociation effective for low water dissociation voltage can be designed and manufactured separately from the second cation exchange resin layer, it is easy to add other functionality. That is. In order to achieve high current efficiency, the cation exchange resin layer may have a three-dimensional crosslinked structure or an ion cluster structure, if necessary. Moreover, it is easy to put a reinforcing cloth in each layer constituting the bipolar film of the present invention in order to improve the mechanical strength.

As described above, according to the present invention, the first layer, the second layer and, if necessary, the third layer can be individually designed and manufactured, so that it is easy to manufacture a large-sized bipolar film used on an industrial scale. Not only that, it is a high performance bipolar membrane that makes it easy to fabricate bipolar membranes according to individual dialysis conditions.

[0024]

EXAMPLE The performance of the bipolar film of the example was measured as follows. A platinum plate plated with platinum black is used as an anode and a cathode, and the layer containing the anion exchange resin of the bipolar membrane is directed to the anode side to divide it into two chambers. 10% NaOH and 3.5%
50 ml of HCl is placed in each chamber and electrodialysis is performed for 1 hour. At this time, the water dissociation voltage of the membrane at a current density of 100 mA / cm ² is read by a voltmeter connected to the reference electrode using a Luggin tube. The production efficiency of hydrogen ions and hydroxide ions of the bipolar film was determined by acid-base titration. The dialysis area is 8 cm ² .

[0025]

Examples 1 to 3 As the metal oxide fine particles, three kinds of commercially available zirconium oxide fine particles and those having a specific surface area measured by the BET adsorption method of 10, 17, 107 m ² / g were used. Using the metal oxide fine particles, a first layer in which the weight of the matrix polymer containing the anion exchange resin part was 1.5 times the weight of the metal oxide fine particles was obtained according to the following procedure. 66.7 parts of fine particles of metal oxide, 6.13 parts of styrene, 17.8 of divinylbenzene (purity 56%) 17.8
6 parts, vinylbenzyl chloride 45.78 parts, polyvinyl chloride resin 5 parts, nitrile butadiene rubber 7.5 parts,
It was mixed with 5 parts of dimethyl phthalate and 0.2 parts of a polymerization initiator azobisisobutyronitrile. A polyvinyl chloride woven fabric was impregnated with a mixed liquid of the monomer and fine particles of a metal oxide, covered with a polyester film, and subjected to bulk polymerization at 60 ° C. for 24 hours to obtain a film. The obtained film-like material was quaternized with an aqueous trimethylamine solution containing acetone to obtain a first layer.
The thickness of the first layer was 90 μm. Next, the surface of the first layer on which the second layer is to be formed was previously polished with sandpaper to partially expose the fine particles of the dispersed metal oxide.

The second layer was formed on the first layer by the following procedure. Styrene was polymerized to obtain a non-crosslinked polymer.
The polymer was sulfonated with concentrated sulfuric acid to give an exchange capacity of 1.
5 meq / g of ion exchange resin was obtained. Furthermore, 90 parts of this ion exchange resin and 10 parts of nitrile butadiene rubber
A solution containing about 20 wt% ion-exchange resin dissolved in dimethylformamide was prepared and cast on the dried first layer. After casting, it was dried at 105 ° C. to 110 ° C. for 10 minutes to form a second layer to obtain a bipolar film. The thickness of the second layer was 35 μm. After equilibrating these bipolar membranes with 1.5 N saline overnight, 100 mA / cm ²
The voltage of the bipolar membrane was measured by performing dialysis at the current density of. The results are shown in Table 1 and FIG. Each of these current efficiencies exceeded 95%.

[0027]

Examples 4 to 5 Using the zirconium oxide fine particles used in Example 2, the weight of the matrix polymer containing the anion exchange resin part is 2.
The first layer, which is 5x and 3.5x, was obtained according to the following procedure. 40 parts of zirconium oxide fine particles and 28.6 parts of styrene 6.13 parts of divinylbenzene (purity 56%)
17.86 parts, vinylbenzyl chloride 45.78
Parts, 5 parts of polyvinyl chloride resin, 7.5 parts of nitrile butadiene rubber, 5 parts of dimethyl phthalate, and 0.2 parts of the polymerization initiator azobisisobutyronitrile. A polyvinyl chloride woven fabric is impregnated with a mixed liquid of this monomer and fine particles of zirconium oxide and covered with a polyester film.
Bulk polymerization was carried out at 24 ° C. for 24 hours to obtain a film. The obtained film-like material was quaternized with an aqueous trimethylamine solution containing acetone to obtain a first layer. Further, a second layer was formed in the same manner as in Examples 1 to 3 to form a bipolar film. A bipolar film having a first layer with different weight ratios of zirconium oxide fine particles and matrix polymer was obtained. After equilibrating these bipolar membranes with 1.5 N saline overnight, 100 mA /
Dialysis was performed at a current density of cm ² , and the voltage of the bipolar membrane was measured. The results of dialysis performance are shown in Table 1 and FIG. Each of these current efficiencies exceeded 95%.

[0028]

Comparative Example 1 Specific surface area smaller than Examples 1 to 3 3 m ² /
A first layer was prepared as follows using g of fine particles of zirconium oxide. A first layer was obtained in which the weight of the matrix polymer containing the anion exchange resin part was 2.5 times the weight of the fine particles of zirconium oxide according to the following procedure. 40 parts of fine particles of zirconium oxide, 6.13 parts of styrene, 17.86 parts of divinylbenzene (purity 56%), 45.78 parts of vinylbenzyl chloride, polyvinyl chloride resin 5
Parts, 7.5 parts of nitrile-butadiene rubber, 5 parts of dimethyl phthalate, and 0.2 parts of the polymerization initiator azobisisobutyronitrile. A polyvinyl chloride woven fabric was impregnated with a mixed liquid of the monomer and fine particles of a metal oxide, covered with a polyester film, and subjected to bulk polymerization at 60 ° C. for 24 hours to obtain a film. The obtained film-like material was quaternized with an aqueous trimethylamine solution containing acetone to obtain a first layer. Further, a second layer was formed in the same manner as in Examples 1 to 3 to form a bipolar film. The results of dialysis performance are shown in Table 1 and FIG. The current efficiency of this bipolar film exceeded 95%.

[0029]

Example 6 The same fine particles of zirconium oxide as in Example 2 were used, and the ion exchange capacity of the matrix polymer was C.
A bipolar film having a first layer of 1 type and 2 meq / g was prepared by the following procedure. Fine particles of zirconium oxide 6
6.7 parts of styrene 27.30 parts, divinylbenzene (purity 56%) 17.86 parts, vinylbenzyl chloride 30.52 parts, polyvinyl chloride resin 5 parts, nitrile butadiene rubber 7.5 parts, dimethyl phthalate 5 Parts and 0.2 parts of the polymerization initiator azobisisobutyronitrile. A polyvinyl chloride woven fabric was impregnated with a mixed liquid of the monomer and fine particles of a metal oxide, covered with a polyester film, and subjected to bulk polymerization at 60 ° C. for 24 hours to obtain a film. The obtained film-like material was quaternized with an aqueous trimethylamine solution containing acetone to obtain a first layer. Example 2 was used to prepare the bipolar film.
Is the same as The results of dialysis performance are shown in Table 1 and FIG.
These current efficiencies were over 95%.

[0030]

Comparative Example 2 The same fine particles of zirconium oxide as in Example 2 were used, and the ion exchange capacity of the matrix polymer was C.
A bipolar film having a first layer of 1 type and 1 meq / g was prepared by the following procedure. Fine particles of zirconium oxide 6
6.7 parts styrene 48.47 parts, divinylbenzene (purity 56%) 17.86 parts, vinylbenzyl chloride 15.26 parts, polyvinyl chloride resin 5 parts, nitrile butadiene rubber 7.5 parts, dimethyl phthalate 5 Parts and 0.2 parts of the polymerization initiator azobisisobutyronitrile. A polyvinyl chloride woven fabric was impregnated with a mixed liquid of the monomer and fine particles of zirconium oxide, covered with a polyester film, and subjected to bulk polymerization at 60 ° C. for 24 hours to obtain a film-shaped product. The obtained film-like material was quaternized with an aqueous trimethylamine solution containing acetone to obtain a first layer. Bipolar film making,
This is the same as the second embodiment. The results of dialysis performance are shown in Table 1 and FIG.
Shown in The current efficiency of this membrane was over 95%.

[0031]

Examples 7 to 8 Commercially available titanium oxide fine particles (specific surface area 43 and 6 m ² / g) were used as the metal oxide fine particles. A first layer in which the weight of the matrix polymer containing the anion exchange resin part was 4.7 times and 1.5 times the weight of the fine particles of titanium oxide was obtained according to the following procedure. 21.3 parts and 66.7 parts of fine particles of titanium oxide were added to styrene 6.
13 parts, divinylbenzene (purity 56%) 17.86
Parts, vinylbenzyl chloride 45.78 parts, polyvinyl chloride resin 5 parts, nitrile butadiene rubber 7.5 parts, dimethyl phthalate 5 parts, and a polymerization initiator azobisisobutyronitrile 0.2 part. A polyvinyl chloride woven fabric was impregnated with a mixed liquid of the monomer and fine particles of titanium oxide, covered with a polyester film, and subjected to bulk polymerization at 60 ° C. for 24 hours to obtain a film. The obtained film-like material was quaternized with an aqueous trimethylamine solution containing acetone to obtain a first layer.
The second layer was formed by the same method as in Examples 1 to 3 to obtain a bipolar film. The same dialysis evaluation as in Examples 1 to 3 was performed, and the results are shown in Table 1. The current efficiency of this film exceeded 95%.

[0032]

[Table 1]

[0033]

EFFECTS OF THE INVENTION The bipolar transistor of the present invention is characterized by a first layer having a novel structure, and since this first layer can be individually designed with a cation exchange resin layer as a second layer, it has a low current density and a low current density. High current efficiency can be obtained at the same time as showing water dissociation voltage. In addition, it is easy to introduce a reinforcing cloth into the first layer, anion exchange resin layer or cation exchange resin layer for increasing the mechanical strength of the membrane, and it is also possible to select the optimum resin and add other functionality. It can be realized with almost no influence on the dialysis performance of the membrane. Further, there is an excellent advantage that an industrial scale membrane can be easily manufactured.

[Brief description of drawings]

FIG. 1 is an example of a schematic view of a bilayer bipolar film of the present invention.

FIG. 2 is an example of a schematic diagram of a three-layer bipolar film of the present invention.

FIG. 3 is a diagram showing the relationship between the specific surface area of the composite particles used in the bipolar membrane shown in Example and Comparative Example and the water dissociation voltage.

[Explanation of symbols]

 1 First Layer 2 Second Layer 3 Metal Oxide Fine Particles 4 Matrix Polymer 5 Third Layer

Claims (2)

[Claims] 1. In a bipolar film comprising at least two layers, the first layer contains metal oxide fine particles and has only an anion exchange group as an ion exchange group, and the metal oxide fine particles are 1) Specific surface area of 5 m ² / g to 25
0 m ² / g, (2) average particle size 0.5 μm to 10 μm
And the anion exchange capacity of the matrix polymer constituting the first layer is 2 meq / g per unit weight of the resin.
A bipolar membrane, which has a thickness of 4.5 meq / g and in which the second layer is made of a polymer having a cation exchange group. 2. The bipolar film according to claim 1, wherein the fine particles of the metal oxide are fine particles containing at least one oxide selected from the group IVA such as titanium, zirconium and hafnium.