JP7257027B2 - Bipolar membrane and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a bipolar membrane in which a cation exchange membrane and an anion exchange membrane are laminated together, and a method for producing the same.

A bipolar membrane is a composite membrane in which a cation exchange membrane and an anion exchange membrane are bonded together. By applying a voltage to both sides of the bipolar membrane immersed in an aqueous solution, the water in the membrane is converted into protons and hydroxide ions. It has the function of causing a phenomenon called water splitting. Using this function, electrodialysis is performed by combining a bipolar membrane with a cation exchange membrane or an anion exchange membrane, for example, acid or alkali can be produced from a neutral salt.

Since such a bipolar membrane has a structure in which a cation exchange membrane and an anion exchange membrane are bonded together, there is a problem that peeling easily occurs at the interface between the cation exchange membrane and the anion exchange membrane.
As a means for solving such a problem, a paste-like adhesive having ion exchange properties is used to bond the cation exchange membrane and the anion exchange membrane together, and then the adhesive is appropriately cured by irradiation with radiation or the like. Such means have long been proposed in Patent Literature 1 and the like.
However, when a bipolar membrane bonded using such an adhesive is immersed in water, the cation exchange membrane and the anion exchange membrane warp due to swelling to a different degree, so the peeling is still effective. It is difficult to prevent it effectively.

In addition, as a means for reliably avoiding separation between the cation exchange membrane and the anion exchange membrane, Patent Document 2 discloses preparing two polymer membranes having functional groups suitable for introducing ion exchange groups. , two polymer membranes are superimposed and integrated such that a covering film (release film) made of polyester, polyvinyl alcohol or cellophane is positioned between them, and the integrated product is sulfonated. A method has been proposed in which cation-exchange groups are introduced by the method, then the coating film is peeled off, and anion-exchange groups are introduced onto the surface from which the coating film was peeled off.
In this method, a cation exchange membrane is formed on one side of polymer membranes that are integrated without bonding, and an anion exchange membrane is formed on the other side of the polymer membrane, so that the two separate. The problem is definitely avoided.

By the way, in a bipolar membrane, in order to dissociate water into protons and hydroxide ions at a low voltage, a water dissociation promoting catalyst (such as tin chloride) is added to the interface between the cation exchange membrane and the anion exchange membrane to promote water dissociation. ) is known.

In the method proposed in Patent Document 2, a water dissociation promoting catalyst cannot be provided. The resin base material forming the cation exchange membrane and the resin base material forming the anion exchange membrane are integrated, and since the cation exchange group and the anion exchange group are introduced later, the interface between both membranes This is because the catalyst for promoting water dissociation cannot be distributed in the region.
Therefore, the bipolar membrane obtained by the method of Patent Document 2 cannot lower the water-splitting voltage, and there is room for improvement.

In addition, the ion exchange membrane is usually provided with a porous sheet as a reinforcing material inside the membrane. This is because such a porous sheet improves mechanical strength and effectively avoids deformation due to swelling or the like. Therefore, when an attempt is made to manufacture the bipolar membrane using an ion exchange membrane having a porous sheet inside such a membrane, the surface of the ion exchange membrane (base ion exchange membrane) is coated with a counter ion exchange resin of opposite polarity. It will form a layer (for example, Patent Document 3). In this case, since the porous sheet exists inside the base ion-exchange membrane, it does not substantially affect the interface between the base ion-exchange membrane and the coating layer of the counter ion-exchange resin. Therefore, nothing contributes to the improvement of the bonding strength between these two layers.
As the porous sheet, a resin sheet such as a porous polyolefin resin sheet or a woven fabric fiber sheet is used, but from the viewpoint of cost reduction, the use of a non-woven fabric fiber sheet has been proposed. . That is, in Patent Document 3, a nonwoven fabric is exemplified as an example of a reinforcing material for a bipolar membrane.
However, as a matter of course, the strength of the non-woven fabric fiber sheet is low, so it is not actually used as a reinforcing material.

Japanese Patent Publication No. 51-4113 Japanese Patent Publication No. 1-14251 Patent No. 6166814

Accordingly, an object of the present invention is to disperse a water dissociation promoting catalyst at the interface between a cation exchange membrane and an anion exchange membrane, so that not only can water be dissociated at a low voltage, but also the cation exchange membrane and the anion exchange membrane can be separated. The object of the present invention is to provide a bipolar film effectively preventing peeling at the interface of the film and a method for producing the same.
Another object of the present invention is to provide a bipolar membrane using a nonwoven fiber sheet as a reinforcing material and a method for manufacturing the same.

According to the present invention, in a bipolar membrane formed by bonding a cation exchange resin layer and an anion exchange resin layer,
A water dissociation promoting catalyst is distributed at the bonding interface between the cation exchange resin layer and the anion exchange resin layer,
Provided is a bipolar membrane comprising a porous sheet straddling the bonding interface between the cation exchange resin layer and the anion exchange resin layer.

In the bipolar membrane of the present invention,
(1) the bonding interface between the cation exchange resin layer and the anion exchange resin layer is located at 2/10 to 8/10 of the thickness of the porous sheet;
(2) the water dissociation promoting catalyst is tin chloride or ruthenium chloride;
(3) the porosity of the porous sheet is in the range of 70 to 90%;
(4) the porous sheet is a nonwoven fiber sheet;
(5) the nonwoven fiber sheet has a basis weight in the range of 3 to 50 g/m ² and a fiber diameter in the range of 8 to 30 μm;
is preferred.

According to the present invention, an ion-exchange resin layer and a counter-ion-exchange resin layer having a polarity opposite to that of the ion-exchange resin layer are bonded together, and a catalyst for promoting a water dissociation reaction is distributed on the bonding interface. In the method for manufacturing a bipolar membrane comprising
A porous sheet, a release film, a first organic solvent solution in which an ion-exchange resin-forming polymer is dissolved, a catalyst solution in which a water dissociation promoting catalyst is dispersed or dissolved, and a counter-ion-exchange resin-forming polymer are dissolved. A second organic solvent solution is prepared, and the following steps (a-1) to (a-3), (b), and (c-1) to (c-3) are included. A method for manufacturing a bipolar membrane is provided.
(a-1) applying a first organic solvent solution to one surface of the release film to form a coating layer of the first organic solvent solution;
(a-2) a step of superimposing the porous sheet on the coating layer of the first organic solvent solution and impregnating the porous sheet with the first organic solvent solution halfway in the thickness direction;
(a-3) drying the coating layer of the first organic solvent solution in a state where the porous sheets are superimposed, and ion exchange resin is applied to a region from the superimposed surface to the middle of the thickness direction of the porous sheets; A step of obtaining an ion-exchange resin sheet in which a release film, an ion-exchange resin layer and a porous sheet are laminated by forming layers;
(b) applying the catalyst solution to the surface of the ion-exchange resin sheet on the porous sheet side, allowing it to penetrate into the porous sheet, and then drying to obtain the catalyst solution on the surface of the ion-exchange resin layer; distributing;
(c-1) applying the second organic solvent solution to the surface of the porous sheet of the ion exchange resin sheet to form a coating layer of the second organic solvent solution;
(c-2) drying the coating layer of the second organic solvent solution to form a counter ion exchange resin layer;
(c-3) Next, a step of producing a bipolar membrane by peeling off the release film;

According to the production method of the present invention,
(1) using a nonwoven fiber sheet as the porous sheet;
(2) When an ion-exchange resin precursor is used as the ion-exchange resin-forming polymer, in the step (a-3), the coating layer is After drying, introducing ion exchange groups into the ion exchange resin precursor;
(3) When a counter ion-exchange resin precursor is used as the polymer for forming the counter ion-exchange resin, in the step (c-2), the coating layer containing the counter ion-exchange resin precursor is dried. After that, introducing a counter ion exchange group into the counter ion exchange resin precursor,
(4) As the first organic solvent solution, a high-viscosity solution having a viscosity of 1.0 to 60 dPa s at 25 ° C. is used, and as the second organic solvent solution, use a low viscosity solution,
is preferred.

In the bipolar membrane of the present invention, since the porous sheet is arranged so as to straddle the cation exchange resin layer and the anion exchange resin layer, the bonding strength between the cation exchange membrane and the anion exchange membrane is increased, and the separation of both membranes is improved. can be effectively avoided. Moreover, since the porous sheet straddles the cation-exchange resin layer and the anion-exchange resin layer, even when the nonwoven fiber sheet is used as the porous sheet, insufficient strength of the nonwoven fiber sheet can be effectively avoided. Therefore, an inexpensive nonwoven fiber sheet can be effectively used as a reinforcing material for the bipolar membrane.
Furthermore, according to the present invention, the porous sheet is permeated with a water dissociation promoting catalyst that promotes dissociation of water, and the water dissociation promoting catalyst is distributed at the bonding interface between the cation exchange resin layer and the anion exchange resin layer. ing. Thereby, the bipolar membrane of the present invention can promote dissociation of water at a low voltage.

FIG. 2 is a diagram showing a schematic cross-sectional structure of the bipolar film of the present invention; 4A to 4C are diagrams showing the manufacturing process of the bipolar film of the present invention;

<Structure of Bipolar Film BP>
Referring to FIG. 1, the bipolar membrane BP of the present invention has a cation exchange resin layer C and an anion exchange resin layer A facing each other. is provided, and a catalyst layer 3 in which a water dissociation promoting catalyst is distributed is formed on the bonding interface S. As shown in FIG.

That is, in the bipolar membrane BP of the present invention, the porous sheet 1 functions not only as a reinforcing material for the bipolar membrane BP, but also as a bonding material between the cation exchange resin layer and the anion exchange resin layer. . That is, since the porous sheet 1 is provided so as to straddle the bonding interface S between the cation exchange resin layer C and the anion exchange resin layer A, the cation exchange resin layer C and the anion exchange resin layer C can be bonded without using a special adhesive. The replacement resin layer A is joined and fixed.

Further, in the above bipolar membrane BP, a catalyst layer 3 in which a water dissociation promoting catalyst is distributed is provided at the bonding interface between the cation exchange resin layer C and the anion exchange resin layer A. The existence of such a catalyst layer 3 can promote the dissociation of water at a low voltage.
In addition, the catalyst layer 3 is applied to the porous sheet 1 held by either the cation exchange resin layer C or the anion exchange resin layer A from the exposed surface side of the porous sheet 1. It can be formed by supplying and permeating a catalyst liquid to form a layer of the catalyst liquid on the surface of the cation exchange resin layer C or the anion exchange resin layer A, followed by drying. That is, after this, the anion-exchange resin layer A or the cation-exchange resin layer C serving as counterions may be formed. Such a method will be described later.

In the present invention, the cation-exchange resin layer C and the anion-exchange resin layer A may each be formed of an ion-exchange resin known per se and have a thickness according to the application.

As the porous sheet 1, a known reinforcing material for ion-exchange resin can be used. A fiber sheet such as is used.
Furthermore, from the viewpoint of ensuring electrical conductivity while maintaining appropriate strength, the porosity of the porous sheet 1 is preferably in the range of 70 to 90%, preferably 75 to 85%.

In the present invention, a nonwoven fiber sheet is most suitable as the porous sheet 1 from the viewpoint of cost and the like.
Such a nonwoven fiber sheet has a basis weight in the range of 3 to 50 g/m ² , preferably 5 to 30 g/m ² , and a fiber diameter in the range of 8 to 30 μm, preferably 10 to 20 μm. This is preferable for imparting appropriate strength to the bipolar film BP.

The fibers of the non-woven fiber sheet are made of a thermoplastic resin. Examples of such thermoplastic resins include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1 - Olefin-based resins that are homopolymers or copolymers of α-olefins such as butene, 4-methyl-1-pentene, and 5-methyl-1-heptene; polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, Vinyl chloride resins such as vinyl chloride-vinylidene chloride copolymer, vinyl chloride-olefin copolymer; polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene Fluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer and other fluorine-based resins; nylon 6, nylon 66 and other polyamide resins; polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, etc. A polyester-based resin and the like can be mentioned.
In the nonwoven fabric fiber sheet suitably used as the porous sheet 1 in the present invention, from the viewpoint of membrane properties (mechanical strength, chemical stability, chemical resistance) when used as an ion exchange membrane, polyester resin fiber , olefin resin fibers (especially polyethylene fibers and polypropylene fibers) are preferred, and polyethylene fibers are most preferred.

In the present invention, when the thickness of the porous sheet 1 is T, the bonding interface S between the cation exchange resin layer C and the anion exchange resin layer A is 2/10 to 8/10 of the thickness T. , more preferably 3/10 to 7/10, in order to secure the strength of the bipolar film BP in a well-balanced manner.
Furthermore, although the thicknesses of the cation exchange resin layer C and the anion exchange resin layer A are substantially the same, the total thickness (t1 + t2) of the thickness t1 of the cation exchange resin layer C and the thickness t2 of the anion exchange resin layer A is 50. It is preferable that the thickness T of the porous sheet 1 is about 90%, preferably about 60 to 85%, in order to ensure proper strength and shape stability of the bipolar membrane BP. Also, the thickness of the bipolar membrane is preferably in the range of 30 to 300 μm, preferably 50 to 200 μm, from the viewpoint of appropriate strength and resistance. Further, from the viewpoint of handleability, the bursting strength is preferably in the range of 50 to 3000 kPa, preferably 100 to 2000 kPa.

In the present invention, as the water dissociation promoting catalyst, salts and oxides capable of releasing heavy metal ions such as iron, tin, chromium and ruthenium are used, preferably chlorides of these heavy metals, particularly chlorides of tin and ruthenium. things are used.
Such a water dissociation promoting catalyst is generally applied on the bonding interface S between the cation exchange resin layer C and the anion exchange resin layer A in an amount of 1 to 5000 mg/m ² , preferably 5 to 2000 mg/m ² in terms of heavy metal. It should be distributed in terms of quantity.

The cation-exchange resin layer C and the anion-exchange resin layer A are both made of an ion-exchange resin that can be dissolved in an organic solvent and formed by coating. Polymers obtained by polymerizing monomers having ethylenically unsaturated double bonds, or polysulfones, polyphenylene sulfides, polyetherketones, polyetheretherketones, polyetherimides, polyphenylene oxides, polyethersulfones, and polybenzimidazoles It has a structure in which an ion-exchange group (e.g., a cation-exchange group or anion-exchange group) that develops ion-exchange ability is introduced into a hydrocarbon-based resin such as a polymer containing an aromatic ring in the main chain such as .

The ion-exchange group is a functional group that can become negatively or positively charged in an aqueous solution. In the case of a cation-exchange group, a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, etc. can be mentioned. Sulfonic acid groups, which are strongly acidic groups, are preferred. In the case of the anion exchange group, primary to tertiary amino groups, quaternary ammonium groups, pyridyl groups, imidazole groups, quaternary pyridinium groups, etc., and generally, strongly basic quaternary ammonium groups and quaternary pyridinium groups are preferred.

Examples of cation exchange resins include sulfonic acid-based monomers such as α-halogenated vinylsulfonic acid, styrenesulfonic acid and vinylsulfonic acid, and carboxylic acid-based monomers such as methacrylic acid, acrylic acid and maleic anhydride. phosphonic acid-based monomers such as vinyl phosphoric acid, and polymers obtained by polymerizing their salts and esters.
Examples of anion exchange resins include amine-based monomers such as vinylbenzyltrimethylamine and vinylbenzyltriethylamine, nitrogen-containing heterocyclic monomers such as vinylpyridine and vinylimidazole, and salts and esters thereof. Polymers obtained by

These ion-exchange resins may have a crosslinked structure as long as a solution dissolved in an organic solvent can be prepared. , divinylnaphthalene, diallylamine, divinylpyridine, and other polyfunctional monomers typified by divinyl compounds. It may also be a copolymer obtained by copolymerizing other monomers such as styrene, acrylonitrile, methylstyrene, acrolein, methylvinylketone, vinylbiphenyl and the like.

In the present invention, the ion exchange resin forming the cation exchange resin layer C and the anion exchange resin layer A has an ion exchange capacity of 0.5 to 3.0 meq/g, particularly 0.8 to 2.5 meq/g. preferably in In particular, when the ion exchange capacity is 0.8 meq/g or more, the membrane resistance is sufficiently low, resulting in high membrane performance. It can be suppressed more effectively, and it becomes difficult to cause shape change and film peeling. Therefore, it is preferable to introduce a cation exchange group or an anion exchange group so as to obtain such an ion exchange capacity.
In the example of FIG. 1, the anion exchange resin layer A is formed on the surface of the cation exchange resin layer C via the catalyst layer 3 in which the water dissociation promoting catalyst is distributed. Alternatively, a cation exchange resin layer C may be provided on the surface of the anion exchange resin layer A with the catalyst layer 3 interposed therebetween.

<Production of Bipolar Membrane BP>
Referring to FIG. 2, the above-described bipolar membrane BP of the present invention comprises a porous sheet 1, a release film 10, a first organic solvent solution in which an ion-exchange resin-forming polymer is dissolved, and a water dissociation promoting catalyst 3. (a-1) to (a-3), (b ), and (c-1) to (c-3).

Both the first organic solvent solution and the second organic solvent solution are those in which a cation exchange resin-forming polymer or an anion exchange resin-forming polymer is dissolved as an ion exchange resin. When the cation-exchange resin-forming polymer is dissolved in the solution, the anion-exchange resin-forming polymer is dissolved in the second organic solvent solution. When the ion-exchange resin-forming polymer dissolved in the solution forms an anion-exchange resin, the cation-exchange resin-forming polymer is dissolved in the second organic solvent solution.

The ion-exchange resin-forming polymer dissolved in the first organic solvent solution or the second organic solvent solution may be, for example, a cation exchange resin or an anion exchange resin into which ion exchange groups have already been introduced. Alternatively, it may be an ion-exchange resin precursor that has not yet been introduced with ion-exchange groups. When an organic solvent solution in which such an ion-exchange resin precursor is dissolved is used, a subsequent treatment for introducing ion-exchange groups is required.

The ion-exchange resin precursor is a polymer having functional groups capable of introducing ion-exchange groups. Examples of polymers having functional groups for introducing cation-exchange groups include styrene, vinyltoluene, vinylxylene, and α-methylstyrene. , vinylnaphthalene, and α-halogenated styrenes. Examples of polymers having functional groups for introducing anion exchange groups include those obtained by polymerizing monomers such as styrene, vinyltoluene, chloromethylstyrene, vinylpyridine, vinylimidazole, α-methylstyrene, and vinylnaphthalene. things can be mentioned.
Of course, these ion-exchange resin precursors may have a crosslinked structure introduced by copolymerizing a polyfunctional monomer such as the aforementioned divinyl compound as long as they are soluble in an organic solvent. However, if necessary, other monomers may be copolymerized.
When an organic solvent solution of such an ion-exchange resin precursor is used, the solution may contain an ion-exchange group-introducing agent so that the ion-exchange groups are introduced in parallel with the formation of the resin layer. good. Examples of ion exchange group introducing agents include polyalkylbenzenesulfonic acids (e.g., 1,3,5-trimethylbenzene-2-sulfonic acid, 1,2,4,5-tetramethylbenzene-3-sulfonic acid, 1, 2,3,4,5-pentamethylbenzene-6-sulfonic acid, etc.), N,N,N′,N′-tetramethyl-1,6-hexanediamine, N,N,N′,N′-tetra methyl-1,6-octanediamine, N,N,N',N'-tetraethyl-1,6-hexanediamine and the like. Alternatively, ion-exchange groups may be introduced by preparing a resin layer of an ion-exchange resin precursor and then treating it with the ion-exchange group-introducing agent.

The organic solvent used for preparing the ion-exchange resin-forming polymer or ion-exchange resin precursor organic solvent solution is not particularly limited as long as it can dissolve the above-described polymer, but it is said that it can be easily removed by drying. From the point of view, ethylene chloride, chloroform, tetrahydrofuran, dimethylformamide, N-methylpyrrolidone, methyl alcohol, butyl acetate, ethyl acetate, toluene, methyl ethyl ketone, etc. are preferably used singly or in the form of a mixed solvent in which two or more are mixed. used.

Further, as will be understood from the following description, the first organic solvent solution forms the coating layer 11, and the porous sheet 1 is placed on the coating layer 11 to form the coating layer 11 in the porous sheet 1. to invade. Therefore, the first organic solvent solution must be able to form the coating layer 11 with an appropriate thickness and must have a high viscosity so that it does not flow even when the porous sheet 1 is stacked. In addition, in the bipolar membrane to be manufactured, the porous sheet needs to exist across the bonding interface between the cation exchange resin layer and the anion exchange resin layer. , the viscosity must be moderately low such that the first organic solvent solution stays and permeates halfway through the thickness. From such a viewpoint, the first organic solvent solution is adjusted so that the viscosity (25° C.) is in the range of 1.0 to 60 dPa·s, more preferably in the range of 5.0 to 55 dPa·s. preferably.
On the other hand, the second organic solvent solution is applied to the surface opposite to the overlapping surface of the porous sheet 1 in which the first organic solvent solution has permeated halfway in the thickness direction, and the remaining voids are filled with the second organic solvent solution. It penetrates. In order to carry out this with high fillability, the second organic solvent solution is required to have higher permeability, and therefore its viscosity is preferably lower than that of the first organic solvent solution. For example, the viscosity (25° C.) is preferably 5 dPa·s or less, particularly 0.1 to 3.0 dPa·s.

The catalyst solution in which the catalyst for promoting water dissociation is dispersed or dissolved may be a solution in which the aforementioned compounds (salts, oxides, etc.) capable of releasing heavy metal ions are dissolved, or a solution in which these compounds are dispersed in the form of granules. A dispersion liquid containing For such a catalyst liquid, water or an organic solvent can be used as a solvent or a dispersion medium as long as the dissolved or dispersed catalyst compound can permeate into the porous sheet 1. The dispersed particle size is not particularly limited, but when dispersed without being dissolved in a solvent, the dispersed particle size is preferably small, for example, 10 μm or less, preferably 0.1 to 5.0 μm. preferably.

step (a-1);
First, a first organic solvent solution in which a cation-exchange resin-forming polymer or an anion-exchange resin-forming polymer is dissolved is applied to one surface of the release film 10 to form a coating layer 11 of the first organic solvent solution. Form.
This release film 10 does not adhere to the ion-exchange resin dissolved in the first organic solvent solution, does not dissolve in the organic solvent in the coating layer 11, and can be easily peeled off at the end. The type and thickness of the film are not limited as long as it is a film, but in general, a polyester film such as polyethylene terephthalate is preferably used from the viewpoint of being excellent in durability, mechanical strength, etc., and being able to be used repeatedly. be.

The thickness of the coating layer 11 is adjusted so that the dry thickness is equal to the thickness of the ion exchange resin layer (cation exchange resin layer C in the example of FIG. 1) that serves as the base of the catalyst layer 3 . For example, when fabricating the bipolar membrane BP of FIG. It corresponds to the thickness t1.
In order to form the coating layer 11 with such a thickness, the first organic solvent solution needs to have a certain degree of high viscosity so as not to cause dripping or the like.

Application of the organic solvent solution can be carried out by means known per se, such as doctor blade coating, knife coating, roll coating, bar coating, and the like.

step (a-2);
After forming the coating layer 11 of the first organic solvent solution as described above, the porous sheet 1 is superimposed on the coating layer 11, and the first organic solvent solution is applied halfway in the thickness direction of the porous sheet 1. Impregnate. The position of the interface S between the cation exchange resin layer C and the anion exchange resin layer A is determined by such impregnation.

By stacking the porous sheets 1 in this manner, the first organic solvent solution penetrates into the porous sheet 1 halfway in the thickness direction. Although it has permeability, it must have such a viscosity that the permeation stops in the middle of the thickness direction of the porous sheet 1 . That is, the first organic solvent solution must have an appropriate viscosity in order to form the coating layer 11 having a certain thickness and to permeate the porous sheet 1 superimposed on the coating layer 11. As a result, the viscosity of the first organic solvent solution is adjusted within the range described above.
In order to allow the coating layer 11 to permeate the porous sheet 1, the porous sheet 1 may be pressurized as appropriate.

step (a-3);
In this step, an ion-exchange resin layer (cation-exchange resin layer C in the example of FIG. 1) that serves as a base for the catalyst layer 3 is determined.
That is, the coating layer 11 of the first organic solvent solution is dried while the porous sheets 1 are superimposed. As a result, an ion-exchange resin layer (for example, a cation-exchange resin layer C) that serves as a base for the catalyst layer 3 is formed in a region from the superimposed surface to the middle of the porous sheet 1 in the thickness direction, and a release film and an ion-exchange resin layer are formed. And the ion-exchange resin sheet 20 laminated with the porous sheet 1 is obtained, and the position of the interface S is determined.

When an ion-exchange resin precursor to which no ion-exchange groups have been introduced is used as the ion-exchange resin-forming polymer in the first organic solvent solution, the ion-exchange group introduction treatment is performed after the above drying. is done.
For example, when a cation-exchange resin precursor is used as the ion-exchange resin-forming polymer, cation-exchange groups are introduced by treatments such as sulfonation, phosphoniumation and hydrolysis. When an anion exchange resin precursor is used as the ion exchange resin-forming polymer, anion exchange groups are introduced by treatments such as amination and alkylation.

step (b);
In this step, the surface of the ion-exchange resin layer (cation-exchange resin layer C in the example of the figure) formed as described above (the surface located within the porous sheet 1 and corresponding to the interface S in FIG. ) to form the catalyst layer 3 .
Specifically, the surface of the porous sheet 1 in the ion-exchange resin sheet 20 is coated with a catalyst solution in which the above-mentioned water dissociation promoting catalyst is dispersed or dissolved, or the surface is immersed in the catalyst solution to form a base. By permeating the catalyst liquid to the surface of the ion-exchange resin layer (for example, cation-exchange resin layer C) and then drying, the catalyst layer 3 in which the water-splitting promoting catalyst is distributed on the interface S is formed.

After the catalyst layer 3 is formed as described above, the catalyst layer 3 is subjected to the following steps (c-1) to (c-3) using a second organic solvent solution to remove underlying ions. A counter ion exchange resin layer having a polarity opposite to that of the exchange resin layer is formed. That is, in FIG. 2, since the ion-exchange resin layer underlying the catalyst layer 3 is shown as the cation-exchange resin layer C, the second organic solvent solution in which the anion-exchange resin-forming polymer is dissolved is used. An anion exchange resin layer A is formed. Further, when the underlying ion-exchange resin layer is the anion-exchange resin layer A, the second organic solvent solution contains a cation-exchange resin-forming polymer, and the cation-exchange resin layer is formed on the anion-exchange resin layer A. C will be formed.

step (c-1);
In this step, the above second organic solvent solution is applied to the surface of the porous sheet 1 of the ion exchange resin sheet 20 . As a result, the second organic solvent solution penetrates into the porous sheet 1 and reaches the surface of the previously formed ion-exchange resin layer (for example, the cation-exchange resin layer C) via the catalyst layer 3. A layer 13 is formed.
That is, the second organic solvent solution forms the coating layer 13 by allowing the second organic solvent solution to permeate the remaining voids of the porous sheet 1 in which the first organic solvent solution has permeated halfway in the thickness direction. Therefore, as mentioned above, higher permeability is required. Therefore, its viscosity is lower than that of the first organic solvent solution, and therefore it is preferable to adjust it within the aforementioned range.

step (c-2);
After the coating layer 13 of the second organic solvent permeating the porous sheet 1 is formed as described above, the coating layer 13 is dried to form a counter ion-exchange resin layer (for example, FIG. 2 An anion exchange resin layer A) is formed in the example of . That is, the dry thickness of the coating layer 13 corresponds to the thickness of the counter ion-exchange resin layer (for example, the thickness t2 of the anion-exchange resin layer A).
In this case, when a precursor to which counter ion exchange groups have not been introduced is used as the polymer in the second organic solvent solution, treatment for introducing counter ion exchange groups is performed after drying. . This is the same as the case of forming the ion-exchange resin layer underlying the catalyst layer 3 .

step (c-3);
After the counter ion exchange resin layer is formed as described above, the release film is finally peeled off to obtain the intended bipolar membrane BP.

In the thus-obtained bipolar membrane BP of the present invention, separation of the cation-exchange resin layer C and the anion-exchange resin layer A is effectively prevented. Since the dissociation promoting catalyst is distributed, the dissociation of water can proceed at a low voltage. The bipolar voltage measured in Examples described later is usually suppressed to 2.0 V or less, preferably 1.5 V or less, more preferably 1.3 V or less.
Furthermore, when a non-woven fiber sheet is used as the porous sheet 1, not only is it extremely inexpensive, but the non-woven fiber sheet is formed across the cation exchange resin layer C and the anion exchange resin layer A. Therefore, the adhesiveness of the interface S is high, and the T-peel strength at a tensile speed of 100 mm/min is 0.5 N/cm or more, preferably 0.8 N/cm or more. Insufficient strength of the nonwoven fiber sheet is also effectively improved.

The excellent effects of the present invention are illustrated by the following examples.
In the examples and comparative examples, the properties of the bipolar membrane, the viscosity of the polymer solution, and the amount of the catalyst were obtained by the following measurements.

1) bipolar voltage;
A four-compartment cell with the following configuration was used.
Anode (Pt plate) (1.0 mol / L-NaOH) / Neosepta BP-1E (manufactured by Astom Co., Ltd.) / (1.0 mol / L-NaOH) / bipolar membrane / (1.0 mol
/ L-HCl) / Neosepta BP-1E (manufactured by Astom Co., Ltd.) / (1.0 mol
/L-HCl) cathode (Pt plate)
Bipolar voltage was measured under conditions of a liquid temperature of 25° C. and a current density of 10 A/dm ² . The bipolar voltage was measured by platinum wire electrodes placed across the bipolar membrane.

2) adhesion of bipolar membranes;
A tape (adhesive strength 3.2 N / 15 mm) was attached to the anion exchange resin surface of the bipolar membrane, and the tape was partially peeled off. The T-peel strength was measured with a load measuring device LTS-500NB manufactured by Minebea Co., Ltd. at a tensile speed of 100 mm/min.

3) measurement of the ion exchange capacity of the ion exchange resin;
The ion exchange resin was immersed in a 1 mol/L-HCl aqueous solution for 10 hours or more.
After that, in the case of a cation exchange membrane, a 1 mol/L-NaCl aqueous solution is used to replace the counter ions of the ion exchange groups from hydrogen ions to sodium ions, and the liberated hydrogen ions are subjected to potentiometric titration using an aqueous sodium hydroxide solution (COMTITE). -900, manufactured by Hiranuma Sangyo Co., Ltd.). On the other hand, in the case of an anion exchange membrane, chloride ions are replaced with nitrate ions with a 1 mol/L-NaNO ₃ aqueous solution, and the liberated chloride ions are measured using a potentiometric titrator (COMTITE-900, COMTITE-900) using an aqueous silver nitrate solution. (manufactured by Hiranuma Sangyo Co., Ltd.). Next, the same ion-exchange membrane was immersed in a 1 mol/L-NaCl aqueous solution for 4 hours or more, and then dried under reduced pressure at 60° C. for 5 hours, and the dry weight (Dg) was measured. Based on the above measured values, the ion exchange capacity of the ion exchange membrane was determined by the following formula.
Ion exchange capacity = A x 1000/D [meq/g-dry mass]

4) burst strength of the bipolar membrane;
The bipolar membrane was immersed in ion-exchanged water for 4 hours or more, and then the bursting strength was measured according to JIS-P8112 using a Mullen bursting tester (manufactured by Toyo Seiki) without drying the membrane.

5) Measurement of bipolar film thickness, ion exchange resin layer thickness, nonwoven fabric layer thickness and interface position;
The asymmetric ion-exchange membrane was cut with a microtome (ESM-150S manufactured by Eruma Co., Ltd.) to form a cross section for measurement. Next, using a color 3D laser microscope VK-8700 (manufactured by Keyence Corporation), the cross section of the membrane sample is observed with a 50x objective lens, and from the observed image, the ion exchange resin layer thickness, the nonwoven fabric layer thickness, and the first and second The interface position of the ion-exchange resin layer was measured. The position of the interface was expressed in units of 1/10, with the nonwoven fabric surface on the first ion-exchange resin layer side being position 0.
Also, the thickness of the bipolar film was measured using a micrometer MED-25PJ (manufactured by Mitutoyo Co., Ltd.).

6) polymer solution viscosity;
Using a rotating cylinder type viscometer ViscoTester VT-04F (manufactured by Rion Co., Ltd.), the viscosity of an ion-exchange resin or an organic solvent solution (polymer solution) of an ion-exchange resin precursor was measured.

7) measurement of the amount of catalyst;
The catalyst-treated cation exchange membrane was measured by fluorescent X-ray analysis to determine the molar ratio of sulfur element and catalyst element, and the amount of catalyst was calculated from the relative ratio of sulfur element to ion exchange capacity.

The cation exchange polymer solutions and anion exchange polymers used in Examples and Comparative Examples were prepared as follows.

preparation of a cation exchange polymer solution;
(1) Preparation of Cation Exchange Polymer (SPPO) Solution (C1) Polyphenylene oxide was dissolved in chloroform, and chlorosulfonic acid was added to the solution to react the polyphenylene oxide with chlorosulfonic acid. Then, sodium hydroxide was added for neutralization, and the solvent was removed to obtain a sulfonated polyphenylene oxide (cation exchange polymer, SPPO) having an ion exchange capacity of 1.6 meq/g.
Next, the cation exchange polymer (SPPO) obtained above was dissolved in N,N-dimethylformamide (DMF) so that its concentration was 28% by mass, and sulfonated polyphenylene oxide (SPPO) was obtained. A solution (C1) of a cation exchange polymer consisting of was prepared.
The viscosity (25° C.) of this cation exchange polymer solution (C1) was 20 dPa·s.

(2) Preparation of Cation Exchange Polymer (SPPO) Solution (C2) A solution (C2) of a cation exchange polymer consisting of sulfonated polyphenylene oxide (SPPO) was prepared in the same manner as above.
The viscosity (25° C.) of this cationic polymer solution (C2) was 2 dPa·s.

(3) Preparation of solution (C3) of cation exchange polymer (SPEEK) Polyetheretherketone was dissolved in concentrated sulfuric acid, and sulfonation reaction was carried out with stirring. After the reaction, the polyetheretherketone/concentrated sulfuric acid solution was quenched in pure water to obtain sulfonated polyetheretherketone (cation exchange polymer, SPEEK). The ion exchange capacity of this polymer was 1.5 meq/g.
Next, the cation exchange polymer (SPEEK) obtained above is dissolved in N,N-dimethylformamide (DMF) so that its concentration is 25% by mass, and the sulfonated polyether ether ketone (SPEEK) is A solution (C3) of a cation exchange polymer was prepared. The viscosity (25° C.) of this cation exchange polymer solution (C3) was 5 dPa·s.

Preparation of an anion exchange polymer solution;
(1) Preparation of solution (A1) of anion exchange polymer (CMPS/CMSEPS) 100 g of a copolymer consisting of polystyrene segments (65% by mass) and hydrogenated polyisoprene segments (35% by mass) was added to 1000 g of chloroform. 100 g of chloromethyl methyl ether and 10 g of tin chloride were added to this solution and reacted at 40° C. for 15 hours to chloromethylate the polystyrene block.
Next, the precipitate was precipitated in methanol, washed, and dried to obtain a chloromethylated styrenic block copolymer.
Next, chloromethylated polystyrene having a molecular weight of 5,000 was mixed with the chloromethylated styrenic block copolymer obtained above, and the proportion of chloromethylated polystyrene was adjusted to 40% by mass.

The chloromethylated polymer mixture thus obtained was dissolved in tetrahydrofuran (THF) to prepare an anion exchange resin precursor solution having a polymer concentration of 25 mass %.
To this anion exchange resin precursor solution, N,N,N',N'-tetramethyl-1,6-hexanediamine (anion exchange group introduction agent) was added so that the concentration was 6.6% by mass. to prepare a solution (A1) of an anion exchange polymer (CMPS/CMSEPS).
The viscosity (25° C.) of this anion exchange polymer solution (A1) was 5 dPa·s.

The anion-exchange polymer solution (A1) thus obtained was coated on a polyethylene terephthalate film, and the anion-exchange membrane obtained by drying was used to measure the ion-exchange capacity. Met.

(2) Preparation of solution (A2) of anion exchange polymer (CMPS/CMSEPS) On the other hand, the chloromethylated polymer mixture was mixed with tetrahydrofuran ( THF) to prepare an anion exchange resin precursor solution.
To this anion exchange resin precursor solution, N,N,N',N'-tetramethyl-1,6-hexanediamine (anion exchange group introducing agent) was added so that the concentration was 5.3% by mass. to prepare a solution (A2) of an anion exchange polymer (CMPS/CMSEPS).
The viscosity (25° C.) of this anion exchange polymer solution (A2) was 3 dPa·s.

The anion-exchange polymer solution (A2) thus obtained was coated on a polyethylene terephthalate film, and the anion-exchange membrane obtained by drying was used to measure the ion-exchange capacity. Met.

(3) Preparation of solution (A3) of anion exchange polymer (QPS) Copolymerization of monomers of styrene and chloromethylstyrene at a molar ratio of 10:1 in toluene at 70°C in the presence of a polymerization initiator benzoyl peroxide for 10 hours. Then, the reaction solution was poured into methanol to obtain a copolymer.
The chloromethyl group of this copolymer was converted to a quaternary ammonium base with N,N,N',N'-tetramethylethane-1,2-diamine, and tetrahydrofuran (THF) was added so that the concentration was 20% by mass. An anion-exchange polymer solution (A3) was prepared which consisted of partially aminated polystyrene (QPC) dissolved in and having a quaternary ammonium base exchange capacity of 0.9 meq/g.
The viscosity (25° C.) of this anion exchange polymer solution (A3) was 10 dPa·s.

nonwoven sheet;
The following nonwoven fabric sheets were used.
(N1) HOP-10 manufactured by Hirose Paper Co., Ltd.
Weight per unit area: 10 g/m ²
Thickness: 0.05mm
Porosity: 78%
Fiber diameter: 12 μm
Material: Polyethylene (N2) HOP-15 manufactured by Hirose Paper Co., Ltd.
Weight per unit area: 15 g/m ²
Thickness: 0.07mm
Porosity: 76%
Fiber diameter: 12 μm
Material: Polyethylene (N3) Novatexx2473 manufactured by Freudenberg
Weight per unit area: 27 g/m ²
Thickness: 0.11mm
Porosity: 73%
Material: Polyethylene/Polypropylene

In the following examples and comparative example 2, the ion-exchange resin layer formed by coating a release film (PET film) is expressed as a first ion-exchange layer, and the ion-exchange resin layer formed on the first ion-exchange layer The counter ion-exchange resin layer that is used is expressed as the second ion-exchange layer.

<Example 1>
manufacture of bipolar membranes;
1. Formation of the first ion exchange layer The cation exchange polymer (SPPO) solution (C1) prepared above is applied to a polyethylene terephthalate (PET) film using a bar coater so as to have a liquid thickness of 100 μm, and the coating layer is formed. formed.
The PET film on which the coating layer is formed is dried at 50 ° C. for 5 minutes, and then the nonwoven fabric sheet (N1) is superimposed on the coating layer and laminated by roller pressing to obtain one side of the nonwoven fabric sheet. to form a cation exchange resin coating layer.
Then, the coating layer was dried by heating at 60° C. to solidify the coating layer to form a first ion exchange layer.

2. Application of Water Dissociation Accelerating Catalyst The obtained first ion-exchange layer was immersed in a 5.0% by mass tin chloride aqueous solution for 60 minutes. The first ion exchange layer was then removed and dried at 60°C.

3. Formation of the second ion exchange layer Next, the nonwoven fabric sheet side of the first ion exchange layer is coated with an anion exchange polymer (CMPS/CMSEPS) solution (A2), dried at 50 ° C. for 30 minutes, and then PET The film was peeled off to obtain a bipolar membrane.

Table 1 shows the composition of the first ion-exchange layer, the type of solvent used to form the first ion-exchange layer, the viscosity of the cation-exchange polymer (ion-exchange polymer) solution, and the coating thickness of the solution for the resulting bipolar membrane. rice field. Table 2 shows the physical properties of the non-woven fabric sheet and the catalyst for promoting water dissociation. Polymer) solution viscosity and coating thickness of the solution are shown.

Adhesion (T-type peel strength), amount of catalyst, and bipolar voltage of the bipolar membrane were evaluated, and the results are shown in Table 4 together with the thickness of the bipolar membrane, the thickness of the nonwoven fabric sheet, and the position of the bonding interface of the bipolar membrane. rice field.

<Examples 2 to 6>
A bipolar membrane was prepared in the same manner as in Example 1, except that the type of ion-exchange resin, the type of non-woven fabric sheet, and the concentration of the catalyst used to prepare the bipolar membrane were changed as shown in Tables 1 to 3. Table 4 shows the configuration of the bipolar membrane and its characteristics.

<Example 7>
A bipolar membrane was obtained in the same procedure except that the first ion-exchange layer obtained in Example 6 was treated with a 2.0 mass % ruthenium (III) chloride aqueous solution instead of the tin chloride aqueous solution. Tables 1 to 3 show the types of ion-exchange resins, non-woven fabric sheets, and catalyst concentrations used to prepare this bipolar membrane, and Table 4 shows the composition of the bipolar membrane and its characteristics.

<Example 8>
A bipolar membrane was obtained in the same manner as in Example 6, except that a QPS solution was used for the first ion exchange layer. The structure of the bipolar membrane is shown in Table 1 and the characteristics are shown in Table 2.

<Example 9>
A nonwoven fabric sheet (N3) (Novatexx2473) was processed by a hot press so as to have a thickness of 0.075 mm to obtain a thickness-adjusted nonwoven fabric sheet (N3') having a porosity of 62%. A bipolar membrane was obtained in the same manner as in Example 1, except that this nonwoven fabric sheet (N3') was used.
Tables 1 to 3 show the types of ion-exchange resins, non-woven fabric sheets, and catalyst concentrations used to prepare this bipolar membrane, and Table 4 shows the composition of the bipolar membrane and its characteristics.
In this example, the porosity of the non-woven fabric sheet (N3') was as low as 62%, so that the bipolar membrane had a small catalytic interface forming area, resulting in a high bipolar voltage.

<Comparative Example 1>
A bipolar membrane was obtained in the same manner as in Example 1, except that the nonwoven fabric sheet was not used. Tables 1 to 3 show the ion-exchange resin species and catalyst concentration used to prepare this bipolar membrane, and Table 4 shows the configuration of the bipolar membrane and its characteristics.
In this example, the absence of the nonwoven sheet resulted in poor adhesion at the interface of the ion exchange layer.

<Comparative Example 2>
A bipolar membrane was obtained in the same manner as in Example 1, except that no catalyst solution was used. Tables 1 to 3 show the types of ion-exchange resins and non-woven fabric sheets used to prepare this bipolar membrane, and Table 4 shows the composition of the bipolar membrane and its characteristics.
In this example, the lack of catalyst resulted in a high water dissociation voltage and a high bipolar voltage.

<Comparative Example 3>
A bipolar membrane was obtained in the same manner as in Example 1, except that the coating thickness of the first ion exchange layer was 200 μm.
Tables 1 to 3 show the types of ion-exchange resins, non-woven fabric sheets, and catalyst concentrations used to prepare this bipolar membrane, and Table 4 shows the composition of the bipolar membrane and its characteristics.
In this example, since the first ion-exchange layer was applied thickly, the non-woven fabric sheet was covered with the first ion-exchange layer, and the non-woven fabric sheet did not straddle the first ion-exchange layer and the second ion-exchange layer. , the adhesion between the first ion-exchange layer and the second ion-exchange layer was low.

1: Porous sheet 3: Catalyst layer C: Cation exchange resin layer A: Anion exchange resin layer BP: Bipolar membrane

Claims (9)

In a bipolar membrane formed by bonding a cation exchange resin layer and an anion exchange resin layer,
A water dissociation promoting catalyst is distributed at the bonding interface between the cation exchange resin layer and the anion exchange resin layer,
A porous sheet is included across the bonding interface between the cation exchange resin layer and the anion exchange resin layer ,
When the thickness of the porous sheet is T, the bonding interface between the cation exchange resin layer and the anion exchange resin layer is located at a location of 3/10 to 7/10 of the thickness T,
T-peel strength at a tensile speed of 100 mm / min is 0.5 N / cm or more,
A bipolar membrane characterized by: 2. The bipolar membrane according to claim 1, wherein the water dissociation promoting catalyst is tin chloride or ruthenium chloride. 2. The bipolar membrane according to claim 1, wherein said porous sheet has a porosity in the range of 70 to 90%. 4. The bipolar membrane according to claim 3 , wherein said porous sheet is a nonwoven fibrous sheet. 5. The bipolar membrane according to claim 4 , wherein said nonwoven fiber sheet has a basis weight in the range of 3 to 50 g/m 2 and a fiber diameter in the range of 8 to 30 μm. In a method for producing a bipolar membrane, wherein an ion-exchange resin layer and a counter-ion-exchange resin layer having a polarity opposite to that of the ion-exchange resin layer are bonded together, and a catalyst for promoting a water dissociation reaction is distributed on the bonding interface,
A first organic solvent solution, which is a high-viscosity solution having a viscosity of 5.0 to 55 dPa s at 25° C., in which a porous sheet, a release film, and an ion-exchange resin-forming polymer are dissolved, and a water dissociation promoting catalyst. A second organic solvent solution in which the dispersed or dissolved catalyst solution and the polymer for forming the counter ion exchange resin are dissolved and which has a lower viscosity than the first organic solvent solution is prepared, and the following ( A method for manufacturing a bipolar membrane, comprising steps a-1) to (a-3), (b), and (c-1) to (c-3):
(a-1) applying a first organic solvent solution to one surface of the release film to form a coating layer of the first organic solvent solution;
(a-2) a step of superimposing the porous sheet on the coating layer of the first organic solvent solution and impregnating the porous sheet with the first organic solvent solution halfway in the thickness direction;
(a-3) drying the coating layer of the first organic solvent solution in a state where the porous sheets are superimposed, and ion exchange resin is applied to a region from the superimposed surface to the middle of the thickness direction of the porous sheets; A step of obtaining an ion-exchange resin sheet in which a release film, an ion-exchange resin layer and a porous sheet are laminated by forming layers;
(b) applying the catalyst solution to the surface of the ion-exchange resin sheet on the porous sheet side, allowing it to penetrate into the porous sheet, and then drying to obtain the catalyst solution on the surface of the ion-exchange resin layer; distributing;
(c-1) applying the second organic solvent solution to the surface of the porous sheet of the ion exchange resin sheet to form a coating layer of the second organic solvent solution;
(c-2) drying the coating layer of the second organic solvent solution to form a counter ion exchange resin layer;
(c-3) Next, a step of producing a bipolar membrane by peeling off the release film; 7. The manufacturing method according to claim 6 , wherein a nonwoven fiber sheet is used as the porous sheet. When an ion-exchange resin precursor is used as the ion-exchange resin-forming polymer, in the step (a-3), the coating layer is dried while the porous sheets are overlapped. 7. The production method according to claim 6 , wherein ion exchange groups are subsequently introduced into the ion exchange resin precursor. When a counter ion-exchange resin precursor is used as the counter ion-exchange resin-forming polymer, in the step (c-2), after drying the coating layer containing the counter ion-exchange resin precursor, the counter 7. The production method according to claim 6 , wherein a counter ion exchange group is introduced into the ion exchange resin precursor.

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