JP2000297164A - Ion-exchange film and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ion-exchange film having a low electrical resistance without causing physical defects on the film by forming a fluoropolymer film which has straight micropores opening from the inside toward the surface of at least one side. SOLUTION: This ion-exchange film is a 50-250 μm-thick laminated film which is prepared by laminating fluoropolymer films each having a thickness of 0.25-150 μm and comprising at least one fluoropolymer containing at least one kind of functional group selected from among sulfo, carboxyl and phosphono groups, etc. The laminated film has straight micropores each of which has an inner diameter of 1 μm to several μm and a depth of 10-230 μm and opens from the inside toward the surface of at least one side, the micropores being arranged at a pitch of 10-500 μm. The ion-exchange capacity of the ion-exchange film is preferably 0.50-2.00 meq/g. Fluorocopolymers prepared by copolymerizing at least one monomer selected from among monomers represented by the formula with tetrafluoroethylene, vinylidene fluoride, etc., are used. In the formula, Y is SO3H, SO3NH2 or the like; (a) and (b) are each 0-6; (c) is 0 or 1; when n>=1, then X is F, Cl or the like; and Rt and Rt' are each perfluoroalkyl or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ion exchange membrane useful for applications such as a polymer electrolyte fuel cell, water electrolysis, salt electrolysis, and various sensors.

[0002]

2. Description of the Related Art An ion exchange membrane has a function as an ion conductor for transferring protons generated by dissociation of hydrogen to the oxygen side. In general, the larger the exchange capacity of a membrane, the higher the proton conductivity. The thinner the thickness, the smaller the electrical resistance of the film, which is preferable. Conventionally, a perfluorocarbon sulfonic acid membrane has been used as an electrolyte membrane for a polymer electrolyte fuel cell, and exhibits relatively good performance. A film having an exchange capacity of about 1.25 meq / g or a film thickness of 50 μm
m perfluorocarbon membrane is produced and commercially available. A typical example is Nafion (registered trademark).
(Manufactured by DuPont, USA; hereinafter simply Nafion),
Aciplex <registered trademark> (manufactured by Asahi Kasei Kogyo Co., Ltd .; hereinafter, simply Aciplex), Flemion <registered trademark> (manufactured by Asahi Glass Co., Ltd., hereinafter, simply Flemion) and the like. In particular,
It is well known in the art that a laminated membrane of at least two or more layers of a perfluorocarbon carboxylic acid layer and a perfluorocarbon sulfonic acid layer is effective as an ion exchange membrane used for a membrane for salt electrolysis.

[0003] By the way, it has been pointed out that in an electrolytic cell using such a membrane, it is a problem to improve the current efficiency and to reduce the power consumption by reducing the electrolytic voltage. Therefore, several attempts have been made to solve this problem. For example, Japanese Patent Application Laid-Open No. Hei 6-128782 discloses an ion exchange membrane having an opening having a surface area of 25% or more of the surface area on the anode side. A method of communicating is disclosed. This method is intended to control the aperture ratio by polishing the surface using a sander or the like, preferably after the film formation is completed by embedding the temporary reinforcing fibers, but the production efficiency is significantly poor, and In addition, there is a fear that cracks may be generated on the film surface, and there is a problem that the mechanical properties of the film are impaired.

[0004]

DISCLOSURE OF THE INVENTION The present invention relates to an ion exchange membrane having a low electric resistance without causing physical defects on the membrane unlike the prior art, and with no difficulty in the membrane production operation. It is an object to provide a manufacturing method.

[0005]

Means for Solving the Problems The present inventor has made intensive studies to overcome the above-mentioned problems, and as a result, by forming microporous films of a specific shape in the film layer, the fluorine-containing polymer laminated film can overcome the problems. Have been found to be remarkably effective, and have accomplished the present invention. That is, the present invention relates to at least one layer of a film made of one or two or more kinds of fluoropolymers having one or more kinds of functional groups, and from an inner layer part of the film toward at least one surface of the film. An ion-exchange membrane characterized in that linear micropores are opened substantially to the surface.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The ion exchange membrane of the present invention is a membrane composed of at least one layer of one or more fluoropolymers having one or more functional groups. As the fluorine-containing polymer having a functional group in the present invention, various polymers having a wide range of fluorine molecules can be selected. In particular, perfluorocarbon is preferable because of its excellent heat resistance and solvent resistance. The functional group of the fluoropolymer refers to a reactive group comprising atoms or atomic groups having various chemical activities. The chemical activity of the functional group includes, for example, ion exchange ability, chelate formation ability, redox ability, and catalyst coordination ability.

Examples of functional groups having these chemical activities include sulfonic acid groups, carboxylic acid groups, phosphonic acid groups, primary to tertiary amines, hydroquinone groups,
And thiol groups. Among the functional groups, particularly those having high chemical reactivity include, for example, isocyanate groups, diazonium groups, chloromethyl groups, aldehyde groups, epoxy groups, halogen groups, carboxyl groups, amino groups, and the like. Among them, salt electrolysis, which conducts protons and sodium ions, is particularly preferable because the sulfonic acid group has a low voltage due to its large acidity and the carboxylic acid group can increase the current efficiency.

Examples of the fluorine-containing resin having such a functional group include an ion-exchange fluorine-containing resin, a chelate fluorine-containing resin containing a chelating ligand, a redox fluorine-containing resin having hydroquinone, thiol, and the like. In addition, the ion exchange fluororesin may be a fluororesin having both cation and anion exchange groups in addition to a fluorinated resin having a cation or anion exchange group. Examples of cation exchange groups include sulfonic, carboxyl or phosphonic groups.

As an example of a particularly useful fluorine-containing polymer, one or more polymerizable monomers represented by the following (Chemical Formula 1) are used, and one of the polymerizable monomers selected from the polymerizable monomer group described below is used. Copolymers obtained by combining a kind or two or more kinds of polymerizable monomers are exemplified. (Chemical formula 1) Y- (CF ₂ ) a- (CFRt) b- (CFRt ′) cO- (CF (CF ₂ X) -CF ₂ -O) n-CF = CF ₂ (where, -Y is _{-SO 3 H, -SO 2 F,} -SO 3 N
_{a, -SO 3 K, -SO 2} NH 2, -SO 2 NH 4, -CO
OH, -CN, -COF, -COOR (R is a carbon number of 1 to
10 alkyl group), - a PO ₃ H ₂ or -PO ₃ H. a is an integer of 0 to 6, b is an integer of 0 to 6, c is 0 or 1, and a + b + c ≠ 0, and n is an integer of 0 to 6. X is any one of Cl, Br or F when n ≧ 1, or a combination of plural kinds thereof. Rt and Rt 'are each a substituent selected from a perfluoroalkyl group having 1 to 10 carbon atoms or a fluorochloroalkyl group. ) And, as the polymerizable monomer group to be copolymerized with these, tetrafluoroethylene, trifluoromonochloroethylene, trifluoroethylene, vinylidene fluoride,
1,1-difluoro-2,2-dichloroethylene, 1,
Examples thereof include 1-difluoro-2-chloroethylene, hexafluoropropylene, 1,1,1,3,3-pentafluoropropylene, octafluoroisobutylene, ethylene, vinyl chloride, and alkyl vinyl esters.

The exchange capacity of the fluorine-containing polymer having a functional group is preferably 0.50 to 2.00 meq / g, more preferably, in order to impart sufficient electric conductivity and mechanical strength to the membrane. Is 0.70 to 1.50 meq / g
It is. The laminated structure of the fluoropolymer film having a functional group is not particularly limited, and can be arbitrarily selected according to the use of the film. For example, in a salt electrolysis application, at least two layers each having a carboxylic acid layer on the cathode side and a sulfonic acid layer on the anode side.
A laminated structure composed of layers is used.

[0011] In these laminated structures, it is preferable that they are in adhesive contact with each other so that there is no gap that becomes an electrically nonconductive portion between adjacent layers. If there is a gap between the layers, that portion may cause an increase in the voltage of the electrolytic device. That is, the stacked layers must not peel off during use. The ion exchange membrane of the present invention,
It is manufactured by laminating a fluoropolymer film having a thickness of about 0.25 μm to about 150 μm. The membrane generally consists of two or three layers of such a fluoropolymer film. The total thickness of the fluoropolymer film used in producing the membrane is generally about 50 μm to 250 μm, more preferably 50 μm to 150 μm, in view of the balance between voltage and strength.

[0012] The fluoropolymers of the films to be laminated are not necessarily the same, and films made of different fluoropolymers may be laminated.
In the ion exchange membrane of the present invention, it is necessary that substantially linear microporous holes are opened from the inner part of the exchange membrane toward one surface of the exchange membrane. The microporous opening may be located on the anode side or the cathode side of the membrane depending on the application, but for the purpose of the present invention, the effect is particularly high when it is located on the anode side.

Here, the membrane includes both a case where it is a precursor of an ion exchange group and a case where a functional group is converted into an ion exchange group. The microporous needs to be substantially straight. If a layer having a certain thickness has microporosity, and the ratio of the total length of the holes to the thickness of this layer is defined as the bending rate, the bending rate is preferably substantially 1 in this case. The microporous is not linear, ie
If the flexural modulus is high, smooth movement of the electrolytic solution inside the membrane is hindered, the liquid displacement resistance increases, and the length of the ion movement path increases, increasing the electrical resistance. Further, as the total length of the pores is longer than that of the linear microporous material, the amount of microporous voids in the film increases, which leads to a decrease in the strength of the film.

The inside diameter of the microporous is about 1 μm to several mm, preferably 10 μm to 500 μm. Microporous depth is 10μ
It is appropriately determined in the range of m to 230 μm. The arrangement in the microporous membrane can be arbitrarily controlled, but a regular arrangement such as a staggered pattern or a lattice pattern is preferable for processing. The pitch (the interval between adjacent holes) is not particularly limited, but is preferably from 10 to 500 μm. The diameter, depth, arrangement, and pitch of these micropores are determined from the balance that can reduce the voltage without impairing the strength of the film.

[0015] In the ion exchange membrane of the present invention, a reinforcing material for contributing to the improvement of the strength of the membrane may be interposed. In that case, the shape of the reinforcing material is not particularly limited, but the thickness is preferably 25 to 125 μm, more preferably 50 to 7 μm.
5 μm. In addition, a woven or non-woven fabric is generally preferred from the viewpoint of good moldability. In this case, these cloths
It consists of reinforcing fibers and temporary reinforcing fibers described below.

Although there is no particular limitation on the material of the reinforcing fiber, a fluoropolymer is particularly suitable because of its large strength and chemical stability. Typically, such polymers are homopolymers made from tetrafluoroethylene and tetrafluoroethylene with hexafluoropropylene and / or perfluoroalkyl vinyl ethers having 1 to 10 alkyl radicals, such as perfluoropropyl And vinyl ethers. An example of the most suitable material is polytetrafluoroethylene (PTF
E).

There is no particular limitation on the diameter of the fluorine-containing fiber made of the above-mentioned fluoropolymer, but in order to give the woven fabric and the film after lamination sufficient strength, 50 to 600 denenyl is preferable, more preferably. Is 200 to 400 denenyl. The temporary reinforcing fiber is a fiber made of a natural or synthetic polymer, and suitable materials include cotton, linen, silk, rayon, 6-6 nylon, polyethylene terephthalate,
And polyacrylonitrile.

These temporary reinforcing fibers can have any aspect ratio selected within the range of 1 to 20, and can have a rectangular, oval, triangular, star, or elliptical cross section. For example, thin ribbons cut from rayon fibers or regenerated cellulose film are preferably of about 40-100 denyl. Like the fluorine reinforcing fiber, the temporary reinforcing fiber is preferably 1
It may have a thickness of 2 to 63 μm, more preferably 25 to 38 μm. The temporary reinforcing fiber of the present invention can be removed from the membrane without impairing the ion-exchange ability of the membrane of the present invention, whereby the electrical resistance of the membrane can be further suppressed. The temporary reinforcing fibers may be removed by a generally known chemical method. For example, in the case of a cellulosic reinforcing material such as rayon, the temporary reinforcing fibers can be removed using sodium hypochlorite.

The woven or non-woven fabric is made of the above-mentioned fluorine reinforcing fiber and / or temporary reinforcing fiber. These fabrics are suitable for weaving, such as normal basket weaving and Leno weaving. Each of the fluorine reinforcing fiber and the temporary reinforcing fiber may be a single filament or a multi-strand. At this time, the fluorine reinforcing fiber and the temporary reinforcing fiber may be twisted.

In this case, the opening ratio in the woven fabric after removing the temporary reinforcing yarn from the woven fabric is in the range of 50% to 95%,
The larger the aperture ratio, the greater the electrical resistance suppressing effect. Here, the opening ratio is the area of the opening area between adjacent fibers in the woven fabric per unit area of the woven fabric. In the case of nonwovens, thin open sheets of suitable component fibers can also be used. The temporary reinforcing fiber may be embedded alone in the laminated film as well as in the woven fabric. It is desirable that the hole at the trace where the temporary reinforcing fiber in the reinforcing material is removed and the hole at the trace where the temporary reinforcing fiber embedded alone is removed communicate with each other.

Next, a method for producing the ion exchange membrane of the present invention will be described. The present invention relates to at least one layer of a film made of one or two or more kinds of fluoropolymers having one or more kinds of functional groups, wherein at least one layer forming a surface has a large number of sword-shaped protrusions. And a method for producing an ion exchange membrane.

That is, in the above-mentioned process for producing a film made of a fluoropolymer, two or more fluoropolymer films may be melt-bonded to each other via a support material between them if necessary, to form a single film. A membrane structure is formed. The molding temperature is usually in the range of about 200 to 300 ° C., but more precisely, the properties of the fluoropolymer used, the adhesiveness between the film component layer and the support member, and the flow of the fluoropolymer in the molten state. Optimized for performance. In any case,
A molding temperature at which a molded film having a uniform thickness is finally obtained is selected. Molding pressures can typically be used from as low as about 2x10 ⁴ Pascal to over 10 ⁷ Pascal.

At the time of lamination, at least one layer of a film made of one or two or more kinds of fluoropolymers having one or more kinds of functional groups, a reinforcing material having temporary reinforcing fibers, and linear microporous are provided. It is preferable to laminate the layers in the order of the layers. Further, only the temporary reinforcing fiber may be added around the reinforcing material having the temporary reinforcing fiber. In this case, it is preferable that the added temporary reinforcing fiber and the reinforcing material are in contact with each other from the viewpoint of achieving the effect.

The method of the present invention is characterized in that a large number of sword-shaped protrusions are pressed against at least one layer forming the surface. The sword-shaped protrusion will be described. Protrusions are provided on a substrate, and the protrusions are pierced into the film surface to open. The material of the substrate is not particularly limited, but stainless steel is preferable because it may be heated. The projection is a polygonal pillar,
Shapes such as polygonal pyramids, cylinders, and cones can be selected depending on workability. A columnar shape is preferred from the viewpoint of workability. The diameter is not particularly limited as long as it is within a processable range, but preferably,
It is about 1 μm to several mm, more preferably 10 μm to 500 μm. The height is determined by the thickness of the linear porous layer,
5 μm to 1 mm, preferably 20 μm to 300 μm. The arrangement may be arbitrary, but conventionally known arrangements such as a staggered pattern and a lattice pattern can be preferably used for processing. The pitch is not limited as long as it is within a processable range, and is preferably 10 to 500 μm.
It is. Each of these standards of the sword mountain protrusion can be arbitrarily changed, and as a result, it is a great feature that the size of the micropore, the number in the film, and the pitch can be freely controlled according to the electrolysis conditions.

It is also possible to apply a temperature when pressing the surface of the film to be opened, so that the layer provided with the linear fine pores has an appropriate fluidity. In that case, the melt flow index of the polymer forming the layer is measured in advance, and the optimal conditions are selected. Usually, a temperature of 200 ° C. or more and a melting point or less is employed. It is also preferable to form a hole in the valley between the ridges and reduce the pressure from there, so that the film is uniformly drawn in and easily opened by the ridge. By forming this sword-shaped plate in the shape of a drum, it is possible to form linear micropores continuously.

After that, the above-mentioned ion-exchange membrane can convert the functional group in the membrane into another kind of functional group by a chemical method according to its use. For example, when the electrolytic membrane is used as a diaphragm for salt electrolysis, all functional groups of the membrane are sulfonic acid and carboxylic acid groups, or an alkali metal salt thereof, etc.
It can be converted to an ionizable functional group in an aqueous solution. Such conversion can usually be effected by hydrolysis in the presence of an acid or a base.

The removal of the temporary reinforcing fibers from the membrane may be performed at any stage before or after the conversion of the functional group.
When the temporary reinforcing fibers are made of a hydrolyzable material, the temporary reinforcing fibers can be removed at the same time in the hydrolysis process of the functional group conversion. Although the formation of the linear microporosity can be performed after the conversion of the functional group, it is more preferable to perform the formation of the precursor before the conversion from the viewpoint of workability and workability.

Further, it is preferable to combine a conventionally known technique such as coating an inorganic substance on the surface of the ion exchange membrane of the present invention, which prevents adhesion of air bubbles.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

[0030]

Example 1 A copolymer of a perfluorocarbon monomer having a carboxylic acid methyl ester skeleton, which is one of the chemical formulas, and tetrafluoroethylene (manufactured by Asahi Kasei Kogyo), exchange capacity 0.85 meq / g, film thickness 20 μm And a film of a copolymer of perfluorocarbon monomer having a sulfonyl fluoride group, which is one of the chemical formulas, and tetrafluoroethylene (manufactured by Asahi Kasei Corporation) having an exchange capacity of 0.97 meq / g and a film thickness of 75 μm. Was extruded to form a film (A). On the other hand, the exchange capacity of a copolymer of a perfluorocarbon monomer having a sulfonyl fluoride group and tetrafluoroethylene (manufactured by Asahi Kasei Kogyo Co., Ltd.), which is one of Chemical Formula 1, was obtained. 05 meq / g, film thickness 5
A 0 μm film (B) was prepared. Polytetrafluoroethylene fiber (150 denier, thickness 110)
μm) to prepare a woven fabric of the support material in a plain weave system. At this time, polyethylene terephthalate fibers were simultaneously woven as temporary reinforcing fibers.

The reinforcing members were sandwiched between films (A) and (B), and were laminated by heating. At this time, the film (B)
A stainless steel sword mountain plate was placed underneath. On a stainless steel base, a large number of sword mountains arranged in a lattice pattern with a diameter of 40 μm, a height of 100 μm, and a pitch of 200 μm are attached,
Further, a hole having a diameter of 100 μm and penetrating the stainless steel substrate was provided on the diagonal line of the lattice. The film (B) side of the membrane was pressed against the projection of the sword while sucking from this, and a linear microporous was formed. At this time, the substrate was heated to 220 ° C.

The obtained laminated film was dissolved in a mixed solution of 16.8 parts of potassium hydroxide (special grade, manufactured by Wako Pure Chemical Industries, Ltd.), 30 parts of dimethyl sulfoxide (primary grade, manufactured by Wako Pure Chemical Industries, Ltd.) and 70 parts of pure water. It was immersed and reacted at 90 ° C. for 1 hour, whereby the sulfonyl fluoride type functional group was converted to potassium sulfonate type. After washing with pure water,
It was immersed in an NNaOH aqueous solution and kept at 85 ° C. for 30 minutes to obtain a sodium sulfonate type. Thereafter, salt electrolysis was performed using the side opened at the sword mountain as the anode side. The measurement was performed at a liquid temperature of 90 ° C. using a 3.5N NaCl aqueous solution as the anolyte and a 33% NaOH aqueous solution as the catholyte. As a result, the electrolysis voltage was 2.90 V, and the breaking strength in a tensile strength and elongation measurement (45 ° direction with respect to the vertical and horizontal support member yarns) was 1.2 kg / cm.

When the cross section was observed with an optical microscope, it was found that linear micropores formed by Kenzan were connected to the elution holes of the temporary reinforcing fibers formed in the membrane.

[0034]

Comparative Example 1 A laminated film was prepared in the same manner as in Example 1 except that the lamination was performed without using a sword mountain. The electrolysis voltage of this laminated film was 2.98 V, and the breaking strength was 1.2 k.
g / cm. Although the breaking strength was not changed as compared with Example 1, the electrolytic voltage was high.

Observation of the cross section with an optical microscope revealed that there was an elution hole for the temporary reinforcing fiber, but it did not open to the salt water supply side.

[0036]

The size of the pores in the ion exchange membrane, the number of pores in the membrane, and the gap between the pores can be arbitrarily set according to the electrolysis conditions, as well as the conventional mechanical cutting of the membrane surface. A decrease in the strength of the film can be suppressed by suppressing the open area ratio and the volume of the film without damaging the film unlike the opening method.

Claims (5)

[Claims] 1. A film comprising at least one layer of one or two or more kinds of fluoropolymers having one or more kinds of functional groups, wherein the film is formed from an inner layer portion of the film toward at least one surface. An ion exchange membrane having substantially linear microporous openings. 2. The ion exchange membrane according to claim 1, wherein the functional group is at least one of a sulfonic acid group and a carboxylic acid group. 3. The method according to claim 1, wherein the reinforcing material is reinforced.
Or the ion exchange membrane according to 2. 4. The ion-exchange membrane according to claim 1, wherein the surface on which the microporous openings are present is disposed on the anode side in the ion-exchange membrane. 5. A film comprising at least one layer of one or two or more kinds of fluoropolymers having one or more kinds of functional groups, wherein at least one surface of the film comprises a large number of sword-like layers. 5. The method for producing an ion exchange membrane according to claim 1, wherein the projections are pressed.