JPH0216336B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to perfluorocarbon cation exchange membranes reinforced with perfluorocarbon fibers having specific tensile properties.

In general, ion exchange membranes utilize their selective permselectivity to produce selective membranes for electrodialysis in salt production, underground brine water and cheese whey desalination, adiponitrile synthesis through electrolytic dimerization of acrylonitrile, water electrolysis, and halogenation. It is used in a wide range of industrial fields, such as diaphragms in alkali metal electrolysis and separators in fuel cells. especially,
In the field of perfluorocarbon cation exchange membranes, from the viewpoint of energy saving and environmental pollution, it is important to utilize the membrane's chemical resistance and heat resistance to use it as a diaphragm for salt electrolysis. It is attracting attention. Usually, this membrane is reinforced by embedding a woven fabric made of perfluorocarbon fibers in the membrane to prevent expansion and contraction of the membrane in the battery container and propagation of tearing from pinholes in the membrane and to improve the strength of the membrane. has been done. Perfluorocarbon fibers, which are used as reinforcing materials for perfluorocarbon cation exchange membranes used as diaphragms for salt electrolysis, are generally made of polytetrafluoroethylene polymers.
These fibers have the advantage of being able to sufficiently withstand high-temperature corrosive atmospheres such as those in salt electrolysis tanks.

However, when a perfluorocarbon cation exchange membrane reinforced with fibers made of polytetrafluoroethylene polymer is incorporated into a filter press type diaphragm electrolytic cell and operated, the gasket part of the electrolytic cell may deteriorate over a long period of time. This has a major drawback in that the ion exchange membrane is cut, which impedes practical use of the membrane.

In order to solve these difficulties,
Japanese Patent No. 124547 discloses a membrane that uses a reinforcing material having high tensile strength in the part that contacts the gasket part. In this membrane, high-strength resins are coated or glued on the gasket contact surface, cloth is embedded or glued, and high-strength weft threads are used or the number of threads is increased. A method has been proposed in which an ion exchange membrane is supported on a gasket. However, in such membranes, the thickness of the surface that touches the gasket tends to be thicker, which increases the distance between the electrodes and increases the voltage, and it is not possible to partially change the number of threads in the manufacturing process. Furthermore, according to the analysis of the present inventors, it is difficult to prevent the ion exchange membrane from being cut at the gasket portion, no matter how much the strength of the reinforcing material is increased. There was found.

Although it is difficult to clearly determine why the membrane is cut at the gasket, it is generally thought to be as follows.

In general, the tensile properties of a perfluorocarbon cation exchange membrane reinforced with perfluorocarbon fibers largely depend on the adhesion between the membrane-constituting resin and the fibers, and on the tensile properties of the fibers themselves. When this reinforced perfluorocarbon cation exchange membrane is installed in a filter press type diaphragm electrolytic cell and operated for a long period of time, a creep phenomenon occurs in the material that makes up the gasket, and as the material stretches, the membrane must be replaced. The membrane is stretched. If the perfluorocarbon fiber has a low elongation and a high initial elastic modulus, it will not be able to absorb the force that stretches the exchange membrane due to the creep of the material that makes up the gasket, and as a result, the fiber will follow the creep of the gasket. This is not possible and the exchange membrane is cut at the gasket. In addition, if the adhesion between the fibers and the resin is poor, when the exchange membrane is stretched due to the creep phenomenon of the gasket part, the fibers and the resin will easily separate, causing cracks in the resin and damaging the membrane. disconnects. That is, the phenomenon that the perfluorocarbon cation exchange membrane breaks at the gasket part of the battery case depends on the elongation and initial elastic modulus of the perfluorocarbon fiber as a reinforcing material, and the relationship between the fiber and the resin constituting the perfluorocarbon cation exchange membrane. It is believed that the adhesion of the On the other hand, if the elongation of the perfluorocarbon fiber is too large, the perfluorocarbon cation exchange membrane will swell.
The dimensional stability of the membrane cannot be maintained upon shrinkage. Therefore, in order to prevent the perfluorocarbon cation exchange membrane from being cut at the gasket part and maintain the dimensional stability of the membrane, the tensile properties of the perfluorocarbon fiber used as a reinforcing material must be adjusted to a certain range of elongation. It is considered that having a high initial elastic modulus is an extremely important factor. Furthermore, it suppresses swelling and contraction of perfluorocarbon cation exchange membrane,
In order to maintain stable electrolytic performance over a long period of time, it is necessary to increase the adhesion between the resin constituting the perfluorocarbon cation exchange membrane and the perfluorocarbon fibers, and the compatibility between the resin and the fibers is important.

To summarize the above, it is thought that the characteristics that perfluorocarbon fibers used as reinforcing materials for perfluorocarbon cation exchange membranes should have can be summarized into the following three points.

It must have heat resistance and chemical resistance. It must have elongation and initial modulus within a specific range. It must have good compatibility with resin. Conventional perfluorocarbon fibers made of polytetrafluoroethylene polymer do not have all of the above characteristics. In particular, there was nothing that satisfied the characteristics of .

The present inventors have conducted extensive research in order to improve the above-mentioned drawbacks of perfluorocarbon cation exchange membranes containing reinforcing materials and to develop perfluorocarbon cation exchange membranes reinforced with perfluorocarbon fibers that are optimal as reinforcing materials. As a result, the present invention has been completed. That is, the present invention is made of a perfluorocarbon polymer containing perfluoroalkyl perfluorovinyl ether as a comonomer, has a tensile elongation of 20% to 250%, and an initial elastic modulus of 1.5 g/denier at 10% elongation. A perfluorocarbon cation exchange membrane reinforced with the following perfluorocarbon fibers is provided. In the present invention, tensile elongation indicates the ratio of the elongation amount at the time of tensile breakage to the original length,
The initial elastic modulus at 10% elongation indicates the stress per unit denier at 10% elongation.

The present invention will be explained in more detail below.

The perfluorocarbon polymer constituting the perfluorocarbon fiber used in the present invention contains perfluoroalkyl perfluorovinyl ether as a comonomer. The fact that the vinyl ether is contained as a comonomer in the polymer means that when the fiber is used as a reinforcing material for a perfluorocarbon cation exchange membrane, it has good affinity with the resin constituting the membrane, and is different from conventional polyester fibers. The adhesion between the resin and the reinforcing material is improved compared to fluorocarbon fibers made of tetrafluoroethylene polymer.

Considering that the perfluorocarbon polymer used in the present invention should take advantage of its properties of heat resistance and chemical resistance, it is not preferable that the perfluorocarbon polymer contains a monomer containing a hydrogen atom as a comonomer. Usually, a perfluoroalkyl perfluorovinyl ether having a perfluoroalkyl group having 1 to 10 carbon atoms, preferably 2 to 6 carbon atoms is used. Incidentally, a copolymer of perfluoroalkyl perfluorovinyl ether and tetrafluoroethylene is used as a preferred polymer in the present invention. Examples of the vinyl ethers include perfluoromethyl perfluorovinyl ether, perfluoroethyl perfluorovinyl ether, perfluoropropyl perfluorovinyl ether, perfluorobutyl perfluorovinyl ether, perfluorooctyl perfluorovinyl ether, perfluorohexyl perfluorovinyl ether, etc. It is. Those containing one or two ether bonds in the perfluoroalkyl group are also preferably used. Examples of the vinyl ether include perfluoro(2-methyl-3-oxerbutyl) perfluoro vinyl ether, perfluoro(2-methyl-3-oxerbutyl)
-Oxa-bentyl) perfluorovinyl ether, perfluoro(2-methyl-3-oxa-hexyl) perfluorovinyl ether, perfluoro(2,5-dimethyl-3,6-dioxa-heptyl) perfluorovinyl ether, perfluoro(2,5-dimethyl-3,6-dioxa-heptyl) perfluorovinyl ether, -dimethyl-3,6-dioxa-octyl) perfluorovinyl ether, perfluoro(2,5-dimethyl-3,6-dioxa-nonyl)
Perfluorovinyl ether, etc. A preferred perfluorocarbon copolymer used in the present invention is a copolymer of perfluoropropyl perfluorovinyl ether and tetrafluoroethylene or a copolymer of perfluoro(2-methyl-3-oxa-hexyl) perfluorovinyl ether and tetrafluoroethylene. It is. The copolymer may contain a small amount of hexafluoropropylene or chlorotrifluoroethylene.

The content of perfluoroalkyl perfluorovinyl ether contained in the copolymer is 0.5 to 50% by weight, preferably 1 to 30% by weight.
If the content exceeds 50% by weight, the elongation of the perfluorocarbon fiber obtained from the copolymer becomes too high, which is not preferable. On the other hand, if it is less than 0.5% by weight, the adhesion between the fiber obtained from the copolymer and the resin constituting the perfluorocarbon cation exchange membrane decreases, which is not preferable. The copolymer is formed into a fiber by various commonly known spinning techniques such as melt spinning and emulsion spinning to obtain a filament. The spinning temperature varies depending on the copolymer composition, molecular weight, etc., but for example, in the case of melt spinning, 250
℃ to 400℃.

The perfluorocarbon fiber used in the present invention can take the form of monofilament, multifilament, yarn, and the like. Furthermore, considering the use of the fiber as a reinforcing material, since the fiber does not substantially conduct electricity, it is preferable that the thickness of the fiber is as thin as possible, usually less than 1000 deniers, preferably less than 500 deniers, Especially less than 400 denier 5
A thickness of denier or more is suitable. If it is less than 5 denier, it is too thin and cannot play a practical role as a reinforcing material in terms of strength and dimensional stability of the perfluorocarbon cation exchange membrane. Moreover, if it exceeds 1000 denier, the film thickness of the perfluorocarbon cation exchange membrane will inevitably become thicker and the electrical resistance will increase. The cross-sectional shape of the fiber can take various shapes, such as circular, elliptical, and angular, depending on the shape of the spinneret used during spinning.

The perfluorocarbon fiber used in the present invention has a tensile elongation of 20% or more and 250% or less, preferably 25% or more and 200% or less, and an initial elastic modulus at 10% elongation of 1.5 g/denier or less, preferably 1.2
It has tensile properties of less than g/denier. The tensile property values in the present invention refer to values measured based on ASTM-D638.

Considering that this fiber is used as a reinforcing material for a perfluorocarbon cation exchange membrane, it is possible to maintain the dimensional stability of the membrane, and in fact, when the membrane is incorporated into a filter press type diaphragm electrolytic cell, the membrane at the gasket part can be In order to prevent breakage, it is necessary to have a tensile elongation and initial elastic modulus within the above ranges. If the tensile elongation is less than 20% and the initial elastic modulus at 10% elongation exceeds 1.5 g/denier, the fibers will not be able to absorb the tensile stress due to creep of the material constituting the gasket part. Becomes easily cut. Further, if the tensile elongation exceeds 250%, the dimensional stability of the membrane cannot be maintained. Therefore, for practical use of perfluorocarbon cation exchange membranes, the tensile elongation and initial elastic modulus of perfluorocarbon fibers as reinforcing materials are extremely important. The tensile elongation and initial elastic modulus of the fiber are optimally controlled by appropriately combining the polymer composition of the polymer constituting the fiber, the type of comonomer, the molecular weight, the spinning method, the drawing method, the fineness of the fiber, etc. .

The perfluorocarbon fiber used in the present invention is usually processed into various forms such as woven and knitted products. Here, the woven and knitted materials refer to molded products with a cross structure, including plain weave, tangle weave, twill weave,
It includes woven fabrics and nets woven using methods such as satin weaving, as well as knitted fabrics woven using methods such as circular knitting and vertical knitting.

The woven or knitted material used as a reinforcing material for the perfluorocarbon cation exchange membrane is preferably thin and coarse because it does not substantially conduct electricity. The roughness is determined by considering the electrical resistance, strength, and dimensional stability of the membrane, but is generally 10 to 600 meshes, preferably 15 to 200 meshes.

The cation exchange membrane of the present invention can be obtained by reinforcing the perfluorocarbon cation exchange membrane with the above-described specific perfluorocarbon fibers. The exchange group that the perfluorocarbon cation exchange membrane of the present invention has is not particularly limited. Examples include carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, and sulfonamide groups. The resin constituting the cation exchange membrane of the present invention is made of a perfluorocarbon polymer containing an ion exchange group, which is made in consideration of heat resistance, chemical resistance, and adhesion with the above-mentioned perfluorocarbon fibers. It is. Such perfluorocarbon polymers include perfluorocarbon polymers containing olefins such as tetratofluoroethylene and chlorotrifluoroethylene, and ion exchange groups such as carboxylic acid groups, sulfonic acid groups, and phosphoric acid groups, or groups that can be converted into such groups. Copolymers with fluorovinyl monomers are used. The copolymer may contain a small amount of hexafluoropropylene, barfluoropropyl perfluorovinyl ether, perfluoromethyl perfluorovinyl ether, perfluoroethyl perfluorovinyl ether, etc. as a third component. An example of the copolymer is tetrafluoroethylene and perfluoro(4,7-dioxa-5-methyl-
A copolymer with 8-nonene)sulfonyl fluoride and a copolymer with tetrafluoroethylene and perfluoro(4-oxer-5-hexene)sulfonyl fluoride are preferably used.

In the present invention, there is no particular restriction on the means for reinforcing the perfluorocarbon cation exchange membrane with perfluorocarbon fibers. For example, a copolymer having a sulfonyl fluoride group as exemplified above is melted in advance and formed into a membrane, the membrane is laminated with perfluorocarbon fibers, and the exchange membrane is reinforced by press-bonding. It is possible to use the method described in Japanese Patent Publication No. 52-16470, that is, by hydrolyzing the surface layer of one side of a pre-formed membrane with an alkali to convert the sulfonyl fluoride group into a salt of the sulfonic acid group. Reinforcement can also be achieved by overlapping the surface having the sulfonyl fluoride group with perfluorocarbon fibers and drawing a vacuum from the side of the surface in a heated atmosphere.
By hydrolyzing the reinforced membrane with an alkali, a perfluorocarbon cation exchange membrane containing a reinforcing material can be obtained.

The reinforcing material-containing perfluorocarbon cation exchange membrane of the present invention obtained by the method described above is particularly useful as a diaphragm for alkali metal halide electrolysis, and can also be operated by incorporating it into a filter press type diaphragm electrolyzer. Since the membrane is reinforced with specific perfluorocarbon fibers, the phenomenon of the membrane being cut at the gasket part of the electrolytic cell is not observed, and stable operation for a long period of time is possible in practice.

Examples of the present invention are shown below.

Example 1 A perfluorocarbon copolymer consisting of tetrafluoroethylene and perfluoropropyl perfluorovinyl ether was spun to obtain a multifilament having a thickness of 200 denier and consisting of seven monofilaments. The elongation of the fiber was 70% and the initial modulus was 0.40 g/denier. Using this fiber, the number of warp and weft threads per inch can be increased.
He made a woven cloth consisting of 25 plain weaves.

On the other hand, tetrafluoroethylene and perfluoro(4,7-dioxa-5-methyl-8-nonene)
Made of sulfonyl fluoride copolymer, thickness
175μ, ion exchange capacity 0.83 milliequivalents/g dry resin, the above woven fabric was coated with the above-mentioned woven fabric.
It was embedded according to the method described in the publication. That is, one surface layer of the film is hydrolyzed with caustic potash to convert the sulfonyl fluoride groups from the surface layer to a thickness of 17 μm into potassium salts of sulfonic acid groups, and the surface of the film having the sulfonyl fluoride groups is The woven fabric and release paper are layered in this order, and placed on a porous metal plate that has both a heating source and a vacuum source.
The film was placed with the film facing up, and the film was heated to 250°C and maintained under reduced pressure of 400 mmHg for 3 minutes. Due to this treatment, the fabric is completely embedded in the film. This reinforced membrane was hydrolyzed with caustic soda to obtain a cation exchange membrane in which the sulfonic acid groups were in the form of sodium salts. The exchange membrane was installed in the filter press type electrolyzer shown in Fig. 1, and each chamber was
The temperature was maintained by flowing hot water at 90°C, and the seal surface pressure at which the membrane was cut at the gasket part was measured. The gasket used was an ethylene/propylene rubber plate with a hardness of Hs 80 degrees and a thickness of 0.5 mm. The seal surface pressure at which the membrane was cut was 130 Kg/cm ² . Also hardness
A 2.5-thick ethylene/propylene rubber plate with a Hs of 80 degrees and lined with two 20-mesh nylon woven fabrics.
The seal surface pressure was maintained at 30 kg/cm ² using a mm gasket, the surface pressure was released every 2 hours, and the number of repetitions before the membrane was broken was measured.
I cut it off on the 15th try.

Comparative Example 1 A woven fabric similar to that in Example 1 was made using a multifilament made of polytetrafluoroethylene polymer and composed of 30 monofilaments each having a thickness of 6.7 deniers. The elongation of the fiber was 30% and the initial modulus was 1.6 g/denier. The woven fabric was embedded in the film described in Example 1 by the same method to obtain a cation exchange membrane containing a reinforcing material. The seal surface pressure at which the membrane was cut and the number of times the membrane was repeatedly cut when pressure was applied repeatedly, measured in the same manner as in Example 1, were 85 Kg/cm ² and 5th time, respectively.
When looking at the cross section of the part where the membrane was cut, it was clear that the resin and fiber had separated.

Example 2 A perfluorocarbon copolymer made of tetrafluoroethylene and perfluoropropyl perfluorovinyl ether was spun to produce a multifilament with a thickness of 100 denier consisting of 10 monofilaments and a thick filament with a thickness of 20 monofilaments. difference
I got it with 200 denier multifilament. The elongation and initial elastic modulus of the multifilament are 105% and 0.29 g/denier for the former, and 120% for the latter.
It was 0.27g/denier. Using the above mentioned fibers of 200 denier for the warp and the above two fibers of 100 denier for the weft, a woven fabric with a leno weave having 25 threads per inch in both the warp and the weft was made.

The woven fabric was embedded in the film described in Example 1 by the same method to obtain a cation exchange membrane containing a reinforcing material. The seal surface pressure at the time of cutting the membrane was measured using the evaluation method of Example 1 and was found to be 145 Kg/cm ² .
In the repeated pressure test, the membrane broke at the 16th time.

Comparative Example 2 A perfluorocarbon copolymer made of tetrafluoroethylene and perfluoroethyl perfluorovinyl ether was spun, and a multifilament with a thickness of 100 denier consisting of 10 monofilaments and a thickness of 20 monofilaments were prepared.
I got a 200 denier multifilament. The elongation and initial elastic modulus of the multifilament are
37%, 1.8 g/denier; the latter was 40%, 1.8 g/denier. The above fibers of 200 denier in the warp,
Using two of the above-mentioned fibers of 100 denier as weft threads, a woven fabric with a twining weave having 25 threads per inch in both the warp and the weft was made. The woven fabric was embedded in the film described in Example 1 in a similar manner to produce a cation exchange membrane containing a reinforcing material, and evaluated based on the evaluation method of Example 1.
The seal surface pressure at the time of membrane cutting was 60 kg/cm ² , and in the repeated pressure test, the membrane was severed on the 4th time.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a filter press type electrolyzer, in which 1 is a perfluorocarbon cation exchange membrane containing a reinforcing material, 2 is a gasket, 3 is a battery case frame, 4 is a hot water inlet, and 5 is a hot water outlet.

Claims (1)

[Scope of Claims] 1. A perfluorocarbon polymer containing perfluoroalkyl perfluorovinyl ether as a comonomer, and having a tensile elongation of 20% or more and 250% or less,
A perfluorocarbon cation exchange membrane reinforced with perfluorocarbon fibers with an initial elastic modulus of 1.5 g/denier or less at 10% elongation. 2. The perfluorocarbon cation exchange membrane according to claim 1, wherein the perfluoroalkyl group has 1 to 10 carbon atoms. 3. The perfluorocarbon cation exchange membrane according to claim 2, wherein the perfluorocarbon polymer is a copolymer of perfluoroalkyl perfluorovinyl ether and tetrafluoroethylene.