JPH0458822B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a fluorine-containing ion exchange membrane. More specifically, the fluorine-containing type is reinforced with a reinforcing material made of porous fibers made of a fluorine-containing polymer, and has a low electrolytic voltage and excellent mechanical properties such as bending resistance and tensile strength. It relates to ion exchange membranes. [Prior art and problems to be solved by the invention] Fluorine-containing ion exchange membranes are used as ion exchange membranes for electrolysis, but fluorine-containing ion exchange membranes are not reinforced with reinforcing materials. The membrane has low tear strength and large dimensional changes due to changes in solution concentration in the environment in which it is used, making it difficult to use it industrially. For this reason, woven fabrics using fibers made of fluorine-containing polymers such as polytetrafluoroethylene are used as reinforcing materials for fluorine-containing ion exchange membranes (Japanese Patent Publication No. 31862/1986). . Fluorine-containing ion-exchange membranes with such reinforcing materials have sufficient mechanical strength, but because the chemical structures of the ion-exchange resin portion and the reinforcing material portion are different, their mutual adhesion may not be sufficient. Without,
In addition, the cell voltage increased because the reinforcing material acted as a shield against ion permeation. Furthermore, porous membranes made of fluorine-containing polymers have been used as reinforcing materials for fluorine-containing ion exchange membranes, but they have had the problem of low mechanical strength such as tear strength. Therefore, the above-mentioned fluorine-containing ion exchange membrane leaves room for improvement in the above points. Reinforcing materials for ion exchange membranes improve properties such as mechanical strength and dimensional stability of ion exchange membranes, but on the other hand, they improve the excellent electrochemical properties that ion exchange membranes inherently have, that is, permselectivity. and ionic conductivity. Therefore, it is necessary to provide reinforcement that has good adhesion to the ion exchange resin portion without adversely affecting the electrochemical properties of the ion exchange membrane, and that can improve the mechanical strength and dimensional stability of the ion exchange membrane. is desired. [Means for Solving the Problems] In order to solve the above-mentioned problems, the present inventors have conducted extensive research on excellent reinforcing materials suitable for fluorine-containing ion exchange membranes, and have found that porous reinforcing materials have been developed. The present inventors have discovered that an excellent fluorine-containing ion exchange membrane can be obtained by using a woven fabric made of fibers, etc., and have completed the present invention. That is, the present invention provides a fluorine-containing ion exchange membrane having a reinforcing material, wherein the reinforcing material is composed of porous fibers made of a fluorine-containing polymer. It is a membrane. The reinforcing material used in the present invention is composed of porous fibers made of a fluorine-containing polymer. As the fluorine-containing polymer, any known fluorine-containing polymer can be used without any restriction. For example, a homopolymer of tetrafluoroethylene, or a vinyl compound having a perfluorovinyl group such as hexafluoropropylene, perfluoroalkyl vinyl ether, a perfluorovinyl compound having a sulfonyl halide group, or a carboxylic acid ester group, and tetrafluoroethylene Perfluorinated polymers typified by copolymers and the like are preferably employed. The size of the pores of the porous fiber is not particularly limited, but if the manufacturing method described below is followed, the pore size of the porous fiber is usually in the range of 0.01 to 10 μm. The porosity of the porous fiber is preferably as large as possible in order for the monomer for forming the ion exchange resin portion to sufficiently penetrate into the fiber and polymerize. On the other hand, if the porosity becomes too large, the tear strength of the fibers may decrease. Therefore, the porosity of the porous fiber used in the present invention is usually 10 to 95%, preferably 20 to 90%.
% most preferably ranges from 40 to 85%. In addition, the porosity as used in the present invention is a value obtained by subtracting the difference between the true specific gravity and the apparent specific gravity of the porous fiber by the true specific gravity and multiplying it by 100. The diameter of the porous fiber used in the present invention is not particularly limited as long as it can be made into a woven or knitted fabric and used as a reinforcing material. However, in consideration of the flexibility and mechanical strength of the reinforcing material, it is preferable to select from the range of 1 to 1000 deniers, more preferably 10 to 600 deniers. Although the method for producing the porous fiber made of the fluorine-containing polymer used in the present invention is not particularly limited, the following methods are preferably employed in the present invention. The above-mentioned fluorine-containing polymers and hydrocarbon oils such as solvent naphtha and white oil; aromatic hydrocarbons such as toluol and xylene; alcohols; ketones; esters; silicone oils; fluorine-containing oils, etc. liquid lubricant and
Liquid lubricant per 100 parts of fluorine-containing polymer
After mixing in a range of 10 to 100 parts and extruding the resulting paste into a film, the liquid lubricant is removed, and the paste is further stretched in at least one direction at a constant temperature, and then this is heat treated at a high temperature. By this, a porous film with a thickness of 10 to 500μ and a porosity of 10 to 95% is obtained, and this porous film is
A method in which the yarn is cut into 0.01 to 10 mm lengths and twisted ~20 times per inch of length under constant tension. A mixture consisting of a fluorine-containing polymer and a liquid lubricant is extruded and formed into fibers, after which the liquid lubricant is removed and the fibers are stretched at a constant temperature or passed through a densification die heated at a constant temperature. A method in which the fibers are stretched at high temperatures and then heat treated at a temperature above the melting point of the fluorine-containing polymer to prevent the fibers from shrinking. The reinforcing material used in the present invention is composed of porous fibers made of the above-mentioned fluorine-containing polymer, and generally woven fabrics, knitted fabrics, nonwoven fabrics, etc. are suitable. When producing the reinforcing material, it is preferable to use only the above-mentioned fluorine-containing polymer, but it is also possible to use a mixture of non-porous fibers such as those produced by ordinary emulsion spinning. . In this case, the average porosity of all fibers constituting the reinforcement is 10-95%, preferably 20-90%.
%, most preferably in the range of 40 to 85%, because the effects of the present invention can be fully exhibited. The porosity of the reinforcing material is generally 10 to 95%, preferably 20 to 90%, taking into account the electrical resistance and mechanical strength of the ion exchange membrane. The porosity here is expressed as a percentage of the volume of spaces other than fibers in the reinforcing material (does not include the volume of pores in porous fibers) in a given volume of the reinforcing material. The thickness of the reinforcing material is not particularly limited, and is selected from known thicknesses of reinforcing materials, for example, in the range of 25 μm to 500 μm. Further, as a method for manufacturing the reinforcing material, known manufacturing methods for woven fabrics, knitted fabrics, nonwoven fabrics, etc. are employed. For example, in the case of woven fabric, the porous fibers made of the above-mentioned fluorine-containing polymer are bundled into 1 to 100 yarns with a circular or flat cross section, and then 5 to 5 fibers per 2.5 cm are made.
With about 100 strands, you can create karami weave, plain weave, twill weave,
Examples include weaving methods such as satin weaving. In the above manufacturing method, porous fibers made of a fluorine-containing polymer are treated with an alkali metal, or porous fibers made of the above fluorine-containing polymer are mixed with tetrafluoroethylene and perfluoroalkyl vinylether, Fibers obtained by impregnation polymerization or graft polymerization of fluoroethylene and perfluorovinylsulfonyl fluoride, tetrafluoroethylene and perfluorovinylcarboxylic acid ester, etc. can also be used. The fluorine-containing ion exchange membrane of the present invention can be manufactured by a known method using a reinforcing material made of porous fibers made of the above-described fluorine-containing polymer. A particularly preferred method in the present invention is to apply a fluorine-containing divinyl compound and an ion-exchange group or an ion-exchange group in the presence of a reinforcing material made of porous fibers made of the above-mentioned fluorine-containing polymer. This is a method in which a fluorine-containing vinyl compound having a functional group that can be converted into is polymerized, and then, if necessary, an ion exchange group is introduced. Specifically, this manufacturing method is as follows (1)
Methods (6) to (6) can be mentioned. (1) A viscous fluorine-containing monomer mixture obtained by polymerizing the fluorine-containing monomer mixture to some extent is applied to the reinforcing material, and both sides are sandwiched between films of tetrafluoroethylene, stainless steel, polyester, polyvinyl alcohol, polyethylene, etc. Polymerizes with Furthermore, the surface of the polymerized film is roughened by polymerizing using a release film roughened by subjecting such a release film to blasting or grinding. (2) After coating a low polymer obtained by polymerizing the crude monomer mixture liquid to some extent as a reinforcing material using a doctor knife, etc., it is sandwiched between release films and polymerized. (3) Place the reinforcing material and release film in a drum autoclave wrapped concentrically, create a vacuum, and then inject the degassed fluorine-containing monomer mixture into the autoclave and polymerize. (4) On a film-like material obtained by polymerizing a fluorine-containing monomer mixture in the presence of a reinforcing material, a mixture of fluorine-containing monomers of the same or different types, or partially polymerizing them. A film-like material having a multilayer structure is obtained by allowing a fluorine-containing monomer mixture to exist or by superimposing films impregnated with these fluorine-containing monomer mixtures and then polymerizing them. (5) After immersing a fluorine-containing ion-exchange membrane with a reinforcing material or a fluorine-containing ion-exchange membrane before introduction of ion exchange groups into a fluorine-containing monomer mixture, immerse it in a film such as polytetrafluoroethylene. They are sandwiched and impregnated for polymerization. (6) Copolymerizing tetrafluoroethylene and a fluorine-containing vinyl compound having an ion exchange group or a functional group convertible to an ion exchange group and extrusion molding the resulting film, overlaying the reinforcing material and hot pressing. A fluorine-containing ion exchange membrane reinforced by The fluorine-containing monomer mixture is a solution containing a fluorine-containing divinyl compound, a fluorine-containing vinyl compound having an ion exchange group or a functional group that can be converted into an ion exchange group, and a polymerization initiator. It is. As each component constituting these fluorine-containing monomer mixture liquids, known compounds can be employed without any restriction. For example, as a fluorine-containing divinyl compound, Compounds represented by _CF2 =CF( _{CF2 ) 0-10CF} = _CF2 can be mentioned. In addition, examples of fluorine-containing vinyl compounds having an ion exchange group or a functional group that can be converted into an ion exchange group include ₍ X is Cl, F, OH, _OCH3 , _OC2H5 ,
ONa, OK, NH ₂ , −NHCH ₂ CH ₂ NH ₂ , −
NHCH ₂ CH ₂ N ⁺ (CH ₃ ) ₃ Cl ^- ), (Y is -CN, -COF, -COOH, _-COOR1 , -
COOM, -CONR ₂ R ₃ , -CONHCH ₂ CH ₂ NH ₂ or -CONHCH ₂ CH ₂ N ⁺ (CH ₃ ) ₃ Cl ^- , where R ₁ has 1 to 10 carbon atoms, preferably 1 to 3 carbon atoms. is an alkyl group, R ₂ and R ₃ are hydrogen or the same alkyl group as R ₁ , and M is sodium,
potassium or cesium), CF ₂ = CFCOOCH ₃ , CF ₂ = CFCOF, CF ₂ =
_CFSO2F , Compounds represented _{by CF2} = _CFOCF2 ( _{CF2CF2 ) 1-3H} and _CF2 =CFO( _CF2CF2 ) _1-5I can be mentioned. In the present invention, in order to obtain a desired ion exchange membrane having a crosslinked structure, the type of fluorine-containing divinyl compound and the fluorine-containing vinyl compound having an ion exchange group or a functional group that can be converted into an ion exchange group are used. Although different, it is generally preferable to use the fluorine-containing divinyl compound in a polymerization range of 30 to 90% based on the total monomers. Furthermore, if necessary,

〔effect〕

The fluorine-containing ion exchange membrane having a reinforcing material made of porous fibers made of a fluorine-containing polymer of the present invention is different from the conventional fluorine-containing ion exchange membrane having a reinforcing material made of non-porous fibers. The adhesion between the fiber and the ion exchange resin is extremely superior to that of an ion exchange membrane, and the fibers and the ion exchange resin are integrated into one. Furthermore, when the fluorine-containing ion exchange membrane of the present invention is used as a diaphragm for alkali chloride electrolysis, it exhibits high current efficiency, and the amount of alkali chloride mixed into the caustic alkali product is reduced. It has the characteristic of being extremely rare. Furthermore, it has excellent mechanical strength. Since the fluorine-containing ion exchange membrane of the present invention has such excellent properties, it can be applied to various fields. For example, it can be used as a diaphragm for electrolytic reduction, fuel cells, pervaporation, gas separation, reverse osmosis, diffusion dialysis, electrodialysis, ultrapermeation, etc., and further as an electrolytic diaphragm for alkali chloride. [Examples] Examples of the present invention will be described in more detail below, but it goes without saying that the present invention is not limited by such explanations. Example 1 A porous film made of polytetrafluoroethylene with a thickness of 25 μm and a porosity of 90% was cut into a width of 2.5 mm.
200 denier with 5 twists per inch for porosity
Obtained 85% yarn. Using this yarn, a reinforcing material with a film thickness of 150 μm and a porosity of 70% was manufactured by plain weaving with 9 threads per inch in each direction. This reinforcing material and a polytetrafluoroethylene release film, both sides of which had been ground with #400 abrasive paper, were simultaneously wound up in a spiral around a glass rod and placed in a stainless steel autoclave.

[Formula] 4 parts by weight, CF ₂ = CFOCF ₂ CF ₂ OCF = CF ₂ 6 parts by weight,
(CF ₃ CF ₂ CF ₂ COO) ₂ 0.3 parts by weight was introduced into an autoclave under reduced pressure, and the fluorine-containing monomer mixture was heated in a reinforcing material at 20°C for 2 days under nitrogen pressure 6.
Polymerization was carried out under Kg/cm ² . After polymerization, the polymer reinforced with porous reinforcement was taken out and 10%
Hydrolysis was carried out using an aqueous NaOH solution at 80°C for 16 hours. After that, it was treated with 1NHCl aqueous solution to convert the ion exchange group into a sulfonic acid type, and then dried.
The ion exchange groups on one side of the membrane were converted to carboxylic acid groups using a germicidal lamp of 20 W for 60 minutes at a temperature of 150° C. in an atmosphere of 15 mm Hg _NO , 5 mm Hg air, and 760 mm Hg N 2 . Thereafter, it was treated with a 10% NaOH aqueous solution at 80°C for 16 hours to obtain an ion exchange membrane for electrolysis. Using this cation exchange membrane, a double electrolytic cell (effective area: 50cm ² , anode: ruthenium oxide coated titanium electrode, cathode: iron, distance between membrane and cathode: 4mm, membrane and anode in close contact, electrolysis temperature: 90℃) ,Current density:
30 A/dm ² ), a 5N NaCl aqueous solution was supplied to the anode chamber, and water was supplied to the cathode chamber to produce a 35% sodium hydroxide aqueous solution. As a result, the cell voltage was 3.31V, the current efficiency was 96%, and the NaCl concentration in the 50% NaOH aqueous solution
It was 30ppm. In addition, when we took out the thread from this ion exchange membrane, cut it into small pieces, and conducted an elemental analysis, we found that sulfur was found.
It was found that it contained 2.1% by weight.
We also investigated the infrared absorption of the surface of this thread and found that it was 1060
There is an absorption based on sodium sulfonate in cm ^-1 in fibers.

[Formula] and CF ₂ = CFOCF ₂ CF ₂ OCF = CF ₂ were clearly impregnated and polymerized. The bursting strength of this membrane was 10 Kg/cm ² in the Müllen bursting test. The tear strength was also high. Comparative Example 1 A cation exchange membrane was prepared in the same manner as in Example 1 using a reinforcing material with a thickness of 150 μm and a porosity of 70%, which was plain woven with 200 denier polytetrafluoroethylene yarn made by emulsion spinning. was synthesized and electrolytically evaluated. As a result, the NaCl concentration in a 50% NaOH aqueous solution with a cell voltage of 3.45V and a current efficiency of 92% is
It was 500ppm. Furthermore, when a portion of the ion-exchange membrane thread was taken out, cut into small pieces, and subjected to elemental analysis, almost no sulfur was detected. Furthermore, when the infrared absorption of the surface of this yarn was measured, there was no absorption at 1060 cm ^-1 , and it was clear that the fiber was not impregnated and polymerized with the ion exchange resin component. It is thought that the poor adhesion between the thread and the resin was the reason why the electrolytic performance was inferior compared to the membranes of Examples. Comparative Example 2 An ion exchange membrane for electrolysis was synthesized in the same manner as in Example 1 using a polytetrafluoroethylene porous film having a pore diameter of 10 μ, a porosity of 90%, and a thickness of 150 μ as a reinforcing material. When the mechanical strength of this membrane was measured, the bursting strength according to the Müllen bursting test was 5 kg/cm ² , and the tearing strength was also low. Example 2 100 parts by weight of polytetrafluoroethylene fine powder and 25 parts by weight of a petroleum fraction having a boiling point between 150 and 200°C were mixed, and the mixture was made into a powder having a diameter of 0.5 mm using a ram extruder.
It was made into a filament. Next, this filament is stretched 10 times to remove the petroleum fraction, passed through a circular densification die heated to 300℃, and then stretched 7 times in a furnace at 300℃ to prevent the filament from shrinking. A short heat treatment was performed at 367°C. A reinforcing material was prepared by leno weaving using the thus obtained 40 denier, 75% porosity matrix filament with a tear strength of 3000 Kg/cm ² and 50 filaments per inch in both length and width. This reinforcing material and a film made of a copolymer of tetrafluoroethylene and hexafluoropropylene were wrapped concentrically around a glass rod using a release film ground with #1200 abrasive paper.
After autoclaving, CF ₂ =
CFOCF ₂ CF ₂ OCF = CF ₂ 7 parts by weight, CF ₂ =
CFOCF ₂ CF ₂ COOCH ₃ 3 parts by weight,
0.2 parts by weight of (CF ₃ CF ₂ COO) ₂ was introduced into an autoclave under reduced pressure and polymerized at 30° C. for 1 day under nitrogen 6 kg/cm ² . After polymerization, take out the polymer and add NaOH15
A cation exchange membrane was obtained by treatment at 85° C. for 6 hours in a hydrolyzed solution containing 55 parts by weight of water, 35 parts by weight of dimethyl sulfoxide. This cation exchange membrane was used in Example 1.
When used for electrolysis using the method described above, the cell voltage was 3.34 V, the current efficiency was 98%, and the salt concentration in 50% NaOH was 20 ppm. When the ion exchange membrane thread was taken out and the infrared absorption of the surface was measured, it was found that there was an absorption based on sodium carboxylate at 1680 cm ^-1 . Comparative Example 3 Using the reinforcing material of Comparative Example 1, a cation exchange membrane was synthesized in the same manner as in Example 2, and electrolytically evaluated. As a result, the cell voltage was 3.55V, the current efficiency was 93%, and the salt concentration in 50% NaOH was 400ppm. The ion exchange membrane strands were taken out and the infrared absorption of the thread surface was measured. As a result, only a characteristic peak due to polytetrafluoroethylene was present, and a carboxylic acid group at 1680 cm ^-1 was not present. Example 3 Four porous films made of polytetrafluoroethylene with a thickness of 20 μm and a porosity of 80% were cut into a width of 0.5 mm and twisted 10 times per inch.
A 200 denier thread with a porosity of 60% was made, and a reinforcing material with a film thickness of 150 μm and a porosity of 60% was created by leno weaving with 15 threads per inch and 10 threads per inch. For this reinforcement, CF ₂ = CFOCF ₂ CF ₂ OCF =
CF ₂ 6.2 parts by weight,

[Formula] 3.8 parts by weight, (CF ₃ CF ₂ CF ₂ COO) ₂ 0.3 parts by weight, and parts by weight of Fomblin oil YRI were mixed and partially polymerized at 10℃ for 4 hours, and then applied to a polytetrafluoroethylene peeler. After covering both sides with film, wind it up on a stainless steel drum and store it in an autoclave at 20℃.
Polymerization took place for 2 days. After polymerization, the polymer was taken out, hydrolyzed by the method of Example 1, and electrolytically evaluated. As a result, the cell voltage was 3.12 V, the current efficiency was 75%, and the NaCl concentration in 50% NaOH was 500 ppm. Comparative Example 4 Using the reinforcing material of Comparative Example 1, a cation exchange membrane was synthesized in the same manner as in Example 3, and electrolytically evaluated. As a result, cell voltage 3.15V, current efficiency 70%, 50% NaOH
The NaCl concentration inside was 3000 ppm. Example 4 Polytetrafluoroethylene film thickness 30 μm,
Cut a porous film with a porosity of 70% to a width of 1 mm,
50% porosity with 5 twists per inch
A reinforcing material with a film thickness of 120 μm and a porosity of 40% was produced by plain knitting the yarns at a density of approximately 40 yarns per inch lengthwise and widthwise. This reinforcing material and a polytetrafluoroethylene release film, both sides of which were ground with #400 abrasive paper, were spirally wound around a glass rod and placed in a stainless steel autoclave.

[Formula] 3.5 parts by weight, CF ₂ = CFOCF ₂ CF ₂ OCF = CF ₂ 7.5 parts by weight,
A monomer mixture containing _0.3 parts by weight of (CF ₃ CF ₂ CF ₂ COO) 2 was introduced into the above stainless steel autoclave under reduced pressure and polymerized at 25° C. for 3 days. After polymerization, the polymer was taken out from the release film, hydrolyzed by the method of Example 1, and then treated with a 1N HCl aqueous solution to convert the ion exchange groups to sulfonic acid type. This membrane was dried under reduced pressure, NO20mmHg, air 5mmH.
g, N ₂ at a temperature of 150℃ in an atmosphere of 760mmHg.
The ion exchange groups on one side of the membrane were converted to carboxylic acids by irradiation with a 10 W germicidal lamp for 30 minutes.
Thereafter, it was hydrolyzed again using a 10% NaOH aqueous solution and electrolytically evaluated in the same manner as in Example 1. As a result, the cell voltage was 3.21V, the current efficiency was 95%, and the NaCl concentration in the 50% NaOH aqueous solution was 50 ppm. Example 5 and CF ₂ = CF ₂ with an exchange capacity of 1meq/g and a 40μ thick film made of dry resin,

[Formula] and CF ₂ = Exchange capacity of CF ₂ and copolymer is 0.9meq/g,
The reinforcing material of Example 1 was placed on the side where the sulfonyl fluoride group of the film laminated with a 150μ dry resin film was sandwiched between polyester films on both sides, and the film was laminated for 50 minutes while degassing.
The reinforcement was introduced by hot pressing at 195° C. for 20 minutes at a pressure of Kg/cm ² . After that, it was hydrolyzed by the method of Example 1, and the electrolytic evaluation was performed with the side containing the carboxylic acid group facing the cathode, and the cell voltage was
3.45V, current efficiency 94%, in 50% NaOH aqueous solution
NaCl concentration was 80 ppm. Comparative Example 5 The reinforcing material was introduced in the same manner as in Example 5 using the laminate film of Example 5 and the cloth of Comparative Example 1 as the reinforcing material by hot pressing.
After that, it was hydrolyzed by the method of Example 1, and electrolytic evaluation was performed with the side containing the carboxylic acid group facing the cathode.The cell voltage was 3.52V, current efficiency was 91%, and 50% NaOH
The NaCl concentration in the aqueous solution was 400 ppm.

Claims (1)

[Claims] 1. A fluorine-containing ion exchange membrane having a reinforcing material, wherein the reinforcing material is composed of porous fibers made of a fluorine-containing polymer.