JPS6031861B2 - Method for manufacturing fluorine-containing cation exchange membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a fluorine-containing cation exchange membrane.
This is a method for producing a fluorine-containing cation exchange membrane, characterized in that a carboxyl group-introducing reaction is performed on a fluorine-containing polymer film having 21 groups to impart carboxyl groups.

The object of the present invention is that under the conditions of use, the electrical resistance of the membrane is 200
The object of the present invention is to obtain a fluorine-containing cation exchange membrane of less than 1 c sea.
Fluorine-containing polymer membranes are used in a wide range of applications simply as membrane materials with excellent heat resistance and chemical resistance, but they can also be used to add new functions to these special properties to create even more value-added materials. Many attempts have been made to make them highly useful, including ultra-moat membranes, reverse osmosis membranes, ion exchange membranes, etc.

In these cases, there are various methods, such as a method of controlling the pore-like distribution using an ultra-moated membrane, and a method of imparting a new function by bonding an ion-exchangeable functional group. Today, the salt electrolysis industry is converting to electrolysis methods that do not use mercury due to the problem of environmental pollution caused by mercury.When using membranes in such an electrolytic atmosphere, fluorine-containing membranes are preferably used from the viewpoint of heat resistance and chemical resistance. It is desirable to use a perfluorinated film. For example, a water-permeable diaphragm has extremely good oxidation resistance, but has strong water repellency due to the low surface energy characteristic of fluorine compounds. There are various proposals for this hydrophilic treatment, but it is preferable that intestinal ion exchange groups are bonded to the fluorine-containing polymer membrane. Also important are ion exchange membranes that are substantially water-impermeable. Furthermore, in the case of ultrafiltration membranes, reverse osmosis membranes, etc., the fact that cation exchange groups are bound thereto affects the selectivity for permeating substances, salt rejection rate, etc. Now, as such a cation exchange group, a sulfonic acid group is generally used due to its thermal stability and other reasons, and a carpoxyl group is rarely used especially from the viewpoint of thermal stability during molding of fluorine-containing polymer compounds. do not have.

Today, such a fluorine-containing polymer film with a cation exchange group bonded to it is produced by hydrolyzing a copolymer film of perfluoroalkyl vinyl ether sulfonyl fluoride and tetrafluoroethylene. There is something like that. Although this is extremely stable against oxidizing agents, when it is used as a diaphragm for the above-mentioned salt electrolysis, etc., there are some difficulties in electrolytic performance. In addition, there are many cases in which a polymeric film having carboxyl groups instead of sulfonic acid groups is required, and from this perspective, we
-96472 and Tokusei Sho 50-108182, proposed an ion exchange membrane using carboxyl groups as intestinal ion exchange groups, and also proposed a conversion from a membrane with sulfonic acid groups to a membrane with carboxyl groups in JP-A-51- 1226
One method was completed in 1977. Many inventions of this type have been made since then, including a method for copolymerizing a monomer having a carpoxyl group with tetrafluoroethylene in Tsubaki 1986-130495, and a method for copolymerizing a monomer having a carboxyl group with tetrafluoroethylene, and a method for copolymerizing a monomer having a carboxyl group with tetrafluoroethylene, and a method for copolymerizing a monomer having a carboxyl group with tetrafluoroethylene; It has been proposed to reduce the do group to convert it into a carboxyl group. Now, in this method of polymerizing a monomer having a carpoxyl group to form a film-like material, unless special measures are taken, there is a high possibility that decarboxylation will occur at the molding temperature, and the method of Samurai Kaisho 51-122677 The compounds that have an amino group and a carboxyl group, or a functional group that can be easily converted to a carboxyl group, to be bonded to the sulfonyl halide are mainly hydrocarbon-based, and even after fluorination treatment, the degree of fluorination is low. There is a limit. In addition, the method of converting a sulfonyl halide group into a carboxyl group by reduction treatment has a low reaction rate, and the sulfonyl halide group is often decomposed and converted into another inert group that is not a carboxyl group. When used as a diaphragm or even an ion exchange membrane, a rise in the electrical resistance of the membrane is unavoidable. Apart from the above, we have conducted research on a method for converting sulfonyl halide groups into carboxyl groups more efficiently. In the presence of radiation, a fluorine polymer having one CFI group and/or one CF21 can be produced by reacting with an iodine compound or by adding an iodine compound to a fluorine-containing polymer membrane having double bonds. Production of a fluorine-containing side ion exchange membrane, characterized in that a raw film of a fluorine-containing polymer film is obtained, then a key acid is reacted with the raw film of a fluorine-containing polymer film, and carboxyl groups are imparted by subsequent hydrolysis. The present invention, which is a method, has been completed. The raw fluorine-containing polymer membrane used in the present invention is not particularly limited as long as it has one CFI group and/or one CF21 group.

However, preferably, at least 1 micron of the surface layer of at least one side of the bride's waist has -CFI- groups and/or -C
F21 group is present, the functional group is 4% by weight as iodine
~40% by weight, and furthermore, fluorine atoms and -CFI- groups and/or -CF21 groups are bonded uniformly or non-uniformly, generally having a thickness of 0.05~2 mm, A film-like material having one or more holes in one direction is preferably used. When a raw material with an iodine content of less than 4% (by weight) is used, the electrical resistance of the fluorine-containing cation exchange membrane obtained by the present invention tends to increase; If a raw membrane containing more than 4% by weight is used, the strength and electrochemical properties of the fluorine-containing cation exchange membrane tend to decrease. Moreover, since the conversion yield of one CFI- group to a carboxyl group is lower than that of one CF21 group, at least 10 mol% or more, preferably 50 mol% or more of iodine contained in these groups is -CF21. As a base, it is desirable to exist.

In this case, the method for introducing -CFI- group and/or -CF21 group is as follows: i) Reaction of an iodine compound to a fluorine-containing polymer film having a functional group that can be easily converted into -CFI group and/or -CF21 group; For example, a method of reacting an iodine compound with a fluorine-containing polymer membrane having a sulfonyl halide group, ii) a fluorine-containing polymer compound, particularly in the case of a fluorine-containing polymer membrane having a double bond, By carrying out an addition reaction of IC1, L, etc. in the presence or absence of a suitable solvent, the desired fluorine-containing polymer film can be produced. In the case of a fluorine-containing polymer film having no unsaturated bonds, there is a method in which an iodine compound is reacted in the presence of ionizing radiation and/or light. Among these, the sulfonyl halide group in case i) refers to sulfonyl fluoride, sulfonyl chloride group, sulfonyl furomide group, sulfonyl iodide and the like. Further, it is important that the fluorine atom is bonded to the carbon at the Q position to which the -CF21 group and the -CFI- group are bonded, and it is more preferably a perfluoro-based atom. Specifically, a copolymer of perfluoroalkyl vinyl ether sulfonyl fluoride containing perfluoro(3,6-dioxa-4-methyl-7-octensulfonyl fluoride) as a main component and tetrafluoroethylene was formed into a film. sulfonyl fluoride or sulfonyl chloride. In the case of i) and ii), the iodine compound is exposed to light and/or
Alternatively, the method of reacting in the presence of ionizing radiation is not limited, for example, in the presence of elemental iodine vapor,
A method of irradiating ultraviolet rays, a method of irradiating ionizing radiation,
Examples include a method of irradiating visible light and ultraviolet rays in the presence of a photosensitizer.

Further, these methods are preferably carried out in the presence of heat or a radical initiator or other catalyst. That is, a method of heat treatment in the presence of elemental iodine and a radical initiator, and a method of heating elemental iodine in the presence of an organic solvent (preferably alcohol, carbon disulfide).
Particularly preferable results can be obtained when the above-mentioned methods are used in combination with methods such as dissolving the material in water and heating it to 50q0 or more, and furthermore, heating in the presence of a radical initiator and simultaneously irradiating ultraviolet rays. Generally, when heat is used, it is 0°C or higher, preferably 50°C or higher.
The temperature range is qo or more and the fluorine-containing polymer film does not decompose. When using light, ultraviolet light is preferred;
It is not necessarily necessary to use ultraviolet light, and visible light may be used in the presence of a sensitizer. In this case, conventionally known photosensitizers can be used without any restriction, and can be appropriately selected depending on the purpose. Ionizing radiation Q, 8, y, and X-rays are used, and the optimum dose is selected within the range of 0.1 to 30 Mrad, but there is no significant decomposition of the fluorine-containing polymer film, or This must be done within a range that does not result in a decrease in mechanical strength. In addition, any known organic or inorganic radical initiator may be used without any restriction, and organic radical initiators may be appropriately selected such as hydrocarbon-based, fluorine-containing, perfluorinated, etc. Those having a decomposition half-life of 40° C. or more and 1q hours or more are preferably used without any restrictions. Specifically, penzoyl peroxide, Q,Q-
Azobisisobutyronitrile, lauryl/f-oxide, ditertiary butyl peroxide, N2F2,
(CF3COO)2 etc. are exemplified.

When light and/or ionizing radiation are used in combination with heat, a radical initiator, etc., an even greater effect appears, but the conditions are selected so that the reaction proceeds most efficiently. The iodine compound used here may be elemental iodine in the form of gas, solution, or solid, and the concentration is not particularly limited, but it is usually 0.
．． 0.001% to saturated solutions are used.

The solvent to be used when in solution form is selected so as to dissolve iodine and to control the degree of reaction to the polymer film when carrying out the reaction. For example, if you want to cause a reaction only near the surface of a polymer film, use a material that has poor affinity for the polymer film so that only the surface layer reacts, and even the inside of the film. When it is desired to advance the reaction, it is preferable to use a solvent that has good affinity for the membrane-like polymer and can swell the membrane-like substance well. Other iodine compounds used include inorganic and organic iodine salts, and in the case of inorganic iodine salts, cations include alkali metal salts, alkali metal salts, transition metal iodine salts, rust salts, etc., and are not particularly limited. More specific examples include sodium iodide, potassium iodide, lithium iodide, cesium iodide, calcium iodide, magnesium iodide, strontium iodide, cobalt iodide, nickel iodide,
Iron iodide, steel iodide, etc. are suitable. In addition, as cations in the case of organic iodine salts, organic substances bonded with so-called onium bases such as primary, secondary, and tertiary amines, quaternary ammonium bases, arsonium bases, phosphonium bases, stibonium bases, and sulfonium bases are used. It will be done. Organic chains of amines include saturated or unsaturated straight chain, branched chain alkyl groups, cyclic ones, aromatic rings,
There are no particular restrictions on those having a rear elemental ring. More specific examples include alkylammonium iodide salts such as tetramethylammonium chloride, aniline hydroiodide salts,
Hydroiodide of diethylamine, hydroiodide of triethylamine, hydroiodide of triethylamine, etc. are suitable.

In addition, iodine compounds that are not in the form of salts, but those that are bonded by covalent bonds may be effective in some cases. For example, iodotyrosine. Now, when these iodine compounds are reacted in the presence of the energy source mentioned above, there are many unclear points about what kind of reaction takes place, and it has not been fully elucidated, but we believe that the following reaction proceeds. It is estimated based on the current situation and various analyses. -CF=CF212→-CFI
-CF21 01-CF2-CF312
→-CF2CF21 IF [21-CF2S
02X+12→-CF2110S02↑10IX [3
'Also, depending on the selection of reaction conditions, -CF
2CF312→-CFICF30IF
'41-CF2CF3-12 → CI2CF3-IF
[5)-CF2S02X+12→-CF2
It is thought that the reaction '71' is also progressing, and in the case of reactions '5', '61, and '71, the reaction is caused by hydrolysis. This is undesirable from the purpose of the present invention as it may generate sulfonic acid groups again or cause undesirable reactions, and it is preferable to select and carry out the reaction under conditions that allow the reaction of the m, '2, and legs to proceed as much as possible. .

Next, after carrying out the reaction under conditions that produce as many compounds as shown in the formulas m, [2' and [3}], the present invention is characterized in that a carboxyl group introduction reaction is carried out to impart a carboxyl group. shall be. The following embodiments are representative of the carboxyl group introduction reaction.

A raw film of a diluted polymer having one CFI group and/or one CF group as a functional group is reacted with hydrogenated acid to convert the functional group into a functional group having an ester bond, and then hydrolyzed. This is the way to do it.

Specifically, the raw film is treated with a mineral acid such as chlorosulfonic acid, fluorosulfonic acid, fuming sulfuric acid, concentrated sulfuric acid, fuming nitric acid, concentrated nitric acid, concentrated hydrochloric acid, etc., particularly preferably chlorosulfonic acid or fluorosulfonic acid, and generally The treatment is carried out within the range of the decomposition temperature of the membrane from 50 o'clock to 250 o'clock, particularly preferably within the range of 100 o to 250 o'clock. Next, a hydrolysis treatment is carried out in an alkaline aqueous solution such as caustic soda or soda carbonate, generally at a temperature ranging from room temperature to reflux, to convert the ester obtained by the hydrochloric acid treatment into a carboxyl group. The raw film for carrying out the carboxyl group introduction reaction has been described above, and a typical preferred film is a film-like raw film of perfluorocarbon.

The carboxyl group introduction reaction described above is a polymer reaction, unlike the conventional case of low molecular weight compounds in which a perfluoroalkyl group and iodine are bonded. Diffusion is slowed down in some cases by differences in the swelling properties of the membrane depending on the solvent used.

Also, the amount of the reaction reagent used is -CFI- present in the raw film,
It is not necessarily necessary to convert all of the CF21 groups into carboxyl groups, and depending on the purpose of use of the cation exchange membrane obtained in the present invention, it is possible to convert the surface layer or a certain thickness of one or both sides of the membrane into carboxyl groups. may be preferable. Therefore, the amount of the reaction reagent used should be 0.1 mol% or more based on the iodine present in the film,
It is necessary to take different considerations than when carrying out a reaction with a low-molecular-weight compound having a secondary perfluoroalkyl group and iodine. In addition, the reaction time cannot be absolutely determined depending on reaction conditions such as reaction temperature, concentration and molar ratio of reaction reagents, solvent used, and purpose of use of the membrane obtained after the reaction, but it is generally between several seconds and 10 q hours. You can select it as appropriate depending on the purpose of use. The present invention shows how efficiently one CFI-group,
It is important to introduce one CF21 group into the membrane and how to efficiently convert it into a carboxyl group.

A preferred and important aspect of the fluorine-containing cation exchange membrane obtained by the present invention is that at least 0.5
There are carboxyl groups in the amount of milliequivalents/gram dry membrane (day type) or more, and the surface layer has at least 0.2 milliequivalents/gram.
This is an embodiment in which there are more intestinal ion exchange groups than in the Gram dry membrane (Japanese type). If the exchange capacity of the surface layer with a thickness of 1 micron is less than 0.5 milliequivalent nogram dry membrane (Nippon type), the electrical resistance of the membrane will rise and may exceed 200-m, in which case it will no longer be suitable for industrial use. significance is lost. Furthermore, if less than 0.2 milliequivalents/gram dry film (day type) of carboxyl groups are present in the surface layer, the effect of the presence of carboxyl groups is diminished, and the industrial significance is likely to be lost. . That is, the effect of improving the fixed ion concentration in the membrane is weakened. Furthermore, the carpoxyl groups may be uniformly dispersed throughout the film, may be present biased toward the surface layer, or may be present only on one surface layer.

Further, there are cases where only carboxyl groups are present, and in this case, it is desirable that the amount is at least 0.5 milliequivalent/g dry membrane. At the same time, sulfonic acid groups may coexist, and the distribution of the sulfonic acid groups and carboxylic acid groups may exist in a gradient manner so that they intersect with each other from opposite sides of the membrane. Of course, layers containing carboxylic acid and sulfonic acid may be present in a layered state. At the same time, cation exchange groups other than sulfonic acid groups and carboxylic acid groups may coexist by impregnation polymerization or other methods, and specifically, phosphoric acid groups,
There is no problem even if a phosphorous acid group, a sulfate ester group, a phosphate ester group, a hydroxyl group, an acid amide group bonding a hydrogen atom that can be dissociated by an acid amide bond, etc. are present together. Now, when carboxylic acid groups are efficiently introduced into the membrane in this way, the water content decreases and the fixed ion concentration increases as described above. Also, when only one side is treated in this way, when used as a diaphragm for electrodialysis or electrode reaction, with the treated membrane side facing the concentrated solution side, salts, bases, acids, etc. The amount of diffusion is reduced, Donnan rejection is increased, and current efficiency can be improved.

The content of the present invention will be explained in more detail in Examples below, but the present invention is not limited to these Examples. Next, regarding the evaluation of membrane properties, the electrical resistance is 3. State-N
aCI and 6. Sail - 8500 with NaOH on both sides of the membrane
This is a value measured by 1000 cycles of alternating current.

The exchange capacity was determined by immersing the acid form in a certain amount of 0.1N NaOH, leaving it for 2 hours, and then back-titrating the amount of NaOH neutralized by the acid in the membrane using 0.1N CI for one day. Find out,
The weight is expressed per 1 g of dry film (Japan type). Water content is 1
The water content when boiled for 30 minutes in pure water at 00:00 was measured at room temperature and expressed as the amount (%) per 1 g of H-type dry film. For electrolysis experiments, we used an electrolytic cell with an effective current-carrying area of ld.
An ordinary metal anode made of titanium lath coated with titanium dioxide and ruthenium dioxide was used for the anode, and a soft iron wire mesh was used for the cathode. The membrane was supported on the anode, and the gap between the cathode and the membrane was maintained at about 3 ribs. The temperature during electrolysis is 8
Pure water was supplied to the cathode chamber so as to maintain the temperature at 0 to 90 qC, so that NaOH at a constant concentration was constantly obtained.
A saturated solution of alkali metal is supplied to the anolyte, and in the case of saline solution, the anolyte is approximately 3.0 to 3. It was decided that the state would discharge the waste.
Also, the sum of both C+ and Mg10 in the brine used is 1
I kept it below skin level. Example 1 Polytetra was placed between two copolymer membranes of tetrafluoroethylene and perfluoro(3,6-dioxer-4-methyl-7-octesosulfonyl fluoride) with a thickness of 0.05 mm. A plain-woven fluoroethylene fabric with 50 400-denier threads inserted both vertically and horizontally is sandwiched between the cloth and fused under heat and pressure to create a polymeric film-like material with a single core. did.

A film of the above copolymer having a thickness of 0.05 mm was further layered and fused to form a perfluoro polymer membrane having a sulfonyl fluoride group. When this is hydrolyzed and converted into a sulfonic acid group, the exchange capacity is approximately 0.
It was 84 milliequivalents/gram dry film (Nippon type). Now,
This polymer membrane containing a core material having a sulfonyl fluoride group is soaked in a saturated ethanol solution of iodine,
The film was left for 2 hours until the film was sufficiently impregnated with iodine, and then irradiated with 7.8 MMd from a Co₂ radiation source at a dose rate of 600 ad/hr. The temperature was maintained at 50° C. and the test was conducted in the absence of oxygen gas. The obtained film was taken out and thoroughly washed with ethanol and carbon disulfide to remove attached or adsorbed iodine, and the iodine content was determined using crab light X-rays. It was calculated that 89% of one CF cross-02F group in the surface layer was converted to -CF21 group.
In addition, when we investigated the reflection infrared absorption spectrum of a model film made of polytetrafluoroethylene without reinforcing cloth by reacting it with iodine under the same conditions, we found that some absorption of the -S02F group was observed. From this, it seems that iodine is mainly bound to the site of the CF2S02F group, but considering the main chain cleavage, side chain cleavage, etc.
It is thought that iodine is combined with this. Now, put this film-like substance in an autoclave and add chlorsulfonic acid to it for 130 minutes.
After soaking in a solution kept at
The mixture was kept in H and left at 60° C. for 1 hour for hydrolysis treatment. When this waist was dyed with crystal violet, about 3 microns of the surface layer of the membrane on both sides was dyed extremely thickly.
The inside of the membrane was also stained, although it was weaker than the surface layer. This membrane was further coated with water, dimethyl sulfoxide, and NaOH.
When the membrane was immersed in a mixed hydrolysis bath and dyed again, the cross section of the membrane was uniformly and extremely clearly dyed.
This is probably because the sulfonyl fluoride groups inside the membrane remained unreacted because iodine was not sufficiently diffused. After drying the membrane into which another carboxyl group was introduced, it was immersed in phosphorous acid at room temperature, and irradiated with Co6O y-rays at a dose rate of 0.1M d/hr for a period of time to obtain sulfonic acid, carboxyl acid, We created a membrane with phosphate groups. When quantified phosphorus using crab light X-rays, it was found to be 0 as a phosphate group.
．． It contained 1 meq/g dry membrane (Nichi type). Now,
Table 1 shows the physical properties of the membrane and the results of electrolysis of saturated saline using these membranes.

The temperature of the cathode chamber during electrolysis was 8 pi. Table 1 Example 2 When hydrolyzed with a copolymer film of tetrafluoroethylene and perfluoro(3,6-dioxer-4-methyl-7-octensulfonyl fluoride), the cross ≠ depth capacity is 0.91 mm. 0 equivalent to equivalent weight/gram dry membrane (day type)
．． A sheet having a thickness of 0.5 sail was treated in a conventional manner with a bath of phosphorus pentachloride and phosphorus oxychloride to convert it into sulfonyl chloride groups.

This thin film was subjected to the following treatments. 1. Iodine and an ultraviolet lamp were sealed in a desiccator, and ultraviolet rays were irradiated to bond the sulfonyl chloride groups with iodine only in the surface layer before iodine was sufficiently adsorbed within the film.

2 Y-ray irradiation was performed in a saturated ethanol solution of iodine under the same conditions as in Example 1. (0.8M at 300ad/hr
rad) 3 Y-ray irradiation was performed under the same conditions as in Example 1 in a saturated ethanol solution of iodine.

(7.8 Mrad at 600 mrad/hr) The thin films subjected to these three treatments were reacted in fluorosulfonic acid at 9000 °C for 5 hours, and further heated in a 10% NaOH aqueous solution to convert them into carboxyl groups. .

This was soaked in an aqueous solution of octadecylamine hydrochloride for sufficient ion exchange. Next, set these three types of waist to 0.
．． The exchange capacity when hydrolyzed with a copolymer of the same thickness on the 05 side is 0.91 milliequivalent/graph. A polymer membrane with a thickness of 0.05 mm containing the above three types of carboxyl groups is formed by sandwiching a plain woven fabric with 60 threads (100 denier threads) and heat-sealing the polymer membrane. The objects were crimped together under pressure at 19 pi. This was soaked in dimethyl sulfoxide, water, and NaOH, and the sulfonyl fluoride groups were hydrolyzed by a conventional method. The three types of membranes obtained here were subjected to electrolysis in saturated saline and measurement of membrane properties. In addition, separately mentioned o. Cross-sections of three types of membranes with different thicknesses on the o5 side were stained with crystal violet and observed under a microscope, and at the same time, the ion exchange capacity was measured. In addition'
In the case of 1) using a thin film, electrolysis was performed with the ultraviolet irradiation surface facing the cathode. These results are shown in Table 2. Table 2 Example 3 A polymer obtained by suspension polymerization of CF2=CFOCF2CF=CF2 was molded into a sheet with a thickness on the 0.15 side.

Claims (1)

[Claims] 1. By reacting a fluorine-containing polymer film with an iodine compound in the presence of light and/or ionizing radiation, or by adding an iodine compound to a fluorine-containing polymer film having double bonds. Then, a raw film of a fluorine-containing polymer film having -CFI- groups and/or -CF_2I groups is obtained, and then the raw film of a fluorine-containing polymer film is reacted with a mineral acid, and then hydrolyzed. A method for producing a fluorine-containing cation exchange membrane, which comprises imparting a carboxyl group.