JPS5938020A - Joining of film - Google Patents

Abstract

PURPOSE:To join films by completely closing holes formed in decomposition and dissolution of reinforcing fibers by a method in which a cationic exchange film in which reinforcing fibers tend to disappear by decomposition, etc., during the electrolysis of saline is beforehand subjected to decomposing or melting treatment and they are hot-bonded. CONSTITUTION:A cationic exchange film in which part or all of reinforcing fibers tends to disappear by decomposition or dissolution during the electrolysis of saline is hot-bonded after the decomposition or dissolution of the reinforcing fibers for varnishing. In the decomposition or dissolution treatment of the reinforcing fibers, a method of contacting the fibers with chlorine gas, a method of dipping the fibers in a chlorine-containing aqueous solution, etc., is preferably used. The film subjected to the dissolution treatment is dipped 4-5 times in pure water to remove the treating agent completely and then dipped in a mineral acid, e.g., hydrochloric acid, etc., to convert it into H-type, and then hot- bonded through water-washing and drying processes by a hot press, etc., at 200- 300 deg.C and under a pressure of 2-150kg/cm<2> for 1-30min.

Description

[Detailed description of the invention] The present invention relates to a method for bonding cation exchange membranes.

More specifically, for a cation exchange membrane in which some or all of the reinforcing fibers may disappear due to decomposition or elution during electrolysis, the reinforcing fibers are decomposed or eluted before joining, and then the reinforcing fibers are joined. It relates to a method of completely closing and joining the holes that have been disassembled or melted.

Bonding of cation exchange membranes is an industrially useful technology. Membrane bonding is extremely useful for industrial use of cation exchange membranes, such as when molding a cation exchange membrane into a desired shape, or when it is difficult to manufacture a membrane large enough for industrial use. It is. It is also useful as a means of repairing undesirable pores and cracks in cation exchange membranes. The present invention thus provides a method for bonding cation exchange membranes that is industrially extremely useful.

Various perfluorinated cation exchange membranes have been put into practical use for electrolysis of aqueous halogenated alkali solutions. The exchange group of the cation exchange membrane is generally composed of either sulfonic acid or carboxylic acid, or a mixture thereof. Since these cation exchange membranes are used in the form of a thin film with a thickness of 100 μm to 1000 μm, it is difficult to use them without reinforcing fibers unless special measures are taken.

Various reinforcing fibers have been put into practical use to prevent damage to cation exchange membranes due to pressure brim elongation, shrinkage, etc. Known materials include tetrafluoroethylene, tetrafluoroethylene-ethylene copolymer, trifluoroethylene-ethylene copolymer, etc. These are made into a network and placed inside the cation exchange membrane to increase its strength. I'm trying. These reinforcing fibers have oxidation resistance and alkali resistance, and will not dissolve or break even if used for long periods of time in electrolysis.

However, the presence of reinforcing fibers disturbs the current distribution on the membrane surface, increases the effective current density of the membrane, and becomes a factor in increasing the electrolytic voltage. On the other hand, due to the need to maintain mechanical strength above a certain level during membrane formation and when attaching the membrane to the electrolytic cell, it is not possible to drastically reduce the amount of reinforcing fibers, and due to the requirements from the voltage and strength aspects, Reinforcing fibers are used that are designed to balance two contradictory aspects.

However, in recent years, cation exchange membranes have appeared in which some of the reinforcing fibers disappear due to decomposition or elution during electrolysis. For example, there is a cation exchange membrane disclosed in Japanese Patent Publication No. 57-20328. The aim is to maintain the strength during film formation above a certain value while minimizing current shielding during electrolysis and lowering the voltage.

The reinforcing fibers called sacrificial fibers of this membrane are acrylic fibers.
It is a natural fiber, etc., and during electrolysis, it is constantly in contact with hypochlorite ions that permeate from the anode chamber and caustic soda that permeates from the anode chamber, and it has the property of decomposing and disappearing due to the chemical action of these. have. Even if the reinforcing fibers elute or disappear during electrolysis, this will not be a problem when used in a filter press type electrolytic cell. However, when converting a well-known diaphragm electrolytic cell into an ion-exchange membrane electrolytic cell using an electrolytic method in which a cation exchange membrane is bonded and molded into a desired shape, the following two problems arise. occurs.

That is, a cation exchange membrane having sacrificial fibers was prepared in 1. .

If the sacrificial fibers are joined using the conventional method and energized without removing the sacrificial fibers in advance, the sacrificial fibers at the joint will dissolve and create small pores, which will increase the salt content in the product and reduce the current efficiency. It cannot be put to practical use.

In view of these circumstances, the inventors of the present invention conducted intensive research to solve these problems, and as a result, they arrived at the present invention in which the sacrificial fibers are melted in advance and then bonded to close the holes.

That is, the present invention provides a cation exchange membrane in which some or all of the reinforcing fibers may disappear due to decomposition or elution during the electrolysis of saline solution, by thermally welding the reinforcing fibers after the reinforcing fibers have been previously eliminated by decomposition or elution treatment. The content is a method for joining membranes characterized by the following.

As for the decomposition or elution treatment of sacrificial fibers, it is preferable to bring them into contact with chlorine gas or to immerse them in an aqueous solution containing chlorine. Alternatively, it may be immersed in hypochlorite water or a solution (sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, etc.). Furthermore, immersion in a caustic alkali aqueous solution is also effective. In the case of solution immersion, the temperature may be at room temperature or may be heated, but it is desirable to heat it if you want to process quickly. Processing time depends on processing liquid composition,
It varies depending on the concentration and temperature, but preferably for 1 hour to 120 hours.
IL< is 2-24 hours. In addition, the treatment may be carried out only on the joining area or on the entire surface, but if the sacrificial fibers are eluted over the entire surface, the membrane will lose its elasticity, and the operation at the time of joining or installing it in the electrolytic bath will be difficult. Therefore, it is preferable to perform elution treatment only on the areas to be bonded. The dissolution-treated membrane is immersed in pure water 4 to 5 times to completely remove the treatment agent, then converted to H-type with mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, etc., washed with water, and then dried to form the H-type. Join using the appropriate method. That is, by hot press, heat impulse, etc.
200-300°C1 preferably 230-260°C1
Press pressure 2~150kg/cI4, preferably lO~L
Heat welding is carried out at OOkV/cd for 1 to 30 minutes, preferably 1 to 10 minutes.

The membrane bonded according to the present invention does not suffer from the phenomenon of holes forming in the bonded portion and deterioration of performance even when energized for a long time, and can be operated stably for a long time. Furthermore, when only the bonded portions are treated and bonded according to the present invention, the membrane as a whole has sufficient mechanical strength, so there is no problem when it is taken into an electrolytic cell.

The present invention will be explained below with reference to Examples, but it goes without saying that the present invention is not limited to these Examples. Also,
It goes without saying that the idea of the present invention is directly applicable not only to saline solutions but also to electrolysis of aqueous halogenated alkali solutions.

Example 1 A 5 cm width at both ends of a cation exchange membrane 76aRX140α having sacrificial fibers was immersed in a sodium hypochlorite solution (available chlorine 12%) at 70'C for 16 hours to dissolve the sacrificial fibers. After confirming complete dissolution by cross-sectional observation using a microscope, the treated area was washed five times with pure water to completely remove the sodium hypochlorite, and then soaked in 2N hydrochloric acid at room temperature for 16 hours.
It was converted to H type by soaking for a period of time. After washing with water and air drying, the sulfonic acid layers of the cation exchange membrane were pressed together using an impulse heater at 280°C and 16.5 kti/cA for 60 seconds to form a cylindrical membrane.
It was installed in a box-type electrolytic cell using the method shown in Publication No. 952, and the amount of current applied was 2KA (current density 28.5 A/(3i)).
Electrolysis of saline solution was carried out at a temperature of 90°C, and the following results were obtained.

Current efficiency 97-98% NaOH concentration 32-33% NaOH in Na, C140-60 pi) rn15
0% Na, OF (After continuing this operation for 4 months, the cation exchange membrane was taken out from the electrolytic cell and the cross section of the joint was observed under a microscope, and no pores were observed at all.

Example 2 A test was conducted in the same manner as in Example 1, except that the cation exchange membrane having sacrificial fibers was treated with chlorinated water (available chlorine a o o o ppm, 50°C for 148 hours), and the same electrolytic performance was obtained. It was done. Furthermore, no small holes were observed in the cross-sectional observation of the joint after the current test.

Example 8 Treatment of a cation exchange membrane with sacrificial fibers using caustic soda <
Example 1 except that 82%, 90°0, 120 hours)
A similar test was conducted and the same electrolytic performance was obtained.

Furthermore, when the cross section of the joint was observed after the current test, no holes were found at all.

Comparative Example 1 The cation exchange membrane having the sacrificial fiber used in Example 1 was immersed in 2N HCI at room temperature for 16 hours without dissolution treatment.
Converted to H type. The membrane was washed with water, air-dried, and bonded by heat welding to form a cylindrical membrane, which was mounted in a box-shaped electrolytic cell and tested under the same conditions as in Example 1. The results obtained are as follows.

Current efficiency 98-94% NaOH concentration 82-88% Na0Ei medium NaC1100-1501)l)I11
After continuing this test with 150% NaOH for one month, the cell was disassembled and the cross section of the joint was observed, and it was found that the sacrificial fibers had completely disappeared and numerous pores with an inner diameter of approximately 100 μm were observed.

Claims (1)

[Scope of Claims] 1. A cation exchange membrane in which some or all of the reinforcing fibers can be decomposed or eluted during the electrolysis of saline solution is prepared by subjecting the reinforcing fibers to decomposition or elution treatment in advance. A method for bonding membranes, which is characterized in that the film is melted and then thermally welded. □2. 8 according to claim 1, wherein the decomposition or elution treatment is a method of contacting with chlorine gas.
The bonding method according to claim 1, wherein the decomposition or elution treatment is a method of immersing in an aqueous solution containing chlorine. 4. The bonding method according to claim 1, wherein the decomposition or elution treatment is a method of immersion in an aqueous hypochlorous acid solution. 5. The joining method according to claim 1, wherein the decomposition or elution treatment is a method of immersing in a caustic aqueous solution. 6. The bonding method according to claim 1, wherein the exchange group of the cation exchange membrane is composed of one of sulfonic acid, carboxylic acid, or a mixture thereof.