METHOD OF MAKING SHEET OR SHAPED CATION EXCHANGE MEMBRANE.

摘要

Normally solid copolymers of a fluorinated vinyl monomer and a perfluorinated vinyl compound having a carboxyl and/or sulfonyl group attached directly to the perfluorinated vinyl group or indirectly through an alkyl or ether linkage have been found to be soluble in low molecular weight polymers of perhalogenated alkyl ethers, low molecular weight polymers of perhalogenated alkyls and perfluoro kerosenes, each of said solvent materials having boiling points between about 200C and 350C. The copolymeric material dissolved in accordance with the instant invention can readily be resolidified by solvent removal and hydrolyzed or converted to the salt form to become a cation exchange material having an equivalent weight in the range of 1000 to 1600. Unreinforced sheet or shaped membrane can be formed using the dissolved copolymeric material and may be made by casting or coating on a removable backing sheet followed by removal of the solvent to result in a continuous, pore-free sheet or shaped membrane. Multiple coatings or other techniques can be used to build up the desired thickness of the membrane. Reinforced sheet or shaped membrane may be produced by similar manufacturing techniques wherein the casting or coating of the membrane is upon a reinforcing backing fabric, which can be polytetrafluoroethylene mesh or the like. Such reinforcing fabrics may be dipped into hot solutions of the copolymeric material using mandrel, frame, continuous roll coating techniques or other methods known to those familiar with the coating art. In the case of reinforced sheet material, no removable backing is necessary in preparing the reinforced membrane sheets. The copolymeric material which is used in making the sheet or shaped membrane can be a single material or it can be of various equivalent weights, structures (carboxyl or sulfonyl, mixtures of same, or the sheets or shaped membranes can be layered of the same or different materials). It is sometimes preferred to purify the surface between coatings by using Freon-type solvents in the process of making asymmetric membranes, when utilizing a multiple coating technique. Such purifications result in better bonds between the layers, especially when different materials are utilized in adjacent layers, although such is not necessary in the practice of the instant invention.