Patent ID: 7045044

Claim:
A process for forming a perfluoro-copolymer layer containing solid particles dispersed therein on a substrate membrane which comprises: (i) mixing and kneading 10 to 1000 parts by weight of one or more-kinds of solid particles selected from at least one group among three groups, i.e., a group of alkali-resistant inorganic material particles, a group of electrode powders and a group of sacrificial particles, with a dispersion composition comprising 100 parts by weight of a perfluoro-copolymer having repeating units represented by the following formula 1 and 10 to 10,000 parts by weight of at least one fluoro-oligomer having repeating units shown in the following formula 2 or formula 3, to form a pasty or powdery dispersion composition: —[CF 2 CX 1 X 2 ] a —[CF 2 —CF(—O—(CF 2 —CF(CF 2 X 3 )—O) b —(CFR 1 ) c —(CFR 2 ) d —(CF 2 ) e —X 4 )]— (formula 1) wherein X 1 , X 2 and X 3 are independently F or Cl, a is a real number of 2 to 20, b is an integer of 0 to 2, c is 0 or 1, d and e are independently an integer of 0 to 6, provided that c+d+e is not equal to 0, R 1 and R 2 are independently F, Cl or a perfluoroalkyl or fluorochloroalkyl group of 1 to 10 carbon atoms, X 4 is CO 2 R 3 or SO 2 F, and R 3 is a hydrocarbon type alkyl group of 1 to 3 carbon atoms; —(CF 2 —CFY) s — (formula 2) wherein Y is F or Cl, and s is a real number of 6 to 10; and —[R f 1 —O] q —[R f 2 —O] r — (formula 3) wherein R f 1 and R f 2 are independently a perfluoroalkylene group of 1 to 4 carbon atoms, and each of q and r is a real number wherein q+r is 6 to 100, (ii) removing the fluoro-oligomer(s) from said dispersion composition by extraction with a fluorine-containing solvent to form a powdery solid-particle dispersion composition containing the perfluoro-copolymer and solid particles as dispersoids, and (iii) fixing said solid-particle dispersion composition on the surface of a substrate membrane by heating at 160° C. to 340° C.