Process for producing a porous membrane material

A fluorine resin porous membrane material having an average pore diameter in the order of 100A is produced by a process comprising the steps of forming a mixture of a fluorine resin and a solution containing two or more components into a film, and then removing all but at least one of components from the solution in the film. The removal can be performed by either physical or chemical methods such as evaporation. The products improve the gas separation efficiency for uranium enrichment. In an example, 100g. of polytetrafluoroethylene powder made by emulsion polymerization and 32g. of a solution consisting of 50 parts by weight of water, 20 parts of ethanol and 50 parts of Triton X-100, namely a nonionic surface active agent, were mixed and compressed under a pressure of 30kg/cm2 in a molding die. The moulded material was extruded through a 30mm by 4mm slit die. After extrusion, it was rolled through rollers lined with a porous nickel material 500 μ thick, first through a 240 μ gap in the direction perpendicular to the extrusion axis, then through a 520 μ gap in the same direction. Next, water and ethanol were removed from the rolled film at 1000C under 10-1mmHg, leaving Triton X-100 in the film. The argon gas permeability of the finished product was 6.2 x 10-6 mol/cm2.cmHg.min. and the separation efficiency of the argon isotope was 88%. (Iwakiri, K.)