VINYLIDENE FLUORIDE RESIN HOLLOW-FIBER POROUS MEMBRANE AND PROCESS FOR PRODUCTION OF THE SAME

摘要

A vinylidene fluoride resin hollow-fiber porous membrane made of vinylidene fluoride resin hollow fibers, characterized in that the F(L=200mm, v=70%)(m/day)/Pm<SUP>4</SUP> ratio is 70,000 or above wherein F(L=200mm, v=70%)(m/day) is a flux rate of water through the membrane (converted into a 70% void basis) as determined under a pressure difference of 100kPa at a water temperature of 25°C with a sample length L of 200mm and Pm<SUP>4</SUP> is the fourth power of a mean pore diameter Pm (µm) as determined on the base of pore diameter distribution measured by a half dry/bubble point method (ASTM F316 and ASTM E1294). This membrane has a smaller mean pore diameter than that of prior art and is thus improved in the fine particle removing performance, while the flux rate of water through the membrane is inhibited from lowering. The membrane can be produced from a raw material composition which comprises a resinous raw material enhanced in the content of an ultra high molecular weight resin as compared with that of prior art and contains a plasticizer and a good solvent at higher ratios than those of prior art through melt extrusion and low-temperature cooling.