POLYVINYLIDENE FLUORIDE HOLLOW YARN TYPE MICROPOROUS FILM AND PROCESS FOR PRODUCTION OF THE SAME

摘要

Problems: To provide a polyvinylidene fluoride microporous membrane which has high water permeability and separation performance and is excellent in mechanical and chemical strength; and a process for producing the film.;Means for Solving Problems: An anisotropic polyvinylidene fluoride hollow fiber microporous membrane characterized in that the porosity of the cross-sectional bulk layer is higher than the membrane surface porosity of the outer layer and that in the cross section of the membrane, the dense microstructure of the outer surface changes substantially discontinuously into the coarse structure of the bulk layer. The microporous membrane can be produced by introducing by a dry-wet method a dope prepared by dissolving a polyvinylidene fluoride resin together with a water-soluble latent solvent at high temperature into a cooling bath consisting of water or a mixture thereof with a water-soluble latent solvent and subjecting the dope to membrane formation wherein the cross-sectional bulk layer is formed mainly by thermally-induced phase separation and the outer layer is formed mainly by nonsolvent-induced phase separation.