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

摘要

[PROBLEMS] To provide a polyvinylidene fluoride microporous film which has high water permeability and separation performance and is excellent in mechanical and chemical strengths; and a process for production of the film. [MEANS FOR SOLVING PROBLEMS] An anisotropic polyvinylidene fluoride hollow yarn type microporous film characterized in that the void content of the sectional bulk layer is higher than the open interstice content of the outer skin and that in the section of the film, the dense microstructure of the outer skin changes substantially discontinuously into the coarse structure of the bulk layer. The microporous film 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 film formation wherein the sectional bulk layer is formed mainly by heat-induced phase separation and the outer skin is formed mainly by nonsolvent-induced phase separation.