PURPOSE: To obtain the title porous membrane having excellent shelf stability, a narrow distribution of pore diameters, and a high opening rate by specifying the mean diameter, major axis/minor axis ratio, coefficient of variation in pore diameter, and opening rate of the pores opened vertically to the membrane plane and the porosity of the whole porous membrane.
CONSTITUTION: For example, the blend of the tetrafluoroethylene-vinylidene fluoride copolymer and methyl methacrylate polymer is dissolved in a good solvent such as methyl ethyl ketone, and the soln. is cast on a glass sheet, etc., to form a thin membranous material. The saturated vapor of a poor solvent such as water is then brought into contact with the surface of the thin membranous material to solidify the material, and a porous membrane is obtained. By this method, a porous membrane, wherein the mean diameter of the pores opened vertically to the membrane plane is controlled to 0.01W100μm, the major axis/minor axis ratio of the pore is adjusted to 1.0W20, the coefficient of variation in the pore diameter is regulated to 0W50%, and the opening rate is controlled to 20W80%, and the porosity of the whole porous membrane is adjusted to 20W90%, is obtained.
TAKAHASHI HIROSHI
OHORI YASUSHI
HABARA HIDEAKI
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