PURPOSE: To prepare the titled porous membrane having excellent permeability and suitable as a membrane filter and a blood-treatment membrane, by forming a solution composed of a polysulfone resin, a solvent of the resin, a cationic metal salt, and an alcohol in the form of a film, and coagulating the film in a coagulation bath.
CONSTITUTION: A polysulfone resin solution is prepared by mixing (A) a polysulfone resin preferably a polymer containing ≥50mol% of the recurring unit of formula I or formula II with (B) a solvent which dissolves ≥15wt% of the polysulfone resin at ≤50°C, (C) a univalent or bivalent cationic metal salt, and (D) a 2W15C monohydric alcohol. The concentration of the resin, the salt and the alcohol in the resin solution are 8W35wt%, 0.3W7wt% and 15W55wt%, respectively, and the weight ratio of alcohol/polysulfone resin is ≥2.5. The solution is cast or spun at a temperature near the clouding point (±30°C) to form a membrane, and the product is immersed and coagulated in a coagulation bath (water or an aqueous organic liquid) to obtain a porous membrane having micropores with 0.05W5μ diameter at the surface layer.
MORI KOU
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