Patent ID: 8883066
Filing Date: 2014-11-11
Classification: B01D,C02F,C12H

Abstract:
1. A process for producing a porous membrane whose membrane wall is constructed of a hydrophobic polymer and a hydrophilic polymer, wherein when the membrane wall is divided into 3 sections in the film thickness direction to form region “a” containing one wall surface A of the membrane wall, region “c” containing the other wall surface C and region “b” between region “a” and region “c,” the hydrophilic polymer content ratio C a in region “a” is greater than the hydrophilic polymer content ratio C c in region “c,” and the mean pore size of the wall surface C is larger than the mean pore size of the wall surface A, which comprises a solidifying step in which an internal solidifying solution is discharged from the internal fluid channel of the double-tube nozzle, while a membrane-forming solution, comprising a hydrophobic polymer, a hydrophilic polymer, a good solvent for both of these polymers and a non-solvent for the hydrophobic polymer, is discharged from the external fluid channel of the double-tube nozzle, for solidification in the external solidifying solution, wherein a portion of the hydrophilic polymer is removed using an oxidizing agent-containing aqueous solution, either during or after the solidifying step.