Patent ID: 8511482

Claim:
A method of producing a porous membrane, the method comprising: preparing a polymer solution, in which an ester derivative of cellulose is dissolved in a mixture of a good solvent, a poor solvent and a non-solvent; casting the polymer solution over a surface, wherein a temperature of the casted surface is maintained in a range of 7.0 to 13.0° C. during the casting step, wherein a temperature of the polymer solution is maintained in a range of 32.0 to 38.0° C. during the casting step; and subjecting the casted polymer solution to a phase separation while drying thereby producing a microporous membrane of cellulose ester derivative; rendering a part of a surface of the microporous membrane of cellulose ester derivative cellulosic by saponification to form a saponified membrane; neutralizing the saponified membrane; rinsing the saponified membrane after the neutralizing; and heating and drying the saponified membrane after the rinsing by using a contact type drum, wherein the contact type drum includes a motor for rotationally driving the contact type drum, a temperature controller for detecting a surface temperature of the contact type drum, and a belt which extends around the contact type drum, and the belt conveys the saponified membrane so that the saponified membrane is interposed between the contact type drum and the belt.