| abstract |
PURPOSE:To obtain the title anisotropic microporous membrane with the surface layer having uniform pore diameter by forming a liq. film from a stable dope, and providing a temp. difference between the front and rear surfaces of the liq. film. CONSTITUTION:Dimethylformamide, dimethylacetamide, dimethyl sulfoxide, etc., for example, are used as the solvent, when polysulfone is used as the polymer, to prepare a 5-30wt% dope. A nonsolvent or a swelling agent is added, as required, to improve the permeability of the microporous membrane. The dope is used to make the liq. membrane. The thickness is preferably controlled to 50-500mum. A temp. difference is provided between the front and rear surfaces of the liq. film of the dope. The temp. difference is adjusted to >=5 deg.C. The temp. difference is preferably kept for 5sec-10min. Then film is the dipped in a coagulation bath, then washed, and dried, and the anisotropic microporous membrane wherein the pore diameter is increased from the front surface layer toward the rear surface layer is obtained. |