Patent ID: 6890436

Claim:
A porous hollow fiber membrane obtained by dry-wet spinning method or a wet spinning method from a spinning dope while using the following components: a spinning dope containing a base polymer as a material for forming said porous hollow fiber membrane, an additive for facilitating a phase separation of said spinning dope, a solvent compatible with both, said base polymer and said additive, and a mass of microparticles insoluble in said solvent, wherein said microparticles are uniformly dispersed in a liquid medium and have an average particle size within the range of 1 to 20 μm, wherein an amount of the additive and/or the particle size is adjusted to enhance the coagulation action of the microparticles; and a coagulating liquid for forming the hollow fiber membrane, to obtain a spun hollow fiber membrane, and extracting said additive with cold water or water at a temperature from 40 to 90 degree C.; and extracting and removing said micropartilces by immersing said spun hollow fiber membrane into an extracting solution effective to dissolve said microparticles, but ineffective to dissolve said base polymer; wherein said hollow fiber membrane has a permselectivity; and wherein a particle weight cutoff is within the range of 1 to 10 um; and a pure water permeate flow is equal to or higher than 30,000 L/M2/100 kpa.