Patent ID: 8881915

Claim:
A polymeric porous hollow fiber membrane comprising a hydrophobic polymer and a hydrophilic polymer, characterized in that (a) the hollow fiber membrane has skin layers on its inner and outer surfaces; (b) the diameters of pores in the inner surface are smaller than the diameters of pores in the outer surface; (c) the porosity increases from the inner surface toward the outer surface, and then decreases from at least one portion having a maximum porosity, of the wall section of the membrane, toward the outer surface; (d) the hollow fiber membrane has a relationship of 2 [%]≦DR≦20 [%], wherein the critical diameter of a fine particle to be removed, found by a fine particle-passing test, is φmax [μm]; the diameter of the pore in the inner surface is dIS [μm]; and the proportion of the pores with dIS exceeding φmax is DR [%]; and (e) the content of the hydrophilic polymer in the entire hollow fiber membrane is from 0.5 to 10% by weight; wherein the following relationships are satisfied: (i) 1 [% by weight]≦Ca≦10 [% by weight], (ii) Ca≦Ci and Ca≦Co, and (iii) Co≦Ci, wherein the content of the hydrophilic polymer in the entire hollow fiber membrane is Ca [% by weight]; the content of the hydrophilic polymer in the inner surface of the hollow fiber membrane is Ci [% by weight]; and the content of the hydrophilic polymer in the outer surface of the hollow fiber membrane is Co [% by weight].