Patent ID: 7087168

Claim:
A hollow fiber blood purification membrane, which is a dry membrane containing no membrane pore holding agent: wherein the dry membrane is prepared by: (i) providing a wet membrane made from a material polymer solution comprising polysulfone-based polymer and polyvinyl pyrrolidone in a solvent but no membrane pore holding agent, the wet membrane having: a pure water permeability of not less than 100 mL/(m 2 ·hr·mmHg), permeability of polyvinyl pyrrolidone with a weight average molecular weight of 40,000 of more than 75%, and permeability of albumin in bovine blood-plasma of not less than 0.3%; (ii) removing the solvent; (iii) drying the wet membrane without addition of a membrane pore holding agent at a temperature of not more than 120° C. to constrict the pore size, and (iv) exposing the dried membrane to radiation, wherein the dry membrane: (a) has a sponge-like structure with the pore size continuously decreasing from the outer surface of the membrane toward the compact layer of the inner surface, (b) has pure water permeability of 10–1,000 mL/(m 2 ·hr·mmHg), (c) has permeability of polyvinyl pyrrolidone with a weight average molecular weight of 40,000 of more than 75%, (d) has permeability of albumin in bovine blood plasma of less than 0.3%, (e) has an absorbance in a membrane elution test solution of less than 0.04, with no membrane pore holding agent contained in the elution test solution, and (f) comprises a polysulfone-based polymer and polyvinyl pyrrolidone, with a polyvinyl pyrrolidone content of 30–45 wt % on the inner surface of the membrane.