Separation membrane with selective permeability and process for producing the same

A permselective separation membrane which is characterized in that:

• (a) the permselective separation membrane is made mainly of a polysulfone-based polymer and polyvinyl pyrrolidone;
• wherein a ratio [D]/[C] between the polyvinyl pyrrolidone content [D] in the uppermost layer of a surface on non-blood contacting side and the polyvinyl pyrrolidone content [C] in the uppermost layer of a surface on blood contacting side is 1.1 or higher, wherein the polyvinyl pyrrolidone content [C] in the uppermost layer of a surface on the blood contacting side of the permselective separation membrane is from 20 to 40% by weight and wherein the polyvinyl pyrrolidone content [D] in the uppermost layer of a surface on non-blood contacting side of the permselective separation membrane is from 25 to 50% by weight;
• (b) when bovine blood at a temperature of 37° C. having hematocrit value of 30% and containing 6 to 7 g/dl of total proteins and sodium citrate is flowed through a module comprising the permselective separation membrane at a flow rate of 200 mL/min, and a filtration rate of 20 ml/min.,
• (i) a sieving coefficient of albumin [A] becomes not less than 0.01 and not more than 0.1 after 15 minutes;
• and
• (ii) a sieving coefficient of albumin [B] becomes not less than 0.005 and less than 0.04 after 2 hours.