Patent ID: 11883786
Assignee: ENTEGRIS, INC.
Field: Chemical engineering (Chemistry)
Classification: CPC B | IPC B

Claim 12:
13. A method of making an integral extruded porous polymeric sheet membrane, the method comprising:
forming a polymer-containing liquid comprising polymer in solvent,
passing the polymer-containing liquid through an extrusion die to form an extruded film of the polymer-containing liquid, and
exposing both sides of the extruded film to a condition that will cause coagulation of the polymer on both sides of the film,
wherein the integral extruded porous polymeric sheet membrane comprises:
a first surface, a second surface, and a thickness between the first surface and the second surface,
a first thickness region that includes the first surface and a portion of the membrane in a direction of the thickness,
a second thickness region that includes the second surface and a portion of the membrane in a direction of the thickness, and
a third thickness region extending in the direction of the thickness between the first thickness region and the second thickness region,
wherein an average pore size of the first thickness region and an average pore size of the second thickness region are both less than an average pore size of the third thickness region, and wherein the membrane exhibits a retention of at least 90% measured using round polystyrene particles having a diameter of 5 to 15 nanometers.