Abrasion process for the manufacture of microporous film

A process for the production of an unoriented microporous film which is moisture permeable and liquid impermeable.

• (a) providing an unoriented film made from a blend of a high molecular weight thermoplastic resin and an inorganic particulate filler, said thermoplastic resin being selected from the group consisting of polyethylene, linear low density polyethylene, polypropylene, polybutylene, ethylenepropylene copolymers and mixtures thereof, the effective average particle diameter of the filler being less than the thickness of the film and ranging between about 3 and about 30 microns, the film having a thickness between about 0.9 and about 6 mils;
• (b) without perforation of the film or causing formation of straight through pores in the film passing the film through at least one set of at least two cooperating nip rollers, each nip roller being provided with an abrasive surface, and
• (c) recovering from the last set of nip rollers an unoriented abraded film having an enhanced MVTR while retaining hydrostatic pressure resistance at levels substantially unchanged as compared to the same properties of the film of step (a).