Filter medium

Claim 1

A PHYSICALLY STRONG AND FLEXIBLE FILTER SHEET CAPABLE OF REMOVING PARTICLES OF BACTERIA SIZE COMPRISING IN COMBINATION A THIN FLEXIBLE MICROPOROUS PLASTIC FLIM SUFFICIENTLY PERMEABLE FOR FILTRATION AND HAVING SUBSTANTIALLY TRANSVERSE PORES OF EFFECTIVE DIAMETER BETWEEN 100 MILLIMIRONS AND 1 MICRONS WHICH IN NUMBER OCCUPY A TOTAL VOLUME IN EXCESS OF 80 PERCENT OF SAID FILM AND RENDER IT INHERENTLY FRAGILE AND BRITTLE, AND A WEB EMBEDDED IN AND SUBSTANTIALLY COMPLETELY SURROUNDED BY SAID FILM, SAID WEB BEING AN OPEN MESH FABRIC FORMED OF SMOOTH SURFACED NYLON STRANDS OF NON-ABSORBENT MONOFILAMENT FIBERS WHICH ARE COMPLETELY WITHIN AND COVERED BY SAID FILM SUCH THAT THE FILTER SURFACE IS NOT DISRUPTED BY SAID STRANDS, SAID STRANDS HAVING A STRAND DIAMETER LESS THAN ABOUT 250 MICRONS AND FORMING BETWEEN THEM OPENING OF LESS THAN ABOUT 1MM. BUT OF SUFFICIENT SIZE THAT THE PERMEABILITY OF THE SHEET IS SUFFICIENT FOR FILTRATION, THE VOLUME WITHIN SAID OPENINGS BEING COMPLETEDLY OCCUPIED BY SAID FILTER FILM AND THE AREA OF SAID OPENINGS BEING OF SUFFICIENT SIZE THAT FILTRATION OCCURS SOLELY BY THE ACTION OF SAID FILM AND SAID FILM BEING OF REDUCED THICKNESS IN THE REGION OF SAID STRANDS.