Flexible sheet materials

Claim 1

A PROCESS FOR PREPARING A FIBEROUS SHEET, COMPRISING FORMING A NON-WOVEN FIBROUS MAT OF MIXED-SPUN FIBERS COMPRISING AT LEAST TWO KINDS OF POLYMERIC MATERIALS SELECTED FROM THE GROUP CONSISTING OF POLYAMIDES, N-METHOXYMETHYLATED POLYAMIDES, POLYESTERS, POLYSTYRENE, POLYOLEFINS, POLYVINYL CHLORIDE, POLYVINYLIDENE CHLORIDE, POLYVINYL ACETATE, POLYMETHACRYLATES, POLYVINYL ALCOHOL, POLYVINYL ACETATE, POLYMETHTHANE ELASTOMER, SAID AT LEAST TWO KINDS OF POLYMERIC MATERIALS HAVING DIFFERENT SOLVENT SOLUBILITIES, IMPREGNATING SAID MAT WITH A FIRST LIQUID WHICH IS A SOVELENT FOR AT LEAST ONE OF SAID POLYMERIC MATERIALS BUT A NONSOLVNT FOR THE OTHER POLYMERIC MATERIALS AT A TEMPERATURE SUFFICIENTLY LOW THAT SAID LIQUID SUBSTANTIALLY DOES NOT DISSOLVE THE POLYMERIC MATERIALS FOR WHICH IT IS A SOLVENT; HEATING THE IMPREGNATED MAT TO A TEMPERATURE AT WHICH SAID POLYMERIC MATERIAL IS PARTIALLY OR WHOLLY DISSOLVED, AND THE SOLUTION OF SAID POLYMERIC MATERIAL IS DISTRIBUTED THROUGH THE FIBROUS MAT, WHILE SUBSTANTIALLY NONE OF THE OTHER POLYMERIC MATERIALS ARE DISSOLVED INTO THE FIRST LIQUID, AND COAGULATING SAID POLYMER SOLUTION BY TREATING SAID MAT WITH A SECOND LIQUID WHICH IS A NON-SOVENT FOR ALL OF THE POLYMERIC MATERIALS WHICH CONSTITUTE SAID MIXED-SPUN FIBERS AND WHICH IS AT LEAST PARTIALLY MISCIBLE WITH SAID FIRST LIQUID TO FORM A POROUS POLYMERIC STRUCTURE WHICH IS SUBSTANTIALLY NONBONDED TO THE FIBERS OF SAID FIBROUS MAT.