Waterproof plastic films of increased water vapor permeability and method of making them

Claim 1

A WATERPROOF PLASTIC SHEET A THICKNESS OF BETWEEN ONE AND 15 MILS AND HAVING WATER VAPOR PERMEABILITY, CONSISTING ESSENTIALLY OF A WATERPROOF, WATER-INSOLUBLE, FILM-FORMING PLASTIC MATERIAL WHICH IS NORMALLY SUBSTANTIALLY IMPREVIOUS TO WATER VAPOR TRANSMISSION AND WHICH IS SELECTED FROM THE GROUP CONSISTING OF POYLVINYL CHLORIDE, POLYTHYLENE, POLYPROPLENE, POLYTETRAFLUOROETHYLENE, POLYVINYLIDENE CHLORIDE, BUTADIENE-STRENE COPOLYMERS, BUTADIENE-ACRYLONITRILE COPOLYMERS, AND NATURAL RUBBER, AND PARTICLES OF WATER-INSOLUBLE CARBOXYMETHYL CELLULOSE COMPOUND UNIFORMLY DISPERSED THEREIN, SAID PARTICLES BEING PRESENT IN AN AMOUNT BETWEEN 20% AND 50% OF SAID PLASTIC MATERIAL, BY WEIGHT, AND INSOLUBLE THEREIN AND PROVIDING DIRECT CONTACT THROUGH SAID PARTICLES FROM ONE FACE TO THE OTHER OF SAID SHEET, SAID SHEET CONTAINING A MAXIMUM OF 5% OF WATER-SOLUBLE MATERIAL, SAID CARBOXYMETHYL CELLULOSE COMPOUND BEING THAT OBTAINABLE BY REPLACING AT LEAST 50% OF THE SODIUM IONS OF A SODIUM CARBOXYMETHYL CELLULOSE HAVING A DEGREE OF SUBSTITUTION OF AT LEAST 0.4 BY IONS OF THE GROUP CONSISTING OF HYDROGEN AND INSOLUBILIZING METALS, SAID INSOLUBILIZATION BEING SUCH THAT THE AFORESAID RANGE OF WATER-SOLUBLE MATERIAL IS ACHIEVED.