Process for the manufacture of moistureproof sheet material

Claim 1

A PROCESS FOR TREATING NONFIBROUS ORGANIC HYDROPHILL FILMS WHICH COMPRISES REDUCING THE MOISTURE CONTENT OF A GEL REGENERATED CELLULOSE FILM, WHICH HAS NEVER BEEN DRIED SUFFICIENTLY TO CONVERT IT FROMA WET GEL STATE, UNTIL THE MOISTURE CONTENT IS BETWEEN 25% AND 65% BY WEIGHT, IMPREGNATING THE FILM THUS OBTAINED WITH AN ACIDIC, AQUEOUS COLLOIDAL SOLUTION CONTAINING FROM ABOUT 0.5% TO 20% BY WEIGHT OF A PARTIALLY POLYMERIZED MELAMINE-FORMALDEHYDE CONDENSATION PRODUCT, SAID PRODUCT BEING IN A STATE OF POLYMERIZATION LESS THAN THAT CHARACTERIZED A GEL, BEING WATERDILUTABLE, COLLOIDAL IN NATURE, AND HAVING POSITIVELY CHARGED, HYDROPHILIC PARTICLES OF LESS THAN ABOUT ONE MICRON IN DIAMETER, ADVANCING THE POLYMERIZATION OF THE MELAMINE-FOMALDEHYDE CONDENSATION PRODUCT TO A STAGE AT WHICH THE RESIN CANNOT BE DISSOLVED OUT OF THE FILM BY AQUEOUS SOLUTIONS, THEN IMPREGNATING THE FILM WITH A PLASTICIZER FOR THE REGENERATED CELLULOSE, AND SUBSEQUENTLY DRYING THE PLASTICIZED FILM.