Coated polyolefin film

Claim 1

THE PROCESS WHICH COMPRISIES IN COMBINATION THE STEPS OF PASSING ONE SURFACE (A) OF A CONTINUOUS BIAXIALLY ORIENTED POLYPROPYLENE FILM THROUGH A FLAME EMANATING FROM THE DISCHARGE OPENING OF A BURNER SUPPLIED WITH A GASEOUS MIXTURE OF HYDROCARBON FUEL AND OXYGEN-ENRICHED AIR, THE FUEL WQUIVALENCE RATION OF THE GASEOUS MIXTURE BEING BETWEEN 0.95 AND 1.10, THE OXYGEN RATIO BEING BETWEEN 0.25 AND 0.30, THE SURFACE ON WHICH THE FILM IS SUPPORTED AS IT TRAVERSES THE FLAME BEING HEATED AND MAINTAINED AT A TEMPERATURE BETWEEN 30*C. AND 80*C.; PASSING THE OTHER SURFACE (B) OF SAID FILM THROUGH A FLAME EMANATING FROM THE DISCHARGE OPENING OF A BURNER SUPPLIED WITH A GASEOUS MIXTURE OF HYDROCARBON FUEL AND OXYGEN-ENRICHED AIR, THE FUEL EQUIVALENCE RATIO OF THE GASEOUS MIXTURE BEING BETWEEN 1.15 AND 1.30 AND AT LEAST 0.10 GREATER THAN THE FUEL EQUIVALENCE RATION OF THE FIRST NAMED GASEOUS MIXTUE, THE OXYGEN RATIO BEING BETWEEN 0.25 AND 0.30, THE SURFACE ON WHICH THE FILM IS SUPPORTED AS IT TRAVERSES THE FLAME BEING HEATED AND MAINTAINED AT A TEMPERATURE BETWEEN 30*C. AND 80*C., THE PATH OF THE FILM AS IT TRAVERSES THE FLAME FROM EACH BURNER BEING LOCATED AT A DISTANCE FROM THE BURNER LESS THAN THE LENGTH OF THE UNIMPEDED PRIMARY ENVELOPE OF THE FLAME BUT NOT LESS THAN THE DISTANCE BELOW WHICH THE VELOCITY OF THE BURNING GASES ESCAPING FROM THE IMMEDIATE VICINITY OF THE DISCHARGE OPENING OF THE BURNER EXCEEDS THE BURNING VELOCITY OF THE FLAME, THE EXPOSURE OF THE FILM TO THE ACTION OF EACH FLAME BEING FROM A TIME BETWEEN 0.0005 AND 0.1 SECOND; THEREAFTER COATING EACH SIDE OF SAID FILM WITH AN AQUEOUS DISPERSION OF A COPOLYMER OF VINYLIDENE CHLORIDE AND AT LEAST ONE ETHYLENICALLY UNSATURATED MONOMER COPOLYMERIZABLE THEREWITH, SAID COOPOLYMER CONTAINING BETWEEN 70 AND 95% BY WEIGHT OF VINYLIDENE CHLORIDE, AND DRYING SAID FILM.