Method and apparatus for severing and edge-sealing thermoplastic films, and product

The method of making an article, including the steps of assembling at least one set of thermoplastic heat-sealable films, each film of said set having heat-sealable material that tends to become thickened when exposed to heat-sealing temperature and the assembled films of said set having their heat-sealable materials disposed against each other, heating a blade well above the fusion temperature of the heat-sealable material, appliying the blade with pressure against one face of the assembled films while so heated and while supporting the films opposite the edge of the blade against such pressure, the amount of pressure and the sharpness of the blade being less than that needed to effect die-cutting of the films in the absence of film-fusing heat, the blade thus providing severed edges of the films, and holding said films of each set together and heating to heat-sealing temperature marginal portions of the films along the severed edges far greater in width than the combined initial thickness of the set of films and thereby forming a wide marginal seal, said heating of the marginal portions of the films being effected both by exposing the films to the heated blade as aforesaid during severing and by subjecting at least one face of said set of films over the width of said marginal portions to heat-sealing temperature that diminishes progressively away from the blade to and beyond a juncture where the unsealed films merge into the marginal seal, said holding being accomplished with pressure limited so as to accommodate substantial thickening of at least part of the width of the seal, whereby the seal formed between the films of said set is of substantially greater thickness than the initial thickness of the set of films, said greater thickness extending across the seal outward from said juncture for a distance greater than said initial thickness.