ANNULAR POLYOLEFIN FILM, MANUFACTURE THEREOF AND USAGE THEREOF

PROBLEM TO BE SOLVED: To provide a polyolefin film with outstanding fusion sealing properties in heat-shrinkable film packaging as well as the method for manufacturing this film and its usage. SOLUTION: This method for manufacturing an annular polyolefin film is to extrude a molten polyolefin resin film a ring die at 130-300 deg.C and regulate the extruded sheet so that the density of the cooled face is 0.888 g/cm or less by quenching the outer or the inner face or both outer and inner faces of the sheet before being stretched, with a liquid or a gas. The annular polypropylene film to be used as the sheet before being stretched is composed of either of an ethylene-propylene random copolymer with an ethylene component content of 2.0-10.0 wt.% or an ethylene-propylene-α olefin tercopolymer with an ethylene component content of 0-5.0 wt.%, an α-olefin component content excepting ethylene and propylene of 2.0-30.0 wt.% and a polypropylene component content of 98.0-65.0 wt.% as the molten polyolefin resin. Further, in the co-biaxially stretched heat-shrinkable polypropylene film, its both faces with a density of 0.888 g/cm or less are sealed together for use.