Method of production of films, tubular and contracting under the effect of heat, and products obtained using this process

摘要

1,069,690. Heat shrinkable tetrafluoroethylene copolymer tubular film. E. I. DU PONT DE NEMOURS & CO. Dec. 23, 1965 [Dec. 31, 1964], No. 54574/65. Heading B5B. Heat-shrinkable tubular film is made by extruding in tubular form at 350‹ to 365‹ C. a copolymer of 5 to 95% by weight of tetrafluoroethylene and a terminally ethylenically unsaturated compound having a " specific melt viscosity" of 300,000 to 1,000,000 poises, quenching the extruded tubing by cooling it to a temperature of 130‹ C. or below, heating the tubing to 80‹ to 200‹ C., expanding the heated tubing diametrically by at least 9% and not more than 200% of its original diameter by applying internal gas pressure in the range of from 1À1 to 16 atmospheres absolute and cooling the expanded tubular film while maintaining its expanded diameter. The expression "specific melt viscosity " is defined as the melt viscosity determined at 380‹ C. in accordance with A.S.T.M. D-1238-52-T. Examples of comonomers copolymerizable with tetrafluoroethylene are the monoethylenic hydrocarbons such as ethylene, propylene, isobutylene and styrene, halogenated compounds such as 1,1-difluoro-2-chloroethylene, trifluoroethylene, chlorotrifluoroethylene, and hexafluoropropylene (also called perfluoropropylene). The preferred copolymer is a tetrafluoroethylene/ hexafluoropropylene copolymer having a specific melt viscosity within the specified range and wherein the hexafluoropropylene constitutes from about 11À2 to 12À8 mol per cent of the monomers. The expression " heatshrinkable tubular film " is defined as tubing which through the application of heat and internal gas pressure has been expanded in diameter and set in its expanded condition, so that, upon reheating, it will shrink in diameter towards its original dimensions. In use the tubing is slipped over an article to be jacketed, such as a pipe or roller and is reheated to a temperature above about 80‹ C. and less than its melting point, for example, with a " hot gas " gun at about 315‹ C. The tubular film is specified to have a diametral shrinkage of at least 5% and not more than 66À7%.