Production of films of organic thermoplastic polymers

摘要

Freshly extruded polymeric film is quenched by extruding molten organic thermoplastic film-forming electrically non-conductive polymeric material in the form of a thin film on to an electrically earthed moving quenching or casting surface and depositing on the upper surface of the film an electrostatic charge sufficient to cause the molten film to adhere firmly to the quenching surface. In a preferred embodiment the polymer is extruded from a hopper 11 through an orifice 12 on to a conventional quenching drum 6 which is cooled by a fluid passing from inlet 7 to outlet 8. A tempered steel wire electrode 5 of diameter 0,001 to 0,125 inch is fitted at the point at which the extruded film 4 touches the drum 6, the wire being supported by insulated electrode supports 3 mounted on a platform 9. Sufficient voltage, which is usually between 15 and 30 kilovolts, is supplied from the D.C. power supply 1 through the high voltage supply cable 2 to the wire electrode 5 to provide at least 1,1 microcoulombs per sq. inch on the upper surface of the film, which is thus forced into intimate contact with the drum. In modifications (Figs. 2 and 4, not shown) the wire electrode is replaced by a rod and a system of needle probes respectively. The electrodes may also be made of tungsten, nickel-iron alloy, copper, brass or stainless steel. Specified polymers are polyethylene terephthalate, polyethylene, polyvinyl chloride, polystyrene, vinyl chloride-vinyl acetate copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene terephthalate-neopentyl terephthalate copolymer, and nylon. Specification 829,600 is referred to.