GB938325A - Treatment of organic thermoplastic film - Google Patents

Abstract

An organic thermoplastic polymeric film is passed on to an electrically grounded moving surface, an electrostatic charge sufficient to cause the film to adhere firmly to the moving surface is deposited on the upper surface of the film and the film, on the moving surface, is then subjected to a treatment with a high frequency electrical spark discharge to improve its adhereability while maintaining firm adhesion during the treatment. The treatment to improve adhereability may comprise passing the film through spaced positive and negative electrodes while continuously applying to the positive electrode an alternating current of 0,5-2,5 radio frequency amperes at a voltage of 10,000-100,000 volts especially 10,000-30,000 volts and p at a frequency of 100,000-1,000,000 cycles per sec. especially 300,000-500,000 cycles/sec. in an atmosphere effective to create an electrical discharge between the electrodes. An electrostatic charge of at least 0,23 microcoulombs per square inch may be deposited in a continuous and uniform manner on the upper surface of the film at least adjacent to each edge of the film. The film may be made of polytetrafluoroethylene of a copolymer of 50-95% <PICT:0938325/IV(a)/1> by weight tetrafluoroethylene and 50-5% hexafluoropropylene, of polyvinyl chloride, polypropylene, polyethylene or polyethylene terephthalate, which are preferred, or may be made of polyvinyl fluoride, polyvinylidene fluoride, vinyl fluoride/vinylidene fluoride interpolymers, polychlorotrifluoroethylene, tetrafluoroethylene/hexafluoropropylene interpolymers in general, vinyl fluoride/tetrafluoroethylene interpolymers, vinylidene fluoride/tetrafluoroethylene interpolymers, vinylidene fluoride/hexafluoropropylene interpolymers, vinyl chloride/vinyl acetate interpolymers, vinyl chloride/vinylidene chloride interpolymers, polyoxymethylene, polyacrylonitrile and polyamides. In apparatus as shown, film 11 enters chamber 12 through opening 13, passes around the electrically grounded rotatable roll 14, and leaves the chamber at 19. The film is electrostatically charged by one or more electrodes 15, which may be wire electrodes of 0,001-0,125 inch diameter, charged from a D.C. power source to 15-30 kilovolts, so as to provide sufficient charge on the upper surface of the film to force it into intimate contact with the driven roll 14. The roll may be replaced by a belt or chain. Its surface may be metallic, or it may be coated with a thin layer of polyethylene, polytetrafluoroethylene, or silica, glass, or aluminium oxide. The film then passes under one or more hollow tubes 16, 17 disposed parallel to the longitudinal axis of the roll and spaced 0,008-0,25 inch therefrom. The tubes are each connected to a power source supplying an alternating, or pulsating direct current of 0,5-2,5 radio frequency amperes at 10,000-100,000 volts and at a frequency of 100,000-1,000,000 cycles/sec. An atmosphere of nitrogen or other gas in which the electrical discharge takes place is fed to the hollow interior of the tubes through ducts 18 and issues from the tubes at narrow slots running lengthwise of each tube and facing the film. Other gaseous atmospheres specified include nitrogen and glycidyl methacrylate vapour, nitrogen and carbon tetrachloride vapour, and chlorine. Specification 829,600 and U.S.A. Specification 2,833,686 are referred to.