GB1252935A - - Google Patents

Abstract

1252935 DC/AC converters UNION CARBIDE CORP 4 Nov 1968 [3 Nov 1967] 52120/68 Heading H2F. Polymeric films are treated with a relatively high voltage (e.g. 2000-15, 000 V) gaseous discharge to improve the affinity of the surface thereof, to inks, adhesives and other polar substrates. The high voltage is derived from an invertor 15, Fig. 1 supplied from variable voltage D.C. source 13 and comprising a step-up transformer 16, a bi-phase arrangement of thyristors 20, 22, a commutating capacitor 28, reactive current feedback diodes 34, 36 and commutating choke 38. Each thyristor is triggered alternately to send current through the half primary windings in turn. With Th20 conducting and Th22 blocked, current flows in the left hand winding. Autotransformer action produces a voltage 2E DC at the anode of Th22 charging C28 to 2E DC so that when Th22 is triggered the capacitor charge reverse biases Th20 turning it off and so on. A substantially square wave output is produced at the secondary winding terminals which are connected to electrodes, one on each side of the film as illustrated in Fig. 4 (not shown). One electrode is spaced from the surface and comprises a "knife edge" while the other is connected to a roller having a dielectric surface layer over which the film sheet is passed. The trigger circuit 40 is a multivibrator, preferably a free-running astable solid state oscillator or a unijunction astable oscillator. Alternatively monostable and bistable oscillators may be used. The operating frequency may be from 1000 Hz to 3000 Hz.