GB1085244A - Improved method and apparatus for treating plastic materials to improve the adehsion of printing inks thereto - Google Patents

Abstract

1,085,244. Discharge apparatus for treating plastics materials. A. V. EISBY. Oct. 13, 1964, No. 41714/64. Heading H1X. Plastics foil 8 passing over a counter electrode 27 is treated to improve the adhesion of printing inks by subjection to voltages having a frequency of the order of 20-50 kc./s. applied to electrode(s) 26, the voltages having a waveform (Fig. 4) which rises steeply to a point a at about 25 kv. when a spark occurs, the voltage then falling to a value about one quarter of the sparking voltage and maintaining a current of the order of 0À5 amp. to the foil for the remainder of the half-cycle. The negative halfcycle b may be limited to -the form c in known manner. The electrode 26 comprises layers of steel or other metal 1 mm. thick, supported at a spacing of 0À5 to 1 mm. from the foil surface. Roller 27 has a tubular insulating covering 28 provided with a metallic layer 29 covered by an inner layer 30 of insulating material containing electrically conductive pulverous material and an outer layer 31 of insulating material, e.g. ceramic, having a higher dielectric constant (8 to 30) than the foil 8, and covered by a lacquer or oil coating 32. The capacitances of the various layers are such that the bulk of the power dissipation occurs in the foil. Two electrodes 26 mounted on opposite sides of the roller 27 may be connected to the output winding of an impulse transformer (Fig. 1, not shown) to form a resonant circuit with a Q greater than 50. The transformer has an open ferrite core and a non-tuned primary fed through power amplifiers from a controllable frequency generator. Both sides of the foil may be treated by employing, two roller electrodes (Fig. 5, not shown). Alternative electrode constructions (Figs. 6 and 7, not shown) enable partly closed plastics bottles to be treated. Two electrodes may be mounted on a carriage (Fig. 8, not shown) provided with supporting rollers and a handle for manual movement along more rigid flat foils.