Method of improving the adhesive properties of polyolefin film by passing a diffuse electrical discharge over the film's surface

摘要

A web of polythene &c. or a plastics article such as a bottle is treated to render its surface more receptive to printing ink by subjecting it to an elongated electrical discharge between two electrically conducting electrodes such as 2, 3, the discharge traversing a gaseous medium only and the surface to be treated entering and leaving the discharge on the same side thereof. The plastics material to be treated may alternatively be polyethylene terephthalate or a polyolefine. The discharge is preferably of the corona type and may be accompanied by sparking, the discharge being caused by either direct or alternating current. A potential between 20-60 thousand volts and a frequency between 60-3,000 c.p.s. may be employed. The web 1, Fig. 4, may be treated by four pairs of electrodes as shown, one electrode of each pair being connected to a high tension source 13 via a resistor such as 6, and the web being arranged over insulating guide rollers 10, 101 and 4, 41. The electrodes are preferably in the form of knife edges, brushes or combs, and one electrode may be a heated wire. A web moving in a linear path, Fig. 1 (not shown), may be similarly treated.