Patent GB-925354-A (GB)
Title: A process and device for the surface treatment of films of synthetic organic thermoplastic polymeric material
IPC: B29C59/10
Filed: 1959-08-18
Abstract: A device for treating the surface of a film of synthetic organic thermoplastic polymeric material to improve the receptivity of the surface for printing inks by subjecting it to a corona electric discharge comprises a rotatable cylindrical electrode 1 (Fig. 1) and a second electrode 4 which is fixed and p  non-rotatable and is disposed close to the cylindrical electrode. The film F is caused to travel round and in contact with the metal electrode 1 with the surface to be treated exposed to the second electrode 4.  The cylindrical electrode 1 is generally made of steel and is earthed through the lead 3.  The electrode 4 may be a copper rod and is connected by means of a lead 7 to one of the output terminals 5 of a transformer 6, the other terminal of the same output winding being earthed <PICT:0925354/IV(a)/1> <PICT:0925354/IV(a)/2> <PICT:0925354/IV(a)/3> <PICT:0925354/IV(a)/4> <PICT:0925354/IV(a)/5> <PICT:0925354/IV(a)/6> <PICT:0925354/IV(a)/7> <PICT:0925354/IV(a)/8> through the lead 9.  A corona electric discharge occurs between the electrodes when the primary winding of the transformer 6 is supplied with A.C. current through the leads 10 and 11.  The electrode 1 may be a roller specially provided for treating the film or may be a roller constituting part of a machine or device such as a spooling frame, a film making machine, an unwinding drum or a rotary printer, the roller in the latter cases having originally served another purpose.  The surface of the electrode 4 facing the electrode 1 may be smooth or provided with protuberances to cause a concentration of brush discharges on the surface of the film passing under the electrode.  The surface of the metal electrode 1 which is in contact with the film is bare, and in the case where the width of the film is equal to the length of the electrode as shown in Fig. 2, the whole of the peripheral surface of the electrode is bare.  When the width of the film is less than the length of the electrode 1, as shown in Figs. 3 and 4, the parts 11 of the electrode not contacted by the film are either made of non-conducting material or are insulated from the main part of the electrode or have a covering of such material. As shown in Fig. 5 the electrode 1 may comprise a central portion of bare conducting material the length of which is equal to the smallest width of film to be processed and a series of discs 11 of either metal or insulating material (or insulation covered material) according to the width of the film to be treated.  The primary winding of the transformer may have several tappings for the purpose of adjusting the transformer output and a lamp may be connected in series with the primary winding to provide visual indication if the film treating apparatus is functioning normally.  Two or more fixed electrodes 4 each connected to the secondary winding of the transformer by separate leads may be provided.  As shown in Figs. 9 and 10, two electrodes 4 may be supported on the fixed shaft 20 of the roller electrode 1 by a bracket 19.  A preferred type of fixed electrode 4 comprises a cylindrical holder 21 of insulating material (Fig. 12) having a groove 22 of T-shaped cross-section.  A metal rod 21 of T-shaped cross-section is a tight fit in the groove 22 and is provided at one end with a terminal 24 for connection with the secondary windings of the transformer.