Patent GB-1013674-A (GB)
Title: Improvements in and relating to a continuous process and apparatus for forming a magnetic layer on a surface of a non-conductive web
IPC: C25D19/00
Filed: 1963-01-22
Abstract: A continuous process for forming a magnetic layer on a surface of a nonconducting web by moving the web through a series of treatment baths comprises electrolessly forming a conducting layer so formed as an electrode during electrodeposition of a layer of magnetic material and maintaining the conducting layer out of frictional contact with the surface of any mechanical element.  As shown, a polyethylene terephthalate tape passes from a supply reel through an aligning device and a pre-washing tank similar to tank 44 and then in succession through separate tanks 41, Fig. 1d (not shown), and 43 containing acidified sodium dichromate, hot sodium hydroxide, acidified dilute stannous chloride, and acidified palladium chloride solutions respectively, an electroless plating tank 45 where a thin nickel layer is deposited on the tape, a depassivating hydrochloric acid tank 47, a series of electroplating tanks 49 where a magnetic phosphorus-containing cobalt-nickel alloy is deposited, and finally over an alignment guide to a take-up spool.  Each treatment tank is provided with gas vents 80 and is followed by a washing and spray rinsing bath as at 44, 46, 48, 50, Since the electroless and electroplated layers are very thin, to avoid damage of not only both these layers but also of the sensitizing surface films formed for securing adherence of the electroless coating, there are provided stationary web guides 10, 11, 12 of the kind in which a layer of air or liquid supports the web so that mechanical contact with the guides is avoided.  The guides are hollow and are as shown in Fig. 6, the area 107 over which the web is supported being defined by perforations 106 in communcation with a fluid supply pipe 102. The guides 10 are provided with compressed air or gas while the guides 11 immersed in liquid are fed with continuously circulated appropriate bath solution or water and the guides 12 following the pre-washing tank and washing baths 46, 48, 50 are provided with warm air to effect drying.  The guides 12 following the bath 46 are located in an oven 90 supplied with hot air for consolidating the electroless nickel layer while those following the bath 50 are in a similar oven for drying the strip.  The electroless coated strip is examined for defects photo-electrically at 200 and the dried finished strip is tested by a magnetic writing and reading check before it is reeled up.  The tape is moved solely by rollers 440 Fig. 1a (not shown), and the tape take-up spool driven by a motor 450, Fig. 1a, and cathode rollers 300, 302 in the electroplating tank 49 driven by a motor 305, the motors being of variable speed and synchronized to avoid tape damage and also controlling pumps supplying the treating and washing tanks.  For threading the tape through the apparatus a leader tape is employed and the tanks which are mounted on platforms supported on scissor legs 62 are lowered clear of the web guides. When this occurs valves in the supply pipe to the guides 11 replace the liquid supply by air until the tanks are again raised to submerge the guides.  Each of the electroplating tanks supports suspended anodes 308 and an anode bar 311 is hung between the runs of the tape around the guide 11 which is of polyvinyl chloride.  The cathode rollers 300, 302 are gold plated and arranged to engage opposite faces of the strip so that plating on both sides of the strip is effected.  The tanks are provided with a constant level device and the plating solution contains nickel and cobalt sulphates, ammonium chloride and small quantities of sodium hypophosphite and a non-ionic wetting agent. The current passed in the successive electroplating stages is raised. The electroless nickel coating bath comprises: .18.g./l..NiSO46H2O .24.g./l..NaH2PO2H2O .16.g./l..sodium succinate .31.ml./l..85% lactic acid .4.8.g./l..sodium acetate .3.6.ml./l..glacial acetic acid .5.p.p.m..Pb ions (added as lead acetate) .10.g./l..NaOH The guides 11 immersed in the electroless plating tank 45 are of glass, passivated stainless steel, or polytetrafluoroethylene.