GB1221677A - Process for anodically cleaning and coating metal substrates - Google Patents

Abstract

1,221,677. Coated metal substrates. C. G. MATTHEWS and R. G. MATTHEWS. 16 April, 1968, No. 17986/68. Heading B2K. [Also in Division C7] A metal substrate is treated such that an adherent polymer coating can be applied thereto, e.g. to produce a coated wire for fabricating into hooks and eyes for garments. A metal substrate, such as a wire, strip or sheet, is anodically cleaned and has a film containing Cr and Cu deposited thereon as it passes through an aqueous bath of chromic acid containing not more than 2% by weight of sulphuric acid and having therein copper in solid form. During part of the substrate's passage through the bath it is connected as an anode and during a later part it has no potential applied thereto, the Cr/Cu film apparently being formed during this later part. Fig. 2 illustrates treatment wherein wire is drawn at 16, anodically cleaned and coated with Cr/Cu in tank 18, rinsed at 23 and coated with molten nylon at 32; Fig. 3 illustrates alternative treatment following rinse bath 23 of Fig. 2. The wire is non-electrolytically coated with metal as it passes through a compartmented tank 49 containing solutions of metal salts. Vertical notch apertures 48 may be provided with "wipe-backs" of plastic foam or sponge rubber to minimise mixing of successive solutions. Subsequently the wire is electroplated in a similar tank 56 and drawn through a die 64. The drawing die box 63 contains a lubricant or a polymer or monomer solution which coats the wire, e.g. the solution may contain caprolactam which becomes polymerized to some extent during the drawing. A heavy plastic film may be extruded over the coated wire. In the case of strip or sheet, rolls are used in place of drawing dies 16, 64. Specified materials. The substrate may be ferrous or non- ferrous, e.g. bare or galvanised steel wire or brass wire. Metals which may be deposited from solutions of their salts non-electrolytically are Sn, Pb, Ni, Mn, Al or Cu; or Al/Zn which may be followed by either Sn/Ni or Sn/Ni/Cu. Metals which may be deposited electrolytically are Al/Zn from a sulphate bath, Cu from a fluoborate bath using a Cu anode, Zn from a fluoborate bath using a Zn anode, and Cu/Zn from a fluoborate bath. Cu and Zn may be deposited one after the other, (Example V). Plastic coatings may be of nylon, epoxy resin, acrylics, polyethylene or polypropylene. Metallic particles, e.g. Al powder may be distributed throughout the external plastic coating.