GB1400264A - Depositing paint by an electrocoating process - Google Patents

Abstract

1400264 Electro-deposition of paint SCM (CANADA) Ltd 13 Oct 1972 47488/72 Heading C7B A process for coating an electrode workpiece by electro-deposition of a paint film thereon from an aqueous bath containing a dispersion of cationic or anionic resin having from 1-30 wt per cent of carboxyl, alcoholic hydroxyl or amide groups or combinations thereof, a dispersal assistant for the cationic or anionic resin, and an aminoplast or phenoplast resin which is cross-linkable with the cationic or anionic resin upon curing, comprises dispersing in the bath a curing accelerator acid codepositable with the cationic or anionic resin and having a pKa in water at 20‹C not greater than 1 or a substance which will transform to such an acid in the bath, selecting a property in the cured paint film on the electrode workpiece dependent on the proportion of curing accelerator acid in the bath, establishing a range of performance specifications for said property in the cured film, where said range may be defined solely by a minimum value or by both a minimum and a maximum value, monitoring said selected property in the cured paint film to determine variation from said performance specifications, establishing and maintaining the concentration of curing accelerator acid or substance which will transform thereto in the bath in a proportion sufficient for sustaining said monitored property within said range of performance specifications, withdrawing the electrode workpiece from the bath and curing the coating. Curing of the deposited coating is by baking which may be assisted by ionizing radiation. The monitored property may be the dielectric breakdown voltage, film hardness, abrasion resistance or solvent resistance. The curing accelerator is added either manually or automatically. The workpiece, which may be precleaned, may be Al or steel strip, foil, strap, ribbon or wire, galvanized Fe or steel or phosphated or chromated steel. Electro-deposition is with the workpiece either immersed in a tub of aqueous paint or in a continuous spray stream which carries the electric current. The electric current used for the deposition has a net resultant D.C. effect and may be rectified A.C. with a 5 to 15% ripple factor, half wave rectified A.C., pulsed current, or current which is periodically reversed for short intervals. The paint may contain pigment, filler,metal flake or powder, and dyes. Many constituents are specified for the aqueous bath. The curing accelerator may be a sulphonate, sulphate, methylarsonic acid, picric acid, or trichloro- or trifluoro-acetic acid.