GB1081767A - Production of synthetic resin or like surface coatings by electrode position - Google Patents

Abstract

A coherent non-metallic coating is formed on a conductive article by electro-deposition from an aqueous bath by effecting deposition under such conditions that a deposit is produced of a thickness dependent mainly on the deposition time and thereafter continuing deposition under conditions which produce a further deposit with resistance which increases with the time of treatment. Typically the initial deposition is effected at a low voltage and the further deposition is performed at a higher voltage which serves also to reduce the water content of the whole coating. The two stages may be carried out in the same or different baths. In one example an aqueous dispersion of styrenebutadiene copolymer stabilized with an anionic surfactant and containing TiO2 pigment is used to anodically coat a metal article using initially an applied voltage of 0.5 to 10 volts to give a current density of 0.1 to 0.6 amp/dm2 followed by a second coating with 40 volts applied to give a final coating thickness of 1.5 to 2 mils. In a further example a similar bath including red iron oxide is used with an applied voltage of 0.5 to 20 volts to provide the initial coating and the article is subsequently subjected to anodic deposition in an ammoniacal solution of an alkyd resin pigmented with TiO2 with an applied voltage of 30 to 100v. A yet further example uses low voltage anodic deposition from a surfactant stabilized pigmented acrylic acid copolymer followed by high voltage anodic deposition from a pigmented ammoniacal solution of an acrylic acid copolymer. Other resin compositions suitable are mixtures or products of chemical reactions of alkyd resins or maleinised oils or fatty acids with phenolic resins with or without copolymerization with a vinyl monomer, e.g. styrene, or modified with epoxy resins; mixtures of alkyd and amino resins; alkyd resins modified with allyl ethers of polyol with or without additional modification with phenolic or amino resins; alkyd resins based on polyethylene oxide; or vinyl or acrylate polymers or copolymers. The deposited coatings may be baked or stoved to drive off the aqueous component and/or to effect curing. To avoid staining when coating iron articles, the articles may be electro-plated with Zn or Cd as in Specification 1,078,199.