GB490851A - Improvements in coating metal containers - Google Patents

Abstract

490,851. Coating metals by electrophoretic deposition. CROSSE & BLACKWELL, Ltd., CLAYTON, W., JOHNSON, R. I., and SUMNER, C. G. feb. 18, 1937, Nos. 4909/37 and 2212/38. [Class 41] Metals, particularly the inner surfaces of metal containers for beverages or parts thereof, are coated by electrophoretic deposition of wax or a waxy material from an aqueous dispersion, the deposit being subjected to such a temperature that the particles coalesce to form a continuous coating. The material deposited may consist of beeswax, ceresin, paraffin wax or compositions containing them. In order to increase the " throwing power " the dispersion medium should include a salt of alkaline reaction having an anion such that addition of acid would produce an insoluble oxide or hydroxide, e.g. sodium silicate or sodium aluminate or mixtures thereof. The composition of the bath should be so chosen as to avoid precipitation by acidic constituents of the waxy material, The alkalinity should be only slightly greater than that necessary to produce stability. The conditions be so adjusted that on passage of current an oxide or hydroxide is deposited at the anode with the wax particles. The initial resistance of the circuit should be low so as to produce a high initial current density which falls rapidly as the wax film builds up, this conducing to uniformity of thickness; the effect may be assisted by progressively introducing resistance into the circuit. After coating, the surface is freed from excess of the dispersion by draining or rinsing ; the dispersion may be of low viscosity to facilitate draining. The deposit is then dried by warm air and heated above the melting point to render it coherent, adherent and impermeable. Electrodeposition may be effected at room temperature or above the melting point of the wax. By addition of known reagents to the dispersion deposition may be caused to take place on the cathode instead of the anode.