IMPROVEMENTS IN PROCESSES FOR APPLYING PAINT BY ELECTROPHORETIC DEPOSITION ON TO FERROUS SURFACES

摘要

1293883 Treating ferrous surfaces; electrodepositing paint AMCHEM PRODUCTS Inc 6 Jan 1971 [6 Jan 1970] 549/71 Headings C7B and C7U A ferrous metal surface is treated with a solution containing between 0À5 and 10 p.p. m. of copper in any soluble form, and is subsequently electro-coated with a light-coloured paint; the pre-treatment with the Cu eliminates irregularities in colour of the paint. The ferrous metal may be treated only with an aqueous solution of a Cu salt, such as the nitrate, acetate, or chloride, but is preferably phosphatized in which case the copper solution treatment is before, during, or after phosphating. Preferably the surface is contacted with a Cu-containing phosphate solution which is either (a) a "coating phosphate" solution of pH 1À8 to 3À5, free acidity 0À3 to 10, and total acidity 5 to 100, which contains an oxidant for ferrous ion or (b) a "non-coating" phosphate solution based on NaH 2 PO 4 , e.g. 2-20 g/l, and containing an accelerator, e.g. 0À05-0À5 g/l Na molybdate, either (a) or (b) being applied by spraying for 1-2 mins. at 60-70‹C., or immersion for 2-5 mins. at 65-76‹C., and desirably being followed by a rinse in a trivalent and/or hexavalent Cr solution. The electro-phoretic paint is a conventional paint containing methacrylic, acrylic, alkyd, melamine, or epoxy resin or a mixture thereof as anionic resins, and may have a solids content of 8-17 wt per cent, pH 7À5-9À5 and be deposited at 15-36‹C. for 30 sec - 5 min. at 50-450V and 1À08-108A/mSP2/SP. Deposition is followed by mixing, e.g. with water and curing, e.g. at 148-205‹C, for 20-30 mins. The process eliminates blotches and stains from light-coloured, particularly white, paint, and where the Cu content of the solution is high, tends to impart a faint bluish tinge to the paint. Specific phosphating solutions (which may also contain Cu) contain (1) NaH 2 PO 4 , Na molybdate, wetting agent, aralic acid and NaF and (2) Zinc, H 2 PO 4 SP-/SP, NaClO 4 , NaNO 2 , and Ni.