GB1076678A - Improvements in the coating of metals - Google Patents

Abstract

A dry conversion coating is formed on e.g. zinc, iron or aluminium surfaces by spraying a coating phosphate, oxalate or acetate or phosphoric acid with an auxiliary acid on to the surface, which is preheated to 200 to 400 DEG F., and then without rinsing, the coating is treated with an insolubilising material, which reacts with the conversion coating, by spraying, flooding, immersion or roller coating. The surface may again be preheated to 65 to 600 DEG F. The treated surface may then be given a chromate rinse. The insolubilising material may be a nitrate, carbonate, halide or acetate salt of Fe, Zn or Cr, amines, oxides or hydroxides of e.g. Zn, Fe, Cr, or Si, a polymeric material, organic reductants e.g. dimethylolurea, hexamethylolmelamine, hydroquinone, pyrocatechol, pyrogallol, p-methylamino-phenyl sulphate, and N-p-hydroxyphenyl glycine, trivalent chromium compounds e.g. nitrate, acetate, carbonate or phosphate, organic complexes of trivalent chromium, e.g. methacrylate chromic chloride, or ammoniated oxides or hydroxides of e.g. iron, zinc or chromium, with colloidal silica. The phosphating solution may contain fluosilicates, fluoborates, fluotitanates, fluostannates, fluozirconates, and fluovanadates or accelerators, e.g. nitrates, nitrites, sulphites, halides e.g. bromides, chlorates, bromates, perchlorates, iodates and periodates, peroxides, permangenates, m-nitrobenzene sulphonate, nitro-guanidine, nitromethane or ethane, 1-nitro propane, nitrobenzene, O-nitro p-nitrophenol, p-nitroanline, p-nitrochloro benzene, and picryc acid. The chromating rinse may be an aqueous solution or suspension of zinc, aluminium, calcium, ferric and ferrous, cobalt, nickel or chromium chromate or dichromate, chromic acid with alumina, colloidal silica, water, glass, solutions of zinc oxide and ammonium hydroxide, chromium acetate, phosphate, nitrate, carbonate, and methacrylate chromium chloride. The auxiliary acid used with phosphoric acid may be nitric, acrylic, methacrylic, polyacrylic, adipic, acetic, hydroxyacetic, gluconic, fumaric, maleic, malic, malonic, lactic, itaconic, tartaric, e.d.t.a., citric, hydroxymethyl phosphonic, oxalic, and chromic.ALSO:A dry conversion coating is formed on e.g. Zn, Al or Fe surfaces by spraying a coating phosphate, oxalate or acetate or phosphoric acid with an auxiliary acid onto the surface which is preheated to 200 to 400 DEG C, and then without rinsing, the coating is treated with an insolubilising material by spraying, flooding, immersion or roller coating. The insolubilizing material may be a polymeric material e.g. melamine acrylic, urea-formaldehyde, urea aldedehyde, amine, epoxy, polyvinylbutryl, and dimethylhydantoin-formaldehyde resins.