Patent GB-1471771-A (GB)
Title: Process for coating aluminium or aluminium alloy
IPC: C23C22/83
Filed: 1974-07-05
Abstract: 1471771 Electrolytic; chemical conversion treatment and electro-phoretic coating of aluminium KANSAI PAINT CO Ltd and FUJI SASHI INDUSTRIES Ltd 5 July 1974 [6 July 1973 3 Aug 1.973 15 Nov 1973(2) 16 Nov 1973  19 Nov 1973] 29834/74 Headings C7B and C7U Al or Al alloy, e.g. Al-Si, Al-Mg, Al-Mn or Al-Si-Mg, is coated by subjecting the Al (alloy) to bochmite or chemical conversion treatment, conducting electrolysis using the treated Al (alloy) as electrode in an aqueous solution of a salt of at least one of the oxyacids silicic, boric, phosphoric, molybdic, vanadic, permanganic, stannic and  tungstic acids, washing with water, then coating the Al (alloy) with an organic coating composition, e.g. by immersion, brush, spray, electro-phoretic or electrostatic coating with a composition comprising a binder resin and liquid medium containing pigment. The binder resin may be (semi) drying oil, (nitro) cellulose, (modified) alkyd or epoxy resin, polybutadiene or rosin; amino or unsaturated polyester resin, polyurethane or acrylic resin. The pigment may be TiO 2 , red Fe 2 O 3 , C black, phthalocyanine blue, talc, clay or CaCO 3 ; other additives may be plasticizer, drying agent, dispersant, wetting agent and defoaming agent. The liquid medium may be water with or without organic solvent such as benzyl alcohol, n-butanol, methyl-, isopropyl- or butyl-bellosolve (Registered Trade Mark), isopropanol, carbitol or ethanol. The substrate may be an Al alloy panel, degreased e.g. by immersion in HNO 3  or H 2 SO 4  and etched e.g. by immersion in NaO<SP>3</SP>H solution. Bochmite treatment may be effected by immersion or spraying with hot water or steam e.g. at 65 to 180 C with or without ammonia or amines e.g. monoethanolamine, di- or tri-ethanolamine or dimethylethanolamine. Conversion treatment may be effected by immersion in an aqueous solution of phosphate and/or chromate, e.g.: (1) Mn (H 2 PO 4 ) 2  and SiF 6 ;(2) ZnH 2 PO 4 , H 3  PO 4  and CrO 3 ;(3) Na 2 CO 3  and Na 2 CrO 4  with or without Na 2 SiO 3 , Na 3 PO 4  or basic Cr carbonate; (4) Na 2 CO 3  and K 2 Cr 2 O 7 ; (5) dilute HNO 3 , HMnO 4 , HF and heavy metal salt; (6) Na 2 SiF 6 , NH 4 NO 3  and Ni or Co salt. The oxyacid salt may be a Li, Na, K, NH 4 , Ba, Ca, Sr, Mg, Al or Pb (ortho-, meta-, di- or poly-) silicate (including triethanol or tetramethanol ammonium silicate), (meta-, tetra-, penta-, per- or bi-) borate (including borate-H 2 O 2  addition product or boroformate), (ortho-, pyro- or polymeta-) phosphate, (ortho-, meta- or pyro-) vanadate, (ortho-, meta-, para-,  penta- or penta- or hepta-) phosphorus wolframate, boratungstate, permanganate, (ortho- or meta-) stannate or molybdate (including triethylamine molybdate). Salts of CrO 3 , e.g. Li, Na, K, NH 4 , Ca or Sr chromate, may be present with the oxyacid salt. Electrolysis may be conducted using A.C. or D.C., with Al (alloy) as anode and mild  steel plate as cathode; subsequent electro-phoretic coating is similarly effected. Electrolysis may be effected in two different baths, e.g. in first a solution of Na 2 Si 2 O 5  then a solution of Na 2 BO 2 .