Solutions and processes for producing phosphate coatings on the surfaces of zinc or zinc-coated steel and iron

摘要

An aqueous nickel-accelerated phosphate coating solution for the surfaces of zinc or zinccoated steel and iron contains: (a) a heavy metal ion, particularly Zn and/or Mn ion, e.g. in concentration of less than 0.5%; (b) phosphate ion in amount at least sufficient to form dihydrogen phosphate with the heavy metal ion, e.g. in concentration of 0.5 to 2.5%; (c) an accelerating amount of Ni ion, e.g. in concentration of 0.01 to 0.4%; (d) an oxidizing accelerator such as nitrate (concentration of 0.2 to 1.0%) and/or nitrite (concentration of 0.0002 to 0.008%); (e) at least 0.009% of soluble titanium such as in the form of a compound or complex including an ion containing titanium fluoride, e.g. H2TiF6, or ammonium, sodium or potassium fluotitanate, or potassium titanium oxalate; with or without (f) copper ion, e.g. in concentration of 0.0003 to 0.005%. The Ni and Cu ions may be introduced in the form of carbonates, nitrates, chlorides or sulphates. For example, the solution may contain ZnO, H3PO4, NiCO3, HNO3, HF and H2TiF6 or (NH4)2TiF6 with or without Cu compounds. Similar comparative solutions are disclosed in which the Ti compound is replaced by hydrofluoric or hydrofluoboric acid. Surfaces of galvanized steel or iron may be contacted with the solution at 120 to 160 DEG F. for 3/4 to 2 minutes to produce thereon phosphate coatings providing a good bond for layers of paint, lacquer, varnish or enamel. Specifications 493,315, 936,937, U.S.A. Specifications 1,221,046, 1,869,121, 1,888,189, 2,197,622, 2,591,479 and 2,835,617 are referred to.