Patent ID: 8435360
Filing Date: 2013-05-07
Classification: C23C

Abstract:
1. A method for producing a coating layer protecting against corrosion wherein a zinc-containing surface provided with a conversion layer is brought into contact with an aqueous treatment solution consisting essentially of chromium(III) ions, at least one phosphate compound selected from the group consisting of esters of orthophosphoric acid, polyphosphoric acids and metaphosphoric acid with organic residues having up to 12 carbon atoms as well as mixtures of these compounds, one or more complexing agents selected from the group consisting of polycarboxylic acids, hydroxycarboxylic acids, hydroxypolycarboxylic acids, aminocarboxylic acids or hydroxyphosphonic acids and aminophosphonic acids, Zinc oxide, optionally one or more water-soluble or water-dispersible polymers selected from the group consisting of polyethylene glycols, polyvinyl pyrrolidones, polyvinyl alcohols, polyitaconic acids, polyacrylates and copolymers of the respective constituent monomers; and optionally one or more metals or metalloids; wherein the ratio of the molar concentration of the chromium(III) ions to the molar concentration of the at least one phosphate compound (calculated as orthophosphate) is between 1:1.5 and 1:3.