Adhesion promoter in conversion solutions

摘要

An aqueous solution for producing a conversion layer on metal surfaces, which has a pH in the range 1.5 to 6 and which contains the complex fluorides of Ti, Zr, Hf, Si and/or B, in an amount such that the concentration of Ti, Zr, Hf, Si and/or B is 20 to 500 mg/l, and 0.1 to 2 g/l of adhesion-promoting lacquer additives and wherein the composition of the aqueous solution is selected so that no crystalline zinc-containing phosphate layer is produced on the metallic surface. The lacquer additive preferably contains an element M selected from the group B, Al, Si, Ti and Zr, wherein at least one hydroxyl group and one or more organic groups R are preferably bonded to the element M, wherein the organic group or organic groups R are selected independently of each other from hydrocarbon groups with 3 to 16 carbon atoms or from —(CH₂)_x—Y groups, wherein x is an integer from 1 to 10 and Y represents a hydroxyl group, a mercapto group, a primary or secondary amine group, a carboxyl group, an acrylic or methacrylic acid group or an oxirane group or each represents a fragment of a molecule which contains one or more of the groups mentioned or acid groups.