Adhesion promoter in conversion solutions

Abstract

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 —(CH 2 ) 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.

1 . 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.  
     
     
         2 . An aqueous solution as claimed in  claim 1 , wherein the adhesion-promoting lacquer additive is selected from water-soluble compounds which contain at least one element M selected from the group B, Al, Si, Ti and Zr.  
     
     
         3 . An aqueous solution as claimed in  claim 2 , wherein at least one hydroxyl group and one or more organic groups R are 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 and from —(CH 2 ) 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.  
     
     
         4 . An aqueous solution as claimed in  claims 1  to  3 , wherein it also contains 50 to 2000 mg/l of organic polymers.  
     
     
         5 . An aqueous solution as claimed in  claim 4 , wherein the organic polymers are selected from epoxide resins, amino resins, tannins, phenol/formaldehyde resins, polycarboxylic acids, polymeric alcohols and esterification products thereof with polycarboxylic acids, poly-4-vinylphenol compounds, amino group-containing homopolymer or copolymer compounds and polymers or copolymers of vinylpyrrolidone.  
     
     
         6 . An aqueous concentrate in one or two containers which, after dilution with water by a factor of between 50 and 500 and if required adjustment of the pH, produces an aqueous solution as claimed in one or more of  claims 1  to  5 .  
     
     
         7 . A process for the corrosion protection treatment of metal surfaces, wherein the metal surfaces are contacted for a period of between 0.5 and 5 minutes with an aqueous solution as claimed in one or more of  claims 1  to  5 .  
     
     
         8 . A process as claimed in  claim 7 , wherein lacquering takes place after the corrosion protection treatment.  
     
     
         9 . A process as claimed in  claim 8 , wherein lacquering is performed with an electrodeposition lacquer or with a powder coating.