Conversion coatings for metal surfaces

Abstract

An aqueous treatment solution for producing conversion coatings on metal surfaces, in particular on zinc or zinc alloy surfaces, contains: Cr(III) ions in an amount of 0.1 g/l to 8.0 g/l; zirconium and/or titanium ions in an amount of 0.1 g/l to 15 g/l; organosilane-modified silicon oxide nanoparticles in an amount of 0.1 g/l to 50 g/l; and fluoride ions in an amount of 0.1 g/l to 15 g/l.

1 . An aqueous treatment solution for producing conversion coatings on metal surfaces, in particular on zinc or zinc alloy surfaces, the treatment solution containing:
 Cr(III) ions in an amount of 0.1 g/l to 8.0 g/l;   zirconium and/or titanium ions in an amount of 0.1 g/l to 15 g/l;   organosilane-modified silicon oxide nanoparticles in an amount of 0.1 g/l to 50 g/l; and   fluoride ions in an amount of 0.1 g/l to 15 g/l.   
     
     
         2 . The treatment solution according to  claim 1 , wherein the treatment solution has a chromium(VI) ion content of less than 1 mg/l and/or a cobalt ion content of less than 10 mg/l and/or a Ni ion content of less than 10 mg/l. 
     
     
         3 . The treatment solution according to  claim 1 , wherein the organosilane-modified silicon oxide nanoparticles have a core of agglomerated silicon oxide, on a surface of which organic silane compounds are arranged. 
     
     
         4 . The treatment solution according to  claim 1 , further comprising oxygen atoms on a surface of the silicon oxide nanoparticles covalently bonded to silicon atoms of an epoxy, amido, ureido, amino, ester, mercapto, and/or isocyanate silane. 
     
     
         5 . The treatment solution according to  claim 1 , wherein the organosilane-modified silicon oxide nanoparticles have an average particle size of 5 to 50 nm. 
     
     
         6 . The treatment solution according to  claim 1 , wherein a molar ratio between Cr(III) ions and zirconium and/or titanium ions in the treatment solution is from 0.1 to 2.0. 
     
     
         7 . The treatment solution according to  claim 1 , wherein a pH of the treatment solution is between about 1.5 and 5. 
     
     
         8 . The treatment solution according to  claim 1 , wherein a volatile organic compound (VOC) content of the treatment solution is less than 10% by weight. 
     
     
         9 . A concentrate for the preparation of the treatment solution according to  claim 1 , the concentrate having an active substance concentration which allows a preparation of the treatment solution by dilution with at least 50% by weight of water, based on a total weight of the treatment solution. 
     
     
         10 . A kit comprising at least two concentrates according to  claim 9 , having a different composition. 
     
     
         11 . A process for producing a conversion coating on workpieces having metallic surfaces, in particular zinc or zinc alloy layers, the process comprising:
 bringing a workpiece to be treated into contact with the treatment solution according to  claim 1 .   
     
     
         12 . A conversion coating produced by the process according to  claim 11 . 
     
     
         13 . The conversion coating according to  claim 12 , wherein the conversion coating contains compounds of elements Cr, Si, O, F, C, H and Zr, and/or Ti. 
     
     
         14 . The conversion coating according to  claim 12 , wherein a weight percentage of zirconium and/or titanium in the conversion coating is higher than a weight percentage of chromium. 
     
     
         15 . The conversion coating according to  claim 12 , the conversion coating having an average layer thickness of 100 nm to 1000 nm. 
     
     
         16 . The concentrate according to  claim 9 , the concentrate having an active substance concentration which allows a preparation of the treatment solution by dilution with at least at least 70% by weight of water, based on the total weight of the treatment solution.