Colored conversion layers on metallic substrates

Abstract

A chromium-free treatment solution for producing colored or fluorescing corrosion prevention layers on metal surfaces which contains phosphoric acid and/or at least one fluoro acid of one or more elements from the group consisting of B, Si, Ti, Zr and Hf or anions thereof and at least one organic polymer, the organic polymer being capable of binding to the metal surface through oxygen and/or nitrogen atoms, and having covalently bonded groups which appear colored to the human eye or which fluoresce discernibly to the human eye on exposure to UV light.

1 . A treatment solution for producing colored corrosion prevention layers on metal surfaces which comprises 
 a) phosphoric acid and/or at least one fluoro acid of one or more elements selected from the group consisting of B, Si, Ti, Zr and Hf or anions thereof; and    b) at least one organic polymer capable of binding to a metal surface through oxygen and/or nitrogen atoms and selected from the group consisting of amino resins, phenol/aldehyde resins, polymers containing carboxyl groups, polymeric alcohols, esterification products of polymeric alcohols with polymers containing carboxylic acid groups, polymers containing amino groups, homo- or copolymers of vinyl pyrrolidone, and copolymers of alkylene phosphonic or alkylene phosphinic acids and one or more unsaturated carboxylic acids,    wherein the treatment solution is chromium-free and the organic polymer carries covalently bonded groups which appear colored to the human eye.    
   
   
       2 . The treatment solution as claimed in  claim 1 , comprising: 
 a) 0.02 to 20 g/l phosphoric acid and/or at least one fluoro acid of one or more elements from the group consisting of B, Si, Ti, Zr and Hf or anions thereof and    b) 0.1 to 200 g/l of the organic polymer.    
   
   
       3 . The treatment solution as claimed in  claim 1 , wherein: 
 a) the phosphoric acid is present in a concentration of at least 1 g/l; and    b) the organic polymer is present in a concentration of at least 5 g/l and not more than 150 g/l.    
   
   
       4 . The treatment solution as claimed in  claim 1 , wherein the organic polymer has an upper molecular weight limit of 20,000,000 Dalton and an average molecular weight of greater than 100,000 Dalton.  
   
   
       5 . The treatment solution as claimed in  claim 1 , wherein the percentage by weight of covalently bonded groups which appear colored to the human eye amounts to 0.1 to 20% by weight, based on the total weight of the organic polymer.  
   
   
       6 . The treatment solution as claimed in  claim 1 , wherein the organic polymer is selected from the group consisting of polymers of acrylate and/or methacrylate monomers, maleic anhydride which may be completely or partly hydrolyzed, and acrylate or methacrylate monomers terminated by phosphate groups.  
   
   
       7 . The treatment solution as claimed in  claim 1 , wherein the covalently bonded groups which appear colored to the human eye are selected from Toluidine Blue and Neutral Red.  
   
   
       8 . The treatment solution as claimed in  claim 1 , further comprising: 
 d) at least one inorganic compound in particle form with a mean particle diameter in the range from 0.005 to 0.2 μm.    
   
   
       9 . The treatment solution as claimed in  claim 1 , wherein the inorganic compound in particle form is present in the aqueous bath solution in a concentration of 0.1 to 80 g/l.  
   
   
       10 . The treatment solution as claimed in  claim 1 , wherein the organic polymer is a copolymer of a) acrylic acid and/or methacrylic acid with b) acrylate and/or methacrylate monomers terminated by phosphate groups which contains covalently bonded molecules of Toluidine Blue or Neutral Red.  
   
   
       11 . The treatment solution as claimed in  claim 1 , comprising at least 0.025 g/l and up to 10 g/l Ti and/or Zr and/or Si ions and at least such a quantity of fluoride that the atomic ratio of Ti to F and/or Zr to F and/or Si to F is in the range from 1:1 to 1:6.  
   
   
       12 . The treatment solution as claimed in  claim 1 , comprising both fluoro acids of Ti and of Zr, wherein the molar ratio of Ti to Zr is in the range from 10:1 to 1:10.  
   
   
       13 . A process for producing colored or fluorescent corrosion prevention layers on metal surfaces, comprising contacting the metal surfaces for 0.5 to 10 minutes with the treatment solution claimed in  claim 1  which has a temperature of 20 to 80° C.  
   
   
       14 . The process as claimed in  claim 9 , wherein the metal surfaces are selected from surfaces of aluminium and aluminium alloys, magnesium and magnesium alloys, titanium and titanium alloys, zinc and zinc alloys, galvanized and alloy-galvanized steel.  
   
   
       15 . A metal part comprising at least one surface comprising a colored corrosion prevention layer produced according to the process claimed in  claim 9 .  
   
   
       16 . A treatment solution for producing colored corrosion prevention layers on metal surfaces which comprises 
 a) 0.02 to 20 g/l phosphoric acid and/or at least one fluoro acid of one or more elements from the group consisting of B, Si, Ti, Zr and Hf or anions thereof and    b) 0.1 to 200 g/l of at least one organic polymer capable of binding to a metal surface through oxygen and/or nitrogen atoms and selected from the group consisting of maleic anhydride/methyl vinyl ether copolymer and acrylic acid and methacrylate monomer terminated by phosphate groups;    wherein the treatment solution is chromium-free and the organic polymer carries 0.1 to 20% by weight, based on the total weight of the organic polymer, of covalently bonded groups which appear colored to the human eye.