Functionalized phenol-formaldehyde resin and method for treating metallic surfaces

Abstract

The invention relates to a functionalized phenol-aldehyde resin which comprises a phenol-aldehyde condensation product, having a phenol component with no carboxyl group, and an aromatic hydroxycarboxylic acid and imidazole as constituents which is useful for corrosion-inhibiting treatment of bare or conversion-coated metal surfaces is provided. Methods of making the functionalized phenol-aldehyde resin, processes for coating metal surfaces using compositions according to the invention and products coated thereby are also included in the invention.

1 . a functionalized phenol-aldehyde resin comprising: 
 a) a phenolic component having no carboxyl functional group;    b) an aromatic hydroxycarboxylic acid; and    c) an imidazole.    
   
   
       2 . the functionalized phenol-aldehyde resin as claimed in  claim 1 , wherein the molar ratio of phenolic component to aromatic hydroxycarboxylic acid and the molar ratio of phenolic component to imidazole are each in the range from 1:1 to 100:1.  
   
   
       3 . the functionalized phenol-aldehyde resin as claimed in  claim 1 , wherein the molar ratio of aromatic hydroxycarboxylic acid to imidazole is in the range from 100:1 to 1:100.  
   
   
       4 . the functionalized phenol-aldehyde resin as claimed in  claim 1 , wherein at least 50% of the phenolic component is phenol.  
   
   
       5 . the functionalized phenol-aldehyde resin as claimed in  claim 1 , wherein the aromatic hydroxycarboxylic acid is selected from hydroxybenzoic acids.  
   
   
       6 . the functionalized phenol-aldehyde resin as claimed in  claim 1 , wherein at least 50% of the resin consists of the phenolic component, aromatic hydroxycarboxylic acid, imidazole and bridging alkylene groups.  
   
   
       7 . the functionalized phenol-aldehyde resin as claimed in  claim 1  having an average molecular weight of at least 500.  
   
   
       8 . a process for the production of the functionalized phenol-aldehyde resin claimed in  claim 1 , comprising adding an aqueous aldehyde solution to an aqueous solution containing the phenolic component, aromatic hydroxycarboxylic acid and imidazole, thereby forming an aqueous reaction solution followed by mixing the aqueous reaction solution for 10 minutes to 10 hours at a temperature between 40° C. and the boiling point of the aqueous reaction solution.  
   
   
       9 . a process for the production of the functionalized phenol-aldehyde resin claimed in  claim 1 , comprising: 
 a) preparing an aqueous solution of a phenol-aldehyde resin containing incorporated aromatic hydroxycarboxylic acids; and    b) adding imidazole and then aqueous aldehyde solution to the aqueous solution of a) and mixing for 10 minutes to 10 hours at a temperature between 40° C. and the boiling point of the mixture.    
   
   
       10 . the process as claimed in  claim 8 , further comprising selecting the concentration of the organic compounds in the aqueous reaction solution such that the functionalized phenol-aldehyde resin produced has a solids content of 10 to 50% by weight.  
   
   
       11 . a process for the corrosion-inhibiting treatment of bare or conversion-coated metal surfaces, comprising contacting bare or conversion-coated metal surfaces with an aqueous treatment solution containing one or more phenol-aldehyde resins, wherein at least one phenol-aldehyde resin comprises the functionalized phenol-aldehyde resin claimed in  claim 1 .  
   
   
       12 . the process as claimed in  claim 11 , wherein the one or more phenol-aldehyde resins comprises 5-2,000 mg/l phenol-aldehyde resin which contains incorporated imidazole.  
   
   
       13 . the process as claimed in  claim 12 , wherein the one or more phenol-aldehyde resins comprises 20-200 mg/l of said functionalized phenol-aldehyde resin.  
   
   
       14 . the process as claimed in  claim 11 , wherein the aqueous treatment solution additionally contains one or more compounds of elements of the fourth main or transition metal group of the periodic system.  
   
   
       15 . the process as claimed in  claim 14 , wherein said elements of the fourth main or transition metal group of the periodic system comprise Si, Ti and/or Zr.  
   
   
       16 . the process as claimed in  claim 15 , wherein the aqueous treatment solution additionally contains fluoride ions.  
   
   
       17 . a process for the production of a structural component containing painted metal parts, in which 
 a) sheets of metal with a coating based on organic polymers are cut and/or stamped and/or formed into metal parts, areas of metal surface of the sheet that are not covered by the coating based on organic polymers being formed thereby,    b) the metal parts obtained are assembled to form the structural component, and the assembled structural component is cleaned,    c) the cleaned, assembled structural component is contacted with a chromium-free aqueous treatment solution which produces a passivation layer that is not a zinc phosphate layer on said areas of metal surface formed in step a) that are not covered by the coating based on organic polymers, the aqueous treatment solution containing one or more phenol-aldehyde resin(s), at least one phenol-aldehyde resin comprising the phenol-formaldehyde resin claimed in  claim 1 ,    d) optionally, the structural component treated in step c) is rinsed one or more times with water, and    e) is coated with a paint layer.    
   
   
       18 . an aqueous treatment solution for treating bare or conversion-coated metal surfaces which contains one or more of the functionalized phenol-aldehyde resins claimed in  claim 1 .  
   
   
       19 . a metal sheet, a metal part or an article containing metal parts, wherein at least one surface of the metal sheet or the metal parts has been treated by the process claimed in  claim 11.