Coatings For Metal Surfaces

Abstract

An iron-containing metal surface, such as a brushed stainless steel, comprises a heat-set layer of a metal phosphate reaction product formed between a surface metal and phosphate precursor wherein the reaction product layer h an average thickness less than 2 micrometers. A metal surface, that resists retention of environmental stains or marks as well as resisting tarnish at elevated temperatures, is formed by forming a reaction product with the metal surface by heat setting a surface liquid layer containing a phosphate precursor such as a phosphate ester-containing solution or phosphoric acid solution, and optionally containing a phospho alumina precursor, onto the metal surface. An article coated in accordance with this invention is similar in appearance to a similar article without such a coating for maintaining original aesthetic properties.

1 : An iron-containing metal surface comprising a heat-set layer of a metal phosphate reaction product formed between a surface metal and phosphate precursor wherein the reaction product layer has an average thickness less than  2  micrometers. 
     
     
         2 : An iron-containing metal surface of  claim 1  in which the phosphate precursor is a phosphate ester-containing or a phosphoric acid-containing solution. 
     
     
         3 : An iron-containing metal surface of  claim 1  further comprising a phospho alumina. 
     
     
         4 : A metal surface of  claim 3  in which heat setting a primary phosphate precursor layer and heat setting one or more secondary phospho alumina layers onto the metal surface are performed in sequential steps. 
     
     
         5 : A metal surface of  claim 1  having a heterogeneous surface microstructure in which metal phosphate is formed within pits or valleys in the surface. 
     
     
         6 : A metal surface of  claim 5  in which the metal is a brushed stainless steel. 
     
     
         7 : A metal surface of  claim 6  in which the stainless steel is 304 or 430 grade brushed stainless steel. 
     
     
         8 : A metal surface of  claim 1  in which the heat-set layer is transparent. 
     
     
         9 : A metal surface of  claim 1  in which the metal is a mild carbon steel. 
     
     
         10 : A metal surface of  claim 1  in which the heat set layer is formed by applying a layer of a phosphate ester-containing alcohol solution, drying, and heating to at least 250° C. 
     
     
         11 : A metal surface of  claim 1  which resists tarnishing at temperature above 300° C. and that resists stains or fingerprints. 
     
     
         12 : A method to protect an iron-containing metal surface comprising applying a layer of a phosphate precursor solution to the surface and heat setting the layer onto the surface by heating above 200° C. 
     
     
         13 : A method of  claim 12  in which the phosphate precursor solution is a phosphate ester-containing solution. 
     
     
         14 : A method of  claim 12  in which at least one secondary layer of a phospho alumina is applied to the metal surface. 
     
     
         15 : A method of  claim 12  in which the phosphate ester-containing solution is a solution containing a C 1 -C 4  alcohol. 
     
     
         16 : A method of  claim 15  in which the alcohol is ethanol. 
     
     
         17 : A method of  claim 13  in which the phosphate ester-containing solution also contains a phospho alumina precursor solution. 
     
     
         18 : An article containing a metal surface of  claim 1 . 
     
     
         19 - 21 . (canceled) 
     
     
         22 : A metal surface of  claim 1  in which at least 25 vol. % of the top 2 microns of the surface is metal and at least 25 vol. % of the top 2 microns of the surface is phosphate reaction product.