Methods and Compositions for Acid Treatment of a Metal Surface

Abstract

The invention relates to compositions and methods that are useful in etching a metal surface. In particular, the invention relates to novel acid compositions and methods of using such compositions in etching a metal surface, preferably an aluminum surface prior to anodizing to dissolve impurities, imperfections, scale, and oxide. The compositions are effective in maintaining their etching capacity and in removing smut produced by the etching of a surface as well as in general cleaning.

1 . A metal-etching composition consisting essentially of
 about 20 to about 80 grams per liter of said ammonium bifluoride;   about 1 to about 50 grams per liter of said diammonium phosphate; and   water.   
     
     
         2 . The metal-etching composition according to  claim 1 , which has a pH of about 2 to about 5. 
     
     
         3 . The metal-etching composition according to  claim 1 , wherein said diammonium phosphate is present at about 5 to about 30 grams per liter. 
     
     
         4 . The metal-etching composition according to  claim 3 , wherein said diammonium phosphate is present at about 10 to about 20 grams per liter. 
     
     
         5 . The metal-etching composition according to  claim 1 , wherein said ammonium bifluoride is present at about 60 to 70 grams per liter. 
     
     
         6 . (canceled) 
     
     
         7 . The etching composition according to  claim 11 , which has a pH of about 2 to about 5. 
     
     
         8 . The etching composition according to  claim 11 , wherein said diammonium phosphate is present at about 5 to about 30 grams per liter. 
     
     
         9 . The etching composition according to  claim 8 , wherein said diammonium phosphate is present at about 10 to about 20 grams per liter. 
     
     
         10 . The etching composition according to claim, wherein said ammonium bifluoride is present at about 60 to 70 grams per liter. 
     
     
         11 . An aqueous acidic aluminum-etching composition comprising (a) about 20 to about 80 grams per liter of ammonium bifluoride; and (b) about 1 to about 50 grams per liter of diammonium phosphate; said composition insensitive to zinc content in said aluminum. 
     
     
         12 . An aqueous acidic aluminum-etching composition comprising: (a) about 20 to about 80 grams per liter of ammonium bifluoride; and (b) about 1 to about 50 grams per liter of said diammonium phosphate; said composition having a pH of about 2 to about 5, and said composition suitable for use imparting a uniform matte finish to said metal. 
     
     
         13 . A metal etching bath comprising (a) about 20 to about 80 grams per liter of ammonium bifluoride; and (b) about 1 to about 50 grams per liter of said diammonium phosphate; said bath having a pH of about 2 to about 5. 
     
     
         14 . The bath according to  claim 13 , further comprising a metal article immersed in the bath. 
     
     
         15 . A metal article having a uniform matte finish, said article etched in a bath according to  claim 13 . 
     
     
         16 . The article according to  claim 15 , which is aluminum or an aluminum alloy. 
     
     
         17 . A method of producing a metal article having a uniform matte finish comprising immersing said metal article in a bath of  claim 13 . 
     
     
         18 . The method according to  claim 7 , further comprising rinsing said etched article prior to anodization.