Process and composition for sealing porous coatings containing metal and oxygen atoms

Abstract

Anodized aluminum surfaces are sealed using a process in which one step involves bringing the anodized aluminum surface into contact for a relatively brief period of time at a relatively low temperature with a liquid sealing composition. The liquid sealing composition contains water, lithium cations, fluoride anions and at least one high capacity buffering agent such as boric acid.

What is claimed is:  
     
         1 . A process for sealing an anodized aluminum surface, said process comprising: 
 (I) bringing the anodized aluminum surface into contact for not more than 30 min at a temperature not greater than 75° C. with a liquid first sealing composition that has a pH value from 7.0 to 10.0, this pH value being sufficiently well buffered that at least 0.15 milliequivalent of strong alkali per liter of sealing composition is required to raise the pH of the sealing composition by 0.50 pH unit and at least 0.15 milliequivalent of strong acid per liter of sealing composition is required to lower the pH of the sealing composition by 0.50 pH unit, said liquid first sealing composition comprising water and: 
 (A) lithium cations; and  
 (B) fluoride anions.  
   
     
     
         2 . The process of  claim 1  wherein the first sealing composition is comprised of less than about 50 ppm of dispersed or dissolved silicon atoms.  
     
     
         3 . The process of  claim 1  comprising an additional step after completion of step (I) of bringing the anodized aluminum surface into contact at a temperature of at least 82° C. with a second sealing composition comprising steam or liquid water.  
     
     
         4 . The process of  claim 1  wherein said liquid first sealing composition is comprised of one or more boron-containing species selected from the group consisting of boric acid, boric acid salts, and mixtures thereof.  
     
     
         5 . The process of  claim 1  wherein the pH value of the liquid first sealing composition is sufficiently well buffered that at least 0.45 milliequivalent of strong alkali per liter of the liquid first sealing composition is required to raise the pH of the liquid first sealing composition by 0.50 pH unit.  
     
     
         6 . The process of  claim 1  wherein the pH value of the liquid first sealing composition is sufficiently well buffered that at least 0.45 milliequivalents of strong acid per liter of liquid first sealing composition is required to lower the pH of the liquid first sealing composition by 0.50 pH unit.  
     
     
         7 . The process of  claim 1  wherein said liquid first sealing composition has a ratio by mass of boron and fluoride that is at least 0.017:1.00.  
     
     
         8 . The process of  claim 1  wherein said liquid first sealing composition has a ratio by mass of boron and fluoride anions that is not more than 0.87:1.00.  
     
     
         9 . The process of  claim 1  wherein said liquid first sealing composition has a ratio by mass of boron to lithium cations that is at least 0.017:1.00.  
     
     
         10 . The process of  claim 1  wherein said liquid first sealing composition has a ratio by mass of boron to lithium cations that is not more than 0.87:1.0.  
     
     
         11 . The process of  claim 1  wherein said liquid first sealing composition is additionally comprised of at least one surfactant.  
     
     
         12 . The process of  claim 1  wherein said liquid first sealing composition is additionally comprised of at least one surfactant having the general structure  
       
         
           
           
               
               
           
         
       
       wherein Y is a direct bond or a group of formula:  
       
         
           
           
               
               
           
         
       
       R 1  and R 2  are each individually selected from H or C 5 -C 25  alkyl, provided that R 1  and R 2  are not both H; n has a value of from 1 to 4; and X is H or alkali metal.  
     
     
         13 . The process of  claim 12  wherein said liquid first sealing composition is additionally comprised of at least one nonionic surfactant which is an ethoxylate of a fatty amine.  
     
     
         14 . The process of  claim 1  wherein the liquid first sealing composition is maintained at a temperature of at least 30° C. during step (I).  
     
     
         15 . A liquid sealing composition useful for sealing an anodized aluminum surface, said liquid sealing composition having a pH value of from 7.0 to 10.0 and comprising water and: 
 (A) lithium cations;    (B) fluoride anions; and    (C) an amount of one or more buffering agents, which in total is effective to buffer the pH value such that at least 0.15 milliequivalent of strong alkali per liter of liquid sealing composition is required to raise said pH value by 0.50 pH unit and at least 0.15 milliequivalent of strong acid per liter of liquid sealing composition is required to lower said pH value by 0.50 pH unit, wherein at least one of said buffering agents is a material other than an acetate or acetic acid.    
     
     
         16 . The liquid sealing composition of  claim 15  wherein said liquid sealing composition is comprised of less than 50 ppm of dispersed or dissolved silicon atoms.  
     
     
         17 . The liquid sealing composition of  claim 15  wherein at least one buffering agent is selected from the group consisting of boric acid, boric acid salts and mixtures thereof.  
     
     
         18 . The liquid sealing composition of  claim 17  additionally comprising acetate, acetic acid or both acetate and acetic acid.  
     
     
         19 . The liquid sealing composition of  claim 15  comprising at least 0.05 g/L boric acid.  
     
     
         20 . The liquid sealing composition of  claim 17  wherein the ratio by mass of boron and fluoride anions is at least 0.017:1.00.  
     
     
         21 . The liquid sealing composition of  claim 17  wherein the ratio by mass of boron and fluoride anions is not more than 0.87:1.00.  
     
     
         22 . The liquid sealing composition of  claim 17  wherein the ratio by mass of boron and lithium cations is at least 0.017:1.00.  
     
     
         23 . The liquid sealing composition of  claim 17  wherein the ratio by mass of boron and lithium cations is not more than 0.87:1.0.  
     
     
         24 . The liquid sealing composition of  claim 15  additionally comprising at least one surfactant.  
     
     
         25 . The liquid sealing composition of  claim 15  additionally comprising at least one surfactant having the general structure  
       
         
           
           
               
               
           
         
       
       wherein R 1  and R 2  are each individually selected from H or C 12 -C 16  alkyl, subject to the proviso that R 1  and R 2  are not both H, n is 1 or 2, and X is Na.  
     
     
         26 . The liquid sealing composition of  claim 25  additionally comprising at least one nonionic surfactant which is an ethoxylate of a fatty amine.  
     
     
         27 . A liquid sealing composition useful for sealing an anodized aluminum surface, said liquid sealing composition having a pH value of from 7.0 to 10.0 and comprising water and: 
 (A) 0.07 to 5.0 g/l lithium cations;    (B) 0.08 to 6.0 g/l fluoride anions;    (C) 0.05 to 9.0 g/l boric acid; and    (D) at least one surfactant.    
     
     
         28 . The liquid sealing composition of  claim 27  wherein at least one surfactant has the general structure  
       
         
           
           
               
               
           
         
       
       wherein R 1  and R 2  are each individually selected from H or C 12 -C 16  alkyl, subject to the proviso that R 1  and R 2  are not both H, n is 1 or 2, and X is Na.  
     
     
         29 . The liquid sealing composition of  claim 27  wherein at least one surfactant is an ethoxylate of a fatty amine.  
     
     
         30 . The liquid sealing composition of  claim 27  wherein the ratio by mass of boric acid and fluoride anions is from 0.10:1.00 to 5:1.00.  
     
     
         31 . The liquid sealing composition of  claim 27  wherein the ratio by mass of boric acid and lithium cations is from 0.10:1.00 to 5:1.0