Coating solution for metal surface

• US 4,148,670 A
• Filed: 12/30/1976
• Issued: 04/10/1979
• Est. Priority Date: 04/05/1976
• Status: Expired due to Term

• Current Assignee: Amchem Products Inc. (Henkel AG & Co KGaA)
• Original Assignee: Amchem Products Inc. (Henkel AG & Co KGaA)
• Inventors: Kelly, Timm L.
• Primary Examiner(s): Kendall, Ralph S.
• Application Number:
  US05/755,922
• Time in Patent Office: 831 Days
• Field of Search: 148/6.15 R, 148/6.15 Z, 148/6.27
• US Class Current: 148/247
• CPC Class Codes: C23C 22/361 containing titanium, zirconium or hafnium compounds
• CPC Class Codes: C23C 22/86 Regeneration of coating baths

Abstract

An acidic aqueous coating solution for forming on an aluminum surface a coating which is corrosion resistant and to which overlying coatings adhere excellently is disclosed. The coating solution contains compounds of zirconium and/or titanium, fluoride and phosphate in dissolved form, and optionally, polyhydroxy compounds having 6 or fewer carbon atoms. The coating solution is capable of forming on an aluminum surface a uniformly colorless and clear coating so that the coated surface has the appearance of the underlying metal surface, that is, the coating can be formed without changing the appearance of the metal surface.

Claims

1. An acidic aqueous coating solution effective in forming a non-chromate coating on aluminum and having a pH within the range of about 1.5 to about 4.0 and consisting essentially of at least about 10 ppm of zirconium or titanium or a mixture thereof, at least about 10 ppm of phosphate and available fluoride, the amounts and proportions thereof being such that said solution is capable, in the presence of dissolved aluminum, of forming on an aluminum surface a uniformly clear and colorless coating and providing a coated surface which resists blackening after the coated surface is subjected to boiling water for a 2 minute period, and wherein said solution includes dissolved aluminum and is substantially free of solids which tend to precipitate.

2. A coating solution according to claim 1 including up to 1000 ppm of phosphate.

3. A coating solution according to claim 1 wherein the available fluoride concentration is no greater than about 500 ppm.

4. A coating solution according to claim 1 wherein the pH of the solution is within the range of about 2.6 to about 3.1.

5. A coating solution according to claim 1 including fluoboric acid in an amount within the range of about 8 to about 200 ppm.

6. A coating solution according to claim 1 including at least 40 ppm of a polyhydroxy compound having no more than 6 carbon atoms.

7. A coating solution according to claim 6 wherein said polyhydroxy compound is selected from the group consisting of gluconic acid and salts thereof, sorbitol, mannitol, dextrose, ethylene glycol and glycerine.

8. A coating solution according to claim 6 including up to about 1000 ppm of said polyhydroxy compound.

9. A coating solution according to claim 1 having a pH within the range of about 2.6 to about 3.1 and comprising:

(A) about 45 to about 125 ppm of zirconium;

(B) about 50 to about 200 ppm of phosphate; and

(C) about 10 to about 200 ppm of available fluoride.

10. A coating solution according to claim 9 wherein the source of said zirconium is ammonium fluozirconate, the source of said phosphate is phosphoric acid, the source of said available fluoride includes HF and including nitric acid in an amount, as needed, to impart said pH to said solution, about 8 to about 200 ppm of fluoboric acid and about 40 to about 400 ppm of gluconic acid.

11. A process for coating an aluminum surface having a bright shiny appearance comprising contacting the surface with the coating solution of claim 10.

12. A process for coating aluminum having a bright shiny surface comprising contacting said surface with the coating solution of claim 9.

13. A process according to claim 12 wherein said solution is sprayed on said surface.

14. A process according to claim 13 wherein the temperature of said solution is within the range of about 80 to about 110°

F.

15. A process according to claim 13, including subjecting the coated surface to pasteurizing conditions.

16. A coating solution according to claim 1 wherein the source of said zirconium is a fluozirconate.

17. A coating solution according to claim 1 wherein the source of said phosphate is phosphoric acid.

18. A coating solution according to claim 1 including nitric acid in an amount sufficient to impart to said solution a pH within said range.

19. A process for coating an aluminum surface comprising contacting the surface with the coating solution of claim 1.

20. A process for coating aluminum comprising contacting said aluminum with a coating solution according to claim 1 and forming thereon a coating having a weight of about 2 to about 20 mg/sq. ft.

21. A process according to claim 20 wherein the weight of coating formed is about 5 to about 10 mg/sq. ft.

23. An aqueous concentrate according to claim 21 wherein said coating solution has a pH within the range of about 2.6 to about 3.1 and consists essentially of:

(A) about 45 to about 125 ppm of zirconium;

(B) about 50 to about 200 ppm of phosphate;

(C) about 8 to about 200 ppm of HBF₄ ;

(d) about 10 to about 50 ppm of HF; and

(E) nitric acid in an amount such that the pH of said solution is within said range.

24. An aqueous concentrate substantially free of precipitate for replenishing the coating solution of claim 1 consisting essentially of:

(A) about 5 to about 10 g/l of zirconium or about 2.5 to about 5 g/l of Ti;

(B) about 5 to about 10 g/l of phosphate; and

(C) a material which is a source of about 5 to about 20 g/l of available fluoride.

25. A concentrate according to claim 24 wherein said source of available fluoride is HF or ammonium bifluoride or a mixture thereof.

22. An aqueous concentration such that an aqueous coating solution containing about 0.5 to about 10 weight percent of the concentrate is effective in forming a non-chromate coating on aluminum, has a pH within the range of about 1.5 to about 4.0 and consists essentially of:

(A) at least about 10 ppm of zirconium or titanium or a mixture thereof;

(B) about 10 ppm to about 1000 ppm of phosphate; and

(C) fluoride in an amount at least sufficient to form a complex with substantially all of said zirconium and/or titanium.

26. An acidic aqueous coating solution effective in forming a non-chromate coating on aluminum and consisting essentially of:

(A) about 20 to about 65 ppm of titanium;

(B) about 50 to about 200 ppm of phosphate; and

(C) about 10 to about 200 ppm of available fluoride;

wherein said solution is capable, in the presence of dissolved aluminum, of forming on an aluminum surface a uniformly clear and colorless coating and providing a coated surface which resists blackening after the coated surface is subjected to boiling water for a 2 minute period, and wherein said solution includes dissolved aluminum and is substantially free of solids which tend to precipitate.

27. A process for coating an aluminum surface having a bright shiny appearance comprising contacting the surface with the coating solution of claim 26.

28. An acidic aqueous coating solution effective in forming a non-chromate coating on aluminum and having a pH within the range of about 1.5 to about 4.0 and consisting essentially of:

(A) about 10 to about 125 ppm of zirconium;

(B) about 10 to about 1000 ppm of phosphate; and

(C) about 10 to about 500 ppm of available fluoride;

wherein said coating solution is substantially free of precipitate.

29. A solution according to claim 28 wherein the source of said zirconium is ammonium fluozirconate, wherein the source of said phosphate is phosphoric acid and the source of said available fluoride is HF or NH₄ F.HF.

30. A process for coating an aluminum surface having a bright shiny appearance comprising contacting the surface with the coating solution of claim 29.

31. A solution according to claim 28 including about 8 to about 200 ppm of fluoboric acid.

32. A solution according to claim 31 including about 40 to about 400 ppm of gluconic acid.

33. A process for coating an aluminum surface having a bright shiny appearance comprising contacting the surface with the coating solution of claim 31.

34. A coating solution according to claim 28 having a pH within the range of about 2.6 to about 3.1 and consisting essentially of:

(A) about 45 to about 125 ppm of zirconium;

(B) about 50 to about 200 ppm of phosphate;

(C) about 10 to about 200 ppm of available fluoride.

35. A process for coating an aluminum surface having a bright shiny appearance comprising contacting the surface with the coating solution of claim 34.

36. A solution according to claim 34 wherein the source of said zirconium is ammonium fluozirconate, wherein the source of said phosphate is phosphoric acid and the source of said available fluoride is HF or NH₄ F.HF.

37. A solution according to claim 36 including about 8 to about 200 ppm of fluoboric acid.

38. A solution according to claim 37 including about 40 to about 400 ppm of gluconic acid.

39. A process for coating an aluminum surface having a bright shiny appearance comprising contacting the surface with the coating solution of claim 38.

40. A process for coating an aluminum surface having a bright shiny appearance comprising contacting the surface with the coating solution of claim 37.

41. A process for coating an aluminum surface having a bright shiny appearance comprising contacting the surface with the coating solution of claim 36.

42. A process for coating an aluminum surface having a bright shiny appearance comprising contacting the surface with the coating solution of claim 28.

43. An acidic aqueous coating solution effective in forming a non-chromate coating on aluminum and having a pH within the range of about 1.5 to about 4.0 and consisting essentially of:

(A) at least about 10 ppm of zirconium;

(B) about 10 to about 1000 ppm of phosphate; and

(C) about 10 to about 500 ppm of available fluoride;

wherein the amount of zirconium in the solution is not in excess of its solubility limit in the solution, and wherein said coating solution is substantially free of precipitate.

44. A process for coating an aluminum surface having a bright shiny appearance comprising contacting the surface with the coating solution of claim 43.