Methods for treating a ferrous metal substrate

Patent metadata

Field	Value
Publication number	US-9428410-B2
Application number	US-201313786914-A
Country	US
Kind code	B2
Filing date	Mar 6, 2013
Priority date	Sep 28, 2007
Publication date	Aug 30, 2016
Grant date	Aug 30, 2016

Abstract

Disclosed are methods for treating and coating a ferrous metal substrate, such as cold rolled steel, hot rolled steel, and electrogalvanized steel. These methods include contacting the ferrous metal substrate with an aqueous pretreatment composition comprising: (a) a Group IIIB and/or IVB metal compound; (b) phosphate ions; and (c) water. Also disclosed are off-shift methods of removing iron from the pretreatment bath.

First claim

We claim:

1. A method for removing iron from a pretreatment bath containing a pretreatment composition comprising a Group IIIB and/or Group IVB metal, comprising:
(a) reducing the pH of the pretreatment bath by at least 0.2;
(b) adding phosphate ions to the pretreatment bath in (a);
(c) raising the pH of the pretreatment bath in (b) by at least 0.2; and
(d) removing an insoluble sludge that forms in the pretreatment bath in (c);
wherein the method is performed in the absence of an article to be coated by the pretreatment composition; and
wherein the pretreatment bath is substantially free of phosphate ions during operation.

2. The method of claim 1 , wherein the pH of the pretreatment bath is reduced by at least 1.0.

3. The method of claim 1 , wherein the reducing comprises adding an acid to the pretreatment bath.

4. The method of claim 3 , wherein the acid comprises a Group IVB flurometal acid, phosphoric acid, sulfuric acid, sulfamic acid, nitric acid, or mixtures thereof.

5. The method of claim 3 , wherein the acid comprises hexafluorozirconic acid.

6. The method of claim 1 , wherein a source of the phosphate ions comprises alkali metal orthophosphates, ammonium orthophosphates, or mixtures thereof.

7. The method of claim 1 , wherein a source of the phosphate ions comprises monosodium phosphate.

8. The method of claim 1 , wherein the pretreatment bath in (c) is substantially free of iron.

9. The method of claim 1 , further comprising adding an oxidizing agent to the pretreatment bath in (b).

10. The method of claim 9 , wherein the oxidizing agent comprises peroxide compounds.

11. The method of claim 1 , wherein (d) removing comprises filtering the pretreatment bath.

12. The method of claim 1 , wherein the Group IIIB and/or Group IVB metal comprises zirconium.

13. The method of claim 1 , wherein the insoluble sludge comprises FePO 4 .

14. A method for removing iron from a pretreatment bath containing a pretreatment composition comprising a Group IIIB and/or Group IVB metal, comprising:
(a) adding an acid to the pretreatment bath to reduce the pH of the pretreatment composition to below 4.0;
(b) adding phosphate ions to the pretreatment bath in (a); and
(c) raising the pH of the pretreatment bath in (b) to 4 to 5.5; and
(d) removing an insoluble sludge that forms in the pretreatment bath in (c);
wherein the method is performed in the absence of an article to be coated by the pretreatment composition; and
wherein the pretreatment bath is substantially free of phosphate ions during operation.

15. The method of claim 14 , wherein the acid comprises hexafluorozirconic acid.

16. The method of claim 14 , wherein a source of the phosphate comprises monosodium phosphate.

17. The method of claim 14 , further comprising adding an oxidizing agent to the pretreatment bath in (b).

18. The method of claim 17 , wherein the oxidizing agent comprises peroxide compounds.

19. The method of claim 14 , wherein (d) removing comprises filtering the pretreatment bath.

20. The method of claim 14 , wherein the insoluble sludge comprises FePO 4 .

Assignees

• Ppg Ind Ohio Inc

Inventors

• Vargas Richard M
• Mcintyre John F

Classifications

• C23C22/86

  Regeneration of coating baths · CPC title

• C02F1/766

  by means of halogens other than chlorine or of halogenated compounds containing halogen other than chlorine · CPC title

• C23C22/361

  containing titanium, zirconium or hafnium compounds · CPC title

• C23C22/08 Primary

  Orthophosphates · CPC title

• C02F1/64 Primary

  of iron or manganese · CPC title