Systems and methods for maintaining pretreatment baths

Patent metadata

Field	Value
Publication number	US-11566330-B2
Application number	US-201916385173-A
Country	US
Kind code	B2
Filing date	Apr 16, 2019
Priority date	Apr 16, 2019
Publication date	Jan 31, 2023
Grant date	Jan 31, 2023

Abstract

Disclosed is a system for maintaining a pretreatment bath containing a pretreatment comprising a Group IVB metal. The system comprises an aqueous reducing agent comprising a metal cation and a latent source of sulfate which, upon reaction with a contaminant in the pretreatment bath, forms a metal sulfate. The contaminant comprises a nitrite source. The metal sulfate salt has a pKsp of 4.5 to 11 at a temperature of 25° C. Also disclosed is a method for maintaining a pretreatment bath containing a pretreatment composition comprising a Group IVB metal. The method comprises supplying the reducing agent to the pretreatment bath in an amount sufficient to reduce a pollution ratio of the pretreatment bath to less than 1:1. Also disclosed are substrates with a pretreatment bath maintained according to the system and method.

First claim

We claim:

1. A method for maintaining a pretreatment bath containing a pretreatment composition comprising a Group IVB metal, the method comprising:
supplying an aqueous reducing agent to the pretreatment bath in an amount sufficient to reduce a pollution ratio of the pretreatment bath to less than 1:1;
wherein the reducing agent comprises a metal cation and a latent source of sulfate which, upon reaction with a contaminant in the pretreatment bath, forms a metal sulfate;
wherein the contaminant comprises a nitrite source; and
wherein the metal sulfate salt has a pKsp of 4.5 to 11 at a temperature of 25° C.

2. The method of claim 1 , wherein the metal cation comprises a cation of calcium, strontium, barium, radium, lead(II), and/or silver(I).

3. The method of claim 1 , wherein the reducing agent further comprises an anion capable of forming a salt with the metal cation.

4. The method of claim 3 , wherein the anion comprises a hydroxide, a carbonate, or combinations thereof.

5. The method of claim 1 , wherein the reducing agent has a pH of less than 7.

6. The method of claim 1 , further comprising supplying a pH adjusting agent to the pretreatment bath.

7. The method of claim 1 , wherein, prior to supplying the reducing agent, the pollution ratio of the pretreatment bath is greater than 1:1.

8. The method of claim 1 , wherein the reducing agent is supplied to the pretreatment bath in an amount sufficient to cause the pretreatment bath to be substantially free of nitrite.

9. The method of claim 1 , wherein the reducing agent is supplied to the pretreatment bath in an amount sufficient to cause the pretreatment bath to be completely free of nitrite.

10. The method of claim 1 , wherein the supplying the reducing agent is performed off-shift.

11. The method of claim 1 , wherein the supplying the reducing agent is performed on-shift.

Assignees

• Ppg Ind Ohio Inc

Inventors

• Sylvester Kevin T
• Silvernail Nathan J

Classifications

• C23C22/05

  using aqueous solutions · CPC title

• C23C22/80 Primary

  with solutions containing titanium or zirconium compounds · CPC title

• B32B15/013

  one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium · CPC title

• C23C22/50

  Treatment of iron or alloys based thereon · CPC title

• C23C22/86 Primary

  Regeneration of coating baths · CPC title