Pretreatment of tinplate prior to the coating thereof with lacquer

Patent metadata

Field	Value
Publication number	US-9909227-B2
Application number	US-201313798353-A
Country	US
Kind code	B2
Filing date	Mar 13, 2013
Priority date	Jan 18, 2011
Publication date	Mar 6, 2018
Grant date	Mar 6, 2018

Abstract

The invention relates to a method for the anti-corrosive pretreatment of tinplate, in which an anti-corrosive primer coating is applied in a single step, said primer coating effectively preventing the shiny metal surface of the pretreated tinplate from turning black when the pretreated tinplate of the invention that is provided with a topcoat is in contact with liquids releasing or containing sulfur compounds and with food containing protein. In the disclosed method, the tinplate is anodically polarized in an electrolyte containing silicates of formula M 2 O.nSiO 2 , where M is an alkali metal ion or quaternary ammonium ion and n is a natural number between 0.8 and 7. Tinplate pretreated according to the invention can be used in particular for the production of food-safe packaging such as beverage cans or tin cans.

First claim

What is claimed is:

1. A method for the electrolytic passivation of tinplate by anodic polarization of the tinplate as an anode in an alkaline aqueous electrolyte, wherein the electrolyte contains at least one water-soluble silicate of the composition M 2 O.nSiO 2 , where “M” is an alkali metal ion or quaternary ammonium ion and “n” is a natural number between 0.8 and 7 and proportion of water-soluble silicates in the electrolyte is at least 0.5 wt. % but less than 30 wt. %, based in each case on SiO 2 ; and wherein the at least one water-soluble silicate comprises water glasses having a molar ratio of SiO 2 :M 2 O in a range of 2 to 5; and the anodic polarization takes place at a current density of at least 0.005 A/dm 2 but no more than 4 A/dm 2 and has a duration of at least 60 seconds such that a silicate layer is produced on the tinplate.

2. The method according to claim 1 , wherein the anodic polarization has a duration of no longer than 300 seconds in total and cathodic polarization of the tinplate in the alkaline aqueous electrolyte is absent.

3. The method according to claim 1 , wherein the anodic polarization takes place at a current density of at least 0.5 A/dm 2 but no more than 4 A/dm 2 .

4. The method according to claim 2 , wherein the anodic polarization takes place galvanostatically.

5. The method according to claim 1 , wherein the proportion of water-soluble silicates in the electrolyte is at least 0.5 wt. %, but less than 20 wt. %, based in each case on SiO 2 .

6. The method according to claim 1 , wherein the electrolyte additionally comprises at least one organosilane with at least one hydrolyzable substituent, which is split off under hydrolysis as an alcohol having a boiling point of less than 100° C., and at least one non-hydrolyzable substituent, which has at least some primary amino functions.

7. The method according to claim 6 , wherein the at least one organosilane comprises compounds corresponding to the general structural formula (I):
H 2 N—[(CH 2 ) m NH] y (CH 2 ) n —Si—X 3   (I)

wherein
X substituents are each independently of one another selected from alkoxy groups with no more than 4 carbon atoms;
m and n, each independently of one another, are integers between 1 and 4; and
y is an integer between 0 and 4.

8. The method according to claim 1 , wherein the electrolyte additionally contains water-soluble aluminum salts that do not contain any halides.

9. The method according to claim 1 , wherein the electrolyte additionally contains organic dicarboxylic acids having no more than 6 carbon atoms, salts of said organic dicarboxylic acids and combinations thereof.

10. The method according to claim 1 , wherein the anodic polarization in the alkaline aqueous electrolyte is followed by a secondary passivation comprising contacting the tinplate with an acidic aqueous composition containing water-soluble inorganic compounds of elements selected from the group consisting of Zr, Ti, Hf, Si and combinations thereof, with or without an intermediate water rinsing and with or without an intermediate drying step.

11. The method according to claim 10 , wherein the water-soluble inorganic compounds of elements selected from the group consisting of Zr, Ti, Hf, Si and combinations thereof, are present as fluoro acids of said elements, salts of the fluoro acids and mixtures thereof.

12. The method according to claim 11 , wherein the water-soluble inorganic compounds are present as the fluoro acids, the salts of the fluoro acids and mixtures thereof of the elements Zr and/or Ti.

13. The method according to claim 11 , wherein the acidic aqueous composition additionally contains phosphate ions.

14. The method according to claim 12 , wherein the secondary passivation step results in deposition of a coating on the tinplate of at least 0.3 mg/m 2 , but no more than 20 mg/m 2 , based on the elements Zr and/or Ti.

15. The method according to claim 14 , wherein the secondary passivation takes place by application of a wet film of the acidic aqueous composition on to the tinplate surface, which is dried immediately after application.

16. The method according to claim 8 , wherein the electrolyte additionally comprises at least one organosilane with at least one hydrolyzable substituent, which is split off under hydrolysis as an alcohol having a boiling point of less than 100° C., and at least one non-hydrolyzable substituent, which has at least some primary amino functions.

17. The method according to claim 1 , wherein the proportion of water-soluble silicates in the electrolyte is at least 0.5 wt. % but less than 20 wt. %, based in each case on SiO 2 ; the at least one water-soluble silicate comprises sodium water glass in which SiO 2 is in a range of 20-40 wt. %; and the anodic polarization takes place at a current density of at least 0.5 A/dm 2 but no more than 4 A/dm 2 .

18. The method according to claim 17 , wherein immediately after the anodic polarization takes place, with or without an intermediate water rinsing and/or drying step, electrolessly performing a post-passivation step of applying an acidic aqueous composition comprising fluoro complex salts, fluoro acids and/or salts of the fluoro acids of the elements Zr and/or Ti, thereby forming a post-passivation coating having a coating weight of at least 0.3 mg/m 2 , but no more than 20 mg/m 2 , based on the elements Zr and/or Ti thereby producing a coated tinplate more resistant to black discoloration from sulfide contact compared to an identical tinplate anodically polarized without the water glass and/or without the post-passivation step.

Assignees

• Henkel Ag & Co Kgaa

Inventors

• Sundermeier Uta
• Wolpers Michael
• Roth Marcel
• Stodt Juergen

Classifications

• C25D9/06 Primary

  by anodic processes · CPC title

• C25D11/34 Primary

  of metals or alloys not provided for in groups C25D11/04 - C25D11/32 · CPC title