CORROSION INHIBITORS IN BREAKABLE MICROCAPSULES TO PASSIVATE SCRATCHED METALS

• US 20110064941A1
• Filed: 09/11/2009
• Published: 03/17/2011
• Est. Priority Date: 09/11/2009
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust)
• Inventors: Pederson, Thomas C., Verbrugge, Mark W., Sachdev, Anil K.
• Granted Patent: US 9,011,977 B2
• Time in Patent Office: Days
• US Class Current: 428/327
• CPC Class Codes: C08K 3/16 Halogen-containing compounds
• CPC Class Codes: C08K 3/28 Nitrogen-containing compounds
• CPC Class Codes: C08K 3/30 Sulfur-, selenium- or tellurium-containing compounds
• CPC Class Codes: C08K 9/10 Encapsulated ingredients
• CPC Class Codes: C09D 5/084 Inorganic compounds
• CPC Class Codes: C09D 7/62 modified by treatment with other compounds
• CPC Class Codes: C09D 7/70 characterised by shape, e.g. fibres, flakes or microspheres
• CPC Class Codes: Y10T 428/25 Web or sheet containing structurally defined element or component and including a second component containing structurally defined particles
• CPC Class Codes: Y10T 428/254 Polymeric or resinous material
• CPC Class Codes: Y10T 428/256 Heavy metal or aluminum or compound thereof
• CPC Class Codes: Y10T 428/258 Alkali metal or alkaline earth metal or compound thereof
• CPC Class Codes: Y10T 428/2985 Solid-walled microcapsule from synthetic polymer

Abstract

Microencapsulated chemical(s), as water-soluble solid particles, are embedded in at least one the paint layers on the surface of a magnesium article used in an automobile. If the protective paint film is scratched or otherwise mechanically disturbed to expose the surface of the magnesium article the capsules will be ruptured. This will expose the encapsulated chemical(s) to ambient water enabling them to dissolve and form an aqueous solution capable of reacting with the exposed magnesium to form a protective passivating layer on the exposed magnesium to resist corrosion. In a second embodiment the encapsulated chemicals include a deliquescing compound for extraction of moisture from the atmosphere sufficient to induce dissolution of the passivating layer-forming chemical(s) and trigger the formation of the passivating layer in the absence of ambient water.

Claims

1. A method of imparting corrosion protection to a painted surface of a magnesium article where the article may be exposed to water in use, the corrosion protection to be provided when the paint layer is damaged, exposing at least a portion of the underlying magnesium surface to water;

the method comprising;

applying a coating of paint to the surface of the article, the paint layer incorporating a dispersed magnesium-passivating chemical composition capable, when wetted with water at the surface of the magnesium article, of reacting with magnesium at the surface of the article to form a corrosion-inhibiting layer integral with the surface, the magnesium-passivating composition being encapsulated in frangible water-insoluble shells dispersed in the paint coating for exposure at a damaged paint site on the surface of the article.

2. The method of claim 1 wherein the paint layer further comprises a deliquescent compound encapsulated in the frangible water-insoluble shells.

3. The method of claim 2 wherein the deliquescent compound comprises at least one of the group consisting of calcium chloride, calcium nitrite, magnesium chloride, magnesium nitrate, zinc chloride, lithium sulfide and magnesium iodide.

4. The method of claim 1 wherein the frangible, water-insoluble shell is a polymer.

5. The method of claim 1 wherein the magnesium-passivating chemical composition comprises a cerium salt.

6. The method of claim 1 wherein the magnesium-passivating chemical composition comprises cerium sulfate.

7. The method of claim 1 wherein the magnesium-passivating chemical composition comprises a cerium salt, an oxidizer and an acid in predetermined proportions for cooperative reaction with magnesium when in aqueous solution.

8. The method of claim 1 wherein the magnesium-passivating chemical compound comprises an alkali metal carboxylate.

9. The method of claim 1 wherein the magnesium-passivating chemical compound comprises sodium decanoate.

10. A method of painting a magnesium article by application of paint comprising solids dispersed in a liquid in which a proportion of the solids comprise at least one solid magnesium-passivating chemical capable, when wetted with water of reacting with magnesium to form a corrosion-inhibiting layer, wherein the magnesium-passivating chemical is encapsulated in a frangible water-insoluble shell.

11. The method of claim 10 wherein the paint is applied proximate to the surface of the magnesium article.

12. The method of claim 10 wherein the magnesium-passivating chemical compound comprises a cerium salt.

13. The method of claim 10 wherein the magnesium-passivating chemical compound comprises an alkali metal carboxylate.

14. The method of claim 10 wherein the magnesium-passivating chemical compound comprises sodium decanoate.

15. A magnesium article at least a portion of the surface of which comprises at least one layer of paint applied to the surface of the article, the layer of paint comprising at least one solid magnesium-passivating chemical capable, when wetted with water of reacting with magnesium to form a corrosion-inhibiting layer, wherein the magnesium-passivating chemical is encapsulated in a frangible water-insoluble shell.

16. The magnesium article of claim 15 wherein the paint layer is proximate to the magnesium surface.

17. The magnesium article of claim 15 wherein the magnesium-passivating chemical comprises a cerium salt.

18. The magnesium article of claim 15 wherein the magnesium-passivating chemical comprises an alkali carboxylate.

19. The magnesium article of claim 15 wherein the magnesium-passivating chemical comprises sodium dodecanate.

20. The frangible frangible water-insoluble shell of claim 15 wherein the shell comprises a polymer.