Corrosion inhibitors in breakable microcapsules to passivate scratched metals

• US 9,011,977 B2
• Filed: 09/11/2009
• Issued: 04/21/2015
• 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 LLC (General Motors Company)
• Inventors: Sachdev, Anil K., Pederson, Thomas C., Verbrugge, Mark W.
• Primary Examiner(s): Kruer, Kevin R
• Application Number:
  US12/557,587
• Publication Number:
  US 20110064941A1
• Time in Patent Office: 2,048 Days
• Field of Search: 428/402.21, 427/388.1, 427/372.2, 252/387
• US Class Current: 427/372.2
• 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 is exposed to ambient water in use, the corrosion protection to be provided if the paint layer is damaged sufficiently to expose at least a portion of the underlying magnesium surface to ambient water;

the method comprising;

applying a coating of uncured paint to a magnesium surface of the article, the uncured paint coating on the magnesium article surface incorporating a dispersed dry particulate magnesium-passivating chemical composition capable, if the paint coating is damaged and the exposed surface of the magnesium article is wetted with ambient water, of reacting with magnesium at the surface of the article to form a corrosion-inhibiting layer integral with the surface, the dry particulate magnesium-passivating composition being encapsulated in frangible water-insoluble shells and dispersed in the uncured paint coating;

curing the paint coating to render a solid paint layer containing the dispersed frangible water-insoluble shells, the paint layer being subject to mechanical damage sufficient to damage the cured paint layer and expose the magnesium article surface, such mechanical damage being accompanied by rupture of the frangible shells and release of the magnesium-passivating composition at the damaged paint layer site on the surface of the article where the released magnesium-passivating composition is exposed to ambient water and reacts with the exposed magnesium surface to form the integral corrosion-inhibiting layer.

2. The method of claim 1 wherein the paint layer further comprises a deliquescent compound encapsulated in 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 to enhance the corrosion resistance of the article in the event of paint film rupture, the method comprising:

applying a coating of uncured liquid paint to a surface of a magnesium article, the uncured liquid paint comprising dispersed solids in which a first proportion of the solids comprise at least one dry, solid magnesium-passivating, chemical compound, capable, if the paint film is damaged and the exposed surface of the magnesium article is wetted with ambient water, of reacting with the magnesium surface to form a corrosion-inhibiting layer, wherein the magnesium-passivating chemical is encapsulated in a frangible, water-insoluble shell, and a second proportion of the solids comprising deliquescent compositions is likewise encapsulated in frangible, water-insoluble shells;

exposing the painted article to a thermal cycle comprising exposure to a temperature of at least 275°

F. for at least 30 minutes to render a dry paint film on the surface of the article, the dry paint film containing dispersed, frangible, water-insoluble shells encapsulating first and second proportions of solids, the paint film being subject to mechanical damage sufficient to damage the cured paint layer and expose the magnesium article surface, such mechanical damage being accompanied by rupture of the frangible shells and release of the magnesium-passivating composition and the deliquescent composition at the damaged paint film site on the surface of the article where the released magnesium-passivating composition is exposed to ambient water and reacts with the exposed magnesium surface to form the integral corrosion-inhibiting layer.

11. The method of claim 10 wherein the liquid 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.