Inorganic pigments
View Patent ↗The present invention provides inorganic pigments including cobalt and aluminum having the spinel crystalline structure that exhibit improved color and/or weatherability in paint and polymer applications. Inorganic pigments according to the invention are formed by adding small quantities of a phosphate compound such as aluminum phosphate and, optionally, chromium (III) oxide, to a raw batch that includes a mixture of cobalt-containing and aluminum-containing inorganic pigment precursors, and calcining the raw batch to obtain the inorganic pigment.
1. A method of forming an inorganic pigment comprising cobalt and aluminum and having a spinel crystalline structure, the method comprising calcining a raw batch comprising a blend of a cobalt-containing inorganic pigment precursor, an aluminum-containing inorganic pigment precursor, and a phosphate compound.
2. The method according to claim 1 wherein the phosphate compound is an aluminum phosphate.
3. The method according to claim 1 wherein the phosphate compound is aluminum metaphosphate.
4. The method according to claim 1 wherein the phosphate compound is aluminum orthophosphate.
5. The method according to claim 1 wherein the phosphate compound comprises from about 0.1% to about 12% of the raw batch by weight.
6. The method according to claim 1 wherein the phosphate compound comprises from about 0.5% to about 2.5% of the raw batch by weight.
7. The method according to claim 1 wherein the raw batch further comprises a chromium-containing inorganic pigment precursor.
8. The method according to claim 7 wherein the chromium-containing inorganic pigment precursor is chromium oxide and is present in an amount up to about 10% of the raw batch by weight.
9. The method according to claim 8 wherein the chromium oxide comprises from about 0.1% to about 2.5% of the raw batch by weight.
10. The method according to claim 1 wherein subsequent to the calcining step, the inorganic pigment is treated with acid to remove soluble salts and dried.
11. An inorganic pigment comprising cobalt and aluminum having the spinel crystalline structure produced by the process comprising calcining a raw batch comprising a blend of a cobalt-containing inorganic pigment precursor, an aluminum-containing inorganic pigment precursor, and a phosphate compound.
12. The inorganic pigment according to claim 11 wherein the phosphate compound is an aluminum phosphate.
13. The inorganic pigment according to claim 11 wherein the phosphate compound is aluminum metaphosphate.
14. The inorganic pigment according to claim 11 wherein the phosphate compound is aluminum orthophosphate.
15. The inorganic pigment according to claim 11 wherein the phosphate compound comprises from about 0.1% to about 12% of the raw batch by weight.
16. The inorganic pigment according to claim 11 wherein the phosphate compound comprises from about 0.5% to about 2.5% of the raw batch by weight.
17. The inorganic pigment according to claim 11 wherein the raw batch further comprises a chromium-containing inorganic pigment precursor.
18. The inorganic pigment according to claim 7 wherein the chromium-containing inorganic pigment precursor is chromium oxide and is present in an amount up to about 10% of the raw batch by weight.
19. The inorganic pigment according to claim 18 wherein the chromium oxide comprises from about 0.1% to about 2.5% of the raw batch by weight.
20. A paint product comprising a paint base having an inorganic pigment comprising cobalt and aluminum having the spinel crystalline structure dispersed therein, wherein the inorganic pigment further comprises a phosphate compound.
21. A polymer product comprising a polymer having an inorganic pigment comprising cobalt and aluminum having the spinel crystalline structure dispersed therein, wherein the inorganic pigment further comprises a phosphate compound.
22. The polymer product according to claim 21 wherein the polymer comprises polyvinylchloride.