Composite pigments
Composite pigments are provided which comprise a mineral pigment (such as kaolin clay, titanium dioxide, talc, mica or a mixture of two or more of these mineral pigments) and calcium carbonate precipitated in-situ on the surfaces of the particles of the mineral pigment.
1. A high brightness composite pigment which comprises a mineral pigment and in-situ precipitated calcium carbonate and which is produced by a plurality of carbonation cycles precipitating a calcium carbonate coating on surfaces of particles of the mineral pigment,
wherein the composite pigment has a reduced amount of particles of less than 0.2 micron compared to the starting mineral pigment and an equivalent amount of particles of less than 2 microns compared to the starting mineral pigment,
wherein the composite pigment comprises a uniform coating of precipitated calcium carbonate on the surfaces of the mineral pigment particles, in contrast to non-uniform unevenly distributed discrete calcium carbonate particles or aggregates of calcium carbonate particles on the surfaces of the mineral pigment particles; and
wherein the content of particles less than 2 microns is at least 84.1% and not more than 93.7%.
2. A composite pigment as defined by claim 1 wherein the mineral pigment is kaolin clay, titanium dioxide, talc, mica or a mixture of two or more of these mineral pigments.
3. A composite pigment as defined by claim 2 wherein the mineral pigment is kaolin clay.
4. A composite pigment as defined by claim 3 wherein the kaolin clay is hydrous kaolin clay.
5. A composite pigment as defined by claim 3 wherein the kaolin clay is delaminated kaolin clay.
6. A composite pigment as defined by claim 3 wherein the kaolin clay is calcined kaolin clay.
7. A composite pigment as defined by claim 3 wherein the kaolin clay is a mixture of hydrous kaolin clay and calcined kaolin clay.
8. A composite pigment as defined by claim 1 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 5.0 to about 90.0 weight percent based on the weight of the dry composite pigment.
9. A composite pigment as defined by claim 1 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 10.0 to about 60.0 weight percent based on the weight of the dry composite pigment.
10. A composite pigment as defined by claim 1 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 20.0 to about 40.0 weight percent based on the weight of the dry composite pigment.
11. A composite pigment as defined by claim 1 wherein the composite pigment additionally comprises titanium dioxide, talc, mica or a mixture of these materials.
12. A composite pigment as defined by claim 1 wherein the difference between the percentage of particles less than 2 microns and the percentage of particles less than 0.2 microns is at least 67.2 and not more than 83.2.
13. A high brightness composite pigment which comprises a mineral pigment and precipitated calcium carbonate particles deposited as a coating on surfaces of particles of the mineral pigment,
(a) wherein the composite pigment comprises a uniform coating of precipitated calcium carbonate on the surfaces of the mineral pigment particles, in contrast to non-uniform unevenly distributed discrete calcium carbonate particles or aggregates of calcium carbonate particles on the surfaces of the mineral pigment particles; and
(b) wherein the difference between the percentage of particles less than 2 microns and the percentage of particles less than 0.2 microns is at least 67.2 and not more than 83.2.
14. A composite pigment as defined by claim 13 wherein the mineral pigment is kaolin clay, titanium dioxide, talc, mica or a mixture of two or more of these mineral pigments.
15. A composite pigment as defined by claim 14 wherein the mineral pigment is kaolin clay.
16. A composite pigment as defined by claim 15 wherein the kaolin clay is hydrous kaolin clay.
17. A composite pigment as defined by claim 15 wherein the kaolin clay is delaminated kaolin clay.
18. A composite pigment as defined by claim 15 wherein the kaolin clay is calcined kaolin clay.
19. A composite pigment as defined by claim 15 wherein the kaolin clay is a mixture of hydrous kaolin clay and calcined kaolin clay.
20. A composite pigment as defined by claim 13 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 5.0 to about 90.0 weight percent based on the weight of the dry composite pigment.
21. A composite pigment as defined by claim 13 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 10.0 to about 60.0 weight percent based on the weight of the dry composite pigment.
22. A composite pigment as defined by claim 13 wherein the amount of calcium carbonate precipitated on the surfaces of the mineral pigment is from about 20.0 to about 40.0 weight percent based on the weight of the dry composite pigment.
23. A composite pigment as defined by claim 13 wherein the composite pigment additionally comprises titanium dioxide, talc, mica or a mixture of these materials.
24. A composite pigment as defined by claim 13 wherein the content of particles less than 2 microns is at least 84.1% and not more than 93.7%.
25. A high brightness composite pigment which comprises a mineral pigment and in-situ precipitated calcium carbonate and which is produced by a plurality of carbonation cycles precipitating a calcium carbonate coating on surfaces of particles of the mineral pigment,
wherein the composite pigment has a reduced amount of particles of less than 0.2 micron compared to the starting mineral pigment and an equivalent amount of particles of 1-2 microns compared to the starting mineral pigment,
wherein the composite pigment comprises a uniform coating of precipitated calcium carbonate on the surfaces of the mineral pigment particles, in contrast to non-uniform unevenly distributed discrete calcium carbonate particles or aggregates of calcium carbonate particles on the surfaces of the mineral pigment particles; and
wherein the content of particles less than 2 microns is at least 84.1% and not more than 93.7%.
26. A high brightness composite pigment as defined by claim 25 , wherein the difference between the percentage of particles in the composite pigment that are less than 2 microns and the percentage of particles in the composite pigment that are less than 0.2 microns is at least 67.2 and not more than 83.2.