Fine platy kaolin composition
View Patent ↗The present invention relates to a kaolin composition having improved physical properties, for example, for use in the production of paper products. The composition can comprise kaolin having a shape factor of at least about 20. The kaolin can have a particle size distribution such that at least about 94% by weight of the kaolin can have an esd of less than about 2 μm and/or at least about 80% by weight of the kaolin can have an esd of less than 1 μm. The amount of the kaolin having an esd of less than about 0.25 μm can range from about 25% to about 60% by weight. The Hercules viscosity of the kaolin product is less than 4000 rpm at 18 dynes at 63% solids and less than 1500 rpm at 18 dynes at 69% solids when measured using the “A” bob. The present invention also relates to an improved method for making the kaolin product from sedimentary kaolin.
1. A composition comprising kaolin having a shape factor ranging from 32 to 49, wherein at least about 85% by weight of the kaolin has an esd of less than about 1 μm, the amount of the kaolin having an esd of less than about 0.25 μm ranges from 35% to about 60% by weight.
2. The composition according to claim 1 , wherein the kaolin has a Hercules viscosity of less than about 4000 rpm at 18 dynes at 63% solids when measured using the “A” bob.
3. The composition according to claim 1 , wherein at least about 94% by weight of the kaolin has an esd of less than about 2 μm.
4. The composition according to claim 1 , wherein at least about 95% by weight of the kaolin has an esd of less than about 2 μm.
5. The composition according to claim 1 , wherein at least about 96% by weight of the kaolin has an esd of less than about 2 μm.
6. The composition according to claim 1 , wherein at least about 98% by weight of the kaolin has an esd of less than about 2 μm.
7. The composition according to claim 1 , wherein the amount of the kaolin having an esd of less than about 2 μm ranges from about 94% to about 99% by weight.
8. The composition according to claim 1 , wherein at least about 88% by weight of the kaolin has an esd of less than about 1 μm.
9. The composition according to claim 1 , wherein at least about 92% by weight of the kaolin has an esd of less than about 1 μm.
10. The composition according to claim 1 , wherein the kaolin has a shape factor ranging from 35 to 49.
11. The composition according to claim 1 , wherein the kaolin has a shape factor ranging from 40 to 49.
12. The composition according to claim 1 , wherein the kaolin has a shape factor ranging from about 35 to about 40.
13. The composition according to claim 1 , wherein the amount of the kaolin having an esd of less than about 0.25 μm ranges from 35% to about 50% by weight.
14. The composition according to claim 1 , wherein the kaolin has a shape factor ranging from 45 to 49, at least about 96% by weight of the kaolin has an esd of less than about 2 μm, at least about 85% by weight of the kaolin has an esd of less than about 1 μm, and the amount of the kaolin having an esd of less than about 0.25 μm ranges from 35% to about 45% by weight.
15. A method of refining kaolin, comprising:
(a) providing a degritted kaolin slurry having a shape factor of at least about 10 and including at least about 80% by weight particles having an esd of less than about 2 μm;
(b) wet media grinding the degritted kaolin slurry consuming in the range of from about 10 to about 200 Kw-hr/ton of energy; and
(c) classifying the slurry to a fine fraction wherein from about 96% to about 98% by weight of the classified kaolin has an esd of about 2 μm and the classified kaolin has a shape factor of less than or equal to 49.
16. The method according to claim 15 , wherein the degritted kaolin slurry provided in (a) has a shape factor of at least about 20.
17. The method according to claim 15 , wherein the degritted kaolin slurry provided in (a) has a shape factor of at least about 30.
18. The method according to claim 15 , wherein the degritted kaolin slurry provided in (a) has a shape factor of at least about 40.
19. The method according to claim 15 , wherein the amount of the kaolin in part (c) having an esd of less than about 0.25 μm ranges from about 25% to about 60% by weight.
20. The method according to claim 15 , further comprising spray-drying the fine fraction.
21. The method according to claim 15 , wherein the kaolin slurry is subjected to a beneficiation step selected from: selective flocculation, ozone treatment, flotation, magnetic separation, leaching, or any combination thereof.
22. The method according to claim 15 , further comprising leaching the kaolin fine fraction and filtering and drying the leached kaolin fine fraction.
23. A coated paper comprising:
a fibrous substrate; and
a coating on the substrate comprising kaolin having a shape factor of at least 32, wherein at least about 85% by weight of the kaolin has an esd of less than about 1 μm, the amount of the kaolin having an esd of less than about 0.25 μm ranges from about 25% to about 60% by weight.
24. The paper according to claim 23 , wherein at least about 94% by weight of the kaolin has an esd of less than about 2 μm.
25. The paper according to claim 23 , wherein the kaolin has a Hercules viscosity of less than 4000 rpm at 18 dynes at 63% solids when measured using the “A” bob.
26. The paper according to claim 23 , wherein the coating further comprises calcium carbonate.
27. A method of making a coated paper comprising:
coating a fibrous substrate with a paper coating composition comprising kaolin having a shape factor of at least 32, at least 85% by weight of the kaolin has an esd of less than 1 μm, the amount of the kaolin having an esd of less than about 0.25 μm ranges from about 25% to about 60% by weight.
28. The method of claim 27 , wherein at least about 94% by weight of the kaolin has an esd of less than about 2 μm.
29. The method of claim 27 , wherein the kaolin has a Hercules viscosity of less than 4000 rpm at 18 dynes at 63% solids when measured using the “A” bob.
30. A coated paper comprising:
a fibrous substrate; and
a coating on the substrate comprising kaolin having a shape factor of at least 32, at least about 85% by weight of the kaolin having an esd of less than about 1 μm and the amount of the kaolin having an esd of less than about 0.25 μm ranges from about 25% to about 60% by weight,
wherein gloss of the coated paper is greater than about 45 TAPPI units.