A coating composition for paper and other substrates, particularly mechanical papers such as lightweight coated (LWC) paper, comprises an aqueous suspension of a particulate pigment together with a binder, wherein the particulate pigment comprises: (a) a first component which is a precipitated calci
A coating composition for paper and other substrates, particularly mechanical papers such as lightweight coated (LWC) paper, comprises an aqueous suspension of a particulate pigment together with a binder, wherein the particulate pigment comprises: (a) a first component which is a precipitated calcium carbonate consisting predominantly of aragonitic or rhombohedral particle shapes or of aragonitic and rhombohedral particle shapes in a weight ratio of between around 40:60 and about 60:40 (e.g. about 50:50) aragonitic:rhombohedral, and a second component which is a processed particulate hydrous kaolin clay having a shape factor greater than or equal to about 25 and a steepness greater than or equal to about 20; or (b) a first component which is a fine particulate calcium carbonate consisting predominantly of particles having a generally spherical particle shape, and a second component which is a processed particulate hydrous kaolin clay having a shape factor greater than or equal to about 45 and a mean equivalent particle diameter (d50) less than about 0.5 μm; or (c) a first component which is a precipitated calcium carbonate consisting predominantly of aragonitic and rhombohedral particle shapes in a weight ratio of between about 40:60 and about 60:40 (e.g. about 50:50) aragonitic:rhombohedral, and a second component which is a processed particulate hydrous kaolin clay having a shape factor less than about 25.
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The invention claimed is: 1. A pigment composition comprising: (a) a precipitated calcium carbonate comprising a mixture of aragonitic particles and rhombohedral particles in a weight ratio ranging from 40:60 to 60:40 based on aragonitic:rhombohedral, and (b) a kaolin clay with a shape factor great
The invention claimed is: 1. A pigment composition comprising: (a) a precipitated calcium carbonate comprising a mixture of aragonitic particles and rhombohedral particles in a weight ratio ranging from 40:60 to 60:40 based on aragonitic:rhombohedral, and (b) a kaolin clay with a shape factor greater than 25 and a steepness greater than or equal to 20. 2. The composition of claim 1, wherein the precipitated calcium carbonate comprises a predominantly rhombohedral precipitated calcium carbonate. 3. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a d50 of less than about 0.8 microns. 4. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a d50 of less than about 0.7 microns. 5. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a d50 of at least about 0.2 microns. 6. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a d50 ranging from about 0.25 microns to about 0.45 microns. 7. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a d50 ranging from about 0.4 microns to about 0.6 microns. 8. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a particle size distribution such that at least about 93% by weight of the particles have an equivalent spherical diameter less than 2 microns. 9. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a particle size distribution such that at least about 86% by weight of the particles have an equivalent spherical diameter less than 1 micron. 10. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a particle size distribution such that at least about 22% by weight of the particles have an equivalent spherical diameter less than 0.5 microns. 11. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a particle size distribution ranging from 5% to 25% by weight of the particles have an equivalent spherical diameter less than 0.25 microns. 12. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a GE brightness of at least 90. 13. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a GE brightness of at least 92. 14. The composition of claim 2, wherein the kaolin clay has a shape factor greater than 30. 15. The composition of claim 2, wherein the predominantly rhombohedral precipitated calcium carbonate has a particle size distribution such that: at least 93% by weight of the particles have an equivalent spherical diameter of less than 2 microns; at least 86% by weight of the particles have an equivalent spherical diameter of less than 1 micron; at least 22% by weight of the particles have an equivalent spherical diameter of less than 0.5 microns; and from 5% to 25% by weight of the particles have an equivalent spherical diameter less than 0.25 microns. 16. The composition of claim 1, wherein the precipitated calcium carbonate comprises a predominantly aragonitic precipitated calcium carbonate. 17. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a d50 of less than about 0.8 microns. 18. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a d50 of less than about 0.7 microns. 19. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a d50 of at least about 0.2 microns. 20. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a d50 ranging from 0.25 microns to about 0.45 microns. 21. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a particle size distribution such that at least about 90% by weight of the particles have an equivalent spherical diameter less than 2 microns. 22. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a particle size distribution such that at least about 75% by weight of the particles have an equivalent spherical diameter less than 1 micron. 23. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a particle size distribution such that at least about 60% by weight of the particles have an equivalent spherical diameter less than 0.5 microns. 24. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a particle size distribution ranging from 15% to 40% by weight of the particles have an equivalent spherical diameter less than 0.25 microns. 25. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a GE brightness of at least 90. 26. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a GE brightness of at least 92. 27. The composition of claim 16, wherein the kaolin clay has a shape factor greater than 25. 28. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a particle size distribution such that: at least 90% by weight of the particles have an equivalent spherical diameter of less than 2 microns; at least 75% by weight of the particles have an equivalent spherical diameter of less than 1 micron; at least 60% by weight of the particles have an equivalent spherical diameter of less than 0.5 microns; and from 15% to 40% by weight of the particles have an equivalent spherical diameter less than 0.25 microns. 29. The composition of claim 16, wherein the predominantly aragonitic precipitated calcium carbonate has a particle size distribution such that: at least 95% by weight of the particles have an equivalent spherical diameter of less than 2 microns; at least 82% by weight of the particles have an equivalent spherical diameter of less than 1 micron; at least 66% by weight of the particles have an equivalent spherical diameter of less than 0.5 microns; and from 23% to 33% by weight of the particles have an equivalent spherical diameter less than 0.25 microns. 30. The composition of claim 1, wherein the kaolin clay has a shape factor greater than about 30. 31. The composition of claim 1, wherein the kaolin clay has a shape factor greater than about 35. 32. The composition of claim 1, wherein the kaolin clay has a shape factor greater than about 45. 33. The composition of claim 1, wherein the kaolin clay has a d50 of less than about 0.5 microns. 34. The composition of claim 1, wherein the kaolin clay has a d50 ranging from about 0.1 microns to about 0.5 microns. 35. The composition of claim 1, wherein the kaolin clay has a d50 of greater than about 0.5 microns. 36. The composition of claim 1, wherein the kaolin clay has a d50 ranging from about 0.5 microns to about 1.5 microns. 37. The composition of claim 1, wherein the kaolin clay has a steepness ranging from about 25 to about 45. 38. The composition of claim 1, wherein the kaolin clay has a steepness ranging from about 35 to about 45. 39. The composition of claim 1, wherein the kaolin clay comprises at least 50% by weight kaolinite. 40. The composition of claim 1, wherein the kaolin clay comprises greater than 75% by weight kaolinite. 41. The composition of claim 1, wherein the kaolin clay comprises greater than 90% by weight kaolinite. 42. The composition of claim 1, wherein the kaolin clay has a GE brightness of at least 85. 43. The composition of claim 1, wherein the kaolin clay has a GE brightness of at least 90. 44. The composition of claim 1, wherein the precipitated calcium carbonate comprises at least about 40% by weight relative to the total composition. 45. The composition of claim 1, wherein the precipitated calcium carbonate comprises at least about 70% by weight relative to the total composition. 46. The composition of claim 1, wherein the precipitated calcium carbonate comprises not more than about 75% by weight relative to the composition. 47. A coating composition for paper and other substrates, the composition comprising an aqueous suspension of a particulate pigment according to claim 1 and a binder. 48. The composition according to claim 47, wherein the binder comprises a modified starch. 49. The composition according to claim 47, further comprising at least one additional component chosen from: cross linkers; water retention aids; viscosity modifiers and thickeners; lubricity/calendering aids; dispersants; antifoamers/defoamers; dry and wet pick improvement additives; dry and wet rub improvement and/or abrasion resistance additives; gloss-ink hold-out additives; optical brightening agents (OBA) and/or fluorescent whitening agents (FWA); dyes; biocides/spoilage control agents; levelling and evening aids; grease and oil resistance additives; water resistance additives; additional pigments; and mixtures thereof. 50. The composition according to claim 49, consisting essentially of the aqueous suspension of the particulate pigment, the binder, and the at least one additional component, with less than about 10% by weight of the at least one additional component. 51. A method for preparing a coating composition comprising an aqueous suspension of a particulate pigment according to claim 1 and a binder, comprising: mixing the particulate pigment and the binder into an aqueous liquid medium to prepare a suspension of the solid components therein. 52. A method for preparing a coated gloss paper comprising: applying to the paper a composition comprising an aqueous suspension of a particulate pigment according to claim 1 and a binder and calendering the paper to form a gloss coating thereon. 53. A paper coated with a gloss coating comprising a dry residue of a composition comprising an aqueous suspension of a particulate pigment according to claim 1 and a binder. 54. The paper according to claim 53, which is a coated mechanical paper. 55. The paper according to claim 53, which is a coated lightweight coated paper (LWC).
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