Claims
- 1. A method of preparing a composite pigment material for use in a composition for making or coating a fibrous sheet material, which method comprises:treating an aqueous medium containing particles of a fine particulate material and fibers, said treating comprises chemically precipitating, by a precipitation reaction in the aqueous medium, crystals of a white pigment compound thereby producing a composite material, said composite material comprising a composite matrix of fibers and precipitated crystals of the white pigment compound and particles of the fine particulate material dispersed and bonded within the matrix, wherein at least 90% by weight of the fine particulate material in the treated aqueous medium has an equivalent spherical diameter as measured by sedimentation of less than 1 μm and comprises dispersed material which has not previously been used in an industrial operation, and wherein the fine particulate material and the fibers are obtained from separate stocks and are added together prior to the precipitation reaction in relative amounts required to be present in the composite pigment material, the ratio by weight of the fine particulate material to the white pigment compound being from 1:100 to 1:1, wherein said white pigment compound comprises an alkaline earth metal carbonate.
- 2. The method of claim 1, wherein at least 50% by weight of the fine particulate material has an equivalent spherical diameter as measured by sedimentation of less than 0.5 μm.
- 3. The method of claim 1, wherein the fine particulate material is selected from TiO2, calcined kaolin-containing material, silica, sodium silicate, aluminium silicate, sodium aluminium silicate, talc and plastic pigment material.
- 4. The method of claim 1, wherein the white pigment compound comprises calcium carbonate.
- 5. The method of claim 1, wherein the fibers employed in the treated aqueous medium comprise fresh fibers from virgin pulp or fibers from broke or recycled paper.
- 6. The method of claim 5, wherein at least 50 per cent by weight of the fibers are fibers which have not previously been used in papermaking.
- 7. The method of claim 5, wherein the fibers employed in the treated aqueous medium comprise fibers which have not previously been used in papermaking and which have been beaten to give substantial fibrillation, the fibers having a freeness of 300 CSF or less.
- 8. The method of claim 7, wherein the fibers comprise fibers which have been subjected to a size classification treatment to separate a fine fraction for use in the treated aqueous medium.
- 9. The method of claim 7, wherein at least one per cent by weight of the fibers in the treated aqueous medium are fines which, as defined in TAPPI Standard T261 cm-90, will pass through a round hole having a diameter of 76 mm.
- 10. The method of claim 1, wherein the precipitation reaction is carried out in a batch reactor and the solids contained in the aqueous medium in which the precipitation reaction is carried out, other than solids to be consumed as reagent to form the white pigment compound by the precipitation reaction, constitute from 0.1% to 20% by weight of the suspension.
- 11. The method of claim 1, wherein the method is carried out as a continuous or semi-continuous process and the solids content of the treated aqueous medium, other than consumable solids, is in the range 20% to 50% by weight.
- 12. The method of claim 1, wherein the aqueous medium is mechanically agitated before and during the precipitation reaction.
- 13. The method of claim 1, wherein at least one preliminary precipitation reaction is carried out in the aqueous medium prior to the fine particulate material being present therein.
- 14. The method of claim 1, wherein the fine particulate material is added to the aqueous medium in multiple additions and a precipitation reaction stage follows each such addition.
- 15. The method of claim 13, wherein the fine particulate material is added to the aqueous medium in multiple additions and a precipitation reaction stage follows each such addition.
- 16. The method of claim 1, wherein the white pigment compound further comprises phosphates or silicates of calcium, aluminium or magnesium.
Parent Case Info
This application claims the benefit of U.S. Provisional Application No: 60/052,456, filed Jul. 14, 1997.
US Referenced Citations (9)
Foreign Referenced Citations (8)
Number |
Date |
Country |
0 604 095 |
Jun 1994 |
EP |
0 658 606 |
Jun 1995 |
EP |
0 737 774 |
Oct 1996 |
EP |
0 768 344 |
Apr 1997 |
EP |
2 306 461 |
May 1997 |
GB |
62-162098 |
Jul 1987 |
JP |
62-199898 |
Sep 1987 |
JP |
WO9632354 |
Oct 1999 |
WO |
Provisional Applications (1)
|
Number |
Date |
Country |
|
60/052456 |
Jul 1997 |
US |