Preparation of systems of ground particulate material

Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...

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106465, 241 16, 516 79, 516928, 524425, B01J 1300, B02C 1912, C08K 326, C09C 304

Patent

active

06087404&

DESCRIPTION:

BRIEF SUMMARY
This invention concerns a method for preparing a rheologically stable, concentrated aqueous suspension of an inorganic particulate mineral such as a finely divided alkaline earth metal pigment.
It is often advantageous to produce and distribute alkaline earth metal pigment or filler materials, especially to the paper and water based paints industries, in the form of a concentrated suspension in water. A user receiving an alkaline earth metal pigment material in this form is able to avoid the high energy and capital costs which would be involved in the mixing of a dry material with water to form a suspension on his own premises, and, if the alkaline earth metal pigment is produced by a wet route, the producer is able to avoid the costs of complete drying of the material. A concentrated aqueous suspension is also easy to handle and convey, and presents no dust problem.
The rheological properties of an aqueous suspension of an alkaline earth metal pigment depend upon a number of factors including the concentration of solid material in the suspension, the particle size distribution of the solid material, as indicated, for example, by the percentage by weight of the particles having an equivalent spherical diameter (e.s.d.) smaller than 2 .mu.m, and the type and amount of dispersing agent which is used. Generally, a suspension becomes more viscous, or less fluid, as the solids concentration is increased, or as the percentage by weight of the particles having an e.s.d. smaller than 2 .mu.m is increased. Also there is an increasing tendency for the suspension to become more viscous with time on storage. Assuming that an effective dispersing agent for the alkaline earth metal pigment is available, it is generally found that there is an optimum amount of the dispersing agent which must be added to the suspension to give maximum fluidity and maximum rheological stability, other factors being kept the same.
EP-A-0216002 describes a process of beneficiating calcite including subjecting a concentrated slurry of the calcite particles to multistage grinding by passing the slurry in series from an upstream grinding stage through one or more downstream grinding stages wherein each downstream grinding stage is charged with a grinding medium having a particle size finer than the grinding medium of the preceding upstream grinding stage. Grinding media comprising particles of alumina, alumina/silica, or zirconia/silica are disclosed. A dispersing agent, eg. an aqueous solution of a water-soluble polyacrylate, such as sodium polyacrylate, is preferably added to the slurry prior to grinding.
U.S. Pat. No. 4,325,514 discloses a grinding method in which a mineral is wet ground in a first grinding chamber in the absence of a grinding medium. The ground mineral may be further ground in a second grinding chamber in the presence of a grinding medium. In the first grinding chamber a dispersing agent is required. The use of a dispersing agent in the second grinding chamber is optional.
EP-A-0595723 discloses a grinding process in which a compact mineral (such as calcium carbonate), a lamellar mineral (such as kaolin) and a plastic pigment are co-ground in the presence of a grinding agent in pre-grinding and final grinding steps, both of which are conducted in the same grinding vessel. The final grinding may be conducted in the presence of a colloidal protective agent.
We have found that the procedures described in the prior art for treating inorganic particulate material such as calcium carbonate by grinding are not optimum and that grinding may be improved by operation in accordance with the present invention.


BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing is a diagrammatic flow chart illustrating the process embodying the present invention.
The present invention provides a process for forming a concentrated aqueous suspension of a particulate inorganic material such as an alkaline earth metal pigment which, when compared with suspensions which are currently available in commerce, will have a higher solids concentration f

REFERENCES:
patent: 3322683 (1967-05-01), Lester
patent: 4278208 (1981-07-01), Falcon-Steward
patent: 4293097 (1981-10-01), Lewis et al.
patent: 4840985 (1989-06-01), Gonnet et al.
patent: 4849128 (1989-07-01), Timmons et al.
patent: 5076846 (1991-12-01), Buri et al.
patent: 5533678 (1996-07-01), Strauch et al.
patent: 6003795 (1999-12-01), Bown et al.

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