Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Patent
1996-11-21
1998-04-28
Bell, Mark L.
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
106400, 106401, 106425, 106437, 106464, 106465, 106483, 106484, 106486, 106487, 106488, 501144, 501145, 501146, 501147, 501148, 501149, C04B 1420
Patent
active
057439524
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method for preparing a rheologically stable, concentrated aqueous suspension of a finely divided particulate inorganic material, particularly a finely divided particulate natural or synthetic mineral material, such as a clay or an alkaline earth metal carbonate pigment.
It is often advantageous to produce and distribute mineral 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 a mineral 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 mineral material 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 a particulate inorganic material 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 median particle diameter of the distribution, 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 median particle diameter of the particle size distribution is reduced. 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 inorganic material 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.
According to a first aspect of the present invention, there is provided a process for improving the rheological properties of an aqueous suspension of a particulate inorganic material which comprises the steps of:
(a) forming an aqueous suspension of the particulate inorganic material and an effective amount of an anionic polyelectrolyte dispersing agent;
(b) diluting the suspension formed in step (a) with water to give a solids concentration of not less than 20% by weight of the particulate inorganic material; and
(c) reconcentrating the diluted suspension formed in step (b) to give a solids concentration of at least 50% by weight of the particulate inorganic material.
The suspension formed in step (c) is suitable for transportation and/or use without the addition of a further quantity of dispersing agent.
Steps (b) and (c) of the process of the invention may advantageously be repeated one or more times.
The suspension formed in step (a) preferably contains at least 50%, and preferably at least 60% by weight of the particulate inorganic material.
In step (a), the particulate inorganic material is typically a natural or synthetic mineral material. The invention has been found to be particularly suited to the treatment of paper coating pigments, paper fillers or pigments or extenders for use in water-based paints. The particulate mineral material may advantageously be kaolin clay or calcium carbonate. Generally the particulate inorganic material will have a particle size distribution such that at least 45% by weight, and preferably at least 50% by weight, of the particles have an equivalent spherical diameter smaller than 2 .mu.m.
The anionic polyelectrolyte is typically used in an amount of at least 0.05% by weight, based on the weight of the particulate inorganic material, although the optimum amount to achieve dispersion of the inorganic material can be determined by the skilled person without difficulty. The anionic polyelectrolyte dispersing agent is advantageously a water soluble salt of poly(acrylic acid) or of poly(methacrylic acid) having a weight average molecular weight of not more than 20,000, as determined by gel permeation chromatogr
REFERENCES:
patent: 3857781 (1974-12-01), Maynard
patent: 5154767 (1992-10-01), Kunkle et al.
patent: 5223463 (1993-06-01), Bilimoria et al.
Eagles Warren Paul
Rogan Keith Robert
Skuse David Robert
Bell Mark L.
ECC International Ltd.
Hertzog Scott L.
Kikel Suzanne
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