Grinding method

Abstract

The invention provides a method of grinding an inorganic particulate material such as calcium carbonate or kaolin in an aqueous suspension, preferably at a solids level below about 50% by weight, wherein the aqueous suspension includes a sub-effective amount of a dispersing agent for the inorganic particulate material.

Description

FIELD OF THE INVENTION [0001] This invention relates to a method of grinding an aqueous suspension of an inorganic particulate material and to products obtained thereby. BACKGROUND OF THE INVENTION [0002] Aqueous suspensions containing inorganic particulate material, for example an alkaline earth metal (e.g. calcium) carbonate or kaolin, are used widely in a number of applications. These include, for example, the production of pigment or filler containing compositions which may be used in paper manufacture or paper coating, and the production of filled compositions for paints, plastics and the like. [0003] The inorganic particulate material typically has a known particle size distribution (psd), dictated by the intended end use in ways which are well known in the art. Generally, the required psd is obtained by a method which includes grinding the inorganic particulate material in an aqueous suspension. The suspension may contain a high (e.g. above about 50% by weight) or low (e.g. b...

AI Technical Summary

Benefits of technology

[0011] In accordance with a second aspect of the present invention, there is provided a method of grinding an aqueous suspension of a particulate inorganic material to obtain a particulate inorganic material of reduced particle size and increased steepness, wherein the grinding is carried out in the presence in the aqueous suspension of a sub-effective amount of a dispersant for the inorganic particulate material.

[0023] The dispersant is a chemical additive capable, at a sufficient amount greater than the amount to be used in the present invention, of acting on the particles of the inorganic material to prevent or effectively restrict flocculation or agglomeration of the particles to a desired extent, according to the normal processing requirements. At the levels used in the present invention, however, the dispersant is not effective in this way, although it serves the useful and unexpected result of assisting to alleviate the problems noted in relation to the prior art, particularly one or more of: reduction in discoloration of the particulate material; improvement of introduction of dispersants in effective amounts at the high solids stages; improvement of comparability of the particulate material in mixtures with other particulate materials including conventional dispersants such as polyacrylates.

[0032] The grinding process may, for example, be conducted at a relatively low temperature, e.g. below about 30° C. Lower temperatures are believed to assist in preventing or restricting discoloration of white inorganic particulates resulting from iron-based corrosion products entering the aqueous suspension.

Problems solved by technology

The term “sub-effective” means that the dispersant is present in a finite amount, but that amount is not sufficient to give rise to deflocculation of the particulate inorganic material, so that the flocculation characteristics of the suspension are substantially the same as would be found in the complete absence of any dispersant.

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