Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Patent
1997-08-12
2000-06-06
Marcheschi, Michael
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
106486, 106487, 428403, 428405, 427212, 427215, 42721331, 427220, 4272481, 4272556, 427535, 427569, C09C 142
Patent
active
060713356
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATION
The present application claims priority from Australian Patent Application No. PM9671/94, filed Nov. 25, 1994, which application is incorporated herein by reference in its entirety.
TECHNICAL FIELD
This invention relates to the surface modification of clay minerals, particularly the plate-like clay minerals and especially (but not exclusively) kaolinite. The invention is especially concerned with the surface modification of such minerals by the use of a water vapour plasma.
BACKGROUND OF THE INVENTION
Kaolinite is a common mineral, the chief constituent of kaolin or clay. It is a member of the clay mineral group of phyllosilicates which group also includes talc (or soapstone) and pyrophyllite. Clay minerals similar to kaolinite include dickite, nacrite, anauxite, halloysite, montmorillonite (dominant clay in bentonite), beidellite, nontronite, hectorite, saponite, and illite. Clay minerals similar to talc include minnesotaite. All of these minerals are referred to herein as "kaolinite and kindred minerals". description.]
Kaolinite has a wide variety of applications in industry, particularly as a paper filler and a coating pigment (5). It is used as an extender in aqueous based paints and ink, a functional additive in polymers and is the major component in ceramics (5). Kaolinite is an inexpensive additive which can improve the properties of the material in which it is dispersed, provided it is able to form stable dispersions. In order to achieve this the surface is usually modified in some way so as to enhance colloid stability in a system whether it be organic, as for polymers, or in aqueous dispersions.
The surface of kaolinite, like other clay minerals, is relatively inert, unlike silica and many other minerals. Kaolinite has two different basal cleavage faces. One face consists of a siloxane surface with very inert --Si--O--Si-- links. The other basal surface consists of an octahedral, gibbsite [Al(OH).sub.3 ] sheet. Both of these surfaces are theoretically electrically neutral. At the edges of a platelet and at the surface ridges the lattice is disrupted and broken bonds occur which are accommodated as OH groups. These edges have been estimated to occupy approximately 10% of the whole kaolinite surface (6).
The hydroxyl groups at the plate edges are considered to be the major reactive sites of clay surfaces including kaolinite (1). Rigorous conditions are required to modify the surface of clay minerals including the use of anhydrous solvents, fluidised beds or autoclaves, the use of coupling agents, encapsulation by polymer synthesised on the surface or adsorption of surfactants from aqueous suspensions (7, 8, 9). Some of these methods are time consuming, polluting and of high cost and often the adhesion between the kaolinite particles and the modifying chemical is not strong as they are not covalently bound over the whole surface but either electrostatically bound or encapsulated (i.e. sheathed) and only bound covalently at the edges of the kaolinite particles. This can mean that the modifying chemical on the surface of kaolinite may not remain attached under certain conditions, (eg. during processing of the polymer into which it has been dispersed) causing the dispersion to become unstable. Methods, such as acid hydrolysis, have been attempted in the past to increase the reactivity of clays, including kaolinite, but these have been unsuccessful on kaolinite (1).
SUMMARY OF THE INVENTION
The present invention is directed to a method for modifying the surface properties of kaolinite or a kindred mineral. The method includes the step of subjecting the kaolinite or kindred mineral to water vapor plasma.
In another aspect, the invention provides a kaolinite or kindred mineral having a modified surface. The modified surface contains additional reactive hydroxyl sites.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 1a are diagrams of an apparatus for treating a mineral powder with a water vapour plasma;
FIGS. 2(a), (b) and (c) show the infrared spectra of
REFERENCES:
patent: 3660134 (1972-05-01), Morris et al.
patent: 3697474 (1972-10-01), Morris et al.
patent: 4080284 (1978-03-01), Mitchell
patent: 5234723 (1993-08-01), Babacz
Braggs Belinda
Ralston John
Smart Roger St. Clair
Comalco Aluminium Limited
Marcheschi Michael
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