Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Patent
1997-12-08
2000-10-24
Koslow, C. Melissa
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
427215, 427216, 427219, 4272133, 42721331, 428363, 428404, 428403, 106401, 106415, 106417, 106419, 106431, 106432, 106434, 106435, 106436, 106442, 106430, 106453, 106454, 106455, 106456, 106457, C09C 306, C09C 100, C04B 3314
Patent
active
06136083&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to coated inorganic pigments, to a process for their preparation by the sol-gel process and to their use for the production of enamels and mouldings.
2. Description of the Background
It is already known to apply one-component (e.g. SiO.sub.2) or multi-component glass coats to planar substrates by the sol-gel process; see, for example, DE 3719339, DE 4117041 and DE 4217432. Also, it is known to provide inorganic particles with ceramic coatings by means of the sol-gel process. For example, SiO.sub.2 particles can be coated with a ZrO.sub.2 layer, or copper chromium spinel particles with a layer of mullite. The layer thickness of the coating in these cases is within the nm range up to about 100 nm. However, thin layers of this kind are unsuitable for protecting redox-sensitive inorganic pigments against oxidation or reduction processes at temperatures in the range from 500 to 700.degree. C., as are employed for the production of enamels, since these layers are unable effectively to suppress the diffusion of gaseous substances. In addition, the very thin coatings break up within a short time in the presence of aggressive glass melts, as are used, for example, for enamel decorations on glassware, and as a result the pigment decomposes, with a change in colour, or is dissolved in the glass matrix.
SUMMARY OF THE INVENTION
It has surprisingly now been found that it is possible, by means of the sol-gel process, to produce intact glass-forming layers on inorganic pigments, whose layer thickness is more than one order of magnitude above that of conventional products.
The invention therefore provides coated inorganic pigments comprising an inorganic pigment which has a coating, prepared by the sol-gel process from glass-forming components and densified to form a xerogel or glass, with a layer thickness of at least 0.8 .mu.m, preferably from 1 to 5 .mu.m.
The invention additionally provides a process for the preparation of these coated inorganic pigments, which is characterized in that sol-gel process, resulting sol, inorganic pigment which has a xerogel coating, and vitreous layer.
Finally, the invention also provides for the use of the coated inorganic pigments for the production of enamels and mouldings. In order to produce enamel decorations, for example, the inorganic pigment coated in accordance with the invention can be employed instead of or together with customary pigments in conventional enamel pastes.
As a result of the novel coating of the inorganic pigments it is possible reduction, decomposition) or physical (melting, sublimation, evaporation, Ostwald ripening) change in the temperature range from 500 to 1200.degree. C. over a period which is sufficient for further processing, so that no change in the optical properties (e.g. colour change) occurs; contents of up to 60% by weight; reduce the firing temperature of the enamel, since the glass of the coating need only be incipiently melted in order to produce the enamel composite and can have a markedly higher viscosity than in the case of conventional enamels based on glass frits; pigments (for example those based on noble metal colloids) to temperatures .ltoreq.1200.degree. C. by encapsulating the nanoscale pigments in a high-melting matrix sheath; and thereby substantially increasing the ease of processing.
DETAILED DESCRIPTION OF THE INVENTION
Examples of inorganic pigments which are suitable for the purposes of the invention are metal pigments such as Ag, Au, Cu, Fe, Pb, Pd and Pt; and metal-oxide pigments such as Al.sub.2 O.sub.3, Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Cr.sub.2 O.sub.3, CuO, Cu.sub.2 O, In.sub.2 O.sub.3, Mn.sub.2 O.sub.3, PbO, PdO, SnO.sub.2, TiO.sub.2, ZnO and ZrO.sub.2. Also suitable are metal halides such as AgCl, AgBr, AgCl.sub.x Br.sub.1-x and CuCl; metal carbides such as TiC and B.sub.4 C; metal nitrides such as BN and TiN; metal arsenides such as Cd.sub.3 As.sub.4 ; metal phosphides such as Cd.sub.3 P.sub.2 ; metal chalcogenides (sulphides, selenide
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Chemical Abstract citation No. 123:92931: abstract for JP 7-133,211, Nov. 1993.
Kalleder Axel
Mennig Martin
Schmidt Helmut
Institut fuer Neue Materialien Gemeinnuetzige GmbH
Koslow C. Melissa
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