Yellow nacreous pigments having calcined CR oxide and phosphate layer for improved light-fastness, process and use
AssigneeMerck Patent GmbH
InventorHorst Bernhard
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Abstract
Nacreous pigments having a yellow powder color and an improved light-fastness comprise a mica platelet coated with titanium dioxide and on the titanium dioxide layer, a thin layer of calcined chromium oxide and/or chromium phosphate as a protective layer. The pigments are produced by coating mica platelets coated with metal oxides and/or hydroxides, with a thin layer of a sparingly soluble chromium(III) compound and calcining at about 500.degree.-1000.degree. C.
Claims11
A nacreous pigment having a yellow powder color and an improved light-fastness comprising a mica platelet coated with a plurality of metal oxide layers, wherein the metal oxide layers comprise the sequence rutile/SnO.sub.2 /rutile and the outermost layer is rutile, and on the outermost rutile layer a thin layer of calcined chromium oxide as a protective layer, and in the chromium oxide layer a phosphate content of up to the stoichiometric amount based on the chromium content.
A process for preparing a yellow nacreous pigment having improved light-fastness and comprising a mica platelet coated with metal oxides, comprising
- (a) coating a mica platelet successively with at least three layers of titanium hydroxide, tin hydroxide and titanium hydroxide, the outermost layer being a titanium hydroxide layer, and optionally washing, drying and calcining the pigment,
- (b) coating this pigment with a thin layer of a sparingly soluble chromium (III) compound, which contains phosphate ions of up to the stoichiometric amount based on the chromium content, and then
- (c) calcining it at a temperature of about 500.degree. to 1000.degree. C.
Dependencies are inferred from the claim text.