Rutile-containing lustrous pigments
AssigneeMerck Patent GmbH
InventorsReiner Esselborn, Horst Bernhard
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Abstract
Mica flake-based lustrous pigments having a plurality of TiO.sub.2 and SnO.sub.2 layers thereon comprising at least one succession of rutile/SnO.sub.2 /rutile have improved properties, including light and weathering fastness.
Claims16
In a lustrous mica flake pigment wherein the mica flakes are coated with a plurality of metal oxide layers consisting essentially of alternating layers of TiO.sub.2 and SnO.sub.2 in which each rutile layer is roentogenographically free from the anatase form, the improvement wherein the metal oxide layers comprise the sequence rutile/SnO.sub.2 /rutile and the innermost layer is rutile and wherein the thickness of the innermost rutile layer is a maximum of about 25 nm.
In a process for the production of a TiO.sub.2 coated mica flake pigment comprising a layer on the mica flakes of TiO.sub.2 in the rutile form only over a layer of SnO.sub.2, wherein tin hydroxide and titanium hydroxide are precipitated successively onto the mica flakes from a tin salt solution and a titanium salt solution, respectively, and the thus-coated flakes are then washed, dried and calcined, the improvement which comprises coating the mica flakes first with a thin layer of titanium hydroxide of up to 25 nm. thickness;
- precipitating the layer of tin hydroxide onto the thus-coated mica flakes from a tin II salt solution;
- in the presence of an oxidizing agent and then depositing a further layer of titanium hydroxide onto the coated mica flakes.
Dependencies are inferred from the claim text.