Iron oxide coated perlescent pigments
AssigneeMerck Patent GmbH
InventorsKlaus D. Franz, Klaus Ambrosius
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Abstract
The application relates to a pearlescent pigments based on platelet-like substrates, such as mica, which are coated with metal oxides, the metal oxide layer containing titanium and also iron, wherein the pigment has a multi-layer structure in which a first layer of TiO.sub.2 in the rutile form is followed by a layer of pseudobrookite and an iron oxide layer.
Claims16
In a pearlescent pigment comprising a plateletlike substrate coated with metal oxides, the metal oxide layer containing titanium dioxide and iron oxide, the improvement wherein the pigment comprises a multi-layer structure in which superimposed on the substrate is a first layer of TiO.sub.2 in the rutile form, formed from a precipitated layer of titanium dioxide or titanium dioxide hydrate, having a thickness of at least 40 nm, the latter being superimposed by a layer of pseudobrookite and the latter being superimposed by an iron oxide layer, formed by the precipitation of an iron oxide or hydroxide layer, having a thickness of at least 15 nm, wherein the TiO.sub.2 concentration, relative to the total pigment, is about 20 to about 50% by weight, and the iron side concentration relative to the total pigment, is about 10 to about 50% by weight.
In a process for preparing pearlescent pigments by coating platelet-like substrates with an iron- and titanium-containing metal oxide layer, the improvement comprising first precipitating a titanium dioxide or titanium dioxide hydrate layer having a thickness of at least 40 nm and a concentration relative to the total pigment of about 20-50% by weight, said layer being calcinable to form a rutile layer, and before or after calcination of resultant pigment, precipitating an iron oxide or hydroxide layer having a thickness of at least 15 nm, and a concentration relative to the total pigment of about 10-50% by weight on the titanium dioxide or the titanium dioxide hydrate layer, and calcining the pigment.
Dependencies are inferred from the claim text.