Weathering-resistant pearlescent pigments
AssigneeMerck Patent GmbH
InventorsKlaus-Dieter Franz, Manfred Kieser, Otto Stahlecker
Life of this patent
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Abstract
Pearlescent pigments having improved weathering resistance are based on mica flakes coated with metal oxides, these pigments possessing on top of the coat of metal oxide a topcoat which contains a polysiloxane and a rare earth metal compound.
Claims20
A pearlescent pigment having improved weathering resistance and comprising mica flakes coated with at least one metal oxide layer, and on top of the metal oxide layer(s), a topcoating comprising amounts of a compatible rare earth metal compound and a polysiloxane of the formula ##STR4## wherein R.sup.1 and R.sup.3 are independently each ##STR5## H, C.sub.1-4 -alkyl or poly-(C.sub.1-4 -alkylene) ether, and R.sup.2 and R.sup.4 are independently each ##STR6## C.sub.1-4 -alkyl, C.sub.1-4 -alkylacrylic ester, C.sub.1-4 -alkylmethacrylic ester or poly-(C.sub.1-4 -alkylene) ether, effective to improve the weathering resistance of the pigment.
A process for preparing pearlescent pigments having improved weathering resistance and based on mica flakes coated with at least one metal oxide layer, comprising treating the coated mica flake pigment at a substantially constant pH in aqueous suspension with an aqueous solution of a siloxane and an aqueous solution of a rare earth metal salt whereby the pigment is topcoated with a layer of polysiloxane and of the rare earth compound, and, thereafter, separating the pigment, washing it and drying it.
Dependencies are inferred from the claim text.