Patent No. U.S. 7,828,890 B2
Eckart has been granted a patent for effect pigments having an aluminum core or aluminum alloy core and an aluminum oxide-containing or aluminum oxide/hydroxide-containing layer enveloping the aluminum core or aluminum alloy core, obtained by chemical wet-process oxidation of lamellar aluminum pigments or aluminum alloy pigments, the content of metallic aluminum in the aluminum core or aluminum alloy core being not more than 90% by weight, based on the total weight of the pigment, characterized in that the oxidized aluminum pigments or aluminum alloy pigments exhibit at least one highly refractive metal chalcogenide layer having a refractive index of >1.95, the at least one metal chalcogenide layer being a layer of an intrinsically colored metal chalcogenide, and a mixed layer is formed between the highly refractive metal chalcogenide layer and the enveloping aluminum oxide-containing or aluminum oxide/hydroxide-containing layer, wherein the aluminum oxide-containing or aluminum oxide/hydroxide containing enveloping layer has a thickness of from 50-300 nm and wherein the effect pigments have a weak color flop having a ΔH*anchor in a range of between 1.5 and 50, and wherein the refractive index of the mixed layer between the aluminum oxide-containing or aluminum oxide/hydroxide-containing layer and the highly refractive metal chalcogenide layer exhibits a gradient perpendicularly to the pigment surface extending from the refractive index of the pure aluminum oxide/hydroxide-containing layer and the refractive index of the highly refractive metal chalcogenide layer.