Electrically conductive, colored interference pigments
The present invention relates to electrically conductive, colored interference pigments, in particular flake-form interference pigments, which have an outermost layer which comprises crystalline carbon in the form of graphite and/or graphene, to a process for the preparation of such pigments, and to the use of the pigments prepared in this way.
1. Electrically conductive, coloured interference pigments comprising a flake-form support and a plurality of layers on said support,
wherein said support is natural or synthetic mica flakes or SiO 2 flakes,
wherein the support has a coating comprising one or more layers and
wherein the outermost layer on the support consists of at least 95% by weight, based on the weight of this layer, of carbon and comprises crystalline carbon in the form of graphite and/or graphene,
wherein said outermost layer surrounds the layer(s) located beneath this outermost layer on the support flake and has a geometrical thickness in the range of 1-5 nm, wherein the interference pigments comprise between the substrate flake and said outermost layer, a layer of titanium dioxide and/or titanium dioxide hydrate or at least a three-layer system of TiO 2 -layer/SiO 2 -layer/TiO 2 -layer,
wherein the geometrical thickness of at least one TiO 2 -layer is greater than 70 nm, and wherein the electrically conductive interference pigments have a specific powder resistance of less than 1×10 6 ohm*cm.
2. Interference pigments of claim 1 , wherein the outermost, crystalline carbon-containing layer consists of at least 98% by weight of carbon.
3. Interference pigments of claim 1 , wherein the proportion of the outermost, crystalline carbon-containing layer, based on the weight of the pigment, is 0.5 to 5% by weight.
4. Interference pigments of claim 1 , wherein the interference pigments have a particle size in the range from 1 to 250 μm, and wherein interference pigments having a particle size of less than 10 μm are present with a percentage proportion by volume of at most 30% in a pigment powder consisting of the interference pigments.
5. Interference pigments of claim 1 , wherein the specific powder resistance is less than 1×10 4 ohm*cm.
6. A process for the preparation of electrically conductive, coloured interference pigments of claim 1 , comprising
coating flake-form support particles comprising natural or synthetic mica or of SiO 2 -flakes, which are optionally coated with one or more layers, said one or more layers comprising a layer of titanium dioxide and/or titanium dioxide hydrate, or an at least three-layer-system of TiO 2 -layer/SiO 2 -layer/TiO 2 -layer,
with an outermost layer which consists of at least 95% by weight, based on the weight of this layer, of carbon and comprises crystalline carbon in the form of graphite and/or graphene, said outermost layer having a geometrical thickness in the range from 1 to 5 nm,
in a reactor in a stream of carrier gas with feed of a gaseous, carbon-containing compound by pyrolytic decomposition of the carbon-containing compound at a temperature in the range of from 500° C. to 700° C., wherein the carbon-containing compound employed is acetone or 2-methyl-3-butyn-2-ol and
wherein the electrically conductive interference pigments have a specific powder resistance of less than 1×10 6 ohm·cm.
7. The process of claim 6 , wherein the flake-form support particles are kept in motion in the reactor.
8. Paints, coatings, printing inks, coating compositions, security applications, plastics, ceramic materials, glasses, paper, films, in heat protection, in floorcoverings, for laser marking, in dry preparations or pigment preparations containing an electrically conductive, coloured interference pigment of claim 1 .