Transparent goniochromatic multilayer effect pigment
A multilayer effect pigment includes a transparent substrate, a layer of high refractive index material on the substrate, and alternating layers of low refractive index and high refractive index materials on the first layer, the total number of layers being an odd number of at least three, all adjacent layers differing in refractive index by at least about 0.2 and at least one of the layers having an optical thickness which is different from all of the other layers. The resulting multilayer effect pigment is not a quarter-wave stack. The present effect pigments may be used in cosmetic and industrial applications.
1. A multilayer effect pigment comprising:
a transparent substrate having a layer of titanium dioxide thereon, the optical thickness of said layer of titanium dioxide being such as to provide a white hue to said substrate;
a layer of a low refractive index material on said titanium dioxide layer and
an outermost layer of a high refractive index material placed on said low refractive index material layer;
said outermost layer comprising a high refractive index material selected from anatase titanium dioxide, rutile titanium dioxide, iron oxide, zirconium dioxide, zinc oxide, zinc sulfide, and bismuth oxychloride, said outermost layer having a optical thickness of from about 45 to 240 nm,
said low refractive index material layer having an optical thickness of at least 150 nm to provide a variable pathlength for light dependent on the angle of incidence of light impinging thereon;
each layer differs in refractive index from any adjacent layer by at least about 0.2 and wherein at least one layer has an optical thickness which is different from all of the other layers, whereby the pigment is not a quarter-wave stack; and
said multilayer effect pigment has a non-white hue.
2. The multilayer effect pigment of claim 1 wherein said transparent substrate is glass flake.
3. The multilayer effect pigment of claim 1 in which the low refractive index material is silicon dioxide.
4. The multilayer effect pigment of claim 3 in which the optical thickness of said layer of titanium dioxide is about 105 to 155 nm.
5. The multilayer effect pigment of claim 1 in which the high refractive index material is iron oxide.
6. A paint or ink composition comprising the effect pigment of claim 1 .
7. A. plastic composition comprising the effect pigment of claim 1 .
8. A cosmetic composition comprising the effect pigment of claim 1 .