Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Patent
1998-04-17
2000-10-17
Hess, Bruce H.
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
428403, 106415, B32B 702
Patent
active
061328731
DESCRIPTION:
BRIEF SUMMARY
The invention relates to multilayer interference pigments consisting of a transparent carrier material coated with alternating layers of metal oxides of low and high refractive index.
Multilayer interference pigments with alternating layers of materials of high and low refractive index are known. They differ in respect of the carrier material and of the material for the individual layers, and in the preparation process. The layers are prepared either by precipitation in a wet process or by vapour deposition or sputtering under vacuum. The layers applied to the carrier or to a release layer are all optically active and contribute to the development of the interference colours. The carrier materials are optically active only in exceptional cases.
U.S. Pat. No. 4,434,010 describes a multilayer interference pigment consisting of a central layer of a reflective material (aluminium) and alternating layers of two transparent, dielectric materials of high and low refractive index, for example titanium dioxide and silicon dioxide, on both sides of the central aluminium layer. This pigment is used for the printing of securities.
JP H7-759 (Kokoku) describes a multilayer interference pigment with a metallic lustre. It consists of a substrate coated with alternating layers of titanium dioxide and silicon dioxide. The substrate is formed from aluminium, gold or silver flakes or flakes of mica and glass coated with metals.
JP H7-246 366 describes a multilayer interference pigment with alternating layers of a material of high refractive index and a material of low refractive index. The substrate used is glass and, for the coating, silicon dioxide and titanium dioxide. The individual layers possess an optical thickness which is an integral multiple of a quarter of the wavelength at which interference is expected. This results, for the titanium dioxide layers, in a layer thickness of 44.4 nm at a refractive index of 2.7 and, for the silicon dioxide layers, in a layer thickness of 80 nm at a refractive index of 1.5.
In the pigments described above, the silicon dioxide layers act as optically active layers. This optically active effect begins with a layer thickness of about 20 nm. Silicon dioxide layers, however, are also employed as diffusion barriers in conductive pigments. For instance, EP 0 373 575 describes conductive platelet-form pigments consisting of a platelet-form metal oxide or of a platelet-form material coated with metal oxide, and a conductive layer, the metal oxide layer and conductive layer being separated by a silicon dioxide layer which prevents ions from the substrate or from the metal oxide layer diffusing into the conductive layer in the course of calcining; otherwise, the conductivity of the antimony-doped tin oxide layer is reduced. The thickness of the silicon dioxide interlayer is between 8 and 30 nm at concentrations of from 5 to 20% by weight of SiO.sub.2 based on the substrate.
It has surprisingly been found that the quality of customary commercial interference pigments in respect of their mechanical properties can be markedly improved if, in the metal oxide layers of high refractive index, at least one interlayer of another metal oxide is arranged which possesses no optical activity.
A feature of appropriate metal oxides is that despite their low thickness they are obtained as a layer even after the calcining of the pigment, since they do not readily form mixed phases with the surrounding metal oxides of high refractive index. Moreover, they have a markedly lower refractive index than the metal oxides which form the optical layer.
The invention therefore provides multilayer interference pigments consisting of a carrier material coated with alternating layers of metal oxides of high and low refractive index, the layer(s) of the metal oxide of low refractive index being optically inactive.
The invention additionally provides a process for preparing the novel pigments, in which the transparent carrier material is suspended in water and coated in alternation with a metal oxide hydrate of high refrac
REFERENCES:
patent: 4867793 (1989-09-01), Franz et al.
patent: 5302199 (1994-04-01), Prengel et al.
patent: 5350448 (1994-09-01), Dietz et al.
patent: 5958125 (1999-09-01), Schmid et al.
Ambrosius Klaus
Dietz Johann
Parusel Manfred
Schilling Matthias
Grendzynski Michael E.
Hess Bruce H.
Merck Patent Gesellschaft mit beschrankter Haftung
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