Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-08-02
2003-12-02
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S430000, C106S431000, C106S435000, C106S436000, C106S426000, C106S446000
Reexamination Certificate
active
06656259
ABSTRACT:
The invention relates to multilayered interference pigments which comprise a platelet-shaped substrate of silicon dioxide which is coated alternately with layers of light-transparent materials having refractive indices of n>1.8 and layers of light-transparent materials having refractive indices of n≦1.8, where the optical thickness of the platelet-shaped substrate and the optical thickness of the individual layers of light-transparent materials having refractive indices of n≦1.8 are the same, and to a process for the preparation of these pigments and to their use.
The use of luster or effect pigments which exhibit interference phenomena is widespread. In automobile paints, decorative coatings of all types and in the coloring of plastics, paints and printing inks, in particular inks for security printing, and in applications in decorative cosmetics, pigments of this type have become indispensable.
In the matrix surrounding them, these pigments ideally line up parallel to the surface of the coating and develop their optical action through a complex interaction of interference, reflection and absorption of the incident light. Bright coloring, changing between various colors depending on the viewing angle, so-called color flops, or varying brightness impressions are of central interest for the various applications.
Pigments of this type are generally prepared by coating platelet-shaped metallic or non-metallic substrates with metal oxide or metal layers. Recent years have seen increased development of pigments which have a multilayered structure on the platelet-shaped support. This enables, in particular, color flops in which the human eye perceives different hues depending on the viewing angle to be set specifically. Most of these pigments are based on platelet-shaped substrates of metals or synthetic or natural phyllosilicates, such as mica, talc or glass.
The phyllosilicates have, in particular, the disadvantage that the thickness of the substrate varies in a broad range and cannot be set specifically, which results, even in the case of transparent substrates, in light transmission and reflection at the substrate proceeding in a substantially uncontrollable manner and therefore not being utilizable in a specific manner.
However, interference pigments with substrates of silicon dioxide are also known. Thus, for example, DE 41 37 764 describes pigments based on silicon dioxide particles which have been coated with iron oxide, where the iron oxide proportion, based on the silicon dioxide particles, is greater than 350% by weight. Pigments of this type have good hiding power, intense hues and a color flop although they are not based on platelet-shaped substrates. The color flop here becomes more pronounced with increasing iron oxide proportion. For pigment applications in which a color flop is desired, very thick iron oxide layers therefore have to be applied. Due to the iron oxide coating, pigments prepared in this way only allow a limited range of hues and are only of limited applicability in preparations in which transparency and thin layer thicknesses are necessary. In addition, a large proportion of the incident light cannot be reflected in an optimum manner since the pigments cannot align parallel to the surface in coatings.
EP 0 608 388 discloses a platelet-shaped pigment which can consist, inter alia, of a silicon dioxide matrix which has been coated with one or more layers of thin, transparent or semi-transparent reflective layers of metal oxides or metals. The matrix here is preferably colored by addition of various colorants. Pigments of high color purity and high tinting strength whose hiding power is determined by the degree of coloring of the matrix are obtained. The thickness of the matrix here can be set in a broad range. This specification does not describe any pigments which have more than one optically active layer on the substrate. These pigments therefore have the action of a pigment having a total of three optically active layers.
DE 196 14 637 discloses goniochromatic luster pigments based on silicon dioxide platelets to which a black, at least partially transparent layer (A) and optionally an outer layer (B) which consists of a colorless or selectively absorbent metal oxide and/or contains phosphate, chromate and/or vanadate has been applied by means of a CVD process.
Layer (A) here, with a thickness of from 1 to 50 nm, preferably consists of metals and/or non-selectively absorbent metal compounds. Layer (B) can consist of high- or low-refractive-index metal oxides.
Due to the black layer (A), these pigments exhibit intense interference colors and striking hue changes depending on the viewing angle. However, metal and metal oxide layers here are applied by gas-phase decomposition of, in particular, organometallic compounds, which makes the preparation process too complex and expensive for mass production of pigments and means that it is associated with major safety precautions.
DE 196 18 569 relates to multilayered interference pigments comprising a transparent support material which is coated with alternating layers of a metal oxide of low refractive index and of a metal oxide of high refractive index.
The transparent support material here can consist of SiO
2
platelets. In one example, TiO
2
, SiO
2
and TiO
2
are applied alternately to an SiO
2
platelet, with the individual layer thicknesses being very different. In these pigments, the interference hue on perpendicular viewing and the number and hues of the colors passed through depending on the viewing angle (color flop) and the chroma (tinting strength) of the pigment only become visible when the final pigment structure has been achieved. In this case, however, color corrections are only perceptible in the outer layer. This can generally only be achieved by application of relatively thick layers, which is economically unfavorable and in extreme cases can result in the product no longer being usable for certain applications merely owing to the greater layer thicknesses.
The chroma of such pigments also varies greatly in the various colors of a color flop, i.e. the various colors are perceived with different intensity and do not have pronounced brightness.
There was therefore a demand for multilayered interference pigments which exhibit intense interference colors and strong angle dependence of the interference color, and for a simple and inexpensive preparation process by means of which the color properties of the end product are definitively determined as early as the first process step.
The object of the invention is therefore to provide further multilayered interference pigments based on silicon dioxide platelets which have a strong angle dependence of the interference colors, with all the hues passed through during a change in the viewing angle having intense chroma and excellent brightness.
A further object of the invention was to provide a process for the preparation of multilayered interference pigments in which the various interference hues to be passed through at different viewing angles can be set definitively as early as the first coating of the substrate.
An additional object of the invention was to indicate uses for the pigments according to the invention.
The object of the invention is achieved by a multilayered interference pigment which comprises a substrate of platelet-shaped silicon dioxide which is coated alternately with two or more layers of light-transparent materials having refractive indices of n>1.8 and therebetween one or more layers of light-transparent materials having refractive indices of n≦1.8, where the optical thickness of the platelet-shaped substrate and the optical thickness of the individual layers of light-transparent materials having refractive indices of n≦1.8 are substantially the same.
The object of the invention is likewise achieved by a process for the preparation of a multilayered interference pigment in which a platelet-shaped substrate of silicon dioxide is suspended in water and coated alternately a number of times with a metal oxide h
Kniess Helge
Pfaff Gerhard
Reynders Peter
Koslow C. Melissa
Manlove Shalie
Merck Patent Gesellschaft mit beschraenkter Haftung
Millen, White, Zelano & Branigan, P.C..
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