Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-11-06
2002-08-27
Wood, Elizabeth D. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S403000, C106S404000, C106S417000, C106S419000, C106S431000, C106S440000, C106S461000, C106S480000, C106S481000, C106S482000
Reexamination Certificate
active
06440208
ABSTRACT:
BACKGROUND OF THE INVENTION
Optically variable pigments have been described in the patent literature since the 1960s. Hanke in U.S. Pat. No. 3,438,796 describes the pigment as being “thin, adherent, translucent, light transmitting films or layers of metallic aluminum, each separated by a thin, translucent film of silica, which are successively deposited under controlled conditions in controlled, selective thicknesses on central aluminum film or substrate”. These materials are recognized as providing unique color travel and optical color effects.
The prior art approaches to optically variable pigments have generally adopted one of two techniques. In the first, a stack of layers is provided on a temporary substrate which is often a flexible web. The layers are generally made up of aluminum and MgF
2
. The stack of film is separated from the substrate and subdivided through powder processing into appropriately dimensioned particles. The pigments are produced by physical techniques such as physical vapor deposition onto the substrate, separation from the substrate and subsequent comminution. In the pigments obtained in this way, the central layer and all other layers in the stack are not completely enclosed by the other layers. The layered structure is visible at the faces formed by the process of comminution.
In the other approach, a platelet shaped opaque metallic substrate is coated or encapsulated with successive layers of selectively absorbing metal oxides and non-selectively absorbing layers of carbon, metal and/or metal oxide. To obtain satisfactory materials using this approach, the layers are typically applied by chemical vapor deposition techniques in a fluidized bed. A major shortcoming of this technique is that fluidized bed processes are cumbersome and require substantial technical infrastructure for production. An additional limitation related to the substrates utilized is that traditional metal flakes usually have structural integrity problems, hydrogen outgassing problems and other pyrophoric concerns.
The prior art approaches suffer from additional disadvantages. For instance, certain metals or metal flake such as chromium and aluminum, specifically when they are used as outer layers may have perceived health and environmental impacts associated with their use. The minimization of their use in optical effect materials should be advantageous due to their perceived impact.
SUMMARY OF THE INVENTION
The present invention provides a color effect material comprising a platelet-shaped substrate encapsulated with (a) a first layer selected from the group consisting of copper, zinc, an alloy of copper, and an alloy of zinc, wherein said first layer is highly reflective to light directed thereon; and (b) a second layer encapsulating the first layer and providing a variable pathlength for light dependent on the angle of incidence of light impinging thereon in accordance with Snell's Law; and (c) a selectively transparent third layer to light directed thereon.
DESCRIPTION OF THE INVENTION
It is an object of the present invention to provide novel color effect materials (CEMs) which can also be prepared in a reliable, reproducible and technically efficient manner. This object is achieved by a CEM comprising a platelet-shaped substrate coated with: (a) a first layer of copper, zinc, an alloy of copper, or an alloy of zinc which is highly reflective to light directed thereon; and (b) a second layer encapsulating the first layer in which the second layer consists of a low index of refraction material, typically a refractive index from 1.3 to 2.5 and more specifically between 1.4 and 2.0, that provides a variable path length for light dependent on the angle of incidence of light impinging thereon; and (c) a selectively transparent third layer to light directed thereon.
The degree of reflectivity for the first encapsulating layer should be from 100% to 5% reflectivity, whereas the selective transparency of the third encapsulating layer should be from 5% to 95% transmission. More specifically, one would prefer to have 50-100% reflectivity and 50-95% transparency for the first and third encapsulating layers, respectively. The degree of reflectivity and transparency for different layers can be determined by a variety of methods such as ASTM method E1347-97, E1348-90 (1996) or F1252-89 (1996).
The substrate can be mica, aluminum oxide, bismuth oxychloride, boron nitride, glass flake, iron oxide-coated mica (ICM), silicon dioxide, titanium dioxide-coated mica (TCM), copper flake, zinc flake, alloy of copper flake, alloy of zinc flake, or any encapsulatable smooth platelet. The first layer encapsulating the substrate can be copper, zinc, an alloy of copper or an alloy of zinc. Of course, when the substrate is copper flake, zinc flake, alloy of copper flake or alloy of zinc flake, there is no need for such a first layer since it would be part of the substrate. The second encapsulating layer can be silicon dioxide or magnesium fluoride. The third encapsulating layer can be a precious metal, i.e., silver, gold, platinum, palladium, rhodium, ruthenium, osmium and/or iridium or alloys thereof. Alternatively, the third layer can be copper, silicon, titanium dioxide, iron oxide, chromium oxide, a mixed metal oxide, aluminum, and zinc.
An advantage of the present invention is that one does not have to start with a traditional metal flake which may have structural integrity problems, hydrogen outgassing problems and a host of other perceived issues (pyrophoric and environmental concerns) typically associated with metal flakes. The brass alloy used in this invention is much more chemically stable than aluminum and is known to have long term weatherability stability. Brass is nearly chemically inert which allows great flexibility in the chemical systems employed in the manufacture of such effect materials and in their applications in end uses such as in paint and polymer systems. Another advantage over the prior art is that brass, as one of the reflecting layers used in this invention, is a good reflector of white light and at the same time provides an attractive bulk color. The same would be true for an aluminum-copper alloy. Such an alloy is advantageous due to its attractive bulk color effect, while maintaining high reflectivity. Additionally, both brass and copper coated substrates provide the decorative/functional attributes of brass and copper, however under more environmentally favorable terms due to the reduced metal concentration since the CEM's of the present invention are not pure brass or copper, rather brass or copper coated inorganic substrates. In addition, one can produce the CEM's where the outer encapsulating layers are not made of brass. Another advantage over the prior art is that silver, or other metals such as gold, platinum, palladium, rhodium, ruthenium, osmium and iridium, as the final (outer) encapsulating layer of the effect material will impart electrical conductivity to the pigment which may be desirable in some applications such as powder coatings.
A surprising aspect of the present invention is that cost effective composite materials are created with desirable optical effect properties.
Metal layers are preferably deposited by electroless deposition and the non-metal layers preferably by sol-gel deposition. An advantage of electroless deposition (Egypt. J. Anal. Chem., Vol. 3, 118-123 (1994)) is that it is a world wide established chemical technique, not requiring cumbersome and expensive infrastructure compared to other techniques. The electroless deposition technique also allows one to control the degree of reflectivity of light quite accurately and easily by varying the metal film thickness. Additionally, the known procedures are generalized procedures capable of being utilized for coating a variety of surfaces. Furthermore, an encapsulating layer of a metal or metal oxide can also be deposited onto any of the substrates by chemical vapor deposition from an appropriate precursor (The Chemistry of Metal CVD, edited by Toivo T. Kodas and Mark J. Hampde
Christie James D.
Fuller Daniel S.
Zimmermann Curtis J.
Dickstein , Shapiro, Morin & Oshinsky, LLP
Engelhard Corporation
Wood Elizabeth D.
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