Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-09-26
2002-11-05
Wood, Elizabeth D. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S436000, C106S453000, C106S456000
Reexamination Certificate
active
06475273
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 decorative optical color effects.
The recent 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, chromium, magnesium fluoride and silicon dioxide. The stack of film is separated from the substrate and subdivided into appropriately dimensioned flakes. The pigments are produced by physical techniques such as physical vapor deposition onto the substrate, separation from the substrate and subsequent comminution or by other. deposition techniques (plasma, sputtering etc.), subsequent deflaking of the decomposition product, etc. 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 sulfide, metal and/or metal oxide. To obtain satisfactory materials using this approach, the layers are applied by multiple techniques such as chemical vapor deposition and/or sol-gel processes. A major shortcoming of this 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, aluminum, copper, brass and bronze 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 (CEM) comprising a platelet-shaped substrate encapsulated with:(a) a highly reflective first layer to light directed thereon and being selected from the group consisting of silicon, aluminum, titanium nitride and mixtures thereof; 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. CEM's provide optically variable pigment attributes as well as additional non-decorative effects such as conductivity, EMI/RFI shielding and/or desirable tactile properties.
DESCRIPTION OF THE INVENTION
It is an object of the present invention to provide novel CEM's which can also be prepared in a reliable and reproducible manner. This object is achieved by a CEM comprising a platelet-shaped substrate encapsulated with:(a) a highly reflective first layer 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 selective 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 measuring 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), iron oxide coated glass flake, silicon dioxide and titanium dioxide-coated mica, titanium dioxide coated glass flake (TCM), variations of the above-mentioned substrate, or any encapsulatable smooth platelet. The first and third layers can be the same or different materials, i.e., aluminum, silicon, titanium nitride or mixtures thereof.
Preferably, all the layers are deposited onto any particulate substrate by chemical vapor deposition (CVD) from an appropriate precursor (The Chemistry of Metal CVD, edited by Toivo T. Kodas and Mark J. Hampden-Smith; VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1994, ISBN 3-527-29071-0). In this case, there is a particular advantage over the prior art in that the products of the present invention can be produced in a reactor without having to be removed during stages of the preparation for additional processing. The CVD reactor can handle the coating of all the layers, calcining, and exterior treatments without the powder substrate being removed from the reactor until completion. No additional processing or communition of the material is necessary for obtaining the desired final particle size and/or effect product.
The products of the present invention are useful in automotive, cosmetic, industrial or any other application where metal flake, pearlescent pigments, or optically variable pigments are traditionally used.
The size of the platelet-shaped substrate is not critical per se and can be adapted to the particular use. In general, the particles have average largest diameters of about 2-250 &mgr;m, in particular 5-100 &mgr;m. Their specific free surface area (BET) is in general from 0.1 to 25 m
2
/g.
The CEM's of the invention are notable for multiple encapsulation of the platelet-shaped substrate.
The first encapsulating layer which is made of the group consisting of silicon, aluminum and titanium nitride, or their mixtures is highly reflective to light directed thereon.
The thickness of the first encapsulating layer is not critical so long as it is sufficient to make the layer highly reflective. If desirable, the thickness of the first layer can be varied to allow for selective transmission of light. When silicon is selected as the component of the first layer, the thickness must be at least about 20-100 nm, preferably from about 30 to 75 nm. However, when aluminum is used, the thickness must be at least about 10-90 nm, preferably from about 20 to 65 nm. The thickness of titanium nitride as the first layer must be at least about 15-95 nm, preferably from about 15 to 60 nm. A thickness outside of the above-mentioned ranges can also be utilized depending on the desired effect. The quantity of the coating will be directly related to the surface area of the particular substrate being utilized.
The second encapsulating layer must provide a variable pathlength for light dependent on the angle of incidence of light impinging thereon and therefore, any low index of refraction material that is visibly transparent may be utilized. Preferably, the second layer is selected from the group consisting of silicon dioxide (SiO
2
), suboxides of silicon dioxide (SiO
0.25
to SiO
1.95
) or magnesium fluoride.
The thickness of the second encapsulating layer varies depending on the degree of color travel desired. In addition, the second encapsulating layer will have a variable thickness depending on a variety of factors, especially refractive index. Materials having a refractive index around 1.5 tend to require a film thickness of a few hundred nanometers for generation of unique extensive color travel. For instance, a sec
Doxey Vivian K.
Fuller Daniel S.
Zimmermann Curtis J.
Dickstein, Shapiro, Morin & Oshinsky L.L.P.
Engelhard Corporation
Wood Elizabeth D.
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