Precious metal color effect materials and production thereof

Details Precious metal color effect materials and production thereof Precious metal color effect materials and production thereof

1999-11-30

2001-12-04

Bell, Mark L. (Department: 1755)

Compositions: coating or plastic

Materials or ingredients

Pigment, filler, or aggregate compositions, e.g., stone,...

C106S403000, C106S415000, C106S418000, C106S419000, C106S425000, C106S436000

Reexamination Certificate

active

06325847

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 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 plasma decomposition, 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 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, aluminum and brass 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 precious metal 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 silver, gold, platinum, palladium, rhodium, ruthenium, osmium, iridium and alloys 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.
DESCRIPTION OF THE INVENTION
It is an object of the present invention to provide novel precious metal 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 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 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 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), silicon dioxide, titanium dioxide-coated mica (TCM) or any encapsulatable smooth platelet. The first and third layers can be the same or different precious metals, i.e., silver, gold, platinum, palladium, rhodium, ruthenium, osmium and/or iridium or alloys thereof.
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 precious metals used in this invention are much more chemically stable than aluminum and generally prefer to be in their non-oxidized metallic ground state. Furthermore, silver is preferred when employed as one of the reflecting layers, as it can maximize the chromaticity of the reflected color(s) of the CEM. In addition, when silver is used as the final (outer) layer of the particle, it imparts electrical conductivity to the CEM 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 color travel optical effect properties.
Metal layers are preferably deposited by electroless deposition and the non-metal layers preferably by sol-gel deposition. Surprisingly, when gold or platinum are used as the first layer of the CEM, another option for the deposition of the encapsulating metal oxide film or outside layers is from an aqueous sol-gel system. 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, a 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. Hampden-Smith; VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1994, ISBN 3-527-29071-0).
An additional surprising aspect of the present invention is the tenacity with which the low index of refraction material adheres to the precious metal surface.
The products of the present invention are useful in automotive, cosmetic, industrial or any other application where metal flake or pearlescent 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 major dimensions of about 5-250 &mgr;m, in particular 5-100 &mgr;m. Their specific free surface area (BET) is in general from 0.2 to 25 m
2
/g.
The CEMs of the invention are notable for multiple encapsulation of the platelet-shaped substrate.
The first encapsulating layer which is made of silver, gold, platinum, palladium, rhodium, ruthenium, osmium, iridium or their alloys is highly reflective to light directed thereon.
The thickness of the first 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. Depending on the metal or alloy utilized for the first encapsulating layer, the thickness may be 2 nm to 100 nm and

Affiliated with

Also associated with

Rating

Precious metal color effect materials and production thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Precious metal color effect materials and production thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Precious metal color effect materials and production thereof will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2576357