Compositions – Organic luminescent material containing compositions
Reexamination Certificate
2000-11-17
2003-06-03
Koslow, C. Melissa (Department: 1755)
Compositions
Organic luminescent material containing compositions
C252S30140R, C252S30140H, C252S30140F, C252S30140P, C252S30140S, C252S301500, C252S30160R, C252S30160S, C252S30160F, C252S30160P, C252S700000, C428S690000, C428S403000, C428S407000, C106S415000, C106S417000, C106S403000, C106S404000, C427S157000, C427S202000, C427S201000, C427S204000, C427S205000, C427S220000, C427S214000, C427S215000, C427S218000, C427S219000
Reexamination Certificate
active
06572784
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to luminescent color-shifting pigments and foils. More particularly, the present invention relates to multilayer color-shifting pigment flakes and foils which have luminescent materials incorporated therein.
2. Background Technology
Various color-shifting pigments, colorants, and foils have been developed for a wide variety of applications. For example, color-shifting pigments have been used in applications such as cosmetics, inks, coating materials, ornaments, ceramics, automobile paints, anti-counterfeiting hot stamps and anti-counterfeiting inks for security documents and currency. Such pigments, colorants, and foils exhibit the property of changing color upon variation of the angle of incident light, or as the viewing angle of the observer is shifted.
The color-shifting properties of the pigments and foils can be controlled through proper design of the optical thin films or orientation of the molecular species used to form the flake or foil coating structure. Desired effects can be achieved through the variation of parameters such as thickness of the layers forming the flakes and foils and the index of refraction of each layer. The changes in perceived color which occur for different viewing angles or angles of incident light are a result of a combination of selective absorption of the materials comprising the layers and wavelength dependent interference effects. The interference effects, which arise from the superposition of light waves that have undergone multiple reflections, are responsible for the shifts in color perceived with different angles. The reflection maxima changes in position and intensity, as the viewing angle changes, due to the absorption characteristics of a material which are selectively enhanced at particular wavelengths from the interference phenomena.
Various approaches have been used to achieve such color-shifting effects. For example, small multilayer flakes, typically composed of multiple layers of thin films, are dispersed throughout a medium such as paint or ink that may then be subsequently applied to the surface of an object. Such flakes may optionally be overcoated to achieve desired colors and optical effects. Another approach is to encapsulate small metallic or silicatic substrates with varying layers and then disperse the encapsulated substrates throughout a medium such as paint or ink. Additionally, foils composed of multiple layers of thin films on a substrate material have been made.
One manner of producing a multilayer thin film structure is by forming it on a flexible web material with a release layer thereon. The various layers are deposited on the web by methods well known in the art of forming thin coating structures, such as PVD, sputtering, or the like. The multilayer thin film structure is then removed from the web material as thin film color-shifting flakes, which can be added to a polymeric medium such as various pigment vehicles for use as an ink or paint. In addition to the color-shifting flakes, additives can be added to the inks or paints to obtain desired color-shifting results.
Color-shifting pigments or foils are formed from a multilayer thin film structure that includes the same basic layers. These include an absorber layer(s), a dielectric layer(s), and optionally a reflector layer, in varying layer orders. The coatings can be formed to have a symmetrical multilayer thin film structure, such as:
absorber/dielectric /reflector/dielectric/absorber; or
absorber/dielectric/absorber.
Coatings can also be formed to have an asymmetrical multilayer thin film structure, such as:
absorber/dielectric/reflector.
For example, U.S. Pat. No. 5,135,812 to Phillips et al., which is incorporated by reference herein, discloses color-shifting thin film flakes having several different configurations of layers such as transparent dielectric and semi-transparent metallic layered stacks. In U.S. Pat. No. 5,278,590 to Phillips et al., which is incorporated by reference herein, a symmetric three layer optical interference coating is disclosed which comprises first and second partially transmitting absorber layers which have essentially the same material and thickness, and a dielectric spacer layer located between the first and second absorber layers.
Color-shifting platelets for use in paints are disclosed in U.S. Pat. No. 5,571,624 to Phillips et al., which is incorporated by reference herein. These platelets are formed from a symmetrical multilayer thin film structure in which a first semi-opaque layer such as chromium is formed on a substrate, with a first dielectric layer formed on the first semi-opaque layer. An opaque reflecting metal layer such as aluminum is formed on the first dielectric layer, followed by a second dielectric layer of the same material and thickness as the first dielectric layer. A second semi-opaque layer of the same material and thickness as the first semi-opaque layer is formed on the second dielectric layer.
As discussed above, there are a wide variety of thin film devices produced today, including many that are used as security devices. Although color-shifting pigments and foils provide properties that make them extremely useful as components of security devices, it is desirable to seek additional levels of security by adding additional features.
In European patent application publication EP 0927749A1 to Bleikolm et al. (hereafter “Bleikolm”) multilayered thin films for security and anti-counterfeiting uses are disclosed. Two or more thin layers are deposited in a film, which is subsequently ground into thin film particles. These particles can be mixed into a coating material or incorporated into a bulk material and are optionally luminescent. Both the sequence of layers and their thicknesses can be used to analyze and identify the particles. Bleikolm further discloses the use of the multilayer thin film structure as a tag. Further, the thin film particles can be used in a mixture with color-shifting pigments to provide an ink with increased properties. Nevertheless, the thin film particles do not themselves have color-shifting properties.
European Patent Application Publication EP 0927750A1 to Rozumek et al. (hereafter “Rozumek”) discloses the use of two distinct inorganic chemicals incorporated into particles in a predefined and analytical ratio. The particles can be mixed into a coating material or incorporated into a bulk material. The particles provide both spatial and chemical information for security and anti-counterfeiting applications based on the material of the particles and their physical location in an ink as applied to a surface. In one embodiment, one or both of the particles are luminescent.
Unfortunately, the performance of prior color-shifting/luminescent inks has several drawbacks. For example, when color-shifting flakes are combined with luminescent particles, separation tends to occur. The color-shifting flakes and luminescent particles also tend to be incompatible with the same ink or coating vehicle, making them difficult to use together. Further, the luminescent particles tend to opacify and dull the color performance of the color-shifting flakes.
Additionally, the simple physical mixing of separate color-shifting and luminescent species does not allow for control of the re-emitted spectrum at differing angles since there is no way to control the optical path within simple physical mixtures. Finally, in the current state of the art, forming a thin film interference coating structure that employs a luminescent material as the dielectric is impractical because the stoichiometry of inorganic luminescent materials is very important and their production usually requires processing at temperatures higher than standard coating temperatures.
Accordingly, there is a need for improved coating structures and methods that avoid the above difficulties in forming luminescent color-shifting compositions.
SUMMARY AND OBJECTS OF THE INVENTION
It is an object of the present invention to provide pigments and foils
Bradley, Jr. Richard A.
Coombs Paul G.
Lantman Christopher W.
Mayer Thomas
Phillips Roger W.
Flex Products, Inc.
Koslow C. Melissa
Workman & Nydegger & Seeley
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