Stock material or miscellaneous articles – Article having latent image or transformation
Reexamination Certificate
2001-03-02
2003-11-04
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Article having latent image or transformation
C428S001100, C428S001310, C428S199000, C359S493010, C359S490020, C252S299010, C252S582000
Reexamination Certificate
active
06641874
ABSTRACT:
The invention relates to multilayer reflective films and pigments showing selective reflection of light wherein the reflection characteristics are dependent on the viewing angle. The invention further relates to the use of these multilayer reflective films and pigments in optical elements, as coatings or in lacquers, inks or paints for cosmetic, decorative or security applications. The invention also relates to inks and paints comprising one or more multilayer reflective pigments dispersed in a light transmissive binder, and to security markings or devices comprising one or more multilayer reflective films or pigments.
Reflective pigments, films or coatings showing viewing angle dependent reflection of light are known in prior art. For example, platelet shaped multilayer interference pigments are known, e.g. from DE 19618563, DE 19618569 and DE 197 46 067, that consist of a platelet shaped substrate, e.g. mica, onto which are coated one or more refractive layers e.g. of metal oxide, and that show iridescent reflection colors that are changing with varying viewing angle.
Furthermore, holographic films of platelet shaped pigments are known, e.g. from EP 0 728 329, which comprise a structured reflecting surface leading to interference effects of incident light reflected by the lower and higher regions of the structured surface. The interference colors are also depending on the viewing angle.
The above described angle dependent color effects can be exploited in various applications, such as inks or lacquers for decorative use like e.g. for car bodies, or security uses like non-forgeable markings on banknotes or documents of value.
The reflective layers, pigments and coatings of prior art do have several drawbacks. Thus, they often show low chemical stability and do not stand the banknote test. Furthermore, they cannot be coupled or combined with security products, like for instance holograms, kinegrams etc. However, such a combination is strongly desirable, since a combination of two security devices would increase security, according to experiences from the security market. As a consequence, the existing films, coatings and pigments have only limited value for security applications.
It was an aim of the present invention to provide reflective films and pigments that do not show the drawbacks of prior art films and pigments as mentioned above. Another aim of the present invention was to provide methods of manufacturing such films and pigments that are especially suitable for mass production. Other aims of the present invention are immediately obvious to the expert from the following description.
The inventors have found that particularly striking viewing angle dependent color effects can be achieved by providing a multilayer pigment, film or coating according to the present invention, which comprises a reflective layer, e.g. a metal layer, covered on one or both sides with a circular polarizing layer. The color effect can be further enhanced by inserting an optical retardation layer between the reflective layer and the circular polarizing layer, leading to a shift of the reflected wavelength. Thereby, a larger color change and a shift of the reflection colors are achieved.
One embodiment of the invention is a multilayer reflective film or multilayer reflective pigment showing selective reflection of light, wherein the reflection characteristics, in particular the central wavelength of reflection, are dependent on the viewing angle, characterized in that it comprises at least one reflective layer, at least one circular polarizing layer and optionally at least one optical retardation layer. The polarizing layer and optical retardation layer can be present on the reflective layer in any order.
Another embodiment of the invention are platelet shaped pigments obtainable by grinding an inventive multilayer reflective film.
Another embodiment of the invention is the use of inventive multilayer reflective films and pigments in optical elements, as coatings or in lacquers, inks or paints for cosmetic, decorative or security applications.
Another embodiment of the invention is an ink, lacquer or paint comprising one or more inventive multilayer reflective pigments dispersed in a light transmissive binder.
Another embodiment of the invention is a security marking or device comprising one or more inventive multilayer reflective films or pigments.
Other embodiments of the invention will be readily apparent to those of skill in the art.
The term ‘film’ as used in this application includes self-supporting, i.e. free-standing, films that show more or less pronounced mechanical stability and flexibility, as well as coatings or layers on a supporting substrate or between two substrates.
The term ‘liquid crystal or mesogenic material’ or ‘liquid crystal or mesogenic compound’ denotes materials or compounds comprising one or more rod-shaped, board-shaped or disk-shaped mesogenic groups, i.e. groups with the ability to induce liquid crystal phase behavior. The compounds or materials comprising mesogenic groups do not necessarily have to exhibit a liquid crystal phase themselves. It is also possible that they show liquid crystal phase behavior only in mixtures with other compounds, or when the mesogenic compounds or materials, or the mixtures thereof, are polymerized.
Suitable binder systems are, e.g., polyesters, alkyd resins, polyurethanes, (meth)acrylate copolymers and resins based on cellulose esters, which may also be dissolved or dispersed in an organic solvent. Alternatively, water soluble binders may also be used, e.g., water soluble polymers selected from polyesters, poly(meth)acrylates and polyurethanes. It is also possible to cover the coating comprising the interference pigments and the transparent binder by a second coating as a clear coating. Suitable methods and components are disclosed in WO 97/27252.
Preferred embodiments of the invention include
a multilayer film or pigment comprising one or more circular polarizing layers and optionally one or more optical retardation layers coated on a reflective substrate,
a multilayer reflective film or pigment wherein the circular polarizing layer comprises a linear polarizer and a quarter wave retardation layer,
a multilayer reflective film or pigment wherein the circular polarizing layer comprises a linear polarizer and a quarter wave retardation layer, and wherein the linear polarizer and/or the quarter wave retardation layer comprise a vitrifed, polymerized or crosslinked liquid crystal material with uniform orientation,
a multilayer reflective film or pigment wherein the circular polarizing layer comprises a linear polarizer and a quarter wave retardation layer, and wherein the quarter wave retardation layer is a stretched or compressed film of isotropic polymer,
a multilayer reflective film or pigment comprising at least one reflective layer, at least one circular polarizing layer and at least one optical retardation layer, wherein said optical retardation layer is a quarter wave retardation layer,
a multilayer reflective film or pigment comprising one central reflective layer, and further comprising one or more circular polarizing layers and one or more optical retardation layers on each side of the reflective layer, wherein the circular polarizing layers are sandwiching the retardation layers,
a multilayer reflective film or pigment wherein the reflective layer is a metal layer,
a multilayer reflective film or pigment wherein the reflective layer is a holographic reflective layer,
a multilayer reflective pigment wherein the reflective layer is an interference pigment,
a multilayer reflective film wherein the reflective layer comprises one or more interference pigments, preferably provided in a light transmissive binder,
a multilayer reflective film-wherein the reflective layer in addition to the interference pigments additionally comprises one or more further pigments or dyes.
A first preferred embodiment of the present invention relates to a multilayer reflective film comprising a reflective film or layer that is covered with a circular
Brueckner Hans-Dieter
Coates David
Kuntz Matthias
Riddle Rodney
Jones Deborah
Koppikar Vivek
Merck Patent Gesellschaft mit beschraenkter Haftung
Millen White Zelano & Branigan P.C.
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