Printed matter – Having revealable concealed information – fraud preventer or... – Utilizing electromagnetic radiation
Reexamination Certificate
1999-08-13
2001-05-22
Fridie, Jr., Willmon (Department: 3722)
Printed matter
Having revealable concealed information, fraud preventer or...
Utilizing electromagnetic radiation
C283S091000
Reexamination Certificate
active
06234537
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to security documents, such as monetary, security or value related documents, wherein the dyes are applied to or embedded in the security document.
2. Description of the Related Art
The invention is based on a technology similar to that described, for example, in U.S. Pat. No. 4,738,901. In this references, a document has phosphor particles embedded therein as protection against copying. Copy protection is enabled, because the laser associated with the copier excites the phosphor particles and the radiation emitted by the phosphor particles is received by a second detector which indicates to the copier that the documents are protected. However, this copy protection process cannot check the authenticity of a security and sensitive document.
SUMMARY OF THE INVENTION
The present invention is based on the fact that certain optically excitable dyes are incorporated in such a way that upon optical excitation of the security documents, the dyes embedded in the security document resonate with the material of the security document and thereby emit a well-defined sharp spectrum of all the excited materials.
It is an object of the present invention to provide an authenticity check of a security document with optically excitable dyes, wherein a predetermined emission spectrum of the optically excited monetary and security document can be captured and a characteristic spectrum for the monetary and security document can thereby be generated, which is characteristic of the dye embedded in the security document as well as for the material of the security documents itself.
This object is accomplished in that the dyes are embedded in a carrier material and in conjunction with the carrier material form a laser-active element.
Accordingly, a resonance is produced between the material of the security document and the dyes embedded therein, which results in a well-defined emission spectrum which depends, on one hand, on the material of the documents and, on the other hand, on the embedded dyes.
Specially developed laser dyes having preferably non-commercial excitation wavelengths (UV to IR) can be integrated with the securities and the sensitive products in different ways. In principle, the laser dyes can be incorporated in the substrate (for example, paper, plastic foils), into paper additives (for example, fibers, planchets), into printing ink and depending on the fabrication techniques, combined with other security features (for example, fluorescence, electroluminescence, up-conversion and phosphorescence pigments, metallized plastic strips, holograms). For example, depending on the application, a suitable UV-absorbing protective jacket is required before liquid dye molecules can be incorporated in a solid matrix (granulate material having a size in the &mgr;m to nm region), especially to protect the dyes from UV light, solvents, or other reagents. It may also be possible to incorporate the laser dyes directly in a coloring component (resins or pigments). In applications using cards and foils, the un-encapsulated or encapsulated dyes can be mixed directly into and affixed to the polymer matrix. Laser dye is referred to a fluorescent material with a high efficiency which can be excited by a laser beam, in any physical form, i.e., solid, liquid or gaseous.
Laser dyes have an advantage over fluorescent materials in that they produce sharp emission peaks with well-defined emission wavelengths across the entire fluorescence range of the laser dyes. According to the invention, the “sharp emission peaks can only be realized if the laser-excitable fluorescent materials are embedded in an optical resonator. Resonant excitation is required for producing the sharp emission peaks which are characteristic for the geometry as well as for the optical properties of the resonator and the fluorescent materials.
The laser dyes may not only be incorporated in a resonator, but may also be used without a resonator, in which case the emission intensities of the securities and secure documents may be reduced.
That emission intensity may be increased by inserting the laser dyes in a resonator. This requires that both sides of the polymer layers of the laser dyes are coated with metallic or dielectric layers having a greater index of refraction. This increases both the radiated intensity and the security, because the number of peaks and their respective position in the wavelengths range of the fluorescence can be adjusted through the geometry and the optical properties of the resonator. The width of the peaks can also be adjusted by changing the geometry.
According to a first embodiment, the dyes are introduced directly into a physical layer or printed layer of the securities and secure documents, wherein the reflecting and/or dielectric layers represent portions of the securities and secure documents. In this way, a laser-active element, i.e., a resonator, is formed which reacts in a unique fashion to excitation with laser light or another high-energy light source.
According to another embodiment, the laser-active element is not a part of the layer structure of the securities and secure documents. Instead, the laser active elements are produced separately from the security document in form of independent resonators and are only subsequently incorporated in or applied to the documents in form of pigments plates or spheres (generally called particles) having a diameter of, for example, several &mgr;m.
Such resonators for application in printed security products can be manufactured, for example, with thin film technology. After depositing the individual layers, i.e., at least one reflecting layer, one layer containing dyes and another reflecting layer, having a thickness in the &mgr;m range on a foil support, the composite layer is broken up into smaller pieces. The two-dimensional fragments, which are commonly called flakes or pigment platelets and have a thickness of 1-10 &mgr;m and a surface area<20×20 &mgr;m
2
, can then be integrated according to their size in the respective printing inks (for example, inks for steel engraving, screen printing, offset, book printing) or in the paper and foil material of the security document.
Different resonators with different geometry produce a characteristic peak pattern (fingerprint) of the “mixture” which is difficult to duplicate. Aside from the non-commercial excitation wavelengths, the threshold energy (minimum energy for the excitation of a laser emission) can also be used as an additional security parameter for authenticating such security features. Laser dyes can be applied as a hidden or two-stage security feature that can be controlled with UV light, since all laser dyes exhibit a broad band UV fluorescence, as mentioned above.
In the following sections, the possibilities for incorporating laser dyes in different sections of securities and sensitive products will be described.
Base Material (Paper, Plastic Foils)
Polymer-bound laser dyes can be incorporated in the paper by either adding bound dyes directly to the mixture of raw material or by applying the dyes by screen printing after the paper has dried. The direct addition is economically disadvantageous, since large quantities have to be added to produce a sufficiently strong light emission intensity. A much smaller quantity is required when the laser dyes are applied to the paper later by screen printing. In addition, a watermark may also be formed. By using transparent, colorless laser dyes, “hidden watermarks” can be embedded in the paper. Hidden watermarks in color can be produced by using different laser dyes.
Unlike paper, where laser dyes can be directly embedded in or applied to the paper, in the case of card stock, a very thin plastic foil can be “doped” or imprinted with the laser dyes. By using a specific card structure, the foil that includes the laser dyes can be incorporated in the center portion of the laminate. In this way, the dyes are chemically and physically protected from the environment, such as UV light,
Ahlers Benedikt
Franz-Burgholz Arnim
Gutmann Roland
Kappe Frank
Paugstadt Ralf
Bundesdruckerei GmbH
Darby & Darby
Fridie Jr. Willmon
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