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Encoded security document
| Details |
Inventors: Weitzen, Edward H.; D'Amato, Salvatore F.; Fleming, Robert M.; Kuehnle, Manfred R.; Ekman, C. Frederick; Kruse, Jurgen; Weber, Harold J.;
Assignee: Coulter Systems Corporation (Bedford, MA)
Primary Examiner: Bell; Paul A.
Assistant Examiner:
Attorney, Agent or Firm: Silverman, Cass & Singer, Ltd.
Documents are encoded with at least one thin, transparent coating, normally invisible, but having a readily detectable physical characteristic such as, electrical conductivity, electrical impedance, electrical capacitance, electroluminescence. Each document consists of a substrate on which is applied (1) at least one of the thin coatings, and (2) conventional printing, preferably intaglio. The thin coating may be applied before or after the printing. The coating includes particles driven into the surface to a substantial depth. The uncoated substrate is free of the detectable physical characteristic. The coating is confined to a limited area of the substrate surface and itself constitutes a code or is laid down in a pattern for identification. A second coating can be applied so that all areas of the surface have the same appearance to mask visual detection of the first coating. The first coating can be of such a nature as to defeat electrostatic copying, particular, color copying, by effecting a discernible difference between the original and the copy. Each coded coating is detectable by a machine which is capable of quickly distinguishing a genuine document from a counterfeit document. |
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DETAILED DESCRIPTION Security documents of value, prepared in accordance with the present invention, are made difficult to counterfeit by placing thereon an invisible coating having a machine-detectable physical characteristic in a limited location of at least one surface of the document.
A subsurface region having the same characteristic underlies the coating.
For example, the limited location of the coating may consititute a bar code, in which both the number and width of the bars are significant.
The code thus identifies a genuine document, and may also function as a denomination code.
The location of the coating is detectable only by suitable apparatus which thus distinguishes between genuine and counterfeit documents.
In its simplest form, the invention comprises a substrate, such as but not limited to paper, on which a coating is applied.
A very thin (preferably less than about 200 Angstrom units thick) coating of electrically conductive material is deposited on the surface of the substrate.
Preferentially coating is deposited by a cathode sputtering wherein particles thereof are driven toward the surface, building up a coating on the surface and driving some particles into the surface to a substantial depth, which may be many times the thickness of the surface coating.
The presence of these particles makes that part of the substrate electrically conductive.
Even though the surface coating becomes worn, the conductive material within the substrate retains its conductivity and therefore retains its ability to identify the document as genuine.
One of the coatings may be of electrically conductive material.
The coating is continuous over one or more areas of the document, even in those locations where it is printed over, or where it is applied over printing.
An electrical characteristic, e.
g.
, impedance or capacitance is measurable by appropriate apparatus.
If the characteristic falls within predetermined limits, the apparatus indicates that the document is genuine.
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Optical Systems 
