EP1732768A1 - Counterfeit-resistant, metal-formed images and security devices and security documents employing same - Google Patents

Abstract

Counterfeit-resistant, metal-formed images (14) for use with security documents such as banknotes and the like are provided. The inventive images (14) are difficult (if not impossible) to effectively simulate using metallic ink printing, foil transfer, or hot stamping techniques. Security devices (10) that employ at least one such metal-formed image (14) and security documents that have at least one metal-formed image (14) located on a surface thereof and/or that have at least one security device (10) at least partially embedded therein or mounted thereon, are also provided.

Description

COUNTERFEIT-RESISTANT. METAL-FORMED IMAGES AND SECURITY DEVICES AND SECURITY DOCUMENTS EMPLOYING SAME

RELATED APPLICATION [0001] This application claims priority from U.S. Provisional Patent Application

Serial No. 60/559,583, filed April 5, 2004.

FIELD OF THE INVENTION [0002] This invention relates generally to counterfeit-resistant, metal-formed images for use with security documents such as banknotes and the like. In particular, the invention is directed to metal-formed images that are difficult (if not impossible) to effectively simulate using metallic inks, foil transfer, or hot stamping techniques. Security devices that employ at least one such metal-formed image are also considered part of the subject invention as are security documents that have at least one metal-formed image located on a surface thereof or that have at least one security device at least partially embedded therein or mounted thereon.

BACKGROUND OF THE INVENTION [0003] Security threads are used extensively in banknotes and other documents of high value, providing visual and/or mechanical means for verifying the authenticity of these documents. Generally constituting a metallized polyester strip measuring between 1.0 and 5.0 millimeters in width, these threads are chemically etched to form indicia that are readily discernable in reflective and/or transmitted light. Security threads may be either fully or partially embedded in these documents. For partially embedded security threads, the threads are embedded into paper during manufacture and alternately rise to the surface of the paper at regular intervals. These so-called "windowed" threads can be found in banknotes throughout the world and are therefore a target of simulation by counterfeiters. In fact, it is generally known in the banknote industry that counterfeiters simulate the surface portions of the "windowed" security threads by applying metallized foil to the surface of the counterfeit.

[0004] One such metal foil simulation technique uses a conventional laser printer to print the intended foil pattern on the surface of the counterfeit. Conventional, adhesiveless metallized artistic foils can be applied to the pattern and heated with a heating element such as a household iron. Under heat, the laser printer's toner acts as an adhesive, pulling the metal layer from the foil carrier according to the printed pattern. As the foil is pulled away from the surface of the counterfeit, the silvery metallic surface of the foil adheres only to the printed areas simultaneously reproducing the simple text and patterns and reflective appearance of typical demetallized security threads. This technique can be further enhanced by using commercially available, color variable, novelty films to simulate color-shifting or holographic windowed security threads. [0005] Alternatively, counterfeiters have been known to produce hot stamping dies according to the desired pattern and then foil stamp counterfeit documents using traditional hot stamp materials and methods.

[0006] The present invention serves to frustrate or defeat these ongoing attempts by counterfeiters to replicate the appearance of security threads in "windowed" banknotes by providing a metal-formed image that is difficult (if not impossible) to effectively simulate using metallic inks, foil transfer, or hot stamping techniques.

[0007] Also being provided by way of the present invention is a counterfeit- resistant security device that employs or displays one or more such metal-formed images, as well as a security document having one or more such metal-formed images located on a surface thereof or that have one or more such security devices at least partially embedded therein or mounted thereon.

SUMMARY [0008] The present invention more specifically provides a metal-formed image that incorporates one or more visible patterns of alternating metal and metal-free regions that may take the form of lines, dots, swirls, or combinations thereof, wherein when the metal-formed image is simulated using metallic inks, foil transfer, or hot stamping techniques; ink or foil bridges and/or is missing from portions of at least some of the metal regions of the visible pattern(s) thereby rendering portions of the simulated image indistinct or blurred.

[0009] In a preferred embodiment, the visible pattern(s) comprises alternating metal and metal-free lines, the width of the metal-free lines within the pattern(s) ranges from about 0.05 to about 0.10 millimeters, while the frequency of metal-free lines ranges from about 4 to about 14 lines per millimeter (i.e., line frequency equal to from about 0.07 to about 0.25 mm).

[0010] The present invention also provides a counterfeit-resistant, demetallized security device that comprises: a carrier substrate having opposing planar surfaces; and at least one metal-formed image, as described above, located on at least one surface of the substrate.

[0011] The present invention further provides a security document that employs at least one metal-formed image and/or at least one counterfeit-resistant, demetallized security device, both as described above.

[0012] Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Particular features of the disclosed invention are illustrated by reference to the accompanying drawings in which: FIG. 1 is a top plan view of a preferred holographic embodiment of a security thread according to the present inventive, on an enlarged scale, as seen in transmitted light, showing negative or reverse-image letters having a pattern of metal and metal-free lines incorporated therein, while FIGS. 1A and 1B are partial top plan views of the FIG. 1 security thread, both on an enlarged scale, detailing the appearance of the thread when viewed at different angles in reflective light; FIG. 2 is a top plan view of another preferred embodiment of the present inventive security thread, on an enlarged scale, as seen in either transmitted or reflective light, showing letters that have a Crosshatch pattern of lines incorporated therein, and metal numbers surrounded by a fine metal-free outline; and FIG. 3 is a pictorial representation of an attempt to simulate the security thread of FIG. 1 using conventional foil transfer or hot stamping techniques.

BEST MODE FOR CARRYING OUT THE INVENTION [0014] The metal-formed images of the present invention increase the effectiveness without compromising the fundamental advantages of demetallized security devices (e.g., security threads) and security documents (e.g., banknotes). By carefully studying foil transfer and hot stamping techniques, as well as metallic ink printing techniques, the present inventors have determined the limitations (i.e., dimensional breakpoints) of these techniques and using this information, while balancing readability and production feasibility, have designed finely resolved demetallized patterns or images that are difficult (if not impossible) to effectively simulate. In fact, any attempt at imitation or replication by means of metallic inks, foil transfer or hot stamping will result in a simulation that is readily discemable (by the untrained and naked eye) from the original (or authentic) security device or security document in that the aesthetics of the security device or document are distorted, omitted or otherwise completely destroyed in the simulation.

[0015] Also considered by the present inventors was the ability of the inventive metal-formed image to function effectively as an optical reflector in "windowed" security papers or banknotes. As is well known to the skilled person, metal layers may serve as optical reflectors in numerous optically variable devices (OVD and DOVD) and interference filter optical devices. It was therefore deemed advantageous for such applications to preserve as much of the metal as possible while incorporating demetalization features. [0016] As noted above, the metal-formed images of the present invention incorporate one or more visible patterns of alternating metal and metal-free regions which may take the form of, for example, complex or simple patterns of lines, dots, swirls, or combinations thereof. The resolution and spacing of each component of the pattem(s) are chosen to avoid effective simulation by metallic inks, foil transfer and hot stamping techniques. More specifically, when the metal-formed image is simulated using these techniques, metallic ink or foil will bridge or link and/or will be missing from portions of at least some of the metal regions of the visible pattem(s). As a result, portions of the simulated image become indistinct or blurred. [0017] Examples of metal or metallic materials, which are suitable for use in forming the counterfeit-resistant images of the present invention, include, but are not limited to, aluminum (Al), chromium (Cr), cobalt (Co), copper (Cu), gold (Au), iron (Fe), nickel (Ni), silver (Ag), or alloys of two or more of the aforementioned materials. In a preferred embodiment, the metal or metallic material is aluminum. [0018] For those embodiments of the counterfeit-resistant images that incorporate alternating metal and metal-free lines, the width of the metal-free lines within the pattem(s) ranges from about 0.05 to about 0.10 millimeters (mm) (preferably, from about 0.06 to about 0.07 mm),- while the metal-free line frequency ranges from about 0.07 to 0.25 mm (preferably, from about 0.16 to about 0.17 mm). [0019] In one such embodiment, the metal-formed image comprises negative or reverse-image characters (e.g., symbols, letters and/or numerals) that have one or more patterns of alternating metal and metal-free lines incorporated therein. For this embodiment, metal-free line frequencies that fall below the lower end of the noted frequency range (i.e., < 0.07 mm) cause the character or text areas to appear grayish similar to forgeries produced by metallic inks, while metal-free line frequencies that exceed the upper end of the noted frequency range (i.e, > 0.25 mm) cause the character or text areas to appear as traditional negative text (as shown and described in U.S. Patent No. 4,943,093 to Melling eif al.) and thus prone to simulation via metallic ink and foil transfer.

[0020] In another such embodiment, the metal-formed image comprises positive characters that are formed by the one or more patterns of alternating metal and metal-free lines. For this embodiment, metal-free line frequencies that fall below 0.07 mm cause the character or text areas to appear as traditional positive text (as shown and described in U.S. Patent No. 4,652,015 to Timothy T. Crane) and thus more susceptible to simulation via metallic ink and foil transfer, while metal-free line frequencies that exceed 0.25 mm render the character or text areas difficult to visually detect and decipher.

[0021] For those embodiments that incorporate metal or metal-free dots, the diameter of the dots within the pattern(s) ranges from about 0.05 to about 0.10 millimeters, while the density (e.g., dots per inch) is selected such that the dots do not touch yet are close enough together to thwart simulation using metallic ink, foil transfer and hot stamping techniques.

[0022] The counterfeit-resistant images of the present invention may be used alone, or in combination with, for example, optical marks, on a surface of a banknote or any document or means of identification for authentication purposes. In one such contemplated embodiment, the inventive images are formed on a release-coated transfer film or sheet (typically, a metallized foil provided on a release coated polyester carrier film) and then transferred from the film or sheet onto a surface of a banknote or other security document using conventional transfer techniques. In another such contemplated embodiment, the inventive images are formed on optical marks (e.g., diffractive gratings, hologram structures) contained on a release-coated transfer film or sheet (typically, a holographic foil secured to a release coated polyester carrier film) and the resulting combination transferred from the film or sheet onto a surface of a security document.

[0023] The counterfeit-resistant images of the present invention may also be non-releasably or permanently formed on a surface of a plastic carrier substrate (e.g., a security strip or thread) and then used with banknotes or other security documents. [0024] Referring now to the figures, in detail, the security device of the present invention is shown generally at 10, and basically comprises: a carrier substrate 12 having opposing planar surfaces; and at least one metal-formed image 14 located on at least one surface of substrate 12. [0025] Carrier substrate 12 is a light-transmitting carrier substrate that has a thickness ranging from about 12 to about 26 microns (preferably from about 17 to about 21 microns). Preferably, substrate 12 is formed using one or more essentially colorless polymers selected from the group of polyester, polypropylene, polyethylene, polyethylene terephthalate, and mixtures thereof. In a more preferred embodiment, carrier substrate 12 is a polyester film. [0026] In another preferred embodiment, carrier substrate 12 is colored and/or luminescent and, in yet another preferred embodiment, substrate 12 contains optical marks such as diffractive gratings and/or hologram structures. [0027] Further to the above, carrier substrate 12 preferably provides adhesive properties to bond security device 10 into or onto a security document such as paper.

[0028] In one preferred embodiment, which is shown in FIG. 1, security device 10 is a security strip or thread that comprises: a carrier substrate 12 having opposing planar surfaces; at least one metal-formed image 14 located on one surface of substrate 12; and a holographic relief pattern (not shown) formed on an opposing surface of substrate 12. The metal-formed image 14, as viewed in transmitted light, is made up of negative or reverse-image letters that have a pattern of alternating metal and metal-free lines 16, 18, incorporated therein.

[0029] Due to the presence of the holographic relief pattern, and as best shown in FIGS. 1A and 1B, two different images will appear when this preferred embodiment of security device 10 is viewed at different angles under reflective light. [0030] In another contemplated embodiment (not shown), security device 10 is a security strip or thread that comprises: a carrier substrate having a holographic relief pattern formed on a surface thereof; and at least one metal-formed image formed on the holographic relief pattern.

[0031] FIG. 2 shows another preferred embodiment of security thread 10 that does not employ a holographic relief pattern. In this embodiment, metal-formed image 14, as seen in either transmitted or reflective light, consists of letters that have a Crosshatch pattern of lines incorporated therein, and metal numbers surrounded by a fine metal-free outline. Security thread 10 also displays a series of interruptions or breaks 20 in the metal contained on substrate 12. As amply described in U.S. Patent No. 5,486,022, the pattern of metal regions formed by these interruptions or metal breaks define a machine-readable code that provides yet a further means for verifying the authenticity of a banknote or other security document containing the thread, as well as a means for denominating the banknote.

[0032] In yet another preferred embodiment (not shown), image 14 consists of letters and numbers that are formed by a pattern of metal dots. [0033] The security device 10 of the present invention may include additional layers, coatings, or devices; provided however that any such additional layer, coating, or device does not interfere with the visual perception of the information conveyed by way of the metal-formed image 14, and/or the signals seen by authenticity testing devices. Contemplated additional layers, coatings, or devices include, but are not limited to, magnetic layers, two-dimensional arrays of non- cylindrical lenses that serve to enlarge metal-formed image 14 (and optionally, to also affect the image's rotation, orthoparallactic movement, and/or apparent visual depth), optically variable devices, interference filter optical devices, outer protective layers, light-transmitting adhesive layers on either or both sides of device 10 that facilitate the incorporation of the device 10 into or onto security documents, and fluorescent coatings made up of eosin, fluorescein, fluorspar, fuchsin, sulphate of quinine, calcium sulphide, Neodymium salicylate, Samarium gluconate, Yttrium salicylate and the like.

[0034] In a preferred embodiment, security device 10 employs an outer protective layer. The outer protective layer is a light-transmitting protective layer that may take the form of a protective film having a thickness ranging from about 3.0 to about 12.0 microns (preferably from about 3.0 to about 6.0 microns) or a printed coating having a thickness ranging from about 1.0 to about 6.0 microns. [0035] More preferably, the protective layer is formed using one or more essentially colorless polymers selected from the group of polyester, polypropylene, polyethylene, polyethylene terephthalate, and mixtures thereof. In a most preferred embodiment, the protective layer is a laminated polyester film.

[0036] In another more preferred embodiment, the protective layer is colored and/or luminescent and, in yet another more preferred embodiment, the protective layer provides adhesive properties to bond the security device 10 into or onto paper. [0037] The outer protective layer may be laminated to the metal layer by using the light-transmitting adhesives described above.

[0038] Security device 10 may be manufactured using conventional techniques. For example, the security thread shown in FIG. 1 may be manufactured by: a) embossing or coating a relief pattern on one surface of a polymeric (e.g., polyester) film; b) coating an opposing surface of the polymeric film with a metal (e.g., aluminum) layer; c) coating the metal layer with a resist material except where the metal-free lines 18 (within each negative or reverse-image character) are to be formed; and d) applying a chemical to the printed metal layer to remove the metal layer except where protected by the resist, so that the metal-free lines 18 become transparent regions in the opaque reflective metal surface. [0039] By way of further example, when the metal-formed image 14 comprises positive characters formed by the pattern of alternating metal and metal-free regions (e.g., lines, dots, swirls, or combinations thereof), the metal layer is coated with resist so as to protect the metal layer only in those regions in which the metal regions of the pattern(s) are to appear in the final thread.

[0040] The resist is preferably applied by a printing process such as flexo printing, rotogravure or silk screening. [0041] As noted above, any attempt to simulate the security device 10 of the present invention using metallic inks, foil transfer or hot stamping techniques will result in a simulation that is readily discernable (by the untrained and naked eye) from the original device. As best shown in FIG. 3, which is a pictorial representation of an attempt to simulate the security thread of FIG. 1 using foil transfer or hot stamping techniques, the aesthetics of the thread are distorted by metal bridging the fine metal lines of the pattern within each letter. This effect results from the inability of the foil to transfer cleanly.

[0042] The security document of the present invention is preferably a security paper and the security device 10, which is preferably in the form of a security thread, is either wholly or partially embedded within the paper. For partially embedded threads, portions thereof are exposed at the surface of the paper at spaced intervals along the length of the thread at windows or apertures in the paper. [0043] As alluded to above, the security thread 10 may be at least partially incorporated in security papers during manufacture by techniques commonly employed in the papermaking industry. For example, the inventive thread 10 may be fed into a cylinder mold papermaking machine, cylinder vat machine, or similar machine of known type, resulting in total or partial embedment of the thread within the body of the finished paper. [0044] In addition to the above, the security device 10 of the present invention may be mounted on the surface of security papers either during or post manufacture. Mounting of the device 10 may be achieved by any number of known techniques including: applying a pressure-sensitive adhesive to a surface of the device 10 and pressing the device 10 to the surface of the paper; and applying a heat activated adhesive to a surface of the device 10 and applying the device 10, using thermal transfer techniques, to the surface of the paper.

[0045] While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the exemplary embodiments. [0046] Having thus described the invention, what is claimed is:

Claims

CLAIMS 1. A counterfeit-resistant, metal-formed image suitable for use on a surface of a security document such as a banknote, or on a surface of a carrier substrate used on or within a security document, wherein the metal-formed image incorporates one or more finely resolved visible patterns of alternating metal and metal-free regions, wherein when the metal-formed image is simulated using metallic ink printing, foil transfer, or hot stamping techniques; ink or foil bridges and/or is missing from portions of at least some of the metal regions of the one or more visible patterns thereby rendering portions of the simulated image indistinct.

2. The counterfeit-resistant, metal-formed image of claim 1, wherein the one or more visible patterns of alternating metal and metal-free regions take the form of lines, dots, swirls, or combinations thereof.

3. The counterfeit-resistant, metal-formed image of claim 2, wherein the one or more visible patterns comprise alternating metal and metal-free lines, wherein the metal-free lines have a width ranging from about 0.05 to about 0.10 millimeters and a frequency ranging from about 4 to about 14 lines per millimeter.

4. The counterfeit-resistant, metal-formed image of claim 3, wherein the metal-free lines have a width ranging from about 0.06 to about 0.07 millimeters and a frequency ranging from about 5 to about 6 lines per millimeter.

5. The counterfeit-resistant, metal-formed image of claim 1 , which comprises negative or reverse-image characters defined by metal boundaries, which have the one or more finely resolved visible patterns of alternating metal and metal- free regions incorporated within the characters.

6. The counterfeit-resistant, metal-formed image of claim 1 , which comprises positive characters that are formed by the one or more finely resolved visible patterns of alternating metal and metal-free regions.

7. The counterfeit-resistant, metal-formed image of claim 1, wherein the metal regions of the one or more finely resolved visible patterns of the metal-formed image are formed using one or more metals selected from the group of aluminum, chromium, cobalt, copper, gold, iron, nickel, silver and alloys thereof.

8. The counterfeit-resistant, metal-formed image of claim 7, wherein the metal lines are formed using aluminum.

9. A security device that comprises: a carrier substrate having opposing planar surfaces; and at least one counterfeit-resistant, metal-formed image located on at least one surface of the substrate, wherein the at least one counterfeit- resistant, metal-formed image incorporates one or more finely resolved visible patterns of alternating metal and metal-free regions, wherein when the at least one metal-formed image is simulated using metallic ink printing, foil transfer, or hot stamping techniques; ink or foil bridges and/or is missing from portions of at least some of the metal regions of the one or more visible patterns thereby rendering portions of the simulated image indistinct.

10. The security device of claim 9, wherein the carrier substrate is a light- transmitting carrier substrate that is formed using one or more essentially colorless polymers selected from the group of polyester, polypropylene, polyethylene, polyethylene terephthalate, and combinations thereof.

11. The security device of claim 10, wherein the carrier substrate is a polyester film.

12. The security device of claim 9, wherein the carrier substrate is a colored carrier substrate.

13. The security device of claim 9, wherein the carrier substrate is a luminescent carrier substrate.

14. The security device of claim 9, wherein the carrier substrate contains one or more optical marks.

15. The security device of claim 14, which is in the form of a security strip or thread, and which comprises: a carrier substrate having opposing planar surfaces; the at least one counterfeit-resistant, metal-formed image located on one surface of the substrate; and a holographic relief pattern formed on an opposing surface of the substrate.

16. The security device of claim 14, which is in the form of a security strip or thread, and which comprises: a carrier substrate having opposing planar surfaces; a holographic relief pattern formed on at least one surface of the carrier substrate; and the at least one counterfeit-resistant, metal-formed image located on the holographic relief pattern.

17. The security device of claim 14, which is in the form of a security strip or thread, and which comprises: a carrier substrate having opposing planar surfaces; the at least one counterfeit-resistant, metal-formed image located on one surface of the substrate; and a two-dimensional array of micro-lenses positioned on an opposing surface of the substrate.

18. The security device of claim 9, which is in the form of a security strip or thread having a length and a width, and which comprises: a carrier substrate having opposing planar surfaces; a plurality of metal regions that extend along the length of the strip or thread, wherein the metal regions are separated by non-metal regions that extend across the entire width of the security strip or thread; and the at least one counterfeit-resistant, metal-formed - image located within the one or more metal regions and/or the one or more non-metal regions.

19. The security device of claim 9, which further comprises at least one outer protective layer.

20. A method for preparing a security device comprising a carrier substrate having a width and opposing planar surfaces, and at least one counterfeit-resistant, metal-formed image located on at least one surface of the substrate, wherein the metal-formed image incorporates one or more finely resolved visible patterns of alternating metal and metal-free regions, wherein the method comprises: a) applying a metal layer to one surface of the carrier substrate; b) coating the metal layer with a resist material, wherein i. when the at least one counterfeit-resistant, metal-formed image comprises negative or reverse-image characters defined by metal boundaries, which characters have the one or more finely resolved visible patterns of alternating metal and metal-free regions incorporated therein, the metal layer is coated with the resist material except where the metal-free regions of the one or more finely resolved visible patterns, and optionally where interruptions or metal breaks extending across the width of the carrier substrate, are to be formed on the substrate, and ii. when the at least one counterfeit-resistant, metal-formed image comprises positive characters that are formed by the one or more finely resolved visible patterns of alternating metal and metal-free regions, the metal layer is coated with the resist material only in those regions in which the metal regions of the one or more finely resolved visible patterns are to be formed on the substrate; and c) applying a chemical to the printed metal layer to remove the metal layer except where protected by the resist material.

21. A security document having at least one counterfeit-resistant, metal- formed image located on or within the document, wherein the at least one metal- formed image incorporates one or more finely resolved visible patterns of alternating metal and metal-free regions, wherein when the at least one metal-formed image is simulated using metallic ink printing, foil transfer, or hot stamping techniques; ink or foil bridges and/or is missing from portions of at least some of the metal regions of the one or more visible patterns thereby rendering portions of the simulated image indistinct.

22. The security document of claim 21 , wherein the security document has two opposing surfaces, and wherein the security document comprises one or more optical marks applied to at least one surface, and at least one counterfeit-resistant, metal-formed image formed on the one or more optical marks.

23. The security document of claim 22, wherein the one or more optical marks are selected from the group of diffractive gratings, hologram structures, and combinations thereof.

24. The security document of claim 23, wherein the one or more optical marks are holographic foils.

25. The security document of claim 21, which comprises at least one security device at least partially embedded therein or mounted thereon, wherein the at least one security device comprises: a carrier substrate having opposing planar surfaces; and the at least one counterfeit-resistant, metal-formed image located on at least one surface of the carrier substrate.