MXPA01003436A

MXPA01003436A - Verifiable holographic article

Info

Publication number: MXPA01003436A
Application number: MXPA/A/2001/003436A
Authority: MX
Inventors: Sergiy Dovgodko; Domenica Kirchmeyer
Original assignee: 3M Innovative Properties Company
Priority date: 1998-10-05
Filing date: 2001-04-03
Publication date: 2001-12-04

Abstract

A verifiable holographic article (1) comprises a substrate (5) comprising at least one hologram (10);and at least one covert image that is convertible to an overt image using a decoding sampling device, e.g., a photocopier, that produces an aliasing or moire effect. The article cost-effectively provides both"first line"and"second line"security features and can be easily, quickly, and safely verified or authenticated.

Description

VERIFIABLE HOLOGRAPHIC ARTICLE Field of the Invention This invention relates to security articles comprising a hologram. BACKGROUND OF THE INVENTION Habitually, holograms have been used as authentication or security devices because they have been considered difficult to manufacture and reproduce or copy. Holograms are records of an interference pattern formed by light at the recording location and can be made, first, by illuminating an object with a coherent beam of light, for example, a laser beam. The light that is reflected from the object is allowed to be struck against a light-sensitive recording medium such as a film or photographic plate and, simultaneously, a reference beam is directed (comprising a part of the light of the light source) so that it passes over the object and directly impacts the recording medium. (In this way, the incident light on the recording medium is the sum of the light that is reflected from the object and the reference beam.) When the recording medium is subsequently illuminated by a light REF .: 128442 coherent (ie, a laser beam or sunlight), an observer will see a virtual image of the object, which seems to exist in a 3D space. Certain types of holograms are visible even under an inconsistent light (for example, a diffuse light). Typically, holograms have been incorporated into credit cards and other similar items as anti-fraud devices, with the belief that counterfeiters do not have sophisticated equipment requirements for the manufacture of holograms. However, counterfeiters have developed counterfeiting methods. One response to the greater preponderance of counterfeiting has been to produce holograms with increasing complexity, but this has led to an increase in cost. Other methods have resorted to the use of disguised images and special authentication or verification equipment, for example a laser, to enable the detection of such images, however, such equipment has often been expensive and difficult to use. Thus, in the art there is still a need to have safe holographic articles that are extremely difficult to falsify and that can be produced economically and that, in addition, can be authenticated or verified in a simple and economical way in the field conditions . SUMMARY OF THE INVENTION Briefly, in one aspect, this invention provides a verifiable holographic article comprising a substrate containing: (a) at least one hologram; and (b) at least one disguised image that can be converted to a manifest image using a decoding sampling device, for example a photocopier, which produces an overlapping or moire effect. Preferably, the disguised image is a high-frequency image that is substantially imperceptible to the human eye and is created, first, by removing the frequency components of a visible original image whose frequency is greater than half the sampling frequency of the decoding sampling device and then by reflecting the frequency components around the axes corresponding to half the sampling frequency. The verifiable holographic article of the invention provides security features of both "first line" (hologram) and "second line" (disguised image) in an economical way, which increases the difficulty for falsification (which requires a sophisticated knowledge). in other fields that go beyond holography) and improve the security level of the holographic article. However, the article can be verified or authenticated simply, quickly and safely using a photocopier or other simple sampling device without requiring, for example, expensive, difficult to use and potentially dangerous laser detection equipment. In other aspects, this invention also provides a security label or a security laminate comprising the verifiable holographic article of the invention and an equipment comprising the article and a decoding sampling device. BRIEF DESCRIPTION OF THE FIGURES These, as well as other features, aspects and advantages of the present invention may be better understood in relation to the description that follows, the appended claims and the accompanying graphs, in which: Figures la and Ib present upper plane views of an embodiment of the verifiable holographic article of the invention before and after, respectively, of the application of a decoding sampling device for converting the concealed (hidden) images of Figure la into the manifest (visible) images of Figure Ib. These figures, idealized, were not drawn to scale and are intended to be merely illustrative and in no way limiting. Detailed Description of the Invention Reference Numbers 1 Verifiable Holographic Article 5 Substrate 10 Hologram 15 Disguised Images (Fig. La); manifest images (Figure Ib) The verifiable holographic article of the invention can be better understood in relation to the attached graphs, in which: the Figure presents an embodiment of the article 1 of the invention, characterized in that a substrate 5 it comprises a hologram 10 and disguised images 15. The hologram 10 can be of any of the types known in the art as those that can be displayed or reconstructed without the use of a coherent monochromatic light source, eg laser. Such types of holograms (sometimes referred to as "visible under the sun" or "visible under a white light") include, for example, reflection, transmission, true color, and composite holograms. can be any of the materials known in the art as useful for producing and / or incorporating such types of holograms, for example, fo-topolimeric films, photochromic glasses / glasses, dichromate gelatin, thermoplastic materials, photoretrictive crystals, materials that can be embossed (eg metallized papers, metallized polymers and metal foils) and the like, as well as combinations thereof, Useful holograms and substrates for these include, for example, those described in US Pat. No. 4,856,857 (Takeuchi et al.) Preferably, the hologram is a transmission hologram (more preferably, a hologram). n rainbow) and the substrate is a reflective substrate, for example, a sheet of metal, a foil or a metallized polymer film. More preferably, the substrate is a sheet of metal and, more preferably still, an aluminum sheet. Preferably, the sheet has an interior thickness of approximately 10 microns, so that it is extremely difficult to remove the sheet from a security article on which it has been applied without breaking or destroying the sheet, at least partially. The disguised images 15 are hidden images that can become manifest (visible) using a decoding sampling device, for example, a digital copying device or a photocopier, which produces an overlapping or moire effect. Preferably, the device produces an overlapping or moire effect during the sufficient amount of disguised image frequencies to render the images at least partially visible (more preferably, substantially visible) to the human eye. The disguised images can be produced following modulation techniques by screen angle. However, disguised images are created, preferably, by eliminating, first, the frequency components of one or more manifest, original images, greater than half the sampling rate of the decoding sampling device and then by reflecting the remaining frequency components around the axes that correspond to half the sampling frequency. The disguised images 15 are prepared, more preferably, with a method comprising the steps of: (a) determining the Fourier transform domain (converting from the spatial domain to the frequency domain) of at least a part of a manifest, original image , sampled or generated with, for example, a computer; (b) removing all frequency components of the Fourier transform greater than half the sampling frequency of the decoding sampling device that is selected to decode that part of the image; (c) reflect the remaining frequency components of the Fourier transform around the axes corresponding to half the sampling frequency; and (d) determining the inverse Fourier transform (which converts the frequency domain back into the spatial domain) from the resulting reflected frequency components. The images disguised 15 prepared with this method can be converted into manifest images 15 (shown in Figure Ib) using a decoding sampling device that samples at twice the frequency on which the elimination and reflex steps described above are based. before. Said sampling device shall not (in accordance with the Sampling Theorem) reproduce the frequencies of the disguised image greater than half the sampling frequency of the device and, instead, they will produce an overlapping effect whereby these frequencies are reflected back around the axes corresponding to half the sampling frequency. In this way, the frequencies are shifted to the range of frequencies visible to the human eye (spatial frequencies less than approximately 250 cycles (0 points) per inch (2.54 cm) at a viewing distance of about 1 foot (approximately 30 cm) , which convert the disguised image into a manifest image.This way, digital copiers or laser scanners can be used as verification or authentication devices that "take a sub-sample" of the hidden image, produce an overlapping effect (so that the disguised image becomes a manifest image) and reproduce the image manifested in, for example, a sheet of paper. (If desired, a correlation analysis or a comparison of the resulting disguised image can also be carried out with a stored version of the original image on which the disguised image was based.) However, as an alternative, it is also possible to use any device Simple optical wave that allows the human eye to take a sample in the spatial domain at the particular sampling frequency for verification. Such a device can, for example, be something as simple as a polymeric sheet (e.g., a substantially transparent polymeric sheet) comprising a pattern or set of elements (produced, for example, using a diffuse printing technique) having a selected, preferably substantially regular, range that produces a frequency function of desired sampling. The reproduction or copying of disguised images, instead of the conversion of disguised images into overt images, can take place if the sampling frequency of a particular digital copier is high enough to meet the requirements of the Sampling Theorem. for those disguised images. However, as all those qualified in the art will be able to recognize, such reproduction or copy made with digital copiers marketed in place (which perform the sweep at spatial frequencies between approximately 400 and 600 cycles (or points) per inch) can be avoided ( 2.54 cm) by choosing, in an appropriate manner, the frequency on which the removal and mirroring steps described above are based, the hologram 10 and the concealed images 15 can be arranged in any way desired, but preferably they are in a position adjacent to each other or are arranged in such a way that one of them surrounds the other, more preferably, the concealed images are integrated within the hologram (for example, by including the disguised images as one of the views). angles that are used to build a 2D / -3D hologram.) The incorporation of the hologram and the images dissimulates In the substrate 5 can be carried out following any of the methods known in the art for the production or copying of holograms.

Preferably, embossing techniques are used. If desired, in the first place, a manifest image can be superimposed on the concealed image provided that any frequency of the manifest image is eliminated (for example, high non-visible frequencies) that can substantially interfere with the decoding of the disguised image. The objects and advantages of this invention will be further illustrated with the examples that follow, but the particular materials and quantities indicated in these examples will not be considered, nor will the other conditions and details be limitative. for this invention. Examples 1 This example describes the preparation of a verifiable holographic article comprising a sheet of embossed metal. Two original digital images were created (one to be used in the production of a manifest hologram and the other for the production of a disguised image) arranged with a selected pattern (characterized in that the images were arranged adjacent to each other) and recorded in an original pattern file using the Illustrator ™ software (marketed by Adobe Corporation, San Jose, California, USA). Next, and using the same software, five different high-resolution graphics files were created from the original pattern file. Each of the five graphics files contained a view with a different requirement of the original image, which was intended to become a manifest hologram (for each of the five different viewing angles), but the view of the second original image (which was intended to become the disguised image) was the same in each of the five files. In parallel, a two-dimensional fast Fourier transformation was performed on the Illustrator ™ file that contained the original image whose purpose was to become a disguised image. The mirror copy axis for each dimension was set to the sampling frequency of a selected decoding sampling device. For each dimension, frequencies higher than the reflex frequency were dropped. Subsequently, the frequencies lower than the frequency of mirror copy in the high frequency area were reflected. Since a manifest image was not going to be used to mask the disguised image, frequencies were not added in the area below the mirror frequency. Finally, a two-dimensional inverse Fourier transformation was carried out to produce a disguised image file containing the disguised image in the spatial domain. Then the disguised image was copied over the corresponding manifest image in each of the five graphic files. Each of the five files was printed using an output device with a very high resolution on a transparent film as a negative image in black and white. A photosensitive plate was created using the five negative films by exposing the plate in such a way that the resulting rainbow hologram had the specified color shifts with the variation of the viewing angle. The photosensitive plate was used to make an embossing tool (or wedge) with a nickel electroforming process. A wedge was reproduced with this method in such a way that shims sufficiently identical to cover the surface of a master embossing roller were available. The master embossing roller was used for hot embossing a hot foil sheet (a standard aluminum foil stamping foil, which is usually used for embossing holograms) on a foil carrier. 19 micron thick polyester (polyethylene terephthalate or PET). The final result was a band comprising a 19 micron polyester carrier with an aluminum foil having a thickness of 5 microns and comprising embossed images. The layer of aluminum foil that carried the hologram and the disguised image on the surface of a security paper were hot stamped. The security paper that had the hot stamping film embossed as the substrate for printing security documents using security printing techniques was used. The authenticity of the selected security documents was verified by first observing the holographic image (first line inspection) and then using the decoding sampling device (second line inspection), which made the hidden image visible to the produce an overlapping effect.

Example 2 Example 1 was repeated using a hologram image with a circular band geometry in the form of a washer. The image of the hologram and the disguised image were arranged in such a way that the disguised image was in the center of, and surrounded by, the image of the hologram. Various modifications and alterations of this invention will become clear to all those skilled in the art without thereby departing from the scope and spirit of this invention. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Claims

The invention having been described as above, the content of the following claims is claimed as property: 1. A verifiable holographic article comprising a substrate that includes (a) at least one hologram; and (b) at least one coverage image that is convertible to an aperture image using a decoding sampling device that produces a pseudonym or moire effect, characterized in that the coverage image is created by a process comprising the steps of: (i) the elimination of any frequency components of an original aperture image, which are greater than half the sampling rate of the decoding sampling device, and (ii) the reflection of the Frequency components remaining with respect to the axes that correspond to half the sampling frequency.
2. The article according to claim 1, characterized in that the hologram is observable or reconstructable without the use of a monochromatic coherent light source; and wherein the substrate is selected from the group consisting of photopolymer films, photographic films, photochromic glasses / glasses, dichromate gelatin, thermoplastic materials, photorefractive crystals, refastenable reflective materials, and combinations thereof.
3. The article according to claim 2, characterized in that the coverage image is prepared by a process comprising the steps of (a) determining the Fourier transformation of at least a portion of an original aperture image, (b) removing all frequency components of the Fourier transform that are greater than half the sampling frequency of a decoding sampling device to be used for decoding the portion of said image, (c ) the reflection of the remaining frequency components of the Fourier transformation around the axes corresponding to half the sampling frequency, and (d) the determination of the inverse Fourier transformation of the resulting reflected frequency components; wherein the hologram is selected from the group consisting of reflection, transmission, true color, and compound holograms; and wherein the substrate comprises an incriminating reflective material.
4. The article according to claim 3, characterized in that the hologram is a transmission hologram; and wherein the incrustable reflective material is selected from the group consisting of metal foil, metallized paper, and metallized polymeric film.
The article according to claim 4, characterized in that the incrustable reflective material is metal sheet
6. The article according to claim 1, characterized in that the cover image is integrated into the hologram.
7. The article according to claim 3, characterized in that the hologram is a rainbow hologram.
The article according to claim 7, characterized in that the substrate comprises an incrustable reflective material, and wherein the hologram and the cover image are embedded on the substrate.
9 A device, characterized in that it comprises (a) the article according to claim 1; and (b) a decoding sample taking device.
10. A security label or security laminate, characterized in that it comprises the article according to claim 1.