EP0377167A1 - Safety element to protect documents against unauthorized reproduction - Google Patents

Abstract

To protect security paper and the information contained thereon against unauthorised reproduction in a copying device, the security paper is provided with light-deflecting structures which reflect the light, applied to the document during the copying operation, into the environment at a defined angle in such a way that they occur at a point on the photoconductive drum, at which normally information is contained at another point on the security document. Due to this bloom, at least some of the information recorded on the security document is not reproduced on the copy. The copy is thus recognisable as such.

Description

The invention relates to a security element according to the preamble of claim 1.

In the production of paper for banknotes, checks, passports, hereinafter referred to briefly as security papers, it corresponds to the state of the art to introduce so-called security threads into the paper. These are narrow tapes made of plastic or metal or any composite materials that are embedded in the paper sheet during the manufacturing process of the paper. Such security threads can be recognized on the finished sheet in transmitted light in accordance with their nature and serve to authenticate the corresponding paper.

A method is known from EP-OS 0 229 645, according to which this security thread can also be introduced into the paper in such a way that it emerges from the paper pulp at some predeterminable points and thus lies on the surface of the paper. This method is of particular interest if the thread has metallic reflective properties and therefore has a specular gloss. It is known that such specular objects cannot be reproduced in the same way in photocopiers. Instead of the glossy surface of the thread, there is only a black spot, which clearly distinguishes the copy as such from the original. However, there are options for creating a corresponding mirror-like surface on the copy afterwards (e.g. by applying appropriate varnish).

The object of the present invention is now to provide a security element which on the one hand can be recognized as an authenticity feature in a corresponding security paper, but which on the other hand is also used for protection against unauthorized copying can be.

This object is achieved by the features specified in the characterizing part of the main claim.

Such a security element, the z. B. may have the form of a security thread embedded in the document, would produce such a clear effect in the attempt to make a copy on this copy that it could no longer be repaired in the sense of the original.

From various documents (DE-PS 25 55 214; EP-C 59 056; EP-C 70 172; US-PS 4,437,935) it is known to provide documents with light-deflecting, in particular light-diffracting structures. Here, however, only the structure per se represents an authenticity feature that is easily reproducible photographically or electrophotographically. However, these light diffractive structures do not prevent the document from being copied in the desired form outside of these structures.

It has now been found that security elements can indeed be produced which have special properties. In general, it is also the known films or film strips from z. B. polyester or polycarbonate with a vapor-deposited metal layer. These foils, foil strips or threads correspond in various designs to the state of the art and can be produced, for example, by vapor deposition of aluminum, nickel, gold, titanium nitride and other materials. In addition, however, a special structure is embossed into the surface of this thread, which deflects, diffracts or reflects the incident light in a special way. The inventive idea is to deflect the light rays by deflecting the incident light so that they only at a predetermined angle - different from the angle of incidence - can be seen. It proves to be particularly advantageous if the deflected, in particular diffracted, beam is on the one hand perpendicular to the thread running direction, but on the other hand forms a given angle to the normal to the thread surface. If one looks at a document containing such a thread, no special effects can be seen with normal observation, ie, observation directed perpendicular to the surface. When the document is held at an angle (the thread advantageously being regarded as an axis for the inclination), bright light reflections appear at defined angles, but these disappear again when the document is inclined further. When the document is moved quickly around the thread axis, a brief flash of the deflected light rays appears. This property of the security thread can advantageously be used as an authenticity feature, since it is not possible, in particular with simple means, to subsequently cause such an appearance on a counterfeit or copy.

It has been found that a thread of the type according to the invention shows particularly advantageous properties when an attempt is made in a copier (irrespective of whether black and white or color) to reproduce the document by unauthorized copying. For this purpose, for example, a gas discharge tube or the like is used to illuminate the template. The light reflected from the original is imaged by a photographic object on a photoconductive drum and a charge image of the original is generated there. Subsequent use of toners and transfer to any substrate results in a copy of the given template. However, the security element according to the invention located in or on the document has the effect of affecting the surface of the security element falling light rays are not diffusely scattered, but a reflective metal layer initially creates a black image at this point. In principle, this is no different from the use of simple metal-coated security threads. In addition, however, it is found that the deflected light beams hit the lens and the photoconductive drum at a location where information from another location of the original would normally be contained. This creates an additional bright light effect at this point, which outshines the information normally present on the photoconductive drum and thus erases it. A copy produced according to the invention from such a document thus shows not only black spots instead of the reflecting security thread, but also spots which are brightly outshone in the area of the text or the illustration and which are easily recognizable as interruptions in the text or in the illustration. Even with an otherwise perfect copy, these spots show immediately that this is not an original, but a fake.

If, for example, a bank note is equipped with the thread according to the invention and it is further provided that this thread comes out of the bank note at at least one point on the surface of the note, the first embodiment of the method according to the invention results. In addition, a banknote usually has a linear background print that covers almost the entire surface of the note. If you now try to copy such a note, there is a dark place in the copy where the exposed thread would otherwise be recognizable. In addition, however, one or more clearly visible interruptions can be found in the area of linear background printing. This copy is therefore easily recognized as a forgery.

In a further embodiment of the invention, the security thread can also be produced in such a way that recognizable or readable information is contained within the light beam bent to the side due to the special design of the surface structure. Thus, in the area of the light spots resulting from the lateral deflection, a black cross or another suitable sign can also arise within the copy, which improves the recognizability of the copy and additionally hinders the secondary improvement of such a copy.

The particular advantage of the security threads mentioned is that they are not only misrepresented in the copy (which can easily be improved by applying secondary varnish), but that they outshine the positively necessary information on other parts of the security paper and thus deface. It follows that the copy is not only easily recognizable as such, but also that part of the information usually present there will no longer be recognizable on the copy.

The production of a thread of the type mentioned is fundamentally possible with the existing technical means. A suitable method consists, for example, of holographically imaging a light source at an oblique angle of incidence and producing an embossing stamp in a known manner on the basis of this hologram. If one stamps the surface of a metallized plastic filament with such a stamp, the result is, in principle, an image of the previously recorded topography, that is to say a light source radiating in a defined manner at a certain angle. This means that incident light rays leave the surface of the film at a defined angle and thus produce the effects described above.

When producing such a picture, it is necessary to take into account the geometry of the usual photocopiers. The arrangement of the light source during the manufacture of the embossing stamp must also be taken into account. It should also be borne in mind that it is not guaranteed from the outset in which orientation the original is placed in the copier.

In the case of the common copying machines, which work with a fluorescent tube as a light source and with a direct photographic image on a photoconductive drum, in principle any directional reflective embossing can be used, which only takes into account the different orientation options of the original in the copier. For example, four to eight reflections grouped at a defined angle symmetrically around the normal of the thread can provide excellent security for documents in these devices. However, it is also possible to use an annular retroreflection, which is mounted on the security thread as a cone jacket around the normal. Such overexposure would then result in annular extinguishments of the print around the thread.

A number of copiers use line-by-line scanning of the original, eliminating the need for a photoconductive drum. Rather, a line consisting of many light-sensitive points slides over the original, which scans the image across the direction of travel of the line. It is understood that such imaging systems are only disturbed if at least one of the reflections falls into one of the light-sensitive sensor points. This means that the previously described direction of reflection in a circle along a conical surface would already be a perfect safeguard. Likewise, the relexes along the cone can also be divided into a group of individuals Decompose points so that a sufficiently large number of point-shaped reflected light bundles are created along a circle in the illustration. These would then outshine at least one point each when scanning (but generally two points due to their symmetrical arrangement). By moving the sensor line, these points would add up to two bright lines along the direction of movement of the sensor.

Finally, there are special and very expensive devices that record a template point by point and initially save the excluded image in digital form. These devices are usually designed so that a point-shaped light sensor is attached perpendicular to the template. To the side of this sensor or in a ring around it is the light source, which illuminates a larger part of the original under the sensor. In this case too, the protection can be carried out by the fact that the diffusely incident light is deflected to the side by the diffraction grating of the security thread. In a preferred embodiment, however, the reflections are designed such that they only form a small angle to the normal to the original. Furthermore, the reflex areas can be widened to a somewhat larger solid angle. With such an arrangement it is achieved that when scanning the printing areas on both sides of the security thread light intensities are also recorded, which originate from the security thread itself. This in turn creates an overexposed zone in the immediate vicinity of the security thread on both sides, ie it does not contain any image.

Claims (5)

1. Security paper with a security element located at least at one point on a surface of the paper in the form of light-deflecting structures, characterized in that the light-deflecting structures emit incident light into the environment at a defined solid angle in such a way that when the security paper is reproduced in a copying device the deflected light causes an overexposure in an area of the copy that lies outside the imaging area of the security element. 2. Security paper according to claim 1, characterized in that the security element is an embedded in the paper, emerging at a predetermined location on the surface security thread. 3. Security paper according to claim 1 or 2, characterized in that the structures are light-deflecting structures and in particular represent a hologram. 4. Security paper according to claim 3, characterized in that the hologram is the holographic image of a light source, in particular an annular light source. 5. Security paper according to one or more of the preceding claims, characterized in that several areas are provided with light-deflecting structures which bend the incident light in different directions.