EP0303725A1 - Security paper - Google Patents

Abstract

The security paper has an embedded security thread running from edge to edge, which is printed with luminescent inks in such away that they are not visible under normal lighting. The luminescent inks are provided in successive, overlapping sections along the security thread, which, when the inks are excited, have a length visible to the naked eye and characteristic mixed fluorescence in the overlapping areas. <IMAGE>

Description

The invention relates to a security paper, in particular bank note, with a security thread running from edge to edge and embedded in the security paper, which is printed with luminescent colors.

Securing securities with security threads that are embedded in the paper during the manufacturing process has long been known.

Of course, the security threads have refined more and more over time. Numerous proposals have also become known for providing security threads with certain properties, so that not only the presence of the security thread alone, but also the presence of the special properties should guarantee the authenticity of the paper in question. For example, DE-A 14 46 851 describes a security thread which has a microprint executed in several colors. The inks can also be fluorescent. The areas printed with different colors can be so small or printed so closely together that they can no longer be resolved with the naked eye or the viewer is given a uniform color impression. Only with a magnifying glass or a microscope can the microprint or the different colors be recognized.

A disadvantage of this known security thread is that the authenticity markings are either relatively difficult to identify for the layperson or that a counterfeiter to deceive laypersons only has to imitate the general color impression which is produced by the micro-areas of different colors that can no longer be resolved with the naked eye. Because, as already mentioned, a forgery can only be detected under a magnifying glass or a microscope. In addition, the colored thread can possibly give the aesthetic impression of a print disrupt what is particularly disadvantageous for banknotes. On the other hand, if the security thread itself is arranged in the printing area of the banknote, the printed image of the banknote also interferes with the identification of the microprint applied to the security thread. The known thread is therefore not suitable for any arrangement in securities and also not for simple visual authenticity checks.

The invention has for its object to provide a security thread for a security or security that is inconspicuous in normal lighting and therefore does not interfere with the appearance of the security, but which nevertheless has a characteristic, easily verifiable identification, based on in a simple manner the authenticity of the security thread and thus the corresponding security can be proven.

This object is achieved in that luminescent colors are used which are not visible under normal lighting and which are provided along the security thread in successive and overlapping sections, which in the excited state of the colors have a length which can be seen with the naked eye and which each have different luminescent colors printed in the overlapping areas result in characteristic mixed luminescence.

Preferably, the mixed color that arises in the overlap areas flows smoothly and continuously into the color of the sections each enclosing the overlap area.

The desired and achievable effect according to the invention is particularly clear and impressive when the luminescent colors are chosen so that the successive sections with the basic color ben of the additive color mixture are printed, the respective mixed colors then also resulting in an almost pure form in the overlapping areas. For example, the sections are printed with luminescent colors which emit red, green and / or blue, the overlapping areas appearing orange, green and / or violet. The sequence of colors can in particular be chosen so that the color sequence of the natural spectrum results, so that a kind of rainbow effect occurs.

In addition to the special aesthetic effect of the security thread according to the invention, it also has a high security value, since it is difficult for a counterfeiter to imitate it. The counterfeiter must first analyze several colors and imitate them accordingly. The mixed colors that occur in the overlap areas due to the mixed luminescence present there are extremely difficult to reconstruct, since basic colors with a slightly different emission spectrum already cause a strong shift in the mixed fluorescence. Because of the neutral color in the non-excited state and the required high luminosity in the excited state, only identical luminescent colors are suitable. Such colors are usually not used and are therefore practically not available on the market, but must be specially manufactured. Overall, the counterfeiter is therefore faced with a number of difficult to overcome physical and technical problems when trying to replicate the security thread, which make imitation or counterfeiting almost impossible.

Apart from the high security standard, the thread is still light and can be checked for authenticity without difficulty. The corresponding security paper only needs to be exposed to UV radiation the. The provision of such a light source at a bank counter and the inconspicuous checking of banknotes is possible without major difficulties. It is even conceivable for this to provide the light source below the table and to carry out the fluorescence excitation through a plate which is embedded in the table and is only permeable to ultraviolet light, so that the fluorescence test is less or not noticed by the customer. A cumbersome, time-consuming and, above all, compromising test for the customer by, for example, microscopic inspection, which can hardly be carried out at a bank counter, can be avoided. UV radiation sources are also available as handheld devices, in the manner of a pocket torch, so that the authenticity of the security paper can also be clearly and reliably ascertained at any location. Also helpful is the fact that the authenticity feature is a memorable and memorable effect, even for lay people. The initially colorless, inconspicuous security thread suddenly receives an intensely colorful color effect when exposed to UV light, the colors following one another, for example, in the order of the natural light spectrum. If the same normal colors are provided near the security thread or elsewhere in the print image, which ideally can also be in the same order, a simple direct comparison with the colors of the security thread is also possible. Of course, an automatic test using appropriate detectors is not excluded.

Fluorescent substances which are suitable for the printing inks proposed according to the invention are known in principle, even if they are difficult to obtain commercially. For example, DE-B 30 32 611 contains rare earth salt discloses fabrics that emit red and green. EP-A 0 007 383 describes blue-emitting europium-doped phosphors and finally, US Pat. No. 3,525,698 mentions rare earth metal phosphates which emit bright green. For the selection of suitable phosphors, reference is expressly made to the disclosure of the publications mentioned; however, the use of other phosphors is not excluded insofar as they meet the requirements according to the invention. When making the selection, it must be taken into account that the body color is white or the materials are colorlessly transparent, that the materials have clearly distinguishable fluorescent emissions, which, when mixed, also differ characteristically from one another. Colors which are of high color purity and whose emission spectra correspond as far as possible to the ideal values of the additive color mixture are particularly suitable for this. It goes without saying that attention should also be paid to resistance to environmental influences. However, the skilled worker is familiar with such aspects.

Instead of the fluorescent substances mentioned, phosphorescent colors can also be used. By printing these colors on top of each other in the overlap area, a change in color can occur due to different long persistence times. This color change would be a further authenticity criterion, which makes counterfeiting even more difficult. Such phosphorescent colors are described, for example, in EP-A 0 003 187. Reference is also expressly made to the disclosure of this publication.

• Fig. 1 die schematische Darstellung der Anordnung der Abschnitte und Überlappungsbereiche auf einem Sicherheitsfaden,
• Fig. 2 die schematische Darstellung der Anordnung der Abschnitte und Überlappungsbereiche, wobei die Farben im Rasterdruckverfahren aufgedruckt sind,
• Fig. 3 die Emissionsspektren der drei Grundfarben der additiven Farbmischung und
• Fig. 4 die schematische Darstellung der Farbmengenver­teilung über die Länge des Sicherheitsfadens für Farben mit gleicher Leuchtstärke.

Embodiments of the invention are described below with reference to the accompanying drawing, for example. In it show:

• 1 is a schematic representation of the arrangement of the sections and overlap areas on a security thread,
• 2 shows the schematic representation of the arrangement of the sections and overlapping areas, the colors being printed using the raster printing method,
• Fig. 3 shows the emission spectra of the three primary colors of the additive color mixture and
• Fig. 4 shows the schematic representation of the color quantity distribution over the length of the security thread for colors with the same luminosity.

The arrangement of the sections 1, 2 and the overlap regions 3 is shown schematically in FIG. 1. Section 1 is printed with a blue-emitting color, for example, area 2 with a red-emitting color. The color in the overlap area would therefore be violet or magenta. In the event that red and green are selected for the basic colors of sections 1 and 2, the mixed color resulting in the overlap area 3 would be yellow, in the event that green and blue are selected as the primary color, the mixed color in the overlap area 3 would be cyan, d. H. blue green.

3 shows the ideal emission spectra of the three primary colors of the additive color mixture blue, green and red, the maximum intensity of the blue color is approximately 450 nm, for green 520 nm and for red 690 nm. The values of those available for counterfeiting Experience has shown that printing inks only approach these curves to a greater or lesser extent. These colors also generally do not have the necessary color purity, so that experience has shown that the spectrum of the mixed color is too strong shifts or instead of the mixed color only more or less dirty shades arise.

If one chooses the primary colors red, green, blue for the successive sections 1, 2, 1, the overlapping areas have the mixed colors yellow, blue-green (cyan) and violet (magenta). The color order corresponds to the color order that is achieved by prismatic decomposition of white daylight or that occurs in the rainbow. The aesthetic effect of such a thread is particularly impressive.

In principle, mixed colors can of course also be used. Because of the problems mentioned, the combination of matching mixed colors, which also result in sufficiently pure and characteristic mixed fluorescence in the overlap area, is extremely difficult. However, if such a useful color combination is available, it is practically impossible to reproduce for outsiders and therefore also for counterfeiters.

4 schematically shows the distribution of the amount of color over the length of the thread, as it should ideally be chosen for colors of the same luminosity. In the overlap area 3, the quantity of color 1 is continuously reduced to zero from a constant maximum value, while color 2 is simultaneously continuously increased to this value starting from zero. The total results in a constant amount of color and smooth, continuous color transitions to the colors of the adjacent areas 1 and 2.

In the event that colors of different luminosity are used, the amount of color can be adjusted accordingly to regulate the luminosity. Since the fluorescence intensity of a printing ink also depends on the amount of ink or layer thickness within certain limits depends, a higher amount of color should be chosen for less bright colors and vice versa. For an aesthetically appealing impression, it is particularly impressive if all the colors used have approximately the same luminosity. In this case, the counterfeiter also has another hurdle in copying, since it is not so easy to match the intensities to one another or to reproduce the necessary layer thicknesses without appropriate specialist knowledge.

For the expert, there is no insurmountable difficulty in compiling the colors, provided that he is equipped with sufficient printing aids and knowledge. To determine the layer thicknesses required in each case, it is so, for. B. by means of screen printing, so-called color intensity wedges, in which the layer thickness and thus the fluorescence intensity increases continuously or in stages from a minimum to a maximum layer thickness. If there is such an intensity wedge of each basic color, these need only be shifted towards each other under UV illumination and covered by a common slit mask until matching intensities lie next to one another. Once such suitable intensities have been determined, the person skilled in the art also has the layer thicknesses required for this. These layer thicknesses can then be reproduced with the specialist knowledge familiar to the person skilled in the art but not necessarily accessible to the counterfeiter.

The above-mentioned method can be used both for matching of one another in homogeneous color areas and of color areas generated in raster printing technology.

Another variant of the security thread according to the invention is shown schematically in FIG. The primary colors 1 and 2 are not distributed homogeneously on the carrier, but only in the form of individual color points ra printed like a star. In the overlapping areas 3 there are color dots of both colors, ie the primary colors 1 and 2, so that, viewed from a distance, the impression of a mixed color is created. Of course, the color dots are so small and so close together that they cannot be resolved by the eye individually or with difficulty.

The respective density of the color dots in the overlapping areas can decrease continuously towards the end of the section according to FIG. 4, while the density of the color dots of the next overlapping section increases continuously from zero to a certain value. The resulting mixed color then does not change abruptly, but continuously and smoothly into the colors of the adjacent sections.

The security threads are produced in a known manner, i. H. by printing flat films in strips and then cutting them. Printing the individual threads is also conceivable in principle, but less suitable for large series. The printing technique to be used depends on the carrier materials used and the properties of the printing ink. Screen printing processes are particularly suitable because they allow particularly simple regulation of the amount of ink. However, local multiple overprinting of defined, uniform layer thicknesses is also possible.

Instead of printing, other application methods for the printing ink are also possible. For example, the paint can be applied by spraying or spraying in a free jet. The layer thicknesses are set by the size of the spray nozzles, the spray duration, multiple spraying, etc.

In principle, any tear-resistant plastic is suitable as a carrier material for the security thread. The tensile strength is important because the security thread is mechanically stressed when it is stored in the security paper. In this context, transparent polyester film has proven itself. If the backing material is transparent, it is not necessary to ensure that the security thread remains in the same orientation during storage, since the colors emitted can also be seen from the back of the security thread through the backing material. If, on the other hand, an opaque backing material is used, care must be taken to ensure that the security thread in the paper remains in the same orientation if the fluorescence effects are to appear on the same page for all securities, otherwise the backing material must be printed on both sides.

In addition to the colored areas, the security threads can of course also have other characteristic features which are additionally evaluated in an authenticity check. For example, only machine-recognizable features such as a metallic or electrically conductive intermediate layer or magnetic inclusions are possible.

The security thread is also embedded in the paper in a known manner, for example by feeding the thread onto the drum of a circular paper machine. It can be useful here if the thread is covered at least on one side only by a relatively thin paper layer, if the color effect is dampened too much by the paper layer. Embedding the thread interrupted by windows is also possible for this. Such a method is described for example in DE-A 36 01 114.

Claims (14)

1. Security paper, in particular bank note, with a continuous from edge to edge, embedded in the security paper, security thread, which is printed with luminescent colors, characterized in that the luminescent colors are colorless and transparent or paper-colored in the non-excited state and that along the Security thread successive and overlapping sections (1, 2, 3) are provided, which in the excited state of the colors have a length recognizable with the naked eye and which are each printed with a different luminescent color and that are characteristic in the overlap areas (3) Mixed color results. 2. Security paper according to claim 1, characterized in that the mixed color of the overlap area (3) blends smoothly and continuously into the color of the sections including the overlap area. 3. Security paper according to claim 1 or 2, characterized in that the luminescent colors are selected so that the successive sections have basic colors of the additive color mixture and the respective substantially pure mixed colors result in the overlapping areas. 4. Security paper according to claim 3, characterized in that the fluorescent colors contain phosphors which emit red, green and / or blue light and the overlap areas appear orange, green and / or violet. 5. Security paper according to claim 4, characterized in that the sections are printed in red, green and blue, so that the sequence of the colors of the sections and overlapping areas corresponds to the color sequence of the natural spectrum. 6. Security paper according to claim 5, characterized in that the overlap of the sections is chosen so that the length of the overlap areas which show a mixed color corresponds to the length of the non-overlapping sections which show a basic color. 7. Security paper according to one of claims 1 to 6, characterized in that two colors are printed one above the other in the overlapping areas. 8. Security paper according to claim 7, characterized in that at the beginning and end of each section the respective amount of color decreases continuously, so that in the overlap areas there is approximately the same amount of color as in the sections. 9. Security paper according to one of claims 1 to 6, characterized in that two colors are printed in a grid-like manner in the overlapping areas. 10. Security paper according to claim 9, characterized in that at the beginning and end of each section, the screen density decreases continuously, so that the overlap areas overall have approximately the same screen density as the sections. 11. Security paper according to one or more of claims 1 to 10, characterized in that the luminescent colors are chosen so that they have high color purity and approximately the same luminosity with the same amount of color. 12. Security paper according to one or more of claims 1 to 10, characterized in that the amount of color in the sections is metered as a function of the respective luminosity of the colors so that there is a constant luminosity over the length of the thread. 13. Security paper according to one or more of the preceding claims, characterized in that the luminescent colors contain phosphorescent phosphors and the afterglow duration of the primary colors used is of different lengths. 14. Security paper according to one or more of the preceding claims, characterized in that the carrier material of the security thread is transparent.

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