EP0426801B1 - Security document with embedded security element with visually and mechanically verifiable distinguishing signs - Google Patents

Abstract

PCT No. PCT/EP90/00765 Sec. 371 Date Mar. 7, 1991 Sec. 102(e) Date Mar. 7, 1991 PCT Filed May 11, 1990 PCT Pub. No. WO90/13878 PCT Pub. Date Nov. 15, 1990.In a security document having an embedded security element in the form of a transparent thread with electrically conductive material in at least two layers, at least one layer is transparent or partly transparent at least in certain areas. The partly transparent layer interacts with marks located on the thread in such a way that the marks are largely concealed in incident light but are recognizable visually in transmitted light.

Description

The invention relates to a security document with a security element embedded in it in the form of a transparent thread or tape, which bears visually recognizable marks in the form of characters, printed images and the like, and which is electrically designed to be able to be checked by machine.

To secure security documents, it is known to embed security elements in these documents, which have special machine-detectable physical properties and / or are designed in terms of their visual appearance in such a way that they can serve as an authenticity feature for the security document. These security elements are such. B. threads or tapes that are embedded directly in the still forming paper layer in the context of paper production.

So z. B. from DE-OS 14 46 851 a security thread is known, which is provided on both sides with micro-printed images. In order to be able to check the print on the front and back independently of one another, an aluminum layer is temporarily stored. This aluminum layer can also serve as a machine-readable feature by determining the electrical conductivity. In practice, this form has proven to be of little use, since the security thread is opaque due to this aluminum layer and, firstly, the writing is only very difficult to recognize in incident light and secondly. It is usually necessary to make the paper transparent at least for the time of the test using chemical agents. In addition, the micro-printed image of the security thread overlaps with the outer printed image, which in many cases is also perceived as annoying.

Since security threads can only be embedded up to a certain width without holes in the sheet formation, it has already been proposed to install porous threads then can be made correspondingly wider (DE-OS 21 52 090). In a special embodiment, a security thread is also described which, when viewed in reflected and transmitted light, shows a different color. For this purpose, the thread is provided with two layers of color, between which there is a semi-transparent aluminum coating. If you look at this thread in reflected light after it is embedded in the paper, the color layer over the reflective aluminum coating is dominant, while when viewed in transmitted light the mixed color of both colors will be the dominant color. With such threads, however, there are adhesion problems between the color layers and the metal layer in between, and in extreme cases the outer color and metal layers can also be detached. Although this thread can in principle also be checked mechanically with regard to its electrical conductivity, this feature does not form a reliable authenticity feature because of the deficiencies with regard to the durability of the metal coating over the entire length of the thread. Cracks or partial detachment of the metal layer already lead to an interruption in the electrical conductivity. Such security documents are therefore classified as forgeries during machine testing, even though they are real security documents.

A security thread that has a very easy to check label after storage in paper is such. B. is known from EP-A 0 279 880. This thread consists of a transparent carrier, which has a lettering in the form of several individual shiny metallic micro characters. The well-known security thread and the micro characters on it are not recognizable in incident light. In transmitted light, on the other hand, only the characters are visible as sharply contoured characters, since the wearer itself is transparent. Such a security thread is produced by vapor-coating a transparent film with an aluminum layer over a large area, then printing this layer with the micro-characters using an acid-resistant printing ink and then etching away the unprinted areas, whereupon the characters remain as separate characters on a transparent background.

Accordingly, this thread has a clearly recognizable visual feature, but loses the property of electrical conductivity due to the splitting into individual characters and the associated interruption of the metal layer and is therefore no longer accessible to machine testing.

In the unpublished DE-P 38 07 126 a security thread with a metal coating is described, wherein characters are incorporated into the metal coating in negative form. When viewing the security document in transmitted light, the characters are visible as bright characters on a dark background. With this form of representation, it is now possible to produce the security thread with a continuous metal coating, so that the electrical conductivity is basically retained over the entire length of the thread. However, the cutouts in the metal layer necessary for the representation of the characters increase the likelihood that this metal layer will crack due to frequent kinking and use of the security document in the area of the narrow metallic webs between the cutouts and the edge of the security thread, through which the electrical conductivity then occurs is no longer verifiable.

The invention is based on the object of creating a security element suitable for embedding in a security document in the form of a thread or tape, which has a clearly recognizable visual identifier in the form of lettering or a print pattern, print image, etc., but the security thread additionally as a machine-readable feature, it has electrically conductive properties and this property can be reliably and reliably ascertained even after heavy mechanical loads on the security document.

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

In its simplest embodiment, the security thread according to the invention consists of a plastic thread printed with alphanumeric characters, the thread being provided with an all-over, at least partially transparent, electrically conductive layer over the print. This thread combines all the advantages of the known security threads without showing the disadvantages mentioned above. The print is practically invisible in reflected light, but in transmitted light the print can be read visually through the partially transparent, electrically conductive layer. Due to the full-surface expansion of the electrically conductive layer, the likelihood of cracks extending across the entire thread width is reduced, which leads to a total loss of electrical conductivity.

The risk of loss of electrical conductivity can be completely avoided by providing the thread with two electrically conductive layers which are capacitively coupled by a non-conductive layer (plastic film, adhesive layer, etc.), which forms a dielectric. The conductivity of such threads is checked according to the invention not by galvanic contacting of the electrically conductive layers, but by capacitive coupling of high-frequency signals. If cracks now appear in the metal layers, the metal layers interrupted by these cracks, with the dielectric in between, act like capacitors connected in series or in parallel, depending on the test setup. This maintains an alternating current conductivity, through which interrupted layers can also be checked, in particular if the two metal layers are not completely interrupted at the same point on the thread. If one measures this AC conductivity by means of capacitive measuring methods known per se, such as are also described, for example, in DE-OS 38 43 077 or DE-PS 17 74 290, the presence of one or both metal coatings can be determined even in the event of one or more breaks two electrically conductive layers are closed and this feature serving to identify authenticity is clearly established.

One of these electrically conductive layers can now be an opaque metal coating which contains cutouts in the form of characters using the method described in DE-P 38 07 126. The second electrically conductive layer is preferably a transparent ITO layer (indium tin oxide), for example applied in the sputtering process, which is applied to the same side of the plastic wire or to the opposite side. Since the second electrically conductive layer is transparent, the lettering in the first opaque metal layer remains visible in the same quality.

Instead of the sputtered transparent layers, which are more expensive from process engineering, it is also possible to vapor-coat correspondingly thin aluminum layers which, for. B. in applied in an amount of approximately 20 mg / m² have a sufficiently good surface conductivity and are sufficiently transparent that the negative writing is at least visually clearly visible in transmitted light.

In a preferred embodiment, however, the security thread according to the invention consists of a transparent carrier film which is provided on one or both sides with a printed image or lettering, an opaque printing ink being used for producing this printed image. This printed image has a partially permeable metal coating on both sides, which gives the thread its electrical conductivity. In addition, due to its reflective properties, the partially permeable metallic coating has the effect that when the security document is viewed in incident light, the printed image on the security thread hardly or not at all appears. There is therefore no perceived interference between the outer print image of the security document and the print image on the security thread embedded in the security document.

Another version of the partially transparent layer consists of the use of a conductive plastic. Such plastics are generally not highly transparent, such as light-conducting, but partially transparent, so that, according to the invention, they can be combined with other properties which can be seen in transparency.

A further development of the invention relates to making properties of a security thread that are visually recognizable in transmitted light also mechanically verifiable. Visually very conspicuous properties of a thread, such as color or micro-printing, are lost in the colored equipment of the security thread that is usually contained in the security document when attempting machine recognition. However, if the security thread is equipped according to the invention with semipermeable conductive material, these can be used to "trigger" the measurement of the other properties, ie that the measurement, e.g. B. the color or structured imprints, takes place exactly at the point where the conductivity occurs. In this way, the coincidence measurement of conductivity and other properties of the security thread that can be recognized in transmitted light makes it possible to reliably assign them.

Another embodiment of the invention relates to the machine detection of transparency properties of the security thread that are not visually detectable, such as. B. infrared absorption. As described above, the infrared absorption of the thread is lost in the various infrared absorption properties of the security document if the measurement cannot be assigned exactly to the location of the security thread. According to the invention, the conductivity of the security thread also helps here for safe triggering for the measurement of the further properties.

In the case of the known security threads, which were distinguished by a print image visible in transmitted light, in the case of positive writing, the feature of electrical conductivity, which can be checked by machine, had to be dispensed with entirely; in the case of negative writing, this property was at least severely at risk of failure due to the mechanical loads, so the value for the machine authenticity check is reduced accordingly.

Since interrupted metal layers also have an alternating current conductivity, at least one or more of the conductive layers can also be designed as a grid, such as a line, hole or cross grid with possibly opaque grid elements. The degree of transparency When using opaque grid elements, these conductive layers can be varied by the structural thickness of the grid elements (line width etc.) and the area coverage (grid spacing etc.).

With the present invention it is now possible to provide security threads with any characters, printed images, etc., without thereby affecting the electrical conductivity. The conductivity as such can still be measured even after relatively high loads, which increases the reliability and the value for automated test systems. In addition to being mechanically testable, this security thread also has a different appearance in reflected light and transmitted light, which cannot be imitated by alternative measures. The change in appearance can thus be used as a visual feature, which also enables an authenticity check without tools. If a security equipped with the security thread according to the invention is reproduced with commercially available copying devices, in particular color copiers, then neither the machine-testable nor the visually visible properties can be produced therewith. The security thread mentioned thus also represents effective copy protection for securities.

Further advantages and advantageous developments result from the description of exemplary embodiments of the invention with reference to the figures.

Fig. 1

einen Sicherheitsfaden mit einem Negativschriftzug in einer Metallschicht,

Fig. 2

einen Sicherheitsfaden mit einem positiven Metallschriftzug und zusätzlichen elektrisch leitfähigen Beschichtungen,

Fig. 3

einen Sicherheitsfaden mit einem Druckbild und elektrisch leitfähigen Schichten,

Fig. 4

einen aus zwei Folien aufgebauten Sicherheitsfaden.

The figures show:

Fig. 1

a security thread with a negative lettering in a metal layer,

Fig. 2

a security thread with a positive metal lettering and additional electrically conductive coatings,

Fig. 3

a security thread with a printed image and electrically conductive layers,

Fig. 4

a security thread made up of two foils.

Fig. 1 shows a usable in security papers security thread 1 consisting of a plastic tape 2 made of a tear-resistant plastic material such as. B. polyester, one surface of which is provided with an opaque coating 3. This coating is preferably a reflective metal layer, e.g. B. an aluminum layer which has recesses 4 in the form of the characters and patterns to be applied to the security thread. After embedding a thread in a security paper, this coating is not visible in incident light, since the light reflected from the metal surface is again diffusely scattered in the paper. The recesses in the opaque layer can therefore only be recognized as bright areas when viewed in transmitted light. An electrically conductive layer 5 is applied to the back of the plastic film, which is preferably transparent, but at least partially permeable. Transparent, electrically conductive layers are e.g. B. indium tin oxide layers, which are applied to the film material in the sputtering process. The vacuum coating of plastic films with such materials is known (Kunststoffe 78 (1988) 9, G. Biekhor, Hanau "Vacuum coating of plastic films", pages 763-765). In many cases, however, "thin" aluminum vapor deposition is sufficient, which is simpler and cheaper in terms of process technology. Aluminum vapor deposition in a quantity of approx. 20 mg / m² or less is characterized by a sufficiently high transparency for most applications.

2 shows a security thread 11 which has a lettering consisting of reflective metallic characters 14, as is known, for example, from EP-A 0 279 880. Since the individual characters are not connected to one another, the thread, provided that it contains only these characters, is not electrically conductive over its entire length. According to the invention, this thread is now one over the The entire thread surface extending electrically conductive layer 15 supplemented, but this - in order not to impair the visibility of the lettering - is at least partially permeable. A transmittance of approx. 50% is usually sufficient to be able to clearly recognize the lettering without aids, even with a thread embedded in paper. With higher demands, fully transparent electrically conductive layers can also be applied, such as. B. the sputtered indium tin oxide layer already mentioned with, for example, 200 ohms per square area. In the security thread shown in FIG. 2, the characters 14 represent one conductive layer and layer 15 the other. The layer 14 consequently corresponds to a layer with many deliberately introduced interruptions. To improve the capacitive measurability, the characters should be formed as large as possible. If the individual characters are connected to one another, continuous conductivity is also present, as in the example shown in FIG. 1.

Instead of incorporating the characters into a metallic coating, the plastic carrier 22 for the security thread 11 can also be printed accordingly (FIG. 3). The printed image 24 can contain characters and / or colored patterns. Characters are preferably applied using an opaque printing ink so that they can be easily recognized as dark areas in transmitted light. In contrast, translucent or glazing colors are preferably used for color samples, so that these color samples are only slightly visible from the ground up in incident light and can only be recognized as colored areas in transmitted light. In order to give this thread the property of electrical conductivity, it is provided on both sides with transparent or translucent electrically conductive layers 25a, 25b. Should the print image too for this thread when viewing the security document in reflected light not competing with the outer printed image of the security document, preference is given to partially reflecting aluminum vapor deposition for the electrically conductive layers, e.g. B. of about 20 mg / m² or 800 ohms per square area. Since a surface conductivity of 10,000 ohms per square surface is sufficient for machine testing, the aluminum layer can, if necessary, also be made much thinner.

In a special embodiment (FIG. 4), the security thread 31 is composed of two carrier films 32, these carrier films including a printed image and / or the electrically conductive coatings 35. This protects the thin and generally sensitive layers (ITO layer, aluminum layer, etc.) against abrasion. Both foils are connected to one another via a non-conductive adhesive layer 36. A particular advantage of this structure is its symmetry. Such a security thread, which is pulled off a roll during paper production and is guided to the paper screen at a predetermined position in the pulp, is less prone to so-called garland formation or twisting after it has been rolled off the bobbin than asymmetrically constructed threads. The reject that arises with threads with an asymmetrical structure due to the flatness of the thread in the paper layer can be avoided in this way.

Due to the shifting of the sensitive layers into the inner areas of the security thread, materials can now also be used which could not be used in the prior art due to their exposed position due to the lack of environmental resistance.

Claims (17)

1. A security document having a security element (1, 11, 21, 31) in the form of a transparent thread or strip (2, 22, 32) embedded therein which bears marks in the form of printed patterns (24), characters (14) or the like that are largely concealed when viewed in incident light but are recognizable in transmitted light, and which is designed to be electrically conductive for machine testability, characterized in that the electrically conductive material (5, 15, 25a, 25b, 35a, 35b) extends all over at least one surface of the security element and is transparent or partly transparent at least in certain areas, and the electrically conductive material (5, 15, 25a, 25b, 35a, 35b) is disposed over and/or under the marks (4, 14, 24).
2. The security document of claim 1, characterized in that, in addition to the transparent or partly transparent layer (5, 15, 25a, 25b, 35a, 35b), at least one further conductive layer (3) is designed as an opaque metal coating containing the marks in the form of gaps (4).
3. The security document of claim 1, characterized in that the marks (14) consist of conductive material and the marks are possibly connected.
4. The security document of at least one of claims 1 to 3, characterized in that the transparent or partly transparent conductive material (5, 15, 25a, 25b, 35a, 35b) is a coating applied by the sputtering technique.
5. The security document of claim 4, characterized in that the transparent or partly transparent material (5, 15, 25a, 25b, 35a, 35b) is an indium tin dioxide layer.
6. The security document of at least one of claims 1 to 3, characterized in that the transparent or partly transparent conductive material (5, 15, 25a, 25b, 35a, 35b) is a vacuum evaporated metal layer.
7. The security document of claim 6, characterized in that the metal layer (5, 15, 25a, 25b, 35a, 35b) is a vacuum evaporated aluminum layer.
8. The security document of claim 7, characterized in that the aluminum layer has an equivalent thickness of 20 mg/m².
9. The security document of claim 1, characterized in that the marks are applied by printing technology.
10. The security document of claim 9, characterized in that the electrically conductive material (3, 5, 15, 25a, 25b, 35a, 35b) covers the entire surface of the marks applied by printing technology.
11. The security document of claim 10, characterized in that the electrically conductive material (3, 5, 15, 25a, 25b, 35a, 35b) is designed as a partly reflective metal coating.
12. The security document of claim 1, characterized in that the electrically conductive material is present in the form of layers separated galvanically by an insulating layer.
13. The security document of claim 12, characterized in that the insulating layer consists of aluminum oxide.
14. The security document of claim 1, characterized in that the security element comprises two carrier films (32), each of the films bearing an electrically conductive layer (35a, 35b) and the films being interconnected by an adhesive layer (36).
15. The security document of claim 14, characterized in that the films (32) enclose the electrically conductive layers (35a, 35b).
16. The security document of claim 14 or 15, characterized in that one of the electrically conductive layers (35a, 35b) is an opaque metal layer containing gaps in the form of the marks.
17. A method for testing security documents having a security element in the form of a transparent thread or strip embedded therein which bears marks in the form of printed patterns, characters or the like that are largely concealed when viewed in incident light but are recognizable in transmitted light, and which is provided for machine testability with electrically conductive material extending all over at least one of the surfaces of the security element and being transparent or partly transparent at least in certain areas, characterized in that the electric conductivity and the presence of defined optical properties are tested at the same place in the document and optionally at the same time.

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