GB2258426A

GB2258426A - A security document having an embedded security element or thread

Info

Publication number: GB2258426A
Application number: GB9216230A
Authority: GB
Inventors: Walter Schneider; Theodor Burchard
Original assignee: GAO Gesellschaft fuer Automation und Organisation mbH
Current assignee: GAO Gesellschaft fuer Automation und Organisation mbH
Priority date: 1991-08-06
Filing date: 1992-07-30
Publication date: 1993-02-10
Anticipated expiration: 2012-07-30
Also published as: DE4126051A1; GB2258426B; DE4126051C2; FR2680423A1; FR2680423B1; GB9216230D0

Description

2 2-3 342 J A security document having an embedded security element The

present invention relates to a security document such as a bank note, identity card or the like having a flat security element, the security element being suitable for both visual and machine authenticity checking.

U.S. patent no. 4,387,112 describes such security elements that can be used for both visual and machine identification of an object of value. For this purpose special luminescent inorganic substances are embedded in inks or in fibers so as to show fluorescent or phosphorescent effects when suitably excited, e.g. by means of an electric field, these effects not being recreatable by usual commercial organic compositions. During the authenticity check the incorporated substance is first excited and the decay of the phosphorescence observed. The stored energy then leads to a new increase in phosphorescence by application of infrared radiation, electric fields and the like. This change in the emitted radiation serves as the authenticity feature. However this method is very complex, and extremely elaborate and expensive due to the double irradiation, on the one hand, and the unusual inorganic compounds, on the other hand.

The invention is therefore based on the problem of providing a versatile security element that can be produced inexpensively in high piece numbers.

main claim.

This problem is solved by the features stated in the 1 Electroluminescence refers to that fluorescence or phosphorescence of a substance that is caused by application of an electric field. Electroluminescence can be observed only in certain substances or compounds since this property is closely connected with the crystalline structure of the particular substance.

Such substances or compounds are embedded according to the invention in safeguarding threads, that are already em bedded in security documents as security features, and therefore increase the protection of the document against forgery. 1 The use of so-called safeguarding threads is commonly known in the production of antifalsification paper. One uses for example metalized plastic films made of polyester, polyethylene or cellophane which can be additionally provided with prints fluorescent under UV light. Such threads are also known which bear microscopically small characters in addition to or instead of a metalization. Finally, a great number of threads are also known with electric conductivity or magnetic properties. Along with all these safeguarding thread materials, numerous combinations of the stated effects are also known.

The inventive material for producing electroluminescent safeguarding threads offers a great number of advantageous properties compared to known safeguarding threads. With electroluminescent safeguarding threads not only the mere presence, but also special physical properties can be tested by machine or measuring technology and recognized by the eye with simple aids. Since it is possible to make such threads glow by applying electric voltages and this glow can be associated with special wave ranges by corresponding selection of the electroluminescent pigments, the human eye as well as an electric or electronic measuring system will be able to perceive and assess this light emission. By contrast, security features incorporated in safeguarding threads and perceptible by measuring technology, such as electric conductivity, magnetism or the like, were hitherto beyond human perception and accessible only to measuring systems.

Furthermore, such thread materials are generally also electrically conductive since electrically conductive layers are required in the thread material for application of the electric voltage. This electric conductivity can be used as an additional test feature for measuring technology, along with the electroluminescence, without any changes having to be made in the structure of the safeguarding thread. one therefore has the possibility of including electric conductivity as an authenticity criterion for mechanical checking, in addition to luminescence. In a given case the test can also be limited to one of these features. The electroluminescent thread according to this invention thus has an advantageous combination of properties detectable by machine and by the human eye.

The inventive safeguarding threads are produced in sheets that are then cut into strips. In a preferred embodiment two plastic films are each provided on one side with a thin aluminum layer. On one of the metal layers an electroluminescent material based on zinc sulfide is printed in strips. Subsequently the plastic films are laminated in such a way that the electroluminescent material comes to lie between the metallic layers. In the last step this laminated sheet is cut into threads in accordance with'the electroluminescent strips.

4 - In addition the conductive layers can be provided by special techniques with so-called negative writing which is visible as interruptions in the conductive layer. In one embodiment one of the electrically conductive layers is highly opaque, i.e. designed with an optical absorption of at least 80 %. Alternatively there is also the possibility of making the electrically conductive layers so thin that they appear quasi transparent, or of using an optically transparent material for their production in the first place. Suitable for the latter method are special doped tin oxides, for example, which can be vacuum metalized as thin layers. Threads of this type are transparent and can there fore be provided additionally with microwriting, or with prints that are fluorescent under UV light.

The safeguarding threads according to the invention can also be used advantageously in identity cards. These cards can consist of a combination of plastics material and special paper layers, but may also be produced using only plastic layers. In extreme.cases it is possible to provide such cards with an electroluminescent layer all over so that the total card is excited to emit light upon application of a corresponding voltage.

Developments of the invention and further advantages can be found in the subclaims and the description of the embodiment examples with reference to the figures, in which:

Fig. 1 shows a bank note having an embedded safeguarding thread, Fig. 2 shows the layer structure of a laminated sheet for producing the inventive safeguarding threads.

z Fig. 1 shows a paper of value 1 having an embedded safeguarding thread 2. Safeguarding thread 2 can be embedded completely in the paper material, as indicated here by the broken lines, so that it can hardly be detected in incident light. However it can also be designed as a so-called window safeguarding thread. In this case the safeguarding thread is quasi woven into the paper material, i.e. it passes directly to the bank note surface at certain intervals and is easy to recognize there even in incident light.

The special structure of inventive safeguarding thread 2 is illustrated in Fig. 2. A polyester film 3 with a thickness of about 25 micrometers (e. g. Hostaphan RG) is first provided with a very thin layer of metallic aluminum in a vacuum. Layer 4 is designed in such a way that an optical absorption in the visible spectral range of approximately 70 % to 80 % results. On the side of this film provided with metal an ink 6 containing the electroluminescent material is printed in strips. One uses strips in the longitudinal direction of the film that are 0.6 mm wide and separated by spaces also 0.6 mm wide, for example. In the spaces one prints strips of heat-sealable ink 5 with a second printing cylinder. This ink consists of a solution of 30 g Vinnapas B100/20 VL (manufactured by Wacker AG) in 70 g ethanol.

The electroluminescent material is produced on a zinc sulfide base conforming to specification (Electroluminescence and related effects, Henry F. Ivey, New York, London 1963). The obtained material is given a particle size of 2 to 5 micrometers by grinding in a polyamide binder. The binder is obtained by dissolving 25 g Versamid 725 (manufactured by Schering AG) in a mixture of 40 g ethanol and g gasoline (boiling range 100 to 130 C). 35 g of the above zinc sulfide is rubbed into this solution per 100 g.

A second polyester film 30 of the same thickness is vacuum coated with metallic aluminum 40 in the above-described way and then printed all over with heat-sealing lacquer 5 according to the above recipe. The two films are laminated together under heat and pressure and then cut into threads 1.2 mm wide. The cut is controlled in such a way that the cutters run in the spaces with the heat-sealable strips. One thus obtains threads which have the electroluminescent compound embedded in the interior and are sealed from the outside by the two films and the heat-sealing compound. This prevents moisture from penetrating into the electroluminescent substances and prematurely disturbing the electroluminescence.

If one applies the electroluminescent material accordingly and adapts the cutter control one can of course also realize other thread widths up to several millimeters. Such wider pieces of thread can for example be applied to the front of documents like holograms.

Also, electroluminescent substance 6 need not be disposed on metalized polyester film 3 in the above-described strip form. A possible variant is to provide interruptions of 1 to 6 mm at regular intervals within the strips (regarded in the longitudinal direction). Heat-sealable ink 5 is then printed both between the electroluminescent strips and in the interruptions within the strips. This results in a grid of heat-sealable ink whose gaps contain electroluminescent elements with a width of e.g. 0. 6 mm which extend in the longitudinal direction of the print over distances from a few millimeters up to a few centimeters.

7 - Second film 30 is prepared as already described and the total structure then laminated in the known way.

The modification of the method results in the electroluminescent substance being surrounded completely by heatsealable ink on all four sides. When this material is cut in the above-described way the thread, which may likewise have a width of 1.2 mm for example, acquires a pattern of electroluminescent fields which offers various advantages. Firstly, if a piece 10 cm long is cut from such a thread for example this piece is also protected from the penetration of moisture. Even if an electroluminescent layer was cut open accidentally at the front or back end of the piece and is therefore exposed, the fields intact within the piece are still just as operative as before.

This division into fields also makes it possible to incorporate a coding in the thread. One could divide up the fields e.g. in the form of a bar code, Morse code or any other special information-bearing code.

A thread obtained in the above way is excited by applying a usual supply alternating voltage of 220 V and 50 Hz (using a protective resistance of 10 KOhm) to each side of the thread. This results in a field strength of about 44 kV/cm. Under these conditions a greenish-blue light emission 7 can be observed within the thread, which is recognizable through thin vacuum metalized layers 4, 40.

The application of the inventive safeguarding thread is not limited to bank notes; it can be used in any type of security document, including identity cards.

In the special case of identity cards the card is provided all over with an electroluminescent layer so that upon application of a corresponding voltage the total card is excited to emit light. The upper side of the card inlay is provided with an electrically conductive layer and the electroluminescent material printed thereabove. A further metallic coating is provided above this layer structure. All-over layers of this type can be designed in such a way for example that at least one of the metal layers is at least semipermeable for light and this layer is then provided with data as the front of the card. Finally the front is covered with a transparent plastic layer by heat-sealing. However it is also possible to use the electroluminescent layer on the back of such a card with or without using applied information.

Combinations with additional properties are also possible in the case of such identity cards. For example one of the electrically conductive layers can be turned to the front of the card and bear recesses in the form of negative writing or a corresponding symbol. When voltage is applied to such a card the symbol appears as a luminous figure on the front of the card.

9

Claims

1. A security document such as a bank note, identity card or the like having a flat security element, the security element being suitable for both visual and machine authenticity checking, in which the security element is of multilayer design and has electroluminescent properties.

2. The security document of claim 1, in which the security element is a multilayer electroluminescent film strip.

3. The security document of claim 2, in which the el ectrolumine scent film strip has a width of 0.4 to 2 MM.

4. The security document of claim 2, in which the security element is embedded completely in the document material.

5. The security document of claim 2, in which the security element passes directly to the document surface in window-like openings so that it is easy to recognize in the area of these windows in incident light.

6. The security document of claim 1, in which the security element is embedded in the security document over the entire surface.

7. The security document of claim 6, in which the security element comprises two metallic layers and an electroluminescent material therebetween.

8. The security document of any of claims 1 to 7, in which the security element is combined with additional information in the form of printed alphanumeric characters.

9. The security document of any of claims 1 to 8, in which the security element is combined with negative writing.

10. The security document of any of claims 1 to 9, in which the security element is combined with colorings or prints that are fluorescent under UV light.

11. A method of producing a multilayer security element to be incorporated in a security document such as a bank note, identity card or the like, the security element being suitable for both visual and machine checking, in which it includes the following steps:

- coating a plastic film with metallic material, - printing a heat-sealable ink in the spaces not provided with electroluminescent material, - coating a second plastic film with metallic material printing an ink mixed with electroluminescent material onto the metalized side of the film in strips, - printing this second metallic layer with heat-sealable ink, 11 laminating the two films so that the electroluminescent material is sealed from the outside by the heat-sealing compound and the films.

- cutting the laminated films into strips, controlling the cutters so that they run in the spaces with the heat-sealable compound.

12. The method of claim 11, in which the plastic films are vacuum coated with aluminium.

13. The method of claim 11, in which the strips of electroluminescent ink are provided with interruptions, giving rise to a coded information field consisting of electroluminescent areas.

14. The method of claim 11, in which the laminated films are cut into strips 1.2 mm wide.

15. The method of claim 11, in which the laminated films are cut into strips a few millimeters wide.

16. A method for producing a security document such as an identity card or the like, a security element suitable for both visual and machine checking being incorporated in the security document, in which it includes the following steps:

coating an inlay with metal, - printing an electroluminent ink on the metallic layer over the surface, coating this electroluminescent layer with metal, 12 - covering this metallic layer with a transparent protective film.

17. The method of claim 16, in which one of the metal layers is at least semipermeable for light.

18. The method of claim 16, in which the applied metal layer is printed with data.

19. The method of claim 18, in which recesses in the form of negative writing or a symbol are provided in the semipermeable metal layer.

20. The method of claim 16, in which the metal layers and the electroluminescent layer embedded therebetween are applied to the back of the document.

21. A security document substantially as described herein with reference to and as illustrated in the accompanying drawings.

22. A method of producing a multilayer security element to be incorporated in a security document substantially as described herein with reference to and as illustrated in the accompanying drawings.