EP1549501B1 - Security element - Google Patents

Abstract

The invention relates to an object of value with a security element having at least a first and a second liquid-crystalline material, the first material having thermochromic properties and the second material an optically variable effect.

Description

The invention relates to a security element for securing valuables, which has at least a first and a second liquid-crystalline material, wherein the first material has thermochromic properties and the second material has an optically variable effect. Furthermore, the invention relates to a valuable article, a transfer material and method for producing such security elements and valuables and a method for checking such a security element or valuable article.

A valuable item in the sense of the invention can be any item intended to be protected, such as branded articles or value documents. Valuables in the context of the present invention are in particular banknotes, but also stocks, certificates, stamps, checks, check cards, credit cards, identity cards, passports, tickets, tickets, airline tickets and the like, as well as labels, seals, packaging or other elements for product assurance. The simplified term "valuable item" or "security element" therefore always includes documents of the type mentioned below.

It has long been known to use thermochromic materials to secure value documents. For example, describes the DE 22 12 350 a security thread of transparent plastic having cavities. In these cavities is a liquid crystalline material which shows a reversible color change upon increase or decrease in temperature.

From the EP 0 608 078 B1 Also known is a security thread with thermochromic properties. In this case, a plastic material is provided with a mark or imprint by partial demetallization a metal layer have emerged. Above this imprint or these negative signs, a thermochromic coating colored at normal temperature is arranged. Upon heating, the thermochromic coating becomes colorless, so that the underlying characters are recognizable. Alternatively, a thermochromic coating may be used which is colorless at normal temperature and becomes colored upon heating so that the characters disappear. This thread is inserted into the security paper so that it comes in certain areas, so-called "windows", directly to the surface.

However, such thermochromic security threads have the disadvantage that the thermochromic effect is already used in many non-safety areas for purely decorative purposes, which is why the caused by the color change of the thermochromic material optical effect is no longer recognized by the viewer as a security feature but only as a design variant. Such security elements therefore offer no high protection against counterfeiting.

The invention is therefore an object of the invention to provide a valuable item, a transfer element and a security element, which provide a high counterfeit protection and avoid the disadvantages of the prior art.

A further object of the invention is to provide methods for producing such a security element and valuable article as well as a method for checking the security element or valuable article.

These objects are achieved by the features of the independent claims. Further developments are the subject of the dependent claims.

According to the invention, the security element comprises at least a first and a second liquid-crystalline material, wherein the first material has thermochromic properties and the second material has an optically variable effect.

The first liquid crystalline material has thermochromic properties, that is, its natural color changes under the influence of temperature. Preferably, the thermochromic material additionally exhibits polarization effects, i.e., it is capable of selectively polarizing light. These substances are preferably encapsulated liquid crystals which are crystalline at a certain temperature and do not polarize, but when the temperature changes, in particular increase in temperature, and change in the liquid-crystalline state change their color and additionally polarize. Depending on the thermochromic material used, the material can change from the liquid-crystalline state into the liquid state upon further increase in temperature, the thermochromic material again being transparent or at least translucent in the liquid state and not being polarized.

The second liquid crystalline material has an optically variable effect. For the purposes of the invention, the term "optically variable effect" is understood to mean the effect that different color impressions are imparted at different viewing angles. One speaks also of the so-called "color shift effect". Green-blue or copper-green color transitions have proven particularly suitable. Preferably, this second material also exhibits light-polarizing properties. In particular, crosslinked liquid-crystalline materials exhibit light-polarizing properties at the same time Presence of a color shift effect without exhibiting thermochromic effects.

In a particularly preferred variant, the thermochromic liquid-crystalline material and the liquid-crystalline material with optically variable effect polarize light respectively different e.g. For example, one material can selectively polarize circularly to the right and selectively polarize the other material circularly to the left.

Preferably, the liquid-crystalline materials are processed in the form of printing inks, in which they are mixed, for example, a transparent binder. The printing ink can of course contain further color pigments. The liquid-crystalline materials can be processed with any suitable printing process, in particular by means of screen printing and intaglio printing, but also in halftone, flexographic and letterpress printing.

In addition to printing inks, the materials can also be added to a transparent plastic layer.

For the liquid-crystalline materials according to the invention, numerous variations are possible within the scope of the invention. Thus, the thermochromic material over the entire surface or preferably only partially, in particular in the form of characters or patterns, can be provided.

Like the thermochromic material, the liquid-crystalline material having an optically variable effect can be processed over the whole area or in regions, with full-area or area-wise processing being preferred depending on the application form.

The thermochromic material can be arranged above and / or below and / or next to the material with an optically variable effect. Particularly suitable effects result in at least partial overlapping of the different liquid-crystalline materials. An overlap of the effects also has the advantage that the viewer can make these easier on the object to be secured and this can check at the same time in suitable embodiments. In particular, when using polarizing filters can be made visible by placing the filter on a certain point of the object, the effects with a "handle".

Substances are preferably used for the thermochromic material which are at least translucent, preferably transparent, below a predetermined temperature and are colored above this temperature. In certain applications, it may be useful to use thermochromic substances that are colored below a predetermined temperature and translucent or transparent above that temperature. The turnover temperature of the thermochromic substances is preferably above the ambient temperature, e.g. in the range of 25 ° C to 60 ° C, preferably 30 ° C to 60 ° C. Depending on the application, however, turnover temperatures below 25 ° C are also conceivable.

The individual layers of the security element can either be created directly on the object of value or prepared on a separate carrier. The valuable article or separate carrier as a substrate on which the security element is located is in no way limited in relation to the material used. Preferably, however, it is paper or plastic, also in the form of films. For a separate carrier, the security element may be preferred, for example, as a self-supporting label on a plastic substrate, be formed. Since it may be difficult in some cases to provide the valuable item directly with the respective layer sequence, it may alternatively be useful to prepare the layer structure of the security element at least partially on a transfer material.

If the entire layer sequence of the security element is prepared on a transfer material, care must be taken that the layer structure shown in the respective figures must be prepared in the reverse order on the carrier tape of the transfer material. The layer structure of the security element can be prepared in an endless form on the carrier tape. The security element is applied to a valuable object to be secured by means of an adhesive layer which is applied either to the valuable article or else to the uppermost layer of the transfer material. Preferably, a hot melt adhesive is used for this purpose. In order to define the outline shape of the security element, an adhesive layer can be provided either only in the areas to be transferred or the adhesive, such as a hot melt adhesive, is activated only in the areas to be transferred. After the transfer, the carrier tape of the transfer material is removed and only the layered structure of the security element shown remains on the valuable item to be secured.

The valuable article to which the security element is applied can be, for example, a security paper, a security document, but also product packaging. Other valuables that require safety-related protection, can of course be provided with the security element according to the invention.

Preferably, the security element is arranged completely on the surface of the object to be secured. If the security element is arranged completely on the surface of the object, it can be made substantially larger area, so that the optically variable effect and the thermally induced color change of the different liquid crystalline materials is much more obvious due to the larger area. Also, the use of a polarizing filter is much easier if a larger observation area is available.

By using different polarizing liquid-crystalline materials, the security element is also made forgery-proof. Because such materials are either expensive to manufacture or can not be obtained in the market readily.

The present invention thus offers additional protection against counterfeiting by combining the thermochromic effect visually discernible without aids and the optically variable effect that can be visually perceived without aids. In particular, the security against counterfeiting is further increased by the additional use of the visually perceptible polarization effect only with aids. In addition to the easily recognizable optically variable effect, in addition, information can be easily hidden or made visible by means of the thermochromic effect, for example, only by touching the viewer can expose the information. The authenticity of the information can be further checked in a next step, for example by means of a polarizing filter, if at least one of the liquid-crystalline materials polarizes light.

Further advantages and embodiments of the invention will be explained in more detail with reference to the figures. The proportions shown in the figures do not necessarily correspond to the conditions existing in reality and serve primarily to improve the clarity.

Fig. 1

ein Sicherheitsdokument mit einem erfindungsgemäßen Sicherheitselement,

Fig. 2, 5, 6

verschiedene Ausführungsformen des Sicherheitsdokuments im Querschnitt,

Fig. 3, 4

Ausführungsform gemäß Fig. 2 in Aufsicht.

Show it:

Fig. 1

a security document with a security element according to the invention,

Fig. 2, 5, 6

various embodiments of the security document in cross-section,

Fig. 3, 4

Embodiment according to Fig. 2 in supervision.

The invention is explained in greater detail for the sake of clarity using the example of a banknote.

Fig. 1 shows such a banknote 1 made of paper or plastic, which is provided with a extending over the entire width of the banknote security element 2 in the form of a strip. The banknote 1 may of course have other security features, such as watermarks, steel gravure, security thread or luminescent or magnetic imprints or the like.

The security element 2 has a thermochromic liquid-crystalline layer which is combined with a liquid-crystalline color-shift effect layer. The security element 2 is arranged completely on the surface of the banknote 1, so that the thermally induced color change of preferably in pattern and / or sign applied thermochromic layer is very well recognizable.

In addition to the thermochromic layer and the color-shift effect layer, the security element 2 can also have further layers which, on their own or in combination with other layers of the security element, produce further conspicuous optical effects. Some preferred embodiments will be described with reference to FIG Fig. 2 to 6 explained in more detail, which show the banknote 1 in plan view or in cross section along the dot-dash line A - A to illustrate the layer structure of the security element 2.

According to Fig. 2 For example, the paper or plastic substrate 3 of the banknote 1, which has a white or light intrinsic color, is provided with a liquid-crystalline thermochromic imprint 4 in the form of characters or patterns. Over the thermochromic layer 4, a liquid-crystalline Farbkippeffektschicht 5 is arranged over the entire surface, which generates different color impressions regardless of the temperature when changing the viewing angle in reflection. This effect is called an "optically variable" effect. The layers 4 and 5 may be, for example, a printing ink consisting of a transparent binder in which liquid crystal pigments are mixed.

Since these pigments are translucent and have no or only a slight own body color, the visually recognizable visual impression of these pigments is strongly influenced by the substrate. On a diffusely reflecting white or light background, the pigments hardly appear, because the diffusely reflected scattered light superimposes the optically variable effect. On a dark background, on the other hand, the play of colors of these pigments is especially good as it transmits them Absorbed radiation. According to the invention, the dark, preferably black background can be provided over the entire surface or in a structured manner. For example, the background can be designed in the form of patterns and / or characters, such as guilloches, negative guilloches or other finely structured patterns. Just as well can be incorporated by means of alphanumeric characters or bar codes information in the security element. Preferably, the substrate is designed so that the vast majority of the surface in question is dark or black.

Due to the light permeability of the liquid crystal pigments, the substrate 3, at least in partial regions of the liquid-crystalline materials 4, 5 preferably a dark, especially black intrinsic color or - as shown here - another dark, preferably black layer 6, which may be printed, for example. In the case of a dark background, the optically variable effect produced by the color-shift effect layer 5 is particularly prominent. In the in Fig. 2 In the variant shown, at least the area provided with liquid-crystalline material is underlaid with a black layer over the whole area. For the layer 4, a thermochromic material is preferably used, which is transparent at normal ambient temperature. Above the turn-over temperature of the thermochromic layer 4, the latter preferably becomes colored, in particular bright, so that the signs represented by the thermochromic layer 4 become visible and the color-shift effect in the area of the signs is virtually imperceptible. The viewer thus has the following picture. Below the turn-over temperature, it only perceives the color-shift effect of the non-thermochromic material 5 with the naked eye. By supplying body heat when touching or rubbing the surface can also - as in Fig. 3 shown - the thermochromic information 4, here the rectangles, are read above the envelope temperature. With the naked eye the viewer can so check two security features already. In a preferred embodiment, at least one of the liquid-crystalline materials used is polarizing substances. Particularly preferably, both the thermochromic material 4 as well as the material with color shift effect 5 has polarizing properties. This in Fig. 2 processed thermochromic material polarized above the transition temperature, ie in the liquid crystalline state, preferably rechtscircular light, while polarizing the material with color shift effect linkscircular. Therefore, when viewed with a polarizing filter that transmits only right circularly polarized light, only the information 4 can be read above the turning temperature, while the area of the color tilting material 7 appears black. This situation is in Fig. 4 shown. When viewed with a polarizing filter that transmits only left circularly polarized light, only the color shift area 5 can be perceived.

Alternatively, a thermochromic material may be used which is bright or colored at normal ambient temperature and becomes transparent above a certain activation temperature. In this case, a previously existing information disappears when exposed to heat.

As in Figure 5 shown, unlike in Fig.2 shown layer sequence on the black coated substrate 3, first the liquid crystalline Farbkippeffektschicht 5 and then only the thermochromic liquid-crystalline layer 4 are applied. Which layer order is preferred depends on the application or production possibilities and can be decided on a case-by-case basis. If the thermochromic layer is located between the substrate and the color-shift effect layer, in some embodiments the thermochromic effect lasts longer in time since the color-shift effect layer could serve as an art heat insulator. This depends, however strong on several other factors, such as applied heat, processed layer thickness, etc. The observed effects on color shift effect, thermochromic information and polarization are with those Fig. 2 comparable.

Fig. 6 shows a layer structure in which the substrate 3 is provided in a first step with a dark, preferably black imprint 6 in the form of patterns and / or characters. In Fig. 2 and 5 a full black layer was used. Over this print 6, a full-surface layer 4 of thermochromic material, followed by a Farbkippeffektschicht 5, applied. If a material is used for the thermochromic layer 4 which is transparent at ambient temperature, then the optically variable layer 5 appears in the regions of the dark or black imprint as a brilliant layer with a color interplay and is barely perceptible in the regions of the light substrate. Above the transition temperature of the thermochromic material, the layer 4 becomes colored and can be well recognized in the region of the underlying label 6. The color shift effect is no longer visible to the naked eye. If the thermochromic material has right circularly polarizing properties, this can be detected in the region of the black imprint 6 above the transition temperature using a corresponding polarization filter. If the color-shift effect material has linkcircular polarizing properties, it can also be measured independently of temperature in the area of the black imprint 6 using a corresponding polarization filter.

The security against counterfeiting is particularly increased if, in addition to the thermal effect and the color-shift effect, additional polarization effects are used. In the embodiments shown in the figures, of course but not limited to this, for example, the liquid-crystalline thermochromic material can polarize light circular right, while the liquid crystal material with color-shift polarized light circular left.

It is likewise possible for the liquid-crystalline layers and / or at least one of the further layers to have further visually and / or machine-testable properties, such as electrical conductivity, magnetism, luminescence or the like. In order to give the respective printing electrically conductive properties, it is sufficient, for example, to add a sufficient amount of carbon black pigments to the printing inks used. Since, in particular, the substrate should have a dark, preferably black intrinsic color, it can be equipped in a very simple way with magnetic properties by using dark magnetic pigments instead of color pigments.

In certain embodiments, eg security elements which are exposed in use to strong mechanical or chemical stress, it is appropriate to cover the liquid-crystalline materials with a protective layer. The protective layer may be a film laminated over the security element or a protective lacquer layer. The protective lacquer layer can be applied over the entire surface or in partial areas. The sub-areas can be arranged with juxtaposed thermochromic material and material with optically variable effect only one, for example, the thermochromic material. In the paint system, for example, UV varnishes, hybrid varnishes, oil-based varnishes or dispersion varnishes of the one- or two-component type can be used. The protective lacquer layer is preferably printed, for example by means of flexographic printing or offset printing.

The thermochromic layer may also have a plurality of thermochromic materials with different transition temperatures. It is also possible to combine the thermochromic layer of several color layers, each containing different thermochromic materials with different transition temperatures. In a particularly attractive embodiment, the thermochromic material exhibits rainbow colors when the temperature increases, i. a color change from colorless to red, yellow, green to blue.

Likewise, different liquid crystalline materials can be combined with different color shift effects.

Claims (30)

1. An object of value with a security element, the security element having at least a first and a second liquid-crystalline material, the first material having thermochromic properties and the second material an optically variable effect, characterized in that the first material is crystalline and does not polarize at a first temperature, and changes its colour and polarizes upon a change of temperature and change to the liquid-crystalline state.
2. An object of value according to claim 1, characterized in that at least one of the liquid-crystalline materials polarizes light selectively.
3. An object of value according to claim 1 or 2, characterized in that the first and second materials polarize light differently.
4. An object of value according to at least one of claims 1 to 3, characterized in that the first material polarizes light right-handed and the second material polarizes light left-handed or vice versa.
5. An object of value according to at least one of claims 1 to 4, characterized in that the optically variable effect is a colour shift effect.
6. An object of value according to at least one of claims 1 to 5, characterized in that the thermochromic material is applied all over.
7. An object of value according to at least one of claims 1 to 5, characterized in that the thermochromic material is provided only in certain areas.
8. An object of value according to claim 7, characterized in that the thermochromic material is provided in the form of characters and/or patterns.
9. An object of value according to at least one of claims 1 to 8, characterized in that the thermochromic material is disposed above or below the material with an optically variable effect.
10. An object of value according to at least one of claims 1 to 8, characterized in that the thermochromic material is disposed beside the material with an optically variable effect.
11. An object of value according to at least one of claims 1 to 10, characterized in that an at least partly dark, preferably black, background is present below the liquid-crystalline materials.
12. An object of value according to claim 11, characterized in that the background is dark all over.
13. An object of value according to claim 11, characterized in that the background is present in the form of patterns and/or characters.
14. An object of value according to at least one of claims 11 to 13, characterized in that the background is printed, produced by colouring a substrate or by laser.
15. An object of value according to at least one of claims 1 to 14, characterized in that one of the materials, the background and/or a further layer has properties that are testable visually and/or by machine.
16. An object of value according to at least one of claims 1 to 15, characterized in that the thermochromic material is coloured below a predetermined temperature and transparent or at least translucent above said temperature.
17. An object of value according to at least one of claims 1 to 15, characterized in that the thermochromic layer is at least translucent or transparent below a predetermined temperature and coloured above said temperature.
18. An object of value according to at least one of claims 1 to 17, characterized in that the security element is a label.
19. An object of value according to at least one of claims 1 to 17, characterized in that the object of value is a security paper, a security document or a product package.
20. An object of value according to at least one of claims 1 to 19, characterized in that at least part of the security element is covered with a protective layer.
21. A security element for protecting objects of value, the security element having at least a first and a second liquid-crystalline material, the first material having thermochromic properties and the second material an optically variable effect, characterized in that the first material is crystalline and does not polarize at a first temperature, and changes its colour and polarizes upon a change of temperature and change to the liquid-crystalline state.
22. A security element according to claim 21, characterized in that the first and second materials polarize light differently.
23. A security element according to claim 21 or 22, characterized in that the optically variable effect is a colour shift effect.
24. A security element according to at least one of claims 21 to 23, characterized in that the thermochromic layer is transparent or at least translucent below a predetermined temperature and coloured above said temperature.
25. A security element according to at least one of claims 21 to 24, characterized in that the security element is a security thread.
26. A transfer material for producing a security element, the transfer material having a carrier material on which at least a first and a second liquid-crystalline material are disposed, the first material having thermochromic properties and the second material an optically variable effect, characterized in that the first material is crystalline and does not polarize at a first temperature, and changes its colour and polarizes upon a change of temperature and change to the liquid-crystalline state.
27. A transfer material according to claim 26, characterized in that the transfer material is formed as a hot embossing foil.
28. A method for producing an object of value or security element, whereby

    - a substrate is provided,

    - thermochromic liquid-crystalline material and liquid-crystalline material with an optically variable effect are applied to said substrate,

    characterized in that the first material selected is a material that is crystalline and does not polarize at a first temperature, and changes its colour and polarizes upon a change of temperature and change to the liquid-crystalline state.
29. A method according to claim 28, characterized in that

    a) the substrate has an at least partly black layer or surface,

    b) the thermochromic material is applied thereabove in the form of characters and/or patterns, and

    c) the liquid-crystalline material with an optically variable effect is applied thereabove; or

    d) the substrate has an at least partly black layer or surface,

    e) the liquid-crystalline material with an optically variable effect is applied thereabove, and

    f) the thermochromic material is applied thereabove in the form of characters and/or patterns.
30. A method for testing an object of value, characterized in that it is verified whether a colour shift effect is present, and whether upon a change of temperature both a thermochromic effect and a polarization effect not existing before the change of temperature are present.

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