Optically variable security element with machine-readable feature substance and optical functional layer, value document and examination method

Abstract

The invention relates to an optically variable security element (20) for protecting a value document (10), having a first machine-readable feature substance (36) and an optical functional layer (24, 26) which gives the security element (20) an optically variable appearance when viewed. According to the invention, the security element (20) is formed from multiple layers, with an interior film layer (30) which has a first side and an opposite second side, wherein the film layer (30) is provided at least on the first side with an adhesive layer (34) for connecting to the value document (10) and on the second side with the optical functional layer (24, 26), and wherein the first machine-readable feature substance (36) is arranged in the film layer (30) or on the second side of the film layer (30).

Description

[0001]Optically variable security element with machine-readable feature substance and optical functional layer, value document and verification method. The invention relates to an optically variable security element for securing a value document with a machine-readable feature substance and an optical functional layer that gives the security element an optically variable appearance when viewed. The invention also includes a value document with such a security element, as well as a method for verifying such a value document. Data carriers, such as valuables or identification documents, but also other valuable objects, such as branded goods, are often provided with security elements for security purposes. These elements allow verification of the authenticity of the data carriers and simultaneously serve as protection against unauthorized reproduction. It has been shownthat security elements are removed from genuine value documents by counterfeiters during attempts to manipulate them and are applied to an unauthorized document, or that the substrate of a genuine value document is provided with a counterfeit security element after such a removal process. This type of removal attack is also referred to as "harvesting" and is often difficult to detect as tampering, both visually and mechanically. Foil security elements often do not bear machine-readable features, so that the replacement of such a security element with a counterfeit is not easily detectable by machine. Therefore, in the publication WO 2023 / 285000 A1, it was proposed to provide both the substrate of a banknote and an applied security element with security components.which, in combination, provide a characteristic signal. The absence of the combination signal then represents a strong indication of manipulation. However, there is a risk that when a security element is removed, part of the security component generating the characteristic signal remains on the banknote substrate, so that despite the manipulation, a combination signal is generated and the manipulated note cannot be reliably identified as a counterfeit. Based on this, the invention is based on the object of specifying a generic security element,which avoids the disadvantages of the prior art. In particular, in the event of a detachment attack on a security element applied to a document, the machine-readable feature substance is to be completely removed from the original document. The invention is also intended to provide a valuable document secured against detachment attacks with such a security element and a testing method for valuable documents secured in this way. This object is achieved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims. The invention contains an optically variable security element with a first machine-readable feature substance and an optical functional layer that gives the security element an optically variable appearance when viewed. The optically variable security element serves, in particular, to secure a valuable document,such as a banknote or an identification document. As a special feature, the security element is multi-layered, with an inner foil layer having a first side and an opposite second side. The foil layer is provided with an adhesive layer for bonding to the value document at least on the first side and with the optical functional layer on the second side. The first machine-readable feature substance is arranged in the foil layer or on the second side of the foil layer. The arrangement on the second side of the foil layer can be either directly on the surface of the second side of the foil layer or, alternatively, in a layer on the second side spaced from the surface of the foil layer by further intermediate layers. In some cases, in this description, the first side of the foil layer is also referred to as the "underside" and the second side as the "top side."This is especially true for security elements bonded to a target document, where the first side is often connected to the target document and the second side faces the viewer. However, a security element can also be arranged in a recessed or transparent area of ​​the target document and designed to be viewed from both sides. For security elements partially or completely embedded in a target substrate, such as security threads, both the first side and the second side can be exposed in window areas and face the viewer. Here, too, the security threads, for example, in the case of pendulum security threads,be viewable from both sides. The terms "underside" and "top side" are therefore not to be understood as limiting in the following description. After the security element according to the invention has been adhered to a target document or incorporated into a target document, the position of the feature substance ensures that the feature substance is completely removed together with the optical functional layer in the event of a detachment attack, and that no residue of the feature substance remains on or in the target document. Without wishing to be bound to a specific explanation, the inner film layer, according to current understanding, stabilizes the overlying or underlying layers of the security element to such an extent that when the optical functional layer is detached, the film layer is also detached. Since the machine-readable feature substance is arranged in or above the film layer, it is completely detached during this process.without leaving residues on or in the target document. In other words, the optical functionality of the security element can only be detached or removed from a document together with the entire feature substance. In an advantageous embodiment, the first machine-readable feature substance is an IR luminescent substance or an optical storage phosphor with optically stimulated luminescence. In an advantageous embodiment, the first machine-readable feature substance is present in a feature layer arranged on the second side of the film layer, in particular in a UV-curable lacquer layer, an embossing lacquer layer, or an adhesive layer, for example a laminating adhesive layer. With particular advantage, the layer containing the first machine-readable feature substance is the optical functional layer itself.a part of the optical functional layer or is directly connected to the optical functional layer. For example, the optical functional layer can contain an embossing lacquer layer provided with a relief structure, and the first machine-readable feature substance can be incorporated into the embossing lacquer layer. In another embodiment, the first machine-readable feature substance can be present in an adhesive layer with which the optical functional layer is connected to the film layer. The first machine-readable feature substance can also be present in a separate, dedicated feature layer.which is arranged in particular between the film layer and the optical functional layer. Furthermore, the first machine-readable feature substance can also be present in the film layer itself. The film layer is advantageously formed by a film with a thickness between 4 µm and 15 µm and is, for example, a PET film. In an advantageous embodiment, the optical functional layer is formed by a hologram or another diffraction structure, an interference structure, a matte structure, a micromirror arrangement, a microlens arrangement, a moth-eye structure, a subwavelength structure, or a combination of these elements. The optical functional layer advantageously has a reflection-enhancing coating, in particular a metal layer, for example made of Al, Cr, Fe, Ni, Cu, Fe:Si, or alloys of these materials, a high-index layer,such as TiO2 or ZnS and / or a color-shifting interference layer structure. The interference layer structure can be formed, in particular, from a color-shifting thin-film element with the layer sequence absorber / dielectric / reflector, for example Cr / SiO2 / Al or Al / SiO2 / Al. The reflection-enhancing coating can be provided with transparent and / or semi-transparent regions using suitable processes. For example, a washing process, structuring using resist and an etching step, or partial laser ablation or laser modification of the reflection-enhancing coating can be considered. According to a preferred embodiment, the first machine-readable feature substance is an IR luminescent substance which has an emission in the near-infrared spectral range, in particular in the wavelength range between 800 nm and 2100 nm and / or in the wavelength range between 400 nm and 2100 nm,preferably in the wavelength range between 700 nm and 2100 nm. In another, equally advantageous embodiment, the first machine-readable feature substance is an optical storage phosphor with optically stimulated luminescence. The functioning of such optical storage phosphors is described in more detail, for example, in the document DE 102017008868 A1. The charging of the optical storage phosphor preferably takes place in the wavelength range of 350 nm - 550 nm, preferably in the VIS (visible) wavelength range of 400 - 550 nm, and the reading preferably in the VIS or IR wavelength range of 550 nm - 1000 nm. An optical storage phosphor is advantageously used as the first machine-readable feature substance, in particular, when the feature substance is arranged on the second side of the film layer above any metal layers that may be present.since then a reading of the feature substance in the VIS or even UV spectral range is easily possible. According to a further development of the invention, the security element contains one or more additional functional layers with further authenticity features such as fluorescence, IR, magnetic, conductivity, polarization effects, colored colors, and / or effect colors. The functional layers can be present over the entire surface or structured. Optically effective functional layers are advantageously only partially concealed by a reflection-enhancing coating of the security element, in particular an opaque reflection-enhancing coating. Sensitive layers can optionally be protected by laminating a film. The film to be laminated can bear any of the aforementioned layers. If light-absorbing layers are used, the use of an optical reflector located on the back,for example, made of supersilver or in the form of a metallization, can be advantageous in order to reduce visibility after embedding in the paper. According to an advantageous variant of the invention, the security element is a security thread, in particular a window security thread or a pendulum security thread. Such a security thread can be applied to a valuable document, but it is advantageously partially or completely embedded in a valuable document. According to another, equally advantageous variant of the invention, the security element is a patch or label for application to a valuable document. If the security element represents a security thread that is at least partially embedded in a paper substrate, the embedding in the paper can be improved by using heat-sealing lacquers on both thread surfaces. The adhesion of the heat-sealing lacquers to the thread can be increased by using primers. In general, it may be necessaryto improve the adhesion of layers through the use of primers. If the security thread contains micro-optical systems with microlenses, such as a moiré magnification arrangement, it may not be possible to use a heat-sealing varnish on the top side (lens side) of the thread. This disadvantage can be avoided by using high- and low-refractive-index varnish systems (for embossing / embedding), which makes the use of primer and heat-sealing varnish possible again. The invention also includes a value document with an optically variable security element of the type described, wherein the optically variable security element is bonded to a substrate of the value document by means of the adhesive layer arranged on the first side (underside) of the foil element. The substrate of the value document contains a second machine-readable feature substance,in particular an IR luminescent substance or an optical storage phosphor with optically stimulated luminescence. The invention further includes a value document with an optically variable security element of the type described, wherein the optically variable security element is a security thread at least partially embedded in the value document, and wherein the substrate of the value document contains a second machine-readable feature substance, in particular an IR luminescent substance or an optical storage phosphor with optically stimulated luminescence. In this case, the security thread can be securely anchored to both the first side and the second side of the film element via an adhesive layer.In particular, a heat-sealing lacquer layer can be bonded to the substrate of the value document. In window areas, the adhesive layer can be omitted. In advantageous embodiments, the substrate of the value document is a paper or plastic substrate or a composite substrate comprising at least one paper layer and at least one plastic layer. Advantageously, the first and second feature substances are each an IR luminescent substance, wherein the first and second IR luminescent substances advantageously have different emission spectra and / or different excitation spectra. In an advantageous variant of the invention, the first and second IR luminescent substances have at least one common spectral band in the emission spectrum and, at the same time, separate spectral bands in the excitation spectrum. This allows separate excitation with a spectrally common detection and thus a technically simpler detector.so that the two IR luminescent substances can be detected independently of each other. In another, equally advantageous variant of the invention, the first and second IR luminescent substances have at least one common spectral band in the excitation spectrum and, at the same time, separate spectral bands in the emission spectrum. This allows the simultaneous excitation of the two IR luminescent substances, for example, with a single light source with separate detection in, for example, two different spectral channels in a single combination sensor, so that here too the two IR luminescent substances can be detected independently of each other. The IR luminescent substances used in the invention can be organic or organometallic luminescent substances,For example, fluorescent organic molecules or phosphorescent organometallic complexes. In a preferred embodiment, these are organometallic complexes. These generally exhibit narrower, more specific emission bands and a large Stokes shift. This facilitates excitation and detection. In particular, the separation of the emission radiation from the excitation radiation and from interfering signals is facilitated. The organometallic complexes are preferably rare earth complexes, particularly preferably rare earth complexes of the rare earths neodymium, ytterbium, erbium, thulium,Holmium or combinations of these or two or more rare earths. In a further advantageous embodiment, one or both IR luminescent substances are inorganic luminescent substances. For example, they are doped inorganic host lattices. Furthermore, the dopants can be the rare earths neodymium, ytterbium, erbium, thulium, holmium or the transition metals vanadium, chromium, manganese, iron. In addition to the dopants mentioned, further dopants can be present, for example to adjust the decay time of the luminescent substance and / or to utilize energy transfers between the rare earth ion and / or the transition metal and the further dopant. Suitable inorganic matrices are, for example: i) oxides, in particular 3- and 4-valent oxides such as e.g. B. Titanium oxide, aluminum oxide, iron oxide, boron oxide, yttrium oxide, cerium oxide, zirconium oxide, bismuth oxide, as well as more complex oxides such as garnets,including, for example, yttrium iron garnets, yttrium aluminum garnets, gadolinium gallium garnets; perovskites, including, among others, yttrium aluminum perovskite, lanthanum gallium perovskite; spinels, including, among others, zinc aluminum spinels, magnesium aluminum spinels, manganese iron spinels; or mixed oxides such as, for example, ITO (indium tin oxide); ii) oxyhalides and oxychalcogenides, in particular oxychlorides such as, for example, yttrium oxychloride, lanthanum oxychloride; and oxysulfides, such as yttrium oxysulfide, gadolinium oxysulfide or yttrium gadolinium oxysulfide iii) sulfides and other chalcogenides, for example zinc sulfide, cadmium sulfide, zinc selenide, cadmium selenide; iv) sulfates, in particular barium sulfate and strontium sulfate; v) phosphates, in particular barium phosphate, strontium phosphate, calcium phosphate, yttrium phosphate, lanthanum phosphate, as well as more complex phosphate-based compounds such as apatites, including calcium hydroxylapatites,Calcium fluoroapatites, calcium chloroapatites; or spodiosites, including, for example, calcium fluoro-spodiosites, calcium chloro-spodiosites; vi) halides, in particular fluorides such as sodium rare earth fluorides; vii) silicates and aluminosilicates, in particular zeolites such as, for example, zeolite A, zeolite Y; zeolite-related compounds such as, for example, sodalites; feldspars such as, for example, alkali feldspars, plagioclase; and / or viii) other inorganic compound classes such as, for example, vanadates, germanates, arsenates, niobates, tantalates. According to a further variant of the invention, the first and second feature substances are each an optical storage phosphor,wherein the first and second optical storage phosphors are advantageously jointly chargeable and differently readable. The latter simplifies the sensor and allows reliable separation of the two features via the readout. The statements made above for the first optical storage phosphor apply equally to the second optical storage phosphor. Within the scope of the present invention, substances such as suitably doped alkaline earth sulfides (e.g. SrS:Eu,Sm), halides (e.g. BaFBr:Eu), aluminates (e.g. SrAl2O4:Eu,Tm or Sr4Al14O25:Eu,Dy), oxides (e.g. MgO:Tb, BeO, Al2O3:C), garnets (e.g. Gd, 3,04 Al2Ga3O 12 : Ce 0,005 , Yb 0,005 or Gd 2,52 La 0,5 Al2Ga3O 12 : Ce 0,04 , Zr 0,005) or other substances can be used which absorb energy in the form of UV or VIS radiation, store it and only release it again in the form of luminescence under targeted stimulation. If light is used as the stimulus, this is referred to as optically stimulated luminescence. Other suitable optical storage phosphors are described in DE 102017008868A1, the disclosure of which is incorporated into the present application in this respect. Finally, in a further advantageous embodiment of the invention, one of the two feature substances can be an IR luminescent substance and the other of the two feature substances can be an optical storage phosphor. Particularly preferably, the first feature substance of the security element is an IR luminescent substance and the second feature substance of the value document substrate is an optical storage phosphor with optically stimulated luminescence.The two luminescence markers are separated via their different emissions; advantageously, the excitation of the IR luminescent substance can also be combined with the charging or reading of the optical storage phosphor. Finally, the invention also includes a method for verifying a valuable document of the type described above, in which the presence of the first feature substance in the optical variable security element and the presence of the second feature substance in the substrate of the valuable document are detected mechanically with spatial resolution, and the detected distributions of the first and second feature substances are compared with expected distributions. Based on the comparison result, the authenticity of the valuable document can then be assessed or a conclusion can be drawn about whether manipulation has occurred.In an advantageous method variant, a value document is checked in which the first and second feature substances are each IR luminescent substances, and the two IR luminescent substances have at least one common spectral band in the excitation spectrum and, at the same time, separate spectral bands in the emission spectrum. In this advantageous method variant, the substrate of the value document and the security element are illuminated with excitation light containing a wavelength of the common spectral band of the excitation spectrum of the first and second IR luminescent substances, the light emissions of the first and second IR luminescent substances are each recorded with spatial resolution, and the recorded distributions of the first and second light emissions are compared with expected distributions. Here, too, the authenticity of the value document can be assessed or conclusions can be drawn about tampering based on the comparison result.Further embodiments and advantages of the invention are explained below with reference to the figures, in which a true to scale and proportions have been omitted in order to increase clarity. They show: Fig. 1 schematically in (a) a banknote according to an embodiment of the invention and in (b) and (c) counterfeit banknotes obtained by a removal attack, Fig. 2 a foil patch according to the invention in cross section, Fig. 3 the foil patch of Fig. 2 after application to the paper substrate of a banknote and removal of the transfer foil, Fig. 4 a foil patch according to another embodiment of the invention on a banknote, Fig. 5 a foil patch according to another embodiment of the invention on a banknote, before removal of the transfer carrier, Fig.Fig. 6 schematically shows in (a) a banknote according to another embodiment of the invention and in (b) and (c) counterfeit banknotes obtained by a stripping attack, Fig. 7 shows a window security thread embedded in a banknote according to an embodiment of the invention schematically in cross section, and Fig. 8 shows a window security thread embedded in a banknote according to a further embodiment of the invention schematically in cross section. The invention will now be explained using banknotes as an example. Figure 1 shows in Fig. 1(a) a banknote 10 according to the invention, which is equipped with a foil patch 12 with an optically variable appearance.For security purposes, the foil patch 12 contains a first machine-readable feature substance in the form of an IR luminescent substance or an optical storage phosphor with optically stimulated emission. The special position of the feature substance in the foil patch 12, described in more detail below, ensures that the feature substance is completely removed from the banknote 10 during a harvesting attack. The paper substrate 14 of the banknote 10 contains a second machine-readable feature substance, which is also formed by an IR luminescent substance or an optical storage phosphor with optically stimulated emission. In a detachment attack, the genuine foil patch 12 is typically removed from the genuine banknote 10 and replaced by a counterfeit 12-V, as shown in Fig.1(b), while the genuine foil patch 12 is transferred to a counterfeit banknote substrate 14-V, as shown in Fig.1(c).During the automated authentication of banknotes, the presence of both the first and second feature substances is checked, and the authenticity of a note is only confirmed if both feature substances are detected. The banknote 10 of Fig. 1(a) is therefore recognized as authentic, while the counterfeit of Fig. 1(c) contains the authentic foil patch 12, but the tampering can be detected by the absence of the second feature substance in the paper substrate 14-V. The counterfeit of Fig. 1(b) can be rejected due to the absence of the first feature substance in the area of ​​the counterfeit foil patch 12-V, since the first feature substance was removed without residue from the banknote substrate 14 when the authentic foil patch 12 was removed. The structure and functioning of security elements according to the invention and value documents according to the invention will now be explained in more detail with reference to the following figures. Figure 2 shows a film patch 20 according to the invention in cross section.The foil patch 20 is a multilayer stack, typically built on a transfer foil 40, which is subsequently removed during the patch's application to a target document. A first UV varnish layer 22 is first applied to the transfer foil 40 as a release layer, which also serves as a print acceptance layer for subsequent printing. A UV embossing varnish layer 24 is applied to the UV varnish layer 22, in which the optical structures for the desired optically variable appearance are embossed. In the exemplary embodiment, the visibility of the optical structures is enhanced by a reflection-enhancing coating 26, which can be formed, in particular, by a metal layer, a high-refractive-index layer, or an interference layer structure. The UV embossing varnish layer 24 with the embossed optical structures, together with the reflection-enhancing coating 26, forms the optical functional layer of the foil patch 20.A thin PET film 30 with a thickness between 4 µm and 15 µm is laminated onto the reflection-enhancing coating 26 of the optical functional layer using a laminating adhesive 28 as a film layer. A primer layer 32 and finally an adhesive layer 34, preferably a heat-sealing lacquer, for bonding to the target substrate are applied to the PET film 30. In the embodiment of Fig. 2, the first machine-readable feature substance 36 is mixed into the laminating adhesive 28 and, like the optical functional layer 24, 26, is therefore located on the upper side of the PET film 30. Before and / or after the lamination of the PET film 30, further functional layers with additional authenticity features such as fluorescence, IR, magnetic, conductivity, polarization effects, colored colors, and effect colors can be introduced. The foil patch can then be defined by punching and released by separating wrapping.The punching step can also be omitted to create a security element in the form of a continuous foil strip. Gradual transitions in the geometric extension up to the full height of the banknote are also possible. A strip cut can then be made to create a coil material from the foil material. Figure 3 shows the foil patch 20 of Fig. 2 after application to the paper substrate 14 of a banknote, such as the banknote 10 of Fig. 1. The carrier foil 40 was removed after the application of the foil patch, so that the UV varnish layer 22, as the uppermost layer, can now function as a print acceptance layer. The paper substrate 14 of the banknote 10 is provided with a second machine-readable feature substance 16, which, together with the first machine-readable feature substance 36 of the foil patch, completes the security of the banknote.The foil patch 20 is stabilized by the inner foil layer 30 and is achieved in that, in the event of a detachment attack, the foil layer 30, along with the optical functional layer 24, 26, and thus also all layers arranged above the foil layer 30 are removed from the banknote 10. This ensures that, in the event of a detachment attack, the feature substance 36 arranged in the laminating adhesive layer 28 is completely removed from the banknote 10. Therefore, no residue of feature substance 36 remains on the banknote 10, so that it can be reliably recognized as tampered with, even after being equipped with a counterfeit foil patch 12-V (Fig. 1(b)). The advantageous materials described above can be used, in particular, for the first and second machine-readable feature substances 16, 36.For example, the feature substances 16, 36 can be two IR-IR luminescent substances that have a common spectral band in the excitation spectrum and, at the same time, different, separate spectral bands in the emission spectrum. This allows the simultaneous excitation of the two feature substances 16, 36, for example, with a single light source and separate detection, for example, in two different spectral channels in a single combination sensor, so that the two IR-IR luminescent substances can be detected independently of one another. As can be seen from the above explanation, the first machine-readable feature substance 36 can be introduced into any layer lying on top of the film layer 30 or even into the film layer 30 itself.Figure 4 shows, by way of example, a film patch 42 according to another exemplary embodiment of the invention, in which the first feature substance 36, in contrast to the film patch 20 of Figures 2 and 3, is present in the UV lacquer layer 22. In the exemplary embodiment of Figure 4, the feature substances 16, 36 can also be two IR-IR luminescent substances. In this embodiment, however, an optical storage phosphor with optically stimulated luminescence can also advantageously be selected as the first feature substance 36, which is excited and read out in the visible or UV range, since, due to the arrangement of the first feature substance 36 above the optical functional layer 24, 26, there is no risk of disruptive absorption by a reflection-enhancing coating, in particular by metallization of the optical functional layer. The second feature substance 16 can then also be an optical storage phosphor or an IR luminescent substance.It is understood that in other embodiments, the first machine-readable feature substance 36 can also be incorporated into the UV embossing lacquer layer 24 or into the film layer 30 itself. The first feature substance 36 can also be present in a dedicated feature layer arranged on top of the film layer 30. Such a dedicated feature layer can be present over the entire surface, as a motif / pattern, or only in the later product areas. A dedicated feature layer can be provided as a UV-curing layer or a solvent-based layer. Since the first feature substance 36 is arranged on top of the film layer 30 in all of these variants, in the event of a detachment attack, the first feature substance 36 is always completely removed together with the film layer 30 and the optical functional layer 24, 26.Figure 5 shows, as a further exemplary embodiment, a banknote 10 with a second feature substance 16 incorporated into the paper substrate 14 and a foil patch 52 applied to the paper substrate, in which the first feature substance 36 is incorporated into the foil layer 30 itself. In the figure, the foil patch 52 is shown immediately after application to the banknote, before the removal of the transfer carrier 50 consisting of two laminated partial foils. To demonstrate the advantages achieved with the invention, a foil security element according to the invention and a comparison element not according to the invention were each applied to a secured substrate, and the detectability of a removal attack was tested. Exemplary embodiment 1: In a foil patch with a structure as in Fig. 2, a luminescence marker A that can be excited in the near-infrared (NIR) and emits in the near-infrared is used as the first feature substance.For this purpose, the luminescence marker A is dispersed in a laminating adhesive in a ball mill, applied to a semi-finished metallized micromirror patch with a wet film thickness of 12 µm, and the metallized micromirror patch is bonded to a 12 µm thin PET film layer. The resulting layer sequence is first coated with a primer layer and then bonded to banknote paper provided with an IR luminescence marker B (NIR / NIR) using a heat-sealing adhesive, and the transfer film is removed. The luminescence marker B forms the second feature substance 16 in Fig. 3; the first feature substance 36 is formed by the luminescence marker A, which is present in the laminating adhesive layer between the optical functional layer—in this case, the metallized micromirrors—and the PET film layer.The luminescence intensities of marker A and marker B were measured from the back of the banknote using a luminescence sensor for banknote applications ("original document" in Table I). The foil patch was then removed from the banknote and stuck with Tesa tape onto a blank sheet representing the recipient document. The corresponding luminescence intensities of the donor document after detachment and of the recipient document were measured again: Table I: Original document Donor document Recipient document after document Detachment after transfer Luminescence intensity A 100% 0% 45% Luminescence intensity B 100% 100% 0% As can be seen from Table I, the luminescence intensity A disappears completely during the detachment process, meaning the donor document can be reliably identified as tampered with. The recipient document can also be reliably identified as a counterfeit due to the absence of luminescence intensity B.Comparative Example 1: The comparison element has the same basic structural design as the film patch according to the invention, but the luminescence marker A in the comparison element was introduced into the primer layer of the substrate adhesive on the underside of the PET film layer. The detachment and transfer process described above is repeated and the luminescence intensities are measured: Table II: Original document Donor document Recipient document Detachment after transfer Luminescence intensity A 100% 16% 40% Luminescence intensity B 100% 100% 0% As can be seen from Table II, in contrast to the inventive embodiment, the luminescence intensity A does not completely disappear from the donor document in the comparison example, since part of the primer layer remains on the donor document during the detachment process. The donor document cannot therefore be reliably recognized as tampered with in the comparison test.The invention can be used not only with wide security elements applied to a value document, such as the foil patch of Figures 1 to 5, but also with narrow security threads that are at least partially incorporated into the substrate of a value document. Figure 6 shows, in Figure 6(a), a banknote 60 according to the invention, which is provided with an optically variable window security thread 62 that protrudes at certain window regions 64 on the surface of the banknote, while being embedded in the intermediate regions inside the banknote. For security purposes, the window security thread 62 contains a first machine-readable feature substance in the form of an IR luminescent substance or an optical storage phosphor with optically stimulated emission.In this embodiment, too, the position of the feature substance in the window security thread 62 ensures that the feature substance is completely removed from the banknote 60 during a detachment attack. The paper substrate 66 of the banknote 60 contains a second machine-readable feature substance, which is also formed by an IR luminescent substance or an optical storage phosphor with optically stimulated emission. During a detachment attack, the genuine window security thread 62 is typically removed from the genuine banknote 60 and replaced with a counterfeit 62-V, as shown in Fig. 6(b), while the genuine window security thread 62 is transferred into a counterfeit banknote substrate 66-V, as shown in Fig. 6(c). During the automated authentication of banknotes, the presence of both the first and the second characteristic substance is checked and the authenticity of a note is confirmed only if both characteristic substances are detected.The banknote 60 of Fig. 6(a) is therefore recognized as genuine, whereas the counterfeit of Fig. 6(c) contains the genuine window security thread 62, but the tampering can be detected by the absence of the second feature substance in the paper substrate 66-V. The counterfeit of Fig. 6(b) can be rejected due to the absence of the first feature substance in the area of ​​the counterfeit window security thread 62-V, since the first feature substance was removed without residue from the banknote substrate 66 when the genuine window security thread 62 was removed. For further explanation, Fig. 7 shows a schematic cross-section of a window security thread 80 embedded in the security paper 70 of a banknote. The security thread 80 is a multi-layer stack with an internal transparent film carrier 82.The film carrier 82 is provided on a first side with a first primer layer 84 and a first adhesive layer 86, in particular a heat-sealing lacquer layer. On the opposite second side, the film carrier 82 is provided with a first UV lacquer layer 90 as a primer and a UV embossing lacquer layer 92 arranged directly on the UV lacquer layer 90, in which the optical structures for the desired optical appearance of the security thread are embossed. The detectability of the optical structures is enhanced by a reflection-enhancing coating 94, which can be formed, for example, by a metal layer, a high-refractive index layer, or an interference layer structure. The UV embossing lacquer layer 92 with the embossed optical structures, together with the reflection-enhancing coating 94, forms the optical functional layer of the security thread 80.A second primer layer 96 and a second adhesive layer 98, preferably a heat-sealing lacquer, are applied to the reflection-enhancing coating 94 for anchoring in the security paper 70. In the embodiment of Fig. 7, the first machine-readable feature substance 36 is present in the transparent film carrier 82 itself, while the second machine-readable feature substance 16 is present in the paper substrate 70 of the banknote 60 and, together with the first machine-readable feature substance 36 of the security thread 80, completes the security of the banknote. The introduction of the second machine-readable feature substance 16 into the paper substrate 70 advantageously takes place in the paper machine during paper formation, where the security thread 80 is embedded between two layers (main former, short former) in the wet paper web and anchored there during paper formation.The windows 64 of the window security threads are created by cutouts in one of the two paper layers, so that no paper fibers are deposited locally there. In the event of a detachment attack in which the thread 80 is pulled out of the banknote 60, the foil carrier 82 and thus the feature substance 36 incorporated in the foil carrier 82 are inevitably completely removed from the banknote 60 together with the optical functional layer 92, 94. The banknote can therefore be reliably detected as tampered with, even after it has been equipped with a counterfeit window security thread 62-V (Fig. 6(b)). Figure 8 shows a further embodiment in which the security thread 100 is equipped with an additional functional layer 102. The security thread 100, like the security thread 80 in Fig. 7, represents a window security thread that is partially embedded in the security paper 70 of a banknote.The security thread 100 is a multi-layer stack with an internal transparent film carrier 82, which is basically constructed like the security thread 80 in Fig. 7, i.e., it carries a first primer layer 84 and a first adhesive layer 86 on a first side of the film carrier 82, and is provided on the second side of the film carrier 82 with a first UV lacquer layer 90, a UV embossing lacquer layer 92 arranged directly on the UV lacquer layer 90, a reflection-enhancing coating 94, a second primer layer 96, and a second adhesive layer 98. Unlike the simpler embodiment in Fig. 7, a functional layer 102 and a third primer layer 104 are additionally provided between the last two elements. The functional layer 102 can, for example, be a magnetic pigment layer or a fluorescent pigment layer. The functional layer is advantageous, as shown in Fig.8, viewed from the main viewing direction (from above in Fig. 8), it is arranged below the reflection-enhancing coating 94. Fig. 8 shows a full-surface configuration of the functional layer 102; however, in other configurations, this can also be structured. In the embodiment of Fig. 8, the first machine-readable feature substance 36 is present in the UV embossing lacquer layer 92, while the second machine-readable feature substance 16 is incorporated into the paper substrate 70 of the banknote 60 and, together with the first machine-readable feature substance 36 of the security thread 100, completes the security of the banknote. In a detachment attack in which the thread 100 is pulled out of the banknote 60, the UV embossing lacquer layer 92 as part of the optical functional layer 92, 94 is inevitably also removed, so that the introduced feature substance 36 is also completely removed from the banknote 60.This can therefore be reliably detected as tampered with, even after being equipped with a counterfeit window security thread 62-V (Fig. 6(b)). In a security thread, the first feature substance 36 is advantageously present in a layer that is optically necessary for the appearance and is transferred as completely as possible in the event of tampered removal of the security thread. Complete transfer is particularly ensured when the feature substance is inserted into the film carrier 82. However, optical security is also provided when the feature substance 36 is inserted in the UV primer layer 90 or in the UV embossing varnish 92, since these layers are inseparably bonded to the film carrier 82. In the case of security threads that contain liquid crystals, the feature substance 36 can also be added to the liquid crystal formulation. In the case of multi-layer threads, use in the laminating adhesive can also be advantageous.Example 2: For a window security thread with a structure as shown in Fig. 7, a luminescence marker A that can be excited in the near-infrared (NIR) and emits near-infrared light is used as the first feature substance. The luminescence marker A is dispersed in a primer lacquer in a ball mill and, immediately after metallization, doctored onto a semi-finished product of a metallized micromirror security thread in a 12 µm wet film thickness. A heat-sealing varnish is then doctored on, the semi-finished product is cut into a 3 mm wide security thread, and incorporated into banknote paper. The banknote paper contains a luminescence marker B which is excitable and emits near-infrared (NIR) and which can be excited at the same NIR wavelength as luminescence marker A. The luminescence marker B forms the second feature substance 16 of Fig. 7, the first feature substance 36 is formed by the luminescence marker A.The luminescence intensities of marker A and marker B are measured from the back of the banknote using a luminescence sensor for banknote applications ("original document" in Table III). The respective maximum is used as the metric for the luminescence intensity of A, and the median of all measurement points is used for B. The intensities were normalized to their original value. The security thread is then removed from the banknote by cutting it out and stuck to a blank sheet of paper ("recipient document") with sticky tape. The corresponding luminescence intensities are measured again: Table III: Original document Donor document Recipient document after document Detachment after transfer Luminescence intensity A 100% 0% 100% Luminescence intensity B 100% 100% 0% As can be seen from Table III, the luminescence intensity A disappears completely during the detachment process, meaning the donor document can be reliably identified as tampered with.The recipient document can also be reliably identified as a forgery due to the absence of luminescence intensity B.

Claims

Patent claims 1. An optically variable security element for securing a valuable document, comprising a first machine-readable feature substance and an optical functional layer that gives the security element an optically variable appearance when viewed, characterized in that the security element is formed in multiple layers with an inner film layer having a first side and an opposite second side, wherein the film layer is provided at least on the first side with an adhesive layer for connection to the valuable document and on the second side with the optical functional layer, and wherein the first machine-readable feature substance is arranged in the film layer or on the second side of the film layer. 2.The security element according to claim 1, characterized in that the first machine-readable feature substance is an IR luminescent substance or an optical storage phosphor with optically stimulated luminescence.

3. The security element according to claim 1 or 2, characterized in that the first machine-readable feature substance is present in a feature layer arranged on the upper side of the film layer, in particular in a UV-curable lacquer layer, an embossing lacquer layer, or an adhesive layer.

4. The security element according to at least one of claims 1 to 3, characterized in that the film layer is formed by a film with a thickness between 4 µm and 15 µm, for example a PET film.

5. The security element according to at least one of claims 1 to 4, characterized in that the optical functional layer is formed by a hologram or another diffraction structure, an interference structure, a matte structure, a micromirror array, a microlens array, a moth-eye structure, a subwavelength structure, or a combination of these elements.

6. The security element according to at least one of claims 1 to 5, characterized in that the optical functional layer has a reflection-enhancing coating, in particular a metal layer, a high-refractive-index layer, and / or a color-shifting interference coating. 7.Security element according to at least one of claims 1 to 6, characterized in that the first machine-readable feature substance is an IR luminescent substance which has an emission in the near-infrared spectral range, in particular in the wavelength range between 800 nm and 2100 nm and / or can be excited in the wavelength range between 400 nm and 2100 nm, preferably in the wavelength range between 700 nm and 2100 nm.

8. Security element according to at least one of claims 1 to 7, characterized in that the security element is a security thread, in particular a window security thread or a pendulum security thread, or a patch or label for application to a value document.

9. Value document with an optically variable security element according to one of claims 1 to 8, wherein the optically variable security element is provided with the adhesive layer arranged on the first side of the film element. is connected to a substrate of the value document, and wherein the substrate of the value document contains a second machine-readable feature substance, in particular an IR luminescent substance or an optical storage phosphor with optically stimulated luminescence.

10. A value document with an optically variable security element according to one of claims 1 to 8, wherein the optically variable security element is a security thread at least partially embedded in the value document, and wherein the substrate of the value document contains a second machine-readable feature substance, in particular an IR luminescent substance or an optical storage phosphor with optically stimulated luminescence. 11.A value document according to claim 9 or 10, characterized in that the first and second feature substances are each an IR luminescent substance, wherein the first and second IR luminescent substances advantageously have different emission spectra and / or different excitation spectra.

12. A value document according to claim 11, characterized in that the first and second IR luminescent substances have at least one common spectral band in the emission spectrum and, at the same time, separate spectral bands in the excitation spectrum.

13. A value document according to claim 11, characterized in that the first and second IR luminescent substances have at least one common spectral band in the excitation spectrum and, at the same time, separate spectral bands in the emission spectrum.

14. A value document according to claim 9 or 10, characterized in that the first and second feature substances are each an optical storage phosphor, wherein the first and second optical storage phosphors are advantageously jointly chargeable and differently readable.

15. A value document according to claim 9 or 10, characterized in that one of the two feature substances is an IR luminescent substance and the other of the two feature substances is an optical storage phosphor.

16. A method for checking a value document according to one of claims 10 to 15, in which the presence of the first feature substance in the optically variable security element and the presence of the second feature substance in the substrate of the value document are detected mechanically with spatial resolution, and the detected distributions of the first and second feature substances are compared with expected distributions. 17.Method in particular according to claim 16 for checking a value document according to claim 13, in which the substrate of the value document and the security element are illuminated with excitation light which contains a wavelength of the common spectral band of the excitation spectrum of the first and the second IR luminescent substance, the light emissions of the first and the second IR luminescent substance are each detected in a spatially resolved manner and the detected distributions of the first and second light emissions are compared with expected distributions.

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