Valuable document comprising security element with interference stack and test method

Abstract

The invention relates to a value document (10) comprising a value document substrate (12) and a security element (14) applied to the substrate, said security element comprising an interference layer stack (20) which makes the security element (14) have an optically variable appearance when viewed in a reflective manner. The interference layer stack (20) provides a characterizing infrared identification as a first authenticity feature, and the value document substrate (12) comprises, on the surface thereof, a bottom layer (30) mixed with an infrared absorber (32) as a second authenticity feature, said bottom layer being arranged at least partially below the security element (14). The first and second authenticity features together form an authenticity mark which can be inspected by a machine under infrared light, the absence or incompleteness of which indicates the tampering of the value document (10).

Description

Technical Field

[0001] The invention relates to a value document comprising a value-document substrate and a security element applied thereto, the security element having an interference layer stack which gives the security element an optically variable appearance when visually observed in reflection. The invention also comprises a method for checking such a value document. Background Art

[0002] Data carriers, such as valuable documents or identification documents, and other valuable objects, such as branded goods, are often provided with security elements for protection, which enable the authenticity of the data carrier to be checked and at the same time serve as protection against unauthorized copying.

[0003] Optically variable security elements are often used for this purpose, whose special visual effects, such as a color-changing effect with tilt angle (German: Farbkippeffekt), can be detected by the observer with the naked eye alone without any other auxiliary means. However, such first-level features are often subject to so-called "harvesting" attacks, in which the counterfeiter removes the security element from the authentic document ("harvesting") and sticks it on a counterfeit, such as a photocopy, in order to thereby visually increase its value.

[0004] There is therefore a need for a technical solution for reliably identifying such tampered banknotes and other valuable documents in the context of machine processing / sorting.

[0005] Film-based security elements conventionally usually do not carry machine-readable features, so that replacement of such a film-based security element by a counterfeit cannot be directly verified by a machine.

[0006] If, for remedial purposes, the film-based security element is printed with an infrared absorber, for example in non-metallized areas, then a forgery with a transferred (authentic) film is assessed as authentic, although the absence of an authentic security element on the value document can be detected with an infrared diffuse reflection sensor.

[0007] In document WO 2023 / 285000 A1, it is suggested to provide security components for both the substrate of the banknote and the security element applied thereto, which provide a representative signal in combination. The absence of the combined signal is a strong indication of tampering. In particular, two different infrared absorbers with separate absorption spectra are used here to mark the substrate and the film. On the one hand, this requires the integration of infrared absorbers in transparent, non-metallized areas of the film element, which requires a larger demetallized area and is therefore a great restriction on the film design. In addition, the combination of two spectrally separated infrared absorbers is difficult in practice because the absorption frequency bands of most infrared absorbers are wide and therefore overlap spectrally in the limited spectral range (750nm to 1050nm) of commonly used low-cost infrared sensors. Summary of the invention

[0008] Based on this, the technical problem to be solved by the present invention is to provide a valuable document which avoids the disadvantages of the prior art and in which valuable documents tampered with by a peeling attack can be reliably identified by a machine. The present invention is also intended to provide a method for checking valuable documents that are protected against forgery in this way.

[0009] This technical problem is solved by the features of the independent claim. Improvements of the invention are the subject matter of the dependent claims.

[0010] The invention comprises a value document with a value-document substrate and a security element applied to the substrate, wherein the security element comprises an interference layer stack which gives the security element an optically variable appearance when visually observed in reflection.

[0011] The interference layer stack provides a characteristic infrared marking as a first authenticity feature of the value document.

[0012] The value-document substrate comprises on its surface a bottom layer mixed with an infrared absorber as a second authenticity feature of the value document, which bottom layer is at least partially arranged below the security element.

[0013] In a first application case, the value-document substrate itself can consist of paper, such as in the case of banknotes or visas. In another application case, for example in the case of polymer banknotes, identity cards or driver's licenses, the value-document substrate can consist of a polymer, such as polycarbonate or polypropylene, or a polymer composite. In other application cases, paper-polymer hybrid composite materials, such as laminated paper layers, can also be used as value-document substrates.

[0014] The first and second authenticity features together form an authenticity mark that can be checked by a machine under infrared light, the absence or incompleteness of which indicates tampering with the value document. In particular, tampering with the value document can be inferred from the absence of the first or second authenticity feature. As explained in more detail below, in the present invention, both a provider document with a peeled-off security element and a recipient document with a transferred genuine security element can be identified as tampered.

[0015] It is particularly advantageous here if the base layer mixed with the infrared absorber adheres better to the substrate than to the security element, so that when the security element is peeled off the second authenticity feature remains essentially completely on the value-document substrate.

[0016] “Substantially completely” means here that more than 90%, more than 94% and in particular more than 98% of the infrared absorber remains on the value-document substrate.

[0017] The bottom layer is preferably formed by a primer layer or an imprint. In the case of a value-document substrate consisting of paper, the bottom layer is preferably formed by a paper primer. The paper primer or a suitable imprint can form a particularly tight connection with the value-document substrate, so that when the security element is peeled off, the adhesive breaks at the interface with the underlying bottom layer and the security element is removed without the bottom layer.

[0018] In an advantageous embodiment, the bottom layer is arranged partially below the security element and partially next to the security element. The presence of the infrared absorber can then also be detected in the region next to the security element.

[0019] In a further, likewise preferred design, the bottom layer is arranged completely below the security element. The latter has the advantage that no additional space is required on the value document for the additional protection by the infrared absorber and an authenticity check can be performed independently of the printed design of the value document.

[0020] In an advantageous embodiment, the interference layer stack is formed by a thin-layer element that changes color with the tilt angle. The thin-layer element can, for example, have a three-layer structure consisting of an absorption layer, a dielectric spacer layer and a reflection layer, or even a five-layer structure consisting of a first absorption layer, a first dielectric spacer layer, a second absorption layer, a second dielectric spacer layer and a reflection layer. The five-layer structure particularly advantageously offers additional degrees of freedom in the optical design, since it can produce different infrared spectral curves and thus different infrared identifications with similar or identical visual appearances. Therefore, the infrared characteristics of the interference layer stack cannot be directly inferred from the observed visual effect, such as the color change determined when the security element is tilted, so that readjustment (German: Nachstellung) of this effect is difficult.

[0021] The reflective layer is preferably designed to be opaque and can be made of aluminum, for example. The absorption layer or layers are advantageously formed by a semi-transparent chromium layer. The dielectric spacer layer can be formed in particular by silicon dioxide.

[0022] Advantageously, the security element contains a metal layer, which is preferably formed by the reflective layer of the interference layer stack. However, it is also possible that the metal layer is an additional layer arranged above or below the interference layer stack.

[0023] The metal layer of the security element is advantageously structured at least in local areas. In particular, the metal layer of the security element can have structured local areas with narrow metal strips, narrow metal lines and / or metal patterns and / or characters with a smaller line thickness, wherein the area coverage of the metal layer in the structured local areas is preferably less than 20%, in particular less than 15%, or even less than 10%. Surprisingly, it has been shown that the infrared detection of the underlying substrate is not significantly impaired by such a narrow metal structure. The narrow metal structure thus allows the designer greater design space without impairing the technical function of the security element in the authenticity check. The geometric extension of the structured local area is preferably selected so that it has at least 8 mm 2 , preferably at least 20 mm 2 In this case, the presence of the infrared absorber in the bottom layer can also be reliably detected by means of inexpensive infrared sensors which may only have a limited position resolution in the millimeter range.

[0024] The infrared absorber of the bottom layer is advantageously substantially transparent or white in the visible spectral range and is thus visually inconspicuous. The infrared absorber can absorb substantially both in a broadband spectrum and in a narrowband spectrum, but infrared absorbers that absorb broadband in the near infrared range (NIR) of 700 nm to 1500 nm, in particular in the range of 750 nm to 1100 nm, are currently particularly preferred.

[0025] Suitable infrared absorbers are known, for example, from the document WO 2007 / 060133 A1, the disclosure of which is incorporated in the present application. As infrared absorbers, for example, iron (II) or copper (II) compounds with Fe2+ ions or Cu2+ ions in a suitable chemical environment are considered, wherein the suitable chemical environment is, for example, phosphate ions or polyphosphate ions, or more generally, groups containing phosphorus and oxygen. Such infrared absorbers have a broadband absorption in the near infrared range of 700 nm to 1100 nm, but are essentially transparent or white in the visible spectrum, with a slight yellow, green or blue hue at most. Therefore, the presence of the infrared absorber in the bottom layer can hardly be recognized visually.

[0026] Also suitable as infrared absorbers are the infrared substances sold by BASF (100 Park Ave, Florham Park, NJ 07932) under the name LUMOGEN-S, the infrared absorbing materials disclosed in the document GB 2168372 (which are invisible or transparent in the visible range of the electromagnetic spectrum), and the infrared marking materials disclosed in the document US Pat. No. 6,926,764. The infrared marking materials are substituted naphthalocyanines, phthalocyanines, metal-containing phthalocyanines or polysubstituted phthalocyanines. Thiophenol-substituted copper phthalocyanines are preferred, especially p-thiotoluene thiophenol-persubstituted copper phthalocyanines.

[0027] In an advantageous development of the invention, the security element comprises a relief structure arranged below the interference layer stack. The relief structure can be formed in particular by a micromirror array with directional reflective micromirrors, in particular a micromirror array with non-diffractive mirrors. However, the relief structure can also be formed by a diffractive structure, in particular a holographic structure, a nanostructure or a diffractive blazed grating. By means of such a relief structure, in addition to the effect of the inclination-dependent color change of the interference layer stack, the security element exhibits a motion effect or a three-dimensional appearance, thereby adding visual value and increasing its security against counterfeiting.

[0028] In an advantageous embodiment, the security element comprises a film layer, in particular a film layer which is transparent in the visible spectral range and advantageously also in the near infrared range. The security element advantageously covers the continuous opening in the value document substrate via the film layer. In other embodiments, the security element can be formed on a transfer film during production, which is then removed after the security element has been transferred to the value document.

[0029] The invention also comprises a method for checking a value document of the above-mentioned type, wherein:

[0030] the value document is exposed to infrared radiation at a plurality of locations, at least in the region of the security element, and the reflected (or diffusely reflected) infrared radiation is detected,

[0031] - determining in a spatially resolved manner the presence of a characteristic infrared marking of the first authenticity feature and the presence of an infrared response of an infrared absorber of the second authenticity feature, respectively, based on the detected reflected infrared radiation,

[0032] - Based on the presence and the determined distribution of the first and second authenticity features, assessing the authenticity of the value document.

[0033] In particular, it is possible to check whether the first and second authenticity features are present and to conclude that the value document has been tampered with if one of the two authenticity features is missing. Even if both authenticity features are present, tampering can be inferred from a distribution of the authenticity features that differs from the expected position distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Further embodiments and advantages of the present invention are described below with reference to the accompanying drawings, in which scales and ratios are not shown in order to improve readability.

[0035] In the attached figure:

[0036] Figure 1 A banknote according to an embodiment of the present invention is schematically shown in a front view,

[0037] Figure 2 Show Figure 1 The cross section of the banknote along the line II-II,

[0038] Figure 3 In (a) it is shown Figure 1 A portion of an unaltered banknote and four measurement tracks for authenticity verification, wherein (b) schematically shows the measurement results of the four measurement tracks in (a),

[0039] Figure 4 (a) shows a detail of a tampered banknote, in which the peeled-off film strip is transferred to an unauthorized substrate, and (b) schematically shows the measurement results of the four measurement tracks in (a).

[0040] Figure 5 In (a) a part of another tampered banknote is shown, in which the paper substrate of the provider banknote is provided with a counterfeit film strip after the original film strip is peeled off, and in (b) the measurement results of the four measurement tracks in (a) are schematically shown,

[0041] Figure 6 A banknote according to another embodiment of the invention is schematically shown in cross-section,

[0042] Figure 7 In (a) it is shown Figure 6 A front view of a banknote of an embodiment, with the corresponding infrared signal detectable by the infrared sensor being shown with position resolution in (b). DETAILED DESCRIPTION

[0043] The invention will now be explained based on the example of banknotes. Figure 1 Here, a schematic front view of a banknote 10 is shown, on which a security element in the form of a partially metallized film strip 14 is applied to a paper substrate 12 . Figure 2 The banknote 10 is shown along the Figure 1 Cross section along line II-II.

[0044] The film strip 14 comprises a film carrier 16, for example a thin PET film, for example 4 μm-40 μm thick, transparent in the visible and near infrared spectral range, which is provided with an interference layer stack 20 that changes color with the tilt angle in local areas 18. In the exemplary embodiment shown, the interference layer stack 20 consists of a three-layer thin-film interference layer system with a reflective layer 22, for example an opaque aluminum layer; a dielectric spacer layer 24, for example a 420 nm thick SiO2 and an absorption layer 26, for example an 8 nm thick chromium layer.

[0045] When observed in reflection, the interference layer stack 20 has an interference maximum not only in the visually visible spectrum from 380 nm to 780 nm, but also in the near infrared spectrum from 780 nm to 3000 nm. This near infrared interference maximum is intrinsically linked to the layer structure, in particular the specific thickness of the dielectric spacer layer 24, which leads to the visually angularly color-changing effect of the interference layer stack 20, and is present for all security elements having such a layer structure, so that the interference layer stack 20 provides a characteristic infrared identification as a first authenticity feature.

[0046] If it is best Figure 2 As can be seen in the figure, a base layer 30 is applied to the paper substrate 12 below the film strip 14 and partially even next to the film strip 14, the base layer 30 being mixed or doped with an infrared absorber 32 and being present in particular in the form of a paper primer or print. The base layer 30 has a higher adhesion to the paper substrate 12, in particular the adhesion of the base layer 30 to the paper substrate 12 is higher than the adhesion to the film strip 14.

[0047] The infrared absorber 32 is ideally transparent in the visible spectrum and has at most a light tint. Therefore, the presence of the bottom layer 30 is not visually noticeable, so Figure 1 The position and extension of the bottom layer 30 are indicated only by dashed lines.

[0048] The bottom layer 30 doped with the infrared absorber 32 constitutes the second authenticity feature of the banknote 10, and the first and second authenticity features together constitute an authenticity mark of the valuable document that can be inspected by a machine with infrared. In the authenticity inspection, the complete presence and correct position of the two authenticity features can be used as evidence of the authenticity of the banknote 10, while the absence of one of the two authenticity features or the position or extension deviation of one of the authenticity features indicates tampering of the banknote 10.

[0049] Figure 3In (a), a detail of an unaltered banknote 10 is shown with four measurement tracks 40, 42, 44 and 46, wherein the infrared reflection (Remission) of the banknote 10 is measured in a spectrally resolved manner by an infrared sensor during the authenticity check. The measurement of the infrared reflection at a plurality of different wavelengths makes it possible to distinguish the characteristic infrared mark of the interference layer stack 20 from the infrared marks of other interference layer stacks with a different layer structure, in particular from the infrared reflection of infrared absorbing materials.

[0050] Figure 3 (b) Schematically shown on banknote 10 Figure 3 (a) shows the measurement results in the four measurement tracks. The measurement tracks 40 and 46 are located outside the local area 18 provided with the interference layer stack in the infrared transparent area of ​​the carrier film 16. In these measurement tracks, the infrared reflection 50 of the infrared absorber 32 of the bottom layer 30 is thus detected by the sensor below and beside the film strip 14.

[0051] The measuring tracks 42, 44 also detect the local area 18 with the interference layer stack 20. On the left and right side of the interference layer stack 20, the infrared reflection 50 of the infrared absorber 32 of the bottom layer 30 is measured by the sensor. In the local area 18, the sensor detects only the characteristic infrared mark 52 of the interference layer stack 20, while the infrared absorber 32 under the film strip 14 is shielded by the metal reflective layer 22 of the interference layer stack 20 and does not contribute to the infrared signal.

[0052] The position and size of the area with the infrared reflection 50 or infrared marking 52 detected in the four measuring tracks 40-46 are then compared with the expected position and size, and the banknote is assessed as authentic if the two match.

[0053] During the peeling attack ("harvesting") of removing the interference layer stack 20 with the visually tilt-dependent color-changing effect from the banknote 10, the infrared marking and the first authenticity feature generated by the layer sequence of the interference layer stack 20 are inevitably removed from the banknote 10. On the other hand, the bottom layer 30 with the infrared absorber 32 also remains essentially completely on the paper substrate 12 of the provider banknote when the film strip 14 is peeled off due to its high adhesion to the paper substrate 12.

[0054] Figure 4 Now, (a) shows a detail of a tampered banknote 10-V1, in which the film strip 14 peeled off from the genuine banknote 10 is transferred to an unauthorized substrate 12-V, such as a copy. The bottom layer remaining on the original paper substrate 12 is not taken away during the peeling attack and is therefore not present on the substrate 12-V.

[0055] Figure 4 (b) schematically shows the process of verifying the authenticity of a tampered banknote 10-V1. Figure 3 In the measurement tracks 40 and 46 located outside the local area 18, no infrared signal is detected due to the absence of the bottom layer 30 and the infrared absorber 32.

[0056] In the measurement tracks 42 , 44 that intersect the partial region 18 with the interference layer stack 20 , characteristic infrared markings 52 of the transferred interference layer stack 20 are detected, but the infrared reflections of the infrared absorbers to the left and right of the interference layer stack 20 are missing in these measurement tracks.

[0057] When comparing the positions and sizes of the areas with detected infrared reflections 50 or infrared markings 52 in the four measurement tracks 40 - 46 , it is clearly concluded that the banknote 10 - V1 has been tampered with due to the absence of infrared reflections 50 in all four measurement tracks.

[0058] Figure 5 In (a) a detail of another tampered banknote 10 -V2 is shown, in which a counterfeit film strip 14 -V is provided in the area of ​​the bottom layer 30 of the paper substrate 12 of the donor banknote after the original film strip 14 has been stripped off.

[0059] For such counterfeiting, simple photocopies or printed strips are usually used which do not have a color-changing effect with an inclination angle, which therefore do not produce a specific infrared marking 54. Even in more complex counterfeit with a color-changing effect with an inclination angle, the counterfeiter does not know the exact layer thickness of the dielectric spacer layer 24, so that the interference layer stack of the counterfeit film strip 14-V in the local area 18 will produce an infrared marking 54 that is different from the original film strip 14, even if the visual appearance is similar, as shown by the different shading in the figure. In addition, the counterfeiter may not know the exact position of the film strip on the banknote and / or the significance of the exact orientation of the interference layer element relative to the bottom layer 30, so that the position of the local area 18 relative to the original banknote 10 may change, as shown in the figure. Figure 5 (a) shown.

[0060] Figure 5 (b) schematically shows the process of verifying the authenticity of a tampered banknote 10-V2. Figure 3 In the measurement tracks 40, 46, which are located outside the local area 18, the infrared reflection 50 of the infrared absorber 32 of the bottom layer 30 is therefore detected by the sensor below and beside the film strip 14. Since the banknote 10-V2 contains the original paper substrate 12, the measured infrared emission 50 corresponds to the expected reflection.

[0061] However, in the measuring tracks 42, 44 intersecting the partial area 18 with the interfering layer stack 20, the infrared marking 54 of the counterfeit film strip 14-V is detected instead of the expected infrared marking 52. In addition, the position of the determined partial area 18, in particular relative to the bottom layer 30, deviates from the expected position.

[0062] By comparing the position and size of the area with the detected infrared reflection 50 or infrared marking 54 with the expected position and size, and by comparing the infrared marking 54 with the expected correct infrared marking 52, it can also be clearly inferred here that the banknote 10-V2 has been tampered with.

[0063] Now refer to Figure 6 and Figure 7 Further advantageous designs and variants are explained, it being clear that not all variants shown in these figures have to be carried out simultaneously.

[0064] The combination of a bottom layer provided with an infrared absorber under the optically variable security element with narrow demetallized grooves and / or largely transparent areas with fine metal strips, lines, characters or patterns in the metal-containing interference layer structure has proven to be particularly attractive. Surprisingly, such a fine metal structure hardly impairs the detection of the infrared absorber located underneath, while on the other hand the narrow demetallized grooves also hardly affect the detection of the infrared marking of the interference layer stack.

[0065] Figure 6 A banknote 10 is schematically shown in cross section with a base layer 30 provided with an infrared absorber 32 and a film strip 80 arranged on the base layer 30. Figure 7 In (a) a detail of a banknote 10 with a film strip 80 is shown in a front view, and in (b) the associated infrared signal measured by an infrared sensor is shown in a spatially resolved manner.

[0066] exist Figure 6 and Figure 7 In the embodiment of the invention, the bottom layer 30 is only located below the film strip 80, but not next to it. This has the advantage that no additional space is required on the banknote 10 for the combined protection by the first and second authenticity features, and the authenticity of the banknote can be checked locally in the area of ​​the film strip 80, regardless of the printed design of the banknote.

[0067] Another feature is that Figure 6In the design of the film strip 80, a more complex interference layer stack 60 is provided, namely a 5-layer thin film interference layer system, an opaque aluminum layer as a reflective layer 62, a 280 nm thick dielectric SiO2 layer as a second dielectric spacer layer 64, a 3 nm thick chromium layer as a second absorption layer 66, a 140 nm thick dielectric SiO2 layer as a first dielectric spacer layer 68, and a 5 nm thick chromium layer as a first absorption layer 70. This 5-layer system provides additional freedom in optical design, because it can produce different infrared spectral curves and thus different infrared markings under similar or identical visual color changes with tilt angle. Potential counterfeiters cannot therefore infer the infrared marking of the interference layer stack 60 from the visual color change effect with tilt angle.

[0068] Another feature is that the aluminum layer 62 of the interference layer stack 60 is present only in the form of a narrow metal strip 84 in a first partial region 82 of the film strip 80, so that the partial region 82 is essentially transparent. In contrast, the film strip is essentially opaque in the partial region 86, where the aluminum layer 62 is present over the entire surface except for the narrow groove 88. The area coverage of the metallization in the partial region 86 is greater than 80%, preferably greater than 90%.

[0069] Figure 7 To this end, an exemplary design is shown in (a), in which narrow metal strips 84 form a regular square grid in the local area 82 and form a value "10" designed with a narrow line width at two locations. In the local area 86, grooves 88 form a geometric shape or pattern. In the local area 82, the area coverage of the metallization is less than 20%, while in the local area 86 it is greater than 80%.

[0070] like Figure 7 As shown in (b), infrared detection is not impaired by metal strips 84 or narrow grooves 88. Instead, the sensor can continuously detect infrared reflections 50 of infrared absorber 32 in local area 82 and infrared signatures 56 of interfering layer stack 60 in local area 86.

Claims

1. A value document comprising a value-document substrate and a security element applied to the substrate, the security element comprising an interference layer stack which gives the security element an optically variable appearance when visually observed in reflection, wherein - the interference layer stack provides a representative infrared signature as a first authenticity feature, - the value-document substrate comprises, on its surface as a second authenticity feature, a bottom layer mixed with an infrared absorber, which bottom layer is at least partially arranged below the security element, wherein the first and the second authenticity feature together form a machine-verifiable authenticity mark under infrared, the absence or incompleteness of which indicates a manipulation of the value document.

2. The valuable document according to claim 1, characterized in that The bottom layer mixed with the infrared absorber adheres better to the substrate than to the security element, so that when the security element is peeled off, the second authenticity feature remains essentially completely on the value-document substrate.

3. The valuable document according to claim 1 or 2, characterized in that The base layer is formed by a print or primer layer, in particular a paper primer.

4. Value document according to at least one of claims 1 to 3, characterized in that The bottom layer is arranged completely below the security element.

5. Value document according to at least one of claims 1 to 4, characterized in that The interference layer stack has a thin-layer element that changes color with the tilt angle, which in particular has a three-layer structure consisting of an absorption layer, a dielectric spacer layer and a reflection layer, or has a five-layer structure consisting of a first absorption layer, a first dielectric spacer layer, a second absorption layer, a second dielectric spacer layer and a reflection layer.

6. Value document according to at least one of claims 1 to 5, characterized in that The security element comprises a metallic layer which preferably consists of a reflective layer of an interference layer stack.

7. Value document according to at least one of claims 1 to 6, characterized in that The metallic layer of the security element is structured at least in partial regions.

8. The valuable document according to claim 7, characterized in that The metal layer of the security element has a structured partial region having narrow metal strips, narrow metal lines and / or metal patterns with a small line thickness, wherein the area of ​​the structured partial region is preferably at least 8 mm 2 , particularly preferably at least 20 mm 2 , and the area coverage of the metal layer in the structured partial area is preferably less than 20%.

9. Value document according to at least one of claims 1 to 8, characterized in that The infrared absorber is substantially white or transparent in the visible spectrum.

10. Value document according to at least one of claims 1 to 9, characterized in that The infrared absorber has broadband absorption in the near infrared range of 700 nm to 1100 nm.

11. Value document according to at least one of claims 1 to 10, characterized in that The security element comprises a relief structure arranged below the interference layer stack, wherein the relief structure is preferably formed by a micromirror array with directional reflecting micromirrors, in particular a micromirror array with non-diffractive mirrors, or by a diffraction structure, in particular a holographic structure, a nanostructure or a diffraction blazed grating.

12. Value document according to at least one of claims 1 to 11, characterized in that The security element comprises a film layer, in particular a film layer which is transparent in the visible spectral range and advantageously also in the near infrared range.

13. The valuable document according to claim 12, characterized in that The security element covers a continuous opening in a value-document substrate via the film layer.

14. A method for checking a value document according to one of claims 1 to 13, wherein - the value document is exposed at least in the region of the security element at a plurality of locations by infrared radiation and the reflected infrared radiation is detected, - determining in a spatially resolved manner the presence of a characteristic infrared marking of the first authenticity feature and the presence of an infrared response of an infrared absorber of the second authenticity feature, respectively, based on the detected reflected infrared radiation, - Based on the presence and the determined distribution of the first and second authenticity features, assessing the authenticity of the value document.

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