EP4488073A1 - Valuable document having a security element with an interference layer stack and testing method - Google Patents

Abstract

The invention relates to a value document (10) comprising a value document substrate (12) and a security element (14) applied to the substrate, which contains an interference layer stack (20) which gives the security element (14) an optically variable appearance when viewed in reflection. The interference layer stack (20) provides a characteristic IR signature as a first authenticity feature, and the value document substrate (12) contains, as a second authenticity feature, a background layer (30) on its surface which is provided with an IR absorber (32) and is arranged at least partially beneath the security element (14). The first and second authenticity features together form an authenticity mark that can be machine-verified in the infrared, the absence or incompleteness of which indicates tampering with the value document (10).

Description

The invention relates to a value document with a value document substrate and a security element applied thereto with an interference layer stack which gives the security element an optically variable appearance when visually observed in reflection. The invention also includes a method for checking such a value document.

Data storage media, such as valuables or identification documents, but also other valuable items, such as branded goods, are often provided with security elements for security purposes. These allow the authenticity of the data storage media to be verified and at the same time serve as protection against unauthorized reproduction.

For this purpose, optically variable security elements are often used, whose special visual effect, for example a color shift effect, can be identified by a viewer with the naked eye without any additional aids. However, such level 1 features are often subject to so-called "harvesting" attacks, in which a counterfeiter removes ("harvests") the security element from a genuine document and sticks it onto a fake, for example a photocopy, in order to visually enhance it.

There is therefore a need for technical solutions that can reliably detect banknotes and other valuable documents that have been manipulated in this way during machine processing/sorting.

Foil-based security elements often do not traditionally carry machine-readable features, so that the replacement of such a foil-based security element with a counterfeit cannot be easily detected by machine.

If, to remedy this, a foil-based security element is printed with an IR absorber, for example in non-metallized areas, the absence of the genuine security element on a value document can be detected with IR remission sensors, but a counterfeit with the transferred (genuine) foil is assessed as genuine.

In the printed publication WO 2023/285000 A1 It was therefore proposed to provide both the substrate of a banknote and an applied security element with security components that, when combined, provide a characteristic signal. The absence of the combination signal then represents a strong indication that manipulation has taken place. In particular, two different IR absorbers that absorb in spectrally separate areas are used to mark the substrate or the foil. On the one hand, this requires the integration of an IR absorber in transparent, non-metallized areas of the foil element, which requires larger demetallized areas and thus represents a considerable limitation of the foil design. In addition, a combination of two spectrally separate IR absorbers represents a significant hurdle in practice, since most IR absorbers absorb over a broad band and therefore spectrally overlap in the limited spectral range of the commonly used, inexpensive IR sensors (750 nm to 1050 nm).

Based on this, the invention is based on the object of specifying a generic value document that avoids the disadvantages of the prior art and in which, in particular, a value document manipulated by a detachment attack can be reliably recognized by machine. The invention is also intended to provide a testing method for value 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 includes a value document with a value document substrate and a security element applied to the substrate, wherein the security element contains an interference layer stack which gives the security element an optically variable appearance when visually observed in reflection.

The interference layer stack provides a characteristic IR signature as a first authenticity feature of the value document.

As a second authenticity feature of the value document, the value document substrate contains on its surface a background layer containing an IR absorber, which is arranged at least partially beneath the security element.

In a first application, the value document substrate itself may consist of paper, such as in the case of paper banknotes or visas. In another application, such as in the case of polymer banknotes, For ID cards or driving licenses, the value document substrate can be made of a polymer, e.g. polycarbonate or polypropylene, or of a polymer composite. In other applications, paper-polymer hybrid composite materials such as laminated paper layers can also be used as a value document substrate.

The first and second authenticity features together form an authenticity mark that can be checked by machine using infrared technology, and the absence or incompleteness of this indicates that the value document has been manipulated. In particular, the absence of the first or second authenticity feature can be used to conclude that the value document has been manipulated. As explained in more detail below, with the invention both the donor document with a detached security element and the recipient document with a transferred, genuine security element can be recognized as manipulated.

It is particularly advantageous that the adhesion of the background layer containing the IR absorber to the substrate is higher than the adhesion to the security element, so that the second authenticity feature remains essentially completely on the value document substrate when the security element is removed.

"Substantially complete" means that more than 90%, more than 94% and in particular more than 98% of the IR absorber remains on the value document substrate.

The base layer is preferably formed by a primer layer or a print. In the case of a value document substrate made of paper, The background layer is preferably formed by a paper primer. A paper primer or a suitable print can form a particularly close bond with the value document substrate, so that when the security element is detached, an adhesion break occurs at the interface with the underlying background layer and the security element is removed without the background layer.

In an advantageous embodiment, the background layer is arranged partly below and partly next to the security element. The presence of the IR absorber can then also be detected in areas next to the security element.

In another, equally advantageous embodiment, the background layer is arranged completely beneath the security element. The latter has the advantage that no additional space is required on the valuable document for the additional protection provided by the IR absorber and authenticity can be checked independently of the print design of the valuable document.

In an advantageous embodiment, the interference layer stack is formed by a color-shifting thin-film element. The thin-film element can, for example, have a three-layer structure consisting of an absorber layer, a dielectric spacer layer and a reflector layer, or a five-layer structure consisting of a first absorber layer, a first dielectric spacer layer, a second absorber layer, a second dielectric spacer layer and a reflector layer. Five-layer structures offer the particular advantage of additional degrees of freedom in optical design, as they enable the generation of different IR spectral profiles and thus different IR signatures with a similar or identical visual appearance. allow. An observed visual effect, for example a certain color change when tilting the security element, cannot therefore be used to easily determine the IR signature of the interference layer stack, so that reproducing the effect is very difficult.

The reflector layer is preferably opaque and can consist of aluminum, for example. The absorber layer or layers are advantageously formed by semi-transparent chrome layers. The dielectric spacer layers can consist in particular of SiO ₂ .

The security element advantageously contains a metal layer, which is preferably formed by the reflector layer of the interference layer stack. However, it is also possible for the metal layer to be an additional layer arranged above or below the interference layer stack.

The metal layer of the security element is advantageously structured at least in some areas. In particular, the metal layer of the security element can have a structured part area with narrow metallic bars, narrow metallic lines and/or metallic patterns and/or characters of low line thickness, the area coverage of the metal layer in the said structured part area preferably being below 20%, in particular below 15% or even below 10%. It has surprisingly been found that the IR detection of an underlying background layer is not significantly impaired by such narrow metal structures. The narrow metal structures therefore allow greater design freedom for the designer without impairing the technical function of the security element during authenticity testing. The geometric extension of the The area of the structured sub-area is preferably selected such that it has an area of at least 8 mm ² , preferably at least 20 mm ² . In this case, the presence of the IR absorber in the subsurface layer can be reliably detected even with inexpensive IR sensors, which may only have a limited spatial resolution in the millimeter range.

The IR absorber of the base layer is advantageously essentially transparent or white in the visible spectral range and is therefore visually inconspicuous. While the IR absorber can in principle absorb both spectrally broadly and spectrally narrow-band, IR absorbers that absorb broadly in the near infrared range (NIR) from 700 nm to 1500 nm, in particular in the range from 750 nm to 1100 nm, are currently particularly preferred.

Suitable IR absorbers can be found, for example, in the publication WO 2007/060133 A1 , the disclosure of which is incorporated into the present application in this respect. Examples of suitable IR absorbers are iron(II) or copper(II) compounds with an Fe2+ ion or a Cu2+ ion in a suitable chemical environment, where a suitable chemical environment is, for example, a phosphate ion or a polyphosphate ion or, more generally, a group containing phosphorus and oxygen. Such IR absorbers absorb over a broad band in the NIR range from 700 nm to 1100 nm, but are essentially transparent or white in the visible spectral range and have at most a slightly yellowish, greenish or bluish tint. The presence of the IR absorber in the background layer is therefore hardly visually recognizable.

Also suitable as IR absorbers are the ones sold under the name LUMOGEN-S by BASF Corporation, 100 Park Ave., Florham Park, NJ 07932. IR substances described in the publication GB 2 168 372 disclosed IR-absorbing materials which are invisible or transparent in the visible range of the electromagnetic spectrum and which are described in the publication US 6,926,764 disclosed IR marking substances. These IR marking substances are substituted naphthalocyanines, phthalocyanines, metal-containing phthalocyanines or poly-substituted phthalocyanines. Thiophenol-substituted copper phthalocyanines, in particular para-toluenethiol-persubstituted copper phthalocyanines, are preferred.

In an advantageous development of the invention, the security element contains a relief structure arranged below the interference layer stack. The relief structure can be formed in particular by a micromirror arrangement with directionally reflecting micromirrors, in particular a micromirror arrangement with non-diffractive mirrors. However, the relief structure can also be formed by a diffractive diffraction structure, in particular a hologram structure, nanostructure or diffractive, blazed grating. Through such relief structures, the security element can show a movement effect or a three-dimensional appearance in addition to the color shift effect of the interference layer stack and can therefore be visually enhanced and its security against forgery increased.

In advantageous embodiments, the security element contains a film layer, in particular a film layer that is transparent in the visible spectral range and advantageously also in the near infrared. The security element advantageously covers a continuous opening in the value document substrate with the film layer. In other embodiments, the security element can be built up on a transfer film during production, which after the Transfer of the security element to the value document is removed again.

• das Wertdokument zumindest im Bereich des Sicherheitselements an mehreren Orten mit Infrarotstrahlung beaufschlagt und die remittierte IR-Strahlung erfasst wird,
• anhand der erfassten remittierten IR-Strahlung das Vorliegen der charakteristischen IR-Signatur des ersten Echtheitsmerkmals und das Vorliegen der IR-Antwort des IR-Absorbers des zweiten Echtheitsmerkmals jeweils ortsaufgelöst ermittelt wird, und
• auf Grundlage des Vorhandenseins und der ermittelten Verteilung des ersten und zweiten Echtheitsmerkmals die Echtheit des Wertdokuments bewertet wird.

The invention also includes a method for checking a value document of the type described, in which

• the value document is exposed to infrared radiation at several locations, at least in the area of the security element, and the remitted IR radiation is recorded,
• based on the detected remitted IR radiation, the presence of the characteristic IR signature of the first authenticity feature and the presence of the IR response of the IR absorber of the second authenticity feature are each determined in a spatially resolved manner, and
• the authenticity of the value document is assessed on the basis of the presence and the determined distribution of the first and second authenticity features.

In particular, it can be checked whether both the first and the second authenticity feature are present and if one of the two authenticity features is missing, it can be concluded that the value document has been manipulated. Even if both authenticity features are present, a distribution of the authenticity features that deviates from the expected spatial distribution can be used to conclude that the document has been manipulated.

Further embodiments and advantages of the invention are explained below with reference to the figures, in which a true-to-scale and true-to-proportion reproduction was omitted in order to increase clarity.

Fig. 1

schematisch eine Banknote nach einem Ausführungsbeispiel der Erfindung in Aufsicht,

Fig. 2

einen Querschnitt der Banknote der Fig. 1 entlang der Linie II-II,

Fig. 3

in (a) einen Ausschnitt der unmanipulierten Banknote der Fig. 1 zusammen mit vier Messspuren für die Echtheitsprüfung, und in (b) schematisch das Messergebnis in den vier Messspuren von (a),

Fig. 4

in (a) einen Ausschnitt einer manipulierten Banknote, bei der ein abgelöster Folienstreifen auf ein nicht autorisiertes Substrat transferiert wurde, und in (b) schematisch das Messergebnis in den vier Messspuren von (a),

Fig. 5

in (a) einen Ausschnitt einer anderen manipulierten Banknote, bei der das Papiersubstrat einer Spender-Banknote nach dem Ablösen des originalen Folienstreifens mit einem gefälschten Folienstreifen versehen wurde, und in (b) schematisch das Messergebnis in den vier Messspuren von (a),

Fig. 6

schematisch eine Banknote nach einem anderen Ausführungsbeispiel der Erfindung im Querschnitt, und

Fig. 7

in (a) eine Aufsicht auf eine Banknote nach dem Ausführungsbeispiel der Fig. 6 und in (b) ortsaufgelöst das von einem IR-Sensor erfassbare zugehörige IR-Signal.

They show:

Fig. 1

schematically a banknote according to an embodiment of the invention in plan view,

Fig. 2

a cross-section of the banknote of the Fig. 1 along line II-II,

Fig. 3

in (a) a section of the untampered banknote of the Fig. 1 together with four measuring tracks for authenticity testing, and in (b) schematically the measurement result in the four measuring tracks of (a),

Fig. 4

in (a) a section of a manipulated banknote in which a detached foil strip was transferred to an unauthorized substrate, and in (b) schematically the measurement result in the four measuring tracks of (a),

Fig. 5

in (a) a section of another manipulated banknote, in which the paper substrate of a donor banknote was provided with a counterfeit foil strip after the original foil strip was removed, and in (b) schematically the measurement result in the four measuring tracks of (a),

Fig. 6

schematically a banknote according to another embodiment of the invention in cross section, and

Fig. 7

in (a) a view of a banknote according to the embodiment of the Fig. 6 and in (b) the spatially resolved IR signal that can be detected by an IR sensor.

The invention will now be explained using the example of banknotes. Fig. 1 shows a schematic top view of a banknote 10, on whose paper substrate 12 a security element in the form of a partially metallized foil strip 14 is applied. Figure 2 shows a cross-section of banknote 10 in the area of the security element along line II-II of Fig. 1 .

The film strip 14 contains a film carrier 16, for example a thin PET film, e.g. 4 µm - 40 µm thick, transparent in the visible and near-infrared spectral ranges, which is provided with a color-shifting interference layer stack 20 in a partial area 18. In the exemplary embodiment shown, the interference layer stack 20 is formed by a three-layer thin film interference layer system with a reflector layer 22, for example an opaque aluminum layer, a dielectric spacer layer 24, for example a 420 nm thick SiO ₂ layer, and an absorber layer, for example an 8 nm thick chromium layer.

When viewed in reflection, the interference layer stack 20 not only has interference maxima in the visually visible spectrum from 380 nm to 780 nm, but also shows interference maxima in the near infrared between 780 nm and 3000 nm. These NIR interference maxima are intrinsically linked to the layer structure responsible for the visual color shift effect of the interference layer stack 20, in particular the specific thickness of the dielectric spacer layer 24, and are equally present for all security elements with this layer structure, so that the interference layer stack 20 provides a characteristic IR signature as a first authenticity feature.

How best in Fig. 2 As can be seen, a base layer 30 is applied to the paper substrate 12 under and partly also next to the film strip 14, which is mixed with an IR absorber 32 and which can be in the form of a paper primer or a print. The base layer 30 has a high level of adhesion to the paper substrate 12, in particular the adhesion of the base layer 30 to the paper substrate 12 is higher than to the film strip 14.

The IR absorber 32 is ideally transparent in the visible spectral range and has at most a slight tint. The presence of the background layer 30 is therefore visually inconspicuous, so that the position and extent of the background layer 30 in Fig. 1 are only indicated with dashed lines.

The background layer 30 offset with the IR absorber 32 forms a second authenticity feature of the banknote 10, and the first and second authenticity features together form an authenticity mark of the value document that can be checked by machine using infrared radiation. In an authenticity check, the complete presence and correct position of the two authenticity features can serve as proof of the authenticity of the banknote 10, while the absence of one of the two authenticity features or a deviating position or extent of one of the authenticity features indicates that the banknote 10 has been manipulated.

For illustration purposes, Fig. 3 in (a) a section of the unmanipulated banknote 10 with four measuring tracks 40, 42, 44, 46, in which the IR remission of the banknote 10 is measured spectrally resolved by an IR sensor during the authenticity check. A measurement of the IR remission at several different wavelengths allows the characteristic IR signature of the interference layer stack 20 from the IR signature of other interference layer stacks with different layer structures and in particular from the IR remission of IR absorber materials.

Figure 3(b) shows schematically the measurement result on banknote 10 in the four measuring tracks of the Fig. 3(a) The measuring tracks 40 and 46 lie outside the partial area 18 provided with the interference layer stack in an infrared-transparent area of the carrier film 16. In these measuring tracks, the sensor therefore detects the IR remission 50 of the IR absorber 32 of the background layer 30 both below and next to the film strip 14.

The measuring tracks 42, 44 also cover the partial area 18 with the interference layer stack 20. To the right and left of the interference layer stack 20, the sensor measures the IR remission 50 of the IR absorber 32 of the background layer 30. In the partial area 18, however, the sensor only detects the characteristic IR signature 52 of the interference layer stack 20, while the IR absorber 32 located below the film strip 14 is shielded by the metallic reflection layer 22 of the interference layer stack 20 and does not contribute to the IR signal.

The positions and sizes of the areas with recorded IR remission 50 or IR signature 52 in the four measuring tracks 40-46 are then compared with expected positions and sizes and the banknote is assessed as genuine if they match.

In a harvesting attack, in which the interference layer stack 20 with its visual color shift effect is removed from the banknote 10, the IR signature generated by the layer sequence of the interference layer stack 20 and thus the first authenticity feature is inevitably removed from the banknote 10. On the other hand, the background layer 30 with the IR absorber 32 remains essentially completely on the paper substrate 12 of the donor banknote due to its high adhesion to the paper substrate 12 even when the film strip 14 is removed.

Figure 4 now shows in (a) a section of a manipulated banknote 10-V1, in which the foil strip 14 detached from the genuine banknote 10 was transferred to an unauthorized substrate 12-V, for example a photocopy. The background layer remaining on the original paper substrate 12 was not transferred during the removal attack and is therefore not present on the substrate 12-V.

Figure 4(b) shows schematically the measurement result on the manipulated banknote 10-V1 during the authenticity test in the four measuring tracks of the Fig. 3 In the measuring tracks 40, 46, which lie outside the partial area 18, no IR signal is detected due to the absence of the background layer 30 and the IR absorber 32.

In the measuring tracks 42, 44, which intersect the partial area 18 with the interference layer stack 20, the characteristic IR signature 52 of the transferred interference layer stack 20 is recorded, but the IR remissions of the IR absorber to the right and left of the interference stack 20 are missing in these measuring tracks.

When comparing the positions and sizes of the areas with recorded IR remission 50 or IR signature 52 in the four measuring tracks 40-46, it can be clearly concluded that the banknote 10-V1 has been manipulated due to the absence of the IR remission 50 in all four measuring tracks.

Figure 5 shows in (a) a section of another manipulated banknote 10-V2, in which the paper substrate 12 of the donor banknote was provided with a counterfeit foil strip 14-V in the area of the background layer 30 after the original foil strip 14 had been removed.

Often, simple photocopies or printed strips without a color shift effect are used for such counterfeits, which consequently do not produce a specific IR signature 54. Even in the case of more complex counterfeits with a color shift effect, the counterfeiter does not know the exact layer thickness of the dielectric spacer layer 24, so that the interference layer stack of the counterfeit foil strip 14-V in the partial area 18 will produce a different IR signature 54 than the original foil strip 14, even with a comparable visual appearance, as indicated in the figure by a different hatching. In addition, the counterfeiter may not know the exact position of the foil strip on the banknote and/or the significance of the exact alignment of the interference layer element relative to the background layer 30, so that the position of the partial area 18 may be different from the original banknote 10, as shown in Fig. 5(a) also shown.

Figure 5(b) shows schematically the measurement result on the manipulated banknote 10-V2 during the authenticity test in the four measuring tracks of the Fig. 3 . In the measuring tracks 40, 46, which lie outside the partial area 18, the sensor measures the IR remission 50 of the IR absorber 32 of the background layer 30 is recorded both below and next to the foil strip 14-V. Since the banknote 10-V2 contains the original paper substrate 12, the measured IR remission 50 corresponds to the expected remission.

However, in the measuring tracks 42, 44, which intersect the partial area 18 with the interference layer stack 20, the IR signature 54 of the counterfeit film strip 14-V is recorded instead of the expected IR signature 52. In addition, the determined position of the partial area 18, in particular relative to the position of the background layer 30, deviates from the expected position.

By comparing the positions and sizes of the areas with recorded IR remission 50 or IR signature 54 with the expected positions and sizes and by comparing the IR signature 54 with the expected, correct IR signature 52, it can also be clearly concluded that the 10-V2 banknote has been manipulated.

Further advantageous embodiments and modifications will now be described with reference to Fig. 6 and 7 explained, it being understood that not all variations shown in these figures need to be made simultaneously.

The combination of a background layer with an IR absorber underneath an optically variable security element in conjunction with narrow demetallized recesses in the metal-containing interference layer structure and/or with predominantly transparent areas with fine metallized bars, lines, characters or patterns has proven to be particularly attractive. Surprisingly, such fine metal structures hardly affect the detection of the underlying IR absorber, while on the other hand, narrow demetallized recesses hardly affect the detection of the IR signature of the interference layer stack.

For illustration purposes, Fig. 6 schematically a banknote 10 with a background layer 30 provided with an IR absorber 32 and a film strip 80 arranged on the background layer 30 in cross section, and Fig. 7 shows in (a) a section of a banknote 10 with such a foil strip 80 in plan view and in (b) the spatially resolved, corresponding IR signal measured by an IR sensor.

In the examples of the Fig. 6 and 7 the background layer 30 is located exclusively under, but not next to, the foil strip 80. This has the advantage that no additional space is required on the banknote 10 for the combined protection provided by the first and second authenticity features, and that the authenticity of the banknote can be checked locally in the area of the foil strip 80, regardless of the print design of the banknote.

Another special feature is the foil strip 80 in the design of the Fig. 6 provided with a more complex interference layer stack 60, namely with a 5-layer thin film interference layer system, which has an opaque aluminum layer as reflector layer 62, a 280 nm thick dielectric SiO ₂ layer as second dielectric spacer layer 64, a 3 nm thick chromium layer as second absorber layer 66, a 140 nm thick dielectric SiO ₂ layer as first dielectric spacer layer 68 and a 5 nm thick chromium layer as first absorber layer 70. Such 5-layer systems allow additional degrees of freedom in optical design, since they allow the generation of different IR spectral profiles and thus different IR signatures with similar or identical visual color shift effects. A potential counterfeiter cannot therefore deduce the IR signature of the interference layer stack 60 from the visual color shift effect.

As a further special feature, the aluminum layer 62 of the interference layer stack 60 is only present in the form of narrow metal webs 84 in a first partial area 82 of the film strip 80, so that the partial area 82 is largely transparent. In the partial area 86, however, the film strip is essentially opaque, the aluminum layer 62 is present over the entire surface except for narrow recesses 88. The surface coverage of the metallization in the partial area 86 is above 80%, preferably above 90%.

Fig. 7 shows an example design in (a) in which the narrow metal bars 84 in the partial area 82 form a regular square grid and in two places the value number "10" executed with a narrow line width. In the partial area 86, the recesses 88 form a geometric shape or pattern. The area coverage of the metallization is below 20% in the partial area 82, but above 80% in the partial area 86.

How Fig. 7(b) illustrated, the IR detection is not impaired by the metallic webs 84 or the narrow recesses 88. Rather, the sensor continuously detects the IR remission 50 of the IR absorber 32 in the partial area 82 and the IR signature 56 of the interference layer stack 60 in the partial area 86.

Claims (14)

A value document comprising a value document substrate and a security element applied to the substrate, which contains 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 characteristic IR signature as a first authenticity feature, - the value document substrate contains, as a second authenticity feature on its surface, a background layer mixed with an IR absorber, which is arranged at least partially below the security element, - whereby the first and second authenticity features together form an authenticity mark that can be checked by machine using infrared technology, the absence or incompleteness of which indicates a manipulation of the value document. Value document according to claim 1, characterized in that the adhesion of the background layer mixed with IR absorber to the substrate is higher than the adhesion to the security element, so that the second authenticity feature remains essentially completely on the value document substrate when the security element is detached, A value document according to claim 1 or 2, characterized in that the background layer is formed by a print or a primer layer, in particular a paper primer. Value document according to at least one of claims 1 to 3, characterized in that the background layer is arranged completely beneath the security element. Value document according to at least one of claims 1 to 4, characterized in that the interference layer stack has a color-shifting thin-film element, in particular with a three-layer structure comprising an absorber layer, a dielectric spacer layer and a reflector layer, or with a five-layer structure comprising a first absorber layer, a first dielectric spacer layer, a second absorber layer, a second dielectric spacer layer and a reflector layer. Value document according to at least one of claims 1 to 5, characterized in that the security element contains a metal layer, which is preferably formed by the reflector layer of the interference layer stack. Value document according to at least one of claims 1 to 6, characterized in that the metal layer of the security element is structured at least in partial areas. A value document according to claim 7, characterized in that the metal layer of the security element has a structured partial area with narrow metallic webs, narrow metallic lines and/or metallic patterns of low line width, wherein preferably the area of the structured partial area is at least 8 mm ² , particularly preferably is at least 20 mm ² and the area coverage of the metal layer in the said structured partial area is preferably below 20 %. Value document according to at least one of claims 1 to 8, characterized in that the IR absorber is substantially white or transparent in the visible spectral range. Value document according to at least one of claims 1 to 9, characterized in that the IR absorber absorbs broadband in the near infrared range from 700 nm to 1100 nm. Value document according to at least one of claims 1 to 10, characterized in that the security element contains a relief structure arranged below the interference layer stack, wherein the relief structure is preferably formed by a micromirror arrangement with directionally reflecting micromirrors, in particular with non-diffractive mirrors, or by a diffractive diffraction structure, in particular a hologram structure, nanostructure or diffractive, blazed grating. Value document according to at least one of claims 1 to 11, characterized in that the security element contains a film layer, in particular a film layer that is transparent in the visible spectral range and advantageously additionally in the near infrared. Value document according to claim 12, characterized in that the security element with the film layer covers a continuous opening in the value document substrate. Method for checking a value document according to one of claims 1 to 13, in which - the value document is exposed to infrared radiation at several locations, at least in the area of the security element, and the remitted IR radiation is recorded, - the presence of the characteristic IR signature of the first authenticity feature and the presence of the IR response of the IR absorber of the second authenticity feature are determined in a spatially resolved manner based on the detected remitted IR radiation, and - the authenticity of the value document is assessed on the basis of the presence and the determined distribution of the first and second authenticity features.

Images