Data carrier with machine-readable security feature, production method and authenticity check method

Abstract

The invention relates to a data carrier (10), in particular a value or security document, having a substrate (20) which comprises at least one transparent plastics layer and two opposing main surfaces. The data carrier additionally contains two opaque-white layers (22, 32) having a white, opaque appearance, which are applied to the opposing main surfaces of the substrate (20). Each of the opaque-white layers (22, 32) consists of a layer sequence of two or more partial layers (24a-c, 34a-c) extending from a lowermost white layer (24a, 34a) to an uppermost white layer (24c, 34c). The data carrier also contains a machine-readable security feature which comprises a machine-readable feature substance (38) which is present in at least one of the partial layers (24c) of at least one of the opaque-white layers (22, 32).

Description

[0001] Data carrier with machine-readable security feature, manufacturing process and authenticity verification process

[0002] The invention relates to a data carrier, in particular a valuable or security document, which contains a substrate comprising at least one transparent plastic layer and is protected by a machine-readable security feature. The invention also relates to a method for producing such a data carrier. The invention further relates to a method for verifying the authenticity of the data carrier.

[0003] 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 elements allow the authenticity of the data storage media to be verified and at the same time serve as protection against unauthorized reproduction.

[0004] For some time now, polymer materials have been used as substrate materials for banknotes alongside paper. Polymer banknotes offer several advantages over paper banknotes, such as greater tear resistance. However, securing polymer banknotes has not yet been as successful as securing banknotes with a paper substrate. It is known that polymer banknotes can be secured by adding machine-readable feature substances to a visible imprint. However, only small quantities of features can be incorporated into such an imprint, and completeness verification is usually not possible with the feature-laden imprints, which are usually only present in certain areas.On the other hand, if machine-readable feature substances are incorporated into the volume of the polymer substrate to also allow for completeness verification, there is a risk that the feature substances will be visually visible in transparent window areas and disrupt the appearance. Based on this, the invention is based on the object of improving the authentication of polymer or composite banknotes.

[0005] This object is achieved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

[0006] The invention provides a data carrier comprising a substrate comprising at least one transparent plastic layer and two opposing main surfaces. The data carrier may, in particular, be a valuable or security document.

[0007] The data carrier further contains two opaque white layers with a white, opaque appearance, applied to the opposite major surfaces of the substrate. Each of the opaque white layers consists of a layer sequence of two or more sublayers, ranging from a bottom white layer to a top white layer.

[0008] The data carrier further contains a machine-readable security feature comprising a machine-readable feature substance present in at least one of the sublayers of at least one of the opaque white layers. The presence of the machine-readable feature substance in at least one of the sublayers of at least one of the opaque white layers means that the feature substance is present in the form of a homogeneous distribution in the respective layer.

[0009] For the purposes of this description, the opaque white layer refers to the layer sequence extending from a bottom white layer to a top white layer. The bottom and top white layers are each enclosed, thus forming part of the opaque white layer's layer sequence. Between the bottom and top white layers, there may be additional white layers, as well as transparent layers. The layers in between are also part of the opaque white layer. The bottom layer is the layer closest to the substrate, and the top layer is the layer furthest from the substrate in the opaque white layer stack.

[0010] The sublayers of an opaque white coating typically have a thickness between 1 μm and 10 μm, preferably between 3 μm and 10 μm. The sublayers can consist of the same or different coating materials and can be transparent, white, or opaque. The sublayers can contain various additives, in particular organic or inorganic white pigments or scatterers for a white color impression. Advantageous white pigments are, for example, TiO2 or SiO2, but organic scatterers can also be considered. The scattering particles can have a round, sharp-edged, or fibrous morphology.

[0011] Furthermore, the opaque white layer has a rough surface for good ink absorption. This can be achieved, in particular, by adding relatively large particles (typically > 10 pm) dispersed in the paint. These particles can be identical to or different from the white pigments.

[0012] The sequence of coatings in the sublayers is advantageously selected to ensure lasting, good adhesion between successive layers and to enable the printing of thin, even layers. The opaque white layer is preferably printed onto the substrate using gravure printing. To create windows, recesses can be provided in one of the two opaque white layers (single-sided windows) and / or congruent recesses in the opposite opaque white layers on both sides (double-sided windows).

[0013] With their described properties, the opaque white layers provide a white, opaque impression and a rough surface for good ink acceptance, so that the substrate with the two applied opaque white layers behaves similarly to paper when printed, despite the existing plastic layer.

[0014] For the purposes of this description, a partial layer of an opaque white layer that contains a machine-readable feature substance is also referred to as an embedding layer. According to the invention, at least one of the two opaque white layers therefore contains such an embedding layer. Each opaque white layer can contain exactly one embedding layer or multiple embedding layers. All partial layers of an opaque white layer, or at least all white partial layers, can also represent embedding layers.

[0015] According to an advantageous embodiment, the machine-readable feature substance is an optically readable feature substance, i.e., a feature substance that can be excited to emit light (signal light) by illumination with light (illumination light), for example, by luminescence, by scattering with spectral change due to narrowband absorption, or by Raman scattering. The machine-readable feature substance is preferably a luminescent substance, particularly preferably an IR-IR luminescent substance, i.e., an infrared-excitable luminescent substance that luminesces in the infrared. An IR absorber or Raman scatterer can also be used as a machine-readable feature substance.

[0016] When using an optically readable feature substance, the scattering of illumination light and signal light in the opaque white layer, both in the feature-containing and non-feature-containing layers, leads to a higher feature intensity compared to insertion variants in which there is less scattering, for example insertion in a window, or insertion in which the scatterers are further away from the feature substance particles, such as insertion into the volume of a polymer substrate.

[0017] Without wishing to be bound to a specific explanation, the following mechanisms in particular are currently understood to contribute to the higher feature intensity: On the one hand, the scattering of the illumination light leads to a longer path length of the illumination light in the feature-bearing layers, so that it is absorbed more efficiently by a feature particle. This has a particularly strong effect when the feature substance concentration is low, i.e., when the feature particles are far apart, and the illumination spot is small. On the other hand, the scattering of the signal light leads to a portion of the signal light that is not emitted towards the detector being directed by a scatterer to the detector and can contribute to the measurement. If the feature substance is a luminescent substance, the illumination light is usually referred to as excitation light and the signal light as luminescent light.

[0018] If a data carrier contains several different machine-readable feature substances, the above and the following requirements apply advantageously to several, in particular to all machine-readable feature substances, even if only one feature substance is referred to in the singular when describing the requirement.

[0019] Advantageously, the machine-readable feature substance is distributed over the entire surface of the embedding layer. In particular, the machine-readable feature substance is distributed uniformly, i.e., with a substantially constant areal density, throughout the respective embedding layer. This simplifies the completeness check of the data carrier.

[0020] The machine-readable feature substance advantageously consists of particles with a D50 particle size of less than 3 μm; particularly preferably, the D50 particle size is between 0.5 μm and 2 μm. This ensures that the particles are sufficiently small to not interfere with the printing of the embedding layer.

[0021] The machine-readable feature substance preferably consists of essentially round particles with an aspect ratio of less than 1:2. This supports a uniform distribution of the feature substance in the embedding layer without the formation of a preferred direction.

[0022] In an advantageous embodiment, an embedding layer of the machine-readable feature substance contains filler particles, for example, white pigments, and the machine-readable feature substance consists of particles that are no larger than the largest filler particles of the embedding layer, for example, measured by the D50 diameter. The filler particles can thus serve as scatterers for the illumination and / or signal light, and separation of filler particles and feature substance particles is avoided. At least one partial layer of an opaque white layer provided with the machine-readable feature substance advantageously occupies essentially the entire surface of the data carrier, thus enabling a completeness check of the data carrier. This does not affect any window areas in one or both opaque white layers.

[0023] In an advantageous variant of the invention, a machine-readable feature substance is present in only one of the two opaque white layers. As explained in more detail below, this makes it easy to detect the orientation of the data carrier during inspection.

[0024] In another, equally advantageous variant of the invention, a machine-readable feature substance is present in each of the two opaque white layers. As explained in more detail below, this allows, for example, the desired total amount of feature substance to be distributed across twice the number of embedding layers, or the total amount of feature substance can be increased with the same feature load per layer. The opposing opaque white layers can be provided with the same or different feature substances. The latter also allows for easy detection of the data carrier's orientation during inspection.

[0025] In a preferred embodiment, the machine-readable feature substance is present in exactly one of the sub-layers of the two opaque white layers.

[0026] According to an advantageous variant of the invention, the machine-readable feature substance is present only in the uppermost sublayer of one or both opaque white layers. The machine-readable feature substance preferably consists of particles with a dimension that essentially corresponds to the layer thickness of the embedding layer or is smaller than the layer thickness of the embedding layer.

[0027] According to another, equally advantageous variant of the invention, the machine-readable feature substance is present only in a lower sublayer, preferably only in the second-highest sublayer of one or both opaque white layers. The machine-readable feature substance preferably consists of particles with a dimension that is smaller than the thickness of the embedding layer. The advantages associated with these two variants of the invention are explained in more detail below.

[0028] According to a further, equally advantageous variant of the invention, a machine-readable feature substance is present in several partial layers of one or both opaque white layers.

[0029] In a practical design, the same feature substance is present in different sublayers. Incorporating it into multiple sublayers allows for a particularly high total amount of feature substance to be incorporated into the opaque white layer.

[0030] Alternatively, different feature substances can advantageously be provided in different sublayers. For example, different, yet interacting, feature substances can be present in different sublayers. This increases counterfeit security, as the feature signal cannot be replicated by a single feature substance. Furthermore, machine-readable feature substances with different particle sizes can also be present in different sublayers, with smaller particles arranged in deeper sublayers and larger particles in the uppermost sublayer of an opaque white layer, for example, measured by the D50 diameter.Machine-readable feature substances with different particle hardness can also be present in different sub-layers, with harder particles arranged in deeper sub-layers and softer particles in the uppermost sub-layer of an opaque white layer, measured, for example, by the Mohs hardness.

[0031] Another advantageous variant of the invention provides for the introduction of a feature substance with large particles into a deeper sub-layer of an opaque white layer and for it to be stabilized by the adjacent, higher sub-layer. This variant is based on the inventors' observation that the sub-layers, in particular the deeper sub-layer, are thinner in the dry state than in the wet state, and that large particles embedded in this way, which are still fully embedded in a deeper layer in the wet state, protrude from their actual embedding layer in the dry state and into the adjacent, higher sub-layer, where they are stabilized. In addition, the particles can also protect the higher sub-layer from abrasion.

[0032] In a further advantageous embodiment, the opaque white layers are designed such that they have an opacity of >1.42 or a remission of more than 30% or even more than 50% in the infrared range, particularly between 800 nm and 2000 nm. This can be achieved by adjusting the quantity, but also the particle size, of the white pigments in the white sublayers of the opaque white layers. To prevent overlapping of white pigment aggregates at high fill levels, so-called extenders are advantageously used to dilute the white pigments. The machine-readable feature substance itself can be used particularly advantageously for this purpose, so that no separate extender is required.

[0033] According to a further development of the invention, at least one of the sublayers comprises a camouflage substance, which in particular has a chemical composition tailored to the machine-readable feature substance, but no feature effect, thus making it difficult for a potential counterfeiter to chemically analyze the feature substance. The tailored chemical composition can, for example, have the same crystal structure as the feature substance, or contain some of the same elements as the feature substance, or contain the same elements as the feature substance but in different proportions. The camouflage substance is preferably present in a higher sublayer or in the same sublayer as the machine-readable feature substance.

[0034] The camouflage material can have the same grain size distribution as the feature substance, but it can also advantageously have a larger average grain size than the feature substance, so that the camouflage material particles additionally protect the feature substance particles from abrasion. In a further variant of the invention, the camouflage material particles have a broader grain size distribution than the feature substance, with the camouflage material containing larger particles than the feature substance. The camouflage material can also have a bimodal size distribution and thus consist of smaller and larger particles. In both cases, the largest camouflage material particles protect the feature substance from abrasion; at the same time, even if the larger camouflage material particles are lost, smaller camouflage material particles remain to ensure the desired camouflage.The substrate of the data carrier is advantageously formed by a plastic substrate or a composite substrate with at least one plastic layer, for example, a composite substrate with a layer sequence of film / paper / film. Suitable plastics for the plastic layer or the plastic substrate are, in particular, biaxially oriented polypropylene (BOPP), polyethylene terephthalate (PET), polypropylene (PP), or polyamide (PA). The use of biaxially oriented polypropylene (BOPP) is particularly preferred.

[0035] The invention also includes a method for producing a data carrier of the type described, in which a substrate is provided which comprises at least one transparent plastic layer and has two opposite main surfaces, two opaque white layers with a white, opaque appearance are applied to the opposite main surfaces of the substrate, each of which is formed from a layer sequence of two or more sub-layers extending from a bottom white layer to a top white layer, and at least one of the sub-layers of at least one of the opaque white layers is produced with a machine-readable feature substance in order to form a machine-readable security feature.

[0036] The partial layers of the opaque white layers are conveniently printed, preferably using the gravure printing process.

[0037] In the process, the machine-readable feature substance is advantageously ground to the desired grain size or provided with the desired grain size and added to the lacquer of the sublayers intended for embedding. The lacquer is then applied together with the added feature substance, thus achieving a substantially uniform distribution of the feature substance in the embedding layer.

[0038] The present invention further relates to a method for checking the authenticity of the data carrier according to the invention, comprising the step of providing the data carrier and the step of reading the machine-readable security feature which comprises a machine-readable feature substance, wherein during the reading, in particular the scattering of illumination light and signal light in the opaque white layer is used to check the authenticity of the data carrier.

[0039] 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 has been omitted in order to increase clarity.

[0040] They show:

[0041] Fig. 1 shows schematically a polymer banknote with a machine-readable security feature according to the invention,

[0042] Fig. 2 shows a schematic cross-sectional view of the structure of a banknote according to an embodiment of the invention, in which the feature substance is present only in the uppermost partial layer of the opaque white layer, Fig. 3 shows a modification of the embodiment of Fig. 2, in which a feature-loaded opaque white layer is present on both sides of the substrate,

[0043] Fig. 4 shows another embodiment of the invention in which the feature substance is present only in the second uppermost sub-layer of the opaque white layers,

[0044] Fig. 5 shows a modification of the embodiment of Fig. 4 with additional camouflage material,

[0045] Fig. 6 shows a further embodiment of the invention in which the feature substance is present in several partial layers of the opaque white layers,

[0046] Fig. 7 shows an embodiment with a first feature substance in the uppermost sub-layer and a second, supplementary feature substance in the second uppermost sub-layer of the opaque white layers, and

[0047] Fig. 8 Layer structures for comparative measurements of feature intensity in a conventional design (Fig. 8a) and two designs according to the invention (Fig. 8b, Fig. 8c).

[0048] The invention will now be explained using banknotes as an example. Figure 1 shows a schematic representation of a polymer banknote 10, which, in addition to conventional printed images 12 and security elements, is also equipped with a machine-readable security feature 14 according to the invention, which occupies the entire surface of the banknote 10 except for the areas of the windows 16, 18.

[0049] Figures 2 to 7 illustrate several advantageous embodiments, each showing a cross-sectional view of the layers of a polymer banknote according to the invention that are essential to the present invention. In the embodiments, the banknote 10 contains a transparent polymer substrate 20, which is preferably formed by a film of biaxially oriented polypropylene (BOPP).

[0050] On the opposite main surfaces of the substrate 20, an opaque white layer 22 or 32 with a white, opaque appearance is applied. Each of the two opaque white layers 22, 32 consists of several, typically two to five, sub-layers. For illustration purposes, the figures show opaque white layers with three sub-layers 24a, 24b, 24c or 34a, 34b, 34c, each extending from a bottommost white layer 24a or 34a to a topmost white layer 24c or 34c. The bottommost layer is the layer closest to the substrate, and the topmost layer is the layer furthest from the substrate of the layer stack of the opaque white layer 22 or 32. Additional, also transparent, layers 24b, 34b, which are also considered part of the opaque white layer 22 or 32, can be located between the bottommost and topmost white layers.

[0051] As already generally explained above, the opaque white layers 22, 32 have an overall white, opaque appearance and provide a rough surface for good ink acceptance, so that the polymer substrate 20 with the two opaque white layers 22, 32 behaves similarly to a paper substrate during printing. In a finished banknote 10, the desired imprints 26, 36 and, if appropriate, white functional and protective layers are applied to the opaque white layers 22, 32, as schematically shown in Fig. 2.

[0052] The opaque white layers 22, 32 cover the entire surface on the front and back of the banknote 10 with the exception of the half window 18, which is only on the front, and the two-sided window 16, which is on the front and back.

[0053] To equip the banknote 10 with the desired machine-readable security feature, in the embodiment shown in Fig. 2, the uppermost sublayer 24c of the opaque white layer 22 is uniformly coated with a machine-readable feature substance 38, for example, an IR-IR luminescent substance, i.e., a luminescent substance that can be excited in the infrared spectral range and also luminesces in the infrared spectral range. Alternatively, the feature substance 38 can also comprise an IR absorber.

[0054] The areas provided with a feature substance 38 therefore extend over the entire surface of the banknote 10, except for the window areas 16, 18, so that a completeness check of the banknote can be performed during the authentication process. The window areas 16, 18, however, do not contain any machine-readable feature substance; therefore, the desired high transparency of the window areas 16, 18 is not impaired by the machine-readable configuration of the opaque white layer 22.

[0055] By being embedded not in an external imprint, but in the underlying opaque white layer 22, the feature substances 38 are well protected from abrasion throughout the lifetime of the banknote 10. In fact, in the case of severe abrasion, which already attacks the opaque white layer and thus the feature substance 38, the visual appearance of the banknote 10 is usually so severely impaired that the banknote is withdrawn from circulation as unfit.

[0056] In contrast, feature substances that are conventionally mixed into one of the overprints 26, 36 are subject to significantly greater abrasion. In a heavily used banknote, so much feature-laden printing ink may be rubbed off that the feature signal is no longer sufficient for a successful authentication, even though the banknote would still be assessed as fit for circulation in a quality control process based on its visual appearance. Furthermore, only relatively small quantities of features can be incorporated into an overprint 26, 36, and a completeness check is usually not possible because the overprints 26, 36 are not present across the entire surface of the banknote.

[0057] To ensure good incorporation of the feature substance 38 into the partial layer 24c, the size of the feature substance particles is selected to be comparable to the layer thickness of the partial layer 24c. Specifically, the white partial layer 24c, for example, has a layer thickness of 3 μm, while the D50 particle size of the feature substance 38 is approximately 2 μm.

[0058] In the embodiment of Fig. 2, the feature substance 38 is only present in the opaque white layer of one side, for example the front of the banknote 10, and thus also enables the orientation of the banknote to be checked. During the authenticity check, two sensors can be used on the top and bottom of the banknotes to be checked in order to be able to detect the signal of the feature substance 38 with the same high intensity regardless of the relative orientation of the banknote 10. However, a single sensor, which is arranged, for example, on the top side of the notes to be checked, can also be sufficient for detection, since the polymer substrate 20, despite the opaque white layer 22, 32 on both sides, transmits a sufficient amount of excitation and luminescence radiation to enable detection of the feature substance 38 even when the banknote 10 is inverted.

[0059] In the first embodiment illustrated in Fig. 2, a feature substance 38 is introduced only into the uppermost layer 24c of the opaque white layer 22. Since the feature substance particles 38 are relatively large relative to the thickness of the partial layer 24c, they increase the overall roughness of the opaque white layer 22 and thus improve its ink acceptance. The two deeper partial layers 24b and 24a of the opaque white layer 22 remain unchanged in this embodiment, so that the adhesion of the opaque white layer to the substrate 20 and to any overlying layers is not disrupted.

[0060] In addition, the uppermost layer 24c of the opaque white layer 22 typically already contains relatively large filler particles to ensure the required surface roughness for ink absorption, so that the feature substance particles 38 can also be particularly well dispersed in this partial layer. This can be ensured either directly through the action of the other fillers and / or by the lacquer used for the uppermost layer 24c being designed for the dispersion of large particles.

[0061] A further advantage of the first embodiment mentioned is that the position of the feature substance 38 close to the surface ensures high excitation and detection efficiency during the authenticity test.

[0062] When equipping the uppermost partial layer 24c of the opaque white layer 22 with a feature substance, it has proven advantageous if the feature substance particles have a D50 diameter of less than 3 gm, advantageously less than or equal to 2 gm, but at the same time more than 0.5 gm. The D99 diameter should be less than 10 μm, preferably less than 6 gm. Thus, the feature substance particles are in a similar size range to the typically used white pigments and can be easily incorporated into a typically 3 to 10 μm thick uppermost partial layer. Such a selection of feature substance particles advantageously results in the aforementioned additional increase in surface roughness, while at the same time ensuring good processability and good printing properties of the varnish.

[0063] With reference to the embodiment of Fig. 3, it is also advantageous to provide the opaque white layers 22, 32 on both opposite sides of the banknote 10 with a machine-readable feature substance. The desired total amount of feature substance can then be distributed across twice the number of embedding layers compared to a single-sided introduction of feature substance, so that the feature load per layer is only half as large. This changes the properties of the embedding layers less than with a single-sided introduction. Alternatively, with the same feature load per layer, the total amount of feature substance can be increased. In the embodiment shown, only the uppermost partial layer 24c, 34c of the opaque white layer 22 or 32 is provided with feature substance, in this case with the same machine-readable feature substance 38'. Compared to layer 24c of the embodiment of Fig.2, the feature load of the layers 24c, 34c can be reduced, for example halved.

[0064] The opposing opaque white layers 22, 32 can also be provided with different feature substances to enable detection of the banknote orientation during authentication. In general, one or more sublayers 24a-c, 34a-c of the opaque white layers 22, 32 on each side can be provided with the same or different machine-readable feature substances.

[0065] The machine-readable feature substance used can consist of inorganic particles, which are generally very hard. This increases the abrasion resistance of the opaque white layer 22, but on the other hand also carries the risk of scratching the printing plates for the visible imprint 26. Therefore, a feature substance 38 with soft particles can also be used, for example with feature substance particles in which at least the outer surface consists of a polymer. The feature substances with soft particles are, for example, organic or organometallic feature substances dissolved or dispersed in a polymer and / or polymer-encapsulated inorganic, organic, or organometallic feature substances. In a further embodiment, inorganic feature substances can be provided with a shell of nanoparticles or with a coating, for example of SiO2, in order to achieve softer behavior while maintaining good compatibility with common printing inks.

[0066] In a second embodiment of the invention, with reference to Fig. 4, a machine-readable feature substance 40 is introduced only into a deeper sub-layer of the opaque white layer 22, preferably into the second-highest sub-layer 24b. This is particularly advantageous when hard feature substance particles 40, for example formed from inorganic particles, are to be used. Since the hard feature substance particles 40 are then present in a deeper sub-layer, they do not scratch the printing plates for the visible imprint 26. The abrasion protection of the feature substance 40 is even further increased in the second embodiment compared to embedding the feature substance in the uppermost sub-layer 24c.Furthermore, the scattering of the excitation light by the white layer 24c above the embedding layer 24b leads to a lateral dispersion of the excitation light, allowing high excitation efficiency to be achieved even with a small excitation spot and a low feature substance load. Furthermore, feature substances with their own body color can also be discreetly applied in the deeper sublayers.

[0067] When equipping a deeper sub-layer of the opaque white layer 22 with feature substance, it has proven effective if the feature substance particles have a D50 diameter of less than 2 gm, advantageously less than or equal to 1.5 μm, but at the same time more than 0.5 gm. The D99 diameter should be less than 8 gm, preferably less than 6 gm. The feature substance particles are thus in a similar size range to the typically used white pigments and can be easily incorporated into a deeper layer that is typically 3 to 10 μm thick. When introducing feature substance into a deeper sub-layer, somewhat finer particles are advantageously used in order to enable better print quality during the subsequent printing of the higher sub-layers of the opaque white layer. These requirements apply in particular if the deeper sub-layer represents the lower layer of a two-layer opaque white layer.

[0068] In the embodiment shown in Fig. 4, both opaque white layers 22, 32 are each provided with the same feature substance 40. However, as in Fig. 3, different feature substances can also be used for the opaque white layers on both sides in order to easily detect the orientation of the banknote during the authentication process.

[0069] The first and second embodiments can also be combined so that, for example, a feature substance 40 as in Fig. 4 is introduced into the second uppermost partial layer 24b of the opaque white layer 22, while on the opposite side of the substrate the same or a different feature substance is introduced into the uppermost partial layer 34c of the opaque white layer 32.

[0070] In all embodiments, the feature substance can be mixed with a camouflage substance, which makes chemical analysis of the feature substance used more difficult for a potential counterfeiter. Figure 5 shows a modification of the embodiment of Figure 4, in which, in addition to the feature substance 40, a camouflage substance 42 is incorporated into the second-highest partial layer 24b of the opaque white layer 22. This camouflage substance 42, for example, has the same grain size distribution as the feature substance 40.

[0071] As illustrated by the white opaque layer 32 arranged on the opposite side, a camouflage substance 44 can also be incorporated into the uppermost sublayer 34c of the white opaque layer, even though the feature substance 40 is present in the second-highest layer 34b. In this case, a larger grain size is advantageously used for the camouflage substance 44, both to increase the roughness of the white opaque layer and to protect the deeper feature substance particles from abrasion.

[0072] Figure 6 illustrates a third embodiment of the invention, in which a feature substance is introduced not just into one but into several sublayers of a white cover layer. In particular, all white sublayers 24a, 24c or even all sublayers 34a, 34b, 34c of a white cover layer can be provided with a feature substance.

[0073] In the exemplary embodiment, the same machine-readable feature substance 38 is incorporated into all white sub-layers 24a, 24c of the upper opaque white layer 22 in order to increase the maximum amount of feature substance that can be incorporated. This increases protection against abrasion; in addition, partial abrasion of the upper sub-layer 24c can be detected via a gradually lower feature intensity, without the risk of a complete loss of feature intensity due to the feature substance being well protected in the deeper sub-layer 24a. Large feature substance particles can also be used in the uppermost white sub-layer 24c, which increase the roughness of the opaque white layer 22 and thus improve ink acceptance.

[0074] As illustrated by the lower opaque white layer 32, feature substance can be introduced not only into the white partial layers 34a, 34c, but into all, i.e. also into the transparent partial layers 34b of an opaque white layer, in order to be able to introduce a maximum amount of feature substance into the opaque white layer 32.

[0075] Different machine-readable feature substances 50, 52, 54 can also be incorporated into the various sub-layers. This variant has the advantage that the banknote can be withdrawn from circulation in a controlled manner once the outer sub-layer (and with it the feature substances carrying them and the signal they generate) has been rubbed off, while the proof of authenticity is still unequivocally provided via the inner layer. In particular, with this variant, feature substances with smaller particles 50, 52 can be incorporated into deeper layers 34b and 34a, respectively, and a feature substance with larger particles 54 can be incorporated into the uppermost layer 34c. The use of finer particles in the deeper sub-layers 34a, 34b enables good print control during the subsequent printing of the higher sub-layers, while the large particles of the uppermost sub-layer 34c increase the roughness of the opaque white layer 32.

[0076] In another variant, feature substances with hard particles can be introduced into deeper layers 34b or 34a, respectively, and a feature substance with soft particles into the uppermost sublayer 34c. It is also possible for visually conspicuous feature substances to be introduced into deeper layers 34b or 34a for camouflage purposes, and for a visually inconspicuous feature substance to be introduced into the uppermost sublayer 34c.

[0077] Different sublayers can also be provided with interacting feature substances, for example, with an IR-excitable luminescent substance on the one hand and an IR absorber on the other, or with two luminescent substances with energy transfer. If different feature substances are used in the sublayers 34a-c, the relative feature intensity can also be used as a measure of abrasion and thus the remaining fitness of the banknote 10, while the proof of authenticity is still unequivocally provided by the inner layer.

[0078] Example 1: Feature substance in the topmost sublayer

[0079] In a specific embodiment based on the principle of Fig. 2, a thulium-doped lithium niobate is used as the machine-readable feature substance 38, the production of which is described in Example 2 of the document DE 10 2010 026 627 Al. By grinding in an air jet mill, the grain size of the feature substance particles is adjusted to D99 = 5-6 pm and D50 = 1.5-2 μm. Upon excitation with IR radiation at approximately 800 nm, the feature substance exhibits a characteristic luminescence in the infrared at approximately 1800 nm.

[0080] A 60 μm thick film of biaxially oriented polypropylene (BOPP) is used as polymer substrate 20. A 2 μm thick transparent lacquer layer can be applied to the BOPP substrate as a primer to improve adhesion properties (not shown in Fig. 2).

[0081] Subsequently, three superimposed partial layers 24a-c and 34a-c are applied to each of the two sides of the polymer substrate 20 by printing with a gravure printing machine. The average layer thickness for the lower two partial layers 24a, 24b and 34a, 34b is 2 μm, and the average layer thickness of the uppermost partial layers 24c, 34c is 3 μm each.

[0082] To produce the partial layers, a commercially available, thermally curing, aqueous aliphatic urethane acrylate copolymer dispersion suitable for gravure printing is used as the varnish, to which 10 wt.% titanium dioxide with a D50 of less than 1 μm has been added as white pigment. Feature substance 38 is selectively added only to the varnish used for printing the uppermost partial layer 24c, in a proportion of 1 wt.%.

[0083] The machine-readable security feature thus produced exhibits the advantages described above; in particular, the application of the uppermost sublayer 24c is not hindered because no feature substance is incorporated into the lower sublayers 24a, 24b. The roughness of the uppermost sublayer 24c is increased by the feature substance, and the efficiency of the feature substance 38 is particularly high compared to its incorporation into deeper sublayers. With the relatively long emission wavelength of the thulium feature, the banknote 10 exhibits high transmission, so that even the detection of the feature substance 38 from the side of the substrate facing away from the embedding layer 24c is possible with good efficiency.

[0084] Example 2: Feature substance in a deeper sublayer

[0085] In a specific embodiment according to the principle of Fig. 4, an ytterbium-doped yttrium-aluminum-chromium mixed garnet is used as the machine-readable feature substance 40, the production of which is described in Example 2 of the document DE 198 03997 Al. By grinding in a stirred ball mill, the grain size of the feature substance particles is adjusted to D99 = 2.5-3.5 pm and D50 = 0.5-1 pm. The resulting particles have an aspect ratio of almost 1. The feature substance 40 has an inherent green color; upon excitation with IR radiation at 945 nm, it exhibits a characteristic luminescence in the infrared range of 950-1100 nm.

[0086] The layer structure of the partial layers 24a-c, 34a-c is basically identical to the structure according to Example 1, but in this example the feature substance 40 is selectively introduced only into the resist used to produce the second uppermost partial layers 24b, 34b.

[0087] The machine-readable security feature produced in this way exhibits the advantages described above; in particular, the application of the uppermost sublayer 24c, 34c is not hindered because the feature substance 40 has a suitable, small grain size. Furthermore, the disruptive influence of the inherent green color of the feature substance is minimal compared to incorporation into an uppermost sublayer. The abrasion of feature substance from the deeper embedding layers 24b, 34b is impeded, and the security feature exhibits high efficiency even when measured with small excitation spots. Example 3: Feature substance in a deeper sublayer, with camouflage material. Based on Example 2, a camouflage material can be used to camouflage the feature substance 40, as illustrated in Fig. 5. For example, a manganese-doped gadolinium gallium garnet is used as camouflage material 42.The elements Gd, Ga and Mn, which were now additionally found in an elemental analysis, behave analogously to the elements Y / Yb, Al and Gr of the characteristic substance and thus increase the number of plausible stoichiometries or mixed forms such as Gd-Y mixed garnets, Al-Ga mixed garnets or Mn-Cr mixed garnets.

[0088] In a first variant, the camouflage material 42 is used with the same grain size as the feature material 40 and is also incorporated into both sides of the second uppermost sublayer 24b or 34b. This advantageously ensures that the camouflage effect is not lost even if one of the uppermost sublayers 24c, 34c is damaged.

[0089] In a second variant, the camouflage material 44 is used with a larger grain size, here, for example, with D99 ​​= 5-6 pm and D50 = 1.5-2 pm, and is also introduced into both sides of the uppermost partial layer 24c and 34c, respectively. This advantageously increases the roughness of the opaque white layers 22, 32, and the hardness of the inorganic camouflage particles 44 protects the underlying partial layer 24b, 34b with the feature substance 40 from abrasion. Furthermore, analysis of the feature substance is made more difficult, since the large camouflage particles attract attention during analysis, and the smaller feature substance particles are more difficult to identify and analyze.

[0090] Example 4: Feature substance in several sublayers: In a concrete embodiment according to the principle of Fig. 7, the structure of the substrate and the sublayers 24a-c, 34a-c basically follows the structure of Example 1.

[0091] As a first feature substance 56, an ytterbium-doped yttrium phosphate with a grain size D99 = 8-9 μm and D50 = 2.5-3.5 μm is used and is selectively incorporated into the uppermost partial layer 24c, 34c of the opaque white layers 22, 32 on both sides of the substrate 20. Upon excitation with radiation having a wavelength of 945 nm, the first feature substance 56 exhibits a characteristic luminescence in the range 950-1100 nm with an increased proportion at wavelengths below 1000 nm.

[0092] As a second feature substance 58, the ytterbium-doped yttrium-aluminum-chromium mixed garnet described in Example 2 is used and selectively incorporated on both sides of the substrate 20 into the second uppermost partial layer 24b, 34b of the opaque white layers 22, 32. When excited with radiation having a wavelength of 945 nm, the second feature substance 58 exhibits a characteristic luminescence in the range 950-1100 nm with an increased proportion at wavelengths above 1000 nm.

[0093] The machine-readable security feature thus generated demonstrates the respective advantages of examples 1 and 2. However, the simultaneous use of the interacting feature substances in different sublayers results in additional synergistic effects.

[0094] If the partial layers 24b, 24c or 34b, 34c are completely present, the respective spectra of the feature substances 56, 58 complement each other and act as a single feature. Therefore, it is not immediately apparent to a counterfeiter that the feature substances 56, 58 are not present in the same layer.

[0095] If the uppermost sublayer 24c or 34c is partially removed or damaged, for example, due to the natural stresses of a circulating banknote or due to deliberate manipulation during a counterfeit attempt, the relative spectral components above 1000 nm increase, or the relative spectral components below 1000 nm decrease in the detected emission spectrum. Thus, the interaction of the two sublayers makes it possible to assess the circulation fitness of the banknote and detect manipulation attempts in which the uppermost sublayer 24c, 34c has been completely or partially damaged.

[0096] Example 5: Feature substance with soft particles:

[0097] In a specific embodiment based on the principle of Fig. 3, PMMA spheres with the dissolved IR absorber CKK-55 (manufacturer: Fujifilm Imaging Colorants) are used as the machine-readable feature substance 38'. Their production is described in Example 7 of the publication DE 102015 0145 26 A1. By grinding in an air jet mill, the grain size of the feature substance is adjusted to D99 = 5.5 μm and D50 = 1.5-2 μm. The particles have an aspect ratio of less than 2:1. The feature substance 38' exhibits a characteristic absorption band in the range of 850 nm.

[0098] The feature substance is incorporated into the uppermost partial layer 24c or 34c of the opaque white layers 22, 32 on both sides of the substrate. In addition to the advantages already mentioned, the low hardness and density of the polymer-based feature substance 38' compared to inorganic particles of the same grain size results in higher compatibility with common printing inks, such as less pronounced settling behavior and a lower tendency to scratch printing plates.

[0099] Comparative measurements

[0100] Figure 8 shows layer structures used for comparative measurements of feature intensity in a conventional design and two designs according to the invention.

[0101] Referring first to Fig. 8(b), an opaque white layer 62 was applied to a transparent polymer substrate 20. The layer consists of two sub-layers 64a, 64b, each 12 μm thick when wet. Both layers are formed from a clear varnish, for example, an aqueous aliphatic urethane acrylate copolymer dispersion, with 20% titanium dioxide (rutile) as the white pigment. The varnish used for printing the lower sub-layer 64a was additionally mixed with 0.2% of an inorganic IR-IR luminescent substance 60, which forms the machine-readable feature substance. The luminescent substance 60 has a grain size D50 = 2.5 μm and D99 = 6 μm, so that the luminescent substance particles can be easily incorporated into one of the 12 μm thick wet varnish layers. Alternatively, a Raman-active substance, in particular a surface-enhanced Raman-active substance, can be used instead of the IR-IR luminescent substance.

[0102] In the embodiment of Fig. 8(b), the lower sublayer 64a contains the machine-readable feature substance 60, while the upper sublayer 64b is feature-free. Figure 8(c) shows a further embodiment in which the feature substance 60 was introduced in the stated amount only into the upper sublayer 64b, while the lower sublayer 64a is feature-free.

[0103] Figure 8(a) shows a comparative example not according to the invention, in which the opaque white layer 72 consists of a single layer into which the above-mentioned amount of feature substance 60 has been incorporated. The embodiments of Figs. 8(a) to (c) therefore all contain the same amount of feature substance 60.

[0104] The excitation and detection of the luminescence of the feature substance 60 occurs from above, i.e., from the side of the opaque white layers. A black background is arranged below the substrate 20. The measurement range was chosen to be large enough to cover a large number (approximately 100) of feature substance particles.

[0105] The measured feature intensities were normalized to the intensity of the comparison example in Fig. 8(a), whose feature intensity is thus 100%.

[0106] Under the same excitation and detection conditions as in the comparative example, a feature intensity of 59% is measured in the first exemplary embodiment of Fig. 8(b). The particular advantage of this configuration, with a sufficiently high feature intensity, is that the feature substance particles 60 are well protected from abrasion and, due to the feature-free partial layer 64b, there is no risk of hard feature substance particles scratching the printing plates for further printing. Under the same excitation and detection conditions as in the comparative example, a feature intensity of 159% is measured in the second exemplary embodiment of Fig. 8(c). The particular advantage of this configuration is a significantly increased feature intensity with the same amount of feature substance used. The mechanisms currently understood to be responsible for the increased feature intensity have already been described above.

[0107] List of reference symbols Polymer banknote Printed images Machine-readable security feature Two-sided window One-sided window Substrate Opaque white layer a, 24b, 24c Sublayers

[0108] imprint

[0109] Opaque white layer a, 34b, 34c Partial layers Print , 38' Machine-readable feature substance Machine-readable feature substance , 44 Camouflage material , 52, 54 Various machine-readable feature substances, 58 Interacting feature substances Luminescent material Opaque white layer a, 64b Partial layers Opaque white layer

Claims

Patent claims 1. A data carrier, in particular a value or security document, comprising a substrate comprising at least one transparent plastic layer and having two opposite main surfaces, two opaque white layers having a white, opaque appearance applied to the opposite main surfaces of the substrate, each of the opaque white layers consisting of a layer sequence of two or more sub-layers extending from a bottom white layer to a top white layer, and a machine-readable security feature comprising a machine-readable feature substance present in at least one of the sub-layers of at least one of the opaque white layers.

2. Data carrier according to claim 1, characterized in that the machine-readable feature substance is an optically readable feature substance, preferably a luminescent substance, particularly preferably an IR-IR luminescent substance.

3. Data carrier according to claim 1 or 2, characterized in that the machine-readable feature substance consists of particles which have a grain size D50 of less than 3 gm, preferably that the grain size D50 of the particles is between 0.5 gm and 2 gm.

4. Data carrier according to at least one of claims 1 to 3, characterized in that the machine-readable feature substance consists of substantially round particles with an aspect ratio of less than 1:

2.

5. Data carrier according to at least one of claims 1 to 4, characterized in that an embedding layer of the machine-readable feature substance contains filler particles, for example white pigments, and in that the machine-readable feature substance consists of particles which are not larger than the largest filler particles of the embedding layer.

6. Data carrier according to at least one of claims 1 to 5, characterized in that a machine-readable feature substance is present in both opaque white layers.

7. Data carrier according to at least one of claims 1 to 6, characterized in that the machine-readable feature substance is present in exactly one of the partial layers of one or both opaque white layers.

8. Data carrier according to at least one of claims 1 to 7, characterized in that the machine-readable feature substance is present only in the uppermost partial layer of one or both opaque white layers, wherein the machine-readable feature substance advantageously consists of particles with a dimension, in particular a D99 diameter, which essentially corresponds to the layer thickness of the embedding layer or is smaller than the layer thickness of the embedding layer.

9. Data carrier according to at least one of claims 1 to 7, characterized in that the machine-readable feature substance is present only in a deeper partial layer, preferably only in the second uppermost partial layer of one or both opaque white layers, wherein the machine-readable feature substance advantageously consists of particles with a dimension that is smaller than the layer thickness of the embedding layer.

10. Data carrier according to at least one of claims 1 to 7, characterized in that a machine-readable feature substance is present in several partial layers of one or both opaque white layers.

11. Data carrier according to claim 10, characterized in that different feature substances are present in different sublayers.

12. Data carrier according to claim 11, characterized in that different, interacting feature substances are present in different sublayers.

13. Data carrier according to claims 10 to 12, characterized in that machine-readable feature substances with different particle sizes are present in different partial layers of a white cover layer, with smaller particles being arranged in deeper partial layers and larger particles in the uppermost partial layer of the white cover layer.

14. Data carrier according to at least one of claims 11 to 13, characterized in that machine-readable feature substances with different particle hardness are present in different partial layers of a cover white layer, with harder particles being arranged in deeper partial layers and softer particles in the uppermost partial layer of the cover white layer.

15. Data carrier according to at least one of claims 1 to 14, characterized in that at least one of the partial layers comprises a camouflage substance which in particular has a chemical composition matched to the machine-readable feature substance, but no feature as an effect, wherein the camouflage substance is preferably in a higher partial layer or is present in the same sublayer as the machine-readable feature substance.

16. A method for producing a data carrier according to one of claims 1 to 15, in which a substrate is provided which comprises at least one transparent plastic layer and has two opposite main surfaces, two opaque white layers with a white, opaque appearance are applied to the opposite main surfaces of the substrate, each of which is formed from a layer sequence of two or more sub-layers which extends from a bottom white layer to a top white layer, and at least one of the sub-layers of at least one of the opaque white layers is produced with a machine-readable feature substance in order to form a machine-readable security feature.

17. A method for verifying the authenticity of the data carrier according to one of claims 1 to 15, comprising the step of providing the data carrier and the step of reading the machine-readable security feature which comprises a machine-readable feature substance, wherein during the reading, in particular the scattering of illumination light and signal light in the opaque white layer is used to verify the authenticity of the data carrier.

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