Data carrier having machine-readable security feature, production method and authenticity testing method

Abstract

The invention relates to a data carrier (10), in particular a value document or security document, comprising a substrate (20), which comprises at least one transparent plastic layer and has two opposite main surfaces. The data carrier further comprises two white cover layers (22, 32), which have a white opaque appearance and are applied to opposite main faces of the substrate (20). Each white cover layer (22, 32) is composed of a layer sequence of two or more sub-layers (24a-c, 34a-c), which layer sequence extends from the lowermost white layer (24a, 34a) to the uppermost white layer (24c, 34c). The data carrier also contains a machine-readable security feature which comprises a machine-readable feature material (38) which is present in at least one sub-layer (24c) in the at least one white cover layer (22, 32).

Description

[0001] The present invention relates to a data carrier, in particular a valuable document or a security document, which comprises a substrate and is protected against forgery by machine-readable security features, and the substrate comprises at least one transparent plastic layer. The present invention also relates to a method for manufacturing such a data carrier. The present invention also relates to a method for verifying the authenticity of a data carrier.

[0002] Data carriers such as valuable documents or identification documents or other valuable items, such as designer goods, are usually provided with anti-counterfeiting elements for anti-counterfeiting protection, and the anti-counterfeiting elements can verify the authenticity of the data carrier and at the same time be used to prevent unauthorized copying.

[0003] For some time, in addition to paper substrates, polymer materials have also been used as substrate materials for banknotes. Compared with paper banknotes, polymer banknotes have advantages such as stronger tear resistance. However, the anti-counterfeiting security of polymer banknotes cannot yet reach the same level as that of banknotes with paper substrates. It is known that polymer banknotes are protected against forgery by adding machine-readable characteristic materials in the visible printing part. However, only a small amount of characteristics can be added to such a printing part, and since the printing part containing the characteristics usually only exists regionally, integrity verification is usually not possible. On the other hand, if the machine-readable characteristic materials are introduced into the volume of the polymer substrate for integrity verification at the same time, there is a risk that these characteristic materials may be visually visible in the transparent window area, thus spoiling the appearance.

[0004] Starting from this, the technical problem to be solved by the present invention is to improve the anti-counterfeiting protection of the authenticity of polymer banknotes or composite banknotes.

[0005] The above technical problem is solved by the features of the independent claims. The further designs of the present invention are the technical solutions of the dependent claims.

[0006] The present invention provides a data carrier which comprises a substrate, the substrate comprises at least one transparent plastic layer and has two opposite main surfaces. The data carrier can in particular be a valuable document or a security document.

[0007] The data carrier further comprises two white covering layers which have a white opaque appearance and are applied to the opposite main surfaces of the substrate. Each white covering layer is composed of a layer sequence of two or more sub-layers, and the layer sequence extends from the lowermost white layer to the uppermost white layer.

[0008] The data carrier also contains a machine-readable anti-counterfeiting feature, which includes a machine-readable feature material that is present in at least one sublayer of at least one white covering layer. The presence of the machine-readable feature material in at least one sublayer of at least one white covering layer means that the feature material is present in the corresponding layer in a uniformly distributed form.

[0009] In the context of this description, the white covering layer refers to a layer sequence that extends from the lowermost white layer to the uppermost white layer. The lowermost and uppermost white layers are included herein, i.e., they are part of the layer sequence of the white covering layer. Other white layers or transparent layers may be present between the lowermost and uppermost white layers. The intermediate layer is also part of the white covering layer. The lowermost layer is here the layer of the white covering layer stack that is closest to the substrate, and the uppermost layer is the layer of the white covering layer stack that is farthest from the substrate.

[0010] The sublayers of the white covering layer typically have a thickness of 1 µm to 10 µm, preferably 3 µm to 10 µm. The sublayers can consist of the same or different paints and can be transparent, white, or turbid, respectively. The sublayers can contain different loadings, especially organic or inorganic white pigments or scatterers, to produce a white color impression. Advantageous white pigments are, for example, TiO2 or SiO2, although organic scatterers can also be considered. The scattering particles can have a round, angular, or fibrous morphology.

[0011] Furthermore, the white covering layer has a rough surface to produce good color acceptability. This can be achieved in particular by adding relatively large (usually >10 µm) dispersing particles to the paint. These particles can be the same as or different from the white pigments.

[0012] The order of the paints of the sublayers is advantageously chosen such that there is a permanently good adhesion between successive layers and thin, uniform layers can be printed. The white covering layer is preferably printed on the substrate by gravure printing.

[0013] To produce a window, an opening can be provided in one of the two white covering layers (one-sided window), and / or openings can be provided in opposite white covering layers on both sides in an overlapping manner (two-sided window).

[0014] The white covering layer provides a white, opaque impression and a rough surface for good color acceptability through its above-mentioned properties, so that a substrate with two applied white covering layers behaves similarly to paper during printing despite the presence of plastic layers.

[0015] In the context of the present description, a sublayer of the white coating that contains machine-readable characteristic material is also referred to as an embedded layer. Thus, according to the invention, at least one of the two white coatings contains such an embedded layer. Each white coating may here contain one embedded layer or multiple embedded layers. All sublayers of the white coating or at least all white sublayers may also be embedded layers.

[0016] According to an advantageous design, the machine-readable characteristic material is an optically readable characteristic material, i.e., a characteristic material that can be excited to emit light (signal light) by irradiating it with light (illuminating light), and the light emission is, for example, light emission generated by fluorescence, by scattering with spectral changes, by narrow-band absorption, or by Raman scattering. The machine-readable characteristic material is preferably a fluorescent material, particularly preferably an infrared-infrared fluorescent material, i.e., a fluorescent material that can be excited by infrared rays and fluoresces in the infrared range. Infrared absorbers or Raman scatterers can also be used as machine-readable characteristic materials.

[0017] When using an optically readable characteristic material, the scattering of the illuminating light and the signal light in the white coating, i.e., in the layer containing the characteristic and the layer not containing the characteristic, results in a higher characteristic intensity than in the introduced variant with less scattering, such as the introduction in a window or the introduction where the scatterer is far from the characteristic material particles, for example, the introduction in the volume of a polymer substrate.

[0018] Without being limited to a certain interpretation, according to the current understanding, in particular the following mechanisms contribute to the increase in characteristic intensity: on the one hand, the scattering of the illuminating light results in a longer path length of the illuminating light in the layer containing the characteristic, so that the illuminating light is more efficiently absorbed by the characteristic material particles. This is particularly effective when the concentration of the characteristic material is low, i.e., the spacing between the characteristic material particles is large, and the illuminating light spot is small. On the other hand, the scattering of the signal light causes the part of the signal light that is not emitted in the direction of the detector to be deflected by the scatterer towards the detector and contribute to the measurement. In the case where the characteristic material is a fluorescent material, the illuminating light is usually referred to as the excitation light, and the signal light is referred to as the fluorescence.

[0019] If the data carrier contains multiple different machine-readable characteristic materials, then even if only one characteristic material is mentioned in the singular when describing the requirements, the above requirements and the following requirements apply to multiple characteristic materials, especially all machine-readable characteristic materials.

[0020] The machine-readable characteristic material advantageously exists on the entire surface of the embedded layer. The machine-readable characteristic material is particularly evenly distributed, i.e., with a substantially constant areal density, in the corresponding embedded layer. This simplifies the integrity check of the data carrier.

[0021] The machine-readable feature material advantageously consists of particles with a D50 particle size of less than 3 μm, and the D50 particle size of the particles is particularly preferably from 0.5 μm to 2 μm in this case. In this way, the particles are small enough so as not to interfere with the printing of the embedding layer.

[0022] The machine-readable feature material suitably consists of substantially circular particles with an aspect ratio of less than 1:2. This helps the feature material to be evenly distributed in the embedding layer without forming a preferred direction.

[0023] In an advantageous design, the embedding layer of the machine-readable feature material contains filler particles, such as white pigments, and the particles contained in the machine-readable feature material are not larger than the largest filler particles in the embedding layer, for example, measured according to the D50 diameter. The filler particles can thus act as scatterers for illumination light and / or signal light, and separation of the filler particles and the feature material particles is avoided.

[0024] At least one sub-layer of the white covering layer provided with the machine-readable feature material advantageously substantially occupies the entire surface of the data carrier, so that an integrity check of the data carrier can be carried out. This does not apply to possible window areas in one or both white covering layers.

[0025] In an advantageous variant of the present invention, the machine-readable feature material is only present in one of the two white covering layers. As will be explained in detail below, the orientation of the data carrier can thus be detected particularly simply during inspection.

[0026] In another equally advantageous variant of the present invention, the machine-readable feature material is present in each of the two white covering layers. As will be explained in more detail below, the desired total amount of the feature material can thus be distributed over twice the number of embedding layers, or the total amount of the feature material can be increased if the amount of features per layer is the same. The opposite white covering layers can be provided with the same or different feature materials here. Providing different feature materials also enables the orientation of the data carrier to be detected simply during inspection.

[0027] In a preferred design, the machine-readable feature material is present in exactly one sub-layer in each of the two white covering layers.

[0028] According to an advantageous variant of the present invention, the machine-readable feature material is only present in the uppermost sub-layer of one or both white covering layers. The machine-readable feature material preferably consists of particles with the following dimensions, which are substantially equal to or less than the layer thickness of the embedding layer.

[0029] According to another equally advantageous variant of the invention, the machine-readable characteristic material is only present in the deeper sublayers, preferably only in the second sublayer from the uppermost side of one or two white cover layers. The machine-readable characteristic material preferably consists here of particles having the following dimensions, which are smaller than the layer thickness of the embedding layer. The advantages of each of these two variants of the invention will be explained in more detail below.

[0030] According to another equally advantageous variant of the invention, the machine-readable characteristic material is present in a plurality of sublayers of one or two white cover layers.

[0031] In a suitable design, the same characteristic material is present in different sublayers. Introducing it into a plurality of sublayers enables a particularly high total amount of characteristic material to be installed in the white cover layer here.

[0032] Alternatively, different characteristic materials can be provided in different sublayers. For example, different, but interacting with each other, characteristic materials can be present in different sublayers. This increases the anti-counterfeiting security because a single characteristic material cannot reproduce the characteristic signal. In addition, machine-readable characteristic materials having different diameters can also be present in different sublayers, where, for example, smaller particles measured according to the D50 diameter are arranged in the deeper sublayers of the white cover layer and larger particles are arranged in the uppermost sublayer of the white cover layer. Machine-readable characteristic materials having different particle hardnesses can also be present in different sublayers, where, for example, harder particles measured according to the Mohs hardness are arranged in the deeper sublayers and softer particles are arranged in the uppermost sublayer of the white cover layer.

[0033] In another advantageous variant of the invention, it is provided that a characteristic material having larger particles is introduced into the deeper sublayers of the white cover layer and is stabilized by the adjacent higher-layer sublayers. This variant is based on the inventor's observation that the sublayers, especially the deeper ones, are thinner in the dry state than in the wet state. Therefore, the embedded larger particles that are still completely embedded in the deeper layer in the wet state protrude from their actual embedding layer in the dry state and penetrate into the adjacent higher sublayers, and are stabilized by the higher sublayers. In addition, the particles can also protect the higher sublayers from wear.

[0034] In another advantageous design, the white covering layer is designed such that it has an opacity > 1.42 or a reflectance of greater than 30% or even greater than 50% in the infrared range, especially in the infrared range from 800 nm to 2000 nm. This can be achieved by adjusting the quantity and particle size of the white pigment in the white sublayer of the white covering layer. To prevent the white pigment aggregates from overlapping at a higher filling degree, a so-called diluent is advantageously used to dilute the white pigment. For this purpose, it is particularly advantageous to use a machine-readable characteristic material, so that no separate diluent is required.

[0035] According to an extended design of the invention, at least one of the sublayers in the sublayer has a camouflage material, which in particular has a chemical composition adapted to the machine-readable characteristic material, but has no characteristic effect, so that potential counterfeiters are thus more difficult to chemically analyze the characteristic material. The adapted chemical composition can, for example, have the same crystal structure as the characteristic material, or contain elements that are partly the same as the characteristic material, or contain the same elements as the characteristic material but in different proportions. The camouflage material is preferably located in the higher sublayer or in the same sublayer as the machine-readable characteristic material.

[0036] The camouflage material can have the same particle size distribution as the characteristic material, but can also advantageously have a larger average particle size than the characteristic material, so that the camouflage material particles additionally protect the characteristic material particles from abrasion. In another variant of the invention, the camouflage material particles have a wider particle size distribution than the characteristic material, where the camouflage material has larger particles than the characteristic material. 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 can protect the characteristic material from abrasion, while even if the larger camouflage particles are lost, the smaller camouflage particles remain to ensure the desired camouflage.

[0037] The substrate of the data carrier is preferably composed of a plastic substrate or a composite substrate having at least one plastic layer, such as a composite substrate having a layer sequence of film / paper / film. Biaxially oriented polypropylene (BOPP), polyethylene terephthalate (PET), polypropylene (PP) or polyamide (PA) are particularly suitable as plastics for the plastic layer or the plastic substrate. Biaxially oriented polypropylene (BOPP) is particularly preferably used here.

[0038] The invention also includes a method for manufacturing a data carrier of the type described, where

[0039] - a substrate is provided, the substrate comprising at least one transparent plastic layer and having two opposite main surfaces,

[0040] - Apply two white overlay layers with a white opaque appearance on opposite major surfaces of the substrate, where each white overlay layer consists of a layer sequence of two or more sub-layers that extends from the lowermost white layer to the uppermost white layer, and

[0041] - where at least one sub-layer of at least one of the white overlay layers is produced from a machine-readable feature material to form a machine-readable anti-counterfeiting feature.

[0042] Here, it is suitably preferred to print the sub-layers of the white overlay layer by intaglio printing.

[0043] In the method, advantageously, the machine-readable feature material is ground to a desired particle size or provided in a desired particle size and added to the paint of the sub-layer set for embedding. Then the paint and the added feature material are applied together, and thereby a substantially uniform distribution of the feature material in the embedding layer is achieved.

[0044] The present invention also relates to a method for verifying the authenticity of a data carrier according to the present invention, the method including the steps of providing the data carrier and reading the machine-readable anti-counterfeiting feature, the machine-readable anti-counterfeiting feature including a machine-readable feature material, wherein, in particular, the authenticity of the data carrier is verified by utilizing the scattering of illumination light and signal light in the white overlay layer during reading.

[0045] The following describes additional embodiments and advantages of the present invention with reference to the drawings, which are not shown to scale for greater clarity.

[0046] In the drawings:

[0047] Figure 1 A polymer banknote with a machine-readable anti-counterfeiting feature according to the present invention is schematically shown,

[0048] Figure 2 The structure of a banknote according to an embodiment of the present invention is schematically shown in cross-section, where the feature material is only present in the uppermost sub-layer of the white overlay layer,

[0049] Figure 3 Shows Figure 2 A variant of the embodiment, where white overlay layers carrying features are present on both sides of the substrate,

[0050] Figure 4 Shows another embodiment of the present invention, where the feature material is only present in the second sub-layer from the uppermost side of the white overlay layer,

[0051] Figure 5 Shows Figure 4 A variant of the embodiment with additional camouflage material,

[0052] Figure 6 shows another embodiment of the present invention, in which the characteristic material is present in a plurality of sub-layers of the white covering layer,

[0053] Figure 7 shows an embodiment in which a first characteristic material is present in the uppermost sub-layer of the white covering layer, a supplementary second characteristic material is present in the second sub-layer from the uppermost side, and

[0054] Figure 8 shows a layer structure for comparative measurement of the characteristic intensities of a conventional design ( Figure 8 a) and two designs according to the present invention ( Figure 8 b, Figure 8 c).

[0055] The present invention will now be explained by taking a banknote as an example. Figure 1 shows a schematic view of a polymer banknote 10 which, in addition to a conventional printed image 12 and anti-counterfeiting elements, is equipped with a machine-readable anti-counterfeiting feature 14 according to the present invention, which occupies the entire face of the banknote 10 except for the areas of windows 16 and 18.

[0056] Figures 2 to 7 illustrates a plurality of advantageous embodiments in which the drawings respectively show in cross-section the layers necessary for the polymer banknote according to the present invention. In the said embodiments, the banknote 10 respectively comprises a transparent polymer substrate 20 which is preferably formed of a biaxially oriented polypropylene (BOPP) film.

[0057] On opposite major surfaces of the substrate 20, a white covering layer 22 or 32 is respectively applied, which has a white opaque appearance. Each of the two white covering layers 22, 32 consists of a plurality of, usually two to five, layers. For the sake of illustration, the white covering layer shown in the figure has three sub-layers 24a, 24b, 24c or 34a, 34b, 34c which respectively extend from the lowermost white layer 24a or 34a to the uppermost white layer 24c or 34c. The lowermost layer is here the layer of the white covering layer 22 or 32 which is closest to the substrate in the layer stack, and the uppermost layer is the layer of the white covering layer which is farthest from the substrate in the layer stack. Between the lowermost and uppermost white layers, other transparent layers 24b, 34b may also be present, which are likewise regarded as part of the white covering layer 22 or 32.

[0058] As described above, the white covering layers 22, 32 as a whole give the impression of being white and opaque, and provide a rough surface for good color acceptance (or ink receptivity), so that during the printing process, the polymer substrate 20 with the two white covering layers 22, 32 behaves similarly to a paper substrate. As Figure 2As shown, in the finished banknote 10, the desired printing portions 26, 36 and, if necessary, the functional layer and the protective layer are applied to the white cover layers 22, 32.

[0059] Except for the half-window 18 which is only located on the front side here and the double-sided, i.e., front and back, windows 16, the white cover layers 22, 32 cover the entire surfaces of the front and back of the banknote 10.

[0060] In order to enable the banknote 10 to have the desired machine-readable anti-counterfeiting features, in Figure 2 the embodiment, the machine-readable feature material 38 is uniformly doped in the uppermost sub-layer 24c of the white cover layer 22, for example, doped with an infrared-infrared fluorescence-emitting material, that is, a fluorescence-emitting material that can be excited in the infrared spectral range and fluoresce in the infrared spectral range. Alternatively, the feature material 38 may also include an infrared absorber.

[0061] Therefore, except for the window regions 16 and 18, the regions provided with the feature material 38 extend over the entire surface of the banknote 10, so that the integrity of the banknote can be inspected during authenticity verification. The window regions 16 and 18 do not contain any machine-readable feature material, so the desired high transparency of the window regions 16 and 18 will not be affected by the machine-readable features of the white cover layer 22.

[0062] Since the feature material 38 is not embedded in the externally located printing portion, but is embedded in the deeper white cover layer 22, the feature material can be well protected against wear during the service life of the banknote 10. In fact, in the case of severe wear that has eroded the white cover layer and thus the feature material 38, the visual appearance of the banknote 10 is usually severely damaged so that the banknote is withdrawn from circulation due to being unfit for circulation.

[0063] In contrast, the feature material added to one of the printing portions 26 and 36 in the traditional way is subject to significantly greater wear. If the banknote is used intensively, the printed pigments carrying the features may be worn, so that the feature signal is no longer sufficient to successfully perform authenticity verification, even if the banknote is still evaluated as suitable for circulation according to the visual appearance during quality inspection. In addition, only a relatively small amount of features can be introduced into the printing portions 26, 36, and usually integrity inspection cannot be performed either, because the printing portions 26 and 36 do not exist on the entire surface of the banknote 10.

[0064] To ensure that the feature material 38 can be well introduced into the lowermost sub-layer 24c, the size of the feature material particles should be selected to be similar to the layer thickness of the sub-layer 24c. Specifically, the white sub-layer 24c has a layer thickness of, for example, 3 μm, while the D50 particle size of the feature material 38 is about 2 μm.

[0065] InFigure 2 In the embodiment, the characteristic material 38 is only present in the white covering layer on one side, for example, the front side of the banknote 10, thereby also enabling the orientation of the banknote to be checked. When performing the authenticity test, two sensors can be used on the upper side and the bottom side of the banknote to be tested, so as to be able to detect the signal of the characteristic material 38 with the same high intensity regardless of the relative orientation of the banknote 10. However, for example, a single sensor arranged on the upper side of the banknote to be tested is also sufficient for detection, because although there are white covering layers 22 and 32 on both sides, the polymer substrate 20 can still transmit sufficient excitation radiation and fluorescence emission radiation so as to detect the characteristic material 38 even when the banknote 10 is inverted.

[0066] In Figure 2 In the first embodiment shown, the characteristic material 38 is only introduced into the uppermost layer 24c of the white covering layer 22. Since the characteristic material particles 38 are relatively large compared to the layer thickness of the sub-layer 24c, the characteristic material particles as a whole increase the roughness of the white covering layer 22, and thus its color acceptability. In this design, the two deeper sub-layers 24b and 24a of the white covering layer 22 remain unchanged, so that the adhesion of the white covering layer to the substrate 20 and the layer that may be located on the substrate is not disturbed.

[0067] In addition, the uppermost layer 24c of the white covering layer 22 usually already contains relatively large filler particles to ensure the surface roughness required for color acceptability, so that the characteristic material particles 38 can also be particularly well dispersed in this sub-layer. This can be ensured directly by the action of other fillers and / or by ensuring that the paint used for the uppermost layer 24c is designed for the dispersion of large particles.

[0068] Another advantage of the first embodiment is that the position of the characteristic material 38 close to the surface ensures high excitation efficiency and detection efficiency during the authenticity test.

[0069] When adding the characteristic material to the uppermost layer 24c of the white covering layer 22, it is appropriate that the characteristic material particles have a D50 diameter of less than 3 μm, preferably less than or equal to 2 μm, but at the same time greater than 0.5 μm. The D99 diameter should be less than 10 μm, preferably less than 6 μm. Thereby, the size range of the characteristic material particles is similar to that of the commonly used white pigments, and they can be well added to the uppermost sub-layer with a thickness usually of 3 to 10 µm. With such a selection of the characteristic material particles, the additional increase in the surface roughness mentioned above is advantageously produced, while ensuring good processability and printing performance of the paint.

[0070] Referring to Figure 3In an embodiment, it is also advantageous to provide machine-readable characteristic materials on the white cover layers 22 and 32 on two opposite sides of the banknote 10. Compared with introducing the characteristic material only on one side, the desired total amount of the characteristic material can be distributed to twice the number of embedding layers, so that the characteristic loading per layer is only half of the original. Therefore, compared with introducing on one side, the degree of change in the characteristics of the embedding layer is smaller. Alternatively, when the characteristic loading per layer is the same, the total amount of the characteristic material can be increased. In the illustrated embodiment, only the uppermost sub-layers 24c, 34c of the white cover layers 22 or 32 are provided with the characteristic material, and the same machine-readable characteristic material 38' is provided here. Compared with the layer 24c of the design solution of Figure 2 the characteristic loading of the layers 24c, 34c can be reduced, for example, halved.

[0071] The opposite white cover layers 22 and 32 can also be provided with different characteristic materials so as to be able to detect the banknote orientation during authenticity verification. Generally, each side of one or more sub-layers 24a-c, 34a-c of the white cover layers 22, 32 can be provided with the same or different machine-readable characteristic materials.

[0072] The machine-readable characteristic material used can consist of usually very hard inorganic particles. This improves the abrasion resistance of the white cover layer 22, but it is also possible to scratch the printing plate for printing the visible printing portion 26. Therefore, a characteristic material 38 with soft particles can also be used, for example, a characteristic material with characteristic material particles whose outermost side is composed of a polymer at least. The characteristic material with soft particles is an organic or organometallic characteristic material dissolved or dispersed in a polymer and / or a polymer-encapsulated inorganic, organic or organometallic characteristic material. In another embodiment, the inorganic characteristic material can have a shell composed of nanoparticles or a coating composed of, for example, silica to achieve soft characteristics that are well compatible with ordinary printing pigments.

[0073] In the second embodiment of the present invention, referring to Figure 4 , the machine-readable characteristic material 40 is only introduced into the deeper sub-layer of the white cover layer 22, preferably into the second sub-layer 24b starting from the uppermost side. This is particularly advantageous when using hard characteristic material particles 40 composed of, for example, inorganic particles. Since the hard characteristic material particles 40 are present in the deeper sub-layer, the printing plate for printing the visible printing portion 26 will not be scratched.

[0074] In the second design, the wear resistance of the feature material 40 is further improved compared to embedding the feature material in the uppermost sublayer 24c. In addition, the scattering of the excitation light at the white layer 24c located above the embedding layer 24b causes the excitation light to spread laterally, enabling a high excitation efficiency even when the excitation spot is small and the feature material loading is low. In addition, feature materials with their own body color can be inconspicuously used in deeper sublayers.

[0075] When adding a feature material to a deeper sublayer of the white cover layer 22, it is appropriate for the feature material particles to have a D50 diameter of less than 2 μm, preferably less than or equal to 1.5 μm, but at the same time greater than 0.5 μm. The D99 diameter should be less than 8 μm, preferably less than 6 μm. This makes the size range of the feature material particles similar to that of commonly used white pigments and enables them to be well incorporated into deeper layers with a thickness typically of 3 to 10 µm. When introducing the feature material into a deeper sublayer, it is advantageous to use finer particles in order to achieve better printing quality when subsequently printing the upper sublayers of the white cover layer. These requirements apply especially if the deeper sublayer is the lower layer of a double-layer white cover layer.

[0076] In Figure 4 the embodiment, the two white cover layers 22, 32 are each provided with the same feature material 40. However, as Figure 3 shown, different feature materials can also be used for the white cover layers on both sides in order to be able to simply detect the orientation of the banknote during authenticity verification.

[0077] The first and second embodiments can also be combined, so that for example as Figure 4 shown, the feature material 40 is introduced into the second sublayer 24b starting from the uppermost side of the white cover layer 22, while the same or different feature material is introduced into the uppermost sublayer 34c of the white cover layer 32 on the opposite side of the substrate.

[0078] In all designs, the feature material can be mixed with a camouflage material to make it difficult for potential counterfeiters to chemically analyze the feature material used. For this purpose, Figure 5 shows Figure 4 a variant of the design, in which, in addition to the feature material 40, a camouflage material 42 is also introduced into the second sublayer 24b starting from the uppermost side of the white cover layer 22, and the camouflage material 42 has, for example, the same particle size distribution as the feature material 40.

[0079] As shown by the white cover layer 32 arranged on opposite sides, although the characteristic material 40 is present in the second layer 34b starting from the uppermost side, the camouflage material 44 can also be introduced into the uppermost sub-layer 34c of the white cover layer. In this case, the camouflage material 44 advantageously uses a larger particle size in order to increase the roughness of the white cover layer on the one hand and to protect the deeper characteristic material particles from wear on the other hand.

[0080] Figure 6 A third design of the present invention is shown, in which the characteristic material is not only introduced into one sub-layer of the white cover layer, but into a plurality of sub-layers. All white sub-layers 24a, 24c of the white cover layer, and even all sub-layers 34a, 34b, 34c can be provided with the characteristic material.

[0081] In the described embodiment, the same machine-readable characteristic material 38 is introduced into all white sub-layers 24a, 24c of the upper white cover layer 22 in order to increase the maximum amount of characteristic material that can be introduced. Thereby, the protection against wear is improved. In addition, the wear of parts of the upper sub-layer 24c can be confirmed by a gradually decreasing characteristic strength without the risk of completely losing the characteristic strength due to the good protection of the characteristic material in the deeper sub-layer 24a. Larger characteristic material particles can also be used in the uppermost white sub-layer 24c in order to increase the roughness of the white cover layer 22 and thus improve the color acceptance.

[0082] As shown by the lower white cover layer 32, in order to be able to introduce the maximum amount of characteristic material into the white cover layer 32, the characteristic material can not only be introduced into the white sub-layers 34a, 34c, but also into all sub-layers of the white cover layer, that is, also into the transparent sub-layer 34b.

[0083] Here, different machine-readable characteristic materials 50, 52, 54 can also be introduced into different sub-layers. The advantage of this variant is that if the outer sub-layer (and the characteristic material contained therein and the signals generated by them) is worn, while the inner layer still provides an unambiguous authenticity proof, the banknote can be taken out of circulation in a controlled manner. In particular, in this variant, characteristic materials with smaller particles 50, 52 can be introduced into the deeper layers 34b or 34a, while characteristic materials with larger particles 54 can be introduced into the uppermost layer 34c. By using finer particles in the deeper sub-layers 34a and 34b, good printing control can be achieved when printing the upper sub-layers later, while the large particles in the uppermost sub-layer 34c increase the roughness of the white cover layer 32.

[0084] In another variant, the characteristic material with hard particles can be introduced into the deeper layers 34b or 34a, while the characteristic material with soft particles can be introduced into the uppermost sublayer 34c. Visually distinct characteristic material can also be introduced into the deeper layers 34b or 34a for camouflage, while visually inconspicuous characteristic material is introduced into the uppermost sublayer 34c.

[0085] It is also possible to provide interacting characteristic materials for the different sublayers, for example, on the one hand, a fluorescence-emitting material that can be excited by infrared radiation, and on the other hand, an infrared absorber is added, or two fluorescence-emitting materials with energy transfer functions are provided. If different characteristic materials are used in the sublayers 34a-c, the relative characteristic intensity can also be used to measure the degree of wear and thus the remaining suitability of the banknote 10, while the inner layer can still be used unambiguously for authenticity verification.

[0086] Example 1: Characteristic material in the uppermost sublayer

[0087] In a specific embodiment according to the Figure 2 principle, thulium-doped lithium niobate is used as the machine-readable characteristic material 38, and its manufacturing method is described in Example 2 of the patent document DE 10 2010 026 627 A1. By grinding in a jet mill, the particle size of the characteristic particles is adjusted to D99 = 5 - 6 µm and D50 = 1.5 - 2 µm. When excited by infrared radiation at approximately 800 nm, the characteristic material exhibits characteristic fluorescence in the infrared range of approximately 1800 nm.

[0088] Biaxially oriented polypropylene (BOPP) with a thickness of 60 µm is used as the polymer substrate 20. A 2-µm-thick transparent lacquer layer can be applied on the BOPP substrate as a primer to improve the adhesion properties ( Figure 2 not shown).

[0089] Then, three overlapping sublayers 24a-c or 34a-c are respectively applied on each side of the two sides of the polymer substrate 20 by intaglio printing. The average layer thickness of the lower two sublayers 24a, 24b and 34a, 34b is 2 µm here, while the average layer thickness of the uppermost sublayers 24c, 34c is 3 µm respectively.

[0090] A commercially available thermosetting aqueous aliphatic polyurethane acrylate copolymer dispersion suitable for intaglio printing is used as the lacquer for producing the sublayers, and 10% by weight of titanium dioxide with a D50 of less than 1 µm is added as a white pigment. The characteristic material 38 is selectively added only in a proportion of 1% by weight to the lacquer for printing the uppermost sublayer 24c.

[0091] The resulting machine-readable security feature has the above advantages and, in particular, does not impede the application of the uppermost sublayer 24c since no feature material is introduced into the underlying sublayers 24a, 24b. The feature material increases the roughness of the uppermost sublayer 24c and, moreover, the efficiency of the feature material 38 is particularly high compared to introducing it into deeper sublayers. Since the emission wavelength of the thulium feature is relatively long, the transmissivity of the banknote 10 is high, so that the feature material 38 can also be detected efficiently from the side of the substrate remote from the embedding layer 24c.

[0092] Example 2: Feature material in a deeper sublayer

[0093] In a specific embodiment according to the Figure 4 principle, yttrium aluminum chromium garnet doped with ytterbium is used as the machine-readable feature material 40, the manufacturing method of which is described in Example 2 of patent document DE 198 03 997 A1. By grinding in a stirred bead mill, the particle size of the feature particles is adjusted to D99 = 2.5 - 3.5 µm and D50 = 0.5 - 1 µm. The resulting particles have an aspect ratio close to 1. The inherent color of the feature material 40 is green, and when excited by infrared radiation at 945 nm, the feature material exhibits characteristic fluorescence in the infrared range of 950 - 1100 nm.

[0094] The layer structures of the sublayers 24a-c, 34a-c are basically the same as those of Example 1. However, in this example, the feature material 40 is only selectively introduced into the varnish for producing the second sublayer 24b, 34b from the top.

[0095] The resulting machine-readable security feature has the above advantages and, in particular, does not impede the application of the uppermost sublayers 24c, 34c since the feature material 40 has a suitable small particle size. Moreover, the disturbing effect of the green inherent color of the feature material is less compared to introducing it into the uppermost sublayer. The feature material in the deeper embedding layers 24b and 34b is difficult to wear and the security feature also has a higher efficiency when measured with a smaller excitation spot.

[0096] Example 3: Feature material in a deeper sublayer with a camouflage material

[0097] Starting from Example 2, a camouflage material can be used to camouflage the feature material 40, as Figure 5 shown. For example, gadolinium gallium garnet doped with manganese can be used as the camouflage material 42. The elements gadolinium, gallium and manganese additionally found in the elemental analysis behave similarly to the elements yttrium / ytterbium, aluminum and chromium of the feature material, thus increasing the number of credible stoichiometric or mixed forms such as gadolinium yttrium garnet, aluminum gallium garnet or manganese chromium garnet.

[0098] In a first variant, the camouflage material 42 has the same particle size as the characteristic material 40 and is also embedded on both sides in the second sublayer 24b or 34b starting from the uppermost side. This advantageously ensures that even if one of the uppermost sublayers 24c, 34c is damaged, the camouflage effect does not disappear.

[0099] In a second variant, a camouflage material 44 with a larger particle size is used, for example D99 = 5 - 6 µm and D50 = 1.5 - 2 µm here, and the camouflage material is also introduced on both sides into the uppermost sublayer 24c or 34c. This advantageously increases the roughness of the white coatings 22, 32 and protects the underlying sublayers 24b, 34b with the characteristic material 40 from wear by the hardness of the inorganic camouflage particles 44. In addition, it makes the analysis of the characteristic material more difficult because the large camouflage particles attract attention during the analysis process, while the smaller characteristic material particles are more difficult to identify and analyze.

[0100] Example 4: Characteristic material in multiple sublayers:

[0101] In a specific embodiment according to the Figure 7 principle, the structure of the substrate and the sublayers 24a - c, 34a - c is substantially the same as the structure of Example 1.

[0102] As a first characteristic material 56, yttrium phosphate doped with ytterbium with a particle size of D99 = 8 - 9 µm and D50 = 2.5 - 3.5 µm is used and is selectively embedded on both sides of the substrate 20 in the uppermost sublayers 24c and 34c of the white coatings 22, 32 respectively. When excited by radiation with a wavelength of 945 nm, the first characteristic material 56 shows characteristic fluorescence in the range of 950 - 1100 nm, and the share of characteristic fluorescence increases in the range with a wavelength below 1000 nm.

[0103] As a second characteristic material 58, the ytterbium - doped yttrium aluminum chromium garnet described in Example 2 is used and is selectively embedded on both sides of the substrate 20 in the second sublayer 24b, 34b starting from the uppermost side of the white coatings 22, 32 respectively. When excited by radiation with a wavelength of 945 nm, the second characteristic material 58 shows characteristic fluorescence in the range of 950 - 1100 nm, and the share of characteristic fluorescence increases in the range with a wavelength above 1000 nm.

[0104] The resulting machine - readable anti - counterfeiting feature shows the corresponding advantages of Example 1 and Example 2. However, an additional synergistic effect is produced by simultaneously using interacting characteristic materials in different sublayers.

[0105] If the sublayers 24b, 24c or 34b, 34c are present in their entirety, the respective spectra of the characteristic materials 56, 58 complement each other and act like a single characteristic. Thus, a forger cannot readily tell that the characteristic materials 56, 58 are not in the same layer.

[0106] For example, if the uppermost sublayer 24c or 34c is partially removed or damaged due to the natural loading of the banknote in circulation or deliberate tampering in the context of a forgery attempt, then in the detected emission spectrum, the relative spectral share above 1000 nm increases and the relative spectral share below 1000 nm decreases. It is thus possible to evaluate whether a banknote is fit for circulation and to identify forgery attempts that completely or partially damage the uppermost sublayers 24c and 34c by means of the interaction of the two sublayers.

[0107] Example 5: Characteristic material with soft particles:

[0108] In a specific embodiment according to the Figure 3 principle, spheres made of PMMA containing the dissolved infrared absorber CKK-55 (manufacturer: Fujifilm Imaging Colorants) are used as the machine-readable characteristic material 38', and the manufacturing method is described in Example 7 of the patent document DE 10 2015 0145 26 A1. By grinding in a jet mill, the particle size of the characteristic material is adjusted to D99 = -6 µm and D50 = 1.5 - 2 µm. The particles have an aspect ratio of less than 2:1. The characteristic material 38' exhibits a characteristic absorption band in the range of 850 nm.

[0109] The characteristic material is embedded in the uppermost sublayer 24c or 34c of the white cover layers 22, 32 on both sides of the substrate. In addition to the above advantages, compared with inorganic particles of the same particle size, the characteristic material 38' based on polymers has lower hardness and density, and thus stronger compatibility with ordinary printing pigments, for example, the sedimentation behavior is not obvious and it is not easy to scratch the printing plate.

[0110] Comparative measurement

[0111] Figure 8 Shows a layer structure for comparative measurement of the characteristic strength of a conventional design and two designs according to the invention.

[0112] First, refer to Figure 8(b), a white covering layer 62 is applied on a transparent polymer substrate 20, and the white covering layer is composed of two sub-layers 64a and 64b each having a thickness of 12 μm in the wet state. Both of these layers are composed of a varnish, such as an aqueous aliphatic polyurethane acrylate copolymer dispersion, and 20% of titanium dioxide (rutile) as a white pigment. The varnish for printing the lower layer 64a is also doped with 0.2% of an inorganic infrared-infrared fluorescent luminescent material 60, which constitutes a machine-readable characteristic material. The fluorescent luminescent material 60 has a particle size of D50 = 2.5 μm and D99 = 6 μm, so that the fluorescent luminescent material particles can be well introduced into one of the wet 12-μm-thick paint layers. Alternatively, a Raman active material, especially a surface-enhanced Raman active material, can also be used to replace the infrared-infrared fluorescent luminescent material.

[0113] In Figure 8 the embodiment of (b), the lower sub-layer 64a contains the machine-readable characteristic material 60, and the upper layer 64b does not have the characteristic.

[0114] Figure 8 (c) shows another embodiment, in which the characteristic material 60 is only introduced into the upper sub-layer 64b in the above-mentioned amount, and the lower sub-layer 64a does not have the characteristic.

[0115] Figure 8 (a) shows a comparative example that is not of the present invention. In this comparative example, the white covering layer 72 is composed of a single layer, and the above-mentioned amount of the characteristic material 60 is introduced into this layer. Therefore, Figure 8 the design schemes of (a) to (c) all contain the same amount of the characteristic material 60.

[0116] The excitation and detection of the fluorescence of the characteristic material 60 are carried out from above, that is, from one side of the white covering layer; a black background is arranged below the substrate 20. The measurement range is selected to be large enough to cover a large number (about 100) of characteristic material particles.

[0117] The measured characteristic intensity is Figure 8 normalized with respect to the intensity of the comparative example of (a), so the characteristic intensity of this comparative example is 100%.

[0118] Under the same excitation- and detection conditions as the comparative example, in Figure 8 the first embodiment of (b), the measured characteristic intensity is 59%. The special advantage of this design scheme when the characteristic intensity is high enough is that the characteristic material particles 60 can be well protected against abrasion, and due to the non-characteristic sub-layer 64b, there is no risk of the printing plate being scratched by hard characteristic material particles during continuous printing.

[0119] In the same excitation and detection conditions as in the comparative example, in Figure 8 the second embodiment of (c), the characteristic intensity measured was 159%. A particular advantage of this design is that, with the same amount of characteristic material used, the characteristic intensity is significantly increased. The mechanism responsible for the increase in characteristic intensity, according to current understanding, has been described above.

[0120] List of reference signs

[0121] 10 Polymer banknote

[0122] 12 Printed image

[0123] 14 Machine-readable security feature

[0124] 16 Bilateral window

[0125] 18 Unilateral window

[0126] 20 Substrate

[0127] 22 White covering

[0128] 24a, 24b, 24c Sub-layers

[0129] 26 Printing unit

[0130] 32 White covering

[0131] 34a, 34b, 34c Sub-layers

[0132] 36 Printing unit

[0133] 38, 38' Machine-readable characteristic material

[0134] 40 Machine-readable characteristic material

[0135] 42, 44 Camouflage material

[0136] 50, 52, 54 Different machine-readable characteristic materials

[0137] 56, 58 Co-acting characteristic materials

[0138] 60 Fluorescent luminescent material

[0139] 62 White covering

[0140] 64a, 64b Sub-layers

[0141] 72 White covering

Claims

1. A data carrier, in particular a valuable document or a security document, the data carrier having - a substrate which comprises at least one transparent plastic layer and has two opposite major surfaces, - Two white cover layers, the two white cover layers having a white opaque appearance and being applied to opposite major surfaces of the substrate, wherein, each white covering layer is composed of a layer sequence of two or more sublayers, the layer sequence extending from the lowermost white layer to the uppermost white layer, and - a machine-readable security feature which comprises a machine-readable feature material, the feature material being present in at least one sublayer of at least one of the white covering layers.

2. The data carrier according to claim 1, characterized in that, The machine-readable feature material is an optically readable feature material, preferably a fluorescent luminescent material, particularly preferably an infrared-infrared fluorescent luminescent material.

3. The data carrier according to claim 1 or 2, characterized in that The machine-readable feature material consists of particles having a D50 particle size of less than 3 μm, preferably the particles having a D50 particle size of 0.5 μm to 2 μm.

4. The data carrier according to at least one of claims 1 to 3, characterized in that The machine-readable feature material consists of substantially circular particles having an aspect ratio of less than 1:

2.

5. The data carrier according to at least one of claims 1 to 4, characterized in that, The embedding layer of the machine-readable feature material contains filler particles, such as white pigments, and the machine-readable feature material consists of particles not larger than the largest filler particles of the embedding layer.

6. The data carrier according to at least one of claims 1 to 5, characterized in that, The machine-readable feature material is present in both of the two white covering layers.

7. The data carrier according to at least one of claims 1 to 6, characterized in that, The machine-readable feature material is present in exactly one sublayer of one or both of the white covering layers.

8. The data carrier according to at least one of claims 1 to 7, characterized in that, The machine-readable feature material is present only in the uppermost sublayer of one or both of the white covering layers, wherein the machine-readable feature material advantageously consists of particles, in particular particles having a D99 diameter, having a size which is substantially equal to or less than the layer thickness of the embedding layer.

9. The data carrier according to at least one of claims 1 to 7, characterized in that, The machine-readable feature material is present only in a deeper sublayer of one or both of the white covering layers, preferably only in the second sublayer from the top, wherein the machine-readable feature material advantageously consists of particles having a size which is less than the layer thickness of the embedding layer.

10. The data carrier according to at least one of claims 1 to 7, characterized in that, The machine-readable feature material is present in a plurality of sublayers of one or both of the white covering layers.

11. The data carrier according to claim 10, characterized in that, Different feature materials are present in different sublayers.

12. The data carrier according to claim 11, characterized in that, Different, interacting feature materials are present in different sublayers.

13. The data carrier according to claims 10 to 12, characterized in that, Machine-readable feature materials having different particle sizes are present in different sublayers of the white covering layer, wherein the smaller particles are arranged in the deeper sublayers of the white covering layer and the larger particles are arranged in the uppermost sublayer of the white covering layer.

14. The data carrier according to at least one of claims 11 to 13, characterized in that Machine-readable feature materials having different particle hardnesses are present in different sublayers of the white covering layer, wherein the harder particles are arranged in the deeper sublayers of the white covering layer and the softer particles are arranged in the uppermost sublayer of the white covering layer.

15. The data carrier according to at least one of claims 1 to 14, characterized in that, At least one of the sublayers has a camouflage material which in particular has a chemical composition adapted to the machine-readable feature material but does not have a feature effect, wherein the camouflage substance is preferably present in the upper sublayers or in the same sublayer as the machine-readable feature material.

16. A method for manufacturing a data carrier according to any one of claims 1 to 15, wherein, - Provide a substrate, the substrate comprising at least one transparent plastic layer and having two opposite major surfaces, - Apply two white cover layers having a white opaque appearance on the opposite major surfaces of the substrate, the white cover layers being formed respectively by a layer sequence of two or more sub-layers, the layer sequence extending from the lowermost white layer to the uppermost white layer, and - wherein at least one sub-layer of at least one of the white cover layers is produced from a machine-readable characteristic material to form a machine-readable anti-counterfeiting feature.

17. A method for verifying the authenticity of a data carrier according to one of claims 1 to 15, the method comprising the steps of providing the data carrier and reading a machine-readable anti-counterfeiting feature, the machine-readable anti-counterfeiting feature comprising a machine-readable feature material, wherein, When reading, the authenticity of the data carrier is especially verified by utilizing the scattering of illumination light and signal light in the white cover layer.

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