OPTICALLY VARIABLE SAFETY ELEMENT

Description

[0001] The invention relates to an optically variable security element for protecting valuables, comprising a reflective surface area that exhibits at least two optically variable effects that can be recognized from different viewing directions. The invention also relates to a method for producing such a security element and a data carrier equipped with such a security element.

[0002] Data storage media, such as valuables or identification documents, as well as other valuable items such as branded goods, are often provided with security elements for security purposes. These elements allow verification of the authenticity of the data storage media and also serve as protection against unauthorized reproduction. These security elements can, for example, take the form of a security thread embedded in a banknote, a cover foil for a banknote with a hole, an applied security strip, a self-supporting transfer element, or even a feature area printed directly onto a valuable document.

[0003] Security elements with a viewing-angle-dependent or three-dimensional appearance play a special role in authenticity assurance, as these cannot be reproduced even with the most modern copying machines. For this purpose, the security elements are equipped with optically variable elements that convey a different image impression to the viewer at different viewing angles. Depending on the viewing angle, they can, for example, display a different color or brightness impression, a different perspective view, and / or a different graphic motif. In the prior art, optically variable effects include, for example, motion effects, pump effects, depth effects, or flip effects, which are realized using holograms, microlenses, or micromirrors.

[0004] Recently, optically variable security elements were proposed in the publications DE 10 2018 005 447 A1 and WO 2020 / 011390 A1, which have two relief structures arranged at different heights and each provided with a color coating. The color coating of the higher relief structure is structured as a grid, so that when the security element is viewed, the color coating of the lower relief structure appears in the spaces between the grids, enabling a seamless transition from a first to a second appearance when the security element is tilted. In practice, however, the realization of the required fine grid of the color coating is technologically very demanding. In addition, the grid limits the reflected light component of the higher or lower relief structure according to the surface area covered by grid elements or grid spaces.WO 2020 / 011392 A1 also shows a similar structure with two relief structures at two height levels. CH 691750 A5 relates to an optical information carrier with diffraction structures. EP 3415964 A1 describes a multilayer optical security element with two reflective interfaces between layers with specific refractive indices. EP 3216620 A1 relates to an optical security element with reflective facets in pixels that are randomly or uniformly aligned in some areas. WO 2020 / 011390 A1 is the closest prior art, but requires two differently colored coatings and also recesses or a grid in the upper coating.

[0005] Based on this, the invention is based on the object of proposing generic optically variable security elements which are particularly easy to manufacture and also have an attractive, bright visual appearance.

[0006] This object is achieved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

[0007] To achieve the stated object, the invention contains an optically variable security element as defined in claim 1.

[0008] The first reflection-enhancing coating is present in the feature area and can be considered at least semi-transparent. It is both reflective and sufficiently transmissive to allow the second relief structure, or its optically variable effect, to be visible.

[0009] According to the invention, the first reflection-enhancing coating is designed with a wavelength-dependent reflection and transmission in the visible spectral range.

[0010] Due to a reflective color effect of the first reflection-enhancing coating, the higher-lying relief structure shows the first optically variable effect in the first color and due to a transmission color effect of the first reflection-enhancing coating, the lower-lying relief structure shows the second optically variable effect in the second color.

[0011] The wavelength dependence of the first reflection-enhancing coating improves the visibility of the two optically variable effects. In particular, the reflectance of the security element is increased. The first reflection-enhancing coating is selected to have a high reflectance for the first color and a high transmittance for the second color. This can increase the brightness of the two optically variable effects. For example, the sum of the reflectances for the two colors (and thus the two effects) can be greater than 1.

[0012] Particularly advantageously, the higher relief structure and / or the deeper relief structure are formed by micromirror arrangements with directionally reflecting micromirrors. The micromirrors are formed in particular by non-diffractive micromirrors. They therefore do not generate or utilize color splitting. Preferably, flat mirrors, concave mirrors and / or Fresnel-type mirrors can be used. The lateral dimensions of the micromirrors (or individual elements of a Fresnel mirror) are expediently below 50 µm, advantageously below 20 µm, preferably around 10 µm, i.e. between 7 µm and 13 µm. On the other hand, the lateral dimensions of the micromirrors can also be above 2 µm, in particular above 3 µm or even above 5 µm. The pitch of the micromirrors is preferably less than 10 µm, more preferably less than 5 µm.

[0013] In principle, other relief structures, in particular embossed Fresnel lenses, concave mirrors, hologram structures, nanostructures, or diffractive blazed gratings, can be used instead of micromirrors. Achromatic diffraction gratings, so-called matte structures, can be used particularly advantageously here. These essentially reflect white light and thus do not interfere with the color effect of the coating or any color layers by generating diffraction colors. To generate bright colors in transmission and / or reflection, the relief structures can also have subwavelength structures, in particular subwavelength gratings, which, in combination with the respective reflection-enhancing coating, determine or at least co-determine its color.For example, a relief structure can represent an overlay of a micromirror structure with subwavelength gratings located thereon, whereby the orientation of the micromirrors determines the direction of the reflected light and the subwavelength gratings modify the color effect of the reflection-enhancing layer applied to the relief structure.

[0014] According to the invention, the optically variable effects of the two relief structures are not congruent; rather, they are at least partially recognizable from different viewing directions. In particular, it is advantageously provided that the first and second relief structures reflect incident parallel light at least in certain regions into different angular ranges, wherein the two different angular ranges preferably do not overlap and are preferably separated by more than 3°, particularly preferably more than 10°.

[0015] The two relief structures are independent relief structures. They can therefore be freely selected, as they are not dependent on each other (in their relief pattern). A relief structure that results solely from coating another relief structure is not an independent relief structure in the present sense. In particular, the relief structures of the surface area do not have the same relief pattern, nor do they have the same relief pattern scaled only in height. Instead, the two relief structures are different and formed with different relief patterns. The two independent relief structures are, in particular, different.The two relief structures can therefore produce similar optically variable effects, for example opposing movement effects or spatial representations visible from different viewing directions, but due to the difference in the relief patterns they will not both always produce the same optically variable effect in the same place.

[0016] Specifically, the formation of the higher relief structure, in particular the orientation of the micromirrors of the higher micromirror arrangement, and / or the formation of the lower relief structure, in particular the orientation of the micromirrors of the lower micromirror arrangement, can advantageously vary depending on the location in order to create a predetermined motif, in particular a three-dimensional motif or a movement motif. The relief pattern, in particular the orientation of the micromirrors, is freely selectable and is essentially determined only by the predetermined motifs, but not by the orientation of laterally or vertically adjacent micromirrors.

[0017] In the present invention, the first reflection-enhancing coating combines two inherently opposing properties. On the one hand, the first reflection-enhancing coating should have a high degree of reflection so that the optically variable effect of the first relief structure is clearly visible. On the other hand, it should also have the highest possible degree of transmission so that the optically variable effect of the second relief structure can be clearly visible.

[0018] Fundamentally, reflectance and transmittance are not independent of each other; rather, energy conservation implies that for any material, the sum of reflectance R, transmittance T, and absorbance A is equal to 1 (or 100%). Maximum reflection and maximum transmittance cannot therefore be achieved simultaneously, and even with negligible absorption, the sum of reflectance and transmittance cannot exceed 100%. However, the present inventors have found that this physical limitation can be practically circumvented by maximizing reflectance and transmittance at different wavelengths. For example, it is quite possible for a coating to have a reflection of 75% (or generally > 50%) in the yellow spectral range and a transmission of 75% (or generally > 50%) in the complementary blue range.This does not constitute a violation of the above relationship, since for each wavelength the relationship R+T+A = 1 is still satisfied.

[0019] The first reflection-enhancing coating expediently has a transmission of at least 35%, preferably of at least 50%, particularly preferably of at least 60%, at least in a partial range of the visible spectral range. Furthermore, the first reflection-enhancing coating has a reflection of at least 30%, preferably of at least 50%, and particularly preferably of 70% or more, at least in a partial range of the visible spectral range. As explained, the partial ranges of particularly high transmission and particularly high reflection are different within the scope of the invention, so that transmission and reflection in these ranges can simultaneously assume particularly high values, in particular values ​​of more than 50%.

[0020] The first reflection-enhancing coating advantageously contains one or more high-refractive index layers, preferably high-refractive index dielectric layers, which have a refractive index of at least 1.7, preferably at least 2.0, and particularly preferably at least 2.2 in at least a partial range of the visible spectrum. For example, high-refractive index dielectric layers made of TiO2 or ZnS can be used. Even a single high-refractive index dielectric layer can be provided with a thickness such that it reflects in a wavelength-dependent manner. For example, a 70-150 nm thick ZnS (or TiO2) layer reflects in color, whereas a 40 nm thick layer reflects in white. These can also be combined with low-refractive index layers, for example made of MgF or SiO2, to create advantageous multilayer systems. In addition to high-refractive index dielectrics, semiconductor materials such as silicon can also be used as high-refractive index layers.Even though these have a higher absorption than high-index dielectrics, comparable effects can be created with thin semiconductor layers.

[0021] It has been shown that simultaneous very high reflection and very high transmission at different wavelengths can be achieved particularly well with multilayer systems, especially with multilayer systems with multiple dielectric layers. Three-layer systems containing two high-refractive-index layers and a low-refractive-index intermediate layer, such as a layer system consisting of a 125 nm thick TiO 2 layer, a 70 nm thick SiO 2 intermediate layer, and another 125 nm thick TiO 2 layer, are advantageous.

[0022] The first reflection-enhancing coating can be a (purely) dielectric reflection-enhancing coating. More preferably, the first dielectric reflection-enhancing coating acts based on the refractive index. It is wavelength-dependently semitransparent, although it can be formed from a transparent material with a corresponding refractive index. Particularly preferably, the first dielectric refractive index-based reflection-enhancing coating in the security element is directionally neutral for light in transmission. The direction of the incoming light and the direction of the light transmitted through the first reflection-enhancing coating are thus the same.

[0023] Particularly preferably, the reflection and transmission color effect of the first reflection-enhancing coating is independent of the viewing angle.

[0024] Thin metal layers can also be advantageously used alone or in a multilayer system. Preferably, a multilayer system is used as the first reflection-enhancing coating, which exhibits a first color in reflection and a second color in transmission (essentially) independent of the viewing angle. For example, a first reflection-enhancing coating can be formed by a triple-layer system of 25 nm Ag / 225 nm SiO 2 / 25 nm Ag, which exhibits a golden color in reflection and a blue color in transmission, each with a high reflection or transmittance of more than 50%.In practice, layer systems with a sequence of metal / dielectric / metal can often be produced more easily or more cost-effectively on existing systems than dielectric multi-layer systems. However, due to the (albeit) low (but still significant) absorption of the thin metal layers, they have a reduced maximum brightness compared to purely dielectric layer systems.

[0025] The first reflection-enhancing coating can also be formed by a liquid crystal layer, which is preferably oriented by the higher relief structure. Semitransparent nanostructured metal layers, in which, for example, structural colors are generated by additional subwavelength structures in the higher relief structure, are also possible.

[0026] The appropriate layer thicknesses of the first reflection-enhancing coating and the associated sublayers in all these designs range from approximately ten to several hundred nanometers. Thin metal layers can also be provided with thicknesses of less than 10 nm.

[0027] It is particularly advantageous in this case that the first reflection-enhancing coating can be applied over the entire surface, since the underlying, deeper relief structure remains visible through the coating due to its semi-transparency, as explained in more detail below.

[0028] According to the invention, the second reflection-enhancing coating has the highest possible reflectance, which is advantageously at least 50%, preferably at least 75%, particularly preferably at least 80% or even at least 85%. This high reflectance is present in at least part of the visible spectrum, advantageously in the color range in which the color of the second optically variable effect is desired. However, the second reflection-enhancing coating can also advantageously be highly reflective across the entire visible spectral range, since a desired color effect can already be created by colored transmission of the first reflection-enhancing coating and / or an intermediate color layer and / or a colored embossing lacquer layer.

[0029] The second reflection-enhancing layer is preferably formed as a reflective metallic coating. The reflection can in particular be so high that the second reflection-enhancing layer is opaque in transmission, i.e., has an optical density of at least 1.0, preferably 2.0 or more. Suitable layers that are highly reflective across the entire visible spectral range include, for example, layers of silver and aluminum. In other advantageous embodiments, colored metallizations are used, in particular a gold-colored metallization (for example, made of Au or alloys such as Al-Cu and the like) or a copper-colored metallization. To achieve a desired color effect, the second reflection-enhancing layer can also consist of a combination of a metallization and a translucent color layer.Thin-film systems can also be considered as a second reflection-enhancing layer, for example color-shifting three-layer structures consisting of an absorber, dielectric, and reflector layer, with which blue or green reflective color contributions can be realized, which are difficult to achieve with individual metal layers.

[0030] The first and second reflection-enhancing layers are preferably coordinated with one another to achieve a high overall reflection of the security element from both relief structures and thus a bright representation of both optically variable effects. Therefore, the reflection of the second reflection-enhancing layer is particularly advantageous, at least in the spectral range in which the first reflection-enhancing layer has a high transmission, since the brightness of the optically variable effect of the deeper relief structure results from the transmission of the first reflection-enhancing layer and the reflection of the second reflection-enhancing layer.

[0031] For example, if the first reflection-enhancing layer has a reflection factor R Green (1) = 75% in the green range and a transmission factor of T Red (1) = 90% in the red range, and if the second reflection-enhancing layer has a reflection factor of R Red (2) = 90% at least in the red range (or in the entire visible spectral range), then, assuming negligible absorption and the absence of further color layers, the reflection factor RH of the higher relief structure in the green range is R HL , Grün = R Grün 1 = 75 % , and the reflectance RT of the higher relief structure in the red to R TL , Rot = T Rot 1 * R Rot 2 * T Rot 1 = 73 % , so that both optically variable effects appear with very high and comparable brightness. When determining the brightness of the optically variable effect of the deeper relief structure, it must be taken into account that the light reflected by the second reflection-enhancing layer passes through the first reflection-enhancing layer once more (see, for example,Fig. 2 ), so their transmittance must be taken into account twice.

[0032] In the above example, if the absorption is neglected for the first reflection-enhancing layer, the transmittance in the green is T Green (1) = 25% and the reflectance in the red is R Red (1) = 10%, so that at the same wavelength R Grün 1 + T Grün 1 = 75 % + 25 % = 100 % , and R Rot 1 + T Rot 1 = 90 % + 10 % = 100 % , holds, so the energy conservation is fulfilled. Nevertheless, the reflection and transmission of the first reflection-enhancing layer at different wavelengths R Grün 1 + T Rot 1 = 75 % + 90 % > 100 % , which for both relief structures a high reflectivity with R HL , Grün + R TL , Rot = 75 % + 73 % > 100 % enabled.

[0033] Advantageously, the coordination of the first and second reflection-enhancing layers provides that the security element, at least in a partial region, directs light from a first wavelength range of the visible spectrum with a reflectance R1 into a first viewing angle range and light from a second wavelength range of the visible spectrum with a reflectance R2 into a second viewing angle range, where R1+R2 > 1 (or 100%) applies. In the above example, the first wavelength range is the green spectral range, the second wavelength range is the red spectral range, and R1=0.75, R2=0.73, so that R1+R2=1.48>1.

[0034] Advantageously, the light transmitted through the first reflection-enhancing layer does not change its direction or changes it only slightly, to ensure that the optically variable effect of the higher-lying relief structure does not shine through to the lower-lying relief structure. To achieve this, the relief-forming layers and the layers adjoining the reflection-enhancing layers have a similar or even identical refractive index, i.e., a refractive index difference of less than 0.25, preferably less than 0.1, and particularly preferably less than 0.05.

[0035] One or more translucent color layers can be provided between the first and second relief structures to influence the color impression of the optically variable effect of the second relief structure. Such a translucent color layer can, in particular, be non-height structured, i.e., formed as a flat layer, or it can be formed by a colored relief-forming layer, for example, a colored embossed lacquer layer.

[0036] The different height levels at which the two relief structures are arranged advantageously have a distance of between 5 µm and 100 µm, preferably between 10 µm and 50 µm, in the z-direction. The small vertical distance between the structures involved is not noticeable when viewing the security element. On the other hand, the vertical distance is large enough to prevent any interference effects from occurring in the intermediate layer(s), so that the coloring of the security element is not disturbed by any interference colors. Interference effects are also prevented by the non-conforming height profiles of the relief structures, which additionally lead to a locally constantly changing vertical distance between the relief structures. The reference point for the height level of a relief structure is the base area of ​​the relief structure, for example at the base point of a micromirror embossing.

[0037] In some embodiments, a translucent color layer can also be expediently provided above the first reflection-enhancing layer in order to influence the color impression of the optically variable effect of the first relief structure. For example, a high-index dielectric layer can be covered with a translucent color. Since such a color layer also influences the color and brightness of the optically variable effect of the second relief structure, light colors are preferably used for such color layers, which also transmit the desired color of the second relief structure as strongly as possible, such as yellow or a very bright red, blue, or green.

[0038] With regard to the surface coverage of the reflection-enhancing layers, in an advantageous embodiment, both reflection-enhancing layers are applied to the surface pattern in an unscreened manner and, in particular, even over the entire surface. A particular advantage of the inventive design lies precisely in the fact that, despite the first reflection-enhancing coating being applied in an unscreened or full-surface manner, the optically variable effect of the deeper relief structure is visible.

[0039] In a further development, the second reflection-enhancing layer can also be provided only in certain regions and thus form negative identifiers, in particular in the form of numbers, symbols, and the like, in the security element. Additionally or alternatively, the first reflection-enhancing coating can also be present only in certain regions. According to the invention, the regions in which the two different reflection-enhancing coatings are provided must, however, at least partially overlap in the feature region. In advantageous embodiments, the two reflection-enhancing coatings are not provided over the entire surface, but in completely or almost congruent partial regions. In particular, a negative identifier can be designed such that both reflection-enhancing coatings are congruently recessed in the form of text, symbols, value numbers, and the like.The first reflection-enhancing layer is therefore advantageously present in the feature area without screening, i.e., without screening, but possibly with individual negative markings. In a preferred embodiment, the first reflection-enhancing layer is even present over the entire surface of the feature area, i.e., without screening or recesses.

[0040] For a particularly good fit of the two layers, known structuring methods can be used, in which, for example, an already structured reflection-enhancing coating is used as a mask for structuring the other layer.

[0041] Particularly when using a dielectric first reflection-enhancing layer, it can be advantageous to suppress the reflectance or color effect in certain areas, thus, for example, simulating a recess in the layer. For this purpose, corresponding modulation structures can be provided in the higher relief structure, which locally reduce the reflectance or color effect of the applied layer. So-called moth-eye structures, which can be present, for example, as regular or irregular subwavelength structures, can be advantageously used for this purpose.

[0042] For the sake of completeness, it should be mentioned that the relief structure closer to the viewer is the higher relief structure. The two optically variable effects appear to the viewer from one viewing side (in this sense, from above).

[0043] The invention further includes a data carrier as defined in claim 14 with a security element of the type described. The data carrier can be, in particular, a value document, such as a banknote, in particular a paper banknote, a polymer banknote, or a composite film banknote, a share, a bond, a certificate, a voucher, a check, a high-value admission ticket, but also an identification card, such as a credit card, a bank card, a cash payment card, an authorization card, an identity card, or a passport personalization page. The lower relief structure is generally closer to a surface of the data carrier than the higher relief structure, which is closer to the viewer's eye. In one expedient variant, the security element is arranged in an opaque area of ​​the data carrier.

[0044] The invention also includes a method for producing an optically variable security element as defined in claim 15.

[0045] 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.

[0046] They show: Fig. 1 a schematic representation of a banknote with an optically variable security element according to the invention, Fig. 2 a section of a security element according to the invention in cross section, Fig. 3 the transmittance and the reflectance of the first reflection-enhancing coating of the Fig. 2 , Fig. 4 another embodiment of the invention, in which the in connection with Fig. 2described layers were applied on the same side of a carrier film, Fig. 5 in (a) to (e) schematically shows the appearance of the security element of the Fig. 4 in plan view from different viewing directions, and Fig. 6 shows a further embodiment of the invention.

[0047] The invention will now be explained using the example of security elements for banknotes. Figure 1shows a schematic representation of a banknote 10 with an optically variable security element 12 according to the invention in the form of an adhesive-applied transfer element. However, it is understood that the invention is not limited to transfer elements and banknotes, but can be used for all types of security elements, for example, labels on goods and packaging or for securing documents, ID cards, passports, credit cards, health cards, and the like. For banknotes and similar documents, in addition to transfer elements (such as patches or strips, each with or without their own carrier layer), security threads or security strips, for example, are also possible.

[0048] The Fig. 1The security element 12 shown conveys a three-dimensional impression to the viewer despite its flat design and simultaneously displays a binary color and effect change when the banknote 10 is tilted. From a first viewing direction, the security element 12 displays a first motif 14-A seemingly bulging out of the plane of the banknote 10, specifically, for example, a curved representation of the value number "10," appearing in a first color, for example, a bright yellow. From a second viewing direction, the security element 12 displays a second motif 14-B seemingly bulging out of the plane of the banknote 10, for example, a curved representation of a coat of arms, appearing in a second color, for example, a bright blue.

[0049] When the banknote 10 is tilted 16 or the viewing direction changes accordingly, the appearance of the security element 12 suddenly jumps from the first to the second appearance, or when tilted back, from the second to the first appearance. The change in the motif (value number or coat of arms) and color (yellow or blue) occurs simultaneously and without an intermediate or transitional stage in which both motifs or colors would be visible simultaneously or one motif would be visible in the color of the other motif. The appearance therefore jumps seamlessly between two appearances 14-A, 14-B and is therefore referred to as a binary color and effect change.

[0050] Security elements with such appearances are already known from the publication DE 10 2018 005 447 A1. However, compared to the security elements described therein, the security element described here is simpler and more cost-effective to produce and also exhibits both optical effects with higher luminosity and thus with greater attention and recognition value.

[0051] The special structure of optically variable security elements according to the invention will now be described with reference to Fig. 2 explained in more detail, which shows a section of the security element 12 schematically in cross section.

[0052] The security element 12 contains a flat, transparent carrier film 18, the surface extent of which defines an xy-plane and a z-axis perpendicular thereto.

[0053] The carrier foil 18 carries a multi-colored reflective surface area 20, which contains two relief structure areas 24, 34, which are arranged in the z-direction at two specific, different height levels. Since the security element of the Fig. 2 is designed for viewing in reflection from the positive z-direction, the relief structure 34 closer to the observer 40 is referred to as the higher relief structure and the relief structure 24 further away from the observer 40 is referred to as the lower relief structure.

[0054] In the exemplary embodiment, the two relief structure regions each represent micromirror embossments or micromirror arrays 24, 34, each formed from a plurality of micromirrors inclined relative to the xy plane with lateral dimensions of approximately 10 µm. The local angles of inclination of the micromirrors are selected precisely so that the relief structures of the micromirror arrays 24, 34 produce a desired optical appearance after the reflection-enhancing coating.

[0055] Specifically, the angles of inclination of the micromirrors in the exemplary embodiment are selected such that the micromirror arrangement 34 generates the curved representation of the value "10" in a viewing angle range of +5° to +20° (viewing position 40-A) relative to the surface normal 42, and the micromirror arrangement 24 generates the curved representation of the coat of arms in a viewing angle range of -5° to -20° (viewing position 40-B).

[0056] To create the desired color impressions, the lower micromirror arrangement 24 is provided over its entire surface with a second reflection-enhancing coating 26 following the relief profile in the form of a highly reflective opaque metal layer, for example, an opaque aluminum layer with a reflectivity of approximately 90%. The higher micromirror arrangement 34 is provided over its entire surface with a first reflection-enhancing coating 36 following the relief profile, which is semi-transparent and has a wavelength-dependent reflection and transmission in the visible spectral range, as shown in Fig. 3 illustrated in more detail.

[0057] Figure 3 shows schematically the transmittance (solid curve 60) and the reflectance (dashed curve 62) of the reflection-enhancing coating 36 as a function of the wavelength λ. As can be seen from Fig. 3As can be seen, the transmittance of coating 36 is particularly high in the blue spectral range (peak 64) and even exceeds the 50% mark there. Accordingly, the reflectance of coating 36 is very low in the blue spectral range (dip 66). Conversely, the reflectance of coating 36 is particularly high in the yellow and red spectral ranges and also significantly exceeds the 50% mark there, whereby the transmittance of the coating is correspondingly very low in this spectral range.

[0058] As explained in more detail above, the spectral separation of reflection and transmission makes it possible for the reflection-enhancing coating 36 to have a reflectance of more than 50% in the yellow spectral range, on the one hand, and therefore produce a bright, golden-yellow reflection color, and to have a transmittance of more than 50% outside the yellow spectral range, on the other hand, and therefore produce a bright, blue transmission color.

[0059] The micromirror arrays 24, 34 are each embossed into a transparent embossing lacquer layer 22, 32 applied to the carrier foil 18 and, after the application of the respective reflection-enhancing coating 26, 36, are leveled with a transparent topcoat layer 28 or 38, respectively. The topcoat layers preferably have substantially the same refractive index as the embossing lacquer layers 22, 32. The layer structure is applied, for example, with the aid of an adhesive layer 44 to the banknote paper of the banknote 10 or the substrate of another data carrier.

[0060] With vertically incident white light 50, the micromirrors of the higher micromirror array 34 are at the glancing angle for the observer from the viewing direction 40-A, producing the curved representation of the value number "10." The first reflection-enhancing coating 36 imparts a bright, golden-yellow reflection color 52 to the image impression. Due to the semi-transparency of the reflection-enhancing coating 36, the micromirrors of the micromirror array 24 are also generally perceptible, but their orientation is far removed from the glancing angle and they therefore appear inconspicuous from the viewing direction 40-A and contribute virtually nothing to the image impression. Overall, the observer from the viewing direction 40-A thus sees the golden-yellow glowing appearance 14-A of the curved value number "10" produced by the micromirror array 34.

[0061] From the viewing direction 40-B, the micromirrors of the lower micromirror arrangement 24 are positioned at the glancing angle for the observer, creating the curved representation of the coat of arms. The semitransparent coating 36 transmits the blue component of the incident white light 50 as a blue transmission color 54. The blue transmission color 54 is reflected in the viewing direction 40-B by the opaque aluminum coating 26, which essentially acts as a mirror, without any color change as a blue reflection 56. Although the micromirrors of the higher micromirror arrangement 34 are also generally perceptible, their orientation is far removed from the glancing angle and they therefore appear inconspicuous from the viewing direction 40-B and contribute virtually nothing to the image impression.Overall, the observer from the viewing direction 40-B thus sees the blue luminous appearance 14-B of the curved coat of arms generated by the micromirror arrangement 24.

[0062] Both the yellow glowing appearance of the domed value number "10" and the blue glowing appearance 14-B of the domed coat of arms have an intensity of more than 50% of the incident light intensity, so that both color impressions appear extraordinarily bright and striking to the observer.

[0063] In conventional designs, in which the deeper relief structure is only visible through a screened color coating of the higher relief structure, the area coverage of the screen limits the relative brightness of the two relief structures, so that at most one of the brightnesses of the two appearances can be above 50%. As already explained in detail above, the increased brightness in the present invention is made possible by spectrally separating the wavelength ranges of maximum reflection and maximum transmission. While it is physically impossible for the reflectance and transmittance at the same wavelength to be greater than 50% at the same time, with spectral separation the reflection in one color (here, for example, yellow) and the transmission in another color (here, for example, blue) can each be greater than 50%.If the transmitted light is then reflected almost without loss by a highly reflective layer, the security element as a whole can display both the first optically variable effect in the first colour (yellow) and the second optically variable effect in the second colour (blue) with a reflection factor of more than 50%.

[0064] However, according to the invention, it is not absolutely necessary for both reflection and transmission to be above 50%, since on the one hand even with smaller values ​​a higher brightness can be achieved than with conventional designs, and on the other hand the semi-transparency of the first reflection-enhancing coating, regardless of the brightness, eliminates the need for a fine screening of the coating of the higher relief structure and the security element can therefore be manufactured more simply and cost-effectively.

[0065] Specifically, for the semi-transparent reflection-enhancing coating 36 of the higher relief structure, a single layer of TiO2 or ZnS with a layer thickness of approximately 10 nm to several hundred nm can be used. For example, with a 125 nm thick high-index TiO2 coating, using a refractive index of 1.41 for the surrounding embossed or protective lacquer, a reflectivity of over 40% in the green range and, at the same time, a very high transmission in the blue and red range, which can be 90% or more, is obtained.

[0066] Multilayers are particularly well suited for the semitransparent reflection-enhancing coating 36, as they can be specifically designed to simultaneously achieve very high reflection and very high transmission at different wavelengths. For example, dielectric triple layers can be used, such as a sandwich of two 125 nm thick TiO2 layers separated by a 70 nm thick SiO2 intermediate layer. Such a coating exhibits almost 80% reflection at wavelengths around 500 nm while still maintaining very high transmission of more than 90%, particularly in the red spectral range.

[0067] Returning to the presentation of the Fig. 2The color impression of the second relief structure 24, and thus of the second optically variable effect, can be modified in several ways. For example, instead of an aluminum coating, a color-reflecting metal, such as copper or gold, can be used for the second reflection-enhancing coating. Alternatively or additionally, a translucent color layer can be arranged between the two reflection-enhancing coatings 26 and 36, as shown in Fig. 6 illustrated. Such a translucent ink layer can, in particular, not be formed with a height structure and can be applied, for example, as a flat layer to the upper or lower surface of the carrier film 18. Alternatively or additionally, one or both of the embossing lacquers 22, 32 can also be colored.

[0068] These measures do not change the reflection color of the first relief structure 34. However, the color impression of the second relief structure 24 is modified and then results from a combination of the transmission color of the first reflection-enhancing coating, the reflection color of the second reflection-enhancing coating, and optionally further color effects of color layers located between the relief structures and / or of colored embossing lacquers.

[0069] Figure 4 shows as a further embodiment of the invention a security element 70 in which the Fig. 2described layers were applied to the same side of a carrier film 18. Starting from the carrier film 18, the security element 70 contains a first transparent embossing lacquer layer 32 with an embossed, higher-lying micromirror structure 34, a first reflection-enhancing coating 36, a second transparent embossing lacquer layer 22 applied to the coating 36 with an embossed, lower-lying micromirror structure 24, a second reflection-enhancing coating 26, a cover lacquer layer 28, and finally an adhesive layer 44 for transferring the security element 70 to a target substrate. The carrier film 18 is preferably designed to be releasable and is peeled off after the transfer of the security element 70. Alternatively, the carrier film 18 can also remain in the transferred layer composite if it is designed to be transparent.

[0070] The first reflection-enhancing coating 36 is in the embodiment of the Fig. 4formed by a dielectric three-layer structure consisting of a 125 nm thick TiO 2 layer, a 70 nm thick SiO 2 layer, and a 125 nm thick TiO 2 layer. The coating 36 exhibits a green reflection color with a reflectivity of almost 80% and a red transmission color with a transmittance of well over 80%. A highly reflective aluminum coating is used as the second reflection-enhancing coating 26, which essentially acts as a mirror surface without its own color contribution. The security element 70 therefore exhibits the optically variable effects described below from the respective viewing directions with a bright green or bright red color.

[0071] It is particularly noteworthy that the sum of the reflection coefficient R1 of the higher relief structure 34 in the green and the reflection coefficient R2 of the lower relief structure 24 in the red is greater than one (or 100%); specifically, each of the two reflection coefficients is greater than 0.5 (or 50%). This is physically impossible with conventional designs based on the partial transmission of incident radiation through the screening of a color layer. For example, with a 50% screening of an opaque, reflective coating of the higher relief structure, no more than 50% of the incident light can be reflected per representation, averaged over the entire surface, so that even a maximum sum of R1 + R2 = 1 can be achieved. The security element 70 of the Fig. 4 therefore appears particularly bright compared to conventional designs.

[0072] With reference to the supervision of the Figures 5(a) to (e)In the security element 70, the angles of inclination of the micromirrors of the deeper micromirror arrangement 24 in the feature area are selected such that they produce a red rolling bar effect, i.e. a bright red bar 72 which, when the security element is tilted, appears to run up or down along the feature area of ​​the security element 70 depending on the tilt direction, as indicated by the arrows in Fig. 5 for one of the two directions of movement. The inclination angles of the micromirrors of the higher micromirror arrangement 34 are selected such that they simultaneously generate a counter-rotating green rolling bar effect in the feature area, i.e., a bright green bar 74 that, when the security element is tilted, runs opposite to the red bar 72 of the lower micromirror arrangement 24.

[0073] Due to the semi-transparency of the coating 36, both the green bar 74 of the higher micromirror arrangement 34 and the red bar 72 of the lower micromirror arrangement 24 are always visible, even in the overlapping position in which both bars 72, 74 partially or completely overlap, so that the two bars 72, 74 appear to run through each other to the observer. In the Fig. 5(c) In the overlapping position shown, the observer sees the red and green colors of the two micromirror arrangements 24, 34 at the same location, resulting in a very bright mixed color through additive color mixing. The angular difference between the tilt angles at which one of the bars illuminates red or green becomes increasingly larger from the center of the security element 70 upwards or downwards, and amounts to, for example, 10° or even more at the upper or lower edge.

[0074] When manufacturing a structure according to Fig. 4Two advantageous variants are shown: In a first variant, the second embossing lacquer layer 22 can be applied directly onto the first reflection-enhancing coating 36 and embossed. In one advantageous embodiment, the embossing lacquer can be colored and then imparts an additional color contribution to the light reflected on the second reflection-enhancing coating 26. In another variant, the second embossing lacquer layer 22 with its embossing 24 and reflection-enhancing coating 26 can also be produced on a different carrier film and then laminated onto the first carrier film 18 with the relief structure 34 and its reflection-enhancing coating 36. In one advantageous embodiment, a colored laminating adhesive can be used to provide an additional color contribution.

[0075] Alternatively, a transparent laminating adhesive and an additional layer of paint can be used.

[0076] As a further embodiment, which is a modification of the design of the Fig. 2 represents, is in Fig. 6 a security element 80 is shown, the structure of which largely corresponds to the structure of the security element 12 of Fig. 2 In this embodiment, however, a translucent color layer 82 is provided on the underside of the carrier film 18, which provides an additional color contribution for the light reflected by the second reflection-enhancing coating 26. On the thus pre-coated carrier film 18, as in Fig. 2 Transparent embossing lacquer layers 22, 32 are applied, embossed with the desired relief pattern and each provided with a reflection-enhancing coating 26, 36.

[0077] The top side of the assembly is laminated to a carrier film 86 with a release layer 88 via a laminating varnish 84. The underside of the assembly is provided with an adhesive layer 44 for transfer to a target substrate. Such an assembly is particularly suitable for producing a patch product by punching and weeding, whereby the assembly, from the release layer 88 down to the carrier film 86, is cut through with a punching tool and removed outside the patch area to be transferred.

[0078] In the presentation of the Fig. 6 At the top left and right edges, weeded areas are indicated, in which only the carrier film 86 remains. It is understood that the color layer 82 can also be omitted if its color effect is not required for the desired appearance. List of reference symbols

[0079] 10 Banknote 12 Security element 14-A Protruding motif "10" 14-B Protruding motif "Coat of arms" 16 Tilt direction 18 Carrier foil 20 Reflective surface area 22 Embossed lacquer layer 24 Micromirror arrangement 26 Second reflection-enhancing coating 28 Top coat layer 32 Embossed lacquer layer 34 Micromirror arrangement 36 First reflection-enhancing coating 38 Top coat layer 40 Viewer 40-A, 40-B Viewing positions 42 Surface normal 44 Adhesive layer 50 Incident white light 52 Golden yellow reflection color 54 Blue transmission color 56 Blue reflection 60 Transmittance curve 62 Reflectance curve 64 Peak transmission in blue 66 Dip reflectance in blue 70 Security element 72red bar 74green bar 80security element 82transparent color layer 84laminating varnish 86carrier film 88release layer

Claims

1. Optically variable security element for safeguarding valuable objects, the surface area of said security element defining a z-axis perpendicular thereto, comprising a reflective surface region exhibiting at least two optically variable effects which are discernible from different viewing directions and appear with different colours, wherein - the reflective surface region (20) contains two independent relief structures, which are arranged at different height levels in the z-direction and form a lower-level relief structure (24) and a higher-level relief structure (34), - the higher-level relief structure (34) is provided with a first reflection-enhancing coating (36) following the course of the relief and the lower-level relief structure (24) is provided with a second reflection-enhancing coating (26) following the course of the relief, - the two relief structures (24, 34) overlap in a feature region, and - the first reflection-enhancing coating (36) in the visible spectral range is embodied with a wavelength-dependent reflection and transmission in the visible spectral range, such that - the higher-level relief structure (34) exhibits a first optically variable effect in a first colour, and - the lower-level relief structure (24) exhibits a second optically variable effect through the first reflection-enhancing coating (36), wherein the second optically variable effect is exhibited in a second, different colour.

2. Security element according to Claim 1, characterized in that the higher-level relief structure exhibits the first optically variable effect in the first colour by virtue of the reflection colour effect of the first reflection-enhancing coating, and the lower-level relief structure exhibits the second optically variable effect in the second colour by virtue of the transmission colour effect of the first reflection-enhancing coating.

3. Security element according to Claim 1 or 2, characterized in that the higher-level relief structure and / or the lower-level relief structure are / is formed by micromirror arrangements with directionally reflective micromirrors, in particular with mirrors having a non-diffractive effect, and preferably with plane mirrors, concave mirrors and / or Fresnel-like mirrors.

4. Security element according to at least one of Claims 1 to 3, characterized in that the two independent relief structures are embodied differently.

5. Security element according to at least one of Claims 1 to 4, characterized in that the first reflection-enhancing coating has a transmission of at least 35%, preferably of at least 50%, particularly preferably of at least 60%, at least in a sub-range of the visible spectral range.

6. Security element according to at least one of Claims 1 to 5, characterized in that the first reflection-enhancing coating has a reflection of at least 30%, preferably of at least 50%, particularly preferably of at least 70%, at least in a sub-range of the visible spectral range.

7. Security element according to at least one of Claims 1 to 6, characterized in that the first reflection-enhancing coating contains one or more high refractive index layers, preferably dielectric high refractive index layers, which have a refractive index of at least 1.7, preferably at least 2.0, and particularly preferably at least 2.2, at least in a sub-range of the visible spectrum.

8. Security element according to at least one of Claims 1 to 7, characterized in that the second reflection-enhancing coating, at least in a sub-range of the visible spectrum, has a reflectance of at least 50%, preferably at least 75%, particularly preferably at least 80%, or even of at least 85%, preferably in that the second reflection-enhancing coating is embodied as opaque with an optical density of more than 1.0, in particular of more than 2.0.

9. Security element according to at least one of Claims 1 to 8, characterized in that the security element, at least in a partial region, directs light in a first wavelength range of the visible spectrum with a reflectance R1 into a first viewing angle range and light in a second wavelength range of the visible spectrum with a reflectance R2 into a second viewing angle range, wherein it holds true that R1+R2 > 1.

10. Security element according to at least one of Claims 1 to 9, characterized in that - the first and / or second reflection-enhancing layer(s) are / is present in the feature region without any grid, preferably over the whole area; and / or - one or more light-transmissive colour layers are provided between the first and second relief structures in order to influence the colour impression of the optically variable effect of the second relief structure; and / or - one or more light-transmissive colour layers are provided above the first reflection-enhancing layer in order to influence the colour impression of the optically variable effects of the first and second relief structures.

11. Security element according to at least one of Claims 1 to 10, characterized in that - the transmission colour effect of the first reflection-enhancing coating determines the second colour; or - the transmission colour effect of the first reflection-enhancing coating together with a reflection colour effect of the second reflection-enhancing coating and / or with at least one of the light-transmissive colour layers determine the second colour; or - a reflection colour effect of the second reflection-enhancing coating and / or the colour effect of at least one of the light-transmissive colour layers determine(s) the second colour.

12. Security element according to at least one of Claims 1 to 11, characterized in that the first and second relief structures reflect at least regionally incident parallel light into different angle ranges, wherein the two different angle ranges preferably do not overlap and are separated from one another by preferably more than 3°, particularly preferably more than 10°.

13. Security element according to at least one of Claims 1 to 12, characterized in that the embodiment of the higher-level relief structure, in particular the alignment of the micromirrors of the higher-level micromirror arrangement, and / or the embodiment of the lower-level relief structure, in particular the alignment of the micromirrors of the lower-level micromirror arrangement, are / is subject to location-dependent variation in order to produce a respectively predefined motif, in particular a motif with a three-dimensional appearance or a movement motif.

14. Data carrier comprising an optically variable security element according to at least one of Claims 1 to 13.

15. Method for producing an optically variable security element comprising a reflective surface region exhibiting at least two optically variable effects which are discernible from different viewing directions and appear with different colours, wherein - a carrier is provided, the surface area of which defines a plane and a z-axis perpendicular thereto, - the carrier is provided with a reflective surface region (20) containing two independent relief structures, which are arranged at different height levels in the z-direction and form a lower-level relief structure (24) and a higher-level relief structure (34), - the higher-level relief structure (34) is provided with a first reflection-enhancing coating (36) following the course of the relief and the lower-level relief structure (24) is provided with a second reflection-enhancing coating (26) following the course of the relief, - the two relief structures (24, 34) are embodied so as to overlap in a feature region, - the first reflection-enhancing coating (36) in the feature region is embodied with a wavelength-dependent reflection and transmission in the visible spectral range, such that - the higher-level relief structure (34), - by virtue of the reflection colour effect of the first reflection-enhancing coating (36), - exhibits a first optically variable effect in a first colour, and - the lower-level relief structure (24), through the first reflection-enhancing coating (36), exhibits a second optically variable effect, which is exhibited in a second, different colour by virtue of the transmission colour effect of the first reflection-enhancing coating (36).