Optically variable representation element

Abstract

The invention relates to an optically variable representation element (12) having at least one reflective surface region (24), having at least two partial regions visible to the naked eye, which display different colours at least in some regions when viewed in reflected light. According to the invention, the at least one reflective surface region (24) is coated at least in some regions with a surface-conforming interference layer structure (32) and the reflective surface region (24) contains a micro-relief structure (26) in a first and in a second partial region, which micro-relief structure produces a dynamic effect and is formed with a plurality of micro-relief structure elements (34, 36). The micro-relief structure (26) of the first partial region and / or the micro-relief structure (26) of the second partial region is further provided at least in some regions with a colour-modifying nanostructure (38), which is formed by at least one subwavelength structure. In addition, in the first and / or second partial region, the colour effect of the interference layer structure is modified by the colour-modifying nanostructure (38) such that the first and / or the second partial region shows at least one of the different colours due to the combined effect of the interference layer structure (32) and the colour-modifying nanostructure (38).

Description

[0001] Optically variable display element

[0002] The invention relates to an optically variable display element with a multi-colored reflective surface area, which can be used as a security element for protecting valuables, a data carrier with such a display element and a method for producing such a display element.

[0003] 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. Security elements with a viewing-angle-dependent or three-dimensional appearance play a special role in authenticity protection, 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. For example, they display a different color or brightness impression and / or a different graphic motif depending on the viewing angle.

[0004] Since the 1980s, holographic gratings with a period typically between 600 nm and 1500 nm have been used as security features in banknotes and ID cards. For decades, they have shaped the visual appearance of these documents and ensured their forgery security. Periodic structures can be used for their implementation. One- or two-dimensional periodic structures ("hologram gratings") with periods of approximately 400 nm to approximately 5 μm typically exhibit colorful "rainbow colors."

[0005] Special optically variable effects can be created by varying, for example, the grating period and / or azimuth angle. The parameters can be varied continuously or at least in small steps (e.g., to realize pumping effects). Even larger structures exhibit diffraction effects, but in practice these are only observable with largely directed illumination. In contrast to gratings with a symmetrical profile (sine-wave gratings, rectangular gratings), blaze gratings have an asymmetrical profile (particularly sawtooth profiles). This allows, for example, more intensity to be diffracted specifically into the +1st diffraction order than into the -1st diffraction order, allowing asymmetric images to be created.

[0006] In recent years, however, the counterfeit security of embossed holograms, which are based on the physical effect of diffraction, has noticeably decreased due to the increasing availability of equipment for their production, so that they can hardly be used anymore for the primary protection of valuable documents.

[0007] Instead of holograms, security features based on the use of non-diffracting microrelief structures, such as micromirrors or microlenses, are therefore preferred. Such features are significantly more difficult to counterfeit and give the security documents equipped with them an unusual and novel appearance combined with a high level of dynamic appeal that quickly attracts attention.

[0008] Highly effective in this context and further increasing counterfeit security is the use of multilayer thin-film elements whose color impression changes for the observer with the viewing angle (hereinafter referred to as the color-shift effect). The color-shift effect in such thin-film elements is based on viewing-angle-dependent interference effects caused by multiple reflections in the various sublayers of the element. The path difference of the light reflected by the various layers depends, on the one hand, on the optical thickness of a dielectric spacer layer, which determines the distance between a semitransparent absorber layer and a reflector layer, and, on the other hand, varies with the respective viewing angle.Since the path difference is on the order of the wavelength of visible light, the extinction and amplification of certain wavelengths results in an angle-dependent color impression for the observer. By appropriately selecting the material and thickness of the dielectric spacer layer, a variety of different color-shift effects can be created. With an increasing number of layers, the color becomes spectrally "purer," meaning the interference peak becomes narrower. Typical examples are three-layer structures with an absorber, dielectric, and reflector, e.g., absorber Gr (approx. 5 nm), dielectric SiCh (200-500 nm), reflector Al (approx. 50 nm).

[0009] The surface and tilt colors (and, accordingly, the perceived color shift effect) of a multilayer thin-film element are uniquely determined by the thickness of the dielectric spacer layer and the refractive index of the dielectric material. This means that the colors of a multilayer thin-film element cannot be arbitrarily selected independently of one another for different lighting situations / tilt angles, but are intrinsically determined. Physically, this limits the number of achievable color shifts, i.e., color changes (e.g., gold / green; blue / red; magenta / green).

[0010] Furthermore, (transparent) security elements with multilayer thin-film elements are known. These elements appear in a first color when viewed in reflected light, i.e., in reflection, and in a second color when viewed in transmitted light, i.e., in transmission. The publication WO 2011 / 082761 A1 describes a thin-film element with a multilayer structure that appears gold when viewed in reflected light and blue when viewed in transmitted light. The multilayer structure is based on two semitransparent mirror layers and a dielectric spacer layer arranged between the two mirror layers.

[0011] Micromirrors are facets that reflect incident light essentially according to the laws of ray optics. They have dimensions that are significantly (approximately a factor of 10) larger than the wavelength of light, especially dimensions of about 5 pm or larger. This makes their reflection behavior largely achromatic. The micromirrors can be arranged periodically ("sawtooth gratings") or aperiodically. Fresnel structures can also consist entirely or partially of micromirror structures or be approximated by micromirrors. Fresnel structures are created from arbitrarily shaped surfaces by cutting them with a constant height. For example, micromirrors can also have an arcuate cross-sectional shape and a three-dimensional shape.

[0012] Micromirrors are often rectangular in shape, but honeycomb (hexagonal) or arbitrarily shaped micromirrors ("mosaic") are also possible. The surfaces of the micromirrors are preferably flat with a defined inclination. At least the most steeply inclined micromirrors have a profile pitch that is significantly greater than the wavelength (> 1 pm). The inclinations of the steepest micromirrors are typically in the range of 20°, and in special designs even in the range of 10°. The reflectance or the color of the reflected light of such microrelief structures can be determined by the coating, which can be, for example, a simple surface-conformal metallization such as aluminum or a high-index coating such as ZnS or in the form of a multilayer interference layer structure.

[0013] The generation of viewing-angle-dependent effects using micromirrors coated with a multilayer interference layer structure is known, for example, from the publications WO 2007 / 079851 A1, WO 2011 / 066991 A2, and WO 2011 / 066990 A2. The color changes that can be generated with an interference layer structure for such security features are limited. The color transition occurs gradually over a larger angular range. Furthermore, the local registration between the embossing responsible for the dynamic effects and the interference layer structure is generally determined by the precision of the pressure with which an etching resist or wash ink can be applied to the embossed structures. In other words, it is not possible to precisely imbue a motif represented by embossed structures with a specific color. Temporal and spatial synchronization of the dynamic effects and the color is also not possible.Accordingly, the color change caused by the interference layer structure occurs gradually when the optically variable security element is tilted, regardless of any dynamic effects.

[0014] Some time ago, more complex, optically variable security elements were proposed that feature two relief structures arranged at different heights, each provided with a colored coating (see WO 2020 / 011390 A1, WO 2020 / 011391 A1, and WO 2020 / 011391 A2). The colored coating of the higher relief structure is either structured as a grid or provided with recesses, so that when viewing the security element, the colored coating of the lower relief structure appears in the spaces between the grids or recesses.

[0015] However, the production of the foil structure consisting of two embossing planes overlapping in the z-direction has proven to be very complex. The manufacturing costs are correspondingly high. Furthermore, the embossings assigned to different colors (on the two overlapping embossing planes) can only be registered to a limited extent. Typical tolerances are many tenths of a millimeter. Parallel to microstructures, optically variable security features have been developed for many years. These are based on the use of nanostructures with typical sizes in the sub-wavelength range, i.e., smaller than 400 nm. One- or two-dimensionally structured nanostructures are used in the form of regular sub-wavelength gratings or in the form of irregular structures, e.g., elevations or depressions irregularly arranged on a base surface.

[0016] Subwavelength structures are so small that no first- or higher-order diffraction effects occur at normal incidence. The structure sizes are smaller than the wavelength of the source. Different effects are utilized in different structures: Subwavelength gratings (also referred to in the literature as "zeroth-order gratings") are regular one- or two-dimensional gratings with periods in the subwavelength range (< 400 nm) and produce colors in the specular reflection ("zeroth-order"). Subwavelength gratings with metallic coatings utilize plasmon effects to generate colors. In gratings with dielectric (especially high-index) coatings, colors are created by a different effect, namely the resonant excitation of polaritons. The profile shape can be rectangular or sinusoidal, for example.

[0017] Moth-eye structures are subwavelength structures that allow a nearly reflectionless transition of light from one medium to another. In dielectric materials, such structures act as an "anti-reflection layer." The structures can be arranged regularly (periodically) or irregularly and can have a tapered cross-section or, for example, binary rectangular structures. If the moth-eye structures are metallically vapor-deposited, they appear very dark, particularly black.

[0018] In nanostructures regularly arranged in a one- or two-dimensional lattice, resonance effects, such as plasmon excitations, typically lead to color phenomena. The transmission, reflection, and absorption of the light incident on the grating depend spectrally on parameters that characterize the subwavelength grating, such as period, depth, profile shape, type of coating, and coating thickness. In particular, the period can be used to adjust a specific color impression. The colors generated in this way and perceived by an observer are generally less brilliant and optically variable than the color phenomena produced by diffraction at a holographic grating. Rather, they tend to be pastel-colored and exhibit a more limited color space.

[0019] Furthermore, they can be observed over a wider angular range without any significant color change. Viewed without a polarizer, the color impression of plasmon resonance-based subwavelength gratings is typically very similar to almost identical, even when the rotation angle in the structural plane is changed, i.e., independent of the azimuth angle.

[0020] The counterfeit security of nanostructures is primarily due to the fact that their production requires high-resolution equipment and processes, such as those used in electron beam lithography. Compared to embossed holograms, the nanostructures to be created are an order of magnitude smaller. Furthermore, the various molding steps for foil production, which primarily occur in the embossing tool manufacturing process, must be carried out with predictable shape fidelity so that the structures embossed on the foil can be seen by the viewer, for example, in the desired color.

[0021] The measures described so far for generating color representations for security features based on structural colors therefore work particularly well when superimposed with microstructures. Such structures are more complex and difficult to manufacture than the subwavelength gratings known in the prior art. The microstructures make an additional contribution to suppressing diffraction phenomena, since the diffraction condition—i.e., when an incident light beam is diffracted toward the observer—also depends on the orientation of the microsurface on which a subwavelength grating is placed. Furthermore, the microstructures provide the dynamics, for example in the form of a motion and / or 3D effect, while the subwavelength gratings provide the corresponding colors.

[0022] An optically variable display element with a reflective surface region, which, when viewed in reflected light, generates a three-dimensional display for at least two different viewing directions using reflective facets, which at least in some regions each has a color generated by subwavelength structures, is known, for example, from WO 2022 / 242912 A1. Finally, it is known, for example, from WO 2024 / 008238 A1, to cover a color-generating or color-effect-generating subwavelength structure in some regions with a spaced-apart translucent color layer to provide an alternative color impression.

[0023] Based on this, the invention is based on the object of providing optically variable display elements with an attractive visual appearance, which have a large color space available for displaying dynamic motifs and which ideally also have a high level of security against counterfeiting.

[0024] The invention is defined in the independent claims. The dependent claims relate to preferred developments.

[0025] In a first aspect, the invention relates to an optically variable display element with at least one reflective surface region with at least two partial regions visible to the naked eye, which, when viewed in reflected light, display different colors at least in some regions, wherein the at least one reflective surface region is coated at least in some regions with a surface-conformal interference layer structure, the at least one reflective surface region in the first and the second partial region each contains a microrelief structure which creates a dynamic effect and is formed with a plurality of microrelief structure elements, the microrelief structure of the first partial region and / or the microrelief structure of the second partial region is / are provided at least in some regions with a color-modifying nanostructure which is formed by at least one subwavelength structure,and in the first and / or second partial region, the color effect of the interference layer structure is modified by the color-modifying nanostructure, so that the first and / or second partial region shows / show at least one of the different colors due to the combined effect of the interference layer structure and the color-modifying nanostructure.

[0026] According to the invention, the color impressions of an interference layer structure are modified via a locally different, or locally present or absent, color-modifying nanostructure. In combination with an underlying light-directing microrelief structure, a viewer perceives different image components in different colors from specific viewing directions. Such a design also ensures precise spatial registration between colors and embossed motifs, which also allows for abrupt and distinct color changes upon tilting. Furthermore, a large color space is opened up for the representation of motifs. In particular, new color changes and color combinations are enabled compared to known color changes that can be generated with interference layer structures. Furthermore, this concept permits synchronization of color and dynamics, so that changes in the displayed motif can occur simultaneously with changes in the colors upon tilting.

[0027] It is understood that the sub-areas do not have to be contiguous, but can also consist of individual, for example pixel-shaped sub-areas, which as such can be designed in at least one dimension, in particular with an extension below the resolution limit of the eye.

[0028] In an advantageous embodiment, the reflective surface region, when viewed in reflected light, generates a representation for at least two different viewing directions, wherein the representations at least partially overlap and, at least in some regions, have different colors in the overlapping region. The microrelief structure of the first sub-region and the microrelief structure of the second sub-region each generate one of the representations for the viewer, and the first and second sub-regions at least partially overlap one another, wherein the first and / or second sub-region further exhibits at least one of the different colors of the representations due to the combined effect of the interference layer structure and the color-modifying nanostructure.To overlap the subregions, the first and second subregions are advantageously nested within one another. For this purpose, the subregions are preferably formed by narrow, alternating strip-shaped subregions arranged next to one another, or by small subregions nested within one another in two dimensions. The subregions advantageously have a dimension of less than 300 µm in at least one direction, in particular of 100 µm or less, in particular of 50 µm or less. In principle, nesting the subregions or the motifs created thereby makes it more difficult for a counterfeiter to replicate them.

[0029] Particularly preferably, the microrelief structure of the first partial region and / or the microrelief structure of the second partial region is coated with the surface-conformal interference layer structure in the regions which are of nanoscale smooth design, i.e. which are not provided with a (color-modifying or color-generating) nanostructure, in order to produce the different colors.

[0030] In the areas that are not coated with the surface-conformal interference layer structure, the microrelief structure of the first sub-area and / or the microrelief structure of the second sub-area is advantageously provided with a color-generating nanostructure, in particular a sub-wavelength structure that displays a color generated essentially on the basis of plasmon resonance, in order to generate the different colors of the images, wherein the color-generating nanostructure is coated in particular with a metallization or a layer of high-refractive-index material.

[0031] The dynamic effect created by the micro-relief structure advantageously produces a movement effect, in particular a bounce effect, a morph effect, a pump effect, a flip effect, a stereographic 3D effect and / or a three-dimensional representation with a surface that protrudes and / or recedes for the observer compared to the actual spatial shape of the surface area.

[0032] The representation created for the viewer with a protruding and / or receding surface is understood here in particular to mean that the subarea is perceived as a continuously curved surface. The curved-appearing representations in the present sense imitate a curvature by simulating the reflective behavior of a curved surface. This indirectly creates an impression of depth or a 3D impression. This impression can therefore also be described as a relief-like representation.

[0033] Particularly preferably, the interference layer structure is designed, at least in some regions, such that the hue of the color generated by the interference layer structure and / or the color generated by the interference layer structure in conjunction with the color-modifying nanostructure is color-stable when tilted up to 30° and preferably up to 45° from a vertical view. While the display element can thus exhibit abrupt color changes (caused by the microrelief structure) when tilted, no continuous color changes occur, or only to a limited extent, as is known from conventional multilayer interference layer systems.

[0034] The interference layer structure is advantageously designed at least in regions such that the color angle h when tilted up to 30° and preferably up to 45° from a vertical view a) starting from a color in a vertical view with a color angle h between 0° and 60° changes by less than 60°, preferably by less than 30°, b) starting from a color in a vertical view with a color angle h between 50° and 80° changes by less than 30°, preferably by less than 15°, c) starting from a color in a vertical view with a color angle h between 75° and 105° changes by less than 30°, preferably by less than 15°, d) starting from a color in a vertical view with a color angle h between 100° and 180° changes by less than 80°, preferably by less than 40°, e) starting from a color in a vertical view with a color angle h between 170° and 220° by less than 50°, preferably by less than 25°,f) starting from a colour shade in vertical view with a colour angle h between 210° and 300° changes by less than 90°, preferably by less than 45°, or g) starting from a colour shade in vertical view with a colour angle h between 290° and 10° changes by less than 80°, preferably by less than 40°.

[0035] For a color angle h that can be assigned to a color tone with a color angle that falls within two of the color angle ranges specified above for the vertical view, the color angle h changes upon tilting preferably by a maximum of the smaller of the values ​​specified for this purpose. - In an advantageous embodiment, the interference layer structure is formed by a multi-layer structure of dielectric and / or metallic layers, preferably by a three-layer thin-film element. As a three-layer thin-film element, in particular color-shifting systems with a structure of semi-transparent metal layer / dielectric layer / metallic reflector layer or a structure of semi-transparent metal layer / dielectric layer / semi-transparent metal layer come into consideration. The material for the reflector layer can be, for example, aluminum, copper, titanium, and the dielectric material for the dielectric layer can be, for example,ZnS, MgF2, TiCh, AI2O3, HfCh and as material for the absorber layer e.g. chromium, titanium, aluminum, nickel can be used.

[0036] Furthermore, it is also possible to achieve interference effects by combining dielectric and / or metallic layers. Optionally, a metallic layer with an overlying dielectric multilayer consisting of dielectric layers with alternating low and high refractive indices, or a metallic layer with an overlying multilayer consisting of semitransparent metallic layers and dielectric layers, can be applied to the microrelief structure. Preferably, the high-index layer is made of, for example, ZnS or TiO2, and the low-index layer is made of, for example, a polymer, SiO2, or MgF2.

[0037] Particularly advantageously, the interference layer structure is a three-layer thin-film element with a structure of semitransparent metal layer / dielectric layer / metallic reflector layer, with the optical thickness of the dielectric layer being a maximum of 250 nm, preferably a maximum of 200 nm (the "optical thickness" here is understood to be the product of the refractive index and the actual layer thickness), and the three-layer thin-film element, in a vertical view, exhibits a reflection maximum only at the short-wave end of the visible spectrum. Advantageously, the optical thickness of the dielectric layer is a maximum of half the wavelength of blue light.

[0038] Likewise advantageously, the interference layer structure contains a high-index dielectric having a refractive index of more than 1.8, preferably more than 2.0, and particularly preferably more than 2.3, across the entire visible spectrum or at least in part of the visible spectrum. In a further advantageous embodiment, the interference layer structure is a two-layer color mirror consisting of a reflective metal layer and an ultra-thin absorber layer made of silicon, a silicon alloy, or SiOx with x < 1 arranged on the metal layer.

[0039] It is understood that different layers or layer systems can be used for the interference layer structure in certain sections.

[0040] The microrelief structure is preferably formed by a micromirror arrangement with microrelief elements in the form of directionally reflecting micromirrors, in particular by a micromirror arrangement with flat micromirrors or by a micromirror arrangement with micromirrors which have a curved profile or a varying, sectionally constant inclination in one or two directions, wherein the micromirrors form in particular a periodic or aperiodic sawtooth grating, by a Fresnel structure, by an arrangement of concave / convex curved microelements and / or by a freeform surface.

[0041] Particularly preferably, the microrelief structure elements of the microrelief structure are formed by directionally reflecting micromirrors, in particular by micromirrors with a linear dimension between 3 μm and 100 μm, preferably between 5 μm and 50 μm. The micromirrors can in particular have a triangular, square, rectangular, hexagonal, or other polygonal base area. The height of the micromirrors is preferably less than 15 μm, more preferably less than 10 μm.

[0042] The subwavelength structure of the color-modifying and / or color-generating nanostructure is advantageously formed by structures with a lateral size between 50 nm and 450 nm, in particular between 100 nm and 300 nm, and / or a depth between 20 nm and 450 nm, in particular between 100 and 300 nm.

[0043] In an advantageous embodiment, the subwavelength structures of the color-modifying and / or color-generating nanostructure are formed by one-dimensional gratings, which may also have a polarizing effect. In another, equally advantageous embodiment, the subwavelength structures of the color-modifying and / or color-generating nanostructure are formed by two-dimensional gratings, in particular with rectangular, square, hexagonal, or parallelogram-shaped grating symmetry. The gratings have a period length in at least one direction between 100 nm and 600 nm, in particular between 50 nm and 450 nm.

[0044] Since such designs exhibit a more color-intensive effect, at least in some viewing situations, than, for example, subwavelength structures formed by gratings with square symmetry, a design of the subwavelength structures with hexagonal lattice symmetry is preferred. In a hexagonal lattice, the distances between the individual structures ("nanodots" or "nanoholes") and their neighbors are equal in all spatial directions, whereas in a square lattice, for example, the diagonally arranged neighbors are spaced further apart than those positioned on the square lattice sites.

[0045] Crossed sine-wave gratings, crossed rectangular gratings (binary structures), hexagonal grating structures, or profile shapes with concave and / or convex sections are particularly suitable for subwavelength structures. Periodic arrangements of nanoholes or nanodots with any contour shape can also be used. The color effect of the nanostructure depends on whether the structures are in the form of elevations ("nanodots") or depressions ("nanoholes").

[0046] In addition to regular arrangements, the use of irregularly arranged structures (nanodots or nanoholes) is also possible. These can, for example, be randomly distributed or quasi-periodically arranged, in particular in such a way that they are shifted from a given lattice position by a random value in a random direction (so-called jitter), and can be characterized by the parameters lateral extent, outline shape, depth, profile shape (e.g., binary or other shapes with concave and / or convex sections). In addition, the rotation of the structures can vary locally, as can their lateral extent, depth, and profile shape. The structures can be arranged completely irregularly, with the areal density kept approximately constant. In this case, too, the rotation, lateral size, depth, and profile shape of the nanodots / nanoholes can vary locally.In principle, structures such as those described in the documents EP 3367140 A1 and EP 3401 712 A1 are also possible, the disclosure content of which is incorporated into the present application.

[0047] For generating the different colors, preferably at least two subwavelength structures are provided which differ in a structural parameter influencing the color, wherein the structural parameter comprises at least one of the following parameters of the subwavelength structure: period length, depth and / or profile shape of the structures of the subwavelength structure.

[0048] It has been found to be advantageous to arrange the subwavelength structures for the different colors registered to the microrelief structure elements of the microrelief structure of the reflective surface area, so that each microrelief structure element is only occupied by a specific type of subwavelength structure.

[0049] In an advantageous development, the microrelief structure elements are formed by micromirrors, and one or more of the structural parameters of the subwavelength structures that influence the color exhibit a variation as a function of a parameter determining the orientation of the micromirrors, in particular as a function of the mirror pitch or as a function of the azimuth angle. This makes it possible, for example, to create a color-shift effect upon tilting (variation as a function of the mirror pitch) or a color change upon rotation about the z-axis (variation as a function of the azimuth angle).

[0050] For example, all micromirrors oriented upwards ("upwards" is understood here to mean that the display element is upright in front of the viewer's eyes) can be equipped with a subwavelength structure that results in a first color impression, and all micromirrors oriented downwards can be equipped with a different subwavelength structure or without a subwavelength structure, so that these micromirrors illuminate in a different second color impression. When tilted about the corresponding axis, depending on the tilt angle, either only micromirrors in the first color or only micromirrors in the second color illuminate, resulting in an abrupt color change in between.

[0051] According to a special design variant, the mirror orientations of the microrelief structure can be randomly selected and assigned a different subwavelength structure depending on the orientation of the micromirrors (e.g., whether the mirror normal has an upward or downward tilt component). This results in a view that is equally bright (but appears "noisy" on a small length scale) across virtually all tilt angles, but exhibits an abrupt color change upon tilting. The subwavelength structure can also be selected in a different way depending on the mirror orientation. A color change then occurs accordingly upon a different (predefined) movement of the display element. For example, the respective subwavelength structure can also be selected depending on the azimuth angle of the micromirrors, thus leading to a color change upon rotation of the display element in its plane.

[0052] The colors visible to a viewer when viewing the display element can, in particular, include mixed colors resulting from a color mixture of colors in pixel-shaped sub-areas with dimensions below the resolution limit of the human eye. The colors of the pixel-shaped sub-areas are each generated by a specific type of sub-wavelength structure characteristic of that color. The surface areas of the sub-wavelength structure in the pixel-shaped sub-areas are selected to produce the desired mixed color.

[0053] In an advantageous development of the invention, it is provided that the surface extension of the display element defines a z-direction perpendicular thereto, wherein the reflective surface area contains a primary structure in the form of a first embossing lacquer layer with a first embossed structure, which is formed by a first of the microrelief structures, the first embossing lacquer layer is partially covered by a secondary structure, so that on the first embossing lacquer layer there are overlapping areas with a secondary structure and free areas without a secondary structure, wherein the secondary structure is formed by the second of the microrelief structures, and the primary structure and / or the secondary structure is / are provided at least in regions with the color-modifying nanostructure,so that the color-modifying nanostructure is arranged in the overlapping areas on the secondary structure and / or in the free areas on the primary structure. In another advantageous development of the invention, the surface area of ​​the display element defines a z-direction perpendicular thereto, wherein the reflective surface area contains two structures arranged at different heights in the z-direction, the structures each formed by one of the microrelief structures and provided with a color coating, wherein at least one of the color coatings is formed by the interference layer structure, the two structures overlap in the reflective surface area, and the color coating of the higher-lying structure in the reflective surface area is designed as a regular or irregular grid with grid elements and grid spaces.so that in the reflective surface area, for an observer from at least one viewing direction, the color coating of the deeper structure appears through the grid spaces of the color coating of the higher relief structure, and the structure provided with the interference layer structure or at least one of the structures provided with the interference layer structure is at least partially provided with the color-modifying nanostructure.

[0054] A first of the color coatings is advantageously formed by the interference layer structure, and a second of the color coatings is formed by a metallization or another interference layer structure. Advantageously, the structure provided with the metallization is provided with a color-generating nanostructure.

[0055] The display element is advantageously a security element for securing valuables, in particular a security thread, a tear-off thread, a security tape, a security strip, a patch or a label for application to or incorporation into a security paper, value document or the like. The invention also includes a method for producing an optically variable display element, in particular of the type described above, in which at least one reflective surface area is produced in the optically variable display element with at least two partial areas visible to the naked eye, which, when viewed in reflected light, display at least slightly different colors, wherein the at least one reflective surface area is provided by, in a first and in a second partial area, which at least partially overlap one another,a microrelief structure is formed in each case with a plurality of microrelief structure elements, which creates a dynamic effect, wherein the microrelief structure of the first partial region and / or the microrelief structure of the second partial region is / are overlaid at least in regions with a color-modifying nanostructure, wherein the color-modifying nanostructure is formed by a subwavelength structure, the reflective surface region is coated at least in regions with a surface-conforming interference layer structure, wherein in the first and / or second partial region, the color effect of the interference layer structure is modified by the color-modifying nanostructure, so that the first and / or second partial region shows / show at least one of the different colors due to the combined effect of the interference layer structure and the color-modifying nanostructure.

[0056] The display element according to the invention can, in particular, be produced in such a way that a further, embossed security feature is produced in the same work step. This can, in particular, be an optically variable security feature, such as a hologram, a noisy or non-noisy sawtooth structure (for generating tilt images, kinematic effects, 3D representations, etc.), microlens or micro concave mirror arrangements or microlens or micro concave mirror images. In a further aspect, the invention relates to an optically variable display element with at least one multicolored reflective surface area which, when viewed in reflected light, produces at least one display, wherein the at least one display has different colors at least in some regions, wherein the at least one multicolored reflective surface area contains a microrelief structure which has a dynamic effect,in particular, a stereographic 3D effect and / or a three-dimensional representation is created with a surface that projects forward and / or backward relative to the actual spatial shape of the surface area and is formed with a plurality of microrelief structure elements, the reflective surface area is coated at least in regions with a surface-conforming interference layer structure, the microrelief structure is provided at least in regions with a color-modifying nanostructure formed by at least one subwavelength structure, and the color effect of the interference layer structure is modified by the color-modifying nanostructure, so that the multicolored reflective surface area displays at least one of the different colors of the representation due to the combined effect of the interference layer structure and the color-modifying nanostructure.

[0057] In an advantageous embodiment, the colors visible to a viewer when viewing the display element contain mixed colors that are created by a color mixture of colors of pixel-shaped sub-areas with a dimension below the resolution limit of the human eye, wherein at least two of the colors of the pixel-shaped sub-areas are each generated by a specific type of sub-wavelength structure that, in interaction with the interference layer structure, is characteristic of this color.

[0058] According to a further advantageous embodiment of this aspect, the display element displays a motif, depending on the viewing angle, with at least one curve representation, which is visible as a default curve in a central position from a first viewing direction within a display area, and which moves away from the central position in different directions when the security element is tilted about two different predetermined axes within the display area. The reflective surface area in the display area is provided with a plurality of reflective, planar micromirrors to display the curve representation, and is provided with a plurality of reflective, planar micromirrors in a background area to display the background area, wherein the micromirrors of the display area and / or the micromirrors of the background area are provided with the color-modifying nanostructure.

[0059] In all aspects of the invention mentioned, the microrelief structural elements can be present in the following advantageous designs:

[0060] Micromirrors, such as those described, for example, in WO 2007 / 079851 A1, WO 2011 / 066991 A2, and WO 2011 / 066990 A2, can be used as microrelief elements of the microstructure, the disclosure content of which is incorporated into the present application in this respect. Sawtooth gratings with a grating period between 2 μm and 300 μm, preferably between 3 μm and 100 μm, particularly preferably between 5 μm and 50 μm, can also be used as micromirrors, with the lateral dimension in the longitudinal direction being up to a few millimeters.

[0061] Fresnel-like structures can be used in some designs. They are created, for example, by dividing a surface relief to be simulated into segments using horizontal cuts, then removing the internal volume segments and lowering the segments containing part of the surface to the ground plane. Vertical cuts can also be used instead of horizontal cuts. The cuts are preferably placed equidistantly, but variable spacing between adjacent cuts is also possible in principle.

[0062] Alternatively, in some designs, concave or convex microelements can be used, which are advantageously arranged in a regular manner. Their lateral dimensions can be between 5 pm and 300 pm, preferably between 10 pm and 100 pm, particularly preferably between 20 pm and 50 pm. The concave / convex microelements can be arranged one-dimensionally and represent a periodic arrangement of groove- or rib-shaped elements. These can preferably also be arranged in a two-dimensional grid, whereby different grid types can be used, e.g. square, rectangular, diamond-shaped, hexagonal or parallelogram-shaped grids. The individual microelements can completely fill the area of ​​the feature, for example in the sense of a Wigner-Seitz cell.However, there may also be gaps between the individual microelements, for example when circularly defined concave or convex spherical segments are arranged on a hexagonal lattice.

[0063] Micromirrors, such as those described, for example, in the pending German patent applications DE 102024128848.5 and DE 102025 107278.7, the disclosure content of which is incorporated into the present application, can also be used as microrelief elements of the microstructure. In particular, the micromirrors can be designed with a constant inclination in a first direction and a (continuous) curvature in a second direction. Alternatively, the micromirrors can be present with a (continuous) curvature in two directions that are perpendicular to each other. The curved profile can be designed as a convex profile, a concave profile, or a partially convex and partially concave profile. Instead of a curved profile, the micromirrors can also have a varying, partially constant inclination.

[0064] Any freeform surface can also be used as a microrelief structure, with topography varying locally on a scale of a few to a few hundred micrometers. Depending on the desired optical effect, the surface sections inclined in certain spatial directions can be evenly distributed. Alternatively, certain directions can be emphasized at the expense of others. In this way, for example, matte effects can be created by radiating the incident light evenly or by preferentially directing it into predetermined solid angle ranges. A combination of the previously mentioned microrelief structures in individual surface areas of the display element is also conceivable and can be used advantageously.

[0065] In all aspects of the invention mentioned, the color-modifying and / or color-generating nanostructures can be present in the following advantageous designs:

[0066] The shape of individual structures of the subwavelength structure, present as nanodots or nanoholes, in plan view can be circular, elliptical, square, rectangular, hexagonal, cross-shaped, star-shaped, approximately circular, elliptical, square, rectangular, hexagonal, cross-shaped, star-shaped, and / or generally formed with a polygonal outline. Elliptical and rectangular nanodots / nanoholes typically exhibit different resonance frequencies in the longitudinal and transverse directions, so that they are preferentially excited by light of different wavelengths in these two directions. Therefore, the spectral absorption, reflection, and transmission properties for nanodots / nanoholes of these geometries generally depend on the polarization state of an exciting light wave with respect to the orientation of the nanodots / nanoholes.The color effect of the nanostructure depends on whether the structures are in the form of elevations ("nanodots") or depressions ("nanoholes"). An SEM image of a subwavelength structure according to the invention with a red or magenta color effect, in which the nanodots are arranged in a lattice with hexagonal symmetry, is shown in Fig.

[0067] 11(a). Fig. 11(b) shows an SEM image of another subwavelength structure according to the invention with a green color effect.

[0068] The individual structures of the subwavelength structure, present as nanodots or nanoholes, can exhibit one of the following profile shapes in cross-section: binary ("Manhattan"), sinusoidal or quasi-sinusoidal, conical or truncated cone. The profile of the structures in cross-section can be approximated by a Gaussian function or any other continuous function. Depending on the fill factor, a constant or approximately constant profile can also result between the nanodots / nanoholes. The shape of regular ones in a one- or two-dimensional lattice or irregularly arranged nanodots / nanoholes can vary locally, e.g., with regard to the profile in cross-section or the shape in plan view.

[0069] The nanostructures can also significantly increase or decrease the brightness of the interference layer structure or metallization. In extreme cases, nearly black or white can be produced. Randomly arranged structures with a high depth-to-width ratio are particularly suitable for producing very dark colors.

[0070] In all aspects of the invention mentioned, the microrelief structures and the color-modifying and / or color-generating nanostructures can be present in the following advantageous designs:

[0071] The microrelief structures and the subwavelength structures can each be present over the entire surface in certain motif areas.

[0072] The representations can each comprise a motif and a background. In at least one of the representations, the color effect of the motif and / or the background can be created by the combined effect of the interference layer structure, which is particularly color-stable, with at least one sub-wavelength structure. The motifs and / or the background within a view can each be formed with different colors and / or can each be multicolored.

[0073] The microrelief structure elements and the subwavelength structures can each be present in a plurality of pixels that are not resolvable with the naked eye. The pixels can have any shape, e.g., square, rectangular, hexagonal, or elongated (quasi-one-dimensional). The pixels are preferably arranged over the entire surface, although the pixels can also be present in different pixel shapes. The dimensions of the pixels are preferably below the resolution of the human eye and are, at least in one direction, less than 300 pm, preferably less than 100 pm, particularly preferably less than 50 pm. The microrelief structure elements within a pixel are preferably identical. In the case of micromirrors, these preferably have the same orientation (mirror pitch and azimuth angle) within a pixel.

[0074] The subwavelength structures within a pixel preferably have the same structural parameters and fill the pixel homogeneously, resulting in a uniform color. Over a larger area (motif area), the structural parameters of the nanostructures can be constant (e.g., a single-color vaulted motif) or spatially vary (e.g., a color gradient or a motif with several different colors). A variation in color intensity can be achieved by changing the pixel size and / or pixel density.

[0075] Preferably, the pixels of the microrelief structures and the pixels of the subwavelength structures are correlated with each other and, for example, are located congruently one above the other. In this case, the microrelief structure elements of a specific orientation are connected to subwavelength structures of a specific color, so that the light reflected by the microrelief structure elements in a given solid angle range exhibits a color determined by this subwavelength structure (possibly in conjunction with the interference layer structure).

[0076] By continuously varying one or more of the structural parameters characterizing a subwavelength structure, a color gradient can be realized across the microrelief structure. Alternatively, a color gradient can also be generated using rasterization. The color gradient can optionally be synchronized with a dynamic effect created by the microrelief structure, such as a scrolling effect.

[0077] While in the case of flat mirrors (to avoid mixed colors and create a uniform color effect) the entire mirror surface is expediently covered evenly with the subwavelength structures, micromirrors with a curved profile or micromirrors with a varying, sectionally constant inclination have the property that the light is reflected in a different direction depending on the inclination of the mirror surface. In other words, a single micromirror has a multitude of different inclinations and thus reflection directions. The multitude of inclinations can therefore advantageously be divided into two or more sections, of which at least one section contains a subwavelength structure that differs in at least one parameter influencing the color (period length, depth and / or profile shape of the structures of the subwavelength structure) and is thus endowed with a different color effect than the other sections.When tilting the display element, a color change along the curvature can be created, which is equivalent to a color flip.

[0078] In micromirrors with a curved profile, at least one of the color-influencing parameters of the subwavelength structure can exhibit continuous variation depending on the inclination along one or both directions of curvature. The continuous change in the structural parameter(s) leads to a continuous change in the color effect depending on the direction of reflection.

[0079] The display elements according to the invention can be combined with further security features. For example, the display elements can additionally comprise information in the form of patterns, characters, or codes formed by coating-free areas or areas left out in a coating within the surface area. The microrelief structure elements can also be combined with holographic or hologram-like diffraction structures, with noisy or non-noisy sawtooth structures for generating tilt images, kinematic effects, 3D representations, etc., microlens or microconcave mirror arrangements, and / or microlens or microconcave mirror images. For example, a nested combination with a hologram, in particular a true-color hologram or a kinegram, is possible.

[0080] The display elements according to the invention can also be provided with machine-readable features, in particular with incorporated phosphorescent, fluorescent, or other luminescent substances, with polarization-dependent effects, with specifically adjusted conductivity (in particular through a specifically adjusted thickness of a metallic layer), with further color-shift effects, for example based on color-shifting pigments, or with colored embossing varnish. By appropriately combining the display element according to the invention with magnetic materials, for example by incorporating magnetic layers or combining it with magnetic inks, magnetic properties can of course also be provided, which can be particularly machine-readable.

[0081] The invention also includes a data carrier with a display element of one of the described types. The data carrier can be, in particular, a valuable object or a valuable 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.

[0082] The data carrier can, in particular, be a paper banknote with a paper substrate, in particular cotton paper, a polymer banknote with a plastic substrate, or a film composite banknote. Of course, paper containing a proportion x of polymeric material in the range of 0 < x < 100 wt.% can also be used as the substrate for the data carrier. If the data carrier is a plastic substrate, plastic films made of polyethylene (PE), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polypropylene (PP), polyamide (PA), or single-layer composite substrates made of these plastic materials are particularly preferred.Furthermore, the substrate can be designed as a multi-layer film composite, in particular as a composite of several different plastic films (composite composite) or as a paper-film composite (film / paper / film or paper / film / paper), wherein the security element can be provided in or on or between each of the layers of such a multi-layer composite.

[0083] The invention is explained in more detail below using exemplary embodiments with reference to the accompanying drawings, which also disclose features essential to the invention. These exemplary embodiments are for illustrative purposes only and are not to be interpreted as restrictive. For example, a description of an embodiment with a large number of elements or components should not be interpreted to mean that all of these elements or components are necessary for implementation. Rather, other embodiments may also contain alternative elements and components, fewer elements or components, or additional elements or components. Elements or components of different embodiments may be combined with one another unless otherwise stated. Modifications and variations described for one of the exemplary embodiments may also be applicable to other embodiments.To avoid repetition, identical or corresponding or functionally identical elements in different figures are designated by the same reference numerals and are not explained more than once. The figures show:

[0084] Fig. 1 is a schematic representation of a banknote with an optically variable security element according to the first aspect of the invention;

[0085] Fig. 2 shows the structure of the security element of Fig. 1 schematically in cross section;

[0086] Fig. 3 shows the calculated spectral reflection curve of a color-shifting three-layer thin-film element with a dielectric layer of MgF2 for different viewing situations;

[0087] Fig. 4 shows the influence of the refractive index of the material of the dielectric layer of three-layer thin-film elements with a blue-green color in vertical view on the course of the color angle H as a function of the angle of incidence;

[0088] Fig. 5 shows the calculated spectral reflection curve of a color-shifting three-layer thin-film element with a ZnS dielectric layer for different viewing situations;

[0089] Fig. 6 the influence of the refractive index of the material of the dielectric layer of three-layer thin-film elements with a blue-red color in vertical view on the course of the color angle H as a function of the angle of incidence;

[0090] Fig. 7 shows the calculated spectral reflection curve of a color-shifting three-layer thin-film element with a dielectric layer of MgF2 for different viewing situations; - T7 -

[0091] Fig. 8 shows the influence of the refractive index of the material of the dielectric layer of three-layer thin-film elements with a violet color in vertical view on the course of the color angle H as a function of the angle of incidence;

[0092] Fig. 9 shows the calculated spectral reflection curve of a two-layer interference layer system with an ultra-thin absorber layer made of silicon for different viewing situations;

[0093] Fig. 10 shows the influence of the refractive index of the material of the dielectric layer of three-layer thin-film elements with a blue-red color in vertical view or the effect of a two-layer color mirror with a blue-red color in vertical view on the course of the color angle H as a function of the angle of incidence;

[0094] Fig. 11 in (a) an SEM image of a subwavelength structure according to the invention with red or magenta color effect, in (b) an SEM image of another subwavelength structure according to the invention with green color effect;

[0095] Fig. 12 is an SEM image of a micromirror arrangement according to the invention;

[0096] Fig. 13 in (a) to (h) the spectral curve of the reflection on three-layer thin-film elements with dielectric layers of different optical thickness with or without nanostructure for different viewing situations;

[0097] Fig. 14 in (a) to (h) the spectral curve of the reflection on three-layer thin-film elements with dielectric layers of different optical thickness with a further nanostructure or without nanostructure for different viewing situations;

[0098] Fig. 15 shows a representation of the CIEEAB color space with the color locations of the reflection spectra of selected structural colors; Fig. 16 shows the first and second views of a security element according to another embodiment of the first aspect of the invention;

[0099] Fig. 17 shows the first and second views of a security element according to a further embodiment of the first aspect of the invention;

[0100] Fig. 18 shows the first and second views of a security element according to a further embodiment of the first aspect of the invention;

[0101] Fig. 19 shows the visual appearance of a relief motif according to a second aspect of the invention with pixel-shaped sub-regions shown in an enlarged detail section;

[0102] Fig. 20 a flat motif area with a circular curve floating below the motif area in different views;

[0103] Fig. 21 schematically shows a section of a security element with structures arranged at different heights according to a further embodiment of the first aspect of the invention; and

[0104] Fig. 22 schematically shows a section of a security element with a primary and secondary structure according to a further embodiment of the first aspect of the invention.

[0105] The invention will now be explained using the example of security elements for banknotes. Figure 1 shows a schematic representation of a banknote 10 with an optically variable security element 12 in the form of an adhesive-applied transfer element. It is understood, however, 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 its own carrier layer), security threads or security strips, for example, are also possible. With reference to Fig.1, the security element 12 applied to the banknote 10 is itself very flat, but nevertheless presents a viewer from at least two different viewing directions 42, 44 with a three-dimensional representation, which creates the impression of a motif seemingly bulging out of the plane of the banknote 10. The replication of the reflective behavior of the bulging motif is achieved by directed reflection. The two three-dimensional representations overlap one another and have a different color, at least in some areas, so that a visually striking flip or tilt effect is observed when the viewing direction is changed, in which a simultaneous color and motif change of the three-dimensional representation occurs at the same location in the security element 12.

[0106] Specifically, the security element 12 can, for example, when viewed from the left side, show as the first view 20 a three-dimensional, bulging value number 14 ("50") in yellow against a flat yellow background, and when viewed from the right side, show as the second view 20' a three-dimensional, bulging star 16 in blue against a flat blue background. When changing the viewing direction or when tilting 18 the banknote 10 from left to right, the appearance of the security element 12 changes between the first view with the three-dimensional yellow value number 14 and the second view with the three-dimensional blue star 16. The two three-dimensional motifs 14, 16 also appear to the observer to overlap one another at the same location in the security element 12, as indicated by the dashed outlines 14', 16' of the respective other motif in each of the views 20, 20'.

[0107] The security element 12 thus exhibits a tilting behavior in which two different colored motifs are visible to a viewer from two viewing directions at the same location ("motif flip"), and the change in motif upon tilting is linked to a simultaneous color change. Such a tilting effect is visually appealing and easy for a user to memorize. It also provides a high level of protection against counterfeiting, since recreating the effect, for example by overprinting a reflective relief structure with translucent colors, is practically impossible with conventional printing presses due to the required registration between the reflective elements of the different motif views and the associated color.As the following description of the structure of security elements according to the invention shows, only one embossing and only one coating with an interference layer structure are required and there is no need to use additional color layers.

[0108] Figure 2 shows a schematic cross-sectional view of the structure of the security element 12. An embossing lacquer layer 22 is applied to a carrier substrate 28, into which a relief structure in the form of a micromirror array 26 is embossed in a surface area 24. The micromirror array 26 is provided with a coating in the form of a thin-film element 32, for example, a three-layer structure consisting of an absorber (4 nm chromium) / dielectric (150 nm SiCh) / reflector (60 nm Al), which is shown only schematically in Figure 2 for the sake of clarity.

[0109] As explained in detail below, the micromirror arrangement 26 contains two groups of micromirrors 34, 36, each of which is inclined relative to the plane of the surface region 24 such that, for an observer 40 from the two viewing directions 42, 44, they imitate the reflection behavior of the views 20, 20' with the three-dimensional motifs value number 14 and star 16, respectively. The individual micromirrors 34, 36 have a lateral dimension between 5 pm and 50 pm, and thus, for example, a square base area of ​​10 pm x 10 pm, and are therefore not recognizable as such by an observer.

[0110] The different color effect of the views 20, 20' with the motifs 14, 16 is generated by a (full-surface) surface-conformal coating of the micromirror arrangement 26 with a thin-film element 32 and an overlay of the micromirrors 34 with a subwavelength structure 38, as shown in the detailed sections 30, 30' of Fig. 2. The modulation of the micromirror arrangement with the coated subwavelength grating gl is only shown in the detailed view 30, while the rough profile of the step profile of the height function can be seen in the relief profile shown without magnification.

[0111] The color generated by the subwavelength structure 38 in interaction with the thin-film element 32 in reflection can be adjusted by selecting the structure parameters, in particular the grating period and the structure depth. The grating period of the subwavelength structure is preferably between 50 nm and 450 nm, in the exemplary embodiment 250 nm, and thus below the wavelength of visible light. The depth of the structures is preferably between 100 nm and 300 nm, in the exemplary embodiment 120 nm. In the exemplary embodiment, the structures of the subwavelength structure are arranged in a hexagonal lattice.

[0112] By modulating the micro-mirror arrangement with the sub-wavelength structure, the subdivision of the relief structure 26 into a plurality of micro-mirrors 34, 36 can be regarded as coarse structuring and the modulation of the micro-mirrors 34 with the sub-wavelength structure 38 can be regarded as fine structuring of the relief structure 26.

[0113] To achieve the desired color effect, the height function is superimposed with a grating function that describes the relief profile of a subwavelength grating gl. Specifically, for example, the height function of the first view 20 is modulated with a subwavelength grating function gl that, in conjunction with the thin-film element, is designed to generate a yellow reflection color. The height function of the second view 20' is nanoscale smooth. The micromirrors 36 for this view have only a coating in the form of the thin-film element 32. The relief structure, which contains micromirrors and one or more subwavelength structures, can be produced in a single embossing step with the advantage of a precise arrangement relative to one another. For further details on the production of the coarse structuring, reference is made to WO 2014 / 060089 A2, the disclosure content of which is incorporated into the present application in this respect.

[0114] As explained in more detail below, the thin-film element is color-stable with a relatively thin dielectric layer and therefore exhibits a largely unchanged blue hue upon tilting, which appears yellow in plan view due to the effect of the subwavelength structure 38 superimposed on the micromirrors 34. The combination of the color-stable thin-film element and the subwavelength structure, in conjunction with the micromirror arrangement, allows for abrupt color-shift effects (from yellow to blue / violet). Viewed from the rear, the interference layer structure appears violet in the nanostructured area.

[0115] In principle, the reflection spectrum and / or the color coordinates of the interference layer structure can be adjusted to achieve a color-stable coating. This can be achieved, for example, by deliberately varying the thickness of the individual sublayers, especially the dielectric layer. The reflection spectrum and / or the color coordinates can be calculated in advance using known models or by

[0116] Test series are determined experimentally.

[0117] In practice, it is often disadvantageous if, in addition to the primarily desired color differences (i.e., those caused by the locally varying nanostructure), further color changes occur depending on the tilt angle and lighting situation, especially if a coating on the nanostructure itself causes a color change upon tilting. Especially when used as a security feature, the visual inspection of the observed optical effects and thus the authenticity of a banknote should be possible for an observer without detailed knowledge or extensive training.

[0118] Given that complex color change scenarios cannot be easily described and thus verified when the viewing and lighting situation varies, it is advantageous for the functioning of the described optically variable security element if the different colors generated with or without subwavelength structures are as "color stable" as possible, ie when tilting a security element in the usual viewing angle range up to, for example, approximately + / -45 0change as little as possible and in particular do not deviate from the (basic) colour tone present in vertical view (e.g. "red", "blue", "green" with the corresponding gradations, e.g. "orange-red", "indigo", "yellow-green"). Contrary to the actual purpose of interference coatings, which is to produce the fastest and most noticeable colour change possible, the present invention therefore also aims to determine interference layer structures which show the smallest possible colour change when the viewing and lighting situation changes.

[0119] In other advantageous embodiments, however, it may also be desirable for the color to change significantly upon tilting in one area (with or without nanostructuring), while remaining constant in another area within this tilt angle range. For example, a yellow motif against a blue background could change color upon tilting, while the background color would not change or change only slightly. In the state of the art, or in the "color-shift" products or color-shifting thin-film elements currently available on the market, chromium is usually used as the absorber, aluminum as the reflector, and MgF2 or S1O2 as the dielectric. The latter has a comparatively low refractive index of slightly below or above 1.4, respectively. The interference colors presented by such thin-film elements change relatively significantly upon tilting.As an example, a color change from green to magenta can be realized, for example, with a layer system consisting of a 5 nm thick chromium absorber layer, an approximately 565 nm thick MgF2 dielectric layer, and an aluminum reflector layer. Figure 3 shows exemplary calculated reflection spectra for this layer system for vertical viewing and for viewing at a tilt angle of 45° and 60°, respectively.

[0120] The green hue in vertical view is due to a strong reflection maximum in the green wavelength range around 550 nm. When tilted to higher angles, this maximum shifts further into the short-wavelength range, while simultaneously another maximum at the upper wavelength range extends into the visible spectrum. Thus, when tilted, the hue changes from green in vertical view through a blue hue to a magenta hue (at a tilt angle of 45°).

[0121] The changes in the spectrum also correspond to a change in the color angle H, which can be calculated from the spectra and here increases from 140° at normal incidence to just over 300° at a tilt angle of 45°.

[0122] The HSV color space is the color space of several color models, in which color is defined using hue, saturation, and value. The following parameters are used to describe the color location in this color space: hue as the hue angle H on the color wheel (e.g., 0° = red, 120° = green, 240° = blue), saturation S in percent (0% = neutral gray, 50% = slightly saturated color, 100% = saturated, pure color) or in an interval from zero to one, and brightness V (also called value of darkness) as a percentage (0% = no brightness, 100% = full brightness) or in an interval from zero to one. Table 1 below shows some examples of colors and their corresponding values ​​in the HSV color space. Table 1 The change in the color angle H from 140° to 300° when tilting the aforementioned thin-film element thus corresponds to a significant color change from green (in Table 1: approximately "light blue-green") via blue to magenta.

[0123] If materials with a higher refractive index, such as S1O2, HfCh or ZnS (with a refractive index increasing in this order), but with approximately the same optical thickness are used instead of MgF2, so that the same color tone with a color angle H = 140° is obtained in plan view, the color or the color angle H changes to varying degrees when tilted depending on the material used as the dielectric layer.

[0124] For further explanation, Figure 4 illustrates the influence of the refractive index of the dielectric material of three-layer thin-film elements with a blue-green color in vertical view on the color angle change upon tilting. As can be seen from the curve in Figure 4, even SiCh as a dielectric with a comparatively low refractive index, for example, at a tilt angle (indicated here by the angle of incidence) of 45°, still leads to a very strong color change with a color angle of approximately H = 270° (violet), although the change is no longer quite as pronounced as with MgF2 as the dielectric.However, with the high-index dielectrics HfCh (refractive index is about 2.0) and ZnS (refractive index is about 2.4), the change is significantly smaller: here, the color angle H only increases from H = 140° to about H = 160° when tilting from 0° to 45° - the color therefore remains green and changes only slightly from light blue-green to green-cyan (see Table 2).

[0125] Table 2 The color produced with the aforementioned high-index dielectrics is likely to be perceived by most observers as green and virtually unchanged across the entire tilt angle range between +45° and -45°. Up to a tilt angle of 30°, the color changes are even smaller, with a hue angle change of only about 10° for the high-index dielectrics (HfCh, ZnS), and thus barely perceptible.

[0126] The significantly smaller color changes observed when using high-index dielectrics such as ZnS are due, among other things, to the fact that the reflection spectrum shifts significantly less into the short-wavelength range with increasing tilt angle. As can be seen from the calculated reflection spectra shown in Fig. 5 for tilt angles of 0°, 45°, and 60°, the green reflection maximum shifts into the short-wavelength range by only slightly more than 20 nm when tilting from 0° to 45°. In comparison, the reflection maximum shifts by approximately 75 nm when using MgF2 as the dielectric at the same tilt angle.

[0127] A similar behavior can also be observed for other colors produced with such three-layer interference layer systems: the higher the refractive index of the dielectric, the smaller the change in color upon tilting.

[0128] Figure 6 shows, as a further example, the influence of the refractive index of the dielectric layer material of three-layer thin-film elements, which appear blue-red in vertical view according to Table 1, on the calculated profile of the color angle H when tilting such interference layer systems. The following layer thicknesses were assumed for the calculation: MgF2: approximately 460 nm; SiCh: approximately 440 nm; HfCh: approximately 330 nm; ZnS: approximately 280 nm.

[0129] The color angles H in vertical view or at a tilt angle of 45° can be found in Table 3 below.

[0130] Table 3

[0131] With reference to Fig. 6 and Table 3, the color and color angle changes are also much smaller when using high-index materials for the dielectric. While MgF2 as a dielectric leads to a change in the color angle from H = -30° (a color angle of -30° corresponds to a color angle of +330°) to just over H = 100° between 0° and a tilt angle of 45°, i.e. the color changes very significantly from blue-red to approximately yellow-green upon tilting, the color angle for HfO2 only changes from H = -30° to H = 10°. According to Table 1, this corresponds to a color change from blue-red to orange-red. The reddish color range is therefore practically not left upon tilting. With ZnS as the dielectric, the change in the color angle H is even smaller at less than approximately 30°.

[0132] Another measure for producing highly angle-stable colors according to the invention is to select the dielectric thickness of a three-layer thin-film element so thin that constructive interference can just barely occur for blue light in the layer system. This behavior typically occurs at a dielectric optical thickness of slightly less than 250 nm. Such layer systems, viewed vertically in the visible spectrum, exhibit a reflection maximum only at the short-wavelength blue (violet) end, which then migrates further into the (invisible) UV range upon tilting (see Figure 7).

[0133] As a result, no new color is created upon tilting, but rather the layer system essentially becomes increasingly darker. This effect was observed equally for all dielectrics tested, i.e., for materials with both high and low refractive indices. This is illustrated in Figure 8. For tilt angles of 0° and 45°, for example, the following values ​​are obtained for selected dielectrics: Table 4

[0134] As a result, even with MgF2 as the dielectric, the color angle H changes only from approximately H = -82° (violet / blue magenta) to H = -72° (blue magenta) when tilting from 0° to 45°. Thus, using such layer systems, even with comparatively low-refractive dielectrics, at least blue / violet shades can be produced. These shades are very color-stable and can be advantageously combined with other shades modified by subwavelength structures, according to the invention.

[0135] Particularly in layer systems with very thin dielectrics and angle-stable colors, it has been observed that very angle-stable colors can be achieved even when the interference layer system is applied on a nanostructure. As explained in detail below, for example, with a 150 nm thick SiCh dielectric (refractive index 1.46) and the subwavelength structure according to Example 1 (hexagonal grating, period = 250 nm, approximately sinusoidal profile, depth = 120 nm, fill factor = 0.5), the (in plan view) blue color of this interference layer system can be changed into equally color-stable yellow / orange tones.

[0136] By providing areas with nanostructuring and areas without nanostructuring, novel color combinations can be created which, in conjunction with a microrelief structure producing a dynamic effect, even enable abrupt, unusual color shift effects.

[0137] A color-stable ink can also be achieved by using a thin semiconductor layer, e.g., silicon, with a thickness between 3 nm and 100 nm on a metal layer. Further details on the creation of the color effect of such a color mirror can be found in WO 2016 / 188619 A1, the disclosure of which is incorporated into the present application in this respect.

[0138] Such layer systems are characterized in the context of the present invention, in particular by a very slight color change upon tilting. For example, with an approximately 85 nm thick Si layer on an Al reflector, a blue-red hue (viewed from above) with a hue angle of H = 330° (or -30°) can be produced, which changes even less upon tilting than found above for a three-layer thin-film element with the very high refractive index ZnS. Here, too, the very slight color change upon tilting is due to a very high refractive index, which for Si is approximately 4 in the visible spectrum. In contrast to ZnS, however, Si already exhibits significant absorption in the visible spectrum.

[0139] This is illustrated in Figure 9. Figure 9 shows the reflection spectrum of the Si / Al color mirror coating system in vertical view and after tilting by 45° or 60°. Even at a tilt angle of 90°, the reflection spectrum changes very little compared to the reflection spectrum in vertical view. Converting the reflection spectra into color angles H yields the curve shown in Figure 10.

[0140] Corresponding values ​​for selected tilt angles are presented in Table 3 above, from which it can be seen that the hue angle H for this layer system actually changes by only about 10°. Such hue angle changes or color changes are barely perceptible in practice and significantly smaller than when using the three-layer systems presented above with different dielectrics, which are also shown for comparison or listed in Table 3.

[0141] Even with a three-layer structure consisting of a semi-transparent metal layer / dielectric layer / semi-transparent metal layer, colors with little color change when tilted and, in particular, color-stable colors can be produced with a small thickness of the dielectric layer.

[0142] The following layer systems shown in Table 5, in which a SiCE dielectric is arranged between two semi-transparent aluminum layers each with a thickness between 3 nm and 20 nm, preferably between 5 nm and 15 nm, particularly preferably about 10 nm, show such an effect.

[0143] Table 5

[0144] These thin-film elements appear colored, especially in transmitted light, and are essentially color-stable when tilted or at least exhibit only a slight color change. Interference layer systems of this type are described, for example, in the publication DE 102009041 583 A1, the disclosure of which is incorporated into the present application.

[0145] Coating systems that appear gold when viewed from above have proven particularly advantageous. This color appears particularly elegant, and in transmitted light (in areas without nanostructures) an attractive, vibrant blue is visible. The golden surface color changes to a nearly colorless metallic tone when tilted, thus advantageously avoiding any noticeable color change when tilted.

[0146] For the following discussion, the assignment of color representations or color designations given above in Table 1 was transferred to the CIE ECh color system or to hue angle h. Table 1 was supplemented by an additional column with the corresponding LCh values:

[0147] Table 6

[0148] In the examples described below, the subwavelength structure is in the form of depressions ("nanoholes"). The described colors are visible through the embossing varnish. When viewed from the back, colors are also visible, although these are usually different from the colors visible from the front.

[0149] Example 1: Micromirror arrangement with / without nanostructuring and thin-film element with low dielectric thickness To produce an element with a yellow color effect, an embossed structure coated with an interference layer structure was produced with the following properties: Surface relief, consisting of microstructure with superimposed nanostructure: Microrelief structure:

[0150] Microrelief structure grid with 20 gm x 20 um pixels;

[0151] Micromirrors with flat mirror pitch (mirror height max. 1.8 pm);

[0152] Micromirrors form aperiodic or quasi-periodic sawtooth gratings with micromirrors having a width of approximately 5 µm to approximately 20 µm (see illustration in Figure 12, which shows an SEM image of the micromirror arrangement used);

[0153] Nanostructure (regionally): nanoholes arranged in a hexagonal lattice;

[0154] Period of the structures: 250 nm;

[0155] Profile of the structures: approximately sinusoidal;

[0156] Depth of structures: approx. 120 nm;

[0157] Fill factor: approx. 0.5 (ie width of structures = period);

[0158] Coating:

[0159] Thin-film element with the following layers:

[0160] Absorber: 4 nm Cr;

[0161] Dielectric: 150 nm SiCh;

[0162] Reflector: 60 nm aluminum.

[0163] The element shows the following color effect compared to the coating applied on a nanoscale smooth surface.

[0164] The blue hue of a smooth nanoscale surface when viewed from above becomes yellow due to the effect of the nanostructuring. At a tilt angle of up to approximately 40°, the colors do not change significantly in either the unstructured or nanostructured area, which is primarily due to the use of a thin SiCh layer. Viewed from the back, this structure appears violet in the nanostructured area.

[0165] Example 2: Variation of the dielectric thickness of a thin-film element on a micromirror array with / without nanostructuring Surface relief consisting of microstructure with superimposed nanostructure:

[0166] Microrelief structure:

[0167] Microrelief structure grid with 20 pm x 20 um pixels;

[0168] Micromirrors with flat mirror pitch (mirror height max. 1.8 μm);

[0169] Micromirrors form aperiodic or quasi-periodic sawtooth gratings with a

[0170] Micromirrors with a width of approximately 5 pm to approximately 20 pm (see illustration in Figure 12);

[0171] Nanostructure (regionally): nanoholes arranged in a hexagonal lattice;

[0172] Period of the structures: 250 nm;

[0173] Profile of the structures: approximately sinusoidal;

[0174] Depth of structures: approx. 120 nm;

[0175] Fill factor: approx. 0.5;

[0176] Coating:

[0177] Thin-film element with the following layers:

[0178] Absorber: 4 nm Cr;

[0179] Dielectric: SiO2; layer thickness see Table 7 or Table 8A / 8B;

[0180] Reflector: 60 nm aluminum.

[0181] The color effect of the elements manufactured with the corresponding dielectric layer thickness can be found in Table 7. The assignment of the measured color angles to corresponding color designations can be found in Table 6.

[0182] Table 7

[0183] This means:

[0184] Vellum = unstructured area

[0185] NS = nanostructured area (period: 250 nm)

[0186] L = Lightness

[0187] C = Chroma h = Hue

[0188] Definition: Ah = color deviation > A — 180° 80° ; A > 180°

[0189] In general, the smaller the hue deviation Ah, the more color-stable the hue is with respect to changes in viewing direction. The absolute values ​​of the deviations that the viewer perceives as color-stable or color-constant vary depending on the primary hue (e.g., "red," "blue," "green").

[0190] In particular, colours are considered to be colour-stable if the colour deviation Ah, starting from a colour in vertical view with a colour angle h between 0° and 60°, is less than 60°, preferably less than 30°, starting from a colour in vertical view with a colour angle h between 50° and 80°, is less than 30°, preferably less than 15°, starting from a colour in vertical view with a colour angle h between 75° and 105°, is less than 30°, preferably less than 15°, starting from a colour in vertical view with a colour angle h between 100° and 180°, is less than 80°, preferably less than 40°, starting from a colour in vertical view with a colour angle h between 170° and 220°, is less than 50°, preferably less than 25°, starting from a colour in vertical view with a colour angle h between 210° and 300° is less than 90°, preferably less than 45°,or starting from a color shade in vertical view with a color angle h between 290° and 10° is less than 80°, preferably less than 40°.

[0191] Figures 13(a) to 13(h) show the spectral reflection curve of the three-layer thin-film elements described above, with and without nanostructuring, for different viewing situations (viewed at a tilt angle of 8°, i.e., with a substantially vertical view, and at a tilt angle of 45°). They also show a fundamental shift and attenuation of the reflection spectra upon tilting toward shorter wavelengths. As can be further seen from Figures 13(a) to 13(h), the reflection spectra with nanostructuring are fundamentally shifted toward longer wavelengths compared to those without nanostructuring.

[0192] Tables 8A and 8B list the values ​​taken from the reflection spectra for the reflection maxima and the wavelengths associated with the reflection maxima for the corresponding interference layer structures and dielectric layer thicknesses, respectively. In addition, the respective shift and attenuation of the reflection maxima upon tilting are indicated. AR corresponds to the attenuation of the reflection (of a specific maximum) and AX to the shift of the corresponding wavelength in the reflection spectrum. The values ​​for the attenuation of the reflection maximum, ARveiin, and the values ​​for the shift of the wavelength associated with the reflection maximum, AXveiin, for the coatings present on a nanoscale smooth area are also listed in Table 8B for comparison purposes. Table 8A

[0193] Table 8B As the measured reflection spectra already show, the reflection maxima in the nanostructured region are shifted by approximately the same amount (toward shorter wavelengths) upon tilting as the reflection spectra of the thin-film elements in the unstructured region. The amount of shift of the wavelength attributable to the (determined) reflection maximum, AX, lies between approximately 50 nm and approximately 100 nm for all dielectric layer thicknesses. Tables 8A and 8B further show that the values ​​for the attenuation of the reflection maxima in the nanostructured region approximately agree with the values ​​for the attenuation of the reflection maxima in the smooth nanoscale region.

[0194] Example 3: Variation of the dielectric thickness of a thin-film element on a micromirror array with / without nanostructuring

[0195] Surface relief consisting of microstructure with superimposed nanostructure: Microrelief structure:

[0196] Microrelief structure grid with 20 pm x 20 um pixels;

[0197] Micromirrors with flat mirror pitch (mirror height max. 1.8 μm);

[0198] Micromirrors form aperiodic or quasi-periodic sawtooth gratings with micromirrors in a width of approximately 5 pm to approximately 20 pm (see illustration in Figure 12);

[0199] Nanostructure (regionally): nanoholes arranged in a hexagonal lattice;

[0200] Period of the structures: 320 nm;

[0201] Profile of the structures: approximately sinusoidal;

[0202] Depth of structures: approx. 150 nm;

[0203] Fill factor: approx. 0.5;

[0204] Coating:

[0205] Thin-film element with the following layers:

[0206] Absorber: 4 nm Cr;

[0207] Dielectric: SiO2; layer thickness see Table 9;

[0208] Reflector: 60 nm aluminum. The color effect of the elements manufactured with the corresponding dielectric layer thickness can be found in Table 9.

[0209] Table 9

[0210] Figures 14(a) to 14(h) show the spectral reflection curve of the three-layer thin-film elements described above, with and without nanostructuring, for different viewing situations (viewed at a tilt angle of 8°, i.e., a substantially vertical view, and at a tilt angle of 45°). They also show a fundamental shift and attenuation of the reflection spectra upon tilting.

[0211] As can be seen from Figures 14(a) to 14(h), the reflection spectra with nanostructuring are generally shifted towards longer wavelengths compared to those without nanostructuring. Example 4: Influence of nanostructuring and interference layer structure on chromaticity (colorfulness) Using four selected colors (yellow, magenta, blue and green), the following Table 10 compares the chroma C of nanostructures without an interference layer structure (NS + aluminum), of nanostructures with an interference layer structure (NS + CS) and of an interference layer structure without nano structures (CS). When selecting the layer systems and nanostructuring, care was taken to ensure that the color tones and color angles h produced in each case are as similar as possible, i.e. the corresponding values ​​for the color angle h differ only slightly from one another.The color locations of the colors produced were also entered in the CIELAB color space for display purposes (Figure 15): the further the measuring points are from the center, the higher the chroma C. The angle h determines the hue (yellow, magenta, blue, green).

[0212] Table 10 The nanostructured surfaces exhibit similar chromaticity, regardless of whether they are coated with aluminum or with a three-layer interference layer structure (here: Cr-SiCh-Al). Depending on the color tone, the pure interference layer structure exhibits the greatest chromaticity. Especially for green colors, the generated chromaticity for such designs increases significantly. Also using the green example, Table 10 further shows that similar chromatic tones can be produced using different nanostructure-interference layer structure / SiCh combinations. In practice, therefore, a specific color impression can be achieved through a multitude of possible combinations. For desired color combinations, this in turn significantly expands the selection of suitable structures / coatings.

[0213] The pure (unstructured) interference layer structure exhibits the highest chroma. Although the attractiveness of a security element is significantly influenced by the color or chroma of the interference layer structure, nanostructuring (despite lower chroma) provides additional colors and thus allows for significantly greater design freedom. The simultaneous use of areas with an unstructured interference layer structure also allows for more brilliant colors overall compared to purely structural color generation with metallized nanostructuring.

[0214] Example 1: Combined color / motif flip (one color per motif)

[0215] With reference to Figure 16, the view 70 is created by an embossed structure formed from a first micromirror set and a first subwavelength structure and coated with a particularly color-stable interference layer structure. For example, the first view 70 or the first motif can show a curved-appearing value number 72 in a first color against a background 74 of the same color, the color effect of which is created by the interaction of the first subwavelength structure and the preferably color-stable interference layer structure.

[0216] View 80 is created by an embossed structure coated with the interference layer structure, which is formed from a second set of micromirrors and a second subwavelength structure. For example, the second view 80 or the second motif can show a curved-looking star 82 in a second color against a background 84 of the same color, the color effect of which is generated by the interaction of the interference layer structure with the second subwavelength structure. When the security element is tilted 18, the appearance alternates between the first view 70 and the second view 80. In this embodiment, the entire surface of the surface area appears either in a first or a second color. As a result, so-called "shadow images" of the respective other motif are less visible than with other multi-colored color / motif flip combinations.

[0217] The main cause of shadow images is seen in the fact that in subject flip displays created with micromirrors, each light source in a room creates its own image, which is reflected back towards the viewer or becomes perceptible to the viewer. In the ideal case of a single light source, both subjects can be easily separated by the viewer during tilting. However, if there is more than one light source or if the light is diffuse (e.g. on a cloudy day), in the worst case scenario two equally bright light sources can be located exactly at the viewing angle and the viewer's eye perceives both subjects with equal intensity. Separating the subjects is then difficult or even impossible. Usually, however, there is a dominant light source (e.g. sun, ceiling light), so the viewer perceives a clear reflection from this light source, which is then overlaid by weak reflections from other light sources.This can lead to the viewer simultaneously perceiving the subject from this direction as a shadowy overlay of the other subject. In the example described above, the shadow image appears only faintly and with a uniform color. The subject actually perceived may thus only have a slight veil of color, unlike designs where the subject and background are each formed in different colors.

[0218] In a configuration not shown, the color flip can also occur only in a portion of the surface area. For example, while the color and motif change in one part of the motif, the color in other parts of the surface area, such as the entire background, can remain the same when switching from the first view to the second view.

[0219] Embodiment 2: Combined color / motif flip (multiple colors per motif) With reference to Figure 17, not only can the colors of the first and second view as a whole differ, but also the motifs and / or the background within a view can be designed with different colors or even be multi-colored each.

[0220] The view 90 is created by an embossed structure coated with the interference layer structure, which is formed from a first set of micromirrors and a first and a second subwavelength structure. For example, the first view 90 shown in Figure 17 contains a curved-appearing value number 92 in a first color against a background 94 of a different color, the color effect of which is created by the interaction of the advantageously color-stable interference layer structure and the first and second subwavelength structures.

[0221] View 100 is created by an embossed structure coated with the interference layer structure, which is formed from a second set of micromirrors and several, in particular three, subwavelength structures. For example, the second view 100 contains a curved, multicolored stem 102, 106 against a differently colored background 104, the color effect of which is generated by the interaction of the interference layer structure and, for example, three different subwavelength structures.

[0222] It has proven particularly attractive if the color scheme for a color / motif flip is chosen such that both motifs have the same first, particularly "striking" color (e.g., orange or red) and both backgrounds in both views are also designed in the same second, particularly "subtle" color (e.g., purple or white) (two-color motif flip). Such designs have a high recognition value.

[0223] In an exemplary embodiment not shown, the first view or the first motif shows a curved-appearing value number "100" in red against a white first background. The color effect of the motif and the background is generated by the interaction of a first or second sub-wavelength structure and the preferably color-stable interference layer structure. The second view or the second motif shows a curved-appearing note (music) in red against a white second background, the color effect of which is also generated by the interaction of the interference layer structure with the first or second sub-wavelength structure. When the security element is tilted, the appearance changes between the first view and the second view.

[0224] In such designs (motifs and backgrounds in the first and second views are each in the same color), the motifs preferably overlap, at least in some areas. However, to ensure a high level of counterfeit protection, the overlap of the motifs should not exceed a certain area.

[0225] To create overlapping images, the sub-areas of the security element providing the first motif and the first background, or the second motif and the second background, are advantageously nested within each other. For this purpose, the sub-areas are formed, for example, by narrow, alternating strip-shaped sub-areas arranged next to each other, or by small sub-areas nested within each other in two dimensions. In principle, nesting the sub-areas or the motifs created thereby makes it more difficult for a counterfeiter to replicate them.

[0226] In contrast to the case of congruently selected motifs of the same color, where, for example, only the structural design or micro-relief structure of the motifs differs, but not their color and outline (e.g., in the case where both motifs create congruent coin depictions in red and only the motif on the coin changes when the views are changed), and thus the security element can be reproduced comparatively easily, for example, by simply overprinting with a printing ink, overprinting with precise registration of motifs that do not completely overlap is only possible with considerable effort. Since the non-overlapping parts of the motifs change color when tilted (from the color of the motif in one view to the color of the background in the other view), reproducing them by overprinting would require 100% registration with the sub-areas or micro-mirrors assigned to the respective depiction.Such designs therefore offer particularly high protection against counterfeiting.

[0227] In principle, the first and second motifs should preferably differ sufficiently that their outlines can be distinguished with the naked eye. In overlapping representations, the area of ​​overlapping motifs should be between 20% and 80%, particularly preferably between 30% and 70%. Example 3: Two-color flow effect with color effects in register for a dynamic effect.

[0228] The exemplary embodiment in Figure 18 shows multi-colored rolling effects with a color effect in register with the dynamic effect. Such effects can be advantageously used in a security thread, for example in the form of successive regions 112, 116 of different colors in which rolling effects generated in different directions 122, 124 by a micromirror arrangement occur. In the exemplary embodiment, the surface area of ​​the security thread displays a two-color so-called RollingCube pattern, in which in each tilt position (shown here by way of example using a first and second view 110 and 120, respectively), two parallel rows of small rectangles or bars 114, 118 (shown in Fig. 18 with close hatching) can be seen. These rectangles or bars, as illustrated in Fig. 18, are spaced a certain distance apart and each appear with a specific color impression.When the security thread is tilted 18, a kinematic effect occurs in which the two rectangular "rows" move towards each other (view 110) or away from each other (view 120) along the arrows 122 and 124, respectively.

[0229] To create the kinematic effect, the micromirror arrangement comprises a plurality of micromirrors with different angles of inclination. The similarly oriented micromirrors are arranged such that the entire group of brightly lit or dark micromirrors shows the viewer the desired motif. In particular, the micromirrors are oriented such that the reflection condition changes equally for all micromirrors when the security thread is tilted. Micromirrors that fulfilled the reflection condition before tilting and appeared bright can no longer fulfill the reflection condition after tilting and therefore appear dark. Conversely, micromirrors that were dark before tilting can appear bright after tilting if the mirror inclination is appropriate. By appropriately arranging and orienting the micromirrors, the desired movement effect, in this example a walking effect, can be created.Alternatively or additionally, the running effects can also be as in the printed text.

[0230] WO 2011 / 066991 A1, the disclosure of which is incorporated into the present application in this respect. Furthermore, the regions 112, 116 are each colored, with the color impression being generated in at least one of the regions by the interaction of an interference layer structure with a subwavelength structure (optionally, the other region is smooth at a nanoscale and coated with the advantageously color-stable interference layer structure).

[0231] It has proven particularly advantageous to select at least some of the subregions of regions 112, 116 so small that simply overprinting the micromirrors with ink to recreate the effect cannot be achieved with precise registration due to printing tolerances. The size of these subregions should preferably be less than 0.5 mm in at least one extension direction of the subregion (e.g., perpendicular to the direction of movement of the effect) and particularly preferably less than or equal to 0.2 mm. Since the subwavelength structure(s) can be precisely exposed to individual micromirrors, motion effect color registration is possible even for very narrow regions.

[0232] Example 4: Arch effect in multi-color display

[0233] The generation of arching effects with the aid of micromirrors, as used in the embodiment shown in Figure 19, is known, for example, from the document WO 2011 / 066990 A2, the disclosure content of which is incorporated into the present application in this respect.

[0234] Fig. 19 illustrates such a reflective curved representation, here in the form of a statue 138. To achieve such an appearance, the security element 130 contains a reflective surface region with a plurality of inclined micromirrors. In practice, the dimensions of the micromirrors are below the resolution limit of the human eye, so that the micromirrors themselves are not visible. For example, the micromirrors have an edge length of only 10 µm and a pitch of less than 10 µm. The micromirrors can be arranged regularly in a continuous grid or irregularly. Due to the locally varying inclination of the micromirrors, the observer sees a three-dimensional motif (here statue 138) that bulges out of the plane and has a surface that protrudes and / or recedes compared to the actual spatial shape of the surface region.To generate a true-color display, the colors visible to a viewer in the exemplary embodiment contain mixed colors that arise from a color mixture of colors of pixel-shaped sub-regions with a dimension below the resolution limit of the human eye. Advantageously, at least two of the colors of the pixel-shaped sub-regions can be generated by a specific type of sub-wavelength structure provided with an interference layer structure, which is characteristic of this color (a third color can optionally be generated by the smooth, nanoscale interference layer structure). In addition, the micromirror arrangement can also be formed with pixel-shaped sub-regions, wherein the arrangement of the pixel-shaped sub-regions of the sub-wavelength structures and the micromirror arrangement can be selected independently of one another or can also be congruent.

[0235] The detailed section of Figure 19 illustrates the generation of such mixed colors by an arrangement of pixels formed from "RGB" subpixels. The pixels are formed here by three-channel color areas 134, which contain subwavelength structures 136-R, 136-G, and 136-B, respectively, coated with an interference layer structure for generating the primary colors red, green, and blue. These structures, through additive color mixing, produce a corresponding mixed color when the three-channel color area is fully occupied with white (or a bright color impression) and when the subpixels are each partially occupied, as indicated in Fig. 19.

[0236] According to an alternative embodiment not shown here, the mixed colors can also be generated by two-channel color areas containing two subpixels with complementary spectral colors generated by the interaction of the interference layer structure and a first and possibly second subwavelength structure, for example cyan and red, or yellow and blue.

[0237] Example 5: Two-color 3D effect

[0238] In addition to the above-described possibility of creating a 3D effect by simulating the reflection behavior of a curved surface, a 3D effect can also be created through stereographic representations, in which a viewer sees an object point slightly offset to the left or right with their left and right eyes (horizontal parallax) and then uses the parallax to infer a spatial position in front of or behind the security element. It is particularly advantageous to provide both a horizontal and a vertical parallax, so that the stereographic 3D impression is retained even after the security element is rotated in its plane or tilted about two different axes, thus providing a 3D impression in virtually any orientation. Fig. 20 illustrates such a 3D representation.

[0239] Referring to Fig. 20, the display area 202 of the security element 220 is provided with a plurality of reflective, planar micromirrors of a micromirror array, which, for example, have a base area of ​​15 pm x 15 pm and a maximum height of a few micrometers. Each of the planar micromirrors is characterized by an angle of inclination relative to the plane of the reflective surface area 224.

[0240] In Fig. 20, the middle view 200-M shows a top view of a reflective surface area 224 with a dashed display area 202, in which a circular curve 204 is visible as a motif in the center position when viewed vertically and appears to float below the surface area 224, and a background area 206 surrounding the display area 202. When viewed from above (view 200-0), the circular curve 204 migrates to the upper edge of the display area 202, and when viewed from below (view 200-U) to the lower edge. Accordingly, the circular curve 204 migrates to the right edge when viewed from the right (view 200-R) and to the left edge of the display area 202 when viewed from the left (view 200-E). Such movement behavior corresponds to the movement behavior of an object arranged in depth and therefore creates the three-dimensional impression of the ring floating in the depth.

[0241] The appearance and movement behavior is achieved, for example, in that the micromirrors in the display area 202 are inclined away from the circular curve in the direction perpendicular to the direction vector of the circular curve 204 and the inclination angles increase linearly with the distance of the facet from the circular curve 204, and that the inclination angles parallel to the direction vector vary randomly or pseudorandomly in a fan-out area regardless of the distance to the circular curve 204.

[0242] Further details on the creation of the three-dimensional appearance and movement effect can be found in document DE 102015005 959 A1, the disclosure of which is incorporated into the present application in this respect. Details on the creation of similar three-dimensional effects and on the generation of 3D tilt effects, in which a first 3D motif can tilt into another 3D motif upon tilting, are described in document DE 102017004586 A1, the disclosure of which is also incorporated into the present application in this respect.

[0243] Furthermore, the display area 202 and the background area 206 are each colored, with the color impression being generated in at least one of the areas by the interaction of an interference layer structure with a subwavelength structure (optionally, one of the areas is formed with a smooth nanoscale, so that the colored appearance is generated only with the preferably color-stable interference layer structure). For example, the surface area can appear as a red circle against a green background.

[0244] In further advantageous embodiments, the reflective surface area is designed as follows: multi-colored 3D motifs, e.g. value number "100" with red "1" and green "00", or a red "100" floating above the reflective surface area, framed by a green rectangle lying in the depth (ie below the reflective surface area), each with a background of the same color or a different color;

[0245] Motif change (motif flip) when tilting foreground motifs of the same colour against a different coloured background, e.g. motif change of a red value number “100” against a green background into a red symbol “PF” against a green background;

[0246] Motif change with color change: e.g. red value number “100” flips into green symbol “PF”.

[0247] Example 6: Two-dimensional color / motif flip

[0248] In the exemplary embodiment described in more detail below, a change takes place between two motifs whose appearance is not based on a three-dimensional effect, in particular not on a stereographic 3D effect or a three-dimensional representation with a surface that protrudes and / or recedes from the actual spatial shape of the surface area, but rather on surfaces of constant brightness. This impression can therefore also be referred to as a "flat" or two-dimensional effect, and the change as a "flat" or 2D color / motif flip. The individual motifs are formed as surfaces of constant brightness (within the viewing angle range in which the respective motif is intended to be perceived) against a dark or differently colored background.

[0249] According to an advantageous embodiment, the motifs can each be realized with a micromirror arrangement, in which each micromirror reflects in a random direction within the desired solid angle range. A statistically uniform distribution of the orientations of the individual micromirrors allows for uniform brightness within the selected solid angle range.

[0250] According to an alternative embodiment, such surfaces of constant brightness can be formed with micromirrors that have a curved profile in two directions (or alternatively, a varying, sectionally constant inclination). It has proven particularly attractive if the color assignment of the sub-areas is selected such that both motifs have the same first, particularly "striking" color (e.g., orange or red) and both backgrounds in both views are also formed in the same second, particularly "subtle" color (e.g., Fila or white) (two-color motif flip). However, it is also conceivable to select the color assignment of the sub-areas such that the colors of the motif and the background in the second view are swapped compared to the colors of the motif and the background in the first view (motif 1 / color 1, background 1 / color 2 vs. motif 2 / color 2, background 2 / color 1; inverse two-color color / motif flip).

[0251] In cases where the background does not stand out from the subject through a different color scheme, it can be covered, for example, with micromirrors that reflect in a different solid angle range than the micromirror arrangement assigned to the subject. When viewed in the solid angle range assigned to the subject, the background then appears correspondingly dark.

[0252] Basically, the optically variable display elements described above are constructed as shown in Figure 2. The structure consists of a structured layer with a microrelief with subwavelength structures present at least in some areas, which is provided with an interference layer structure. In addition to the optically variable layer structure, the display element can contain further functional layers, such as fluorescent or magnetic layers. A functioning security feature also requires protective layers, primer layers, and adhesive layers. For the function of the display element, it is irrelevant whether the film is located above or below the structured layer.

[0253] Example 7: Color / motif flip with layer-dependent color design

[0254] With reference to Fig. 21, the manufacturing of a security element 140 can, for example, be carried out as follows:

[0255] Printing a release varnish or primer layer onto a carrier film;

[0256] Printing a first embossing varnish (e.g. UV varnish), embossing the first microrelief with partially superimposed subwavelength grating, curing the UV embossing varnish;

[0257] Printing a wash ink to create a rasterization and structuring of the first layer system;

[0258] Evaporation of the absorber, e.g. B. Cr, Al, Ti;

[0259] Evaporation of the dielectric, e.g. SiCh, MgF2, TiCh, ZnS;

[0260] Evaporation of the reflector, e.g. B. Al, Ti, Fe, Cr, Cu;

[0261] Demetallizing by removing the wash paint and the overlying layer system;

[0262] Applying a primer layer or laminating a film; optionally printing a translucent color layer;

[0263] Printing a second embossing varnish (e.g., UV varnish), embossing the second microrelief with a partially superimposed subwavelength grating, curing the UV embossing varnish; optionally printing a wash ink for structuring the second layer system; vapor deposition of the second layer system (single metallic layer or interference layer structure); optionally demetallizing by removing the wash ink and the overlying second layer system.

[0264] Application of primer, protective lacquer layers, and adhesives (e.g., heat-sealing lacquers). The special structure of the security element 140 is explained in more detail with reference to Fig. 21, which shows a section of the security element schematically in cross-section.

[0265] With reference to the cross-section of Fig. 21, the surface area of ​​the carrier substrate 28 defines an xy plane and a z axis perpendicular thereto. A layer sequence is provided on the carrier substrate 28, for example a PET film, and the release lacquer layer 160. Starting from the carrier substrate 28 and the release lacquer layer 160, this layer sequence comprises a first embossing lacquer layer 152 with an embossed first embossed structure 154, a first ink coating 156, a first primer layer 158, a partially present translucent ink layer 150, a second embossing lacquer layer 142 with an embossed second embossed structure 144, a second ink coating 146, a second primer layer 148, and a heat-seal lacquer layer 162.

[0266] The security element 140 is designed for viewing in reflection from the positive z-direction, so that of the two embossed structures 144, 154 arranged at different heights in the z-direction, the first embossed lacquer layer 152 located closer to the observer is also referred to as the higher relief layer and the embossed lacquer layer 142 located further away from the observer is referred to as the lower relief layer.

[0267] In the exemplary embodiment, the embossed structures 144, 154 each represent micromirror embossments or micromirror arrangements, which are each formed from a plurality of micromirrors inclined relative to the xy plane and having lateral dimensions of approximately 10 pm, wherein the micromirror arrangements are each also overlaid in some regions with a subwavelength structure 164, 176.

[0268] The local angles of inclination of the micromirrors are selected precisely such that the relief structure of the micromirror arrangements 144, 154 produces a desired optical appearance after the color coating. Specifically, the angles of inclination of the micromirrors in the exemplary embodiment are selected such that the micromirror arrangement 144 produces a curved representation of a value number in one viewing angle range, and the micromirror arrangement 154 produces a curved representation of a coat of arms in another viewing angle range. To give the appearance a desired color impression, the defer micromirror arrangement 144 is provided with a color coating 146 following the relief profile in the form of a highly reflective, opaque metallization, which in the exemplary embodiment consists of an aluminum layer. The metallization 146 is recessed in a partial region 168 in order to produce a negative marking, for example, negative writing.To generate colored areas, the micromirror arrangement 144 in the exemplary embodiment is also provided with a color-generating subwavelength structure 164.

[0269] The higher micromirror array 154 is provided with a gridded color coating 156 following the relief contour in the form of an advantageously color-stable three-layer interference layer structure, in the exemplary embodiment with a layer sequence of chromium / silicon dioxide / aluminum. Furthermore, the micromirror array is multicolored, with the color impression being generated at least in some areas by the interaction of the color coating 156 present as an interference layer structure with a subwavelength structure 176. The other regions of the micromirror array 154 coated with the interference layer structure are nanoscale smooth.

[0270] According to an alternative embodiment, the deeper micromirror arrangement 144 can also be provided with a three-layer interference layer structure and, for generating multicolor, with a subwavelength structure which, through interaction with the interference layer structure, creates a color impression.

[0271] The color coating 156 of the higher micromirror arrangement 154 is formed in a surface area of ​​the security element in the form of a regular grid 170 comprising grid elements 172 and grid spaces 174, with a viewer in the area of ​​the grid spaces 174 looking at the lower micromirror arrangement 144. In the area of ​​the grid spaces 174, the viewer can in principle perceive the micromirrors of the lower micromirror arrangement 144, but their orientation from a viewing direction other than the predetermined one is far removed from the gloss angle, so that in this case, they contribute practically nothing to the image impression.

[0272] Specifically, in the exemplary embodiment, the grid elements 172 and grid spaces 174 form a checkerboard pattern in which each field, i.e., each grid element 172 and each grid space 174, has dimensions of 100 m x 100 m. Since the micromirrors are generally significantly smaller, for example, having an edge length of only 10 m, the grid 170 of the color coating 156, unlike in the simplified schematic representation of Fig. 21, generally does not coincide with the grid of the micromirrors of the micromirror arrangement 154. The removal of the color coating 156 in grid spaces 174 can be achieved by a washing process, etching process, or a laser process.

[0273] In addition, a translucent color layer 150 is provided between the two micromirror arrangements 144, 154, which is only present in some areas, for example a blue color layer left out in the area 168 of the negative writing.

[0274] Overall, the two micromirror arrangements 144, 154 produce different images and color effects for different viewing directions, whereby the viewing direction from which the respective colored image of the higher or lower micromirror arrangement becomes visible is determined by the orientation of the micromirrors.

[0275] Further details on the creation of the image and color effects of such designs can be found in the documents WO 2020 / 011390 A1, WO 2020 / 011391 A1, and WO 2021 / 155999 A1, the disclosure content of which is incorporated into the present application in this respect.

[0276] Example 8: Color / motif flip with layer-dependent color design (primary / secondary structure)

[0277] With reference to Fig. 22, the manufacturing of a security element 50 can, for example, be carried out as follows:

[0278] Printing a release varnish layer onto a carrier film;

[0279] Printing a transparent embossing varnish (e.g., UV varnish), embossing the first microrelief with a partially superimposed subwavelength grating, curing the UV embossing varnish; printing a colored UV varnish in partial areas; embossing the second microrelief with a partially superimposed subwavelength grating, curing the colored UV varnish; metallizing or coating the embossing in multiple layers to create an interference layer structure.

[0280] Such a layer structure can be produced very efficiently.

[0281] The special structure will now be explained in more detail with reference to Figure 22, wherein Figure 22 schematically shows a section of the security element 50 applied to a banknote 10 in cross section.

[0282] The security element 50 comprises a flat, transparent, colorless carrier 28, for example, a transparent, colorless PET film, whose surface area defines an xy plane and a z axis perpendicular thereto. Arranged on the carrier 28 is a multicolored reflective surface area containing an embossed structure area with two micromirror embossments 48, 64 at two different heights.

[0283] A first embossed region 48, which forms the primary structure, is provided by micromirror embossings embossed into a first transparent embossing lacquer layer 46 applied to the carrier 28, the base areas of which lie at a first height above the carrier 28. The first embossing lacquer layer 46 is partially covered by a secondary structure in the form of a second embossing lacquer layer 52 with a second embossed relief structure 64 with micromirror embossings, so that on the first embossing lacquer layer 46, there are overlapping regions 68", 68"' with the second embossing lacquer layer 52 and free regions 68, 68' without the second embossing lacquer layer 52.

[0284] The second embossing lacquer layer 52 is formed as a colored translucent layer. The base surfaces of the micromirrors of the second embossing region 64 are located at a second, greater height above the carrier 28, with the height and the direction of the positive z-axis being indicated starting from the carrier 28. Since the security element 50 is designed to be viewed from the side of the carrier 28, the z-axis extends downwards away from the carrier in the illustration in Fig. 22.

[0285] The micromirror embossments or micromirror arrangements 48, 64 each contain a plurality of micromirrors inclined relative to the xy plane, the local angles of which are selected precisely such that the relief structures of the micromirror embossments 48, 64, in interaction with the color effect of the interference layer structure 60 described below and, if appropriate, a superimposed subwavelength structure 62, produce a desired optical appearance. Specifically, the angles of inclination of the micromirrors in the exemplary embodiment are selected such that the micromirror arrangements 48, 64 produce a curved, three-dimensional impression, e.g., a value number, or a movement effect, e.g., a rolling bar effect. In the exemplary embodiment, the micromirrors of the micromirror embossments 48, 64 have a lateral dimension of 10 pm x 10 pm and a maximum pitch of 3.5 pm.

[0286] As a special feature, the two micromirror arrangements 48, 64 are provided with a common coating in the form of a preferably color-stable three-layer interference layer structure 60, which follows the relief profile of the embossing lacquer layer 46 or 52, respectively, and which lies in the overlapping regions 68", 68"' on the second embossing lacquer layer 52 and in the free regions 68, 68' on the first embossing lacquer layer 46. In the exemplary embodiment, the three-layer interference layer structure 60 consists of a layer sequence of absorber 54 (4 nm chromium) / dielectric 56 (150 nm SiCh) / reflector 58 (60 nm Al), starting from the embossing lacquer layers.

[0287] In the overlap region 68", 68"', the observer looks through the two embossing lacquer layers 46, 52 onto the micromirror arrangement 64, which is higher (in the direction of the positive z-axis), so that it appears with a first color impression, which is generated in the partial region 68" by the interaction of the translucent colored embossing lacquer 52 and the interference layer structure 60 with the subwavelength structure 62 and in the nanoscale smooth partial region 68"' by the interaction of the translucent colored embossing lacquer and the interference layer structure.

[0288] In the free area 68, 68' surrounding the overlap area, the observer only looks through the first transparent embossing lacquer layer 46 onto the deeper micromirror arrangement 48, so that the latter appears in a second, different color impression, which is generated in the partial area 68 by the interaction of the interference layer structure 60 with the subwavelength structure 62 and in the nanoscale smooth partial area 68' by the interference layer structure. Since the height difference between the two micromirror arrangements 24, 34 is in the range of a few micrometers, it is not perceptible to the observer, so that the two differently colored motifs and the different effects appear to be arranged next to one another in exact registration. A further coloring can be integrated into the security element 50 both via the colored embossing lacquer layer and via the nanostructuring.

[0289] Further details on the creation of the image and color effects of such designs can be found in the document WO 2020 / 244806 A1, the disclosure content of which is incorporated into the present application.

[0290] In Figures 21 and 22, the layer thicknesses of the layers 54, 56 and 58 of the interference layer structure 60 and the layer thickness of the layers of the reflection-enhancing coating or the layer systems of the interference layer structure 146, 156 as well as the period and depth of the subwavelength structures 62 (Fig. 22) and 164, 176 (Fig. 21) are shown greatly exaggerated for illustration. In fact, the layer thicknesses in a three-layer system with semi-transparent metal layer / dielectric layer / metallic reflector layer are advantageously between 50 nm and 600 nm (dielectric spacer layer) or between 3 nm and 20 nm (semi-transparent metal layer) and thus amount to only a fraction of the dimensions of the embossed structures 48, 64 (Fig. 22) or the micromirror arrangements 144, 154 (Fig. 21).

[0291] The production of a security thread according to the invention is carried out, for example, by the following process:

[0292] Printing an optional primer layer onto a PET film;

[0293] Printing a UV embossing varnish, embossing the microrelief with a partially superimposed subwavelength grating, curing the UV embossing varnish; optionally printing a wash ink;

[0294] Coating with a metallic absorber layer, e.g. chromium, in a layer thickness such that the chromium layer has a transmission between 30% and 90%, preferably approximately 50%;

[0295] Coating with a dielectric layer, e.g., SiCh, in a suitable layer thickness to generate at least one reflection maximum or minimum of the three-layer interference structure in the optically visible spectral range; coating with a metallic reflector layer, e.g., aluminum, in a layer thickness corresponding to an optical density (oD) of 1 to 5, preferably 1.5 to 3; optionally, demetallizing the film, including washing (the wash color and overlying metallic / dielectric coating(s) are removed);

[0296] Printing of primer and protective varnish layers; optional printing of magnetic areas and / or one or more fluorescent colors; printing of primer, protective varnish, opaque white, and heat seal varnish layers;

[0297] Cut.

[0298] The production of an L-patch according to the invention is carried out, for example, by the following process:

[0299] Printing a release varnish layer onto a PET film;

[0300] Printing a UV embossing varnish, then embossing the microrelief with a partially superimposed subwavelength grating, curing the UV embossing varnish; optionally printing a wash ink;

[0301] Coating with a metallic absorber layer, e.g. chromium, in a layer thickness such that the chromium layer has a transmission between 30% and 90%, preferably approximately 50%;

[0302] Coating with a dielectric layer, e.g. SiCh, in a suitable layer thickness to generate at least one reflection maximum or reflection minimum of the three-layer interference structure in the optically visible spectral range;

[0303] Coating with a metallic reflector layer, e.g., aluminum, in a layer thickness corresponding to an optical density (OD) of 1 to 5, preferably 1.5 to 3; optionally, demetallizing the PET film, including washing;

[0304] Laminating a foil onto the microrelief;

[0305] Laminating a second film;

[0306] Printing of primer, protective varnish and heat seal varnish layers;

[0307] Punching the patch shape and screening off the area not belonging to the security feature;

[0308] Cutting. The production of a T-LEAD strip according to the invention is carried out, for example, by the following process:

[0309] Printing a release varnish layer onto a PET film;

[0310] Printing a UV embossing varnish, then embossing the microrelief with a partially superimposed subwavelength grating, curing the UV embossing varnish; optionally printing a wash ink;

[0311] Coating with a metallic absorber layer, e.g. chromium, in a layer thickness such that the chromium layer has a transmission between 30% and 90%, preferably approximately 50%;

[0312] Coating with a dielectric layer, e.g. SiCh, in a suitable layer thickness to generate at least one reflection maximum or reflection minimum of the three-layer interference structure in the optically visible spectral range;

[0313] Coating with a metallic reflector layer, e.g., aluminum, in a layer thickness corresponding to an optical density (OD) of 1 to 5, preferably 1.5 to 3; optionally, demetallizing the PET film, including washing;

[0314] Printing of primer, protective varnish and heat seal coatings Cutting.

[0315] With a T-LEAD strip (T: "Transfer"), any carrier film (here: PET film) is usually removed after application to the security paper or valuable document.

[0316] List of reference symbols

[0317] Banknote security element, 14' motif value number, 16' motif star

[0318] Tilt , 20' views

[0319] Embossing lacquer layer surface area

[0320] Micromirror array carrier substrate, 30' detail sections

[0321] Thin-film element, 36 micromirrors Subwavelength structure Viewer, 44 viewing directions First embossed lacquer layer First embossed structure50 Security element Second embossed lacquer layer Absorber

[0322] dielectric

[0323] reflector

[0324] Interference layer structure Subwavelength structure Second embossed structure Lacquer coating, 68', 68", 68'" Subareas

[0325] Opinion

[0326] Motif Value Background View

[0327] Star motif

[0328] background

[0329] Opinion

[0330] Motif Value

[0331] background

[0332] View , 106 two-tone motif star

[0333] Background first view first areas bright bars second areas bright bars second view , 124 Direction of travel first / second areas

[0334] Security element

[0335] Detail section of three-channel color areas -B, 136-G, 136-R Subwavelength structures Vault motif Security element Second embossed lacquer layer Micromirror arrangement / first embossed structure Reflection-enhancing coating / Interference layer structure Primer layer Color layer First embossed lacquer layer Micromirror arrangement / second embossed structure Interference layer structure Primer layer Release layer Heat seal lacquer layer 164 Subwavelength structure

[0336] 168 sub-area

[0337] 170 grids

[0338] 172 grid elements 174 grid spaces

[0339] 176 Subwavelength structure

[0340] 200- M, O, U, R, L first views

[0341] 202 Display area

[0342] 204 Circular curve 206 Background area

[0343] 220 security element

[0344] 224 area

Claims

Patent claims 1. An optically variable display element comprising at least one reflective surface region with at least two partial regions visible to the naked eye, which, when viewed in reflected light, display at least slightly different colors, wherein the at least one reflective surface region is coated at least partially with a surface-conformal interference layer structure, the at least one reflective surface region in the first and second partial regions each contains a microrelief structure that creates a dynamic effect and is formed with a plurality of microrelief structure elements, the microrelief structure of the first partial region and / or the microrelief structure of the second partial region is / are provided at least partially with a color-modifying nanostructure formed by at least one subwavelength structure,and in the first and / or second sub-region, the color effect of the interference layer structure is modified by the color-modifying nanostructure, so that the first and / or second sub-region shows / show at least one of the different colors due to the combined effect of the interference layer structure and the color-modifying nanostructure.

2. Display element according to claim 1, characterized in that the reflective surface area, when viewed in reflected light, generates a display for at least two different viewing directions, wherein the displays at least partially overlap and have different colors at least in some areas in the overlapping area, wherein the microrelief structure of the first partial area and the microrelief structure of the second partial area each generate one of the displays for the viewer and the first and the second partial area at least partially overlap each other, wherein the the first and / or the second partial region shows / show at least one of the different colors of the representations due to the combined effect of the interference layer structure and the color-modifying nanostructure.

3. Display element according to claim 2, characterized in that the first and second partial areas are nested within one another, wherein the partial areas are preferably formed by narrow, strip-shaped sub-areas arranged alternately next to one another or by small sub-areas nested within one another in two dimensions.

4. Display element according to one of claims 1 to 3, characterized in that the microrelief structure of the first partial area and / or the microrelief structure of the second partial area in the areas which are formed to be smooth on a nanoscale is / are coated with the surface-conformal interference layer structure to produce the different colors.

5. Display element according to one of claims 1 to 4, characterized in that the microrelief structure of the first partial region and / or the microrelief structure of the second partial region in the regions which are not coated with the surface-conformal interference layer structure is / are provided with a color-generating nanostructure for generating the different colors of the displays, in particular a subwavelength structure which shows a color generated essentially on the basis of plasmon resonance, wherein the color-generating nanostructure is coated in particular with a metallization or a layer of high-refractive-index material.

6. Display element according to one of claims 1 to 5, characterized in that the dynamic effect causes a movement effect, in particular a bounce effect, a morph effect, a pump effect, a flip effect, a stereographic 3D effect and / or a three-dimensional display with a surface that projects forward and / or backward relative to the actual spatial shape of the surface area.

7. Display element according to one of the above claims, characterized in that the interference layer structure is designed at least in regions such that the color tone of the color produced by the interference layer structure and / or the color produced by the - 7 - The color produced by the interference layer structure in conjunction with the color-modifying nanostructure is color-stable when tilted up to 30° and preferably up to 45° from a vertical view.

8. Display element according to claim 7, characterized in that the interference layer structure is designed at least in regions such that the color angle h when tilted up to 30° and preferably up to 45° from a vertical view h) changes from a color tone in a vertical view with a color angle h between 0° and 60° by less than 60°, preferably by less than 30°, i) changes from a color tone in a vertical view with a color angle h between 50° and 80° by less than 30°, preferably by less than 15°, j) changes from a color tone in a vertical view with a color angle h between 75° and 105° by less than 30°, preferably by less than 15°, k) changes from a color tone in a vertical view with a color angle h between 100° and 180° by less than 80°, preferably by less than 40°, l) changes from a Colour shade in vertical view with a colour angle h between 170° and 220° by less than 50°,preferably changes by less than 25°, m) starting from a color shade in vertical view with a color angle h between 210° and 300° changes by less than 90°, preferably by less than 45°, or n) starting from a color shade in vertical view with a color angle h between 290° and 10° changes by less than 80°, preferably by less than 40°.

9. Display element according to one of the above claims, characterized in that the interference layer structure is formed by a multi-layer structure of dielectric and / or metallic layers, preferably by a three-layer thin-film element, in particular with a structure of semi-transparent metal layer / dielectric layer / metallic reflector layer or a structure of semi-transparent metal layer / Dielectric layer / semi-transparent metal layer is formed.

10. Display element according to one of the above claims, characterized in that the interference layer structure is a three-layer thin-film element with a structure of semi-transparent metal layer / dielectric layer / metallic reflector layer, the optical thickness of the dielectric layer is at most 250 nm, preferably at most 200 nm and the three-layer thin-film element in vertical view shows a reflection maximum only at the short-wave end of the visible spectrum.

11. Display element according to one of the above claims, characterized in that the interference layer structure contains a high-index dielectric which has a refractive index of more than 1.8, preferably more than 2.0 and particularly preferably more than 2.3, over the entire visible spectrum or at least in a part of the visible spectrum.

12. Display element according to one of claims 1 to 8, characterized in that the interference layer structure is a two-layer color mirror consisting of a reflective metal layer and an ultra-thin absorber layer made of silicon, a silicon alloy or SiOx with x < 1 arranged on the metal layer.

13. Display element according to one of the above claims, characterized in that the microrelief structure is formed by a micromirror arrangement with directionally reflecting micromirrors, in particular by a micromirror arrangement with flat micromirrors or by a micromirror arrangement with micromirrors which have a curved profile or a varying, partially constant inclination in one or two directions, wherein the micromirrors form in particular a periodic or aperiodic sawtooth grating, by a Fresnel structure, by an arrangement of concave / convex curved microelements and / or by a freeform surface.

14. Display element according to one of the above claims, characterized in that the subwavelength structure of the color-modifying and / or the color-generating nanostructure is formed by structures with a lateral size between 50 nm and 450 nm, in particular between 100 nm and 300 nm, and / or a depth between 20 nm and 450 nm, in particular between 100 and 300 nm.

15. Display element according to one of the above claims, characterized in that the subwavelength structure of the color-modifying and / or the color-generating nanostructure is formed by one-dimensional grids or by two-dimensional grids, in particular with rectangular, square, diamond-shaped, hexagonal or parallelogram-shaped Lattice symmetry, with a period length in at least one direction between 100 nm and 600 nm, in particular between 50 nm and 450 nm.

16. Display element according to one of the above claims, characterized in that at least two subwavelength structures are provided for generating the different colors, which differ in a structural parameter influencing the color, wherein the structural parameter comprises at least one of the following parameters of the subwavelength structure: period length, depth and / or profile shape of the structures of the subwavelength structure.

17. Display element according to one of claims 13 to 16, characterized in that the subwavelength structures for the different colors are arranged registered to the microrelief structure elements of the microrelief structure of the reflective surface region, so that each microrelief structure element is occupied only by a specific type of subwavelength structure.

18. Display element according to claim 16 or 17, characterized in that the microrelief structure elements are formed by micromirrors and one or more of the structural parameters of the subwavelength structures influencing the color exhibit a variation as a function of a parameter determining the orientation of the micromirrors, in particular as a function of the mirror pitch or as a function of the azimuth angle.

19. Display element according to one of claims 1 to 16, characterized in that the colors visible to a viewer when viewing the display element contain mixed colors that are created by a color mixture of colors of pixel-shaped sub-areas with a dimension below the resolution limit of the human eye, wherein the colors of the pixel-shaped sub-areas are each generated by a specific type of sub-wavelength structure that is characteristic of this color.

20. Display element according to one of the above claims, characterized in that the surface extension of the display element defines a z-direction perpendicular thereto, wherein the reflective surface area contains a primary structure in the form of a first embossing lacquer layer with a first embossed structure which is formed by a first of the micro-relief structures, the first embossing lacquer layer is partially covered by a secondary structure, so that on the first embossing lacquer layer there are overlapping areas with a secondary structure and free areas without a secondary structure, wherein the secondary structure is formed by the second of the micro-relief structures, and the primary structure and / or the secondary structure is / are provided at least in regions with the color-modifying nanostructure, so that the color-modifying nanostructure is arranged in the overlapping areas on the secondary structure and / or in the free areas on the primary structure.

21. Display element according to one of claims 1 to 19, characterized in that the surface extension of the display element defines a z-direction perpendicular thereto, wherein the reflective surface area contains two structures which are arranged at different heights in the z-direction, the structures are each formed by one of the microrelief structures and are provided with a color coating, wherein at least one of the color coatings is formed by the interference layer structure, the two structures overlap in the reflective surface area and the color coating of the higher-lying structure in the reflective surface area is designed as a regular or irregular grid with grid elements and grid spaces,so that in the reflective surface area, the colour coating of the deeper structure appears to a viewer from at least one viewing direction through the grid spaces of the colour coating of the higher relief structure, and, the structure provided with the interference layer structure or at least one of the structures provided with the interference layer structure is provided at least in regions with the color-modifying nanostructure.

22. Display element according to claim 21, characterized in that a first of the color coatings is formed by the interference layer structure and a second of the color coatings is formed by a metallization or a further interference layer structure, wherein the structure provided with the metallization is preferably provided with a color-generating nanostructure.

23. Display element according to one of claims 1 to 22, characterized in that the display element is a security element for protecting valuables.

24. A data carrier with an optically variable display element according to one of claims 1 to 23.

25. A method for producing an optically variable display element, in particular according to one of claims 1 to 23, in which at least one reflective surface area with at least two partial areas visible to the naked eye, which, when viewed in reflected light, display different colors at least in some areas, is produced in the optically variable display element, wherein the at least one reflective surface area is provided by forming in a first and in a second partial area a microrelief structure with a plurality of microrelief structure elements, which produces a dynamic effect, wherein the microrelief structure of the first partial area and / or the microrelief structure of the second partial area is / are overlaid at least in some areas with a color-modifying nanostructure, wherein the color-modifying nanostructure is formed by a subwavelength structure, the reflective surface area is at least partially covered with a surface-conforming Interference layer structure is coated, wherein in the first and / or in the second partial area the color effect of the interference layer structure is modified by the color-modifying nanostructure, so that the first and / or the second partial area shows / show at least one of the different colors due to the combined effect of the interference layer structure and the color-modifying nanostructure.

26. An optically variable display element having a reflective surface region which, when viewed in reflected light, produces different displays for at least two different viewing directions, wherein the displays individually or in relation to one another have different colors at least in certain regions, wherein the reflective surface region is coated with a surface-conformal interference layer structure, the reflective surface region produces a dynamic effect and contains, in at least a first and a second sub-region, a microrelief structure which is formed with a plurality of microrelief structure elements, the microrelief structure of the first sub-region being provided, at least in some regions, with a color-modifying first nanostructure which is formed by at least one first sub-wavelength structure,the microrelief structure of the second partial area is not provided with a color-modifying nanostructure or is provided with a second nanostructure which modifies the color generated by the interference layer structure in a visibly different manner than the first nanostructure, and which is formed by at least one second subwavelength structure, and the differences between the different colors of the representations are caused by the different color modification of the color of the interference layer by the in the first, and second sub-area, the first and optionally second nanostructure are generated.

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