Optically variable security element, article of value, and production method

Abstract

The invention relates to an optically variable security element (12) for securing articles of value (10), comprising a reflective surface region (14) which contains a plurality of reflective pixel elements (20) that together produce an optically variable motif representation, the appearance of which changes in the plane of the reflective surface region when the security element is tilted in a first direction (16). According to the invention, the pixel elements (20) each have a constant inclination, except for any isolated discontinuities, with respect to the reflective surface region (14) in the first direction (16), the pixel elements (20), in a second direction (18) perpendicular to the first direction, in the plane of the reflective surface region, each have an inclination with respect to the reflective surface region (14) that varies, except for any isolated discontinuities, in a predetermined inclination range in the entire surface region (14) or in two or more partial surface regions (52, 54; 60, 62, 64) visible to the naked eye, as a result of which the optically variable motif representation, when tilted in the second direction (18), appears with substantially uniform brightness in the entire surface region or in said partial surface regions.

Description

[0001]Optically Variable Security Element, Valuables, and Manufacturing Method. The invention relates to an optically variable security element for securing valuables, comprising a reflective surface area containing a plurality of reflective pixel elements that together generate an optically variable motif representation, the appearance of which changes when the security element is tilted along a first direction in the plane of the reflective surface area. The invention also relates to a valuable document with such an optically variable security element and a method for manufacturing such an optically variable security element. Data carriers, such as valuables or identification documents, but also other valuables, such as branded goods, are often provided with security elements for protection, which allow verification of the authenticity of the data carriers and simultaneously serve as protection against unauthorized reproduction.For a long time, foil-based security elements have been used to protect banknotes, securities, and identification documents. Embossed holograms, which have been used since the late 1980s, are now very widespread and therefore no longer offer a high level of protection against counterfeiting. For this reason, micro-optical systems, for example, based on micromirrors, are increasingly being used for authentication. Security elements with micro-optical systems are generally still easily visible even under unfavorable lighting conditions and also allow for the creation of attractive optical effects. For example, micromirrors can be used to create scrolling effects that exhibit high optical variability when the security element is tilted in a specific direction.However, it has been found that when the element is tilted perpendicular to the direction of the effect, the running effects or other optically variable effects are often only visible in a narrow area, or exhibit a grainy, gritty appearance in a wider area. Based on this, the invention aims to provide a security element of the type with high counterfeit protection and an attractive visual appearance. The invention is also intended to provide a security document and a method for manufacturing such a security element. This objective is achieved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims. The invention comprises an optically variable security element with a reflective surface area containing a plurality of reflective pixel elements.The pixel elements together create an optically variable motif display, the appearance of which changes when the safety element is tilted along a first direction in the plane of the reflective surface. This first direction is also referred to in this description as the effect direction or north-south direction. The safety element is designed so that the pixel elements along the first direction each exhibit a constant inclination to the reflective surface, except for any isolated discontinuities. Along a second direction, perpendicular to the first direction in the plane of the reflective surface, the pixel elements each exhibit an inclination to the reflective surface that varies within a predefined range across the entire surface area or in two or more sub-areas visible to the naked eye, except for any isolated discontinuities.This second direction is also referred to in this description as the east-west direction. Due to this configuration of the pixel elements, the optically variable image representation appears with essentially uniform brightness across the entire surface area or in the aforementioned sub-areas when tilted along the second direction. The security element serves in particular to protect valuables, such as banknotes or other valuable documents. Each pixel element can contain one or more reflective facets. If a pixel element contains multiple facets, the height profile of the pixel element typically exhibits a discontinuity at the interface between adjacent facets, which also results in an isolated discontinuity in the tilt of the pixel element along the first and / or second direction. In an advantageous embodiment, all pixel elements contain the same number of reflective facets.The facets of a pixel element advantageously exhibit the same inclination distribution in both the first and second directions. Essentially uniform brightness means that while the brightness of the area or sub-areas may vary in intensity when tilted along the second direction, the brightness within the visible range varies only slowly, and the brightness distribution is smooth, i.e., not grainy or gritty. Furthermore, any intensity variations within the visible range are advantageously small, particularly less than 10% or even less than 5% of the maximum brightness. In a preferred embodiment of the invention, the inclination of the pixel elements varies continuously along the second direction, except for any isolated discontinuities, so that the pixel elements have a curved profile in the second direction.In particular, with a continuous variation of the inclination, all inclination values ​​within the specified inclination range are actually assumed at least once. For example, the specified inclination range can extend from -10° to +10°, whereby, due to the continuous curvature, all inclination values ​​between -10° and +10° are assumed. In a preferred embodiment, the inclination of the pixel elements is described, except for any isolated discontinuities, by a second-order polynomial function (parabola). This ensures that incident light in the second direction is reflected uniformly in all directions, thus producing a matte, uniform appearance in the second direction. In another, equally advantageous embodiment, the inclination in the second direction deviates specifically from a parabolic shape to make certain reflection angles appear brighter or darker.For example, a fourth-order polynomial can be used to describe the inclination. This results in brighter central reflection angles compared to using a second-order polynomial. However, the inclination in the second direction can also be described independently of mathematical functions and form an arbitrarily curved, continuous surface. In particular, the pixel elements in the second direction can have a convex profile, a concave profile, or a partially convex and partially concave profile, except for any isolated discontinuities. In an advantageous embodiment, a subset of the pixel elements is convex and another subset is concave. This is advantageous, for example, when the first direction is in the direction of travel of the production machines.In this case, for example, all pixel elements inclined in the first direction (in the machine direction) can be concave in the second direction, and all pixel elements inclined in the first direction (against the machine direction) can be convex in the second direction. The reverse assignment of concave / convex pixel elements is also possible. In this way, it can be achieved that during production, all pixel elements with their "rounded tip" (see Fig. 3 or Fig. 4a) lead into the embossing lacquer and thus, similar to the bow of a ship, glide more easily through the lacquer, thereby trapping fewer disruptive air bubbles.In another, equally advantageous embodiment of the invention, the inclination of the pixel elements along the second direction is constant section by section, except for any isolated discontinuities, and assumes at least 3, preferably at least 5, different inclination values ​​within the specified inclination range. The sections with different inclinations seamlessly connect to one another at the transitions. In particular, with a section by section constant variation of the inclination, the maximum and minimum values ​​of the inclination range, as well as at least one, preferably at least 3, different values ​​from within the inclination range, are assumed. For example, the specified inclination range can extend from -10° to +10°, whereby the section by section constant curvature results in the inclination values ​​-10°, -5°, 0°, +5°, and +10°.A sectionally constant inclination results in a particularly high, smooth brightness when tilted east-west, although the intensity may vary slightly. To ensure particularly small intensity fluctuations, the angular spacing of adjacent inclination values ​​is advantageously chosen to be smaller than the scattering angle range of the planar facet sections. The specified inclination range advantageously has an angular extent between 10° and 90°, preferably between 15° and 40°, and most preferably between 15° and 25°. Furthermore, it is advantageously provided that the specified inclination range is essentially symmetrical to the normal of the reflective surface area. If the normal direction is thus associated with an angle of 0°, as is customary, the inclination range can, for example, extend from -45° to +45°, from -20° to +20°, or from -10° to +10°.In other, equally advantageous embodiments, the specified inclination range is not symmetrical to the normal. For example, in the case of a parabola, only the portion with a positive slope can be used to selectively reflect light only in the "east" direction and not in the "west" direction. However, other asymmetric curvature distributions are also possible. The pixel elements advantageously have dimensions between 3 µm and 100 µm, preferably between 5 µm and 20 µm. Advantageously, the pixel elements all have the same shape, for example, they are all square or rectangular. The pixel elements advantageously have a maximum pitch that lies between 0.5 µm and 10 µm, preferably between 1 µm and 5 µm. In a preferred embodiment of the invention, it is provided that all pixel elements have the same inclination profile in the second direction, for example, the same concave or convex curvature profile.Alternatively, the reflective surface area can be configured to contain several groups of pixel elements, each group exhibiting a uniform inclination profile, but differing inclination profiles within the other group. For example, the pixel elements in a first group are all concave in the same way, while those in a second group are all convex in the same way. The pixel elements can also be concave (or convex) over a wide inclination range in a first group and concave (or convex) over a narrow inclination range in a second group. In all of these variations, the reflective pixel elements can be equipped with one property from Group A and / or one property from Group B below.Group A, Structure Combinations: a) Without nanostructures, i.e., only curved / planar mirror surfaces; b) All pixel elements are covered with nanostructures, including the following possibilities: i) Structures with the same structural parameters everywhere, in particular height, diameter, period, arrangement in one or two dimensions, or also specifically aperiodic randomly distributed nanostructures; ii) Nanostructures with different structural parameters are used across the surface of the security element.Among other possibilities are the following: α) Area-specific constant structural parameters, for example, multi-colored images or differently colored flip motifs; β) Continuous variation of one or more structural parameters to create, for example, color gradients; c) There are areas without nanostructures and areas with nanostructures: i) the areas with nanostructures all have the same structural parameters; ii) the areas with nanostructures can all have different structural parameters (more color, color gradients). The curved or flat mirror surfaces of the reflective pixel elements essentially determine the direction in which incident light is reflected. Any additional nanostructures do not change the direction of reflection of the incident light, but rather create a color that differs from the color of the coated area without nanostructures.The nanostructures thus modify the natural color effect (with a constant color or a color-shifting effect) of the coating, making it possible to create colors or color combinations that would not be possible without nanostructures. It is possible for the curved mirror surfaces of the pixel elements to be completely coated with a specific nanostructure (and thus color). Advantageously, the surface of a pixel element can also be divided into sub-areas with different nanostructures. In particular, the nanostructure can be chosen depending on the local orientation of the curved mirrors. For example, the surface areas of a curved mirror oriented in one direction (e.g., "north") can be coated with red-producing nanostructures, and all surface areas oriented in a second direction (e.g., "south") can be coated with green-producing nanostructures.This means that the effect presented by this curved mirror appears red from the first (north) direction and green from the second (south) direction. It goes without saying that other color combinations can also be chosen. The dependence of the chosen nanostructure on the local orientation of the pixel elements can be the same for all pixel elements (resulting in a full-surface, angle-dependent color change) or it can be chosen differently for individual pixel elements or groups of pixel elements (resulting, for example, in a multicolored image viewed from a specific angle that exhibits locally different color changes when tilted).In an advantageous embodiment, continuously curved mirror surfaces can be provided with a continuously changing nanostructure such that, when tilting the safety element, an observer perceives a dynamic effect caused by the mirror's curvature, coupled with a continuous color transition. This assignment can be achieved by determining the local slope (normal vector) at a specific location on the curved mirror and then assigning the corresponding specific nanostructure to this normal vector. Locations with the same local orientation then exhibit, for example, the same nanostructure. The nanostructures can be designed as elevations and / or depressions relative to the surrounding surface.Advantageously, these nanostructures have a lateral size between 50 nm and 450 nm, particularly between 100 nm and 300 nm, and / or a depth between 20 nm and 450 nm, particularly between 100 nm and 300 nm. In the case of periodic arrangements of the nanostructures (in one or two dimensions), the period length in at least one direction can be chosen between 50 nm and 600 nm, particularly between 50 nm and 450 nm. In the case of two-dimensional periodic arrangements, the nanostructures form, in particular, lattices with rectangular, square, rhomboid, hexagonal, or parallelogram-shaped lattice symmetry. In cross-section, the nanostructures can advantageously have a nearly binary or rectangular profile with steep, ideally perpendicular, flanks. They can also have a rounded, for example, sinusoidal or sinusoidal profile, which offers other advantages, such as improved moldability.Group B, Coatings: a) Reflective metal layers, for example made of aluminum, silicon, silver, gold, copper, chromium, titanium, iron, nickel, or an alloy of two or more of these metals; b) Dielectrics, in particular with a refractive index different from that of an embossing / sealing lacquer used in the security element, for example ZnS, MgF2, HfO2, SiO2. Furthermore, low-refractive-index dielectric materials with a refractive index of 1.65 or less are suitable, in particular selected from the group consisting of silicon dioxide (SiOx), silicon dioxide (SiO2), aluminum oxide (Al2O3), metal fluorides, for example magnesium fluoride (MgF2), aluminum fluoride (AlF3), cerium fluoride (CeF3), sodium aluminum fluorides (e.g. Na3AlF6 or Na5Al3F). 14), neodymium fluoride (NdF3), lanthanum fluoride (LaF3), samarium fluoride (SmF3), barium fluoride (BaF2), calcium fluoride (CaF2), lithium fluoride (LiF), low-refractive-index organic monomers and / or low-refractive-index organic polymers or at least a high-refractive-index dielectric material with a refractive index greater than 1.65, in particular selected from the group consisting of zinc sulfide (ZnS), zinc oxide (ZnO), titanium dioxide (TiO2), carbon (C), indium oxide (In2O3), indium tin oxide (ITO), tantalum pentoxide (Ta2O5), cerium oxide (CeO2), yttrium oxide (Y2O3), europium oxide (Eu2O3), iron oxides such as (II) iron(III) oxide (Fe3O4) and iron oxide (Fe2O3), hafnium nitride (HfN), hafni- umcarbide (HfC), hafnium oxide (HfO2), lanthanum oxide (La2O3), magnesium oxide (MgO), neodymium oxide (Nd2O3), praseodymium oxide (Pr6O 11), Samarium oxide (Sm₂O₃), antimony trioxide (Sb₂O₃), silicon carbide (SiC), silicon nitride (Si₃N₄), silicon monoxide (SiO₂), selenium trioxide (Se₂O₃), tin oxide (SnO₂), tungsten trioxide (WO₃), high-refractive-index organic monomers and / or high-refractive-index organic polymers. c) Layer systems: i) Color-shifting coating consisting of: - a semi-transparent reflector (especially thin Cr / Ti / Al; thicknesses of a few nm or around 10 nm) or a metallic material selected from the group consisting of nickel, titanium, vanadium, chromium, cobalt, palladium, iron, tungsten, molybdenum, niobium, aluminum, silver, copper and / or alloys of these materials; - a dielectric, for example SiO₂ / ZnS; with thicknesses of a few to several hundred nm; – Reflector layer, for example made of Al / Ag / Cu / Au, with thicknesses ranging from a few tens of nm to thicker, opaque reflector layers, or made of a metallic material selected from the group consisting of aluminum, silver, copper, gold, platinum, niobium, tin, or nickel, titanium, vanadium,Chromium, cobalt, and palladium, or alloys of these materials; ii) Color-changing coating made of: – a semi-transparent reflector, for example, thin Al / Cr / Ti; with thicknesses of approximately 10 nm; – a dielectric, for example, SiO2 / ZnS; with thicknesses of a few to several hundred nm; – a semi-transparent reflector, for example, thin Al / Cr / Ti; with thicknesses of approximately 10 nm. iii) Other multilayer systems consisting of different dielectrics / metals (materials as above), wherein a refractive index transition occurs at the interface between the layers, leading to reflection. The layer thicknesses can be chosen to produce a controlled constructive interference, or to avoid controlled interference.to obtain increased broadband reflection. Alternating dielectric layers with different refractive indices (interference at a multilayer system) are advantageous. Layer systems consisting of a metallic reflector and a semiconductor, for example Si, are also advantageous. High-refractive-index or low-refractive-index materials (relative to the adjacent material) over a metallic reflector, for example ZnS-aluminum, are also advantageous. d) Liquid crystals, especially cholesteric liquid crystals, can also be used as color-shifting layers. For all these coatings of group B, additional adhesion promoter layers, for example very thin layers of chromium, titanium, or polymer primers, can be used.to create better adhesion. These can be used between the embossing varnish / sealing varnish and the coating, but also between individual layers of the coating. In a preferred embodiment, the reflective surface area in all variants can have at least one metallized sub-area and one demetalized sub-area. In a preferred embodiment, at least one demetalized sub-area is created by a washing process in which a wash ink, i.e., a printing ink with low adhesion, is applied to the desired sub-area before the coating steps.and the wash color is removed along with the coating layers after coating. In another preferred variant, at least one demetallized sub-area has etch support structures to increase the etch rate of a coating. After coating both the subsequently metallized and the subsequently demetallized sub-areas, the coating is completely removed (or in desired layers) from the latter sub-areas in an etching process, while sufficient material remains on the former sub-areas. By equipping sub-areas with such etch support structures, a perfect match of the reflection properties (reflective / non-reflective, e.g., transparent) with other effects, such as motif boundaries, can be achieved, since both the effect-generating structures and the etch support structures are created in the same operation.in particular, they can be embossed. In this context, demetallization refers to the removal of one or more, in particular reflective and typically metallic, coating layers. In an advantageous embodiment of the invention, the reflective surface area is divided into at least two sub-areas, which are in particular designed in the form of a pattern, motif, or coding, wherein – at least a first sub-area is covered with pixel elements that are designed in the manner described above and that generate a movement effect, in particular a running effect, in an effect direction, which is visible in a visibility area perpendicular to the effect direction, and – at least a further, second sub-area is provided with pixel elements that are not designed in the manner described above.and which macroscopically produce essentially the same motion effect in the direction of the effect. The at least one second sub-surface is advantageously provided with non-curved pixel elements that have a constant inclination to the reflective surface area in a first direction, and whose inclination in a second direction, perpendicular to the first direction, exhibits an essentially random variation around a region-specific mean orientation. Such pixel elements are described in more detail, for example, in publication WO 2011 / 066991 A2, the disclosure content of which is incorporated into the present description to the extent necessary. The pixel elements of the at least one second sub-surface can, in particular, be designed such thatthat they generate essentially the same visibility area for the motion effect perpendicular to the direction of the effect as the pixel elements of at least one first sub-area. From a certain distance or only superficially viewed, the first and second sub-areas then appear identical or at least very similar; however, upon closer inspection or with a magnifying glass, the uniform brightness generated by the pixel elements according to the invention can be distinguished from the grainier, gritty brightness distribution of conventional designs with randomly varying inclinations. The different design of the first and second sub-areas therefore constitutes a hidden security feature of the security element. In other embodiments, it is also possible toto design at least one second sub-area with a different visibility area perpendicular to the effect direction. Motifs with fine lines or delicate elements are advantageously designed as the first sub-areas, since the inventive mirrors provide the complete desired east-west visibility in a single pixel element, whereas conventional mirrors with east-west noise require a larger number of pixel elements to achieve complete east-west visibility. In some cases, it is desirable for motif areas to be selectively visible in a running effect. In this case, the sub-areas with conventional pixel elements can be assigned a different east-west noise pattern than the main area of ​​the effect, while the north-south pattern is identical or at least similar. It is also possible toThe invention allows for the targeted use of different north-south tilting effects for the subject and background of a motif. For example, the walking effect in the motif can be positioned slightly offset behind the background effect. Opposing directions of movement are also conceivable, as are completely different movement effects. In these cases, the structures according to the invention also have the advantage that they can provide full visibility during east-west tilting, even with intricate motifs. The invention also includes a security document, in particular a banknote, with a security element of the described type. The invention further includes a method for producing an optically variable security element of the described type, in which a reflective surface area is formed with a plurality of reflective pixel elements that together generate an optically variable motif representation.whose appearance changes when the safety element is tilted along a first direction in the plane of the reflective surface area. It is provided that: – the pixel elements along the first direction are each formed with a constant inclination to the reflective surface area, except for any isolated discontinuities; – the pixel elements along a second direction, perpendicular to the first direction in the plane of the reflective surface area, are each formed with an inclination to the reflective surface area that varies within a predefined inclination range in the entire surface area or in two or more sub-areas visible to the naked eye, except for any isolated discontinuities.– whereby the optically variable motif representation appears with a substantially uniform brightness across the entire surface area or in the aforementioned sub-areas when tilted along the second direction. According to an advantageous embodiment, the pixel elements of the reflective surface area are embossed in the same step as at least one other embossed security feature of the security element. This can be, in particular, an optically variable security feature such as a hologram, a sawtooth structure (tilting images, cinematic effects, 3D representations, etc.), a microlens or microconcave mirror array, or a microlens or microconcave mirror image. The at least one other security feature is advantageously metallized or coated with a metallic layer or an interference layer structure in the same step as the facets of the pixel elements.such as a color-shifting thin-film element. The preferred embodiments and their advantages presented with reference to the respective method according to the invention apply accordingly to the security element according to the invention. The components of the security element according to the invention are each designed to perform the respective steps of the method. Further features of the invention will become apparent from the claims, the figures, and the description of the figures. Exemplary embodiments of the invention are explained in more detail below with reference to schematic drawings. In the figures, identical or functionally equivalent elements are provided with the same reference numerals. Figure 1 shows a schematic representation of a banknote with an optically variable security element according to the invention, and Figure 2 shows a schematic view of the security element of Figure 1 in various tilting positions.Fig. 3 shows a detailed section of the reflective surface area of ​​the safety element of Fig. 1 with 3x3 pixel elements in top view; Fig. 4 shows the height profile within a pixel element of Fig. 3, where (a) shows a grayscale representation and (b) and (c) show the height profile of the mirror surface within the pixel element in the north-south direction and east-west direction, respectively; Fig. 5 shows a three-dimensional representation of the height profile of a pixel element; Fig. 6 shows a detailed section of the reflective surface area of ​​a safety element according to another embodiment; Fig. 7 shows a schematic diagram illustrating the tilting behavior of a safety element according to the invention; Fig. 8 in (a) to (d) shows schematic diagrams for further variants of safety elements according to the invention with different tilting behavior when tilted east-west.Figure 9 shows a security element according to a further development of the invention with a hidden authentication feature. 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 according to the invention in the form of an affixed 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, for labels on goods and packaging or for securing documents, identity cards, passports, credit cards, etc.Health cards and the like. In banknotes and similar documents, in addition to transfer elements (such as strips or patches with or without their own backing film), security threads or security strips partially or completely embedded in the document substrate are also considered. The security element 12 has a reflective surface area 14, which in the exemplary embodiment is formed with an outer contour in the shape of the value numeral "10". As shown in the detailed view of Fig. 3, the reflective surface area 14 is divided into a plurality of small, reflective pixel elements 20, which together generate the optically variable motif representation of the value numeral "10" of the security element 12. The pixel elements 20 have, for example, an area of ​​20 µm x 20 µm and each contains three ray-optically effective reflective facets 22.The pixel elements 20, acting like tiny mirrors, direct the incident light into a reflection direction determined by the condition "angle of incidence equals angle of reflection". Therefore, in this description, the pixel elements 20 are also referred to as micromirrors. The inclination of the facets or pixel elements is adjusted, as described in more detail below, such that the appearance of the motif representation of the number "10" changes when the security element 12 is tilted, thus creating an optically variable appearance. The security element 12 exhibits different behavior depending on the tilting direction 16, 18. With reference to Figures 1 and 2, a tilt in a first direction 16 is hereinafter referred to as north-south tilting, and a tilt in the perpendicular second tilting direction 18 as east-west tilting. The use of cardinal directions serves only for the simple naming and illustration of the different tilting processes; it is understood thatthat the first and second directions do not necessarily coincide with the actual cardinal directions. Without tilting, i.e., when viewed essentially vertically, the surface area 14 of the security element 12 appears as a metallic, shiny number "10" with a bright horizontal bar 15 approximately in the middle of the two digits (Fig. 1 and view 20 in Fig. 2). If the banknote 10, and thus the security element 12, is tilted by a user in a north-south direction 16, the bright bar 15 within the number "10" appears to run continuously towards the upper or lower edge of the digits, thereby creating a so-called rolling bar effect (view 20-N or 20-S in Fig. 2). However, conventional designs often have the disadvantage that the rolling bar effect is only visible within a very narrow angular range when the banknote is tilted in an east-west direction 18, i.e., perpendicular to the main effect direction 16.or that the appearance is not smooth, but grainy and gritty over a wider viewing area. In contrast, the optically variable rolling bar effect of the security element 12 is visible from a wide angle in the east-west direction and also appears with a smooth, uniform brightness. More precisely, when viewed vertically, the security element 12 displays the value "10" with a bright, central, horizontal bar 15. When the security element 12 is tilted in the east-west direction 18, the brightness of the area 14 and the bar 15 does not change practically within a viewing area extending up to a tilt of approximately 15° to the west (view 20-W) and up to a tilt of approximately 15° to the east (view 20-E). If the security element 12 is first tilted northward from the vertical viewing direction,So that the bright bar 15 is located at the upper edge of the value number "10" (view 20-N), the safety element 12, when subsequently tilted in an east-west direction (views 20-NE and 20-NW), also shows a smooth, uniform brightness of the area 14 with the bright bar 15 at the top. If the safety element 12 is first tilted southwards from the vertical viewing direction, so that the bright bar 15 is located at the lower edge of the value number "10" (view 20-S), the safety element 12, when subsequently tilted in an east-west direction (views 20-SE and 20-SW), again shows a smooth, uniform brightness of the area 14 with the bright bar 15 at the top.Uniform brightness of the surface area 14 with the bright bar 15 at the top. The uniform visibility and brightness of the rolling bar effect across a wide range of east-west tilt angles increases the recognizability range of the motif 14 compared to conventional designs and significantly improves the visual appearance of the security element 12. This increases the security effect and the recognition value of the security element 12, and thus also its counterfeit resistance. To illustrate how the described appearance of the security element 12 is achieved, Fig. 3 shows a detail of the surface area 14 with 3x3 pixel elements 20 in a top view. In the exemplary embodiment, the pixel elements 20 have a base area of ​​20 µm x 20 µm and a maximum pitch of 3.5 µm. The height profile within a pixel element 20 is illustrated in Fig. 4, where Fig. 4(a) shows a grayscale representation.where the minimum pitch of 0 µm is represented by black and the maximum pitch of 3.5 µm by white. Figures 4(b) and (c) show the height profile of the mirror surfaces along a cross-sectional line within the pixel element 20. Figure 4(b) shows the height profile in the north-south direction 16 along line B1-B1 (curve 30) or line B2-B2 (curve 32) of Figure 4(a), and Figure 4(c) shows the height profile in the east-west direction 18 along line C1-C1 (curve 34) or line C2-C2 (curve 36) of Figure 4(a). The pixel elements 20 of the illustrated embodiment each consist of three facets 22 with the same slope profile in the north-south and east-west directions. At the interfaces where adjacent facets 22 meet, discontinuities occur in the height profile (Fig. 4(b), 4(c)) and thus, in the illustrated embodiment, also up to two isolated discontinuities in the inclination of the pixel elements. As can be seen from Figures 3 and 4,The course of the mirror inclination in the pixel elements in the north-south direction 16 differs significantly from the course of the mirror inclination in the east-west direction 18. In the north-south direction 16, the pixel elements exhibit a constant inclination to the reflective surface area 14, except for two isolated discontinuities, as can be seen from the piecewise linear height profile curves 30, 32 of Fig. 4(b). The inclination, which is constant within each pixel element, changes slowly from south to north across the extent of the surface area 14 from pixel element to pixel element.For example, from -15° at the southern (lower in Fig. 1) edge of area 14 to +15° at the northern (upper) edge of area 14. As a result, for every viewing angle, only the pixel elements 20 located in a narrow horizontal strip precisely fulfill the reflection condition "angle of incidence equals angle of reflection". Since each pixel element reflects the incident light within a certain scattering angle range of a few degrees, the result is a wide, horizontal bright bar. Due to the continuous increase in the tilt angle from south to north, when the safety element 12 is tilted in the north-south direction, the narrow strip of specular reflection shifts accordingly in the north-south direction.so that the bright horizontal bar appears to run from bottom to top or from top to bottom within the area 14 when tilted in this direction. In contrast, the pixel elements 20 do not have a constant or randomly chosen inclination in the east-west direction 18. As shown in Fig. 4(c), the height profile curves 34, 36 are concave except for any isolated discontinuities. As a result, the inclination of each individual pixel element 20 varies continuously in the east-west direction within a predefined inclination range, for example, in the inclination range from -15° to +15°. This means that each of the pixel elements 20 in the east-west direction is visible from any viewing direction within a wide angular range around the reflecting reflection direction and contributes to the appearance of the area from that viewing direction. The area 14 therefore appears smooth when tilted east-west,uniform brightness. Figure 5 shows, for further illustration, a three-dimensional representation of the height profile 40 of a pixel element 20, where the height component h is greatly exaggerated for clarity. As can be seen in Fig. 5, the height profile 42 of the pixel element is linear in the north-south direction, meaning the inclination of the pixel element 20 is constant in the north-south direction. In the east-west direction, the height profile 44 exhibits a concave curvature; there, the inclination varies continuously within a predetermined, larger symmetrical inclination range. Another embodiment of the invention is illustrated in Fig. 6, which shows a section of the reflective surface area 14 of another safety element 12 according to the invention. The height profile within each of the depicted pixel elements 20 is indicated, as in Fig. 4(a), by a grayscale representation, where the minimum pitch of 0 µm is represented by black and the maximum pitch of 3,5 µm is represented by white. The pixel elements 20 of the embodiment shown in Fig. 6 also exhibit a constant inclination in the north-south direction 16, except for isolated discontinuities, while the inclination in the east-west direction 18 varies within a predetermined range. Unlike the embodiment shown in Figures 3 and 4, however, the inclination of the pixel elements in the east-west direction does not vary continuously, but rather abruptly with 5 discrete steps, for example, with the inclination values ​​-10°, -5°, 0°, +5°, and +10°. With such a sectionally constant inclination, the safety element exhibits a particularly high brightness when tilted from east to west, with a smooth brightness gradient that varies slightly in intensity. Figure 6 also illustrates that the facets 22 belonging to pixel elements 20 adjacent in the east-west direction can be offset from each other in the north-south direction. However, the facets can also be, as shown in Fig. 3,The pixels are arranged at the same height in the north-south direction. In the embodiments described so far, the inclination of the pixel elements is chosen such that an optically variable effect occurs when tilted north-south, while the reflective surface area appears with uniform brightness in an angular range symmetrically around the specular reflection direction when tilted east-west. This behavior is generally illustrated in the schematic diagram of Fig. 7. The safety element 50 exhibits an optically variable effect when tilted north-south 16, which is schematically represented by symbols that transform from a circle to a star. When viewed from the south at an angle of -2α (lowest horizontal line), the reflective surface area shows an initial appearance (circles).which, when the viewing direction changes to a northerly direction, transitions through several intermediate stages into a final appearance (stars) at a viewing angle of +2α (top horizontal line). The viewing angles -α, 0, and +α are each indicated by horizontal lines as intermediate stages. It is understood that the symbols represent any optically variable effect. For example, in the design of Fig. 2, the circles from a southerly viewing direction correspond to the number "10" with the bright bar at the bottom of the digits, the stars from a northerly viewing direction correspond to the number "10" with the bright bar at the top of the digits, and the intermediate stages represent the bar positions in between. When tilting from east to west 18, the optically variable effect of the safety element 50 is shown for a view from a westerly direction.Visible from an angle of -2β (left vertical line) up to an eastward view, here from an angle of +2β (right vertical line), with uniform brightness. The visibility range -2β … +2β is symmetrical to the specular reflection direction at 0°. As explained in Figures 3 and 4, this can be achieved, for example, by selecting the tilt range of each pixel element in the east-west direction symmetrically to 0°, for example, from -20° to +20°. The angles α and β can be adjusted as desired over a wide range by the tilt profile of the pixel elements in the first and second directions, respectively. Figure 8 (a) to (d) shows some further variants of the inventive design with different behavior of the safety element 50 when tilted east-west. The embodiment in Fig. 8(a) shows a safety element 50',where the visibility range in the east-west direction is selected as non-symmetrically to the specular reflection direction. While the optically variable effect is visible with uniform brightness from the east direction of the security element up to an angle of +2β, the visibility range ends at an angle of -β from the west direction. Such a non-symmetrical visibility range can be achieved, for example, by selecting the tilt range of each pixel element in the east-west direction as non-symmetrically to 0°, for example, from -10° to +20°. In the embodiment shown in Fig. 8(b), the security element 50'' exhibits a strongly asymmetrical visibility range, where the optically variable effect is visible with uniform brightness only from the east direction, while it is not visible from the west direction. Such a,A strongly asymmetrical visibility range can be achieved, for example, by a tilt range of each pixel element that ends at 0° from the top or bottom, thus extending, for example, from 0° to +20° in the exemplary embodiment. The exemplary embodiments in Fig. 8(c) and (d) illustrate that a safety element can also have sub-areas with different visibility ranges. For example, the reflective surface area of ​​the safety element 50''' in Fig. 8(c) contains a first sub-area 52 in which the optically variable effect is visible when tilted in an east-west direction in a wide, symmetrical angular range from -2β to +2β, while in a second sub-area 54 it is only visible from eastern directions, but not from western directions. In the exemplary embodiment of Fig. 8(d), the safety element 50'''' shows a wide, symmetrical visibility range from -2β to +2β only in a first sub-area 60 around a perpendicular viewing angle (0°) in an east-west direction.symmetrical visibility range from -2β to +2β. In two second sub-areas 62, located to the north and south respectively, the optically variable effect is visible only in a smaller symmetrical visibility range from -β to +β in an east-west direction, and in two third sub-areas 64, located furthest north and south respectively, the optically variable effect is visible only in a narrower visibility range around 0°. Such designs with different visibility ranges can create a complex and therefore difficult-to-reproduce appearance of the safety element, in which certain parts of the optically variable effect are only recognizable from specific, predetermined visibility ranges. Figure 9 illustrates a further development of the invention.in which a security element 70 is equipped with a hidden authentication feature. In the illustrated embodiment, the reflective surface area 72 of the security element 70 is divided into four sub-areas 80, 90 and 82, 92, wherein the first sub-areas 80, 90 are designed in the form of a positive representation of the digit "5" and the currency symbol "€", respectively. The second sub-areas 82, 92 are designed in the form of a negative representation of these two symbols, i.e., they contain the symbols "5" and "€" as cutouts that are filled by the first sub-areas 80, 90. The first sub-areas 80, 90 are covered with pixel elements that are designed in the manner described above, i.e., they have a constant inclination to the reflective surface area along the north-south direction 16, except for any isolated discontinuities, and a curved profile along the east-west direction 18. The pixel elements of the first sub-areas 80,The pixels 90 generate a rolling bar effect as described above, in which, when the security element 70 is tilted in the north-south direction 16, a bright bar 84, 94 appears to run continuously towards the upper and lower edges of the symbols "5" and "€", respectively. The curvature of the pixel elements in the east-west direction also ensures uniform visibility and brightness of the rolling bar effect when the security element 70 is tilted in the east-west direction. The second sub-areas 82, 92 are provided with conventional, non-inventive pixel elements, specifically, for example, pixel elements that have a constant inclination towards the reflective surface area in the north-south direction 16, but are not curved in the east-west direction.but whose inclination in the east-west direction exhibits an essentially random variation around a region-specific mean orientation. The pixel elements of the second sub-areas 82, 92 can be adjusted with their inclination in the north-south direction such that, when tilted in the north-south direction, they macroscopically produce essentially the same rolling bar effect as the pixel elements of the first sub-areas 80, 90, i.e., they show a bright bar 86, 96 which, together with the bars 84, 94, appears to run continuously to the upper and lower ends of the sub-areas 82, 92, respectively. The random variation of the inclination of the pixel elements in the east-west direction can be adjusted such that the pixel elements of the second sub-areas 82, 92 produce essentially the same visibility area when tilted in the east-west direction as the pixel elements of the first sub-areas 80, 92.90. The first and second sub-surfaces differ, however, in the uniformity of their representation. While the first sub-surfaces 80, 90, with their curved mirrors, show a smooth, uniform gradient of brightness, the second sub-surfaces 82, 92 appear grainy or gritty upon closer inspection due to the random variation of the mirror orientations. From a certain distance or only superficially, this difference is hardly noticeable, but upon closer inspection from near or with a magnifying glass, the different appearance of the first and second sub-surfaces is recognizable, so that the different design of the first and second sub-surfaces constitutes a hidden mark of authenticity.

Claims

Patent claims 1. Optically variable security element for securing valuables, with a reflective surface area containing a plurality of reflective pixel elements which together generate an optically variable motif representation, the appearance of which changes when the security element is tilted along a first direction in the plane of the reflective surface area, characterized in that – the pixel elements along the first direction each have a constant inclination to the reflective surface area except for any isolated discontinuities, – the pixel elements along a second direction perpendicular to the first direction in the plane of the reflective surface area each have an inclination to the reflective surface area which is constant in the entire surface area or in two or more,The brightness of the visible partial areas is varied within a predetermined tilt range, except for any isolated discontinuities, in the sub-areas visible to the naked eye, resulting in the optically variable motif display appearing with a substantially uniform brightness in the entire area or in the aforementioned partial areas when tilted along the second direction.

2. Security element according to claim 1, characterized in that the tilt of the pixel elements along the second direction is varied, except for any isolated discontinuities, within a predetermined tilt range. Any isolated discontinuities are continuously varied, such that the pixel elements have a curved profile in the second direction.

3. Security element according to claim 2, characterized in that the pixel elements in the second direction, except for any isolated discontinuities, have a convex profile, a concave profile, or, in at least one sub-area, a convex profile and, in at least another sub-area, a concave profile.

4. Security element according to claim 1, characterized in that the inclination of the pixel elements along the second direction, except for any isolated discontinuities, is sectionally constant and assumes at least 3, preferably at least 5, different inclination values ​​in the specified inclination range. 5.A safety element according to at least one of claims 1 to 4, characterized in that the predetermined inclination range has an angular extent between 10° and 90°, preferably between 15° and 40°, and particularly preferably between 15° and 25°. A safety element according to at least one of claims 1 to 5, characterized in that the predetermined inclination range is essentially symmetrical to the normal of the reflective surface area. A safety element according to at least one of claims 1 to 6, characterized in that the pixel elements have a dimension between 3 µm and 100 µm, preferably between 5 µm and 20 µm.

8. Safety element according to at least one of claims 1 to 7, characterized in that the pixel elements have a maximum pitch between 0.5 µm and 10 µm, preferably between 1 µm and 5 µm.

9. Safety element according to at least one of claims 1 to 8, characterized in that all pixel elements have the same inclination profile in the second direction.

10. Safety element according to at least one of claims 1 to 8, characterized in that the reflective surface area contains several groups of pixel elements, in which the pixel elements have a uniform inclination profile within each group, but different inclination profiles within different groups. 11.A security element according to at least one of claims 1 to 10, characterized in that at least a portion of the pixel elements is provided with nanostructures and / or a coating, in particular with a reflective metal layer, a dielectric layer, a multilayer system, or a liquid crystal layer. A security element according to at least one of claims 1 to 11, characterized in that the reflective surface area comprises at least one metallized sub-area and one demetallized sub-area, wherein, in a preferred embodiment, at least one demetallized sub-area comprises etch support structures for increasing the etch rate of a coating.

13. Security element according to at least one of claims 1 to 12, characterized in that the reflective surface area is divided into at least two sub-areas, which are in particular designed in the form of a pattern, motif or encoding, wherein – at least a first sub-area is covered with pixel elements which are designed according to one of claims 1 to 12 and which generate a movement effect, in particular a running effect, in an effect direction which is visible in a visibility area perpendicular to the effect direction, and – at least a further, second sub-area is provided with pixel elements which are not designed according to one of claims 1 to 12, and which macroscopically generate essentially the same movement effect in the effect direction.

14. Security document with a security element according to at least one of claims 1 to 13. 15.Method for manufacturing an optically variable security element according to one of claims 1 to 13, in which a reflective surface area is formed with a plurality of reflective pixel elements which together generate an optically variable motif representation, the appearance of which changes when the security element is tilted along a first direction in the plane of the reflective surface area, wherein – the pixel elements along the first direction are each formed with an inclination to the reflective surface area that is constant except for any isolated discontinuities. – the pixel elements along a second direction perpendicular to the first direction in the plane of the reflective surface area are each formed with an inclination towards the reflective surface area 5, which varies in the entire surface area or in two or more sub-areas visible to the naked eye, except for possible isolated discontinuities, within a specified inclination range, 10 – whereby the optically variable motif representation appears with a substantially uniform brightness when tilted along the second direction in the entire surface area or in the aforementioned sub-areas. 15

Images