Visually variable security element and valuable document with such a security element

Abstract

The invention relates to optically variable security elements for securing valuables, with a reflective surface area containing a plurality of reflective pixel elements which - together, depending on the viewing angle, show a motif with at least one curve representation that is visible as a predetermined curve from a first viewing direction within a display area in a central position, and moves away from the central position in different directions when the safety element is tilted about two different predetermined axes within the display area, or which - together they create an optically variable motif display, the appearance of which changes when the safety element is tilted around two independent axes.

Description

[0001] The invention relates to an optically variable security element for securing valuables, comprising a reflective surface area containing a plurality of reflective pixel elements which together display a motif with at least one curve representation, depending on the viewing angle. This curve is visible from a first viewing direction within a display area in a central position and 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 invention also relates to an optically variable security element for securing valuables, comprising a reflective surface area containing a plurality of reflective pixel elements which together generate an optically variable motif representation whose appearance changes when the security element is tilted about two independent axes.The invention further relates to a security document with one of the aforementioned security elements.

[0002] Data carriers, such as valuables or identification documents, but also other valuables, such as branded goods, are often equipped with security elements for protection, which allow verification of the authenticity of the data carriers and also serve as protection against unauthorized reproduction.

[0003] 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, such as those 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.

[0004] However, it has been found that the running effects or other optically variable effects are often only visible in a narrow visibility range when the element is tilted perpendicular to the effect direction, or exhibit a grainy, gritty appearance in a wider visibility range, which is generated by a random orientation offset of the micromirrors perpendicular to the effect direction.

[0005] Based on this, the invention aims to provide a generic security element with high counterfeit protection and an attractive visual appearance. The invention also aims to provide a security document and a method for manufacturing such a security element.

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

[0007] The invention, in a first aspect, comprises an optically variable security element for securing valuables, with a reflective surface area containing a plurality of reflective pixel elements. The reflective pixel elements together display, depending on the viewing angle, a motif with at least one curve representation, which is visible from a first viewing direction within a display area in a central position as a predetermined curve, and which moves away from the central position in different directions from the central position when the security element is tilted about two different predetermined axes within the display area.

[0008] For each pixel element, a parallel direction is defined parallel to the target curve in the center position and a normal direction perpendicular to the target curve in the center position.

[0009] Each pixel element further has a first direction in the plane of the reflective surface area, along which the pixel element has a constant inclination to the reflective surface area, except for possible isolated jump points, whereby the constant inclination in the first direction is chosen depending on the distance of the respective pixel element to the target curve.

[0010] Each pixel element has a second direction in the plane of the reflective surface area, perpendicular to the first direction, along which the pixel element has an inclination towards the reflective surface area, which varies in the entire surface area or in two or more sub-surface areas visible to the naked eye, except for possible isolated discontinuities within a specified inclination range.

[0011] In this case, either the first direction corresponds to the aforementioned parallel direction and the second direction to the aforementioned normal direction, or conversely, the first direction corresponds to the normal direction and the second direction to the parallel direction. These two different assignments lead to different movement behavior of the curve representation when the safety element is tilted, as explained in more detail below.

[0012] The curve representation is particularly advantageous because this design of the pixel elements results in a largely uniform brightness in their different movement positions.

[0013] 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, resulting 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 each have the same tilt distribution in the first and second directions.

[0014] Essentially uniform brightness means that while the brightness of the surface 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, in particular less than 10% or even less than 5% of the maximum brightness.

[0015] In an advantageous embodiment, 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.

[0016] Preferably, the pixel elements have a convex profile, a concave profile, or a convex profile in at least one sub-area and a concave profile in at least another sub-area, except for any isolated discontinuities, in the second direction.

[0017] In another, equally advantageous embodiment, the inclination of the pixel elements along the second direction is constant section by section, except for any isolated discontinuities, wherein the inclination assumes at least 3, preferably at least 5, different inclination values ​​within the specified inclination range. 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°, with the section by section constant inclination values ​​being -10°, -5°, 0°, +5°, and +10°.

[0018] A section-wise constant inclination results in a particularly high, smooth brightness when tilted, although the intensity may vary slightly. To ensure particularly small intensity fluctuations, the angular distance between adjacent inclination values ​​is advantageously chosen to be smaller than the scattering angle range of the planar facet sections.

[0019] The specified inclination range expediently has an angular extent between 10° and 90°, preferably between 15° and 40°, and particularly preferably between 15° and 25°. The inclination range can be asymmetrical to the normal; for example, an inclination can exist only in the east direction but not in the west direction. Advantageously, however, the specified inclination range is essentially symmetrical to the normal of the reflective surface area.

[0020] Advantageously, the pixel elements have an axis-symmetric profile with respect to an axis in the normal direction, wherein the axis preferably runs through the center of the respective pixel element.

[0021] In an advantageous embodiment, it is provided that the constant inclination in the first direction increases or decreases monotonically, in particular strictly monotonically, with the distance of the respective pixel element to the target curve, preferably that the constant inclination in the first direction increases or decreases linearly with the distance of the respective pixel element to the target curve.

[0022] The curve representation advantageously shows at least one closed curve as the target curve, in particular two concentric ellipses or concentric rings.

[0023] In an advantageous further development, the motif includes at least a first and a second curve representation, which is visible from a first and second viewing direction within a first and second representation area in a central position as the first and second target curve, respectively, wherein the two curve representations move in different, preferably opposite, directions when the safety element is tilted.

[0024] In a second aspect, the invention includes an optically variable security element for securing valuables, with a reflective surface area containing a plurality of reflective pixel elements. The reflective pixel elements together create an optically variable motif representation, the appearance of which changes when the security element is tilted about two independent axes.

[0025] Each pixel element has a first direction in the plane of the reflective surface area, along which the pixel element exhibits a constant, pixel-specific inclination to the plane of the reflective surface area, except for possible isolated discontinuities.

[0026] Each pixel element also has a second direction perpendicular to the first direction in the plane of the reflective surface area, along which the pixel element has an inclination to the plane of the reflective surface area, which varies in the entire surface area or in two or more sub-surface areas visible to the naked eye, except for possible isolated discontinuities in a pixel-specific inclination range.

[0027] The motif representation, or at least parts of the motif representation, generated by the multitude of reflective pixel elements, move in different directions when the security element is tilted around the two independent axes.

[0028] A particular advantage is that it is further provided that - the optically variable motif representation is formed by a plurality of line elements or is approximated by a plurality of line elements, - the constant inclination in the first direction and the inclination range in the second direction are chosen for each pixel element to generate one of the aforementioned line elements of the motif representation, and - the line elements generated by the multitude of reflective pixel elements create an appearance in which the motif representation, or at least parts of the motif representation, move in different directions when the security element is tilted around the two independent axes.

[0029] In an advantageous embodiment, it is provided that the motif representation or at least parts of the motif representation move parallactically when the safety element is tilted about the two independent axes, so that the motif or the motif parts appear three-dimensional and seem to lie above and / or below the safety element.

[0030] The constant inclination in the first direction is advantageously selected as a function of the distance of the respective pixel element to the generated line element. It is further advantageous that the constant inclination in the first direction increases or decreases monotonically, and in particular strictly monotonically, with the distance of the respective pixel element to the generated line element; preferably, that the constant inclination in the first direction increases or decreases linearly with the distance of the respective pixel element to the generated line element.

[0031] According to a preferred embodiment, the motif representation includes an elliptical ring, in particular a circular ring, which appears to float above or below the security element, wherein the first direction for the pixel elements contributing to the generation of the circular ring is the radial direction towards the center of the elliptical ring or circular ring. Preferably, the elliptical ring or circular ring is approximated by a group of line elements, and the first direction for the pixel elements that generate the line elements of said group is the radial direction towards the center of the elliptical ring or circular ring.

[0032] The motif representation advantageously includes at least two elliptical rings, in particular two circular rings, which appear to float at different heights or depths, preferably one ring appearing to float above and one ring below the safety element, and wherein the rings are concentric to each other from a certain viewing direction of the safety element.

[0033] In a suitable design, neighboring pixel elements each exhibit a similar first direction in certain areas, resulting in an essentially continuous progression of the first direction in each of the aforementioned areas.

[0034] In both aspects, a further development of the invention may provide that the reflective surface area contains at least two subgroups, each with a plurality of pixel elements, as well as at least one coexistence area in which pixel elements from at least two of the aforementioned subgroups are located. The pixel elements are each covered with optical structures, and the pixel elements of at least one subgroup involved in the coexistence area are configured as described for the first or second aspect. Each of the subgroups involved in the coexistence area generates a partial motif visible from a specific visibility area. The visibility areas of the involved subgroups are not congruent, so that for each involved subgroup there is a partial visibility area in which the partial motifs generated by the other involved subgroups are not visible.

[0035] Preferably, the dimensions of the pixel elements are below the resolution limit of the human eye, or at least the surface areas of the subgroups cannot be separated with the naked eye.

[0036] The pixel elements of one of the participating subgroups can also be provided with planar facets of the type described in publication WO 2016 / 180522 A1, in which the planar facets have a first inclination component that is selected depending on the distance of the respective facet to the target curve or the motif representation, and a second of the two inclination components in a predetermined fanning area is selected independently of the distance of the respective facet to the target curve or the motif representation, and is preferably irregularly varied in the fanning area, in particular according to a random number distribution or a pseudorandom number distribution.

[0037] In an advantageous embodiment, there is no overlap between the visibility areas of the subgroups involved. In a further preferred embodiment, the pixel elements are divided into exactly two subgroups, so that an optical flip (switch) between two different sub-motifs or different optical effects occurs.

[0038] In both aspects, an advantageous embodiment of the invention may provide that the reflective surface area is divided into at least two sub-areas, which are configured in particular as a pattern, motif, or encoding. At least one first sub-area is covered with pixel elements configured as described for the first or second aspect of the invention and which generate a motion effect, in particular a running effect, in an effect direction that is visible in a visibility range perpendicular to the effect direction. At least one further, second sub-area is provided with pixel elements that are not configured as described for the first or second aspect and which macroscopically generate essentially the same motion effect in the effect direction and essentially the same visibility range perpendicular to the effect direction as the pixel elements of the first sub-area.

[0039] In an advantageous modification of the invention, it can be provided that the at least one further, second sub-area is provided with pixel elements that are not designed according to the type described for the first or second aspect, and which macroscopically produce essentially the same movement effect in the direction of effect, but perpendicular to the direction of effect, specifically generate a different visibility area than the pixel elements of the first sub-area.

[0040] The pixel elements of the second sub-area can in particular be provided with planar facets of the type described in publication WO 2016 / 180522 A1, in which the planar facets have a first inclination component which is selected depending on the distance of the respective facet to the target curve or the motif representation and a second of the two inclination components in a predetermined fanning area is selected independently of the distance of the respective facet to the target curve or the motif representation, and is preferably varied irregularly in the fanning area, in particular according to a random number distribution or a pseudorandom number distribution.

[0041] The two modifications described above allow the security element to be equipped with an additional, hidden authentication feature, since the appearance of the first and second sections is very similar upon superficial inspection or from a greater distance, and differences in the appearance of the two sections only become apparent upon closer examination. For example, the generated motifs may appear smooth and uniform in the first section upon close inspection, but grainy and gritty in the second, or the visibility areas of the motifs may differ when the security element is tilted perpendicular to the direction of the effect.

[0042] In all the aforementioned variants, the pixel elements advantageously have dimensions between 3 µm and 100 µm, preferably between 5 µm and 20 µm. Alternatively or additionally, the pixel elements have a maximum pitch between 0.5 µm and 10 µm, preferably between 1 µm and 5 µm. Advantageously, the pixel elements all have the same shape, for example, they are all square or rectangular.

[0043] In another further development, it is provided that all pixel elements exhibit the same inclination profile in the second direction, for example, the same concave or convex curvature. Alternatively, it can be provided 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. For example, the pixel elements in a first group are all concave in the same way, and in a second group, they are all convex in the same way. The pixel elements can also be, for example, concave (or convex) in a wide range of inclination in a first group and concave (or convex) in a narrow range of inclination in a second group.

[0044] In all the variants mentioned, the reflective pixel elements can each be equipped with a property from the following group A and / or a property from the following group B.

[0045] 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 identical 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 safety element. These include, among others, the following possibilities: α) Regionally constant structural parameters, for example multicolor image 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)

[0046] The curved or flat mirror surfaces of the reflective pixel elements largely determine the direction in which incident light is reflected. Any additional nanostructures do not alter the direction of reflection of the incident light, but rather create a color that differs from the color of the coated surface without nanostructures. Thus, the nanostructures modify the natural color effect (with a constant color or a color shift) of the coating, making it possible to create colors or color combinations that would not be possible without nanostructures.

[0047] It is possible for the curved reflective surfaces of the pixel elements to be completely coated with a specific nanostructure (and thus color). However, it is also advantageous for the surface of a pixel element to be divided into sub-areas with different nanostructures.

[0048] In particular, the nanostructure can be chosen depending on the local orientation of the curved mirrors. For example, the surfaces of a curved mirror oriented in one direction (e.g., "north") can be equipped with red-producing nanostructures, and all surfaces oriented in a second direction (e.g., "south") with green-producing nanostructures. As a result, the effect presented by this curved mirror is observed as red from the first (north) direction and as green from the second (south) direction. It goes without saying that other color combinations can also be chosen.

[0049] 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 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, a viewer perceives a dynamic effect caused by the mirror curvature coupled with a continuous color transition.The assignment can be carried out by determining the local slope (normal vector) at a specific point on a 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.

[0050] The nanostructures can be configured as protrusions 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 selected 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, offering other advantages such as improved moldability.

[0051] Group B, coatings: a) Reflective metal layers, for example made of aluminium, 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 varnish 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 silicon dioxide (SiO2) group. x), 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), hafnium carbide (HfC), Hafnium oxide (HfO2), lanthanum oxide (La2O3), magnesium oxide (MgO), neodymium oxide (Nd2O3), praseodymium oxide (Pr6O11 ), Samarium oxide (Sm2O3), antimony trioxide (Sb2O3), silicon carbide (SiC), silicon nitride (Si3N4), silicon monoxide (SiO), 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 made of: - 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; - 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 from a few tens of nm up to thicker, opaque reflector layers, or made of a metallic material selected from the group aluminum, silver, copper, gold, platinum, niobium, tin, or from nickel, titanium, vanadium, chromium, cobalt and palladium or alloys of these materials; ii) Color-changing coating made of: - semi-transparent reflector, for example made of thin Al / Cr / Ti; with thicknesses of about 10 nm; - Dielectric, for example SiO2 / ZnS; with thicknesses of a few to several hundred nm; - semi-transparent reflector, for example made of thin Al / Cr / Ti; with thicknesses of about 10 nm. iii) Other multilayer systems consisting of different dielectrics / metals (materials as above), where a refractive index transition occurs at the interface between the layers, leading to reflection. The layer thicknesses can be chosen to deliberately produce constructive interference, or to avoid deliberately producing interference in order to achieve increased broadband reflection. Alternating dielectric layers with different refractive indices (interference in a multilayer system) are advantageous. Layer systems consisting of a metallic reflector and a semiconductor, for example silicon, are also advantageous. Furthermore, high-refractive-index or low-refractive-index materials (relative to the adjacent material) over a metallic reflector, for example zinc-aluminum, are advantageous. d) Liquid crystals, especially cholesteric liquid crystals, can also be used as a color-shifting layer.

[0052] All these coatings in group B can have additional adhesion-promoting layers applied, for example, very thin layers of chromium, titanium, or polymer primers, to improve adhesion. These can be used between the embossing lacquer / sealing lacquer and the coating, but also between individual layers of the coating.

[0053] In a beneficial further development, the reflective surface area in all variants can have at least one metallized sub-area and one demetallized sub-area. In a particularly advantageous variant, at least one demetallized 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 ink is removed after coating along with the coating layers.

[0054] In another preferred variant, at least one demetallized sub-area features 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 can be created, in particular embossed, in the same operation.

[0055] In this context, demetallization refers to the removal of one or more, in particular reflective and typically metallic, coating layers.

[0056] The invention also includes a security document, in particular a banknote, with a security element of the type described according to the first and / or second aspect of the invention.

[0057] Further features of the invention can be found in the claims, the figures and the description of the figures.

[0058] 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 designated with the same reference numerals.

[0059] This shows: Fig. 1 a schematic representation of a banknote with an optically variable security element according to the invention, Fig. 2 a schematic view of a safety element in various tilting positions, wherein the safety element is designed with a reflective surface area with an outer contour in the form of the value number “10”, Fig. 3 a detailed section of the reflective surface area of ​​the safety element of the Fig. 2 with 3x3 pixel elements in top view, Fig. 4. the height profile within a pixel element of the 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 a three-dimensional representation of the height profile of a pixel element, Fig. 6 a detailed section of the reflective surface area of ​​a safety element according to another embodiment, Fig. 7 in (a) schematically a top view of a flat motif area with a curved line and in (b) a detail view, Fig. 8 a flat motif area with a circular ring floating below the motif area in different views, Fig. 9 a representation of the motif in the form of the letter “P” to illustrate the procedure for the design of the pixel elements in the second aspect of the invention, and Fig. 10 an illustration of an alternative approach to the interpretation of the pixel elements.

[0060] The invention will now be explained using the example of security features for banknotes. Fig. Figure 1 shows a schematic representation of a banknote 10 with an optically variable security element 100 according to the invention in the form of an adhered 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, health insurance 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 that are partially or completely embedded in the document substrate are also suitable.

[0061] The security element 100 has a reflective surface area 102 displaying a motif 104 with two circular rings 106, 108, whereby the first circular ring 106 appears to float below the security element and the second circular ring 108 above it. From a certain viewing angle, the circular rings 106, 108 appear to be arranged concentrically. However, when the security element is tilted in different directions 116, 118, the circular rings 106, 108 appear to move away from their concentric center position. More precisely, when the security element is tilted, the circular rings 106, 108 exhibit a parallactic movement pattern, corresponding to the movement of two real, superimposed circular rings when the viewing angle changes, thus creating a convincing three-dimensional appearance for the viewer.

[0062] Another special feature was that the two circular rings 106, 108 appeared to the viewer in their different positions of movement with an essentially uniform brightness.

[0063] To generate the described motion effect and the uniform brightness of the circular rings, an arrangement of reflective pixel elements is used, each of which has an essentially constant inclination in one direction and is curved in a suitable manner in a direction perpendicular to it or is provided with several sections of constant inclination.

[0064] As a preliminary step, some basic designs with reflective pixel elements exhibiting direction-dependent constant or curved inclination are described in more detail, and the emergence of the special effects generated by the mirror curvature is explained. Such reflective pixel elements can also be used in the designs according to the invention.

[0065] Fig. Figure 2 shows a safety element 12 with a reflective surface area 14, which is formed with an outer contour in the shape of the value number "10". As shown in the detailed illustration of the Fig. As shown in Figure 3, the reflective surface area 14 is divided into a multitude of small, reflective pixel elements 20, which together create the optically variable motif representation of the value number “10” of the security element 12.

[0066] The pixel elements 20, for example, have dimensions of 20 µm × 20 µm and each contains three ray-optically acting reflective facets 22, which direct incident light like small mirrors into a reflection direction determined by the condition "angle of incidence equals angle of reflection". The pixel elements 20 are therefore also referred to as micromirrors in this description. The inclination of the facets or pixel elements is set, 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.

[0067] The safety element 12 exhibits different behavior depending on the tilting direction 16, 18. With reference to the Fig. 1 and Fig. 2. A tilting in a first direction 16 is hereinafter referred to as a north-south tilting, and a tilting in the second tilting direction perpendicular to it 18 is referred to as an east-west tilting. The use of cardinal directions serves only to simplify the naming and illustration of the different tilting processes; it is understood that the first and second directions do not necessarily coincide with the actual cardinal directions.

[0068] Without tilting, i.e., when viewed essentially vertically, the surface area 14 of the safety element 12 appears as a metallic, shiny number “10” with a bright horizontal bar 15 approximately in the middle of the two digits (view 20 in Fig. 2).

[0069] If the security element 12 is tilted by a user in a north-south direction 16, the light bar 15 within the number "10" appears to run continuously to the top or bottom edge of the digits, thereby creating a so-called rolling bar effect (view 20-N or 20-S in Fig. 2).

[0070] Conventional designs often have the disadvantage that the rolling bar effect, when the security element 12 is tilted in an east-west direction 18, i.e., perpendicular to the main effect direction 16, is either only visible within a very narrow angular range, 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 in an east-west direction is visible from a wide angular range and also appears with a smooth, uniform brightness.

[0071] 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 an east-west direction 18, the brightness of the surface area 14 and the bar 15 does not change practically within a visibility range that extends 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-O).

[0072] If the security element 12 is first tilted northwards from the vertical viewing direction, so that the bright bar 15 is located at the upper edge of the value "10" (view 20-N), then, when subsequently tilted in an east-west direction (views 20-NE and 20-NW), the security element 12 also shows a smooth, uniform brightness of the area 14 with the bright bar 15 at the top. If the security 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 "10" (view 20-S), then, when subsequently tilted in an east-west direction (views 20-SE and 20-SW), the security element 12 again shows a smooth, uniform brightness of the area 14 with the bright bar 15 at the top.

[0073] 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 enhances the security effect and the recognizability of the security element 12, and thus also its counterfeit protection.

[0074] To explain how the described appearance of the security element 12 came about, the following is shown. Fig. Figure 3 shows a detailed section of the surface area 14 with 3x3 pixel elements 20 in plan 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.

[0075] The height profile within a pixel element 20 is in Fig. 4 illustrated, where Fig. 4(a) shows a greyscale representation where the minimum pitch of 0 µm is represented by black and the maximum pitch of 3.5 µm is represented by white.

[0076] The Fig. Figures 4(b) and (c) show the height profile of the mirror surfaces along a cross-sectional line within pixel element 20. Fig. 4(b) the elevation profile in north-south direction 16 along the line B1-B1 (curve 30) or the line B2-B2 (curve 32) of the Fig. 4(a), and Fig. Figure 4(c) shows the elevation profile in an east-west direction 18 along the line C1-C1 (curve 34) or the line C2-C2 (curve 36) of the Fig. 4(a).

[0077] The pixel elements 20 of the illustrated embodiment each consist of three facets 22 with the same slope in the north-south and east-west directions. At the interfaces where adjacent facets 22 meet, discontinuities in the height profile occur ( Fig. 4(b), Fig. 4(c)) and thus, in the embodiment shown, also up to two isolated discontinuities in the inclination of the pixel elements.

[0078] As from the Fig. 3 and Fig. As can be seen in Figure 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 the Fig. 4(b) is evident.

[0079] The constant inclination within each pixel element changes gradually from south to north across the area 14, for example, from -15° at the southern (lower in the figures) 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.

[0080] Because of the continuous increase in the angle of inclination from south to north, when the safety element 12 is tilted in a north-south direction, the narrow strip of specular reflection shifts accordingly in a 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 in this tilting direction.

[0081] In the east-west direction 18, the pixel elements 20, however, do not exhibit a constant or randomly chosen inclination. As in Fig. As shown in Figure 4(c), the elevation 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, from -15° to +15°.

[0082] This means that each of the pixel elements 20 is visible in an east-west direction from any viewing angle within a wide angular range around the specular reflection direction and contributes to the appearance of the surface area from that viewing direction. The surface area 14 therefore appears with a smooth, uniform brightness when tilted east-west.

[0083] Fig. 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 in Fig. As can be seen in Figure 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 predefined, larger symmetrical inclination range.

[0084] Another embodiment of the invention is described in Fig. Figure 6 illustrates 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 as shown in Figure 6. Fig. 4(a) is indicated by a greyscale representation in which the minimum pitch of 0 µm is represented by black and the maximum pitch of 3.5 µm is represented by white.

[0085] The pixel elements 20 of the exemplary embodiment of the Fig. 6 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 inclination range. Unlike in the embodiment of the Fig. 3 and Fig. However, option 4 does not continuously vary the tilt of the pixel elements in an east-west direction, but rather in jumps with 5 discrete steps, for example with the tilt values ​​-10°, -5°, 0°, +5° and +10°. With such a sectionally constant tilt, the safety element exhibits a particularly high brightness when tilted east-west, with a smooth brightness gradient that varies slightly in intensity.

[0086] Fig. Figure 6 also illustrates that the facets 22 belonging to pixel elements 20 adjacent in an east-west direction can be offset from each other in a north-south direction. However, the facets can also be, as in Fig. As shown in Figure 3, they should be arranged at the same height in a north-south direction.

[0087] Returning to the design of the Fig. 1. Curved mirrors or mirrors varying in an inclination range can also be used according to the invention for curve representations, such as the representation of the circle lines 106, 108 of the Fig. 1. can be used advantageously.

[0088] To illustrate the principle in the design of the pixel elements, Fig. Figure 7 shows a planar motif area 120 of a safety element with a display area 122, in the center of which a curved curve 124 is visible as a reference curve. For a viewer, the curve 124 appears to float a few millimeters above or below the plane of the planar motif area 120 and, when tilted around the x-axis or y-axis, moves in different directions within the display area 122 according to its apparent height or depth of suspension.

[0089] The curved curve 124 can be defined at each location by a local direction vector K. ||parallel to curve 124 and a local direction vector K ⊥ perpendicular to curve 124, as described in detail section 126 of the Fig. 7(b) shown.

[0090] To generate the curve representation, the display area 122 contains a multitude of reflective pixel elements 128, each of which has a parallel direction R. ∥ parallel to the target curve in the middle position (parallel to K) ∥ ) and a normal direction R ⊥ perpendicular to the target curve in the middle position (parallel to K) ⊥ ) can be defined.

[0091] The pixel elements 128 each point along the normal direction R ⊥A constant inclination to the reflective surface area 120 is applied, except at possible isolated discontinuities, where the magnitude of the constant inclination is chosen depending on the distance of the respective pixel element 128 to the reference curve 124. In other words, while the inclination in the normal direction is constant within each individual pixel element 128, the magnitude of the inclination generally changes from pixel element to pixel element.

[0092] In particular, the magnitude of the constant inclination can increase or decrease monotonically and preferably linearly with the distance of a pixel element 128 from the curve 124. If the pixel elements 128 are inclined increasingly away from the curve with increasing distance from it, the curve appears to float below the plane of the two-dimensional subject area 120. Conversely, if the pixel elements 128 are inclined increasingly towards the curve with increasing distance from it, the curve appears to float above the plane of the two-dimensional subject area 120. It is understood that a curve need not have a constant floating height, but that the floating height can change along the curve and can even transition from a floating height above the two-dimensional subject area to a floating height below the two-dimensional subject area, or vice versa.

[0093] Along the parallel direction R perpendicular to the normal direction ∥The pixel elements 128 exhibit a continuously varying inclination within a given inclination range, except for possible isolated jump points, such that the pixel elements 128 in the parallel direction R ∥ each have a curved profile.

[0094] The size of the tilt range is predetermined and chosen independently of the distance of a pixel element 128 from the reference curve. The tilt range can, for example, lie between 15° and 25°, and in practice can be approximately 20°. Such a distance-independent variation of the tilt in the parallel direction results in a dispersion of the incident light parallel to the local direction of the reference curve 124, the magnitude of which is advantageously comparable to the parallax effect caused by changing the constant tilt.

[0095] The continuous variation of the tilt of the pixel elements in the parallel direction ensures that the three-dimensional depth impression, in particular the apparent floating of the target curve 124 at a certain height or depth, is maintained even if the viewer tilts the safety element within a certain angular range or rotates it in the plane of the safety element.

[0096] The curve 124 can basically have any shape, but preferably represents letters, numbers, symbols or simple geometric shapes such as circles, ovals, triangles, rectangles or squares.

[0097] Circular rings, especially two circular rings suspended at different heights, as seen in [reference to a specific example], have proven to be a particularly easy-to-understand design. Fig. Figure 1 shows that the principle just described allows for both a parallactic and an orthoparallactic movement of such circular rings when the safety element is tilted.

[0098] Fig. Figure 8 first explains the motion effects for a motif with a single circular ring 106. The figure, in the central view 130-M, shows a flat motif area 120 with a dashed representation area 122. When viewed vertically, the circular ring 106 is visible in the center of this area and appears to float below the flat motif area 120. When viewed from above (view 130-O), the circular ring 106 moves to the upper edge of the representation area 122; when viewed from below (view 130-U), it moves to the lower edge. Similarly, when viewed from the right (view 130-R), the circular ring 106 moves to the right edge, and when viewed from the left (view 130-L), it moves to the left edge of the representation area 122. This movement behavior corresponds to the movement of an object positioned in depth and therefore reinforces the three-dimensional impression of the ring floating in the distance.

[0099] As in Fig. As described in section 7, such an appearance and movement behavior can be achieved by orienting the pixel elements in the display area 122 in a direction perpendicular to the direction vector K. ∥ The pixels are inclined away from the circular ring 106 at a constant angle, with the angles of inclination increasing linearly with the distance of the pixel elements from the circular ring 106. This inclination is in the direction parallel to the direction vector K. || In contrast, the pixel elements have a curved profile with an inclination that varies independently of the distance to the circular ring 106. The resulting fanning area in the parallel direction allows the viewer to perceive the circular ring with uniform brightness within a certain range, even when the security element is tilted or rotated.

[0100] For a second circular ring 108, the appearance and movement behavior of an object hovering above the safety element can be generated by aligning the pixel elements in the display area 122 in a direction perpendicular to the direction vector K. || of the circular ring 108 are inclined with a constant inclination towards the circular ring 108 and the inclination angles increase linearly with the distance of the pixel elements from the circular ring 108.

[0101] Through the interaction of two such circular rings 106, 108, the following can be achieved: Fig. 1. The described appearance and movement behavior are generated.

[0102] Instead of intuitively correct parallactic motion behavior, the pixel elements can also be used to generate curve representations with counterintuitive, orthoparallactic motion behavior, where the motion does not correspond to that of a real object. For this, the assignments of the first direction (constant inclination) and the second direction (variation in inclination range) to the parallel and normal directions of the pixel elements simply need to be reversed. The pixel elements then point along the parallel direction R. ∥ a constant inclination towards the reflective surface area, except for possible isolated discontinuities, while in the normal direction R ⊥The resulting profile exhibits a continuously varying inclination within a given tilt range, except for any isolated jump points. This corresponds precisely to a rotation of the pixel elements by +90° or -90°. Combinations of height / depth effects and orthoparallel motion effects can also be generated by rotating the pixel elements from a height or depth effect by any angle that is not an integer multiple of 90°.

[0103] Curved mirrors, or mirrors that generally vary in an inclination range, can be used not only for optically variable curve representations, but also for generating more general, optically variable motifs composed of line elements.

[0104] The inventive method is based on an implementation for planar pixel elements, in which the following procedure is used for a motif consisting of a plurality of points: 1) In a first step, each sub-motif and thus each point of this sub-motif is assigned a range of movement within which the sub-motif should move when viewed. 2) Then, for each pixel element, it is checked which points (which may also originate from different sub-motifs) can reach this pixel element within their range of movement. 3) From the list of possible points, a point is then selected, for example randomly, and the orientation and slope of the mirrors in this pixel are calculated based on the relative position of the selected point to the pixel element. 4) Pixel elements that cannot be reached from any single point are assigned a predefined background setting of alignment and slope.

[0105] Since, in this implementation, a pixel element can usually be reached from several adjacent points of a motif, one of the possible points must be selected in these cases, which sometimes leads to a grainy, gritty appearance.

[0106] Here, the current inventors have recognized that the neighboring points relevant for generating a partial motif generally yield very similar values ​​when calculating the orientation and slope of the plane mirrors. Instead of randomly selecting one of these values ​​for the slope each time, the use of curved mirrors allows a multitude of similar slopes to be implemented simultaneously within a curved pixel element. This makes neighboring pixel elements more similar to each other, resulting in a more homogeneous and uniform pixel distribution overall, and thus a more consistent brightness in the appearance produced by the pixel elements.

[0107] The specific procedure will now be explained based on the Fig. Figure 9 illustrates, as a simple example, a motif representation 140 in the form of the letter “P”, which is formed by a plurality of line elements 142.

[0108] Considering first the straight vertical stem (line 144) of the letter "P" and a pixel element 150 located horizontally next to line 144, there is a point 146 on line 144 that lies horizontally directly next to this pixel element 150. If pixel element 150 is to contribute to the representation of this point 146, it must be formed with a certain tilt in the horizontal east-west direction (OW), but without a tilt in the vertical north-south direction (NS).

[0109] The points 148 adjacent to point 146 lie on the same vertical line 144, and therefore, due to the identical horizontal distance, produce the same east-west slope at the location of pixel element 150 as point 146. In the north-south direction, however, the points 148 produce slightly different slopes, since the vertical distance of the points to pixel element 150 changes.

[0110] The inclinations generated by points 146 and 148 of line 144 within a defined range of motion 152 can be implemented in a single pixel element 150. For this purpose, pixel element 150 is given a constant inclination in a first direction, namely the east-west direction OW, except for any isolated discontinuities. The magnitude of this inclination is determined by the horizontal distance of pixel element 150 to line 144.

[0111] In the second, perpendicular direction, namely the north-south direction NS, the pixel element 150 is curved or formed with a plurality of piecewise constant sections, so that it exhibits a multitude of inclinations in this direction, which are necessary for representing the points 146, 148 lying within the range of motion 152. The inclinations occurring within the range of motion 152 in the north-south direction therefore precisely determine the inclination range of the pixel element 150 in the second direction.

[0112] The described procedure can easily be extended to lines or line elements 142 of any orientation. The first direction (east-west direction for pixel element 150) corresponds, for a general line element 142, to the normal direction perpendicular to the line element 142, and the second direction (north-south direction for pixel element 150) to the parallel direction parallel to the line element 142.

[0113] In this way, virtually any image representation can be given an optically variable effect using pixel elements that are constantly inclined in one direction and curved in another. The image representation simply needs to be decomposed into line elements or approximated by a plurality of line elements, and the layout of the pixel elements calculated based on the line elements they are intended to represent.

[0114] If a pixel element can be reached by points of several line elements of the motif representation, one of these lines can be selected, for example, randomly. Specifically, in the case of Fig. 9 For example, two lines 142A, 142B of the arc of the letter "P" within the predefined range of motion 162 of the pixel element 160. In the exemplary embodiment, line 142A is selected randomly for the pixel element 160, and accordingly, only the points 164 of this line are used to calculate the magnitude of the constant inclination in the first direction and the inclination range in the second direction. In an adjacent pixel element, the second line 142B with its associated points 166 can then be taken into account.

[0115] In such a random selection, not just a single point is chosen at a time; rather, each selected line 142A, 142B covers a plurality of points 162 or 164, respectively. Since the size of the pixel elements 160 is below the resolving power of the eye, it is perfectly sufficient for a smooth rendering of the motif 140 if the lines not selected for a pixel element 160 are taken into account in one of the neighboring pixel elements.

[0116] During a Fig.In the 10 illustrated alternative procedure, suitable for any motif representation, the motif representation 140 is locally approximated by straight line elements. For a pixel element 170, the points 176 of the motif representation that the pixel element can reach with its predefined range of motion 172 are approximated by a line element 174. This line element can be selected separately and differently for each pixel element 170. This procedure works particularly well for motif sections that are straight or have only a slight curvature. With strong curvatures or even abrupt changes in direction of the motif representation, this procedure can reach its limits, and the method described above is preferred.

[0117] In a further development of the invention, it is possible to generate a changing image by partially nesting the pixel elements, in which different motif representations become visible from different viewing directions. The nesting can, in particular, consist of dividing the multitude of pixel elements into several subgroups, whereby the assignment to these subgroups can be made by a regular pattern, such as a checkerboard pattern, or by an irregular, for example, random distribution. The division into subgroups can be carried out such that each subgroup contains the same number of pixel elements, or such that individual groups are deliberately provided with a higher / lower proportion of pixel elements.

[0118] At least one of the aforementioned subgroups is covered with structures according to the invention. The other subgroups can be covered with structures according to the invention or with other optical structures. Crucially, each of the subgroups generates an optical effect under a different viewing range, so that when the security feature is tilted, an ideally abrupt transition / change occurs between the individual effects of the subgroups. This allows, for example, the creation of alternating images between two motif representations according to the invention or between a motif representation according to the invention and another optical effect, such as a warping effect. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2016 / 180522 A1 [0036, 0040]

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