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

Abstract

An optically variable security element for security paper, value documents and other value articles is disclosed, comprising a substrate body (2) having a front side (4) and a back side (6), a dielectric layer (30) applied to the front side (4) of the substrate body (2), the dielectric layer comprising a microfacet structure, the microfacet structure comprising first micro mirror facets (20) and different second micro mirror facets (22), and a reflective layer (32, 36) applied to the microfacet arrangement and thus forming a micro mirror arrangement (18). The first micro mirror facets (20) have a smooth surface shape or a curved focusing surface shape, and the second micro mirror facets (22) have a curved surface shape without focusing effect.

Description

Technical Field

[0001] The present invention relates to an optically variable security element for protecting security paper, valuable documents and other valuable articles, comprising: a substrate having a front side and a back side; a dielectric layer applied to the front side of the substrate, the dielectric layer comprising a microfaceted arrangement including a first micromirror and a second micromirror; and a reflective layer applied to the microfaceted arrangement and thus forming the micromirror arrangement. Background Technology

[0002] To protect valuable documents, they are typically equipped with security elements featuring a micromirror arrangement. This allows for verification of the document's authenticity and simultaneously enhances anti-counterfeiting security, as they cannot be copied even using the most modern copiers. For example, such a micromirror arrangement is described in EP 2 507 069 B1. They are particularly well-suited for creating patterns that appear three-dimensional to the viewer. This is especially true for Fresnel structures, which can be used to replicate arched surfaces. The micromirrors can also be arranged to additionally create a sense of motion when the pattern is tilted or rotated.

[0003] Furthermore, it is known that patterns can be endowed with colored structures. This is achieved by coating the surface of a micromirror with a multilayer coating or by superimposing colored nanostructures onto the micromirror. These nanostructures can be coated with a single metal layer or a multilayer coating. The regions where colored nanostructures are set exhibit a glossy effect because incident light is reflected at the electron gas on the smooth surface and therefore undergoes almost no scattering. Specular reflection also occurs on imprinted subwavelength structures located on flat surfaces. On the other hand, pigment colors exhibit broad scattering of reflected light and appear matte. The scattering and absorption properties of the coloring system are practically known to be described by the Kubelka-Munk theory.

[0004] A similarly known practice is to produce patterns with a metallic sheen using conventional printing methods, particularly by using metallic-effect pigments in inks. As is known, printing with glossy metallic-effect pigments can certainly be combined with printing with matte pigment colors. However, this printing method, especially their combination, is limited in terms of spatial resolution. Furthermore, combining two conventional printing methods cannot produce a matte-gloss pattern that creates a motion effect when tilted or rotated.

[0005] The purpose of this invention is to provide a universal type of security element that avoids the shortcomings of existing technologies, particularly improving anti-counterfeiting security, while being easy to mass-produce, whereas copying it is very costly and complex for counterfeiters. A corresponding valuable document and a method for manufacturing the security element are also provided. Summary of the Invention

[0006] The objective is achieved through the features of the independent claim. Improvements to the invention are the subject of the dependent claim.

[0007] An optically variable security element is provided for protecting paper documents, valuable documents, and other valuable items. The security element has a substrate having a front and a back. The substrate may be a polymer substrate, such as a PET substrate, a paper substrate, or a combination of paper and polymer substrates.

[0008] A dielectric layer is applied to the front side of the substrate and includes a micro-faceted arrangement as a structure for the arrangement of micromirrors. Preferably, the dielectric layer is provided by imprinting an embossed varnish having the desired micro-faceted arrangement. The embossed varnish may be transparent, colored translucent, or colored. The micro-faceted arrangement includes a first micromirror facet and different second micromirror facets, each individually indistinguishable to the naked eye. The lateral extent of the micromirrors is less than 50 μm, so that the individual micromirror facets of the pattern are indistinguishable to the naked eye of a viewer. However, they are greater than 2 μm to reduce light diffraction at the boundaries of the micromirror facets. More preferably, the micromirror facets have a lateral extent of 3 μm to 10 μm. The first micromirror facet has a smooth surface shape or a curved focusing surface shape. More preferably, the first micromirror facet has a concave curved surface shape, so that reflected light is concentrated at a distance of 20 cm to 50 cm. This distance corresponds to typical viewing conditions. Therefore, the focal point of the first micromirror facet lies precisely in the viewer's plane. The second micromirror facet has a curved surface shape that, at this distance, has a light scattering effect rather than a focusing effect. For the purposes of this patent application, the term "focusing" is used when parallel incident light rays are bundled together at the focal point. A glossy or matte appearance is a result of the scattering distribution of the reflected light components. The glossiness of a surface can be quantified by the ratio of the directional reflection component to the diffuse reflection component. Essentially, surfaces with an average scattering angle width of less than 5° appear glossy to the observer. On the other hand, surfaces with a larger average scattering angle width appear matte.

[0009] The reflective layer is applied to a micro-faceted arrangement within the dielectric layer, thus forming a micromirror arrangement. A preferred arrangement of the micromirror facets in the micro-faceted arrangement is a Fresnel structure. After coating with the reflective layer, the micromirror arrangement preferably also has a Fresnel structure.

[0010] By using a micromirror arrangement, patterns combining glossy and matte areas can be produced, and these patterns further exhibit arching or motion effects. This is achieved through the fact that, on the one hand, the arching or motion effect is created by the micromirror arrangement, and on the other hand, glossy and matte areas are created due to the change in the flatness of the surface shape between the first and second micromirror facets. In the glossy areas, the surface shape of the first micromirror facet is smooth or slightly curved, thus having a focusing effect at a distance of 20 cm to 50 cm in the observer's plane. In the matte areas, the surface shape of the second micromirror facet is curved, but it does not have a focusing effect at a distance from the viewer's plane. The curved shape of the second micromirror facet ensures that incident light is scattered. In a preferred embodiment, the matte and glossy areas are directly adjacent to each other or scattered among each other.

[0011] When the incident light has a low scattering component and the light is reflected at a relatively high intensity and narrow spatial angle at the surface, the observer perceives the surface as having a metallic luster with the naked eye. On the other hand, light scattering at a large spatial angle makes the surface appear matte. The glossy areas of the pattern are produced by a first micromirror facet, whose surface shape is smooth or slightly concave and curved, thus causing a high-concentration of the reflected light component at the viewer's distance. The matte areas of the pattern are produced by a second micromirror facet, whose surface shape is curved but does not have a focusing effect, thus scattering the incident light. This scattering effect and the matte appearance of the matte areas are caused by the concave and convex curvature of the second micromirror facet surface. The curvature of the second micromirror facet surface can preferably be spherical or parabolic. The focal point of the spherical sphere is given by f = r / 2, where r is the radius of the sphere. The deflection h at the midpoint of the circular segment of length s can be estimated as follows:

[0012]

[0013] Where the segment height is h, the chord is s, and the focus is f.

[0014] In some embodiments, the curved surface shape of the second micromirror facet can vary laterally along its surface. For example, the curvature may initially extend laterally along the surface of the second micromirror facet in a concave manner, but then transition to a convex curvature (concave-convex) – the reverse (convex-concave) is of course equally possible. In this case, the second micromirror facet has a surface shape with at least one protrusion and / or at least one depression.

[0015] The uniformly curved surface shape of the second micromirror facet results in a uniform scattering distribution of light within a boundary angle, which is defined by the maximum tilt angle relative to the average mirror plane. By varying the curvature laterally along the surface of the second micromirror facet, i.e., if the surface shape of the second micromirror facet has at least one protrusion and / or depression, a scattering distribution with maximum and decreasing intensity in the direction of the boundary angle can be produced.

[0016] The surface shape of the second micromirror facet can also have a unilateral descending slope in three-dimensional space, looking at their vertical profile—in this case, the surface of the second micromirror facet is inclined or arched in two spatial directions of the plane.

[0017] Furthermore, the surface shape of the second micromirror facet can have a diagonal line in the vertical profile, extending towards or away from the central pole. Thus, the surface is curved, for example, in two spatial directions of the plane, making it possible, for example, for the second micromirror facet to be configured as a collimator. This shape promotes a high-intensity component in the glossy region of the pattern. Then, the surface shape of the second micromirror facet can, for example, be rotationally symmetric.

[0018] Preferably, the surface shape of the second micromirror facet can have oblique lines in the vertical profile, the oblique lines extending away from at least two poles at the edge. In this case, the surface curvature of the second micromirror facet is non-rotationally symmetric about the center of the facet, such as a saddle-shaped surface, which is concave in one spatial direction and convex in another. Surfaces with multiple symmetries and a central tilt are also possible. This irregular shape of the surface of the second micromirror facet can have a focusing effect in some spatial directions and a scattering effect in others. This means that an external observer can see the pattern as glossy or matte areas, depending on the azimuth angle. Therefore, by making the second micromirror facet the same as the first micromirror facet at certain azimuth angles, glossy areas can be produced that then appear matte at different azimuth angles.

[0019] The curvature of the second micromirror's surface determines the light scattering distribution. Uniform curvature results in a uniform scattering distribution within the boundary angles, which are determined by the maximum tilt of the surface relative to the mirror. The curved surface of the collimator causes reflected light to be strongly concentrated in the direction of an external observer, who perceives these areas as having a metallic luster. When the surface has a light scattering effect, the patterned areas are considered matte. Metallic surfaces are characterized by relatively high light intensity in reflection and low scattering in the angular distribution. Conversely, incident light is strongly scattered by matte surfaces within a certain angular range. Particularly preferred is that the full width at half maximum (FWHM) of the scattering distribution in matte regions is greater than 5°, preferably greater than 10°.

[0020] The surfaces of the first and / or second micromirror facets can also be constructed to produce a matte appearance. An example of structuring could be providing a structure with multiple protrusions and recesses, such as a random structure, on the surface of the micromirror facets.

[0021] Micromirror arrangements are created by imprinting in a dielectric layer. Therefore, matte effects, including combinations with color effects, can be produced using positional precision, as the imprinting method used to produce optical effects has a much higher positional precision than known printing methods. Furthermore, additional matte effects with arched or motion effects produced by the micromirror arrangement can be produced by the imprinting method. The matte effect can also have color, and the color changes when the security element is tilted / rotated, for example, by applying a color-changing coating. Therefore, this type of micromirror arrangement increases the anti-counterfeiting security of valuable documents while ensuring they can be produced efficiently in high-volume and cost-effectively.

[0022] The reflective layer of the micromirror arrangement can be metallized or a high-refractive-index coating. Metallization can include Al, Ag, Au, Ni, Fe, Cu, W, Cr, and / or alloys of these metals. High-refractive-index layers can include, for example, ZnS, ZnO, Ta2O5, TiO2, or organic materials or nanocomposite materials. It is also possible that the reflective layer is a multilayer coating, such as a color-shifting coating. This color-shifting coating has a translucent metallic layer, an underlying metallic mirror layer, and an intermediate dielectric spacer layer. This layer structure causes only a portion of the incident spectrum to be reflected, so the reflection of white light (sunlight) appears colored to an external observer. The hue here depends on the angle of incidence of the light. Due to its multilayer structure, the color-shifting coating provides the observer with a perceptual image of different colors at different viewing angles and displays, for example, different perceived colors or brightness depending on the viewing angle. This allows for additional color and / or brightness effects when the security element is tilted, which further enhances anti-counterfeiting security.

[0023] In the embodiments, the dielectric spacer layer includes SiO2, MgF2, Ta2O5, TiO2, Al2O3, MgO, HfO2, ZnO, ZnS, and / or transparent organic materials. Of course, the same materials can also be used for the dielectric layer described above.

[0024] In embodiments, the micromirror arrangement or microfacet arrangement may have color-enhanced nanostructures superimposed thereon. The overall structure including the color-enhanced nanostructures and the microfacet arrangement or micromirror arrangement is coated with a single metal coating or has multiple layers. The color-enhanced nanostructures may be one-dimensional or two-dimensional periodic. In particular, the first and second micromirror facets can have different color-enhanced nanostructures superimposed thereon by selecting different lattice parameters. This increases anti-counterfeiting security to a certain extent because, in addition to the matte effect and motion effect, there is also color switching between areas.

[0025] In another embodiment, the dielectric layer may have a semi-transparent color. Similarly, the security element may be regionally overprinted with one or more semi-transparent colors over the entire area or on one side.

[0026] The described micromirror arrangements are preferably suited for the color configuration of security features on valuable documents, such as banknotes, ID cards, or cards used for payment transactions. With the aid of these micromirror arrangements, patterns that additionally possess a three-dimensional appearance and / or have color-shifting effects can be reproduced, for example. They are particularly suitable as human features visible to the naked eye by an external observer. They can be arranged side-by-side with known structures such as holograms, colored nanostructures, moth-eye structures, microcavities, and microlens arrays. In particular, they can be directly adjacent to such structures because the described micromirror arrangements are introduced into the dielectric layer by imprinting and thus produced with very high positional accuracy—significantly higher positional accuracy compared to known printing methods. Furthermore, multiple different imprinted structures and thus multiple different security features can be produced in a single imprinting step, which greatly reduces the workload of producing security elements and, consequently, lowers production costs.

[0027] More preferably, the optically variable security element is a foil security element, such as a security thread, security tape, or security patch. It can then be easily applied as a transfer element to valuable documents. The foil security element can also be equipped with additional functional layers, such as machine-readable magnetic coding, UV luminescence, phosphorescence, infrared coding, etc.

[0028] Similarly, valuable documents with optically variable security elements, such as banknotes, checks, credit cards or other payment cards, and identity cards, are also provided. It is evident that valuable documents can be modified as optically variable security elements in the same manner as already described. Here, the dielectric layer can also be applied directly to the valuable document or its substrate.

[0029] A method for producing the optical variable safety element in one of the above embodiments is also provided. A substrate having a front and a back side is provided, and a dielectric layer is applied to the front side of the substrate. A structure comprising a micromirror arrangement including a first micromirror facet and different second micromirror facets is introduced into the dielectric layer. Furthermore, a reflective layer is applied to the structure, thus the reflective layer and the structure combine to form the micromirror arrangement. The first micromirror facet has a smooth surface shape or a curved surface shape having a focusing effect in the viewing plane, and the second micromirror facet has a curved surface shape having a light scattering effect rather than a focusing effect.

[0030] It is obvious that the method for producing optically variable safety elements can be modified in the same way as the optically variable safety elements and valuable documents already described.

[0031] The original of the described structure is preferably produced by photolithography, particularly using a laser writer. Alternatively, a two-photon absorption-based device is also an option. Electron beam lithography is also suitable as a manufacturing method, especially for fabricating structures in which micromirror facets have superimposed nanostructures or holographic / diffractive structures. After photoresist development, the exposed original is replicated using electroplating or photopolymers (e.g., Ormocers) to form a mechanically stable die. In large-scale production applications, multiple arrangements of the original structure are required on a die by hot stamping or nanoimprinting to create an imprinting roller for subsequent replication. This imprinting roller ultimately allows for continuous replication of the original structure in a UV varnish or hot stamping on a foil in a roll-to-roll process. Hot stamping or nanocasting in a UV varnish is a suitable modeling method.

[0032] The imprinted structure embodies a micro-faceted arrangement and is subsequently coated with metal vapor. Common vapor deposition methods include electron beam deposition, sputtering, or thermal evaporation. Particularly suitable metals are Al, Ag, Au, Ni, Fe, Cu, W, or Cr, and alloys of these metals. If a multilayer coating is applied, a dielectric spacer layer is subsequently applied via vapor deposition. Materials for the dielectric spacer layer include SiO2, MgF2, Ta2O5, TiO2, Al2O3, MgO, HfO2, or ZnO. Polymer or inorganic coatings, as well as combinations of materials and high molecular weight polymers, can also be used. The same materials can, of course, be used for the dielectric layer. Instead of a metal layer, a high refractive index coating can be used for the reflective layer. Suitable materials for this purpose are ZnS, Ta2O5, ZnO, TiO2, or organic materials, or nanocomposites. Finally, the metallized surface is preferably coated with a transparent outer layer. However, the outer layer can also be coated with a translucent color.

[0033] Furthermore, original components can be assembled from different masters using methods such as nanoimprinting with precise positioning. This method is particularly suitable for combinations of these structures with other known structures such as relief holograms or nanostructures. The described arrangement of micromirrors with nanostructures or scattering holographic structures superimposed thereon can also be produced in a single photolithographic exposure process, particularly using electron beam equipment, via a grayscale exposure process, or using equipment based on two-photon absorption.

[0034] It should be understood that, without departing from the scope of the invention, the above features and the features which will still be set forth below can be used not only in the specified combination, but also in different combinations or individually. Attached Figure Description

[0035] The invention is illustrated in more detail below with reference to the accompanying drawings, which also disclose the essential features of the invention. These working examples are for illustrative purposes only and should not be construed as limiting. For instance, the description of a working example having multiple elements or components should not be construed as implying that all of these elements or components are necessary for implementation. Rather, other working examples may include alternative elements and components, fewer elements or components, or additional elements or components. Unless otherwise stated, elements or components in different working examples may be combined with each other. Modifications and changes described for one working example may also apply to other working examples. To avoid repetition, elements that are identical or corresponding to each other in different drawings are indicated by the same reference numerals and are not described again. In the drawings,

[0036] Figure 1 A first embodiment of the valuable document is shown in a plan view.

[0037] Figure 2 A second embodiment of the valuable document is shown in plan view.

[0038] Figure 3 The beam analysis of the first micromirror arrangement is shown.

[0039] Figure 4 The beam analysis of the second micromirror arrangement is shown.

[0040] Figure 5 The beam analysis of the third micromirror arrangement is shown.

[0041] Figure 6 The beam analysis of the fourth micromirror arrangement is shown.

[0042] Figure 7 A cross-sectional view shows a safety element with a metallized micromirror arrangement.

[0043] Figure 8 The cross-sectional view shows the figure based on Figure 7 The safety element is arranged in a micromirror configuration and is coated with multiple layers of coating.

[0044] Figure 9 The cross-sectional view shows the figure based on Figure 7 The safety element is arranged in a micromirror configuration and printed with colored nanostructures.

[0045] Figure 10 A cross-sectional view shows a safety element of a metallized micromirror assembly in another embodiment.

[0046] Figure 11 An isometric view of the micromirror facets in the first embodiment is shown.

[0047] Figure 12An isometric view of the micromirror facets in the second embodiment is shown.

[0048] Figure 13 An isometric view of the micromirror facets in the third embodiment is shown.

[0049] Figure 14 An isometric diagram of the micromirror arrangement is shown.

[0050] Figure 15 An isometric view of the micromirror facet with a non-rotationally symmetric surface in the first embodiment is shown.

[0051] Figure 16 An isometric view of the micromirror facet with a non-rotationally symmetric surface in the second embodiment is shown.

[0052] Figure 17 The scattering distribution of reflected light from three different surface shapes of the micromirror facets along the spatial direction is shown.

[0053] Figure 18 A cross-section of a micromirror arrangement in the form of a Fresnel structure is shown, and

[0054] Figure 19 It shows that according to Figure 18 A top view of the arrangement of micromirrors, as a vertical section with drawn micromirror facets.

[0055] Structures that correspond to each other in terms of structure or function are given the same reference numerals in the accompanying drawings. Detailed Implementation

[0056] Figure 1 The first embodiment of valuable document 1 is shown in plan view. An optically variable safety element 8 is applied to a substrate 2 having a front side 4 and a back side 6. The safety element 8 has a glossy area 10 embodying a goblet and a matte area 12 embodying a laurel wreath.

[0057] Figure 2 A second embodiment of the valuable document 1 is shown in plan view. In this embodiment, the security element 8 presents a colorful, deformed butterfly to the observer in the glossy area 10, which appears to have a metallic sheen and stands out from the matte background in the matte area 12.

[0058] The substrate 2 can be, for example, a polymer substrate (such as a PET substrate), but a paper substrate or a combination of paper and polymer substrates is also possible.

[0059] Figures 3 to 6The scattering characteristics of different micromirror arrangements are analyzed using beam analysis. A sun 14 is shown as a schematic illumination source; due to its distance, the sun 14 emits light 16 as a parallel beam onto the micromirror arrangement 18, which has a first micromirror facet 20 and / or a second micromirror facet 22. Irradiation sources emitting parallel beams at shorter distances can also be used. For simplicity, in... Figures 3 to 6 The beam path is observed only in two dimensions, and the second micromirror facet 22 has its surface curvature in only one spatial direction; the surface curvature of each second micromirror facet 22 can be different. The external observer is located at a distance of approximately 30 cm to 50 cm.

[0060] Figure 3 The micromirror arrangement 18 has four first micromirror facets 20, from which light 16 is deflected and guided toward or away from the eye 28 of an external viewer. Figure 3 The first micromirror facets 20 have slightly curved surfaces, thus exhibiting a focusing effect at the distance of an external observer. The micromirror arrangement 18 generally appears as a glossy area 10 because almost all beams 16 are guided in the direction of the external observer's eye 28 and focused there.

[0061] Figure 4 The micromirror arrangement 18 includes four second micromirror facets 22 with curved surface shapes, which scatter incident light 16 and thus appear as a matte region 12 at the distance of an external observer.

[0062] Figure 5 The micromirror arrangement 18 includes two first micromirror facets 20 and two second micromirror facets 22, which have different scattering effects. The first micromirror facets 20 are configured similar to... Figure 3 The first micromirror facet 20, and therefore has a focusing effect at the viewer's distance. The second micromirror facet 22 exhibits a scattering effect, such as... Figure 4 The second micromirror facets 22 are depicted in the diagram—they do not have a focusing effect. The surface of the second micromirror facet 22 is curved and can be, for example, spherical or parabolic. In this case, the eye 28 of an external observer will perceive the area where the first micromirror facet 20 is located as a glossy area 10 because its surface is flat or slightly curved (focusing). Another area where the second micromirror facet 22 is located is perceived as a dull area 12 because the surface of the second micromirror facet 22 is curved or arched, and therefore scatters the incident light 16 into a light cone.

[0063] Figure 6The micromirror arrangement 18 also has micromirror facets 20 and 22 with different scattering effects. A first micromirror facet 20 is arranged between three second micromirror facets 22. The two second micromirror facets 22 on the left each have a convex, curved surface. The second micromirror facet 22 on the right has a concave, curved surface. The three second micromirror facets 22 scatter light 16 and are presented to the external observer as a matte area 12. Conversely, the first micromirror facet 20 has a smooth or slightly curved surface, thus reflecting the incident light 16 almost completely into the eye 28 of the external observer—this area appears as a glossy area 10 to them.

[0064] Figures 7 to 9 The safety element 8 is shown in cross-section. A micromirror arrangement 18 with four second micromirror facets 22 is inserted into a dielectric layer 30, which is located on the front side 4 of the substrate 2. A transparent protective layer 34 is applied to the dielectric layer 30. Figures 7 to 9 Each of them depicts the same micromirror arrangement 18, but is coated differently in each case – in Figure 7 In this configuration, metal layer 32 is set as a reflective layer on the micromirror arrangement 18; Figure 8 In this process, a multilayer coating 36 is used instead of the metal layer 32 to coat the micromirror arrangement as a reflective layer. This multilayer coating 36 has a three-layer structure consisting of a translucent metal layer 38, a dielectric spacer layer 40, and a metal mirror layer 42. Figure 9 In this process, the colored nanostructure 44 is applied to the micromirror arrangement 18, and the metal layer 32 is located on the micromirror arrangement 18.

[0065] exist Figures 7 to 9 In the diagram, each of the second micromirror facets 22 has a laterally varying curvature on its surface, meaning that it has at least one protrusion and / or recess in its surface shape. The micromirror facet 22 on the left has a concave-convex curvature on its surface, the second micromirror facet 22 from the left has a convex-concave curvature on its surface, the next micromirror facet 22 has a concave curvature on its surface, and the micromirror facet 22 on the right has a convex curvature on its surface. The different laterally varying surface curvatures of the depicted second micromirror facets 22 produce a scattering distribution with a maximum and decreasing intensity in the direction of each boundary angle.

[0066] Figure 10A cross-sectional view illustrates a security element with a metallized micromirror arrangement 18 in different embodiments. The two micromirror facets 22 on the left are finely structured on their surfaces, with multiple protrusions and recesses that can produce extinction in reflection. In this embodiment, a random structure is applied to the surfaces of the two second micromirror facets 22 on the left, a structure particularly suitable for producing a Gaussian scattering angle effect in reflection. The surface of the first micromirror facet 20 is planar, and the second micromirror facet 22 on the right has a concave, curved surface. The micromirror arrangement 18 is coated with a metal layer 32, i.e., metallized.

[0067] like Figures 7 to 10 As shown, the micromirror arrangement 18 is imprinted into the dielectric layer 30, and preferably directly embedded therein. In this case, the protective layer 34, the dielectric layer 30, and the substrate 2 are more preferably transparent. A coloring layer is applied to the micromirror arrangement 18. Figures 7 to 10 In an exemplary embodiment, the micromirror arrangement 18 is coated with a reflective layer by vapor. Figure 7 , Figure 9 and Figure 10 In this context, the reflective layer is a metal layer 32, which... Figure 9 Additionally, it contains a color-enhancing nanostructure 44 superimposed on it. Figure 8 In the middle, the reflective layer is a multilayer coating 36, which includes a layer sequence of a translucent metal layer 38, a dielectric spacer layer 40 and a metal mirror layer 42, thus embodying a color shift coating.

[0068] like Figure 8 The effect of the multilayer coating 36 shown is that only a portion of the incident spectrum is reflected, thus the reflection of incident white light appears colored. Here, the hue depends on the angle of incidence of light 16. By superimposing the colored nanostructure 44 onto the reflective layer, both the glossy region 10 and the matte region 12 of the pattern can be given different colors because the lattice parameters of the colored nanostructure 44 are chosen differently for each region. For this purpose, the colored nanostructure 44 can be metallized in its simplest case using a single layer, but multilayer coatings can also be applied, particularly color-shifting coatings.

[0069] The color-shifting coating of the micromirror arrangement 18 produces color for the entire pattern, which changes when tilted or for a tilted mirror surface. If the color-enhancing nanostructures 44 are arranged on the micromirror arrangement 18, the contour parameters of the color-enhancing nanostructures 44 can be varied laterally, thereby forming different colors laterally, which can change according to tilt.

[0070] Figures 11 to 13 An isometric view of the second micromirror facet 22 is shown. In a vertical cross-section, the second micromirror facet 22 has a unilateral descending oblique line along the spatial direction. This second micromirror facet 22 scatters incident light rays 16. (As shown...) Figure 14As shown, the surface of the second micromirror facet 22 in the micromirror arrangement 18 can also be curved in two spatial directions, and then, for example, have an extreme point at the center (in this case, the minimum value), and in a vertical cross-section, the oblique line extends to that extreme point, or, in the opposite case of the maximum value, the oblique line extends from that extreme point. Figure 14 In the diagram, the micromirror facets 22 of the micromirror arrangement 18 are schematically shown in three-dimensional space, having different curvatures. Their surfaces are concave and can be implemented as rotationally symmetric, for example, as collimators—a form that promotes high-intensity components in the glossy region 10 of the pattern.

[0071] However, the second micromirror facet 22 can also have a curvature on its surface that is not rotationally symmetric relative to its center, such as... Figure 15 and Figure 16 As shown in the example. Figure 15 The surface of the second micromirror facet 22 in the form of a saddle is shown, that is, a geometry that is concave in one spatial direction and convex in another spatial direction. Figure 16 The surface shape of the second micromirror facet 22 is shown, which has multiple symmetries and a central depression. Both surface shapes have multiple extreme points at the edges of the surface, as seen in the vertical cross-section, from which the diagonal lines begin. Figure 15 and Figure 16 The surface shapes depicted can have a focusing effect in certain spatial directions and a scattering effect in other spatial directions. Depending on the viewing angle, they can represent glossy areas 10 or matte areas 12. Therefore, the second micromirror facet 22 can be used to generate glossy areas 10 for one viewing angle and matte areas 12 for a second, different viewing angle.

[0072] Figure 17 The intensity on the y-axis is compared with the scattering angle on the x-axis, thus illustrating the scattering distribution of surfaces with different curvatures within a scattering angle range of + / -40° along the spatial direction. In this example, the maximum tilt angle of the surface of the second micromirror facet 22 is + / -15°. Curve A is the result of a surface shape with uniform curvature, which produces a uniform scattering angle distribution of light scattering. Curves B and C are produced by surface shapes with different curvatures laterally. Although not explicitly depicted, asymmetric scattering distributions can also be produced. For example, random structures result in a scattered portion produced by light diffraction in first-order diffraction. This can also be used, for example, to generate Gaussian scattering distributions.

[0073] exist Figure 18 and 19 The image depicts a micromirror arrangement 18 formed as a Fresnel structure 48. The Fresnel structure 48 has a glossy region 10 and an matte region 12, and produces a three-dimensional appearance. Figure 18A cross-section of the Fresnel structure 48 is shown, its surface consisting of a first micromirror facet 20 and a second micromirror facet 22. The first micromirror facet 20 is arranged in the glossy region 10, and the second micromirror facet 22 is arranged in the matte region 12, and both are oriented along the vertical section 50 of the three-dimensional structure. Figure 19 A top view of vertical section 50 is shown.

[0074] In this exemplary embodiment, the surface of the first micromirror facet 20 is flat in the glossy region 10; the surface of the second micromirror facet 22 is concave and curved in the matte region 12. Furthermore, a colored nanostructure 44 is superimposed on the first and second micromirror facets 20 and 22, which is vapor-coated as a three-layer (i.e., multilayer) coating 36. In this way, patterns with spatial or motion effects in reflection can be produced. Such patterns can exhibit color changes when tilted or rotated. If this micromirror arrangement 18 has the colored nanostructure 44 and / or multilayer coating 36 superimposed thereon, multicolor patterns or true-color images can also be produced. Finally, each of the first and / or second micromirror facets 20 can also be selectively colored using a moth-eye structure, allowing for the depiction of portraits, animals, or natural objects with high contrast, for example. Using this micromirror arrangement 18 as a security feature increases anti-counterfeiting security and attractiveness to human features.

[0075] List of reference numerals

[0076] 1 Valuable Document

[0077] 2 Substrate

[0078] 4 front

[0079] 6 Back

[0080] 8 safety elements

[0081] 10 Glossy Areas

[0082] 12 matte areas

[0083] 14. The Sun (a distant light source)

[0084] 16 rays

[0085] 18 Microscope Setup

[0086] 20 First Microscope Facets

[0087] 22 Second Micromirror Facet

[0088] 28 The Eyes of an External Observer

[0089] 30 dielectric layers

[0090] 32 metal layers

[0091] 34 protective layers

[0092] 36+ layers of coating

[0093] 38 translucent metal layers

[0094] 40 dielectric spacers

[0095] 42 Metal Mirror Layer

[0096] 44 Colored Nanostructures

[0097] 48 Fresnel Structure

[0098] 50 vertical section

Claims

1. An optically variable security element for protecting paper documents, valuable documents, valuable items, etc., comprising: - Substrate (2), which has a front side (4) and a back side (6). - A dielectric layer (30) is applied to the front side (4) of the substrate (2) and includes a micro-faceted arrangement comprising a first micromirror facet (20) and different second micromirror facets (22), and - A reflective layer (32, 36) is applied to the microfaceted arrangement and thus forms the micromirror arrangement (18). in - The first micromirror facet (20) has a smooth surface shape or a curved, focused surface shape, and - The second micromirror facet (22) has a curved surface shape without focusing effect.

2. The safety element according to claim 1, wherein, The curved surface shape of the first micromirror facet (20) has a focusing effect in a plane 20 cm to 50 cm away from the observer.

3. The safety element according to claim 1 or 2, wherein, The microfacet arrangement is a Fresnel structure.

4. The safety element according to any one of the preceding claims, wherein, The first micromirror facet (20) is arranged in the first region, and the second micromirror facet (22) is arranged in the second region, wherein the first region and the second region are directly adjacent to each other or scattered among each other.

5. The safety element according to any one of the preceding claims, wherein, The surface shape of the second micromirror facet (22) is concave and / or convex curved.

6. The safety element according to any one of the preceding claims, wherein, The surface shape of the second micromirror facet (22) is spherical or parabolic curved.

7. The safety element according to any one of the preceding claims, wherein, The surface shape of the second micromirror facet (22) has at least one protrusion and / or at least one depression.

8. The safety element according to any one of the preceding claims, wherein, The surface shape of the second micromirror facet (22) has a sloping line that descends on one side.

9. The safety element according to any one of claims 1 to 7, wherein, The surface shape of the second micromirror facet (22) has oblique lines extending from at least two poles at the edge.

10. The safety element according to any one of claims 1 to 7, wherein, The surface shape of the second micromirror facet (22) has a diagonal line extending toward or away from the center pole.

11. The safety element according to any one of the preceding claims, wherein, The reflective layer is a multilayer coating (36), and more particularly a color-shifting coating.

12. The safety element according to any one of the preceding claims, wherein, The micromirror arrangement (18) has at least partially superimposed a colored nanostructure (44) thereon, wherein the colored nanostructure (44) includes a metal layer (32) or a multilayer coating (36) on its surface.

13. The safety element according to claim 12, wherein, The colored nanostructure (44) is a one-dimensional periodic nanostructure or a two-dimensional periodic nanostructure.

14. A valuable document, such as banknotes, checks, credit cards or other payment cards, identity cards, etc., having an optically variable security element (1) according to any one of claims 1 to 13.

15. A method for manufacturing an optically variable safety element (1) according to any one of claims 1 to 13, wherein, - Provide a substrate (2) having a front (4) and a back (6). - A dielectric layer (30) is applied to the front side (4) of the substrate (2), wherein a micro-facet arrangement including a first micromirror facet (20) and different second micromirror facets (22) is introduced into the dielectric layer (30), and - Apply the reflective layer (32, 36) to the microfaceted arrangement and thus form the micromirror arrangement (18). in, - The first micromirror facet (20) has a smooth surface shape or a curved, focused surface shape, and - The second micromirror facet (22) has a curved surface shape without focusing effect.

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