Security element, valuable document and method for manufacturing a security element

Abstract

A security element for protecting valuable objects is disclosed. The security element comprises a substantially planar substrate (2) having a surface defining a base plane, a microrelief structure (6) on the substrate (4) comprising a plurality of microrelief structure elements (9, 11), each microrelief structure element (9, 11) comprising an element surface (10, 12), a color-generating nanostructure (20) being arranged at each element surface (10, 12). The color-generating nanostructure comprises a plurality of nano-protrusions (24) or nano-recesses, the nano-protrusions (24) or nano-recesses being arranged according to a two-dimensional arrangement, there being a nearest neighbor distance (n) between the centers of adjacent nano-protrusions (24) or nano-recesses. The nano-protrusions (24) or nano-recesses are non-periodically distributed over the respective element surface (10, 12) in the arrangement, the nearest neighbor distance (n) varies non-periodically over the respective element surface (10, 12), wherein the average value of the nearest neighbor distance (n) is in the range of 170 nm to 600 nm, and there is a gap (g) between all adjacent nano-protrusions (24) or nano-recesses.

Description

Technical Field

[0001] This invention relates to a security element for protecting anti-counterfeiting paper, valuable documents, or other valuable items. The security element comprises a substrate having a substantially flat surface, a micro-relief structure on the substrate including multiple micro-relief structural elements, and a nanostructure including multiple nano-protrusions or nano-recesses arranged two-dimensionally on the micro-relief structural elements. Background Technology

[0002] For security purposes, security elements with a micro-relief structure are often added to security documents. This allows for verification of the document's authenticity and enhances anti-counterfeiting protection, as they cannot be replicated even using the most modern copying equipment. This micro-relief structure is particularly well-suited for creating patterns that appear three-dimensional to the observer. This is especially true for micromirror structures (i.e., Fresnel structures) used to simulate curved surfaces. Micro-relief elements can also be arranged in such a way that the pattern exhibits a dynamic effect, or motion effect, when the security element is tilted or rotated.

[0003] It is known that patterns generated by the arrangement of micro-relief structures can be colored. This is achieved by coating the surface of the micro-relief structure with a multilayer coating and / or by covering the micro-relief structural elements with color-generating nanostructures. Known color-generating nanostructures are periodic photonic structures, i.e., they have periodically arranged protrusions or depressions and can be covered with simple metallic layers or multilayer coatings. Conventional photonic structures, such as diffraction gratings and photonic crystals, require periodicity of protrusions or depressions to produce constructive interference and structural colors. Therefore, disorder within such structures is considered a defect, as localized variations in the periodicity of these photonic structures cause scattering and reduce the brightness / saturation of the generated structural colors.

[0004] Completely disordered structures are typically used to emit white light because these structures scatter light of all wavelengths. Such structures cannot produce structural color.

[0005] Therefore, the object of the present invention is to provide a security element, a valuable document, and a method for manufacturing a security element, the security element including enhanced optical effects, which are achieved in particular by reducing iridescence, minimizing grating effects, and increasing defect tolerance. Summary of the Invention

[0006] This invention is defined by the independent claims. The dependent claims relate to preferred embodiments.

[0007] This invention provides a security element for protecting anti-counterfeiting paper, valuable documents, and other valuable items. The security element comprises a substantially flat substrate having a surface. For the purposes of this application, the flat surface defines the base plane. The substrate can be optically transparent or translucent and can be a polymer substrate or a polymer composite substrate. The polymer substrate is preferably made of polyethylene terephthalate (PET), or of polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyesters such as polycarbonate (PC), cellophane, polylactic acid (PLA), cellulose acetate, or other common polymer types. Polymer substrates are preferred because they resist external (e.g., physical or chemical) factors.

[0008] A micro-relief structure comprising multiple micro-relief structural elements is applied to the surface of a substrate. Each micro-relief structural element includes an element surface. In the micro-relief structure, the micro-relief structural elements can be arranged in any manner; they can be ordered or disordered, periodic or aperiodic. Preferably, the micro-relief structure is a micromirror arrangement comprising multiple directional reflective micromirrors. The micromirrors specifically form periodic or aperiodic zigzag lattices. Preferably, the linear dimensions of the micromirrors are between 2 μm and 100 μm, more preferably between 5 μm and 50 μm. In particular, the micromirrors can have triangular, square, rectangular, hexagonal, or other polygonal bases. The height of the micromirrors is preferably less than 15 μm, more preferably less than 10 μm. In embodiments, the micromirrors are randomly oriented in the micromirror arrangement. They can be oriented in at least two different directions to produce a view-dependent effect.

[0009] To provide a substrate with a micromirror arrangement, a dielectric layer is applied to the surface of the substrate, which has a micro-faceted arrangement as a structure for the micromirror arrangement. Preferably, the dielectric layer is provided with the desired micro-faceted arrangement by imprinting an imprinting varnish. The imprinting varnish can be transparent or colored. The micro-faceted arrangement comprises a plurality of microfacets, each of which is invisible to the naked eye of an observer. The lateral extent of the microfacets is preferably less than 50 μm, such that the individual microfacets of the pattern are not distinguishable to the naked eye of an observer. However, the microfacets are preferably larger than 2 μm to minimize light diffraction at the boundaries of adjacent microfacets. Preferably, the microfacets have a lateral dimension of 3 μm to 10 μm. A reflective layer is applied to the micro-faceted arrangement in the dielectric layer such that they together form a micromirror arrangement. A preferred arrangement of the microfacets 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] Furthermore, the micro-relief structural elements include color-generating nanostructures disposed on the surface of the element, preferably at each of them. The color-generating nanostructures comprise a plurality of nanoprotrusions or nanorecesses arranged in a two-dimensional configuration. Typically, the color-generating nanostructures are disposed on the surface of the element, i.e., on the surface of the aforementioned micro-facet, meaning below the reflective layer; however, the color-generating nanostructures can also be disposed above the reflective layer. The two-dimensional arrangement of the nanoprotrusions or nanorecesses on each element surface is aperiodic, wherein there exists a nearest neighbor distance between the centers of adjacent nanoprotrusions or nanorecesses, which varies aperiodically across the respective element surface, and gaps exist between all adjacent nanoprotrusions or nanorecesses. Therefore, no nanoprotrusions or nanorecesses are adjacent to each other, meaning that the nearest neighbor distance is greater than zero in all cases.

[0011] The average nearest neighbor distance on the corresponding element surface is in the range of 170 nm to 600 nm, preferably in the range of 230 nm to 450 nm. For the purposes of this disclosure, this average nearest neighbor distance corresponds to an average spacing value P on the corresponding element surface. av Smaller and larger nearest neighbor distances may exist between some adjacent nanoprotrusions or nanodepressions, as long as the average spacing value is within the range described above. Preferably, the mathematical distribution of the nearest neighbor distance counts varies in shape on the corresponding element surface with a Gaussian, normal, Poisson, or Schulz-Flory distribution.

[0012] The gaps between adjacent nanoprotrusions or nanodepressions vary aperiodically on the respective element surface, ranging from 50 nm to 380 nm, preferably 100 nm to 350 nm, and most preferably 120 nm to 300 nm. The nearest neighbor distance should be in the range of 170 nm to 600 nm. Therefore, gaps of different sizes within the gap range are provided on each respective element surface. By varying the gap size within the gap range, the colors generated by the color-generating nanostructures can be tuned.

[0013] Due to the average spacing value P av Within the range of 170 nm to 600 nm, preferably between 230 nm and 450 nm, optical effects, especially color effects, are produced. The average spacing value P can be adjusted by changing at least some nearest-neighbor distances between nanoprotrusions or nanodepressions on the surface of the corresponding element. av This allows for the adjustment of colors generated by the color-generating nanostructure.

[0014] Alternatively or concurrently, the gap range and thus the color generated by the color-generating nanostructure can be tuned by varying the diameter of at least some of the nanoprotrusions or nanorecesses. In embodiments, the maximum diameter of the nanoprotrusions or nanorecesses is in the range of 80 nm to 400 nm, preferably in the range of 100 nm to 300 nm. It is possible that the diameter of the nanoprotrusions or nanorecesses varies on the respective element surface, meaning that some diameters of the nanoprotrusions or nanorecesses on the element surface differ from other diameters of other nanoprotrusions or nanorecesses on the element surface. This also affects the color generated by the nanostructure, but results in color loss. To enhance the optical effect, the diameter of the nanoprotrusions or nanorecesses remains constant, while only the distribution of the dots is changed. Thus, the color-generating nanostructure is a subwavelength structure.

[0015] Color-generating nanostructures are applied in a form of so-called "correlated disorder," which appears to be a random photonic structure but produces structured colors. The hidden order within the structure enables color generation based on coherent scattering and interference. These color-generating nanostructures arranged in a correlated disorder are characterized by reduced iridescence, minimized grating effects, and greater defect tolerance. The disordered nature of these nanostructures makes them more difficult to define than their ordered counterparts, which periodically repeat constant unit cells and possess translational symmetry. Therefore, color-generating nanostructures arranged in a correlated disorder enhance anti-counterfeiting protection. The correlated disorder arrangement of nanostructures helps to reduce grating effects in reflective structures and decrease iridescence in plasmonic color filters while maintaining color saturation. Color generation using correlated disordered color-generating nanostructures minimizes diffraction effects, thereby minimizing iridescence. Therefore, color-generating nanostructures improve the optical performance of security elements.

[0016] By arranging nanobumps and nanodepressions in a correlated disordered manner, the nanobumps and nanodepressions are maintained at a certain distance from each other. The nanobumps and nanodepressions have a random distribution, but the desired average spacing value is within the aforementioned range, which is the average of the nearest neighbor distances on the surface of an element. This random arrangement of nanobumps and nanodepressions minimizes grating effects. Introducing ordered elements into the correlated disordered arrangement of nanobumps and nanodepressions maximizes their brightness while minimizing grating effects, thus producing attractive color effects.

[0017] Various algorithms can be used to generate color-generated nanostructures with correlated disorder, such as the two algorithms described below. These algorithms are used to create the aforementioned gap, nearest neighbor distance, and average spacing values.

[0018] In the first algorithm, the color-generating nanostructure, comprising nanoprotrusions or nanorecesses arranged in a related disordered manner, is generated using an algorithm that employs random placement and isolation zones of the nanoprotrusions or nanorecesses. In this algorithm, the nanoprotrusions or nanorecesses are randomly set, for example, using a Python-based random function. However, a single exclusionary feature is incorporated into the encoding, ensuring that no nanoprotrusion or nanorecess can come into contact with each other. Furthermore, the nanoprotrusions or nanorecesses are maintained at a constant size. Preferably, the optical effect of the color-generating nanostructure is enhanced by reducing the variation in gaps between adjacent nanoprotrusions or nanorecesses by forcing them to maintain a predetermined minimum distance from their neighboring nanoprotrusions or nanorecesses.

[0019] The second algorithm works in the same way as the first algorithm, but it reduces the gap variation between adjacent nano-protrusions or nano-depressions by forcing them to maintain a set minimum distance from each other, thereby enhancing the optical effect of the color-generating nanostructure. A certain number of predefined nano-protrusions or nano-depressions maintain a constant distance from each other.

[0020] In the third algorithm, color-generating nanostructures, including nanobumps or nanodepressions arranged in a correlated disordered manner, are generated using an algorithm based on ultrauniformly arranged nanobumps or nanodepressions. In the first step, initial points are randomly placed within a region on the micromirror. In the second step, new candidate points are created around existing points at distances between (P) and (2P), where P is a predefined period. In the third step, it is then ensured that the candidate points are at least (P) distances from all existing points, and in the fourth step, steps two and three are repeated until no more valid points can be added. Ultrauniform components are defined as those whose density fluctuations are suppressed on a large scale. These have been found to enhance the absorption of solar cells when compared to ordered components. These ultrauniform components offer more color than completely disordered components. It should be understood that the location of the point corresponds to the location of the nanobumps or nanodepressions on the micromirror.

[0021] It is worth noting that a wide range of other methods can be used to generate the relevant disorders.

[0022] Preferably, the color-generating nanostructure comprises at least two sub-regions visible to the naked eye and whose colors are at least partially different when viewed in reflected light. The different colors of the sub-regions are preferably achieved by designing different color-generating nanostructures in the two sub-regions. The nearest neighbor distance n, gap g, diameter d, and / or height h of the color-generating nanostructure can vary according to each sub-region to produce different color effects.

[0023] The micro-relief structure includes a reflective layer. Preferably, the reflective layer includes at least a metal layer and / or a dielectric layer. Most preferably, the reflective layer is an interference layer stack comprising at least two metal layers separated by a dielectric layer. In embodiments, the described layer stack has a translucent metal layer, an underlying metal mirror layer, and dielectric layers spaced apart therebetween. Due to this layer structure, only a portion of the incident spectrum is reflected, making the reflection of white light appear colored to the observer. The perceived color depends on the angle of incidence of the light. Due to its multi-layered structure, this color-shifting structure provides the observer with different image impressions at different viewing angles and, for example, displays different colors or brightness depending on the viewing angle.

[0024] Preferably, the interference layer stack is a thin film structure, wherein each layer has a thickness in the micrometer or nanometer range. These layers are preferably applied by physical vapor deposition (PVD) or chemical vapor deposition (CVD). The maximum thickness of the reflective layer is 20 μm, preferably 10 μm, very preferably 2 μm, and preferably has a symmetrical structure in its layer stack. The layer stack preferably comprises the following layer sequences: absorber / dielectric material / reflector / dielectric material / absorber; absorber / dielectric material / magnetic reflector / dielectric material / absorber; absorber / dielectric material / reflector / magnet / reflector / dielectric material / absorber; absorber / dielectric material / absorber. The absorber, reflector, and / or magnetic reflector comprises Cr, Ti, Cu, Ni, Al, Si, Ge, Ga, Fe, Co, Mn, Mg, Zn, Sn, V, Ag, or alloys thereof. The dielectric layer comprises MgF2, SiO2, TiO2, ZnS, Al2O3, ZnO, ZrO2, or Sn2O3. Preferably, the dielectric layer comprises SiO2.

[0025] The micro-relief structures with the aforementioned color-generating nanostructures are preferably suitable for color design of security features in secure documents such as banknotes, ID cards, or cards used for payment transactions. These micromirror arrangements can, for example, be used to produce patterns with the same three-dimensional appearance and / or color tilting effect. They are particularly suitable for human features visible to the naked eye of an external observer. They can be arranged side-by-side with known structures such as holograms, periodic nanostructures, moth-eye structures, microcavities, and microlens arrays. In particular, they can be directly adjacent to such structures because the described micromirror arrangements with color-generating nanostructures are directly imprinted into the dielectric layer, and thus produced with very high positional accuracy compared to known printing processes, achieving significantly higher positional precision. Furthermore, several different imprinted structures and thus several different security features can be produced in a single imprinting step, which significantly reduces manufacturing workload and therefore lowers the manufacturing cost of security elements.

[0026] Preferably, the optically variable security element is a foil element, such as a security thread, security tape, or security patch. It can then be easily applied to the security document as a transfer element. The foil element may also be equipped with other functional layers, such as machine-readable magnetic coding, UV luminescence, phosphorescence, infrared coding, etc.

[0027] Although valuable documents, such as banknotes, checks, credit cards or other payment cards, identity cards, etc., with the described optically variable security elements are provided, it should be understood that the valuable documents can be modified in the same manner as described for optically variable security elements. Here, it is equally possible to apply the described dielectric layer directly to the security document or its substrate.

[0028] The present invention also provides a method for manufacturing a security element for protecting anti-counterfeiting paper, valuable documents, or other valuable items, the security element comprising the steps of: providing a substantially flat substrate having a surface defining a base plane; applying a micro-relief structure to the substrate, the micro-relief structure comprising a plurality of micro-relief structural elements, wherein each micro-relief structural element includes an element surface; and applying a color-generating nanostructure disposed at each element surface and comprising a plurality of nano-protrusions or nano-recesses. The nano-protrusions or nano-recesses are arranged according to a two-dimensional arrangement, wherein a nearest neighbor distance exists between the centers of adjacent nano-protrusions or nano-recesses. The two-dimensional arrangement of the nano-protrusions or nano-recesses on the respective element surfaces is aperiodic, wherein the nearest neighbor distance between the centers of adjacent nano-protrusions or nano-recesses varies aperiodically on the respective element surfaces, wherein the average nearest neighbor distance is in the range of 200 nm to 500 nm, and gaps exist between all adjacent nano-protrusions or nano-recesses.

[0029] It should be understood that this method can be modified in the same manner as that described for a safety element. Attached Figure Description

[0030] In the following description, embodiments of the invention are illustrated with reference to the accompanying drawings, which also disclose features of the invention. These embodiments are for illustrative purposes only and should not be construed as limiting the invention. If an embodiment includes a particular combination of elements or components, the description should not be construed as implying that all such elements or components are essential to the invention. Rather, other embodiments may include alternative elements or components, fewer elements or components, or additional elements or components.

[0031] Figure 1 A schematic cross-sectional view of the safety element is shown;

[0032] Figure 2 The periodic nanostructure is shown in a top view;

[0033] Figure 3 A schematic top view is shown. Figure 2 Periodic nanostructures;

[0034] Figure 4 Detailed illustration Figure 3 The structure;

[0035] Figure 5 It shows Figure 2 Histograms of periodic nanostructures, showing the distribution of nearest neighbor distances on a point distribution on a micromirror;

[0036] Figure 6 The aperiodic color-generating nanostructure is shown in a top view.

[0037] Figure 7 A schematic top view is shown. Figure 6 Non-periodic color generation nanostructure;

[0038] Figure 8 Detailed illustration Figure 7 The structure;

[0039] Figure 9 It shows Figure 6 The histogram of the non-periodic color-generating nanostructure shows the distribution of nearest neighbor distances on a point distribution on a micromirror;

[0040] Figure 10 The safety components, comprising three distinct zones, are shown in a top-down view.

[0041] Figure 11 It shows Figure 10 A histogram of a region shows the distribution of nearest neighbor distances for points within that region; and

[0042] Figure 12 An array of k-sphere images is shown. Detailed Implementation

[0043] Figure 1 A schematic cross-sectional view of the safety element 1 is shown. A dielectric layer 2 (i.e., an embossed coating layer) is applied to a carrier substrate 4, in which an embossed structure in the form of a micromirror arrangement 6 is embossed. The micromirror arrangement 6 is provided with a reflective layer 8, i.e., a coating in the form of a metal layer or a multilayer film.

[0044] In this exemplary embodiment, the micromirror arrangement 6 includes a first set of relief structural elements 9 and a second set of relief structural elements 11. The first set of relief structural elements 9 includes a first element surface serving as a first micromirror 10, and the second set of relief structural elements 11 includes a second element surface serving as a second micromirror 12. Each of these elements is inclined relative to the surface plane of the substrate 4, such that they present two different optical effects, i.e., two different three-dimensional patterns, to the observer 14 from two different viewing directions 16, 18. Each micromirror 10, 12 has a lateral dimension between 5 μm and 50 μm, and therefore has, for example, a square base area of ​​10 μm × 10 μm, and is therefore unrecognizable to the observer 14.

[0045] The different color effects visible from two different viewing directions 16 and 18 are produced by using a reflective layer 8 to perform a (full-surface) conformal coating on the micromirror arrangement 6 and by covering the micromirrors 10 and 12 with a color-generating nanostructure 20, which is a subwavelength structure. This color-generating nanostructure 20... Figure 1 The first detail 22 shows the color-generating nanostructure 20, which includes a plurality of protrusions 24. These protrusions 24 are arranged non-periodically. For the sake of simplicity, we will discuss the protrusions 24 further, but the same applies to the depressions. The modulation of the micromirror arrangement 6 by the coated color-generating nanostructure 20 is shown only in the first detail 22, while the serrated contour of the micromirror arrangement 6 can be identified in the outline shown without magnification.

[0046] Figure 2 A periodic nanostructure 28 is shown in a top view, which can be disposed on micromirrors 10, 12, meaning on the surface of the relief structural elements 9, 11, rather than on the non-periodic color-generating nanostructure 20. The periodic nanostructure 28 includes protrusions 24 (or recesses). A first optical effect 30 of this periodic nanostructure 28 is shown in the lower left corner, and a scale bar 32 with a scale bar value s of 2 μm is shown in the lower right corner. Figure 3 The periodic nanostructure 28 is schematically shown in a top view, and it is... Figure 4 The second detail 34 is shown schematically. Figure 5 The distribution of nearest neighbor distances n on the point distributions on the corresponding micromirrors 10, 12 on which periodic nanostructures 28 are disposed in the first histogram 36 is shown.

[0047] As in Figure 4As can be seen in the first detail 22, the periodic nanostructure 28 comprises a plurality of regularly arranged protrusions 24 (or recesses). Adjacent protrusions 24 are spaced apart by a nearest neighbor distance n, which is the same for each adjacent protrusion 24 on the corresponding micromirrors 10, 12 on which the periodic nanostructure 28 is applied. The periodic nanostructure 28 is arranged in a periodic lattice, wherein the spacing value corresponds to the nearest neighbor distance n, and in the case of the periodic nanostructure 28, the nearest neighbor distance n corresponds to a period P, which is the distance between the centers of adjacent protrusions 24.

[0048] This is Figure 5 As clearly shown in the first histogram 36, the count (y-axis) of projections 24 at one of the micromirrors 10, 12, which is a periodic lattice, is shown as the nearest neighbor distance n (x-axis) above the projection 24. It can be seen that the nearest neighbor distance n between each protrusion 24 on the micromirrors 10, 12 is equal and corresponds to the period P of the periodic nanostructure 28.

[0049] Figure 6 A top view is shown as follows Figure 1 The color-generating nanostructure 20 shown is disposed on the micromirrors 10, 12 of the safety element 1. The color-generating nanostructure 20 includes protrusions 24 (or recesses) arranged non-periodically. A second optical effect 38 of the structure is shown in the lower left corner, and a scale bar 32 with a scale bar value s of 2 μm is shown in the lower right corner.

[0050] exist Figure 7 The diagram schematically illustrates the aperiodic arrangement of color-generating nanostructures 20 from a top view, and... Figure 8 The third detail 40 is shown schematically. Figure 9 The distribution of nearest neighbor distances n on the point distribution on the corresponding micromirrors 10, 12 that provide the color-generating nanostructure 20 is shown in the second histogram 42.

[0051] As in Figure 8 As can be seen in the third detail 40, the color-generating nanostructure 20 includes a plurality of irregularly arranged protrusions 24 (or depressions), meaning that at least some of the protrusions 24 are different at their nearest neighbor distance n. In the color-generating nanostructure 20, as... Figure 6 As shown, at least some adjacent protrusions 24 differ in their nearest neighbor distance n, and therefore the gaps g between protrusions 24 also differ. These gaps g differ on the corresponding micromirrors 10 and 12. Figures 6 to 8 It can be seen that the non-periodic arrangement of the color-generating nanostructures 20 is isotropic and non-periodic. The protrusions 24 are arranged in a correlated disordered manner. Therefore, these color-generating nanostructures 20 are capable of producing structural colors.

[0052] exist Figure 9 The second histogram 42 clearly illustrates this related disorder, where the counts (y-axis) of projections 24 on micromirrors 10, 12 are shown as the nearest neighbor distance n (x-axis) above the projections 24. It can be seen that the nearest neighbor distance n between the protrusions 24 on micromirrors 10, 12 varies, therefore the color-generating nanostructures 20 are arranged aperiodically. Even though the color-generating nanostructures 20 are aperiodic, the average spacing value P... av It also falls within the average spacing range of 170 nm to 600 nm. Average spacing value P av This corresponds to the average nearest neighbor distance n on the respective micromirrors 10 and 12. This average spacing value P av exist Figure 9 As shown in the second histogram 42, the mathematical distribution of the nearest neighbor distance n on micromirrors 10 and 12 varies in shape with a Gaussian distribution; alternatively, a normal distribution, a Poisson distribution, or a Schulz-Flory distribution is also possible. Some nearest neighbor distances n are higher than the average spacing value P. av While some are below the average spacing value P av However, the average nearest neighbor distance remains within the range mentioned above.

[0053] In the case of correlated disordered samples, there is no fixed period on the corresponding micromirrors 10, 12, and the distance between adjacent protrusions 24 (or depressions) (the so-called nearest neighbor distance n) varies. However, within this distribution of correlated disorder, protrusions 24 can cluster around the nearest neighbor distance n of the assembly (average spacing value P). av The average spacing value P is around the color-generating nanostructure 20. av The distribution of protrusions 24 within the color-generating nanostructure 20 is altered, enabling color tuning. Various algorithms can be used to distribute the projections 24, as long as they maintain an isotropic point distribution and average spacing value P within the optical length scale. av That's all.

[0054] The above color tuning is as follows Figure 10 As shown in the top view, the safety element 1 comprises three regions (first region 44, second region 46, and third region 48), wherein color-generating nanostructures 20 are arranged at their gaps g and their average spacing value P. avThe color-generating nanostructures 20 differ in at least one of their diameter d or the height h of their protrusions 24. In the first region 44, the color-generating nanostructures 20 display a pale yellow. In the second region 46, the color-generating nanostructures 20 display a darker, slightly reddish hue, and in the third region 48, the color-generating nanostructures 20 display a darker, slightly blue hue. This color tuning is achieved by changing the diameter d of some of the protrusions 24 (or recesses) and / or changing the gap size g between adjacent protrusions 24 (or recesses) and / or changing the height h of adjacent protrusions 24 (or recesses). In this case, the diameter d of the protrusions 24 changes, which automatically changes the gap g between the protrusions 24.

[0055] Figure 11 A third histogram 50 is shown for the distribution in the first region 44, where the counts (y-axis) of the protrusions 24 in the first region 44 are shown as the nearest neighbor distance n (x-axis) above the protrusion 24. The same histogram will also correspond to the other two regions 46 and 48, since the same encoding is used to generate the color-generating nanostructures 20. It can be seen that the nearest neighbor distance n between the protrusions 24 in this region varies. The third histogram 50 shows the distribution of the nearest neighbor distance n for samples with correlated disorder and shows the average spacing value P of the first region 44. av .

[0056] Figure 12 A schematic diagram is shown illustrating k-sphere images obtained from three different arrangements of color-generating nanostructures 20 coated with color shift coating. The color scattering effect depends on the structural type of the protrusions 24. Figure 12 Part A shows a schematic diagram illustrating the angle dependence of the k-space hemispherical projection 24, Part B shows a k-space image with a quasi-ordered arrangement in magenta, Part C shows a k-space image with a square arrangement in magenta, and Part D shows a k-space image with a hexagonal arrangement in magenta.

[0057] To demonstrate the effect of order on the rainbow, from... Figure 12Three different arrangements of color-shifted plasmonic nanopillar structures were used to capture images of k-space spheres. These images demonstrate how these structures reflect light on a hemispherical projection when viewed from above. In Part A, the positions of angles φ and θ are shown in a typical hemispherical schematic. As angle θ changes, the quasi-ordered structures do exhibit some iridescence, changing from magenta to pale blue. This pale blue is similar to the pale blue seen from the color-shifted coating. However, the color of these quasi-ordered structures does not change when φ changes, therefore their color is considered isotropic. On the other hand, the square (Part C) and hexagonal (Part D) samples show color changes when both φ and θ change. These effects are likely due to the periodic arrangement of the structures and the variation from yellow, orange, red, and blue when viewed from different angles.

[0058] List of reference numerals

[0059] 1 safety element

[0060] 2 dielectric layers

[0061] 4 substrates

[0062] 6-microscope setup

[0063] 8 reflective layers

[0064] 9 First relief structural element

[0065] 10 First Microscope

[0066] 11 Second relief structural element

[0067] 12 Second Microscope

[0068] 14 Observers

[0069] 16 First-person perspective

[0070] 18 Second Perspective

[0071] 20 colors generate nanostructures

[0072] 22 First Detail

[0073] 24 protrusions

[0074] 28 periodic nanostructures

[0075] 30 First optical effect

[0076] 32 scale

[0077] 34 Second Detail

[0078] 36 First Histogram

[0079] 38 Second optical effect

[0080] 40 Third Detail

[0081] 42 Second Histogram

[0082] 44 First District

[0083] 46 Second Area

[0084] 48 Third District

[0085] 50 Third Histogram

[0086] d diameter

[0087] g gap

[0088] h height

[0089] p-cycle

[0090] P AV Average pitch value

[0091] s scale size

Claims

1. A security element for protecting anti-counterfeiting paper, valuable documents, or other valuable items, said security element comprising: -A substantially flat substrate (4), said substrate (4) having a surface defining a base plane, - A micro-relief structure (6) on the substrate (4), the micro-relief structure (6) comprising a plurality of micro-relief structural elements (9, 11), wherein - Each micro-relief structural element (9, 11) includes an element surface (10, 12), wherein a color-generating nanostructure (20) is placed at each of the element surfaces (10, 12), and - The color-generating nanostructure includes a plurality of nanoprotrusions (24) or nanodepressions, wherein the nanoprotrusions (24) or nanodepressions are arranged in a two-dimensional arrangement, wherein there is a nearest neighbor distance (n) between the centers of adjacent nanoprotrusions (24) or nanodepressions. Its features are, - The nanoprotrusions (24) or nanorecesses are non-periodicly distributed on the respective element surfaces (10, 12) in the arrangement. The nearest neighbor distance (n) varies non-periodically on the respective element surfaces (10, 12), wherein the average value of the nearest neighbor distance (n) is in the range of 170 nm to 600 nm, and - There is a gap (g) between all adjacent nanoprotrusions (24) or nanodepressions.

2. The safety element according to claim 1, characterized in that, The average value of the nearest neighbor distance (n) is in the range of 230 nm to 450 nm.

3. The safety element according to any one of the preceding claims, characterized in that, The gap (g) between adjacent nanoprotrusions (24) or nanodepressions varies non-periodically on the respective element surfaces (10, 12) within a gap range of 50 nm to 380 nm, preferably from 100 nm to 350 nm, and most preferably from 120 nm to 300 nm.

4. The safety element according to any one of the preceding claims, characterized in that, The maximum diameter (d) of the nanoprotrusion (24) or the nanodepression is in the range of 80 nm to 400 nm, preferably in the range of 100 nm to 300 nm.

5. The safety element according to claim 4, characterized in that, The diameter (d) of the nanoprotrusion (24) or the nanodepression varies on the respective element surface (10, 12).

6. The safety element according to any one of the preceding claims, characterized in that, The maximum height (h) of each nanoprotrusion (24) or nanodepression is in the range of 50 nm to 400 nm, preferably from 80 nm to 350 nm, and most preferably from 100 nm to 300 nm.

7. The safety element according to claim 6, characterized in that, The height (h) of the nanoprotrusion (24) or the nanodepression varies on the respective element surface (10, 12).

8. The safety element according to any one of the preceding claims, characterized in that, The nanoprotrusions (24) are not adjacent to each other.

9. The safety element according to any one of the preceding claims, characterized in that, The mathematical distribution of the nearest neighbor distance (n) varies in shape on the corresponding element surface (10, 12) as a Gaussian distribution, a normal distribution, a Poisson distribution, or a Schulz-Flory distribution.

10. The safety element according to any one of the preceding claims, characterized in that, A reflective layer (8) is disposed on the micro-relief structure (6) and includes at least a metal layer and / or a dielectric layer.

11. The safety element according to any one of the preceding claims, characterized in that, The reflective layer (8) is a color shift layer, which comprises at least two metal layers separated by a dielectric layer.

12. The safety element according to any one of the preceding claims, characterized in that, The micro-relief structure (6) is a micromirror structure comprising multiple micromirrors (10, 12).

13. A valuable document comprising a security element (1) as described in any of the preceding claims.

14. A method for manufacturing a security element (1) for protecting anti-counterfeiting paper, valuable documents, or other valuable items, said security element comprising the following steps: - Provide a substantially flat substrate (4) having a surface defining a base plane, - A micro-relief structure (6) is applied to the substrate (4), the micro-relief structure (6) comprising a plurality of micro-relief structural elements (9, 11), wherein - Each micro-relief structural element (9, 11) includes element surfaces (10, 12), and - Apply a color-generating nanostructure (20) and place it on each of the element surfaces (10, 12), the color-generating nanostructure (20) comprising a plurality of nano-protrusions (24) or nano-recesses, wherein the nano-protrusions (24) or nano-recesses are arranged in a two-dimensional arrangement, wherein there is a nearest neighbor distance (n) between the centers of adjacent nano-protrusions (24) or nano-recesses. Its features are, - The nanoprotrusions (24) or nanorecesses are non-periodicly distributed on the respective element surfaces (10, 12) in the arrangement. The nearest neighbor distance (n) varies non-periodically on the respective element surfaces (10, 12), wherein the average value of the nearest neighbor distance (n) is in the range of 170 nm to 600 nm, and - There is a gap (g) between all adjacent nanoprotrusions (24) or nanodepressions.

Images