Security element with differently colored sub-areas, valuable document and method of manufacture

Abstract

The invention relates to a security element (12) for protecting valuable objects, having a feature region (14) which has at least two optically visible subregions (16, 18) which exhibit different colors in an overhead view. According to the invention it is provided here that the feature region (14) is coated in the subregions (16, 18) with a common, form-fitting and color-generating multilayer structure (30). The surface of the feature region (14) is designed in a first of the subregions (16) to be nanoscale smooth and in a second of the subregions (18) is equipped with a random, shallow nanotexture (28) having a plurality of nanostructured elements (54) having an average spacing of 50 nm to 500 nm. The first subregion (16) exhibits a first color in an overhead view as a result of the color-generating multilayer structure (30). In the second subregion (18) the color effect of the color-generating multilayer structure (30) is changed by the random nanotexture (28) such that the second subregion (18) exhibits a different second color in an overhead view as a result of the combined effect of the color-generating multilayer structure (30) and the random nanotexture (28).

Description

Technical Field

[0001] This invention relates to a security element for protecting valuable articles, the security element having a characteristic region having at least two sub-regions visible to the naked eye, these sub-regions displaying different colors when viewed from above. The invention also relates to a valuable document having such a security element and a method for manufacturing such a security element. Background Technology

[0002] Data carriers, such as valuable documents or identity documents, and other valuable items, such as branded goods, are typically equipped with security elements for protection. These security elements allow verification of the authenticity of the data carrier and also serve as protection against unauthorized copying.

[0003] Since embossed holograms, used since the late 1980s, are now widespread and no longer provide high levels of anti-counterfeiting security, micro-optical systems, such as those based on small micromirrors, are increasingly being used for authenticity protection. Security elements with micro-optical systems can be reliably identified even under adverse lighting conditions, and also allow for attractive optical effects.

[0004] Micromirror effects typically appear neutral or metallic due to the achromatic reflection of the mirror element itself, and are therefore often achieved in combination with a color-generating coating. However, if a safety element is required to exhibit different micromirror effects with varying color outcomes, transition zones often arise due to registration fluctuations during the application of the color coating, resulting in one or more micromirror effects with undesirable color results. If such safety elements should not be used with a suboptimal visual appearance, they must be painstakingly sorted out during quality control. Summary of the Invention

[0005] Therefore, the technical problem to be solved by this invention is to provide a security element of this type that has an attractive visual appearance, particularly precise alignment of color effects with different color sub-regions. This invention should also provide a valuable document and a method for manufacturing such a security element.

[0006] The technical problem described herein is solved by the features of the independent claim. Extended designs of the invention are the subject of the dependent claims.

[0007] According to the present invention, in a safety element of the type described at the beginning, the feature area is coated with a common, conformal, and color-producing multilayer structure in the sub-region.

[0008] Here, the surface of the feature region is designed to be nanoscale smooth in the first sub-region of the sub-region. In the second sub-region of the sub-region, the surface of the feature region is provided with random, shallow nanotextured portions, which have multiple nanostructural elements with an average spacing of 50 nm to 500 nm.

[0009] The first sub-region displays a first color when viewed from above due to the effect of the multi-layered structure that generates color. In the second sub-region, the color effect of the multi-layered structure that generates color is altered by random nanotexturing, so that the second sub-region displays a different second color when viewed from above due to the combined effect of the multi-layered structure that generates color and the random nanotexturing.

[0010] Here, a shallow nanotextured region is a nanotextured region in which the average depth of the nanostructure elements is less than the average spacing between the nanostructure elements. Preferably, the average depth of the nanostructure elements is even less than 1 / 2, 1 / 3, or even 1 / 4 of the average spacing between the nanostructure elements.

[0011] The term "random nanotextured portion" refers to the irregular arrangement of nanostructured elements, as opposed to an ordered, regular arrangement, such as in a grating. Random nanotextured portions can be produced, for example, by etching processes, but especially by electron beam lithography, where the randomness of the textured portion can be ensured, for example, by using pseudo-random numbers when creating the exposure dataset.

[0012] Pseudo-random numbers are sequences of numbers that appear random but are calculated using deterministic algorithms and are therefore not truly random in the strict sense. However, pseudo-random numbers are widely used because the statistical properties of their distribution, such as the equal probability of individual numbers or the statistical independence of successive numbers, are irregular enough for practical purposes, such as generating random nanotextured parts, and unlike truly random numbers, they can be easily generated by computers.

[0013] In one advantageous design, the multilayer structure that produces color has nanoscale variations in optical density and / or complex refractive index in the second sub-region.

[0014] In a preferred design, the multilayer structure that generates color is formed by angle-dependent color-changing thin-film elements, particularly by three-layer angle-dependent color-changing thin-film elements. Here, angle-dependent color-changing thin-film elements with an absorption layer / spacer layer / reflective layer structure have proven particularly suitable. Here, the absorption layer is advantageously formed by a chromium layer, for example, having a layer thickness of 3 nm to 6 nm. The spacer layer is advantageously formed by a dielectric, particularly a SiO2 layer with a thickness of 100 nm to 450 nm, and the reflective layer is advantageously formed by an opaque aluminum layer, for example, having a thickness of about 60 nm.

[0015] Also proven suitable are angle-dependent colorimetric thin-film elements with a translucent metal layer / spacer layer / translucent metal layer structure, which also exhibit angle-dependent colorimetric effects during transmission. As the translucent metal layer, a thin aluminum layer of about 5 nm thickness can advantageously be used, but other translucent metal layers composed of Al, Cr, Ag, Cu, Fe, Ni, Au, or alloys of these elements with a layer thickness of 3 nm to 20 nm can also be considered. The spacer layer can advantageously be formed by a SiO2 layer of about 240 nm thickness, or other dielectrics such as ZnS, SiO2, MgF2, or Al2O3 with a layer thickness of 50 nm to 600 nm can be used.

[0016] Multilayer structures can also be formed by a combination of metal layers, high refractive index layers, dielectrics, and true colors, preferably having 2 to 10 layers. While the use of multilayer structures is currently preferred, the feature regions in the sub-regions can, in principle, also be coated with conformal, color-generating coatings, which can be in the form of metal layers, high refractive index layers, dielectrics, or true colors.

[0017] The nanostructure elements of the randomized nanotextured portion preferably have a random distribution in terms of one or more of the characteristics of spacing, depth, base area, and shape. The nanostructure elements can also have a random distribution in all these characteristics. This distribution can be, for example, a normal distribution or a Poisson distribution.

[0018] Nanostructured elements can be formed in the form of cylinders, lenses, cuboids, pyramids, stars, arbitrary top-view shapes, deformable objects, or combinations of these shapes. Advantageously, the nanostructured elements taper gradually from their base to a pointed tip or to an arbitrary shaped end face, thus having an upwardly tapering shape. The average base area of ​​the nanostructured elements is preferably 50 nm to 400 nm, particularly preferably 100 nm to 350 nm. Advantageously, the base surface of the nanostructured elements covers 30% to 70% of the area of ​​the second sub-region.

[0019] The average spacing of the nanostructure elements is preferably from 100 nm to 350 nm, and particularly preferably from 200 nm to 250 nm. The average depth of the nanostructure elements is preferably from 5 nm to 300 nm, and particularly preferably from 10 nm to 175 nm. It goes without saying that the average depth is always less than the average spacing of the nanostructure elements in order to obtain shallow nanotextured portions.

[0020] Random nanotextured nanostructure elements are advantageously formed in printing inks, especially UV printing inks.

[0021] In an advantageous design, the first sub-region and / or the second sub-region are designed as flat regions or microstructured regions, preferably having multiple microlenses, micromirrors, Fresnel structures, and / or freeform surfaces. Flat regions or textureless regions refer to regions without microstructures, particularly regions without microlenses, micromirrors, Fresnel structures, or freeform surfaces.

[0022] It can be specified here that one of the two sub-regions is designed as a flat region and the other of the two sub-regions is designed as a microstructured region. In different equally advantageous variations, both sub-regions are designed as microstructured regions, particularly microstructured regions with different configurations of microlenses, micromirrors, Fresnel structures, and / or freeform surfaces. Here, micromirrors are preferably designed in the two sub-regions to produce their respective micromirror effects, for example, producing a motion effect in one sub-region and a 3D effect in the other.

[0023] In advantageous designs, the micromirrors are designed as planar micromirrors or as micromirrors with curved profiles in one or both directions, wherein the micromirrors particularly form periodic or non-periodic sawtooth gratings.

[0024] In particular, micromirrors described, for example, in pending German patent applications DE 10 2024 128 848.5 and DE 102025 107 278.7, the disclosure of which is incorporated herein by reference. Here, the micromirror can be designed to have a constant tilt in a first direction and a (continuous) curvature in a second direction. Alternatively, the micromirror can exist in a manner having (continuous) curvature in two mutually perpendicular directions. Here, the curved profile can be designed as a convex profile, a concave profile, or a profile that is partially convex and partially concave. Instead of a curved profile, the micromirror can also have a varying, segmented, constant tilt.

[0025] It goes without saying that a feature region can also contain more than two sub-regions visible to the naked eye, which display different colors when viewed from above. To this end, the surfaces of different sub-regions can be equipped with different random, shallow nanotextured portions, which result in different changes to the color effect of the multilayered structure that produces the color. For example, nanotextured portions with different texture depths can be used, resulting in color shifts of varying intensities.

[0026] If at least one sub-region contains a microlens or micromirror, the lateral dimension of the micromirror or microlens is suitably less than 50 µm, advantageously less than 20 µm, and particularly preferably about 10 µm, i.e., between 7 µm and 13 µm. On the other hand, to avoid color separation, the lateral dimension of the micromirror is suitably greater than 2 µm, especially greater than 3 µm or even greater than 5 µm. The step height (Ganghöhe) of the micromirror is preferably less than 10 µm, and more preferably less than 5 µm.

[0027] In an advantageous design, the two sub-regions, when viewed from above, each have at least one maximum and / or at least one minimum reflectance value for different colors, said maximum and / or minimum reflectance values ​​being offset from each other by more than 10 nm, particularly more than 25 nm, within the different colors of the sub-regions. Specifically, for example, the reflectance spectrum of the first sub-region may have maximum reflectance values ​​at 380 nm and 575 nm (first color), while the reflectance spectrum of the second sub-region may have maximum reflectance values ​​at 390 nm and 605 nm (second color). The offset of the first short-wavelength reflectance value is 10 nm, while the offset of the second long-wavelength reflectance value is 30 nm.

[0028] In an advantageous extension of the invention, the two sub-regions are specified to also exhibit different colors when viewed in transmission. Here, the different colors visible in transmission of the two sub-regions advantageously each have at least one maximum transmission value and / or at least one minimum transmission value, which are offset from each other by more than 10 nm, and particularly more than 25 nm, in the different colors of the sub-regions.

[0029] In an advantageous design, the total reflection of the multi-layered structure that produces color is reduced in the second sub-region relative to the first sub-region.

[0030] Furthermore, the second sub-region can have a lower reflectance relative to the first sub-region, particularly in the blue spectral range below 450 nm. Therefore, the second sub-region can have a reflectance that is more significantly reduced relative to the first sub-region in the blue spectral range than in the red spectral range. Specifically, if the reflectance spectra of the two colors have a first short-wavelength maximum reflectance and a second longer-wavelength maximum reflectance in the blue spectral range, then the short-wavelength maximum reflectance in the second sub-region can be attenuated more significantly than the second longer-wavelength maximum reflectance relative to the first sub-region.

[0031] The random nanotexturing advantageously avoids producing static additional reflection peaks in the second sub-region when the viewing angle changes. Therefore, while the random nanotexturing alters the color effect of the applied multilayer structure, it itself has no inherent color or at most a very faint inherent color. Thus, the angle-dependent color variation effect of the multilayer structure retains its full functionality.

[0032] The present invention also includes a valuable document, particularly a banknote, having a security element of the type described.

[0033] The present invention also includes a method for manufacturing a safety element, particularly a safety element of the type described, wherein a characteristic region is generated in the safety element, the characteristic region having at least two sub-regions visible to the naked eye, these sub-regions displaying different colors when viewed from above. Hereinafter,

[0034] –The feature regions are coated with a common, conformal, multi-layered structure that produces color in the sub-regions.

[0035] – The surface of the feature region is designed to be nanoscale smooth in the first sub-region of the sub-region.

[0036] – In the second sub-region of the sub-region, the surface of the feature region is provided with random, shallow nanotextured portions, each nanotextured portion having multiple upwardly tapering nanostructural elements with an average spacing of 50 nm to 500 nm.

[0037] –The first sub-region displays the first color when viewed from above due to the multi-layered structure that produces the color, and

[0038] – In the second sub-region, the color effect of the multi-layered structure that produces color is altered by random nanotexturing, so that the second sub-region displays a different second color when viewed from above due to the combined effect of the multi-layered structure that produces color and the random nanotexturing.

[0039] In a preferred embodiment of the method, the multilayer structure that produces color is simultaneously applied, in particular printed or vapor-deposited, onto the sub-regions of the feature area.

[0040] Particularly advantageously, the characteristic regions having nanoscale smooth surfaces and random, shallow nanotextured areas are produced by imprinting using an imprinting master. Here, imprinting can be performed, particularly in an imprinting varnish layer, preferably a UV varnish. Advantageously, the random, shallow nanotextured areas are provided to the imprinting master by an etching step or, particularly preferably, by electron beam lithography.

[0041] If at least one sub-region contains microlenses or micromirrors, these microstructures are advantageously produced together with random, shallow nanotextured portions in the same imprinting step. For this purpose, the imprinting master is advantageously equipped with both microstructured portions for producing the microstructures and the aforementioned random, shallow nanotextured portions.

[0042] The preferred embodiments and advantages described with respect to the methods of the present invention are correspondingly applicable to the safety element of the present invention. The physical components of the safety element of the present invention are designed to perform the respective steps of the method.

[0043] Other features of the invention are derived from the claims, drawings, and description of the drawings. Attached Figure Description

[0044] Embodiments of the present invention will then be described in detail with the aid of illustrative drawings. In the drawings, elements that are the same or have the same function are given the same reference numerals.

[0045] In the attached diagram:

[0046] Figure 1 A banknote having a security element according to the invention is shown schematically.

[0047] Figure 2 schematically shown Figure 1 The safety element's cross-section along line II-II,

[0048] Figure 3 (a) shows measurements taken using an atomic force microscope. Figure 2 A top view of the nanotextured portion of the second sub-region is shown in (b), and a local portion of the measured height profile of the nanotextured portion along a position coordinate is shown in (c), and the power spectral density function in frequency space calculated from the measured height profile is shown in (c).

[0049] Figure 4 This demonstrates the effect of nanotextured portions with increased average texture depth on the reflectance spectrum of angle-dependent color thin-film elements, and...

[0050] Figure 5Schematic diagrams are shown in (a) and (b) to illustrate the nanoscale variations in the optical density or complex refractive index of thin-film elements caused by the influence of random nanotexturation. Detailed Implementation

[0051] The present invention will now be described using a security element for banknotes as an example. Here, Figure 1 A schematic diagram of a banknote 10 having an optically variable security element 12 according to the invention in the form of an adhesive transfer element is shown, and Figure 2 Safety element 12 is schematically shown along Figure 1 The cross-section of line II-II. However, it goes without saying that the invention is not limited to transfer strips and banknotes, but can be used for all types of security elements, such as labels for goods and packaging, or for protecting documents, ID cards, passports, credit cards, health cards, etc. In the case of banknotes and similar documents, in addition to transfer elements (e.g., strips or patches with or without their own carrier film), security threads or security strips partially or completely embedded in the document substrate are also considered.

[0052] The safety element 12 includes a feature region 14, which has two large, visually identifiable sub-regions 16 and 18. These sub-regions exhibit both a micromirror effect and an angle-dependent color distortion when viewed from above. The micromirror effect and angle-dependent color distortion of the two sub-regions 16 and 18 are different from each other, but they are perfectly aligned with each other in the plane of the feature region 14.

[0053] More precisely, the first sub-region 16 exhibits a first micromirror effect, such as an arching effect, which combines with a first angle-dependent color variation effect, such as the angle-dependent color variation effect from gold when viewed from a vertical top view (or reflective view) 40 to green when viewed from an oblique angle 42. The second sub-region 18 exhibits a second micromirror effect, such as a flowing effect, which combines with a second angle-dependent color variation effect, such as the angle-dependent color variation effect from magenta when viewed from a vertical top view 40 to yellowish-green when viewed from an oblique angle 42. Here, the transition from the first micromirror effect to the second micromirror effect occurs at the exact same location in the feature region 14 as the transition from the first angle-dependent color variation effect to the second angle-dependent color variation effect, i.e., at the contact line 15 of sub-regions 16 and 18. Therefore, there is no transition zone in which the first micromirror effect appears together with the second angle-dependent color variation effect, or vice versa.

[0054] The perfect alignment of the micromirror effect and the angle-dependent color variation effect is then referenced. Figures 2 to 5 To elaborate further.

[0055] First refer to Figure 2In the cross-section, safety element 12 includes a transparent membrane carrier 20, on one side of which, on the lower side opposite to the observation directions 40, 42, an imprinted micromirror arrangement structure 22 is disposed. The tilt and orientation of each micromirror are set in a manner known per se such that they produce the desired micromirror effect during observation, namely, the arching effect in the first sub-region 16 and the flow effect in the second sub-region 18. In this embodiment, the micromirrors of the micromirror arrangement structure 22 are imprinted into a transparent imprinting layer and have dimensions of 10µm x 10µm and a maximum step height of 3.5µm.

[0056] For coloring, the micromirror arrangement 22 is coated with a common conformal, color-generating multilayer structure 30 across both sub-regions 16 and 18. In this embodiment, the multilayer structure 30 is formed by three-layered, angle-differentiated thin-film elements, each having a thin absorption layer, a spacer layer, and an opaque reflective layer extending from the micromirror arrangement.

[0057] The absorption layer of the thin-film element is formed, for example, by a 5 nm thick chromium layer, the reflective layer by an approximately 60 nm thick aluminum layer, and the spacer layer by a SiO2 layer with a thickness of 100 nm to 450 nm. The thickness of the SiO2 layer here essentially determines the color effect of the thin-film element through the constructive and destructive interference of the incident light at a specific wavelength, so that different angle-dependent color effects can be achieved by appropriately selecting the thickness of the SiO2 layer. A carrier film having a coated micromirror arrangement structure (or micromirror array) is applied to the banknote paper 34 of the banknote 10, for example, by an adhesive layer 32.

[0058] In order to produce different angle-dependent color effects even though the same coating 30 is applied to the two sub-regions 16 and 18, the surfaces of the two sub-regions 16 and 18 are designed in a nanoscale different manner.

[0059] In the first sub-region 16, the surface of the micromirror arrangement structure 22 has a nanoscale smooth texture 26—there, the color effect of the applied thin-film element 30 is not altered by the surface texture, so that the first sub-region 16 appears with the nominal angle-dependent color effect of the thin-film element, in the embodiment, for example, a gold-green angle-dependent color effect (or color shift effect).

[0060] In the second sub-region 18, the surface of the micromirror arrangement structure 22 is provided with random, shallow nanotextured portions 28. These nanotextured portions alter the color effect of the applied thin-film element 30 in a manner described in more detail below, producing a magenta-yellowish-green color shift towards red with angle-dependent color variation. Therefore, in a substantially vertical top-down view, the first sub-region 16 appears golden, and the second sub-region 18 appears magenta with a clear contrast. In an oblique view, the two sub-regions also appear in different colors, i.e., the first sub-region 16 is green and the second sub-region 18 is yellowish-green.

[0061] Since the nanotextured portion 28 that causes color shift exists only on the micromirrors of the second sub-region 18, while the micromirrors of the first sub-region 16 are nanoscale smooth, the two angle-dependent color shift effects and the two micromirror effects are perfectly aligned with each other.

[0062] In this embodiment, the nanotextured portion is created on an imprinting master for the micromirror arrangement structure 22 by electron beam lithography, and is precisely introduced only into the surface of the micromirrors in the second sub-region, while the micromirrors in the first sub-region remain nanoscale smooth. When imprinting the micromirror arrangement structure 22, nanotextured micromirrors are imprinted in the second sub-region 18, while nanoscale smooth micromirrors are imprinted in the first sub-region 16.

[0063] To represent more accurately, Figure 3 A top view 50 of the nanotextured portion 28 of the second sub-region 18, measured by means of an atomic force microscope, is shown in (a). Figure 3 (b) shows a portion of the measured height profile 52 of the nanotextured portion along a position coordinate, and Figure 3 (c) shows the power spectral density function in frequency space calculated from the measured height profile 56.

[0064] As from Figure 3 As shown in the illustration, the nanotextured portion 28 is formed by multiple nanostructure elements 54, whose base area, spacing, depth, and shape are randomly distributed. (Optimally, in...) Figure 3 As can be identified in the height profile 52 (b), the nanostructure element 54 has a maximum height of h ≈ 30 nm, and the root mean square (rms) roughness of the height profile is calculated as r q = 5.4nm.

[0065] The nanostructure element 54 has an upward (i.e., away from the micromirror surface) tapering shape, wherein the degree of tapering varies, and the tapering element terminates either at a tip or at an arbitrarily shaped end face.

[0066] The average spacing of the nanostructure elements 54 is given by the centroid 58 of the spacing distribution, which can be derived, for example, from the power spectral density function 56 in the frequency space, as shown in... Figure 3 As shown in (c). In this embodiment, the average spacing of the nanostructure elements is thus determined to be dm = 210 nm.

[0067] Therefore, the nanotextured portion 28 represents a high-frequency and simultaneously shallow textured portion, in which the maximum height h and root mean square roughness r of the nanostructure element are... q Significantly smaller than the average spacing d of the nanostructure elements 54. This is in Figure 3 This is also visible in (b) because the height coordinates are magnified approximately 100 times relative to the position coordinates there.

[0068] These shallow nanostructured portions according to the invention are fundamentally different from known deep nanostructured portions, such as those described, for example, in document DE 10 2004 016 596 A1, in which the depth of the relief structure is greater than, preferably even significantly greater than, the width and spacing of the relief structure elements. In contrast to the shallow nanotextures now proposed, deep nanostructured portions do not result in color changes, but rather in complete suppression of the angle-dependent color variation effect of the applied thin-layer elements.

[0069] In addition to the first observation of color changes caused by shallow nanotexturation, it was further discovered that the degree of color shift can be adjusted over a wide range by the height or depth of the nanostructure element 54. Generally, the nanotexturation 28 produces a color shift towards longer wavelengths, i.e., towards red, and the deeper the nanostructure element 54 is constructed on average, the greater the magnitude of the color shift.

[0070] To further explain, Figure 4 The effect of nanotextured portions with increased average texture depth on the reflectance spectrum of angle-dependent color thin-film elements is shown. Reflectance spectrum 60 shows the starting point, i.e., the reflectance spectrum of the thin-film element in a vertical top view on a nanoscale smooth surface. This spectrum specifically includes a narrower short-wavelength reflectance peak 62 and a wider long-wavelength reflectance peak 64.

[0071] Spectra 70, 72, and 74 are the reflection spectra of the same thin-film element on a randomly nanotextured surface with increasing texture depth. As can be seen, both the short-wavelength reflection peak 62 and the long-wavelength reflection peak 64 shift to longer wavelengths with increasing texture depth, thereby altering the color effect of the thin-film element. Here, color shifts of more than 10 nm, more than 25 nm, or even more than 50 nm are achieved for the reflection peaks 62 and 64. In extreme cases, color shifts up to 350 nm have been achieved using shallow, random nanotextured sections.

[0072] Figure 4 Although only the spectrum is shown in a vertical top view, a completely similar shift in the reflection peak also appears in an oblique view of the thin-film element, so that the color effect there is changed accordingly by the nanotexturing section.

[0073] Based on current understanding, the alteration of the color effect of the nanotextured part on the color-producing multilayer structure is based on nanoscale changes in the optical density or complex refractive index of the conformal multilayer structure.

[0074] To illustrate, Figure 5 Figure (a) shows a three-layer thin-film element 80 having a chromium absorbing layer 82, a SiO2 dielectric layer 84, and an aluminum reflective layer 86, which is applied onto a nanoscale smooth imprinted enamel layer 88. The curve 90 showing the change in refractive index n exhibits sharp, abrupt changes 92 at the boundaries between the different sublayers.

[0075] If the layer sequence 82, 84, 86 of this thin-film element 80 is applied to the imprinted paint layer 94 with a nanotextured surface, then the result is... Figure 5 The situation is illustrated in (b). Layers 82, 84, and 86 follow the shape predetermined by the nanotextured portion in their extension direction, and thereby are non-periodically offset from each other in the vertical direction at the nanoscale in terms of the height or depth of the nanostructure elements 54. Furthermore, the layer growth of the chromium absorption layer 82 on the imprinted paint layer 94 can also be altered by the nanotexturing; for example, nanoscale misalignments can be used as nucleation centers for the island-like growth of the chromium layer.

[0076] As a result, the refractive index n variation curve 96 of the thin-layer element 80 is altered by the nanotexturation portion, that is, averaged vertically on the scale of the average spacing of the nanostructure elements 54 and thus partially "verschmiert" at high frequencies. Consequently, sharp abrupt changes in refractive index no longer occur at the layer boundaries, but instead, gentle, gradual transition regions 98 are generated. These gentle transition regions result in a higher effective refractive index of the chromium absorption layer 82 and a lower effective optical path length n in the SiO2 layer 84. The change in d. Since the color effect of the thin-film element is based on the constructive or destructive interference of a specific wavelength of incident light, the interference conditions altered by the nanotexturing part lead to a shift in the maximum and minimum values ​​of the reflection spectrum of the thin-film element.

[0077] Aside from color shift, the short-wavelength reflection peak 62 is mostly observed to attenuate with increasing nanotexturation depth (see [link]). Figure 4 This is likely attributed to Rayleigh scattering at the interface of adjacent nanostructure elements 54. Rayleigh scattering exhibits a strong increase in scattering intensity toward shorter wavelengths, which results in blue light being scattered more strongly than red light and thus removed from the directional reflection spectrum.

[0078] Finally, it is important to emphasize that while the shallow nanotexturing on the surface alters the color effect of the applied multilayer structure, such as a thin-layer element, the nanotexturing itself does not possess an inherent color, or at most a very faint one. This specifically means that the nanotexturing does not produce additional static reflection peaks in the reflection spectrum, i.e., it does not produce reflection peaks whose spectral positions remain unchanged when the viewing angle changes. Therefore, the angle-dependent anisochromatic effect of the multilayer structure retains its full functionality even in the presence of the nanotexturing, changing its color with changing viewing angles just like the original angle-dependent anisochromatic effect.

Claims

1. A security element for protecting valuable articles, having a feature region having at least two sub-regions visible to the naked eye, the sub-regions displaying different colors when viewed from above, characterized in that, –The feature regions are coated with a common, conformal, and color-producing multilayer structure in the sub-regions. – The surface of the feature region is designed to be nanoscale smooth in the first sub-region of the sub-region. – The surface of the feature region is provided with random, shallow nanotextured portions in a second sub-region of the sub-region. These nanotextured portions have multiple nanostructural elements with an average spacing of 50 nm to 500 nm. –The first sub-region displays the first color when viewed from above due to the multi-layered structure that produces the color, and – In the second sub-region, the color effect of the multi-layered structure that produces color is altered by random nanotexturing, so that the second sub-region displays a different second color when viewed from above due to the combined effect of the multi-layered structure that produces color and the random nanotexturing.

2. The safety element according to claim 1, characterized in that, The multilayer structure that produces color has nanoscale variations in optical density and / or complex refractive index in the second subregion.

3. The safety element according to claim 1 or 2, characterized in that, The multilayer structure that generates color is formed by an angle-dependent color thin-layer element, preferably a three-layer angle-dependent color thin-layer element, especially an angle-dependent color thin-layer element having an absorption layer / dielectric layer / reflection layer structure or a translucent metal layer / dielectric layer / translucent metal layer structure.

4. The safety element according to at least one of claims 1 to 3, characterized in that, The nanostructure elements of the randomized nanotextured part have a random distribution in terms of one or more of the following characteristics: spacing, depth, base area, and shape.

5. The safety element according to at least one of claims 1 to 4, characterized in that, The nanostructured elements have an average spacing of 100 nm to 350 nm, advantageously 200 nm to 250 nm.

6. The safety element according to at least one of claims 1 to 5, characterized in that, The nanostructured elements have an average depth of 5 nm to 300 nm, and advantageously 10 nm to 175 nm.

7. The safety element according to at least one of claims 1 to 6, characterized in that, The first sub-region and / or the second sub-region are designed as flat regions or microstructure regions. The microstructure region preferably has multiple microlenses, micromirrors, Fresnel structures and / or freeform surfaces. Preferably, one of the two sub-regions is designed as a flat region and the other of the two sub-regions is designed as a microstructure region, or both sub-regions are designed as microstructure regions with different configurations of microlenses, micromirrors, Fresnel structures and / or freeform surfaces.

8. The safety element according to claim 7, characterized in that, The micromirrors are designed as planar micromirrors or as micromirrors with curved profiles in one or both directions, wherein the micromirrors particularly form periodic or non-periodic sawtooth gratings.

9. The safety element according to at least one of claims 1 to 8, characterized in that, The two sub-regions, when viewed from above, each have at least one maximum and / or at least one minimum reflectance, and the maximum and / or minimum reflectance are offset from each other by more than 10 nm, and especially more than 25 nm, in the different colors of the sub-regions.

10. The safety element according to at least one of claims 1 to 9, characterized in that, The two sub-regions also show different colors when viewed through transmission. Preferably, the different colors visible in the two sub-regions when viewed through transmission have at least one maximum transmission value and / or at least one minimum transmission value, and the maximum transmission value and / or minimum transmission value are offset from each other by more than 10 nm, especially more than 25 nm, in the different colors of the sub-regions.

11. The safety element according to at least one of claims 1 to 10, characterized in that, The second sub-region has a lower reflectance relative to the first sub-region in the blue spectral range below 450 nm.

12. The safety element according to at least one of claims 1 to 11, characterized in that, Random nanotexturation does not produce static additional reflection peaks in the second sub-region when the viewing angle changes.

13. A method for manufacturing a safety element, particularly a safety element according to any one of claims 1 to 12, wherein a characteristic region is generated in the safety element, the characteristic region having at least two sub-regions visible to the naked eye, the sub-regions displaying different colors when viewed from above. in, –The feature regions are coated with a common, conformal, and color-producing multilayer structure in the sub-regions. – The surface of the feature region is designed to be nanoscale smooth in the first sub-region of the sub-region. – In the second sub-region of the sub-region, the surface of the feature region is provided with random, shallow nanotextured portions, each nanotextured portion having multiple upwardly tapering nanostructural elements with an average spacing of 50 nm to 500 nm. –The first sub-region displays the first color when viewed from above due to the multi-layered structure that produces the color, and – In the second sub-region, the color effect of the multi-layered structure that produces color is altered by random nanotexturing, so that the second sub-region displays a different second color when viewed from above due to the combined effect of the multi-layered structure that produces color and the random nanotexturing.

14. The method according to claim 13, characterized in that, The multi-layered structure that produces color is simultaneously applied, in particular printed or vapor-deposited, onto the sub-regions of the feature area.

15. The method according to claim 13 or 14, characterized in that, The feature regions with nanoscale smooth surfaces and random, shallow nanotextured areas are produced by imprinting using an imprinting master.

16. The method according to claim 15, characterized in that, The random, shallow nanotextured portions are applied to the embossing master by an etching step or preferably by electron beam lithography.

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