DE102020005607A1 - Optically variable security element - Google Patents

Abstract

The invention relates to an optically variable security element (12) with a reflective surface area (20) which, when viewed from above, shows at least two optically variable effects which can be seen from different viewing directions and appear with different first and second colors, and which when viewed through has an appearance in one third, different color shows. It is provided that the reflective surface area (20) contains two independent relief structures (24, 34), which form a lower-lying and a higher-lying relief structure and which overlap in a feature area. The higher and lower relief structures (24, 34) are each provided with a reflection-increasing coating (26, 36) following the course of the relief, which has wavelength-dependent reflection and transmission in the visible spectral range and has at least one reflection band and at least one transmission band. A reflection band of the second reflection enhancing coating (26) lies at least partially in a transmission band of the first reflection enhancing coating (36) and at least one transmission band of the two reflection enhancing coatings (26, 36) overlaps.

Description

The invention relates to an optically variable security element for protecting objects of value with a reflective surface area which exhibits at least two optically variable effects that can be seen from different viewing directions. The invention also relates to a method for producing such a security element and to a data carrier equipped with such a security element.

Data carriers, such as value or ID documents, but also other valuables, such as branded items, are often provided with security elements for protection, which allow the authenticity of the data carrier to be checked and which also serve as protection against unauthorized reproduction. The security elements can be designed, for example, in the form of a security thread embedded in a banknote, a cover film for a banknote with a hole, an applied security strip, a self-supporting transfer element or also in the form of a feature area printed directly onto a document of value.

Security elements with a viewing angle-dependent or three-dimensional appearance play a special role in authenticity protection, as these cannot be reproduced even with the most modern copiers. For this purpose, the security elements are equipped with optically variable elements that give the viewer a different image impression from different viewing angles and, for example, depending on the viewing angle, show a different color or brightness impression, a different perspective view and/or a different graphic motif.

The prior art describes, for example, movement effects, pump effects, depth effects or flip effects as optically variable effects, which are realized with the aid of holograms, microlenses or micromirrors.

Some time ago were in the pamphlet DE 10 2018 005 447 A1 proposed optically variable security elements which have two relief structures arranged at different height levels and each provided with a color coating. The color coating of the higher-lying relief structure is structured as a grid, so that the color coating of the lower-lying relief structure appears in the interstices of the grid when the security element is viewed. This configuration enables a transition-free change from a first to a second appearance when the security element is tilted. In practice, however, the realization of the necessary fine screening of the color coating is technologically very demanding.

Proceeding from this, the invention is based on the object of proposing a generic optically variable security element that is easy to produce, has an attractive visual appearance and can be used in a variety of ways to authenticate data carriers.

This object is solved by the features of the independent claims. Developments of the invention are the subject matter of the dependent claims.

To achieve the above object, the invention contains an optically variable security element with a multicolored reflective surface area, which can be used in particular to protect valuables. When viewed from above, the reflective surface area shows at least two optically variable effects that are recognizable from different viewing directions and appear with different first and second colors, and when viewed through it shows an appearance in a third, different color.

The third color is different from both the first and the second color. The term color includes not only chromatic colors, but also achromatic colors, ie in particular white, black, gray, and essentially silvery metallic colors, such as the color of a reflective aluminum or silver layer.

The reflective surface area contains two independent relief structures, which are arranged at different height levels in the z-direction and form a lower-lying and a higher-lying relief structure. The two relief structures overlap in a feature area, with partial overlapping or complete overlapping, ie formation in congruent surface areas, being possible.

The higher-lying relief structure is provided with a first reflection-increasing coating following the course of the relief, which has wavelength-dependent reflection and transmission in the visible spectral range and thereby at least one reflection band and at least one transmission band.

The lower-lying relief structure is provided with a second reflection-increasing coating which follows the course of the relief and which has a wavelength-dependent reflection and transmission in the visible spectral range and also has at least one reflection band and at least one transmission band.

The higher-lying relief structure and the lower-lying relief structure are matched to one another in that a reflection band of the second reflection-enhancing coating lies at least partially in a transmission band of the first reflection-enhancing coating, and that at least one transmission band of the two reflection-enhancing coatings also overlaps.

In plan view, the higher-lying relief structure then shows a first optically variable effect in the first color and the lower-lying relief structure shows a second optically variable effect in the second, different color through the first reflection-enhancing coating. When viewed through the higher-lying and the lower-lying relief structure, an appearance appears in the third color, which is different from the first and second color.

In an advantageous embodiment, the first and/or second reflection-increasing coating has a transmission of at least 35%, preferably at least 50%, particularly preferably at least 65% in its transmission bands of the visible spectral range.

The first and/or second reflection-increasing coating advantageously has a reflection of at least 20%, preferably at least 30%, particularly preferably at least 40%, in its reflection bands of the visible spectral range.

The first reflection-increasing coating preferably contains one or more high-index layers, preferably dielectric high-index layers, which have a refractive index of at least 1.7, preferably at least 2.0 and particularly preferably at least 2.2 in at least a portion of the visible spectrum. In particular, the first reflection-increasing coating can be formed by a ZnS layer with a thickness between 50 nm and 400 nm.

Alternatively or additionally, the second reflection-enhancing coating advantageously contains one or more high-index layers, preferably dielectric high-index layers, which have a refractive index of at least 1.7, preferably at least 2.0 and particularly preferably at least 2.2, at least in a portion of the visible spectrum . In particular, the second reflection-increasing coating can be formed by a ZnS layer with a thickness between 50 nm and 400 nm.

In a particularly advantageous embodiment, the first and second reflection-increasing coatings are each formed by a ZnS layer, with the layer thicknesses of the two coatings differing by 35 nm or more. It can thereby be achieved with the aid of two ZnS layers that a reflection band of the second reflection-enhancing coating lies at least partially in a transmission band of the first reflection-enhancing coating, as desired.

In a further, likewise advantageous embodiment, the second reflection-increasing coating is a multi-layer system with a layer sequence of metal/dielectric/metal, in particular aluminum/SiO _2/ aluminium, the metal layers of the multi-layer system, in particular the aluminum layers, preferably having a layer thickness of 5 nm or less of 4 nm or less. The multilayer system is advantageously designed in such a way that its reflection and transmission are between 30% and 70%. The first reflection-increasing coating can also be formed by a multi-layer system of the type mentioned, even if high-index individual layers, for example a ZnS layer, are currently particularly preferred for the first reflection-increasing coating.

In an advantageous embodiment, the higher-lying relief structure and/or the lower-lying relief structure are formed by micromirror arrangements with specularly reflecting micromirrors, in particular with non-diffractive mirrors, and preferably with flat mirrors, concave mirrors and/or Fresnel-like mirrors. The lateral dimensions of the micromirrors are expediently below 50 μm, advantageously below 20 μm, preferably around 10 μm, ie between 7 μm and 13 μm. On the other hand, the lateral dimensions of the micromirrors are also above 2 μm, in particular above 3 μm or even above 5 μm. The pitch of the micromirrors is preferably less than 10 μm, preferably less than 5 μm.

Instead of micromirrors, the relief structures can also include other embossed relief structures, in particular Fresnel lenses, concave mirrors, hologram structures, nanostructures or diffractive blazed gratings. Advantageously, achromatic diffraction gratings, so-called matte structures, which essentially reflect white light, can also be used. In order to produce bright colors, the relief structures of at least the second relief structure can also have subwave structures, in particular subwavelength gratings, which increase reflection in combination with the respective one determines the layer whose color or at least partly determines it.

In further advantageous configurations, one or both relief structures can also be formed by a layer with a multiplicity of three-dimensionally aligned platelet-shaped pigments. The flake-form pigments are particularly advantageously flake-form magnetic pigments that can be aligned by a magnetic field, but they can also be flake-form effect pigments that can be aligned by other fields, for example electric fields. The aligned pigments not only lie flat in the plane of the surface area, but are at least partially tilted with respect to this plane. Due to their three-dimensional alignment with a tilting component against the plane, the surface formed by the pigments, similar to the embossed structures described above, also represents a relief structure.

In an advantageous embodiment, a first of the three colors mentioned is red or reddish, a second is green or greenish and a third is blue or bluish. Also advantageously, the color that is visible when viewed through is an achromatic color, in particular with a gray or metallic appearance.

With regard to the area coverage of the reflection-increasing layers, in an advantageous embodiment, both reflection-increasing layers are not screened and in particular are even applied to the surface pattern over the entire surface. A particular advantage of the design according to the invention consists precisely in the fact that the optically variable effect of the underlying relief structure is visible despite a first reflection-increasing coating that is present without a grid or over the entire surface.

In a further development, the second reflection-increasing layer can also be provided only in regions and thereby form negative identifiers, in particular in the form of numbers, symbols and the like, in the security element. In addition or as an alternative, the first reflection-increasing coating can also be present only in certain areas. According to the invention, however, the areas in which the two different reflection-increasing coatings are provided must overlap at least in areas in the feature area. In advantageous embodiments, the two reflection-increasing coatings are not provided over the entire area, but in partial areas that are completely or almost congruent. In particular, a negative identifier can be designed in such a way that both reflection-increasing coatings are left out congruently in the form of text, symbols, numerical values and the like. The first reflection-increasing layer is therefore advantageously unrastered in the feature area, that is to say without a raster, but possibly with individual negative features. In a preferred configuration, the first reflection-increasing layer is even present over the entire area in the feature region, ie without grids and gaps.

In a development of the invention, one or more translucent color layers can be provided between the first and second relief structure and/or above the first reflection-enhancing coating and/or below the second reflection-enhancing coating in order to influence the color impression of the security element. Each of these color layers can be present over the entire surface or only in certain areas, in particular in the form of patterns, characters or a code.

For example, a color layer can be provided below the second reflection-increasing coating, which absorbs more strongly in some areas and less in some areas in the overlapping transmission range of the two reflection-increasing coatings, resulting in a structured appearance when viewed through.

According to the invention, the optically variable effects of the two relief structures are not congruent; rather, they are at least partially recognizable from different viewing directions. In particular, it is advantageously provided that the first and second relief structure at least partially reflect incident parallel light in different angular ranges, the two different angular ranges preferably not overlapping and preferably being separated from one another by more than 3°, particularly preferably more than 10°.

The two relief structures are independent relief structures. They can therefore be chosen freely, since they do not depend on one another (in terms of their relief pattern). A relief structure that results solely from coating another relief structure is not an independent relief structure in the present sense. In particular, the relief structures of the surface area do not have the same relief pattern, nor the same relief pattern that is only scaled in height, but rather the two relief structures are designed differently and with different relief patterns. The two independent relief structures are particularly different. The two relief structures can therefore produce optically variable effects of the same type, for example opposing movement effects or three-dimensional representations visible from different viewing directions However, due to the diversity of the relief patterns, both cannot always produce the same optically variable effect in the same place.

Specifically, the formation of the higher-lying relief structure, in particular the alignment of the micromirrors of the higher-lying micromirror arrangement and/or the formation of the lower-lying relief structure, in particular the alignment of the micromirrors of the lower-lying micromirror arrangement, can advantageously vary depending on the location, around a given motif in each case, in particular a to produce a three-dimensional motif or a movement motif. The relief pattern, in particular the alignment of the micromirrors, can be freely selected and essentially only determined by the specified motifs, but not by the alignment of laterally or vertically adjacent micromirrors.

The invention also includes a data carrier with a security element of the type described. The data carrier can in particular be a document of value, such as a banknote, in particular a paper banknote, a polymer banknote or a foil composite banknote, a share, a bond, a certificate, a voucher , a check, a premium ticket, but also an identification card, such as a credit card, a bank card, a cash card, an authorization card, an ID card or a passport personalization page. The lower-lying relief structure is generally closer to a surface of the data carrier than the higher-lying relief structure, which is closer to the viewer's eye.

In order to also be able to use the see-through feature for the authenticity check, in a particularly expedient variant the security element is arranged in a window area, ie in a transparent or perforated area of the data carrier. Alternatively, the security element can also be arranged over an opaque area of the data carrier and, for example, enable information on the data carrier to be viewed.

• - ein Träger bereitgestellt wird, dessen Flächenausdehnung eine Ebene und eine darauf senkrecht stehende z-Achse definiert,
• - der Träger mit einem reflektiven Flächenbereich versehen wird, der zwei eigenständige Reliefstrukturen enthält, die in z-Richtung in unterschiedlichen Höhenstufen angeordnet sind, und eine tiefer liegende und eine höher liegende Reliefstruktur bilden, und die in einem Merkmalsbereich überlappend ausgebildet werden,
• - die höher liegende Reliefstruktur mit einer dem Reliefverlauf folgenden ersten reflexionserhöhenden Beschichtung mit einer wellenlängenabhängigen Reflexion und Transmission im sichtbaren Spektralbereich versehen wird, die zumindest ein Reflexionsband und zumindest ein Transmissionsband aufweist,
• - die tiefer liegende Reliefstruktur mit einer dem Reliefverlauf folgenden zweiten reflexionserhöhenden Beschichtung mit einer wellenlängenabhängigen Reflexion und Transmission im sichtbaren Spektralbereich versehen wird, die zumindest ein Reflexionsband und zumindest ein Transmissionsband aufweist,
• - wobei die reflexionserhöhenden Beschichtungen so aufeinander abgestimmt werden, dass ein Reflexionsband der zweiten reflexionserhöhenden Beschichtung zumindest teilweise in einem Transmissionsband der ersten reflexionserhöhenden Beschichtung liegt, und zumindest ein Transmissionsband der beiden reflexionserhöhenden Beschichtungen überlappt, so dass
• - die höher liegende Reliefstruktur in Aufsicht einen ersten optisch variablen Effekt in einer ersten Farbe zeigt, die tiefer liegende Reliefstruktur in Aufsicht durch die erste reflexionserhöhende Beschichtung hindurch einen zweiten optisch variablen Effekt in einer zweiten, unterschiedlichen Farbe zeigt, und wobei sich in Durchsicht durch die höher liegende und tiefer liegende Reliefstruktur ein Erscheinungsbild in einer dritten, unterschiedlichen Farbe zeigt.

The invention also includes a method for producing an optically variable security element with a reflective surface area that shows at least two optically variable effects that can be seen from different viewing directions and appear with different colors, and in particular provides a method for producing a security element of the type described above ready at which

• - a carrier is provided, the surface area of which defines a plane and a z-axis perpendicular thereto,
• - the carrier is provided with a reflective surface area, which contains two independent relief structures, which are arranged at different height levels in the z-direction and form a lower and a higher relief structure, and which are designed to overlap in a feature area,
• - the higher-lying relief structure is provided with a first reflection-increasing coating following the course of the relief with a wavelength-dependent reflection and transmission in the visible spectral range, which has at least one reflection band and at least one transmission band,
• - the lower-lying relief structure is provided with a second reflection-increasing coating following the course of the relief with a wavelength-dependent reflection and transmission in the visible spectral range, which has at least one reflection band and at least one transmission band,
• - wherein the reflection-enhancing coatings are matched to one another in such a way that a reflection band of the second reflection-enhancing coating lies at least partially in a transmission band of the first reflection-enhancing coating, and at least one transmission band of the two reflection-enhancing coatings overlaps, so that
• - the higher-lying relief structure shows a first optically variable effect in a first color in plan view, the lower-lying relief structure shows a second optically variable effect in a second, different color in plan view through the first reflection-enhancing coating, and when viewed through the higher-lying and lower-lying relief structure shows an appearance in a third, different color.

Further exemplary embodiments and advantages of the invention are explained below with reference to the figures, which are not shown to scale and proportions in order to improve clarity.

• 1 eine schematische Darstellung einer Banknote mit einem erfindungsgemäßen optisch variablen Sicherheitselement,
• 2 einen Ausschnitt eines erfindungsgemäßen Sicherheitselements im Querschnitt,
• 3 stark schematisiert in (a) und (b) die unterschiedliche wellenlängenabhängige Reflexion und Transmission der beiden reflexionserhöhenden Beschichtungen und in (c) die sich ergebenden Transmissions- und Reflexionsspektren des gesamten Flächenbereichs, und
• 4 ein anderes Ausführungsbeispiel der Erfindung, bei dem die im Zusammenhang mit 2 beschriebenen Schichten auf derselben Seite einer Trägerfolie aufgebracht wurden.

Show it:

• 1 a schematic representation of a banknote with an optically variable security element according to the invention,
• 2 a section of a security element according to the invention in cross section,
• 3 strongly schematized in (a) and (b) the different wavelength-dependent reflection and transmission of the two reflection-enhancing coatings and in (c) the resulting transmission and reflection spectra of the entire surface area, and
• 4 another embodiment of the invention in which the related 2 layers described were applied to the same side of a carrier film.

The invention will now be explained using the example of security elements for banknotes. 1 shows a schematic representation of a banknote 10 with an optically variable security element 12 according to the invention in the form of a transfer element glued on. It goes without saying, however, that the invention is not limited to transfer elements and banknotes, but can be used with all types of security elements, for example labels on goods and packaging or to protect documents, ID cards, passports, credit cards, health cards and the like. In the case of banknotes and similar documents, in addition to transfer elements (such as patches or strips, each with or without their own backing layer), security threads or security strips, for example, can also be considered.

This in 1 The security element 12 shown is arranged in a window area 15 of the bank note 10 and covers there, for example, a continuous opening of the bank note. When looking at the banknote in the in 1 In the top view shown, the security element 12 gives the viewer a three-dimensional impression despite its flat design and at the same time shows a binary color and effect change when the banknote 10 is tilted. The security element 12 shows a first view from a first viewing direction, apparently from the plane of the banknote 10 bulging motif 14-A, specifically, for example, a curved representation of the value number “10”, which appears with a first color, for example a green color impression. From a second viewing direction, the security element 12 shows a second motif 14-B that appears to bulge out of the plane of the banknote 10, for example a curved depiction of a coat of arms that appears in a second color, for example a reddish color impression.

When the bank note 10 is tilted 16 or when the viewing direction changes accordingly, the appearance of the security element 12 suddenly jumps from the first to the second appearance, or when it is tilted back from the second to the first appearance. The change in motif (number or coat of arms) and color (green or reddish) takes place simultaneously and without an intermediate or transition stage in which both motifs or colors would be visible at the same time or one motif would be visible in the color of the other motif would. The appearance therefore jumps seamlessly between two appearances 14-A, 14-B and is therefore referred to as a binary color and effect change.

The security element 12 also allows a view through the security element and the window area 15 of the bank note, with the security element appearing in a third color that is different from the two supervisory colors, for example with a blue color impression.

The special structure of optically variable security elements according to the invention will now be discussed with reference to FIG 2 explained in more detail, which shows a section of the security element 12 schematically in cross section.

The security element 12 contains a flat, transparent carrier film 18, the surface extent of which defines an x-y plane and a z-axis perpendicular thereto.

The carrier film 18 carries a multicolored reflective surface area 20, which contains two relief structure areas 24, 34, which are arranged in the z-direction at two specific, different height levels. The relief structure 34 that is closer to the viewer 40-A, 40-B when viewed from above is referred to as the higher relief structure, and the relief structure 24 that is further away from the viewer is referred to as the lower relief structure.

In the exemplary embodiment, the two relief structure areas each represent micromirror embossings or micromirror arrangements 24, 34, which are each formed from a multiplicity of micromirrors inclined with respect to the x-y plane and having lateral dimensions of approximately 10 μm. The local angles of inclination of the micromirrors are selected in such a way that the relief structures of the micromirror arrangements 24, 34 produce a desired optical appearance after the reflection-increasing coating.

Specifically, the angles of inclination of the micromirrors in the exemplary embodiment are selected such that the micromirror arrangement 34 generates the curved representation of the value number “10” in a viewing angle range of +5° to +20° (viewing position 40-A) related to the surface normal and the micromirror arrangement 24 in a viewing angle range of -5° to -20° (viewing position 40-B) produces the curved representation of the coat of arms.

In order to generate the desired color impressions, the higher-lying micromirror arrangement 34 is covered over the entire surface with a first layer following the course of the relief th reflection-increasing coating 36 in the form of a semi-transparent, high-index ZnS layer, which has a wavelength-dependent reflection and transmission. The layer thickness of the ZnS layer is chosen with d= 160 nm so that it has a reflection band in the green spectral range (R=0.42) and transmission bands in the red (T=0.9) and blue (T=0.75) spectral range, i.e. it has a high reflection in the green spectral range and a high transmission in the red and blue spectral range.

The lower-lying micromirror arrangement 24 is provided over the entire surface with a second reflection-increasing coating 26 following the relief pattern, which is formed by a semitransparent three-layer system of 3 nm Al/200 nm SiO ₂ /3 nm Al and has wavelength-dependent reflection and transmission. The layer thicknesses of the two aluminum layers and the dielectric layer are selected in such a way that the three-layer system has a reflection band in the red spectral range (R=0.55) and a transmission band in the blue spectral range (T=0.6), i.e. it has a high reflection in the red spectral range and a high transmission blue spectral range.

The micromirror arrays 24, 34 are each embossed into a transparent embossed lacquer layer 22, 32 applied to opposite sides of the carrier film 18 and leveled with a transparent top lacquer layer 28 or 38 after the respective reflection-increasing coating 26, 36 has been applied. In this case, the cover lacquer layers preferably have essentially the same refractive index as the embossing lacquer layers 22 , 32 .

When white light 50 is incident perpendicularly on the surface area 20, the micromirrors of the higher-lying micromirror arrangement 34 are at the glancing angle for the observer from the viewing direction 40-A, which produce the curved representation of the value number “10”. The first reflection-enhancing coating 36 produces an image impression with a green reflection color 52 because of its reflection band in the green spectral range. Because of the semi-transparency of the reflection-enhancing coating 36, the micromirrors of the micromirror arrangement 24 are basically also perceptible, but their alignment is far removed from the glancing angle and they appear therefore inconspicuous from the viewing direction 40-A and practically do not contribute to the image impression. Overall, the viewer from the viewing direction 40-A sees the green appearance 14-A of the curved denomination “10” generated by the micromirror arrangement 34 in plan view.

In a top view from the viewing direction 40-B, the micromirrors of the lower-lying micromirror arrangement 24 are in the glancing angle for the viewer, which produce the curved representation of the coat of arms. Due to its transmission bands in the red and blue spectral range, the first reflection-enhancing coating 36 of the higher-lying micro-mirror arrangement 34 transmits the red portion 54 and the blue portion 56 of the incident white light 50 to the second reflection-enhancing coating 26 of the lower-lying micro-mirror arrangement 24.

Due to its reflection band in the red spectral range, the second reflection-enhancing coating 26 reflects the red spectral component 54 in the viewing direction 40-B, which is also transmitted by the first reflection-enhancing coating 36 because of its transmission band in the red spectral range. Although the micromirrors of the micromirror arrangement 34 located higher are basically also perceptible from the viewing direction 40-B, their orientation is far removed from the specular angle and they therefore appear inconspicuous and practically do not contribute to the image impression. Overall, the observer from the viewing direction 40-B thus sees the reddish appearance 14-B of the arched coat of arms generated by the micromirror arrangement 24.

In a see-through view from the viewing direction 40-C, the glancing angle of the micromirrors 24, 34 is irrelevant for reflection; the appearance is rather determined by the transmitted radiation components of the two reflection-increasing coatings 26, 36. Since the first reflection-enhancing coating 36 transmits the red portion 54 and the blue portion 56 of the incident white light 50 and the second reflection-enhancing coating 26 still transmits the blue spectral portion 56 due to its transmission band in the blue spectral range, the viewer from the viewing direction 40-C sees in Inspection of the surface area 20 with a blue color impression.

3 shows highly schematized the different wavelength-dependent reflection and transmission of the two reflection-increasing coatings 36, 26 and the resulting transmission and reflection spectra of the entire surface area 20.

First, the diagram 60 shows the 3(a) for the first reflection-enhancing coating 36, the wavelength-dependent reflection as a solid curve R ₁ (λ) and the wavelength-dependent transmission as a dashed curve T ₁ (λ). As can be seen immediately, the coating 36 shown has a reflective band in the green spectral range (G) and transmission bands in the red spectral range (R) and blue spectral range (B).

The diagram 62 of the 3(b) 12 correspondingly shows the wavelength-dependent reflection for the second reflection-increasing coating 26 as a solid curve R ₂ (λ) and the wavelength-dependent transmission as a dashed curve T ₂ (λ). The coating 26 shown has a reflection band in the red spectral range (R) and a transmission band in the green spectral range (G) and blue spectral range (B).

und es ergibt sich wegen des genannten Reflexionsbands der ersten reflexionserhöhenden Beschichtung 36 ein grünes Erscheinungsbild.The Diagram 64 of the 3(c) shows a summary of the resulting transmission and reflection spectra of the entire surface area 20. From the viewing direction 40-A, the appearance of the surface area 20 is determined by the reflectivity of the first reflection-increasing coating 36, ie $${\text{R}}_{\text{A}}\left(\mathrm{\lambda }\right)={\text{R}}_1\left(\mathrm{\lambda }\right),$$

and a green appearance results because of said reflection band of the first anti-reflective coating 36.

so dass sich aus dieser Betrachtungsrichtung durch die Transmissionsbänder der ersten reflexionserhöhenden Beschichtung im roten und blauen Spektralbereich und das Reflexionsband der ersten reflexionserhöhenden Beschichtung im roten Spektralbereich insgesamt ein rötliches Erscheinungsbild ergibt.From the viewing direction 40-B, the appearance of the surface area 20 results from the light transmitted by the first reflection-enhancing coating 36 and the light reflected by the second reflection-enhancing coating 26 . When determining the brightness of the total reflection, it must be taken into account that the incident light, after being reflected at the second reflection-enhancing coating 26, passes through the first reflection-enhancing coating 36 one more time (see, for example, 2 ), so their transmission has to be considered twice. The result for the reflectivity viewing direction 40-B is: $${\text{R}}_{\text{B}}\left(\mathrm{\lambda }\right)={\text{T}}_1\left(\mathrm{\lambda }\right)*{\text{R}}_2\left(\mathrm{\lambda }\right)*{\text{T}}_1\left(\mathrm{\lambda }\right),$$

so that an overall reddish appearance results from this viewing direction due to the transmission bands of the first reflection-enhancing coating in the red and blue spectral range and the reflection band of the first reflection-enhancing coating in the red spectral range.

so dass sich durch die Transmissionsbänder der ersten reflexionserhöhenden Beschichtung 36 im roten und blauen Spektralbereich und das Transmissionsband der zweiten reflexionserhöhenden Beschichtung 26 im blauen Spektralbereich insgesamt ein blauer Farbeindruck ergibt.When viewed through, from viewing direction 40-C, the appearance of the surface area results from the light transmitted by the two reflection-enhancing coatings 26, 36: $${\text{T}}_{\text{C}}\left(\mathrm{\lambda }\right)={\text{T}}_1\left(\mathrm{\lambda }\right)*{\text{T}}_2\left(\mathrm{\lambda }\right),$$

so that an overall blue color impression results from the transmission bands of the first reflection-enhancing coating 36 in the red and blue spectral range and the transmission band of the second reflection-enhancing coating 26 in the blue spectral range.

4 shows as a further embodiment of the invention, a security element 70, in which the associated with 2 already described layers were applied to the same side of a carrier film 18. Starting from the carrier film 18, the security element 70 contains a first transparent embossed lacquer layer 32 with an embossed, higher-lying micromirror structure 34, a first reflection-increasing coating 36, a second transparent embossed lacquer layer 22 applied to the coating 36 with an embossed, lower-lying micromirror structure 24, a second reflection-enhancing coating 26, a topcoat layer 28, and finally an adhesive layer 44 for transferring the security element 70 to a target substrate. The carrier film 18 is preferably designed to be releasable and is pulled off after the security element 70 has been transferred. Alternatively, the carrier film 18 can also remain in the transferred layered composite if it is transparent.

The first reflection-enhancing coating 36 is in the embodiment 4 formed by a semi-transparent, highly refractive ZnS layer with wavelength-dependent reflection and transmission. The layer thickness of the ZnS layer 36 is selected at d=104 nm in such a way that it has reflection bands in the red and blue spectral range and a transmission band in the green spectral range. Although the ZnS layer 36 primarily reflects the incident red and blue light, a small proportion of red and blue light is also transmitted.

In this exemplary embodiment, the second reflection-increasing coating 26 is likewise formed by a semitransparent, high-index ZnS layer with wavelength-dependent reflection and transmission. The layer thickness of the ZnS layer 26 is selected at d=140 nm in such a way that it has pronounced reflection bands in the blue and green spectral range and a transmission band in the red spectral range.

When white light is incident perpendicularly and viewed at the glancing angle of the micromirror of the micromirror arrangement 34 located higher, the first reflection-increasing coating 36 produces an image impression with a violet reflection color because of its reflection bands in the red and blue spectral range. The micromirrors of the micromirror array that are not in the glancing angle 24 appear inconspicuous from this viewing direction and practically do not contribute to the image impression.

When viewed at the glancing angle of the micromirrors of the micromirror arrangement 24 lying deeper, the color impression results, as described above, from an interaction of the spectral component transmitted by the first reflection-enhancing coating 36 and the spectral component reflected therefrom at the second reflection-enhancing coating 26 . In the exemplary embodiment, the first reflection-increasing coating 36 has a transmission band in the green spectral range, with a small portion of blue light also being transmitted. Because of the pronounced reflection bands of the second reflection-enhancing coating 26 in the blue and green spectral range, the micromirrors of the lower-lying micromirror array 24 therefore appear to the viewer with a blue/green/turquoise color. The micromirrors of the micromirror arrangement 34 that are not in the specular angle appear inconspicuous from this viewing direction and practically do not contribute to the image impression.

When viewed through, the appearance is determined by the respective transmitted radiation components, with the first reflection-increasing coating 36 transmitting green light to a large extent and red and blue light to a small extent. The second reflection-enhancing coating 26 transmits red light strongly, but also transmits blue and green light to a small extent. As a result, the total transmission of the two reflection-increasing coatings is an almost balanced spectrum with a slight emphasis on the transmission in the red, so that the observer sees an essentially achromatic color, namely an aluminum-colored transparent color with a reddish hue.

Reference List

10

bank note

12

security element

14-A, 14-B

bulging motifs

15

pane

16

tilt direction

18

carrier

20

reflective surface area

22

embossing layer

24

micromirror array

26

anti-reflective coating

28

topcoat layer

32

embossing layer

34

micromirror array

36

anti-reflective coating

38

topcoat layer

40-A, 40-B, 40-C

viewer

50

incident white light

52

green component, green reflection color

54

red portion, reddish reflection color

56

blue portion, blue transmission color

60,62,64

charts

70

security element

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102018005447 A1 [0005]

Claims (17)

Optically variable security element for protecting valuables, the surface area of which defines a z-axis perpendicular to it, with a reflective surface area which, when viewed from above, shows at least two optically variable effects that can be seen from different viewing directions and appear with different first and second colors, and the shows an appearance in a third, different color when viewed through, - the reflective surface area contains two independent relief structures, which are arranged at different height levels in the z-direction and form a lower and a higher relief structure, and which overlap in a feature area, - the higher relief structure is provided with a first reflection-increasing coating following the course of the relief with a wavelength-dependent reflection and transmission in the visible spectral range, which has at least one reflection band and at least one transmission band, - the lower-lying relief structure is provided with a second reflection-increasing coating following the course of the relief with a wavelength-dependent reflection and transmission in the visible spectral range, which has at least one reflection band and at least one transmission band, - wherein a reflection band of the second anti-reflective coating lies at least partially in a transmission band of the first anti-reflective coating, and at least one transmission band of the two anti-reflective coatings overlaps such that - the higher-lying relief structure shows a first optically variable effect in the first color in plan view, the lower-lying relief structure shows a second optically variable effect in the second, different color in plan view through the first reflection-enhancing coating, and when viewed through the higher-lying and lower-lying relief structure shows an appearance in the third, different color. security element after claim 1 , characterized in that the first and/or the second reflection-increasing coating has a transmission of at least 35%, preferably at least 50%, particularly preferably at least 65% in their transmission bands of the visible spectral range. security element after claim 1 or 2 , characterized in that the first and/or the second reflection-increasing coating has a reflection of at least 20%, preferably at least 30%, particularly preferably at least 40% in their reflection bands of the visible spectral range. Security element according to at least one of Claims 1 until 3 , characterized in that the first reflection-increasing coating contains one or more high-index layers, preferably dielectric high-index layers, which have a refractive index of at least 1.7, preferably at least 2.0 and particularly preferably at least 2.2, at least in a portion of the visible spectrum , in particular that the first anti-reflective coating is a ZnS layer with a thickness between 50 nm and 400 nm. Security element according to at least one of Claims 1 until 4 , characterized in that the second reflection-increasing coating contains one or more high-index layers, preferably dielectric high-index layers, which have a refractive index of at least 1.7, preferably at least 2.0 and particularly preferably at least 2.2, at least in a portion of the visible spectrum , in particular that the second anti-reflective coating is a ZnS layer with a thickness between 50 nm and 400 nm. security element after claim 4 and 5 , in which the first and second anti-reflective coatings are each a ZnS layer, and the layer thicknesses of the two coatings differ by 35 nm or more. Security element according to at least one of Claims 1 until 4 , characterized in that the second reflection-increasing coating is a multi-layer system with a layer sequence metal/dielectric/metal, in particular aluminum/SiO ₂ /aluminium, the metal layers, in particular the aluminum layers, having a layer thickness of 5 nm or less, preferably 4 nm or less . Security element according to at least one of Claims 1 until 7 , characterized in that the higher-lying relief structure and/or the lower-lying relief structure are formed by micromirror arrangements with specularly reflecting micromirrors, in particular with non-diffractive mirrors, and preferably with flat mirrors, concave mirrors and/or Fresnel-like mirrors. Security element according to at least one of Claims 1 until 8th , characterized in that a first of the three colors mentioned is red or reddish, a second is green or greenish, and a third is blue or bluish. Security element according to at least one of Claims 1 until 8th , characterized in that the color visible in transmission is an achromatic color, in particular with a gray or metallic appearance. Security element according to at least one of Claims 1 until 10 , characterized in that the first and/or second reflection-increasing layer is present in the feature area without a grid, preferably over the entire surface. Security element according to at least one of Claims 1 until 11 , characterized in that one or more translucent color layers are provided between the first and second relief structure and/or above the first reflection-increasing coating and/or below the second reflection-increasing coating in order to influence the color impression of the security element. Security element according to at least one of Claims 1 until 12 , characterized in that the first and second relief structure at least partially reflect incident parallel light in different angular ranges, wherein the two different angular ranges preferably do not overlap and preferably more than 3 °, particularly preferably more than 10 ° are separated from each other. Security element according to at least one of Claims 1 until 13 , characterized in that the two independent relief structures are designed differently. Security element according to at least one of Claims 1 until 14 , characterized in that the formation of the higher-lying relief structure, in particular the alignment of the micromirrors of the higher-lying micromirror arrangement and/or the formation of the lower-lying relief structure, in particular the alignment of the micromirrors of the lower-lying micromirror arrangement, varies depending on the location around a given motif, in particular a to produce a three-dimensional motif or a movement motif. Data carrier with an optically variable security element according to at least one of Claims 1 until 15 . Method for producing an optically variable security element with a reflective surface area that shows at least two optically variable effects that can be seen from different viewing directions and appear with different colors, in particular according to at least one of Claims 1 until 15 , in which a carrier is provided, the surface extent of which defines a plane and a z-axis perpendicular thereto, - the carrier is provided with a reflective surface area which contains two independent relief structures which are arranged at different height levels in the z-direction, and form a lower-lying and a higher-lying relief structure, and which are designed to overlap in a feature area, - the higher-lying relief structure is provided with a first reflection-increasing coating that follows the course of the relief and has wavelength-dependent reflection and transmission in the visible spectral range, which has at least one reflection band and at least has a transmission band, - the deeper-lying relief structure is provided with a second reflection-increasing coating which follows the course of the relief and has a wavelength-dependent reflection and transmission in the visible spectral range, which has at least one reflection band and at least one transmission band, - wherein the reflection-enhancing coatings are matched to one another in such a way that a reflection band of the second reflection-enhancing coating lies at least partially in a transmission band of the first reflection-enhancing coating, and at least one transmission band of the two reflection-enhancing coatings overlaps, so that - the higher lying relief structure shows a first optically variable effect in a first color in plan view, the lower-lying relief structure shows a second optically variable effect in a second, different color in plan view through the first reflection-enhancing coating, and when viewed through the higher-lying and underlying relief structure shows an appearance in a third, different color.

Images