EP3967508B1 - Optically variable security element - Google Patents

Description

The invention relates to an optically variable security element for protecting objects of value, whose surface area defines a z-axis perpendicular thereto, with a reflective surface area. 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 at the same time 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, show a different color or brightness impression and/or a different graphic motif depending on the viewing angle. In the prior art, the optically variable effects are, for example, movement effects, Described pump effects, depth effects or flip effects, which are realized with the help of holograms, microlenses or micromirrors.

Some time ago, optically variable security elements were proposed which have two relief structures arranged at different height levels and each provided with a color coating (see Fig DE 10 2018 009912 A1 , EP 3 466 711 A1 , 2020/011390 A1 , WO 2020/011391 A1 and WO 2020/011391 A2 ).

Proceeding from this, the invention is based on the object of proposing an optically variable security element of the generic type with an attractive appearance and high protection against forgery, which should also be simple and inexpensive to produce. With the associated production method, security elements with two or more different appearances or effects in different colors should in particular be able to be produced with a few work steps. In addition, the security elements should ideally be able to be produced with a small layer thickness in order to facilitate incorporation or application in security documents and documents of value.

This object is solved by the features of the independent claim. 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 reflective surface area, which can be used in particular to protect valuables. The surface extent of the security element defines a plane and a z-axis perpendicular to the surface.

The reflective surface area contains a primary structure in the form of a first embossing lacquer layer with a first embossed relief structure. The first embossing lacquer layer is partially covered by a secondary structure, so that there are covering areas with a secondary structure and free areas without a secondary structure on the first embossing lacquer layer.

The primary structure and the secondary structure are provided with a common reflection-enhancing coating, so that the reflection-enhancing coating is arranged in the overlapping areas on the secondary structure and in the free areas on the primary structure.

The reflection-increasing coating contains a layer of a phase change material, which produces a different color impression and/or a different reflectivity of the coating in the crystalline and amorphous material state.

The phase change material is present--in at least one section--in an amorphous material state in the overlapping areas and in a crystalline material state in the free areas, or conversely is present in a crystalline material state in the overlapping areas and in an amorphous material state in the free areas.

The two material states of the phase change material, crystalline and amorphous, are also referred to in this description as defined material states of the phase change material. The material state of a phase change material can be changed by the action of heat, in particular by the action of heat associated with the absorption of radiation, ie change from one of the defined material states to the other defined material state. In concrete terms, this means that a phase change material that is in the crystalline state, which changes to the amorphous state, or that a phase change material that is in the amorphous state changes to the crystalline state.

The reflection-increasing coating advantageously contains Ge _x Sb _y Te _z or Ag _x In _y Sb _z Te _w , in particular Ge ₂ Sb ₂ Te ₅ or Ag ₃ In ₄ Sb ₇₆ Te ₁₇ , as phase change material. In principle, however, other phase change materials such as VO _x , NbO _x , GeTe, GeSb, GaSb, InSb, InSbTe, InSe, SbTe, TeGeSbS, AgSbSe, SbSe, GeSbMnSn, AgSbTe, AuSbTe, or AlSb can also be used within the scope of the invention.

The phase change material is preferably present in the reflection-increasing coating as an effect layer with a layer thickness between 1 nm and 60 nm, in particular between 3 nm and 30 nm.

Advantageously, the reflection-increasing coating is designed to follow the relief profile of the relief structure of the first embossing lacquer layer.

The reflection-increasing coating advantageously forms a multilayer interference layer element whose different color impression is created by a different refractive index of the phase change material contained in the crystalline and amorphous states. The interference layer element can, in particular, be designed to be reflective and, for this purpose, contain a mirror layer, in particular a metal layer, for example made of aluminum. In an advantageous structure, the interference layer element contains an optional barrier layer, an effect layer made from the phase change material mentioned, a dielectric layer and a mirror layer. The interference layer element therefore preferably has exactly three, at least three or more than three sub-layers. In configurations can the interference layer element comprises five (or six, barrier layer) partial layers, for example absorber, dielectric, reflector (or absorber), dielectric and absorber, wherein one or more of the absorber partial layers can be present as phase change material.

The difference in refractive index of the phase change material in the crystalline and amorphous states is expediently greater than 0.2, in particular greater than 0.4 or even greater than 0.6. The refractive index difference is determined for a given wavelength range with a size of at least 50 nm. The predetermined wavelength range is in the visible light range and more preferably has a size of 100 nm or 150 nm there and preferably corresponds to the visible light range.

In a preferred embodiment of the security element, the reflective surface area shows at least two appearances recognizable from different viewing directions. The secondary structure is formed by a second embossing lacquer layer with a second embossed relief structure that differs from the first relief structure, and the two embossed relief structures are arranged at different levels in the z-direction and form a lower-lying and a higher-lying relief structure. The reflection-increasing coating follows the relief profile of the relief structure of the first and second embossing lacquer layer.

In other configurations that are also advantageous, the secondary structure is formed by an imprint, an etching mask or a washed-in color area. Classic printing methods such as offset printing, relief printing, indirect relief printing, flexographic printing, gravure printing or screen printing, but also digital printing methods such as ink-jet printing, laser printing, Thermal sublimation printing, thermal transfer printing, or indirect ink jet printing such as nanoprinting can be used. The imprint can be colorless or coloured, can be transparent, translucent or opaque and can also contain luminescent substances, IR-absorbing substances, magnetic substances or other machine-readable feature substances.

Although advantageous because of the noticeable change in the interference color, the phase change material does not necessarily have to be a component of an interference layer element. The different refractive indices of the amorphous or crystalline phase can also be used to produce other regional changes in the color impression and/or the reflectivity of the reflection-enhancing coating.

In an advantageous embodiment of the security element, it is provided that the secondary structure is colorless and transparent in the visible spectral range and contains an absorber or reflector for a wavelength range lying outside the visible spectral range. In this case, the secondary structure preferably represents the named second embossing lacquer layer with the second relief structure and forms the underlying relief structure of the security element.

In another, likewise advantageous configuration of the security element, provision is made for the secondary structure to contain an absorber or reflector which acts in the visible spectral range. In this case, the secondary structure preferably represents the named second embossing lacquer layer with the second relief structure and forms the higher-lying relief structure of the security element.

Depending on the desired color effect of the security element, the first embossing lacquer layer can be colorless or specifically colored. The second embossing lacquer layer optionally forming the secondary structure can also be colorless or specifically colored in order to achieve a desired color effect of the security element together with the reflection-increasing coating. Colored embossing lacquer layers are preferably provided with a translucent color or achromatic color. However, other configurations are also expedient in which one or both embossing lacquer layers are colored with a luminescent color or a nanoparticle color.

In an advantageous embodiment, the first relief structure and/or the second relief structure optionally forming the secondary structure are formed by micromirror arrangements with specularly reflecting micromirrors, in particular with non-diffractive mirrors, and preferably with planar 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.

In principle, other embossed relief structures, in particular Fresnel lenses, concave mirrors, hologram structures, nanostructures or diffractive blazed gratings can also be used instead of micromirrors. Advantageously, achromatic diffraction gratings, so-called matte structures, which essentially reflect white light, can also be used. To generate bright colors, the relief structures can at least the second Relief structure also have sub-wave structures, in particular sub-wavelength gratings, which, in combination with the respective reflection-enhancing layer, determine or at least co-determine its color.

If there are two relief structures, the first relief structure is advantageously designed and configured to exhibit a first optically variable effect in a first color, and the second relief structure is designed and configured to exhibit a second optically variable effect in a second, different color show.

In an advantageous embodiment, the overlapping areas and free areas are designed as a regular or irregular grid with grid elements and grid gaps, at least in a partial area of the surface area, with the dimensions of the grid elements and grid gaps in one or both lateral directions being less than 140 µm, preferably between 20 µm and 100 microns, in particular between 20 microns and 60 microns.

In the grid areas formed by the overlapping areas and free areas, the security element advantageously shows an appearance when tilted or a corresponding change in the viewing direction that suddenly jumps from a first to a second appearance (or when tilted back from the second to the first appearance). Simultaneously and without intermediate or transitional stages, the displayed motif (e.g. a value number or a coat of arms) and the color (e.g. magenta, green or blue) are changed. Such an appearance that changes seamlessly between two different motifs with two different colors is referred to as a binary color and effect change.

The grid formed by the overlapping areas and free areas advantageously has a constant area coverage by the grid elements, which is expediently between 30% and 70%, preferably between 40% and 60%, in particular around 50%.

Alternatively or additionally, it is provided that the overlapping areas and free areas are formed as an effect area at least in a partial area of the surface area, in which the overlapping areas and/or the free areas have lateral dimensions of more than 140 μm.

In these effect areas, the security element preferably shows two different effects (for example a three-dimensional motif and a movement effect such as a moving bar), which appear in two different colors. The areas with different color impressions and different effects are registered exactly to one another, which is also referred to below as color-to-effect registration.

In this configuration, at least one overlapping area and/or at least one free area is advantageously formed with lateral dimensions of more than 250 μm, preferably more than 500 μm and in particular more than 1 mm.

In an advantageous embodiment, the reflection-increasing coating is formed over the entire surface and without cutouts. Alternatively, negative identifiers can also be provided in the security element, which are formed by gaps in the reflection-increasing coating are. The negative indicators can form text, symbols or value numbers, for example.

The phase change material of the common reflection-increasing coating can be present in the described area-dependent material state in the at least one section of the security element, ie in exactly one section, in several sections or completely. The section can, for example, comprise one or more of the partial areas and/or recesses mentioned. For example, the security element can have been irradiated completely or only selectively in the section(s), the secondary structure present only in certain areas also having acted as an exposure mask.

The described reflective surface area of the security element can be combined with other security features, for example with holograms, in particular true-color holograms, with sub-wavelength gratings or other sub-wavelength structures, with micromirror arrangements without diffractive gratings, or with machine-readable security features that are based on special material properties such as electrical conductivity, magnetic properties, Luminescence, fluorescence or the like are based.

The optically variable security element can contain further layers, such as a protective, covering or an additional functional layer, a primer layer or a heat-sealing lacquer layer. However, these are not essential for the present invention and are therefore not described in more detail.

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.

• B) ein Träger bereitgestellt wird, dessen Flächenausdehnung eine darauf senkrecht stehende z-Achse definiert,
• A1) in einem Flächenbereich eine erste Prägelackschicht auf den Träger aufgebracht wird,
• P1) in die erste Prägelackschicht eine erste Reliefstruktur geprägt wird, so dass eine Primärstruktur in Form der ersten Prägelackschicht mit der ersten eingeprägten Reliefstruktur entsteht,
• A2) eine Sekundärstruktur auf die erste Prägelackschicht aufgebracht wird, wobei die Primärstruktur teilweise von der Sekundärstruktur überdeckt wird (Überdeckungsbereiche) und teilweise nicht überdeckt wird (Freibereiche),
• R1) eine reflexionserhöhende Beschichtung auf einen nicht überdeckten Anteil der Primärstruktur und auf die Sekundärstruktur aufgebracht wird,
• R2) beim Aufbringen der reflexionserhöhenden Beschichtung ein Phasenwechselmaterial aufgebracht wird, das in kristallinem und amorphem Materialzustand unterschiedlichen Brechungsindex aufweist, und das in einem definierten dieser Materialzustände auf den genannten, nicht überdeckten Anteil der Primärstruktur und auf die Sekundärstruktur aufgebracht wird, und
• R3) das Phasenwechselmaterial der reflexionserhöhenden Beschichtung von der Seite der Primär- und Sekundärstruktur her - optional in zumindest einem Abschnitt des Sicherheitselements - mit Strahlung beaufschlagt wird, so dass die nur teilweise vorliegende Sekundärstruktur als Belichtungsmaske wirkt, wodurch der Materialzustand des Phasenwechselmaterials in dem nicht überdeckten Anteil der Primärstruktur (Freibereiche) durch die Strahlungseinwirkung geändert wird und der Materialzustand des Phasenwechselmaterials auf der Sekundärstruktur (Überdeckungsbereiche) unverändert bleibt.

The invention further includes a method for producing an optically variable security element in which

• B) a carrier is provided, the surface area of which defines a z-axis perpendicular thereto,
• A1) a first embossing lacquer layer is applied to the carrier in a surface area,
• P1) a first relief structure is embossed into the first embossing lacquer layer, so that a primary structure is created in the form of the first embossing lacquer layer with the first embossed relief structure,
• A2) a secondary structure is applied to the first embossing lacquer layer, the primary structure being partially covered by the secondary structure (coverage areas) and being partially not covered (free areas),
• R1) a reflection-increasing coating is applied to an uncovered portion of the primary structure and to the secondary structure,
• R2) when applying the reflection-increasing coating, a phase change material is applied which has different refractive indices in the crystalline and amorphous material state, and which is applied in one of these material states to the named, uncovered portion of the primary structure and to the secondary structure, and
• R3) the phase change material of the reflection-enhancing coating is exposed to radiation from the side of the primary and secondary structure - optionally in at least one section of the security element - so that the only partially present secondary structure acts as an exposure mask, whereby the material state of the phase change material is in the non-covered one Proportion of the primary structure (free areas) is changed by the radiation exposure and the material state of the phase change material on the secondary structure (coverage areas) remains unchanged.

The phase change material can be exposed in particular to UV radiation, radiation from the visible spectral range or IR radiation. In the latter case, the use of radiation in the near infrared (0.78-3 μm) or in the middle infrared (3-50 μm), preferably at about 8-12 μm (CO ₂ laser and related gas lasers), has proven particularly effective.

In an advantageous variant of the method, it is provided that the secondary structure is colorless and transparent in the visible spectral range and contains an absorber or reflector for a spectral range lying outside the visible spectral range, and the effect layer of the phase change material is exposed to radiation in this spectral range lying outside the visible spectral range, in particular with UV -Radiation or near or medium IR radiation is applied.

In another, likewise advantageous variant of the method, it is provided that the secondary structure contains an absorber that acts in the visible spectral range, and the effect layer of the phase change material is exposed to radiation from this visible spectral range.

In a particularly advantageous variant of the method, it is provided that in step A2) a second embossing lacquer layer is applied to the first embossing lacquer layer as a secondary structure, and that between step A2) and step R1) in a step P2) a second embossing lacquer layer is inserted into the second embossing lacquer layer, differing from the relief structure differentiating the first relief structure is embossed, so that the first relief structure and the second relief structure are arranged at different height levels in the z-direction relative to the carrier.

The radiation can be applied with a powerful lamp, preferably a laser source is used.

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.

Fig. 1

eine schematische Darstellung einer Banknote mit einem erfindungsgemäßen optisch variablen Sicherheitselement,

Fig. 2

schematisch einen Ausschnitt des Sicherheitselements der Fig. 1 im Querschnitt,

Fig. 3

in (a) bis (e) Zwischenschritte bei der Herstellung des Sicherheitselements der Fig. 2,

Fig. 4

schematisch einen Ausschnitt des Sicherheitselements nach einem weiteren Ausführungsbeispiel der Erfindung, und

Fig. 5

in (a) bis (d) Zwischenschritte bei der Herstellung des Sicherheitselements der Fig. 4.

Show it:

1

a schematic representation of a banknote with an optically variable security element according to the invention,

2

schematically shows a section of the security element 1 in cross section,

3

in (a) to (e) intermediate steps in the production of the security element of 2 ,

4

schematically shows a section of the security element according to a further exemplary embodiment of the invention, and

figure 5

in (a) to (d) intermediate steps in the production of the security element of 4 .

The invention will now be explained using the example of security elements for banknotes. figure 1 shows a schematic representation of a banknote 10 with an optically variable security element 12 according to the invention in the form of an adhesively bonded transfer element. 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 with or without their own carrier layer) For example, security threads or security strips are also considered.

The security element 12 applied to the banknote 10 is itself very flat, but nevertheless gives the viewer the three-dimensional impression of a motif 14 apparently arching out of the plane of the banknote 10 and appearing in a first color. In practice, the motif 14 can represent, for example, a denomination, a portrait or some other graphic motif. A movement effect in a second color is visible in a partial area 16 within the motif 14 . For example, when the bank note 10 is tilted, a bright bar can move back and forth along the curved partial area 16 and produce a so-called rolling bar effect. The areas with different colors (first and second color) and different effects (three-dimensional motif or running bar) are precisely matched to each other. This registration is also referred to below as color-to-effect registration.

The special structure and the production of the security element 12 according to the invention will now be described with reference to FIG figures 2 and 3 explained in more detail, where 2 schematically a section of the security element 12 applied to the bank note 10 in cross section and 3 show various intermediate steps in the production of the security element 12.

The security element 12 contains a flat, transparent, colorless carrier 18, for example a transparent, colorless PET film, the surface extent of which defines an xy plane and a z-axis perpendicular thereto. A multicolored reflective surface area is arranged on the carrier 18 and contains an embossed structure area with two micromirror embossings 24, 34 at two different height levels.

A first embossed area 24, which forms the above-mentioned primary structure, is given by micromirror embossings, which are embossed in a first transparent embossing lacquer layer 22 applied to the carrier 18 and whose base areas lie at a first height above the carrier 18. The first embossing lacquer layer 22 is partially covered by a secondary structure in the form of a second embossing lacquer layer 32 with a second embossed relief structure 34 with micromirror embossing, so that on the first embossing lacquer layer 22 there are covering areas 66 with a second embossing lacquer layer 32 and free areas 64 without a second embossing lacquer layer.

The second embossing lacquer layer is transparent and colorless in the visible spectral range, but contains an absorber 38 for IR radiation with a wavelength of approximately 10 μm, as explained in more detail below. The base areas of the micromirrors of the second embossed area 34 lie at a second, greater height above the carrier 18, the height and the direction of the positive z-axis starting from the carrier 18 being specified. Since the security element 12 of the embodiment of figures 2 and 3 is designed to be viewed from the side of support 18, the z-axis is shown extending 2 down away from the wearer.

The micromirror embossings or micromirror arrangements 24, 34 each contain a large number of micromirrors which are inclined relative to the xy plane and whose local angles of inclination are selected in such a way that the relief structures of the micromirror embossings 24, 34 interact with the color effect of the reflection-enhancing coating 40 described below to have a desired create visual appearance. Specifically, the angles of inclination of the micro-mirror in the embodiment are chosen so that the micro-mirror arrays 24, 26 the bulging three-dimensional Impression of the subject 14 and the rolling bar effect of the portion 16 produce.

In the exemplary embodiment, the micromirrors of the micromirror embossings 24, 34 have a lateral dimension of 10×10 μm ² and a maximum height of 3.5 μm. The height offset related to the base areas can be 6 μm, for example.

As a special feature, the two micromirror arrays 24, 34 are provided with a common reflection-increasing coating 40, which follows the relief profile of the embossing lacquer layer 22 or 32, and which lies on the second embossing lacquer layer 32 in the overlapping areas 66 and on the first embossing lacquer layer 22 in the free areas 64 .

The reflection-increasing coating 40 forms a multilayer interference layer element, which in the exemplary embodiment consists of the embossing lacquer layers of a 5 to 30 nm thick barrier layer 42 made of SiO ₂ , a 3 to 30 nm thick effect layer 44 of a phase change material, a 50 to 500 nm thick dielectric layer 46 made of SiO ₂ and a 10 to 50 nm thick mirror layer 48 consists of aluminum. For example, GeSbTe or AgInSbTe can be used as the phase change material.

In this case, the phase change material is present in the amorphous state 44-A in the overlapping regions 66, while it is present in the free regions 64 in the crystalline state 44-K. As explained above, the phase change material has a different refractive index in the crystalline and amorphous state, so that the color impression of the interference layer element differs depending on the material state of the phase change material contained. The interference layer element formed by layers 42, 44-A/44-K, 46, 48 therefore appears in the overlapping areas 66 with a first color impression and in the free areas 64 with a second, different color impression.

The difference in the refractive indices in the crystalline and amorphous state of the phase change material is typically more than 0.2, so that a significantly different color impression results in the overlapping areas 66 and the free areas 64 . For visible light, the refractive indices can be, for example, n=2.4 in the high-refractive state and n=1.6 in the low-refractive state, resulting in a refractive index difference of Δn=0.8.

Since the presence of the different material states of the phase change material is precisely aligned with the boundaries of the micromirror arrays of the overlapping areas 66 and the free areas 64, the viewer 50 has a perfect registration of the different effects produced by the micromirrors and the different color impressions produced by the phase change material.

Specifically, in the embodiment 2 the two micromirror arrangements 24, 34 are arranged directly adjacent to one another in the surface area of the security element 12, with an overlapping area 66 being formed, for example, by a 5 mm wide and 2 cm long curved strip within a surface area measuring 2.5 × 2.5 cm ² .

In the overlapping area 66, the observer looks through the two transparent embossing lacquer layers 22, 32 onto the micromirror arrangement 34 lying deeper, in which the phase change material in its amorphous Phase with refractive index n _A is present, so that the reflective interference layer element 42/44-A/46/48 appears with a first color impression.

In the free area 64 surrounding the overlapping area, the observer looks only through the first transparent embossing lacquer layer 22 onto the higher-lying micromirror arrangement 24, in which the phase change material in its crystalline phase with refractive index n _K , with |n _K -n _A | > 0.2 is present, so that the reflective interference layer element 42/44-K/46/48 appears there with a second, different color impression.

Since the difference in height between the two micromirror arrangements 24, 34 is in the range of a few micrometers, it is imperceptible to the viewer, so that the two differently colored motifs and the different effects appear to be arranged next to one another in exact register.

The production of the security element 12 according to the invention will now be described with reference to FIG figure 3 described in more detail, with (a) to (e) each showing intermediate steps in the production of the security element.

First, with reference to 3(a) a transparent carrier 18, for example a transparent, colorless PET film, is provided and provided with a primary structure in the form of a first, transparent and colorless embossing lacquer layer 22. The micromirror embossing 24 that produces the desired motif 14 of the security element 12 is embossed into the first embossing lacquer layer 22 using an embossing tool that is not shown itself. When using a UV embossing varnish, the embossing varnish layer 22 is then hardened.

A secondary structure in the form of a second embossing lacquer layer 32 is printed onto the first embossing lacquer layer 22 using a printing cylinder (not shown) in the desired overlapping area 66 of the running bar, as shown in FIG 3(b) shown. The second embossing lacquer layer 32 contains an absorber 38 for the infrared radiation of a CO ₂ laser at 10.6 μm, but is transparent and colorless in the visible spectral range.

Regarding 3(c) the second embossing lacquer layer 32 is then provided with the micromirror embossing 34 that produces the rolling bar effect using an embossing tool that is not shown itself. If a UV embossing varnish is used, the embossing varnish layer 32 is then hardened.

A multi-layer reflection-increasing coating 40' is then applied over the entire surface of the overall relief structure formed in this way, which is formed by the first relief structure 24 of the first embossing lacquer layer 22 and the second relief structure 34 of the second embossing lacquer layer 32 lying in the overlapping region 66 above the first embossing lacquer layer 22 . For this purpose, a 5 to 30 nm thick SiO ₂ layer 42 is first applied, which serves as a barrier layer. A 3 to 30 nm thick effect layer 44 of a phase change material, for example Ge ₂ Sb ₂ Te ₅ , is applied to the barrier layer, which after its application is initially present throughout in its amorphous state 44-A and is therefore present both in the covering region 66 and in the free region 64 has a refractive index n _A . In order to complete the reflective interference layer element, a 50 to 500 nm thick SiO ₂ layer is applied as a dielectric layer 46 and a 10 to 50 nm thick aluminum mirror layer 48 is applied.

The structural side of the coated overall relief structure is then provided with a lacquer coating 36 and optionally further coatings and thereby the layer structure itself is completed, as in 3(d) shown.

The color effect of the applied reflection-increasing coating 40' is the same in this state in the overlapping area 66 and in the free area 64 and is essentially determined by the refractive index n _A of the phase change material of the interference layer element formed.

The reflection-increasing coating 40' is now exposed to the full surface of the infrared radiation 60 from a CO ₂ laser with a wavelength of 10.6 μm from the side of the carrier film 18, as in FIG 3(e) shown. In the free area 64, the phase change material of the layer 40' is crystallized by the heat generated by the IR radiation 60 and thereby converted into the crystalline phase 44-K with a refractive index _nK . In the overlapping area 66, the radiation 60 is absorbed by the IR absorber 38 of the second embossing lacquer layer 32 and therefore does not reach the phase change material of the layer 40′—the phase change material remains there in the amorphous state with a refractive index n _A .

Since the second embossing lacquer layer 32 with the contained IR absorber acts in this way as an exposure mask for the IR radiation 60, the conversion of the amorphous into the crystalline phase of the phase change material takes place in perfect register with the shape and position of the overlapping area 66 and the free area 64 instead of.

The anti-reflective coating 40 formed by the exposure and conversion step contains two portions of different refractive index of the phase change material and hence different color effect of the coating, which are in perfect register with the mold and location of micromirror embossings 24,34. In the overlapping area 66 the color effect of the coating 40 is still determined by the refractive index n _A of the amorphous phase change material in the interference layer stack 42/44-A/46/48, while in the free area 64 the color effect of the coating 40 is determined by the refractive index n _K of the crystalline phase change material in the interference layer stack 42/44-K/46/48. When viewed, the finished security element 12 therefore shows the color-to-effect registration described above.

In a modification of the method described, an embossing lacquer layer 32 without an absorber can also be used - for this purpose, the layer thicknesses of the embossing lacquer layer 22 and the embossing lacquer layer 32 can be matched in such a way that the absorption of the embossing lacquer itself, which increases exponentially with the layer thickness, is sufficient on the one hand to cause a conversion of the phase change material to bring about a lower overall layer thickness in the free area 64, and on the other hand to exclude a walling in the overlapping area 66 due to the higher absorbing layer thickness.

Furthermore, the phase change material can also be converted by exposure to radiation of a different wavelength, in particular to IR radiation, visible light or UV radiation. It is only necessary to ensure a sufficiently strong discrimination between the radiation transmission inside and outside of the overlapping area 66 in order to bring about a selective conversion of the phase change material only outside of the overlapping area 66 .

The Figures 4 and 5 illustrate a further exemplary embodiment of the invention with an inverted layer structure, in which the view is not through the carrier film but from the opposite side of the embossed structures done here. In this variant, the second embossing lacquer layer can be provided with an absorber that absorbs what is visible, since this embossing lacquer layer cannot be seen through when viewed.

figure 4 shows schematically a section of a finished security element 70 according to this variant of the invention, while figure 5 shows various intermediate steps in the production of the security element 70.

The security element 70 contains a flat, transparent and colorless carrier 18, whose surface extent defines an xy plane and a z-axis perpendicular thereto. As with the design of the figures 2 and 3 a multicolored reflective surface area is arranged on the carrier 18, which contains an embossed structure area with two micromirror embossings 24, 34 at two different height levels.

A first embossed area 24, which forms the above-mentioned primary structure, is given by micromirror embossings, which are embossed in a first transparent embossing lacquer layer 22 applied to the carrier 18 and whose base areas lie at a first height above the carrier 18. The first embossing lacquer layer 22 is partially covered by a second embossing lacquer layer 72 with a secondary structure in the form of a second embossed relief structure 34 with micromirror embossing, so that on the first embossing lacquer layer 22 there are covering areas 66 with a second embossing lacquer layer 72 and free areas 64 without a second embossing lacquer layer.

The second embossing lacquer layer 72 contains an absorber for UV or blue light, which appears blue/violet in the visible spectral range. The bases of the micromirrors of the second embossing area are at a second, greater height above the carrier 18, the height and the direction is measured starting from the carrier 18 along the positive z-axis. Since the security element 70 of the embodiment of Figures 4 and 5 viewed from the top, ie the side of the micromirror embossings 24, 34, the z-axis extends in the illustration 4 up away from the wearer.

In this configuration, too, the embossed micromirrors or micromirror arrangements 24, 34 each contain a large number of micromirrors which are inclined relative to the xy plane and whose local angles of inclination are selected in such a way that the relief structures of the embossed micromirrors 24, 34 interact with the color effect of the reflection-increasing coating 80 create a desired visual appearance. In concrete terms, the angle of inclination of the micromirrors can again be chosen such that the micromirror arrangements 24, 26 produce the arched three-dimensional impression of the motif 14 and the rolling bar effect of the partial area 16. The sizes and heights of the micromirrors can be as in the design of the figures 2 and 3 be elected.

The two micromirror arrays 24, 34 are provided with a common reflection-increasing coating 80, which follows the relief pattern of the relief structure of the embossed lacquer layer 22 or 72, and which is arranged in the overlapping areas 66 on the second embossed lacquer layer 72 and in the free areas 64 on the first embossed lacquer layer 22 .

As with the design of the figures 2 and 3 the reflection-enhancing coating 80 forms a multilayer interference layer element, but with the layer order reversed. Starting from the embossing lacquer layers, the reflection-increasing coating 80 consists of a 10 to 50 nm thick aluminum mirror layer 82, a 50 to 500 nm thick Dielectric layer 84 made of SiO ₂ , a 3 to 30 nm thick effect layer 86 of a phase change material and a 5 to 30 nm thick barrier layer 88 made of SiO ₂ . For example, GeSbTe or AgInSbTe can be used as phase change material. The coated micromirror arrays are leveled with a transparent lacquer layer 36 .

In the overlap region 66, the phase change material is in an amorphous form 86-A with a refractive index n _A , while in the free region 64 it is in a crystalline state 86-K with a refractive index n _K , with |n _K -n _A | > 0.2 is present. Since the different crystalline or amorphous material states of the phase change material are precisely aligned with the boundaries of the micromirror arrays of the overlapping areas and the free areas, a perfect color-to-effect match also results for the viewer 50 in this exemplary embodiment.

Specifically, in the embodiment of 4 the two micromirror arrangements 24, 34 are arranged directly adjacent to one another in the surface area of the security element 70, with an overlapping area 66 being formed, for example, by a 5 mm wide and 2 cm long curved strip within a surface area measuring 2.5 × 2.5 cm ² .

In the overlap area 66, the viewer 50 looks through the transparent lacquer layer 36 to the higher-lying micromirror arrangement 34, in which the phase change material is present in its amorphous phase with refractive index n _A , so that the reflective interference layer element 82/84/86-A/88 with a first color impression appears.

In the free area 64, the observer looks at the underlying micromirror arrangement 24 in which the phase change material is present in its crystalline phase with a refractive index _nK , so that the reflective interference layer element 82/84/86-K/88 appears there with a second color impression.

Since the difference in height between the two micromirror arrangements 24, 34 is in the range of a few micrometers, it is imperceptible to the viewer, so that the two differently colored motifs and the different effects appear to be arranged next to one another in exact register.

The production of the security element 70 according to the invention will now be described with reference to FIG figure 5 described in more detail, with (a) to (d) each showing intermediate steps in the production of the security element.

First, with reference to Fig.5(a) a transparent carrier 18, for example a transparent colorless PET film, is provided and provided with a primary structure in the form of a first, transparent and colorless embossing lacquer layer 22. Micromirror embossing 24, which produces desired motif 14 of security element 70, is embossed into first embossing lacquer layer 22 using an embossing tool that is not shown itself. When using a UV embossing varnish, the embossing varnish layer 22 is then hardened.

A secondary structure in the form of a second embossing lacquer layer 72 is printed onto the first embossing lacquer layer 22 using a printing cylinder (not shown) in the desired overlapping area 66 of the running bar, as shown in FIG 3(b) shown. The second embossing lacquer layer 32 contains an absorber for UV or blue light in the visible spectral range appears blue/purple. The second embossing lacquer layer 72 is then provided with the micromirror embossing 34 that produces the rolling bar effect, using an embossing tool that is not shown itself. If a UV embossing varnish is used, the embossing varnish layer 72 is then hardened.

A multi-layer reflection-increasing coating 80' is then applied over the entire surface of the overall relief structure formed in this way, which is formed by the first relief structure 24 of the first embossing lacquer layer 22 and the second relief structure 34 of the second embossing lacquer layer 72 lying in the overlapping regions above the first embossing lacquer layer 22. For this purpose, a 10 to 50 nm thick mirror layer 82 made of aluminum, a 50 to 500 nm thick dielectric layer 84 made of SiO ₂ , a 3 to 30 nm thick effect layer 86 of a phase change material and a 5 to 30 nm thick barrier layer 88 made of SiO ₂ are applied.

The structural side of the coated overall relief structure is then provided with a lacquer coating 36 and optionally further coatings, thereby completing the layer structure itself, as in Fig.5(c) shown.

After it has been applied, the phase change material of the effect layer 86 is initially continuously in its amorphous state. The color effect of the applied reflection-increasing coating 80' is the same in this state in the overlapping area 66 and in the free area 64 and is essentially determined by the refractive index n _A of the phase change material of the interference layer element formed.

The reflection-increasing coating 80' is now exposed to radiation 90 from a UV source or blue light source over the entire surface from the side of the carrier film 18, as shown in FIG Fig.5(d) shown.

The thin aluminum layer 82 is sufficiently transparent in this spectral range to transmit a large part of the incident radiation 90 to the phase change material 86 in the free area 64 and to crystallize it through the heat generated and convert it into the crystalline phase with a refractive index _nK . On the other hand, in the overlapping area 66 the incident radiation 90 is absorbed by the UV or blue absorber of the embossing lacquer layer 72 and therefore does not reach the phase change material 86 of the layer 80′—there the phase change material remains in the amorphous state with refractive index n _A .

Since the second embossing lacquer layer 72 with its UV or blue absorber acts in this way as an exposure mask for the radiation 90, the conversion from the amorphous to the crystalline phase of the phase change material takes place in perfect register with the shape and position of the overlapping area 66 and the free area 64.

The reflection-enhancing coating 80 formed by the exposure and conversion step contains two sub-areas with different refractive index of the phase change material and thus different color effect of the coating, which are in perfect register with the shape and position of the micromirror embossings 24, 34. In the overlapping area 66 the color effect of the coating 80 is still determined by the refractive index n _A of the amorphous phase change material in the interference layer stack, while in the free area 64 the color effect of the coating 80 is determined by the refractive index n _K of the crystalline phase change material is determined in the interference layer stack. When viewed, the finished security element 70 therefore shows the color-to-effect registration described above.

In this configuration, too, the conversion of the phase-change material can, of course, also be carried out by exposure to radiation of a different wavelength. It is only necessary to ensure sufficient discrimination between the radiation transmission inside and outside of the coverage area 66 in order to effect selective conversion of the phase change material only outside of the coverage area 66 .

Reference List

10

bank note

12

security element

14

motive

16

subdivision

18

carrier

22

first embossing layer

24

first embossing structure

32

second embossing layer

34

second embossing structure

36

lacquer coating

38

absorber

40, 40'

anti-reflective coating

42

barrier layer

44

effect layer

44-A, 44-K

Material states of the phase change material

46

dielectric layer

48

mirror layer

50

viewer

60

infrared radiation

64

free area

66

coverage area

70

security element

72

second embossing layer

80, 80'

anti-reflective coating

82

mirror layer

84

dielectric layer

86

effect layer

86-A, 86-K

Material states of the phase change material

88

barrier layer

90

radiation

Claims (18)

1. An optically variable security element for securing objects of value, the areal expansion of which defines a z-axis standing perpendicularly thereon, with a reflective areal region, wherein

   - the reflective areal region contains a primary structure in the form of a first embossing lacquer layer with a fist embossed relief structure,

   - the first embossing lacquer layer is covered partially by a secondary structure, so that on the first embossing lacquer layer there are overlap regions present with the secondary structure and there are free regions present without the secondary structure,

   - the primary structure and the secondary structure are supplied with a common reflection-enhancing coating, so that the reflection-enhancing coating is arranged in the overlap regions on the secondary structure and in the free regions on the primary structure,

   - characterized in that the reflection-enhancing coating contains a layer of a phase-change material, which produces a different color impression and/or a different reflectivity of the coating in the crystalline and the amorphous material state, and in that

   - in at least one section the phase-change material is present in the overlap regions in the amorphous state and in the free regions in the crystalline state, or vice versa.
2. The security element according to claim 1, characterized in that the reflection-enhancing coating contains as the phase-change material Ge_xSb_yTe_z or Ag_xIn_ySb_zTe_w, in particular Ge₂Sb₂Te₅ or Ag₃In₄Sb₇₆Te₁₇.
3. The security element according to claim 1 or 2, characterized in that the phase-change material is present the reflection-enhancing coating as an effect layer with a layer thickness between 1 nm and 60 nm, in particular between 3 nm and 30 nm.
4. The security element according to at least one of claims 1 to 3, characterized in that the reflection-enhancing coating forms a multilayer interference layer element, the different color impression of which is created by a different refractive index of the contained phase-change material in the crystalline and the amorphous state.
5. The security element according to at least one of claims 1 to 4, characterized in that the difference in refractive index of the phase-change material in the crystalline and the amorphous state is greater than 0.2, in particular greater than 0.4 or even greater than 0.6, for a predetermined wavelength range of a size of at least 50 nm.
6. The security element according to at least one of claims 1 to 5, characterized in that

   - the reflective areal region shows at least two appearances recognizable from different viewing directions,

   - the secondary structure is formed by a second embossing lacquer layer with a second embossed relief structure that differs from the first relief structure, and the two embossed relief structures are arranged at different height levels in the z-direction and form a lower-level and a higher-level relief structure, and

   - the reflection-enhancing coating respectively follows the relief profile of the relief structure of the first and the second embossing lacquer layer.
7. The security element according to at least one of claims 1 to 5, characterized in that the secondary structure is formed by a print, an etching mask or a washing-ink region.
8. The security element according to at least one of claims 1 to 7, characterized in that the secondary structure is colorless and transparent in the visual spectral range and contains an absorber or reflector for a wavelength range outside of the visible spectral range, preferably that the secondary structure represents the stated second embossing lacquer layer with the second relief structure and forms the lower-level relief structure of the security element.
9. The security element according to at least one of claims 1 to 7, characterized in that the secondary structure contains an absorber or reflector effective in the visible spectral range, preferably that the secondary structure represents the stated second embossing lacquer layer with the second relief structure and forms the higher-level relief structure of the security element.
10. The security element according to at least one of claims 1 to 9, characterized in that the first relief structure and/or the second relief structure possibly forming the secondary structure are formed by micromirror arrangements with directionally reflective micromirrors, in particular with mirrors with non-diffractive effect, and preferably with planar mirrors, concave mirrors and/or or Fresnel-like mirrors.
11. The security element according to at least one of claims 1 to 10, characterized in that the overlap regions and the free regions are formed at least in a partial region of the areal region as a regular or irregular grid with grid elements and grid spaces, wherein the dimensions of the grid elements and grid spaces in one or both lateral directions are below 140 µm, preferably between 20 µm and 100 µm, in particular between 20 µm and 60 µm.
12. The security element according to at least one of claims 1 to 11, characterized in that the overlap regions and the free regions are formed at least in a partial region of the areal region as an effect region in which the overlap regions and/or the free regions have lateral dimensions of more than 140 µm.
13. The security element according to at least one of claims 1 to 12, characterized in that negative features are formed in the security element by gaps in the reflection-enhancing coating.
14. A data carrier with an optically variable security element according to at least one of claims 1 to 13.
15. A method for manufacturing an optically variable security element, in which

    B) a carrier is made available, the areal expansion of which defines a z-axis standing perpendicularly thereon,

    A1) a first embossing lacquer layer is applied to the carrier in an areal region,

    P1) a first relief structure is embossed into the first embossing lacquer layer, whereby a primary structure is created in the form of the first embossing lacquer layer with the first embossed relief structure,

    A2) a secondary structure is applied to the first embossing lacquer layer, wherein the primary structure is partially covered and partially not covered by the secondary structure,

    R1) a reflection-enhancing coating is applied to a non-covered portion of the primary structure and to the secondary structure,

    R2) when applying the reflection-enhancing coating, a phase-change material is applied, which has a different refractive index in the crystalline and in the amorphous state and which is applied in a defined one of these material states to the stated, non-covered portion of the primary structure and to the secondary structure, and

    R3) radiation is applied to the phase-change material of the reflection-enhancing coating - optionally in at least one section of the security element - from the side of the primary and the secondary structure, so that the only partially present secondary structure has the effect of an exposure mask, whereby the material state of the phase-change material in the non-covered portion of the primary structure is changed by the action of radiation and the material state of the phase-change material remains unchanged on the secondary structure.
16. The method according to claim 15, characterized in that the secondary structure is colorless and transparent in the visible spectral range and contains an absorber or reflector for a spectral range outside of the visible spectral range, and radiation from this spectral range outside of the visible spectral range, in particular UV radiation or medium IR radiation, is applied to the effect layer of the phase-change material.
17. The method according to claim 15, characterized in that the secondary structure contains an absorber or reflector effective in the visible spectral range, and radiation from this visible spectral range is applied to the effect layer of the phase-change material.
18. The method according to any of claims 15 to 17, characterized in that

    - in step A2) a second embossing lacquer layer is applied as the secondary structure to the first embossing lacquer layer, and that

    - between the step A2) and the step R1), in a step P2) there is embossed into the second embossing lacquer layer a second relief structure which differs from the first relief structure, so that the first relief structure and the second relief structure are arranged at different height levels in the z-direction with reference to the carrier.

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