Flat security elements with optical security features

Abstract

The present invention relates to a flat security element (4) with an optical security feature, comprising at least one first surface region (1) with a first subwavelength structure, wherein the structural elements defining said first subwavelength structure are periodically repeated in the plane of the security element (4).It is provided that the first subwavelength structure of at least one partial region of the first surface region (1) additionally comprises an interference coating (5) for producing a color-shifting effect, in order to be able to convey motifs with an enhanced security against counterfeiting by means of an impression of at least two different colors that is easy to produce.

Description

[Technical field]

[0001] The present invention relates to a planar security element with an optical security feature, comprising at least one first surface area with a first subwavelength structure, said planar security element being characterized by a periodic repetition of structural elements defining said first subwavelength structure in the plane of the security element. Said periodic repetition can occur in one direction, i.e. in one dimension, for example when the structural element comprises straight walls and a number of such walls are periodically arranged next to each other. Said periodic repetition can occur in two directions, i.e. in two dimensions, for example when the structural element comprises columns and a number of columns are arranged in a grid, or when the structural element comprises recesses and a number of recesses are arranged in a grid. [Background technology]

[0002] From DE 10 2012 015 900 A1, a monolayer security element with a subwavelength structure is known, i.e. this flat security element has in a first surface region a so-called basic element structure, which conveys different color impressions due to the subwavelength structure when viewed from above from the front and back, and in a second surface region likewise has a basic element structure, but in the form of a mirror image of the first surface region, so that the first and second regions show a motif when viewed from above from both sides, but this motif is not recognizable when viewed through. For the realization of this basic element structure, in a first variant, a grating basic structure in the first surface region and an inverted grating basic structure in the second surface region are now disclosed. In a second variant, a substrate with mutually inverted interference coatings is shown on the first and second flat elements.

[0003] DE 10 2012015 900 A1 therefore makes it possible, due to two different surface areas with mutually inverted basic element structures, to convey a motif through two different colour impressions when viewed from above, i.e. when reflected on one surface of the security element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] DE102012015900A1 [Patent Document 2] EP1558449A Summary of the Invention [Problem to be solved by the invention]

[0005] One of the objectives of the present invention is to provide an alternative security element with optical security features, which has increased security against counterfeiting, is simple to manufacture and can also convey a motif via at least two different color impressions.

[0006] The starting point of the invention is a planar security element with an optical security feature, comprising at least one first surface region with a first subwavelength structure, the structural elements defining said first subwavelength structure being periodically repeated in the plane of the security element. In order to vary the color effect caused by the subwavelength structure, it is provided that the first subwavelength structure of at least one partial region of the first surface region additionally comprises an interference coating for producing a color shifting effect.

[0007] This color shift effect is a change in color impression depending on the viewing angle, i.e. the interference coating changes color depending on the viewing angle.

[0008] This additional interference coating results in a further change in the color effect caused by the subwavelength structure: since the effects based on the subwavelength structure and the interference coating overlap, the overall effect is difficult to produce in other ways, which enhances the counterfeit-proofing of the security element according to the invention.

[0009] Here, interference coatings for producing color shift effects are understood to mean in particular thin-layer constructions which cause the color shift effect by thin-film interference. Security elements based on thin-film interference are known, for example, from EP 1 558 449 A. Interference coatings for producing color shift effects, hereinafter referred to for short as interference coatings, usually consist of at least two partial layers, namely a dielectric layer and an absorber layer. An additional reflector layer on the other side of the dielectric layer, i.e. on the opposite side of the absorber layer to the dielectric layer, reflects electromagnetic waves (here light in the visible range) and thus enhances the interference effect. The dielectric layer optionally serves as a spacer layer between the reflector layer and the absorber layer. The color shift effect occurs when the interference coating is viewed from the absorber layer side, i.e. when light hits the dielectric layer through the absorber layer.

[0010] For the dielectric layer of the interference coating, a dielectric material having a refractive index of 1.65 or less, such as aluminum oxide (Al 2 O 3 ) 、 Metal fluorides, such as magnesium fluoride (MgF 2 ), aluminum fluoride (AlF 3 ), silicon oxide (SiO x ), silicon dioxide (SiO 2 ), cerium fluoride (CeF 3 ), sodium aluminum fluoride (e.g., Na 3 AlF 6 or Na 5 Al 3 F 14 ), neodymium fluoride (NdF 3 ), lanthanum fluoride (LaF 3 ), Samarium Fluoride (SmF 3 ), barium fluoride (BaF 2 ), calcium fluoride (CaF 2 ), lithium fluoride (LiF), low refractive index organic monomers and / or low refractive index organic polymers, etc. are considered.

[0011] However, for the dielectric layers of interference coatings, dielectric materials with refractive indices greater than 1.65, such as zinc sulfide (ZnS), zinc oxide (ZnO), titanium dioxide (TiO 2 ), carbon (C), indium oxide (In 2 O 3 ), indium tin oxide (ITO), tantalum pentoxide (Ta 2 O 5 ), cerium oxide (CeO 2 ), yttrium oxide (Y 2 O 3 ), europium oxide (Eu 2 O 3 ), iron oxides, such as iron(II,III) oxide (Fe 3 O 4 ) and iron(III) oxide (Fe 2 O 3 ), hafnium nitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO 2 ), lanthanum oxide (La 2 O 3 ), magnesium oxide (MgO), neodymium oxide (Nd 2 O 3 ), praseodymium oxide (Pr 6 O 11 ), samarium oxide (Sm 2 O 3 ), antimony trioxide (Sb 2 O 3 ), silicon carbide (SiC), silicon nitride (Si 3 N 4 ), silicon monoxide (SiO), selenium trioxide (Se 2 O 3 ), tin oxide (SnO 2 ), tungsten trioxide (WO 3 ), high refractive index organic monomers and / or high refractive index organic polymers are also contemplated.

[0012] As absorber layer of the interference coating, a metal layer can be used, which can be, for example, a pure metal layer or a layer containing metal clusters.Preferably, the absorber layer comprises at least one metal from the group consisting of aluminum, gold, titanium, vanadium, cobalt, tungsten, niobium, iron, molybdenum, palladium, platinum, chromium, silver, copper, nickel, tantalum, tin and / or alloys thereof, such as gold / palladium, copper / nickel, copper / aluminum or chromium / nickel.

[0013] As the reflective layer of the interference coating, a metal layer can be used, which preferably comprises at least one metal selected from the group consisting of aluminum, gold, chromium, silver, copper, tin, platinum, nickel and their alloys, for example nickel / chromium or copper / aluminum. It is also conceivable that the reflective layer comprises a semiconductor, for example silicon. Finally, it is also conceivable that the reflective layer is produced by application of a printing ink with a metallic pigment, preferably a pigment consisting of a metal from the above-mentioned group. The reflective layer is applied over the entire surface or partially by known methods, for example spraying, vapor deposition, sputtering, or as a printing ink, by known printing methods (intaglio printing, flexographic printing, screen printing, digital printing), by lacquering, roll coating, slot die coating, immersion coating (roll dip coating) or curtain coating and similar methods.

[0014] As reflective layers of interference coatings, so-called HRI layers (high refractive index layers) can also be used, which contain materials with a refractive index of more than 1.5. Such HRI layers are, for example, dielectric materials with a refractive index of 1.65 or more, such as zinc sulfide (ZnS), zinc oxide (ZnO), titanium dioxide (TiO 2 ), carbon (C), indium oxide (In 2 O 3 ), indium tin oxide (ITO), tantalum pentoxide (Ta 2 O 5 ), cerium oxide (CeO 2), yttrium oxide (Y 2 O 3 ), europium oxide (Eu 2 O 3 ), iron oxides, such as iron(II,III) oxide (Fe 3 O 4 ) and iron(III) oxide (Fe 2 O 3 ), hafnium nitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO 2 ), lanthanum oxide (La 2 O 3 ), magnesium oxide (MgO), niodymium oxide (Nd 2 O 3 ), praseodymium oxide (Pr 6 O 11 ), samarium oxide (Sm 2 O 3 ), antimony trioxide (Sb 2 O 3 ), silicon carbide (SiC), silicon nitride (Si 3 N 4 ), silicon monoxide (SiO), selenium trioxide (Se 2 O 3 ), tin oxide (SnO 2 ), tungsten trioxide (WO 3 ), high refractive index organic monomers and / or high refractive index organic polymers. These materials can be vapor deposited or printed (among them the monomers and polymers mentioned above).

[0015] However, cholesteric liquid crystal layers in combination with dark, preferably black, printed layers or metallizations can also be used as interference coatings to produce color-shifting effects. However, printed layers with interference or liquid crystal pigments can also be used as interference coatings to produce color-shifting effects.

[0016] The feature that the first subwavelength structure of at least one partial area of ​​the first surface area additionally comprises an interference coating for producing a color shift effect means that the interference coating can cover this first surface area only partially or completely. If only a partial area of ​​the first surface area is provided with an interference coating, two different colors can be recognized in the first surface area. If the entire first surface area is provided with an interference coating, at a certain observation angle this surface area appears in only one color, which is difficult to reproduce at different observation angles, since this changes to two colors at at least one other observation angle.

[0017] In any case, the invention also includes that there can be several first surface areas with a first subwavelength structure per security element. In this way, for example, a pattern consisting of several separate pattern elements or a lettering consisting of several characters can be produced, with all possible variations of the first surface area being possible, i.e. one or more first surface areas completely provided with an interference coating and / or one or more first surface areas only partially provided with an interference coating.

[0018] A flat security element has a small height or thickness compared to its length and width. A flat security element can be, for example, a film or a plate. The flat security element usually has a constant height or thickness. The first and second surfaces forming the front and back surfaces of the security element are usually planar and arranged parallel to each other. The subwavelength structures usually extend parallel to the plane of the security element, i.e. the direction of the periodic repetition of the structural elements is parallel to the plane of the security element, whereas the structural elements themselves, for example columns or recesses, can of course also and usually do extend perpendicular to the plane of the security element.

[0019] Subwavelength structures are understood here to consist of periodically repeating structural elements at least in the plane of the security element, the dimensions of the individual structural elements being less than the wavelength of the light used. The periodic repetition of the structural elements can take place in one direction, i.e. in one dimension, or in two directions, i.e. in two dimensions. As subwavelength structures, for example, two-dimensional periodic column structures or two-dimensional periodic hole structures are known (for example as described in DE102012015900A1). In this case, the columns protrude from the layer, whereas the holes are realized by recesses into the layer. The columns are therefore negative in relation to the holes. In this case, the diameter of the holes in the column or hole structure is less than the wavelength of the light used for illumination, which is usually visible light. The height of the columns or the depth of the holes are selected such that certain wavelengths are lost and thus the reflected (and possibly transmitted) light has a different color than the incident light, usually white light. A further possibility would be to generate additional plasmons and thus achieve a further color shift of the light. To that end, the subwavelength structure is realized using a thin metal layer: in the case of a column structure, the top surface of the columns and the surface between the columns at the height of the bottom of the columns will have a metal layer, but the side surfaces of the columns will not have a metal layer, if the manufacturing conditions allow. Similarly, in the case of a hole structure, the surface where the holes are and the bottom of the holes will have a metal layer, but the walls of the holes will not have a metal layer, if the manufacturing conditions allow.

[0020] The subwavelength structure is usually formed mainly by a lacquer layer (for example made of UV lacquer) on whose surface a nanostructure is provided, for example by embossing. The interference coating according to the invention is then applied onto this structured lacquer layer. If this is a thin-layer construction comprising an absorber layer, a dielectric layer and a reflector layer, a metallic reflector layer can be used to excite additional surface plasmons. Optionally, a thin dielectric layer can also be applied between the lacquer layer and the metallic reflector layer.

[0021] If a metallic reflector layer is not available, for example if the interference coating is not a thin-layer composition with dielectric and absorber layers and reflector layers, it would be conceivable to apply an additional metal layer onto the subwavelength structure before application of the interference coating for the excitation of surface plasmons. Optionally, a thin dielectric layer can also be applied between the lacquer layer and the additional metal layer.

[0022] The deposition of the metallic reflective layer or additional metallic layer is preferably performed in a directional manner, for example by thermal evaporation or sputtering deposition. The directional deposition of metal results in small metallic disks at the bottom of the holes or on the columns, while the remaining areas form a perforated aperture film. The electrical separation of the small metallic disks and the perforated aperture film allows the incident light to excite surface plasmons. The excitation of surface plasmons causes enhanced reflection or absorption in a certain spectral region, which is accompanied by coloration. The additional metallic layer of the subwavelength structure can be composed of Al, Cu, Ag, Au, Pd, Pt, Sn, In or their alloys.

[0023] After application of the interference coating, the subwavelength structures coated with the interference coating can be filled, for example, with the same lacquer that constitutes the subwavelength structures.

[0024] The period of the subwavelength structures can be in the range of 200-500 nm, the dimensions of the columns or holes or grating openings can be in the range of 100-300 nm, the height of the columns or the depth of the holes can be between 30 and 400 nm, in particular in the range of 150-250 nm, for example approximately 200 nm.

[0025] If the interference coating is a thin-layer construction with a dielectric and an absorber layer, the dielectric layer typically has a thickness in the range of 100 to 500 nm. The absorber layer typically has a thickness in the range of 5 to 10 nm. The optional reflective layer of the thin-layer construction can typically have a thickness of 20 to 50 nm. A thickness of less than 20 nm, for example 5 to 10 nm, can also be considered, but in this case the reflective properties will be less. If the interference coating is not a thin-layer construction, the optional additional metal layer for exciting surface plasmons can have a thickness of 5 to 100 nm, preferably a thickness of less than 40 nm, particularly preferably a thickness of less than 20 nm, for example a thickness of 5 to 10 nm.

[0026] Additionally, the security element may include one or more surface regions that do not have subwavelength structures or interference coatings, which may be printed with, for example, color and / or information, or may be provided with other security features.

[0027] In one embodiment of the present invention, adjacent to the first surface region there is an unstructured surface region, which does not have a subwavelength structure but has, at least in a partial region, the same interference coating as at least one partial region of the first surface region. That is, at least one first surface region with a subwavelength structure and a surface region adjacent to the former without a subwavelength structure are provided, with both surface regions being partially, in particular completely, provided with the same interference coating. That is, for example, there is at least one continuous interference coating, which covers both the surface region with the subwavelength structure and the surface region without the subwavelength structure. In particular, a single continuous interference coating can cover all the first surface regions with the subwavelength structure and all the surface regions without the subwavelength structure. The single continuous interference coating can then extend over the entire surface of the planar security element. A continuous interference coating can be produced more simply than a plurality of mutually separated surface regions with an interference coating.

[0028] When using a correspondingly large number and a correspondingly small number of first surface regions and a correspondingly large number and a correspondingly small number of unstructured surface regions, a high-resolution two-color image can be produced.

[0029] In one implementation variant of the invention, it is envisaged that the security element comprises, besides a first surface region with a first sub-wavelength structure, at least one second surface region with a second sub-wavelength structure, the first surface region being arranged side by side with the second surface region, and in which the structural elements which define the first and second sub-wavelength structures and which repeat periodically in the plane of the security element are different for both surface regions.

[0030] In this case, even three different colors can be generated for incident light at a certain observation angle, one due to the first subwavelength structure of the first surface region, one due to the second subwavelength structure of the second surface region, and one due to the additional interference coating on a partial region of the first surface region. If the entire first surface region is covered with the same interference coating, only two different colors can be produced at a certain observation angle, but the colors of the first surface region that change at different observation angles are difficult to reproduce.

[0031] In another embodiment variant of the invention, it is envisaged that the security element comprises, besides a first surface region with a first subwavelength structure, at least one second surface region with a second subwavelength structure, the first surface region being arranged side by side with the second surface region, in which the structural elements defining the first and second subwavelength structures and repeating periodically in the plane of the security element are the same for both surface regions but are oriented in the first surface region towards a first surface of the security element and in the second surface region towards a second surface of the security element opposite the first surface.

[0032] That is to say, if a first sub-wavelength structure of a first surface region is mirrored in the security element in a plane extending parallel to the plane of the security element and then moved along the mirrored plane to a second surface region, a second sub-wavelength structure of the second surface region is obtained.

[0033] In this case, even three different colors can be generated in the incident light, one due to the first subwavelength structure of the first surface region, one due to the second subwavelength structure of the second surface region, and one due to an additional interference coating on a partial region of the first surface region.

[0034] If the entire first surface region is covered with the same interference coating, only two different colors can be produced at a given observation angle, but the color of the first surface region that changes with different observation angles is difficult to reproduce.

[0035] In a further design of both embodiments with two different or two mutually inverted subwavelength structures, it can be provided that the second subwavelength structure of at least one part of the second surface region is additionally provided with an interference coating for producing a color shift effect. In this way, at a certain observation angle, up to four colors can be generated for the incident light, since the partial arrangement of the interference coating in the second surface region also causes a change in the reflected light in this region of the second surface region. The interference coating can be designed identically in terms of structure for the first and second surface regions, i.e. exhibit the same optical behavior. That is to say, for example, the interference coating can completely fill the first and second surface regions. The security element will then exhibit two colors, each of which is difficult to reproduce, at a certain observation angle.

[0036] However, the interference coating in the first surface region may have a different layer structure (e.g. a different thickness of the spacer layer) than in the second surface region, such that the interference coating in the second surface region has a different optical behavior and therefore produces another color than in the first surface region.

[0037] Of course, different interference coatings can also be applied side by side per surface area, i.e. on the same subwavelength structure, for example to generate different colors per surface area based on different layer structures of the interference coatings. Accordingly, in one embodiment of the present invention, it is contemplated that the first subwavelength structure of the first surface area and / or possibly the second subwavelength structure of the second surface area have two or more different interference coatings side by side to produce a color shift effect. The reference "different interference coatings" is understood to mean that these coatings each achieve different color effects. To this end, the different interference coatings can be constructed according to the same principle, for example they can all comprise a thin layer composition with at least an absorber layer and a dielectric layer, but can differ in terms of the material and / or thickness of the dielectric layer. Alternatively, the different interference coatings can use different principles, for example by one interference coating comprising a thin layer composition and another interference coating comprising a cholesteric liquid crystal layer or a layer comprising an interference pigment or liquid crystal pigment.

[0038] It can be envisaged that at least one first surface region (having a first subwavelength structure) is arranged adjacent to a second surface region (having a second subwavelength structure), i.e. the first and second surface regions can be immediately adjacent to each other, which allows the formation of a continuous anti-counterfeiting motif, or the first and second surface regions can be arranged spaced apart from each other, which allows the placement of additional security features between both surface regions.

[0039] In particular, it can be envisaged that the first surface region is arranged apart from the second surface region, with an unstructured surface region having no subwavelength structures being present between the first surface region and the second surface region.

[0040] In one embodiment of the invention, it is contemplated that the structural elements defining the first and second subwavelength structures include columns or holes, and the plane of the top surface of the columns in the first surface region coincides with the plane of the surrounding surface of the columns in the second surface region, or the plane of the bottom of the holes in the first surface region coincides with the plane of the surrounding surface of the holes in the second surface region.

[0041] In one embodiment of the invention, it is contemplated that the interference coating is applied directly onto the subwavelength structure, at least in a surface region. The interference coating is usually applied directly onto the subwavelength structure. It can also be applied conversely, that the subwavelength structure is applied onto the interference coating. In both cases, there is no further layer between the subwavelength structure and the interference coating, and the subwavelength structure and the interference coating are directly adjacent to each other. However, it can also be considered that there are one or more further layers between the subwavelength structure and the interference coating.

[0042] In one embodiment of the invention, it is contemplated that the effective depth of the subwavelength structure is less than the thickness of the interference coating. The effective depth corresponds to the height of the structural element. In the case of a column, the effective depth is the height of the column, and in the case of a hole, the effective depth is the depth of the hole. In the case of a thin-layer structure without a reflecting layer, the thickness of the interference coating corresponds to the sum of the thicknesses of the dielectric layer and the absorber layer. In the case of a thin-layer structure with a reflecting layer, the thickness of the interference coating corresponds to the sum of the thicknesses of the dielectric layer, the absorber layer and the reflecting layer.

[0043] The security element according to the invention typically comprises a carrier substrate, onto which the subwavelength structure and the interference coating are applied, e.g. a transparent carrier film, preferably a flexible plastic film, such as polyimide (PI), polypropylene (PP), monoaxially oriented polypropylene (MOPP), biaxially oriented polypropylene (BOPP), polyethylene (PE), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyetherketone (PEK), polyethyleneimide (PEI), polysulfone (PSU), polyaryletherketone (PAEK), polyethylenenaphthalate (PEN), liquid crystal polymer (LCP), polyester, polybutylene terephthalate, etc. Carrier films made of polyvinyl chloride (PBT), polyethylene terephthalate (PET), polyamide (PA), polycarbonate (PC), cycloolefin copolymer (COC), polyoxymethylene (POM), acrylonitrile-butadiene-styrene (ABS), polyvinyl chloride (PVC), ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF) and ethylene-tetrafluoroethylene-hexafluoropropylene-fluoro terpolymer (EFEP) are considered. The carrier film can be transparent, translucent, semi-opaque or opaque.

[0044] The carrier substrate preferably has a thickness of 7 to 700 μm, particularly preferably 5 to 200 μm, and particularly preferably 5 to 50 μm.

[0045] The security element comprising the subwavelength structure and the interference coating can be surface-treated, coated or laminated, for example coated or laminated with plastics or lacquered, on one or both surfaces in order to protect the security functions present on the security element from mechanical, physical and / or chemical influences. The protective lacquer layer can be formed, for example, on the basis of nitrocellulose, acrylates and their copolymers, polyamides and their copolymers, polyvinyl chloride and their copolymers or can consist of a crosslinked lacquer. Furthermore, the security element can be provided with an adhesive layer on one or both sides in order to enable fixing on or in a data carrier or value document. This adhesive layer can be designed in the form of a hot-seal coating, a cold-seal coating or a self-adhesive coating.

[0046] In this case, the security features according to the invention formed by the subwavelength structures and the interference coating can be applied onto a carrier substrate to form a security element. This security element can then be customized before or after surface treatment and can be at least partially embedded in or applied onto a data carrier or value document as a strip, thread or patch. The invention therefore also includes a data carrier or value document, such as a banknote, which comprises a security element according to the invention.

[0047] The invention will now be explained in more detail on the basis of schematic drawings which represent an embodiment of a device according to the invention. [Brief description of the drawings]

[0048] [Figure 1] FIG. 1 shows a top view of a flat security element according to the invention, not yet provided with an interference coating. [Diagram 2]FIG. 2 shows a top view of the security element of FIG. 1 with an interference coating. [Diagram 3] FIG. 3 is a longitudinal section through the security element of FIG. 2, taken along the section line AA. [Figure 4] FIG. 4 is a longitudinal section of a security element according to the invention comprising two subwavelength structures and an interference coating. [Diagram 5] FIG. 5 is a longitudinal section of a security element according to the invention comprising two mutually inverted subwavelength structures and an interference coating. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] Figure 1 shows a top view of a flat, here rectangular, security element 4. In a first surface region 1, it has a first subwavelength structure. An adjacent surface region is not provided with a subwavelength structure and is the unstructured surface region 3. The boundary between both surface regions 1, 3 is formed by the diagonal of the rectangle.

[0050] In order to provide the security element 4 with the inventive functionality of the interference coating 5, the interference coating 5 is applied here in a rectangular partial area of ​​the security element 4, but not to the remaining part of the security element 4. See FIG. 2, in which the interference coating 5 covers, on the right side, just over the right half of the security element 4. Here, the interference coating 5 has the same properties everywhere, i.e. it is a shared and identically designed interference coating for both surface areas 1, 3, i.e. the interference coating 5 has the same thickness and the same configuration everywhere. Nevertheless, four different color effects can be achieved in this way.

[0051] Of course, on the security element 4, there can be one or more differently formed first surface areas 1 with a first subwavelength structure, and there can be a plurality of separate first surface areas 1 with a first subwavelength structure, with one continuous or a plurality of separate unstructured surface areas 3 between and / or around these first surface areas 1. All surface areas 1, 3 can then be provided with the same continuous interference coating 5, or only some surface areas 1, 3 can be covered with a full or partially continuous interference coating. Alternatively, an interference coating 5 that covers only the first surface area 1 in a fully coincident manner can be provided in a plurality of separate areas. Alternatively, one or more areas of the interference coating 5 do not fully coincide with the first surface area 1, but form an independent pattern therefrom.

[0052] The illustrated security element 4 may be part of the value document, for example covering a surface of part of the value document.

[0053] FIG. 3 shows a longitudinal section of the security element 4 to show the arrangement of the subwavelength structure and the interference coating 5, i.e. here the plane of the security element 4 runs horizontally. A first surface area 1 is provided with a first subwavelength structure. It consists of columns 8 which repeat periodically in two directions with a period P respectively. Here only the period P in the direction from left to right is visible in the illustrated plane. The period in the direction perpendicular to the illustrated plane can be the same or different from that in the illustrated plane. The height of the columns 8 corresponds to the effective depth T of the subwavelength structure. The columns 8 can have any cross section, for example circular, elliptical, rectangular or square. The cross section should be constant at best over the height of the columns 8, if manufacturing technology allows.

[0054] Here, on the subwavelength structures of the first surface region 1 and on the unstructured surface region 3, an interference coating 5 is applied, which here consists of three layers; a reflecting layer 13 is applied directly to the top surface 9 of the columns 8, to the surface 10 around the columns 8 and to the surface of the unstructured surface region 3. On this reflecting layer 13, a dielectric layer 6 is applied. On this dielectric layer 6, an absorber layer 7 is applied. Optionally, the reflecting layer 13 can be dispensed with. On top of the absorber layer 7, a coating or a laminate can be applied.

[0055] Plasmonic effects can also be excited by the usually metallic reflective layer 13 of the interference coating 5 .

[0056] Here, light is incident on the security element from above, and the color effects caused by the subwavelength structures together with the interference coating will accordingly be visible in the reflected light, i.e. from above. Light can also be incident on the security element from below (if the carrier substrate 12 is light-transmitting), and the color effects caused by the subwavelength structures will likewise accordingly be visible in the reflected light, i.e. from below. However, color effects in transmission (if the carrier substrate 12 is light-transmitting) are not excluded. FIG. 4 shows a longitudinal section of a security element 4 with two different subwavelength structures. A first surface region 1 is provided with a first subwavelength structure. A second surface region 2 is provided with a second subwavelength structure, which differs from the first subwavelength structure in that the height and width of the columns 11 are relatively short. These columns 11 also repeat periodically in two directions with a period, which can be the same in the illustrated plane as perpendicular to the illustrated plane or can be different from perpendicular to the illustrated plane. The period of the subwavelength structures of the first surface region 1 can be different from that of the second surface region 2. Both surface regions 1, 2 with subwavelength structures are separated by a non-structured surface region 3 without subwavelength structures. All three surface regions 1-3 are provided with the same interference coating 5.

[0057] In this way, up to six different color impressions can be conveyed at different viewing angles, i.e. two different color impressions per surface area 1 to 3. If the first surface area 1 and / or the second surface area 2 is not completely covered with the interference coating 5, i.e. in Fig. 4, for example the areas further to the left or right do not carry an interference coating, then two different color impressions can also be achieved at the same viewing angle per structured surface area 1, 2.

[0058] However, it is also possible to omit the unstructured surface region 3 and have the first surface region 1 and the second surface region 2 directly adjacent to one another, again with further surface regions having further subwavelength structures.

[0059] Figure 5 shows a longitudinal section through a security element 4 with two different subwavelength structures. Both subwavelength structures are constituted by the same structural elements, namely columns 11, which in this case repeat periodically in two directions in the plane of the security element 4 and are oriented in a first surface region 1 towards a first surface of the security element 4 and in a second surface region 2 towards a second surface of the security element 4 opposite the first surface. Both surface regions 1, 2 are provided with the same interference coating 5. Both surface regions 1, 2 with subwavelength structures may be separated by a non-structured surface region 3 which does not have subwavelength structures. In this embodiment, the subwavelength structure of the second surface region 2 is the same as in Fig. 4. Here, the subwavelength structure of the first surface region 1 is mirrored relative to the subwavelength structure of the second surface region 2, in particular relative to a horizontal surface in this case. In this case, the columns 11 of the first surface region 1 point downwards and are formed when the recesses of the carrier substrate 12 are filled.

[0060] In this case, the plane of the upper surface 9 of the columns 11 in the first surface region 1 lies in the plane of the surrounding surface 10 of the columns 11 in the second surface region 1 . [Explanation of symbols] 1. First Surface Region 2. Second Surface Region 3 Unstructured surface area 4. Security Elements 5 Interference Coating 6 Dielectric Layer 7 Absorber layer 8 Columns 9 Top of column 10 Column Surroundings 11 Column 12 Carrier substrate 13 Reflective layer P period T Effective depth While this application is directed to the invention set forth in the claims, the disclosure of this application also includes: 1. A flat security element (4) with an optical security feature comprising at least one first surface region (1) with a first subwavelength structure, characterized in that the structural elements defining the first subwavelength structure repeat periodically in the plane of the security element (4), said first subwavelength structure of at least one partial region of the first surface region (1) additionally comprises an interference coating (5) for producing a color shift effect. 2. A flat security element (4) according to claim 1, characterized in that adjacent to the first surface region (1) there is an unstructured surface region (3) which does not have a subwavelength structure but which has, at least in a partial region, the same interference coating (5) as at least one partial region of the first surface region (1). 3. A flat security element according to claim 1 or 2, characterized in that besides a first surface region (1) with a first subwavelength structure, it comprises at least one second surface region (2) with a second subwavelength structure, in which the first surface region (1) is arranged side by side with the second surface region (2) and in that the structural elements which define the first and second subwavelength structures and which repeat periodically in the plane of the security element (4) are different between both surface regions. 4. A flat security element (4) according to claim 1 or 2, characterized in that besides a first surface region (1) with a first subwavelength structure, it comprises at least one second surface region (2) with a second subwavelength structure, wherein the first surface region (1) is arranged side by side with the second surface region (2) and the structural elements defining the first and second subwavelength structures and repeating periodically in the plane of the security element (4) are identical in both surface regions but are oriented in the first surface region (1) towards a first surface of the security element and in the second surface region towards a second surface of the security element opposite to the first surface. 5. A flat security element (4) according to claim 3 or 4, characterized in that at least a portion of the second subwavelength structure of the second surface region (2) additionally comprises an interference coating (5) for producing a color shifting effect. 6. A flat security element (4) according to any one of claims 1 to 5, characterized in that the first subwavelength structure of the first surface region (1) and / or optionally the second subwavelength structure of the second surface region (2) have two or more different interference coatings (5) next to each other for producing a color shifting effect. 7. A flat security element (4) according to any one of claims 2 to 6, characterized in that at least one first surface area (1) is arranged adjacent to a second surface area (2). 8. A flat security element (4) according to any one of claims 3 to 7, characterized in that the first surface region (1) is arranged spaced apart from the second surface region (2), with a non-structured surface region (3) having no subwavelength structures being present between the first surface region and the second surface region. 9. A flat security element (4) according to any one of claims 3 to 7, characterized in that the structural elements defining the first and second subwavelength structures comprise columns (8, 11) or holes, and the plane of the top surface of the columns (8, 11) in the first surface region (1) coincides with the plane of the surrounding surface of the columns (8, 11) in the second surface region (2), or the plane of the bottom of the hole in the first surface region (1) coincides with the plane of the surrounding surface of the hole in the second surface region (2). 10. A flat security element (4) according to any one of claims 1 to 9, characterized in that an interference coating (5) is applied directly onto the subwavelength structure, at least in the surface regions (1, 2). 11. A flat security element (4) according to any one of claims 1 to 10, characterized in that the effective depth (T) of the subwavelength structure is shorter than the thickness of the interference coating (5). 12. A data carrier or value document including a security element according to any one of 1. to 11.

Claims

1. 1. A flat security element (4) with an optical security feature, comprising at least one first surface region (1) with a first sub-wavelength structure, wherein the structural elements defining the first sub-wavelength structure repeat periodically in the plane of the security element (4), and wherein said first sub-wavelength structure in at least one partial region of the first surface region (1) is additionally provided with an interference coating (5) for producing a color shift effect, wherein adjacent to the first surface region (1) there is an unstructured surface region (3), which does not have a sub-wavelength structure but which in at least one partial region has the same interference coating (5) as at least one partial region of the first surface region (1), wherein the motif is conveyed by the first surface region (1) and the unstructured surface region (3) via at least two different color impressions.

2. 2. A flat security element (4) according to claim 1, characterized in that besides a first surface region (1) with a first sub-wavelength structure it comprises at least one second surface region (2) with a second sub-wavelength structure, wherein said first surface region (1) is arranged side by side with said second surface region (2) and wherein the structural elements which define said first and second sub-wavelength structures and which repeat periodically in the plane of the security element (4) are different between both surface regions.

3. 2. A flat security element (4) according to claim 1, characterized in that besides a first surface region (1) with a first sub-wavelength structure, it comprises at least one second surface region (2) with a second sub-wavelength structure, wherein the first surface region (1) is arranged side by side with the second surface region (2), and the structural elements which define the first and second sub-wavelength structures and which repeat periodically in the plane of the security element (4) are identical in both surface regions but are oriented in the first surface region (1) towards a first surface of the security element and in the second surface region (2) towards a second surface of the security element opposite to the first surface.

4. 4. A flat security element (4) according to claim 2 or 3, characterized in that at least a part of the second subwavelength structure of the second surface region (2) is additionally provided with an interference coating (5) for producing a color-shifting effect.

5. 5. A flat security element (4) according to any one of claims 1 to 4, characterized in that the first subwavelength structure of the first surface region (1) comprises two or more different interference coatings (5) next to each other for producing a color shift effect.

6. A flat security element (4) according to any one of claims 2 to 5, characterized in that the second subwavelength structure of the second surface region (2) has two or more different interference coatings (5) arranged side by side to produce a color shift effect.

7. A flat security element (4) according to any one of claims 2 to 6, characterized in that at least one first surface area (1) is arranged adjacent to a second surface area (2).

8. 8. A flat security element (4) according to any one of claims 2 to 7, characterized in that the first surface region (1) is arranged spaced apart from the second surface region (2), with an unstructured surface region (3) having no subwavelength structures present between the first and second surface regions.

9. 9. A flat security element (4) according to any one of claims 2 to 8, characterized in that the structural elements defining the first and second subwavelength structures comprise columns (8, 11) or holes, and that the plane of the top surfaces of the columns (8, 11) in the first surface region (1) coincides with the plane of the surrounding surface of the columns (8, 11) in the second surface region (2), or the plane of the bottom of the holes in the first surface region (1) coincides with the plane of the surrounding surface of the holes in the second surface region (2).

10. A flat security element (4) according to any one of claims 1 to 9, characterized in that an interference coating (5) is applied directly onto the subwavelength structure, at least in the surface regions (1, 2).

11. Planar security element (4) according to any one of claims 1 to 10, characterized in that the effective depth of the subwavelength structure is less than the thickness of the interference coating (5).

12. A data carrier comprising a security element according to any one of claims 1 to 11.

13. A value document including a security element according to any one of claims 1 to 11.

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