EP3727870B1 - Security element with two-dimensional nanostructure, and production method for said security element - Google Patents

Security element with two-dimensional nanostructure, and production method for said security element Download PDF

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Publication number
EP3727870B1
EP3727870B1 EP18829361.7A EP18829361A EP3727870B1 EP 3727870 B1 EP3727870 B1 EP 3727870B1 EP 18829361 A EP18829361 A EP 18829361A EP 3727870 B1 EP3727870 B1 EP 3727870B1
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Prior art keywords
surface elements
security element
base
nano structure
base plane
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EP18829361.7A
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German (de)
French (fr)
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EP3727870A1 (en
Inventor
Hans Lochbihler
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Giesecke and Devrient Currency Technology GmbH
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Giesecke and Devrient Currency Technology GmbH
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/324—Reliefs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/328—Diffraction gratings; Holograms
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B42—BOOKBINDING; ALBUMS; FILES; SPECIAL PRINTED MATTER
    • B42D—BOOKS; BOOK COVERS; LOOSE LEAVES; PRINTED MATTER CHARACTERISED BY IDENTIFICATION OR SECURITY FEATURES; PRINTED MATTER OF SPECIAL FORMAT OR STYLE NOT OTHERWISE PROVIDED FOR; DEVICES FOR USE THEREWITH AND NOT OTHERWISE PROVIDED FOR; MOVABLE-STRIP WRITING OR READING APPARATUS
    • B42D25/00—Information-bearing cards or sheet-like structures characterised by identification or security features; Manufacture thereof
    • B42D25/30—Identification or security features, e.g. for preventing forgery
    • B42D25/36—Identification or security features, e.g. for preventing forgery comprising special materials
    • B42D25/373—Metallic materials

Definitions

  • the invention relates to a security element for a document of value, wherein the security element has a dielectric substrate in which a two-dimensionally periodic nanostructure is formed, which has a plurality of base surface elements that define a base plane and, in contrast, raised or lowered surface elements, with between the base surface elements and the surface elements each have a distance measured perpendicular to the base plane and connecting flanks are formed between the base surface elements and the surface elements, the base surface elements and the surface elements each being covered with a metal layer that is thinner than the distance, and the base surface elements and the surface elements in the nanostructure are arranged alternately in a regular pattern and in two directions that run parallel to the ground plane, the associated period of the arrangement of the surface elements is between 100 nm and 450 nm.
  • the invention further relates to a manufacturing method for such a security element.
  • the DE 102011101635 A1 , DE 102015008655 A1 or DE 102012105571 A1 describe such security elements and manufacturing processes.
  • surface elements that are raised or lowered relative to a metallized base plane are arranged in a two-dimensional pattern and are located above holes of the same size in the metallized base plane.
  • the surface elements act as an antenna and form electromagnetic resonances between the metallization in the ground plane and the surface elements for certain wavelengths. This results in a color for visible light in reflected light and transmitted light. The reflection on the top and bottom is different due to the different area coverage by the metal layer.
  • L. Lin, and Y. Zheng. Multiple plasmonic-photonic couplings in the Au nanobeaker arrays: enhanced robustness and wavelength tunability.”
  • Optics letters, 2060-2063 (2015 ) so-called nanocup arrays made of gold are known, which also produce color effects.
  • the known two-dimensional periodic subwavelength gratings are very complex to produce. Structuring on a subwavelength scale is required in order to form the metal layer in the base plane and the raised or lowered metallized surface elements.
  • the EP 3124283 A1 which discloses a security element according to the preamble of claim 1, describes as well as the EP 3255468 A1 a display element and an observation method for the display element.
  • the DE 10 2012 110 630 A1 discloses a multilayer body and a method for producing a security element.
  • the WO 2014/023415 A1 describes a security element with a structure that creates a color effect and the DE 10 2012 025 262 A1 discloses a method for producing a security element.
  • the invention is based on the object of specifying a two-dimensional, color-filtering structure which, on the one hand, has good color filter properties and, on the other hand, can be manufactured more easily.
  • the security element is designed for a document of value, banknote paper or the like. It has a dielectric substrate. A two-dimensional periodic nanostructure is formed in the dielectric substrate. This defines a large number of base area elements that define a base level. Compared to the base surface elements, there are raised or lowered surface elements in the nanostructure. There is a distance between the base surface elements and the surface elements, which is measured perpendicular to the base plane. The base surface elements and the surface elements are connected to one another by connecting flanks. The nanostructure can therefore be designed, for example, by columnar elevations or depressions in the dielectric substrate. The base surface elements and the surface elements as well as the connecting flanks are covered with a metal layer that is thinner than the distance. The nanostructure is therefore provided with the metal layer throughout.
  • the base surface elements and the surface elements are arranged alternately in a regular pattern. This means that they are periodic in two non-coincident directions that run parallel to the ground plane. The period directions can vary. Overall, the periods in which the surface elements are arranged are between 100 nm and 450 nm, which is where the term “nanostructure” comes from. Instead of a metal layer, another high-index layer can also be used. In addition to metal, silicon, zinc sulfide or titanium dioxide are particularly suitable materials for the high-index layer. In this description, the term “metallic” is taken to be synonymous with “high-refractive index,” unless expressly stated otherwise.
  • a closed metal film is formed on the nanostructure. It covers a variety of elevations and those in between Sections, especially all flanks of the large number of elevations. Unlike in the prior art, in which elevations or depressions of the profile are only covered with metal on the plateaus, a closed metal film is now formed.
  • the nanostructure metallized in this way reflects incident light in the zeroth order of diffraction, whereby an interference effect occurs that changes the color of the reflection, so that a color effect is created.
  • the uncoated nanostructure consists of a dielectric material, which z. B. has a refractive index of about 1.5.
  • Plastic films are particularly suitable, e.g. B. PET films as a substrate.
  • the actual basic structure is e.g. B. also made of plastic, preferably UV varnish, or is created by thermoplastic deformation of the film. After vapor deposition, the structure is finally filled with UV varnish and laminated with a cover film. This results in a layer structure in which the top and bottom have essentially the same refractive index.
  • the following materials are suitable for the metal layers: Al, Ag, Pt, Pd, Au, Cu, Cr and alloys thereof.
  • ZnS, ZnO, TiO 2 , ZnSe, SiO, Ta 2 O 5 or silicon are particularly suitable as high-index layers.
  • a dielectric with the nanostructure is first suitably structured and then coated over the entire surface. It is preferred that the nanostructure is embedded in an embedding dielectric, which preferably has the same refractive index as the dielectric of the substrate.
  • the refractive index can be between 1.4 and 1.6, for example. However, the same refractive index on the bottom and top of the structure is not essential for the desired optical effect.
  • the color effects of the two-dimensional nanostructure strongly depend on the periodicity of the pattern. This is used in further training to create colored symbols or images.
  • the area filling factor and/or the distance between the area elements and base area elements is varied locally.
  • DE 102011101635 A1 known to design a group of several surface elements and base surface elements laterally with constant dimensions so that a desired color effect occurs. This group then forms a sub-pixel. Several sub-pixels are given different color properties through appropriate geometric design and then combined into one pixel. This allows a colored image display.
  • the different colors can be varied by the corresponding local variation of one or more of the parameters of the grid (distance between surface elements and base surface elements, periods of the pattern in two spatial directions and extent of the surface elements).
  • basic colors pixel by pixel e.g. B. RGB colors
  • true color images can be produced in subpixel areas.
  • the advantage of such structures compared to conventional printing technology is that very fine motif structuring down to the micrometer range can be carried out. However, no complex sampling of metallization, etc. is required since the metal layer can be formed continuously. This fine structuring is particularly suitable for applications in moiré magnification arrangements, as also in DE 102011101635 A1 described.
  • the substrate with the coated two-dimensional periodic nanostructure can be used in particular in a security element for a document of value. It can be used in particular in a security thread, Tear thread, security tape, security strip, patch or label can be integrated.
  • the security element provided with the grid can span transparent areas or recesses.
  • the substrate with the two-dimensional periodic nanostructure with a closed metal film shows pronounced color effects in reflection.
  • the desired color can be adjusted by choosing structural parameters of the nanostructure.
  • the distance between surface elements and base surface elements i.e. the height of the elevations or depressions, comes into question.
  • Another question is the period or the different periods of the arrangements of elevations and depressions in the spatial directions parallel to the ground plane.
  • Another possible parameter is the dimensions of the surface elements and their geometric shape in plan view. This can be rotationally symmetrical. In other designs it has a two-fold symmetry, for example it is rectangular or elliptical.
  • the proportion of the expansion of the surface element in the period is also a variable parameter that influences the color effect.
  • These parameters can of course be varied laterally across the security element in order to vary the color effect and thus create a motif.
  • a colored motif or a true-color image in reflection can easily be provided by arranging nanostructure sections with laterally different structural parameters.
  • the structures can be made by simply embossing. A metallic coating, for example vapor deposition, then takes place. This layer then no longer needs to be structured in a complex manner, but rather covers the nanostructure over the surface. In this way, security elements with optical properties that cannot be counterfeited can be produced cost-effectively in large series.
  • the color of the structure results from the embossing and not from a structuring of the metallization, which can, for example, be carried out very cost-effectively in aluminum.
  • the security element can in particular be part of a not yet fit for circulation (e.g. banknote paper) to a document of value, which can additionally have further authenticity features so that the later documents of value have non-copiable authenticity features in order to enable an authenticity check and to prevent unwanted copies.
  • Bank or credit cards or ID cards are examples of a document of value.
  • Banknote paper is an example of a precursor.
  • Figure 1 shows a color-filtering nanostructure 1, which is intended to form a security element S for a document of value.
  • the nanostructure 1 is produced in that a carrier 2 is provided with a profile that has elevations with lateral flanks 4 above a base surface 5. The sides form the flanks 4 and the top surface form surface elements 3.
  • the nanostructure is provided with a metal layer 6, which is applied both to the base surface 5 and to the surface elements 3.
  • the flanks 4 are also provided with the cover layer 6.
  • Figure 1 shows an embodiment in which the elevations have a rectangular or square cross section in a top view of a base plane defined by the base layer 5
  • Figure 2 an embodiment with round elevations.
  • the elevations are arranged in the form of a two-dimensional periodic pattern, with at least one period d being provided along two mutually perpendicular directions in the base plane defined by the base surface, according to which the arrangement of the elevations is repeated.
  • the Figures 3A to 3B show different embodiments for the profile of the nanostructure in cross section, for example along the direction in which the extension w 2 is present. In Figure 3A the profile is trapezoidal. In Figure 3B is the profile opposite the Figure 3A inverted. Instead of elevations, there are depressions.
  • the profile representations of the Figures 3A to 3B clearly show that the elevations 7 or depressions 8 in the surface elements are also provided with the metal layer as on the flanks 4. Likewise, the metal layer 6 is provided in the remaining base surface elements 9 of the base surface 5, which as a result is continuous and over the entire surface . If unpolarized light falls on the nanostructure 1 at an angle ⁇ , it is reflected in the zeroth order of diffraction.
  • the grating period d is smaller than the wavelength of the visible light spectrum and lies in the range between 100 nm and 450 nm.
  • the nanostructure 1 is in two spatial directions Basic level 5 periodically. The period can be different in both directions. Periods with different periods can show a polarization effect.
  • the metal layer 6 has a refractive index v. It is embedded in a dielectric with the refractive index n through the nanostructure 1 on the substrate 2 and a cover lamination 10. This is preferably a UV varnish that is located on a film, for example PET film, which forms the substrate 2.
  • the refractive index of both materials is around 1.5.
  • the thickness of the metal layer is between 20 nm and 150 nm. It is marked t in the figures.
  • a rounded structure often results from the manufacturing process, as strictly sharp-edged corners, as in the Figures 3A and 3B , are very difficult or even impossible to achieve in practice with embossing processes with nanostructure fineness.
  • the Figures 4 to 6 show possible patterns in which the elevations 7 or depressions 8 can be arranged.
  • the structure of the pattern can be orthogonal ( Figure 4 ) or hexagonal ( Figures 5 and 6 ) be.
  • the periods d are in the subwavelength range, ie in the range between 100 nm and 450 nm.
  • the filling factors w 1 /d 1 and w 2 /d 2 are between 0.2 and 0.8, preferably between 0.3 and 0.7.
  • the periodicity directions are perpendicular to one another. This is also optional. Spatially asymmetrical arrangements of the profile and periodicity are also conceivable. In other words, pattern 6 does not have to, as in Figure 1 shown to be a Cartesian pattern.
  • the columns 4 can also be designed asymmetrically.
  • the following materials are suitable for the metal layers: Al, Ag, Pt, Pd, Au, Cu, Cr and alloys thereof.
  • ZnS, ZnO, TiO 2 , ZnSe, SiO, Ta 2 O 5 or silicon are suitable as high refractive index layers.
  • the dielectric carrier is formed with the elevations 7 or depressions 8 arranged in the pattern and then coated. It is important that the coating 6 is coherent, i.e. the flanks 4 are also coated.
  • the nanostructures can be reproduced in a molding process so that cost-effective mass production can be achieved.
  • Nanoimprint processes are particularly suitable for this.
  • Transparent areas can also be realized within the structure described above, for example by laser demetallization in areas or by a wash color process.

Description

Die Erfindung betrifft ein Sicherheitselement für ein Wertdokument, wobei das Sicherheitselement ein dielektrisches Substrat aufweist, in dem eine zweidimensional periodische Nanostruktur geformt ist, die eine Vielzahl von Grundflächenelementen, die eine Grundebene definieren, und demgegenüber angehobenen oder abgesenkten Flächenelemente aufweist, wobei zwischen den Grundflächenelementen und den Flächenelemente jeweils ein senkrecht zur Grundebene gemessener Abstand besteht und zwischen den Grundflächenelementen und den Flächenelementen Verbindungsflanken ausgebildet sind, wobei die Grundflächenelemente und die Flächenelemente jeweils mit einer Metallschicht bedeckt sind, die dünner ist als der Abstand, und die Grundflächenelemente und die Flächenelemente in der Nanostruktur in einem regelmäßigen Muster abwechselnd angeordnet sind und in zwei Richtungen, die parallel zur Grundebene verlaufen, die zugeordnete Periode der Anordnung der Flächenelemente zwischen 100 nm und 450 nm beträgt. Die Erfindung betrifft weiter ein Herstellverfahren für ein solches Sicherheitselement.The invention relates to a security element for a document of value, wherein the security element has a dielectric substrate in which a two-dimensionally periodic nanostructure is formed, which has a plurality of base surface elements that define a base plane and, in contrast, raised or lowered surface elements, with between the base surface elements and the surface elements each have a distance measured perpendicular to the base plane and connecting flanks are formed between the base surface elements and the surface elements, the base surface elements and the surface elements each being covered with a metal layer that is thinner than the distance, and the base surface elements and the surface elements in the nanostructure are arranged alternately in a regular pattern and in two directions that run parallel to the ground plane, the associated period of the arrangement of the surface elements is between 100 nm and 450 nm. The invention further relates to a manufacturing method for such a security element.

Die DE 102011101635 A1 , DE 102015008655 A1 oder DE 102012105571 A1 beschreiben solcher Sicherheitselemente und Herstellverfahren. In diesen Nanostrukturen aus dem Stand der Technik sind gegenüber einer metallisierten Grundebene angehobene oder abgesenkte Flächenelemente in einem zweidimensionalen Muster angeordnet, die sich über gleichgroßen Löchern in der metallisierten Grundebene befinden. Die Flächenelemente wirken als Antenne und bilden für bestimmte Wellenlängen elektromagnetische Resonanzen zwischen der Metallisierung in der Grundebene und den Flächenelementen aus. Dadurch ergibt sich eine Farbigkeit für sichtbares Licht in Auflicht und Durchlicht. Die Reflexion an der Ober- und der Unterseite ist aufgrund der unterschiedlichen Flächenbedeckung durch die Metallschicht unterschiedlich. Aus der Veröffentlichung L. Lin, and Y. Zheng. "Multiple plasmonic-photonic couplings in the Au nanobeaker arrays: enhanced robustness and wavelength tunability." Optics letters, 2060-2063 (2015 ) sind sogenannte Nanobecher-Arrays aus Gold bekannt, welche ebenfalls Farbeffekte ausbilden.The DE 102011101635 A1 , DE 102015008655 A1 or DE 102012105571 A1 describe such security elements and manufacturing processes. In these nanostructures from the prior art, surface elements that are raised or lowered relative to a metallized base plane are arranged in a two-dimensional pattern and are located above holes of the same size in the metallized base plane. The surface elements act as an antenna and form electromagnetic resonances between the metallization in the ground plane and the surface elements for certain wavelengths. This results in a color for visible light in reflected light and transmitted light. The reflection on the top and bottom is different due to the different area coverage by the metal layer. From the publication L. Lin, and Y. Zheng. "Multiple plasmonic-photonic couplings in the Au nanobeaker arrays: enhanced robustness and wavelength tunability." Optics letters, 2060-2063 (2015 ) so-called nanocup arrays made of gold are known, which also produce color effects.

Die bekannten zweidimensional periodischen Subwellenlängengitter sind jedoch sehr aufwendig herzustellen. Es ist eine Strukturierung im Subwellenlängenmaßstab erforderlich, um die Metallschicht in der Grundebene und die demgegenüber angehobenen oder abgesenkten metallisierten Flächenelemente zu bilden.However, the known two-dimensional periodic subwavelength gratings are very complex to produce. Structuring on a subwavelength scale is required in order to form the metal layer in the base plane and the raised or lowered metallized surface elements.

Die EP 3124283 A1 , die ein Sicherheitselement nach dem Oberbegriff des Anspruchs 1 offenbart, beschreibt ebenso wie die EP 3255468 A1 ein Displayelement und eine Beobachtungsmethode für das Displayelement. Die DE 10 2012 110 630 A1 offenbart einen Mehrschichtkörper sowie ein Verfahren zur Herstellung eines Sicherheitselements. Die WO 2014/023415 A1 beschreibt ein Sicherheitselement mit einer farbeffekterzeugenden Struktur und die DE 10 2012 025 262 A1 offenbart ein Verfahren zur Herstellung eines Sicherheitselements.The EP 3124283 A1 , which discloses a security element according to the preamble of claim 1, describes as well as the EP 3255468 A1 a display element and an observation method for the display element. The DE 10 2012 110 630 A1 discloses a multilayer body and a method for producing a security element. The WO 2014/023415 A1 describes a security element with a structure that creates a color effect and the DE 10 2012 025 262 A1 discloses a method for producing a security element.

Der Erfindung liegt die Aufgabe zugrunde, eine zweidimensionale, farbfilternde Struktur anzugeben, die zum einen eine gute Farbfiltereigenschaft aufweist und sich zum anderen einfacher herstellen lässt.The invention is based on the object of specifying a two-dimensional, color-filtering structure which, on the one hand, has good color filter properties and, on the other hand, can be manufactured more easily.

Die Erfindung ist in den unabhängigen Ansprüchen definiert.The invention is defined in the independent claims.

Das Sicherheitselement ist für ein Wertdokument, ein Banknotenpapier o. ä. ausgebildet. Es weist ein dielektrisches Substrat auf. In dem dielektrischen Substrat ist eine zweidimensional periodische Nanostruktur geformt. Diese definiert eine Vielzahl von Grundflächenelementen, die eine Grundebene definieren. Gegenüber den Grundflächenelementen befinden sich in der Nanostruktur angehobene oder abgesenkte Flächenelemente. Zwischen den Grundflächenelementen und den Flächenelementen besteht ein Abstand, wobei dieser senkrecht zur Grundebene gemessen ist. Die Grundflächenelemente und die Flächenelemente sind durch Verbindungsflanken miteinander verbunden. Die Nanostruktur kann somit beispielsweise durch säulenförmige Erhebungen oder Vertiefungen im dielektrischen Substrat ausgestaltet sein. Die Grundflächenelemente und die Flächenelemente sowie auch die Verbindungsflanken sind mit einer Metallschicht bedeckt, die dünner ist als der Abstand. Somit ist die Nanostruktur durchgängig mit der Metallschicht versehen. Die Grundflächenelemente und die Flächenelemente sind in einem regelmäßigen Muster abwechselnd angeordnet. Damit sind sie in zwei, nichtzusammenfallenden Richtungen, die parallel zur Grundebene verlaufen, periodisch. Die Periodenrichtungen können variieren. Insgesamt liegen die Perioden, in denen die Flächenelemente angeordnet sind, zwischen 100 nm und 450 nm, wodurch sich der Begriff der "Nanostruktur" ableitet. Anstelle einer Metallschicht kann auch eine andere hochbrechende Schicht verwendet werden. Somit kommen neben Metall für die hochbrechende Schicht als Material insbesondere Silizium, Zinksulfid oder Titandioxid in Frage. In dieser Beschreibung wird der Begriff "metallisch" als gleichbedeutend mit "hochbrechend" aufgefasst, soweit nicht ausdrücklich anderes beschrieben ist.The security element is designed for a document of value, banknote paper or the like. It has a dielectric substrate. A two-dimensional periodic nanostructure is formed in the dielectric substrate. This defines a large number of base area elements that define a base level. Compared to the base surface elements, there are raised or lowered surface elements in the nanostructure. There is a distance between the base surface elements and the surface elements, which is measured perpendicular to the base plane. The base surface elements and the surface elements are connected to one another by connecting flanks. The nanostructure can therefore be designed, for example, by columnar elevations or depressions in the dielectric substrate. The base surface elements and the surface elements as well as the connecting flanks are covered with a metal layer that is thinner than the distance. The nanostructure is therefore provided with the metal layer throughout. The base surface elements and the surface elements are arranged alternately in a regular pattern. This means that they are periodic in two non-coincident directions that run parallel to the ground plane. The period directions can vary. Overall, the periods in which the surface elements are arranged are between 100 nm and 450 nm, which is where the term “nanostructure” comes from. Instead of a metal layer, another high-index layer can also be used. In addition to metal, silicon, zinc sulfide or titanium dioxide are particularly suitable materials for the high-index layer. In this description, the term “metallic” is taken to be synonymous with “high-refractive index,” unless expressly stated otherwise.

Wesentlich für die Wirkung der Nanostruktur und damit des Sicherheitselementes ist es, dass auf der Nanostruktur ein geschlossener Metallfilm gebildet ist. Er deckt eine Vielzahl von Erhebungen und die dazwischenliegenden Abschnitte, insbesondere alle Flanken der Vielzahl von Erhebungen ab. Anders als im Stand der Technik, in dem Erhebungen oder Vertiefungen des Profils nur auf den Plateaus metallisch überzogen sind, ist nun ein geschlossener Metallfilm ausgebildet. Die derart metallisierte Nanostruktur reflektiert einfallendes Licht in der nullten Beugungsordnung, wobei ein Interferenzeffekt auftritt, der die Reflexion farblich verändert, so dass ein Farbeffekt entsteht.It is essential for the effect of the nanostructure and thus of the security element that a closed metal film is formed on the nanostructure. It covers a variety of elevations and those in between Sections, especially all flanks of the large number of elevations. Unlike in the prior art, in which elevations or depressions of the profile are only covered with metal on the plateaus, a closed metal film is now formed. The nanostructure metallized in this way reflects incident light in the zeroth order of diffraction, whereby an interference effect occurs that changes the color of the reflection, so that a color effect is created.

Die unbeschichtete Nanostruktur besteht dabei aus einem dielektrischen Material, welches z. B. eine Brechzahl von etwa 1,5 aufweist. Dabei eignen sich besonders Kunststofffolien, z. B. PET-Folien, als Substrat. Die eigentliche Basisstruktur ist z. B. ebenfalls in Kunststoff, bevorzugt UV-Lack, ausgebildet oder entsteht durch thermoplastische Verformung der Folie. Nach der Bedampfung wird schließlich die Struktur mit UV-Lack aufgefüllt und mit einer Deckfolie kaschiert. Somit liegt ein Schichtaufbau vor, bei dem die Ober- und die Unterseite im Wesentlichen dieselbe Brechzahl besitzt.The uncoated nanostructure consists of a dielectric material, which z. B. has a refractive index of about 1.5. Plastic films are particularly suitable, e.g. B. PET films as a substrate. The actual basic structure is e.g. B. also made of plastic, preferably UV varnish, or is created by thermoplastic deformation of the film. After vapor deposition, the structure is finally filled with UV varnish and laminated with a cover film. This results in a layer structure in which the top and bottom have essentially the same refractive index.

Für die Metallschichten kommen folgende Materialien in Frage: Al, Ag, Pt, Pd, Au, Cu, Cr und Legierungen davon. Als hochbrechende Schichten eignen sich besonders ZnS, ZnO, TiO2, ZnSe, SiO, Ta2O5 oder Silizium.The following materials are suitable for the metal layers: Al, Ag, Pt, Pd, Au, Cu, Cr and alloys thereof. ZnS, ZnO, TiO 2 , ZnSe, SiO, Ta 2 O 5 or silicon are particularly suitable as high-index layers.

Bei einem besonders zweckmäßigen Herstellverfahren wird zuerst ein Dielektrikum mit der Nanostruktur geeignet strukturiert und dann vollflächig beschichtet. Es ist bevorzugt, dass die Nanostruktur in ein Einbett-Dielektrikum eingebettet ist, welches vorzugsweise dieselbe Brechzahl hat wie das Dielektrikum des Substrates. Die Brechzahl kann beispielsweise zwischen 1,4 und 1,6 liegen. Dieselbe Brechzahl auf der Unter- und Oberseite der Struktur ist jedoch für den gewünschten optischen Effekt nicht zwingend.In a particularly useful manufacturing process, a dielectric with the nanostructure is first suitably structured and then coated over the entire surface. It is preferred that the nanostructure is embedded in an embedding dielectric, which preferably has the same refractive index as the dielectric of the substrate. The refractive index can be between 1.4 and 1.6, for example. However, the same refractive index on the bottom and top of the structure is not essential for the desired optical effect.

Die Farbeffekte der zweidimensionalen Nanostruktur hängen stark von der Periodizität des Musters ab. Dies ist dazu in Weiterbildungen ausgenutzt, farbige Symbole bzw. Bilder zu erzeugen. Dazu ist der Flächenfüllfaktor und/oder der Abstand zwischen den Flächenelementen und Grundflächenelementen lokal variiert. Insbesondere ist es möglich, wie aus DE 102011101635 A1 bekannt, eine Gruppe mehrerer Flächenelemente und Grundflächenelemente lateral mit gleichbleibenden Abmessungen so zu gestalten, dass ein gewünschter Farbeffekt eintritt. Diese Gruppe bildet dann ein Sub-Pixel. Mehrere Sub-Pixel werden durch entsprechende geometrische Gestaltung mit unterschiedlichen Farbeigenschaften versehen und dann zu einem Pixel zusammengefasst. Dies erlaubt eine farbige Bilddarstellung. Die unterschiedlichen Farben können dabei durch die entsprechende lokale Variation eines oder mehrerer der Parameter des Gitters (Abstand zwischen Flächenelementen und Grundflächenelementen, Perioden des Musters in zwei Raumrichtungen sowie Ausdehnung der Flächenelemente) variiert werden. Durch die pixelweise Farbmischung von Basisfarben, z. B. RGB-Farben, in Subpixelbereichen können Echtfarbenbilder hergestellt werden. Der Vorteil von solchen Strukturen gegenüber der herkömmlichen Drucktechnik ist, dass hierbei eine sehr feine Motiv-Strukturierung bis in den Mikrometerbereich vorgenommen werden kann. Dennoch ist keine aufwendige Bemusterung von Metallisierungen etc. erforderlich, da die Metallschicht durchgängig ausgebildet sein kann. Diese Feinstrukturierung eignet sich besonders für Anwendungen in Moiré-Vergrößerungsanordnungen, wie ebenfalls in DE 102011101635 A1 beschrieben.The color effects of the two-dimensional nanostructure strongly depend on the periodicity of the pattern. This is used in further training to create colored symbols or images. For this purpose, the area filling factor and/or the distance between the area elements and base area elements is varied locally. In particular, it is possible as follows DE 102011101635 A1 known to design a group of several surface elements and base surface elements laterally with constant dimensions so that a desired color effect occurs. This group then forms a sub-pixel. Several sub-pixels are given different color properties through appropriate geometric design and then combined into one pixel. This allows a colored image display. The different colors can be varied by the corresponding local variation of one or more of the parameters of the grid (distance between surface elements and base surface elements, periods of the pattern in two spatial directions and extent of the surface elements). By mixing basic colors pixel by pixel, e.g. B. RGB colors, true color images can be produced in subpixel areas. The advantage of such structures compared to conventional printing technology is that very fine motif structuring down to the micrometer range can be carried out. However, no complex sampling of metallization, etc. is required since the metal layer can be formed continuously. This fine structuring is particularly suitable for applications in moiré magnification arrangements, as also in DE 102011101635 A1 described.

Das Substrat mit der beschichteten zweidimensional periodischen Nanostruktur kann insbesondere in einem Sicherheitselement für ein Wertdokument verwendet werden. Es kann insbesondere in einem Sicherheitsfaden, Aufreißfaden, Sicherheitsband, Sicherheitsstreifen, Patch oder Etikett integriert sein. Insbesondere kann das mit dem Gitter versehene Sicherheitselement transparente Bereiche oder Ausnehmungen überspannen.The substrate with the coated two-dimensional periodic nanostructure can be used in particular in a security element for a document of value. It can be used in particular in a security thread, Tear thread, security tape, security strip, patch or label can be integrated. In particular, the security element provided with the grid can span transparent areas or recesses.

Das Substrat mit der zweidimensional periodischen Nanostruktur mit geschlossenem Metallfilm zeigt ausgeprägte Farbeffekte in Reflexion. Die gewünschte Farbe kann durch die Wahl von Strukturparametern der Nanostruktur eingestellt werden. Infrage kommen der Abstand zwischen Flächenelementen und Grundflächenelementen, also die Höhe der Erhebungen oder Vertiefungen. Infrage kommt weiter die Periode bzw. die unterschiedlichen Perioden der Anordnungen von Erhöhungen und Vertiefungen in den Raumrichtungen parallel zur Grundebene. Ein weiterer möglicher Parameter ist die Abmessung der Flächenelemente sowie deren geometrische Form in Draufsicht. Diese kann rotationssymmetrisch sein. In anderen Ausbildungen hat sie eine zweizählige Symmetrie, ist beispielsweise rechteckig oder elliptisch. Der Anteil der Ausdehnung des Flächenelements an der Periode ist ebenfalls ein variierbarer Parameter, der Einfluss auf den Farbeffekt hat. Diese Parameter können natürlich lateral über das Sicherheitselement hinweg variiert werden, um den Farbeffekt zu variieren und so ein Motiv zu erzeugen. Auf diese Weise kann durch Anordnung von Nanostrukturabschnitten mit lateral unterschiedlichen Strukturparametern einfach ein farbiges Motiv oder ein Echtfarbenbild in Reflexion bereitgestellt werden. Die Strukturen können durch einfaches Prägen hergestellt werden. Anschließend findet eine metallische Beschichtung, beispielsweise Bedampfung statt. Diese Schicht muss dann nicht mehr aufwendig strukturiert werden, sondern bedeckt die Nanostruktur flächig. Auf diese Weise lassen sich Sicherheitselemente mit nicht fälschbaren optischen Eigenschaften kostengünstig in Großserie herstellen. Die Farbigkeit der Struktur ergibt sich aufgrund der Prägung und nicht aufgrund einer Strukturierung der Metallisierung, die beispielsweise sehr kostengünstig in Aluminium ausgeführt werden kann.The substrate with the two-dimensional periodic nanostructure with a closed metal film shows pronounced color effects in reflection. The desired color can be adjusted by choosing structural parameters of the nanostructure. The distance between surface elements and base surface elements, i.e. the height of the elevations or depressions, comes into question. Another question is the period or the different periods of the arrangements of elevations and depressions in the spatial directions parallel to the ground plane. Another possible parameter is the dimensions of the surface elements and their geometric shape in plan view. This can be rotationally symmetrical. In other designs it has a two-fold symmetry, for example it is rectangular or elliptical. The proportion of the expansion of the surface element in the period is also a variable parameter that influences the color effect. These parameters can of course be varied laterally across the security element in order to vary the color effect and thus create a motif. In this way, a colored motif or a true-color image in reflection can easily be provided by arranging nanostructure sections with laterally different structural parameters. The structures can be made by simply embossing. A metallic coating, for example vapor deposition, then takes place. This layer then no longer needs to be structured in a complex manner, but rather covers the nanostructure over the surface. In this way, security elements with optical properties that cannot be counterfeited can be produced cost-effectively in large series. The color of the structure results from the embossing and not from a structuring of the metallization, which can, for example, be carried out very cost-effectively in aluminum.

Das Sicherheitselement kann insbesondere Teil einer noch nicht umlauffähigen Vorstufe (z. B. Banknotenpapier) zu einem Wertdokument sein, das zusätzlich noch weitere Echtheitsmerkmale aufweisen kann, damit die späteren Wertdokumente nicht kopierbare Echtheitsmerkmale aufweisen, um eine Echtheitsüberprüfung zu ermöglichen und unerwünschte Kopien zu verhindern. Banknoten, Chip- oder Sicherheitskarten, wie z. B. Bank- oder Kreditkarten oder Ausweise, sind Beispiele für ein Wertdokument. Ein Banknotenpapier ist ein Beispiel für eine Vorstufe.The security element can in particular be part of a not yet fit for circulation (e.g. banknote paper) to a document of value, which can additionally have further authenticity features so that the later documents of value have non-copiable authenticity features in order to enable an authenticity check and to prevent unwanted copies. Banknotes, chip or security cards, such as B. Bank or credit cards or ID cards are examples of a document of value. Banknote paper is an example of a precursor.

Es versteht sich, dass die vorstehend genannten und die nachstehend noch zu erläuternden Merkmale nicht nur in den angegebenen Kombinationen, sondern auch in anderen Kombinationen oder in Alleinstellung einsetzbar sind, ohne den Rahmen der Ansprüche zu verlassen.It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or alone, without departing from the scope of the claims.

Nachfolgend wird die Erfindung beispielshalber anhand der beigefügten Zeichnungen, die auch erfindungswesentliche Merkmale offenbaren, noch näher erläutert. Es zeigen:

Fig. 1 und 2
perspektivische Schemadarstellungen zweier Varianten einer Nanostruktur für ein Sicherheitselement;
Fig. 3A bis 3B
Profile, die die Nanostruktur im Querschnitt haben kann und
Fig. 4 bis 6
Beispiele für die laterale Anordnung von Erhebungen oder Vertiefungen in der Nanostruktur des Sicherheitselementes in Aufsicht.
The invention will be explained in more detail below using the accompanying drawings, which also reveal features essential to the invention. Show it:
Fig. 1 and 2
perspective schematic representations of two variants of a nanostructure for a security element;
3A to 3B
Profiles that the nanostructure can have in cross section and
Fig. 4 to 6
Examples of the lateral arrangement of elevations or depressions in the nanostructure of the security element in top view.

Figur 1 zeigt eine farbfilternde Nanostruktur 1, die zum Ausbilden eines Sicherheitselementes S für ein Wertdokument vorgesehen ist. Die Nanostruktur 1 ist dadurch hergestellt, dass ein Träger 2 mit einem Profil versehen wird, das Erhebungen mit seitlichen Flanken 4 über einer Grundfläche 5 besitzt. Die Seiten bilden die Flanken 4 und die Deckfläche bilden Flächenelemente 3. Die Nanostruktur ist mit einer Metallschicht 6 versehen, die sowohl auf der Grundfläche 5 als auch auf den Flächenelementen 3 aufgebracht ist. Auch die Flanken 4 sind mit der Deckschicht 6 versehen. Figur 1 zeigt eine Ausführungsform, bei der die Erhebungen in Draufsicht auf eine Grundebene, die durch die Grundschicht 5 definiert ist, rechteckigen oder quadratischen Querschnitt haben, die Figur 2 eine Ausführungsform mit runden Erhebungen. Die Erhebungen sind in Form eines zweidimensional periodischen Musters angeordnet, wobei entlang zweier senkrecht zueinander liegenden Richtungen in der durch die Grundfläche definierten Grundebene mindestens eine Periode d vorgesehen ist, dergemäß sich die Anordnung der Erhebungen wiederholt. Die Figuren 3A bis 3B zeigen unterschiedliche Ausführungsformen für das Profil der Nanostruktur im Querschnitt, beispielsweise längs der Richtung, in der die Ausdehnung w2 vorhanden ist. In Figur 3A ist das Profil trapezförmig. In Figur 3B ist das Profil gegenüber der Figur 3A invertiert. Statt Erhebungen liegen somit Vertiefungen vor. Figure 1 shows a color-filtering nanostructure 1, which is intended to form a security element S for a document of value. The nanostructure 1 is produced in that a carrier 2 is provided with a profile that has elevations with lateral flanks 4 above a base surface 5. The sides form the flanks 4 and the top surface form surface elements 3. The nanostructure is provided with a metal layer 6, which is applied both to the base surface 5 and to the surface elements 3. The flanks 4 are also provided with the cover layer 6. Figure 1 shows an embodiment in which the elevations have a rectangular or square cross section in a top view of a base plane defined by the base layer 5 Figure 2 an embodiment with round elevations. The elevations are arranged in the form of a two-dimensional periodic pattern, with at least one period d being provided along two mutually perpendicular directions in the base plane defined by the base surface, according to which the arrangement of the elevations is repeated. The Figures 3A to 3B show different embodiments for the profile of the nanostructure in cross section, for example along the direction in which the extension w 2 is present. In Figure 3A the profile is trapezoidal. In Figure 3B is the profile opposite the Figure 3A inverted. Instead of elevations, there are depressions.

Die Profildarstellungen der Figuren 3A bis 3B zeigen deutlich, dass die Erhebungen 7 bzw. Vertiefungen 8 in den Flächenelementen ebenso mit der Metallschicht versehen sind, wie an den Flanken 4. Ebenso ist in den verbleibenden Grundflächenelementen 9 der Grundfläche 5 die Metallschicht 6 vorgesehen, die im Ergebnis damit durchgängig und vollflächig ist. Fällt auf die Nanostruktur 1 unpolarisiertes Licht unter den Winkel Θ, wird es in der nullten Beugungsordnung reflektiert. Die Gitterperiode d ist kleiner als die Wellenlänge des sichtbaren Lichtspektrums und liegt im Bereich zwischen 100 nm und 450 nm. Die Nanostruktur 1 ist in zwei Raumrichtungen in der Grundebene 5 periodisch. Die Periode kann in beiden Richtungen unterschiedlich sein. Perioden mit unterschiedlicher Periode können einen Polarisationseffekt zeigen. Möchte man diesen nicht, wählt man vorteilhafter Weise in beiden Raumrichtungen dieselbe Periode. Die Metallschicht 6 hat einen Brechungsindex v. Sie ist durch die Nanostruktur 1 auf dem Substrat 2 sowie eine Deckkaschierung 10 in ein Dielektrikum mit dem Brechungsindex n eingebettet. Hier handelt es sich bevorzugt um einen UV-Lack, der sich auf einer Folie, beispielsweise PET-Folie, befindet, die das Substrat 2 bildet. Der Brechungsindex beider Materialien liegt etwa bei 1,5.The profile representations of the Figures 3A to 3B clearly show that the elevations 7 or depressions 8 in the surface elements are also provided with the metal layer as on the flanks 4. Likewise, the metal layer 6 is provided in the remaining base surface elements 9 of the base surface 5, which as a result is continuous and over the entire surface . If unpolarized light falls on the nanostructure 1 at an angle Θ, it is reflected in the zeroth order of diffraction. The grating period d is smaller than the wavelength of the visible light spectrum and lies in the range between 100 nm and 450 nm. The nanostructure 1 is in two spatial directions Basic level 5 periodically. The period can be different in both directions. Periods with different periods can show a polarization effect. If you don't want this, it is advantageous to choose the same period in both spatial directions. The metal layer 6 has a refractive index v. It is embedded in a dielectric with the refractive index n through the nanostructure 1 on the substrate 2 and a cover lamination 10. This is preferably a UV varnish that is located on a film, for example PET film, which forms the substrate 2. The refractive index of both materials is around 1.5.

Die Dicke der Metallschicht beträgt zwischen 20 nm und 150 nm. Sie ist in den Figuren mit t eingezeichnet.The thickness of the metal layer is between 20 nm and 150 nm. It is marked t in the figures.

Für die Nanostruktur 1 kommen verschiedenste Profile infrage; die Figuren 3A bis 3B zeigen lediglich exemplarische Beispiele. Gemein ist den Beispielen, dass die Flanken 4 ebenfalls mit der Metallschicht 6 versehen sind.A wide variety of profiles are possible for the nanostructure 1; the Figures 3A to 3B only show exemplary examples. What the examples have in common is that the flanks 4 are also provided with the metal layer 6.

Eine verrundete Struktur ergibt sich vielfach herstellungsbedingt, da strikt scharfkantige Ecken, wie in den Figuren 3A und 3B, bei Prägeprozessen in Nanostrukturfeinheit nur sehr schwer oder in Praxis gar nicht zu erzielen sind.A rounded structure often results from the manufacturing process, as strictly sharp-edged corners, as in the Figures 3A and 3B , are very difficult or even impossible to achieve in practice with embossing processes with nanostructure fineness.

Die Figuren 4 bis 6 zeigen mögliche Muster, in denen die Erhebungen 7 bzw. Vertiefungen 8 angeordnet werden können. Die Struktur des Musters kann beispielsweise orthogonal (Figur 4) oder hexagonal (Figuren 5 und 6) sein.The Figures 4 to 6 show possible patterns in which the elevations 7 or depressions 8 can be arranged. For example, the structure of the pattern can be orthogonal ( Figure 4 ) or hexagonal ( Figures 5 and 6 ) be.

Um farbige Motive oder Echtfarbenbilder auszubilden, ist eine laterale Variation von Strukturparametern der Nanostruktur erforderlich. Es werden Teilbereiche vorgesehen, die unterschiedliche Strukturparameter haben. Aus dem Stand der Technik ist hierfür die Anordnung in Form Sub-Pixeln und Pixeln bekannt, wie oben erwähnt.In order to form colored motifs or true color images, a lateral variation of structural parameters of the nanostructure is required. Subareas are provided that have different structural parameters. Out of The arrangement in the form of sub-pixels and pixels is known from the prior art, as mentioned above.

Die Perioden d liegen im Subwellenlängenbereich, d. h. im Bereich zwischen 100 nm und 450 nm. Die Füllfaktoren w1/d1 und w2/d2 liegen zwischen 0,2 und 0,8, bevorzugt zwischen 0,3 und 0,7. Um eine polarisationsunabhängige Farbfilterung zu erzielen, werden die Profilparameter für die beiden Raumrichtungen möglichst identisch gewählt, also p1 = p2 und s1 = s2. Dies ist jedoch optional. Ebenso sind im beschriebenen Ausführungsbeispiel die Periodizitätsrichtungen senkrecht zueinander. Auch dies ist optional. Auch räumlich asymmetrische Anordnungen des Profils und der Periodizität sind denkbar. Mit anderen Worten, das Muster 6 muss nicht, wie in Figur 1 dargestellt, ein kartesisches Muster sein. Auch können die Säulen 4 asymmetrisch gestaltet sein.The periods d are in the subwavelength range, ie in the range between 100 nm and 450 nm. The filling factors w 1 /d 1 and w 2 /d 2 are between 0.2 and 0.8, preferably between 0.3 and 0.7. In order to achieve polarization-independent color filtering, the profile parameters for the two spatial directions are chosen to be as identical as possible, i.e. p 1 = p 2 and s 1 = s 2 . However, this is optional. Likewise, in the exemplary embodiment described, the periodicity directions are perpendicular to one another. This is also optional. Spatially asymmetrical arrangements of the profile and periodicity are also conceivable. In other words, pattern 6 does not have to, as in Figure 1 shown to be a Cartesian pattern. The columns 4 can also be designed asymmetrically.

Für die Metallschichten kommen folgende Materialien in Frage: Al, Ag, Pt, Pd, Au, Cu, Cr und Legierungen davon. Als hoch brechende Schichten eignen sich beispielsweise ZnS, ZnO, TiO2, ZnSe, SiO, Ta2O5 oder Silizium.The following materials are suitable for the metal layers: Al, Ag, Pt, Pd, Au, Cu, Cr and alloys thereof. For example, ZnS, ZnO, TiO 2 , ZnSe, SiO, Ta 2 O 5 or silicon are suitable as high refractive index layers.

Zur Herstellung kommen verschiedene Prozesse in Frage. Zuerst wird der dielektrische Träger mit den im Muster angeordneten Erhebungen 7 oder Vertiefungen 8 ausgebildet und dann beschichtet. Wesentlich ist, dass die Beschichtung 6 zusammenhängend ist, also auch die Flanken 4 beschichtet sind.Various processes can be used for production. First, the dielectric carrier is formed with the elevations 7 or depressions 8 arranged in the pattern and then coated. It is important that the coating 6 is coherent, i.e. the flanks 4 are also coated.

Die Nanostrukturen können in einem Abformverfahren vervielfältig werden, so dass eine kostengünstige Massenproduktion realisiert werden kann. Hierzu wird auf die DE 102011101635 A1 verwiesen.The nanostructures can be reproduced in a molding process so that cost-effective mass production can be achieved. For this purpose, refer to the DE 102011101635 A1 referred.

Weiter ist es möglich, ein Original, welches die oben beschriebenen Strukturen enthält, mit weiteren bekannten Strukturen, wie Reliefhologrammen, Mikrospiegel oder anderen bekannten Nanostrukturen, passergenau zusammenzusetzen. Dafür eignen sich insbesondere Nanoimprint-Verfahren. Es können auch transparente Bereiche innerhalb der oben beschriebenen Struktur, z.B. durch eine bereichsweise Laserdemetallisierung oder durch einen Waschfarbenprozess, realisiert werden.Furthermore, it is possible to assemble an original containing the structures described above with other known structures, such as relief holograms, micromirrors or other known nanostructures, with precise registration. Nanoimprint processes are particularly suitable for this. Transparent areas can also be realized within the structure described above, for example by laser demetallization in areas or by a wash color process.

Claims (10)

  1. Security element for a valuable document, wherein the security element (S) has:
    - a dielectric substrate (2) in which a two-dimensionally periodic nano structure (1) is formed which has a multiplicity of base surface elements (9), which define a base plane (5), and flat surface elements (3) which are raised or lowered in relation to said base plane,
    - wherein there is in each case a spacing, as measured perpendicularly to the base plane (5), between the base surface elements (9) and the surface elements (3), and connecting flanks are formed between the base surface elements (9) and the surface elements (3),
    - wherein the base surface elements (9) and the surface elements (3) are each covered by a metallic or highly refractive layer which is thinner than the spacing, and
    - the base surface elements (9) and the surface elements (3) in the nano structure (1) are arranged in an alternating manner in a regular pattern and, in two directions running parallel to the base plane (5), the associated period (d) of the arrangement of the surface elements (3) is between 100 nm and 450 nm, and
    - the connecting flanks are also covered by the metallic or highly refractive layer, and therefore the latter covers the nano structure (1) continuously,
    characterized in that
    the connecting flanks run at an angle of between 90 degrees and 70 degrees in relation to the base plane (5), and
    the nano structure covered by the metallic or semi-refractive layer reflects incident light in the zeroth order of diffraction, wherein an interference effect occurs which changes the reflection in colour such that a colour effect arises.
  2. Security element according to Claim 1, characterized in that the nano structure (1) is embedded in a dielectric.
  3. Security element according to Claim 1 or 2, characterized in that the metal layer (6) has a thickness between 20 nm and 250 nm, preferably a thickness between 25 nm and 150 nm, furthermore preferably a uniform normal thickness.
  4. Security element according to one of the preceding claims, characterized in that the nano structure (1) has a trapezoidal profile in cross section.
  5. Security element according to one of the preceding claims, characterized in that the regular pattern has a rectangular or hexagonal basic shape in a top view of the base plane (5).
  6. Security element according to one of the preceding claims, characterized in that the spacing is between 50 nm and 500 nm and varies laterally for the colour variation.
  7. Security element according to one of the preceding claims, characterized in that the periods (d) and/or the extent (w) of the surface elements (3) vary laterally for the colour variation.
  8. Valuable document having a security element (S) according to one of the preceding claims.
  9. Method for producing a security element (S), wherein
    - in a dielectric substrate a two-dimensionally periodic nano structure (1) is formed which has a multiplicity of base surface elements (9), which define a base plane (5), and flat surface elements (3) which are raised or lowered in relation to said base plane,
    - wherein there is in each case a spacing, as measured perpendicularly to the base plane (5), between the base surface elements (9) and the surface elements (3), and connecting flanks are formed between the base surface elements (9) and the surface elements (3),
    - wherein the base surface elements (9) and the surface elements (3) are each covered by a metallic or highly refractive layer (6) which is thinner than the spacing, and
    - the base surface elements (9) and the surface elements (3) in the nano structure (1) are arranged in an alternating manner in a regular pattern and, in two directions running parallel to the base plane (5), the associated period (d) of the arrangement of the surface elements (3) is between 100 nm and 450 nm, and
    the connecting flanks are also covered by the layer (6), and therefore the latter covers the nano structure (1) continuously,
    characterized in that
    the connecting flanks run at an angle of between 90 degrees and 70 degrees in relation to the base plane (5), and
    the nano structure continuously covered by the metallic or highly refractive layer reflects incident light in the zeroth order of diffraction, wherein an interference effect occurs which changes the reflection in colour such that a colour effect arises.
  10. Method according to Claim 9,
    characterized in that a security element (S) according to one of Claims 1 to 7 is produced.
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