EP1972463B1 - Security element - Google Patents

Description

The invention relates to a security element for security papers, documents of value and the like with an incident electromagnetic radiation selectively influencing feature area. The invention further relates to a corresponding security paper and a corresponding security film for the production of security or value documents, a data carrier with such a feature area and an associated manufacturing method.

Data carriers, such as valuables or identity documents, but also other valuables, such as branded goods, are often provided with security features for security, which allow a verification of the authenticity of the data carrier and at the same time serve as protection against unauthorized reproduction. The security features can be present, for example, in the form of separately produced security elements which are inserted or applied to the data carriers, for example in the form of a security thread embedded in a banknote, a cover foil for a banknote with a hole, an applied security strip or a self-supporting transfer element which is in accordance with his Production is applied to a document of value. In some cases, the security features are also printed directly on the disk to be protected or introduced into the volume of the data carrier substrate.

Because of the ready availability and high quality of reproductions that can be made with modern color copiers or high resolution scanners in conjunction with good color printers, there is a need to further increase the counterfeit security of such security features.

The pamphlets EP 2 054 242 A1 and WO 2008/095481 A2 , which are both documents under Art. 54 (3) EPC, concern security documents with a photonic crystal. The publication DE 10 2004 039 A1 relates to pigments based on cylinders or prisms, the document US 2003/0179364 A1 concerns micro-optics for document identification, the publication WO 2004/096894 A2 refers to shaped articles with optical effect, which consist essentially of core-shell particles, and the WO 2008/097397 A1 , which is a document under Art. 54 (3) EPC, refers to crystalline colloidal arrays reacting to an activator.

Based on this, the object of the present invention is to further improve security elements, security papers, security films and value documents of the type mentioned above with regard to their security against imitation.

This object is achieved by the security element having the features of the main claim. A corresponding security paper and a corresponding security film, a data carrier and an associated manufacturing method are specified in the independent claims. Further developments of the invention are the subject of the dependent claims.

According to the invention, it is provided in a generic security element that the feature area contains a material with a photonic band gap. Such materials, often referred to as photonic crystals, are periodically constructed nanostructures that act on light waves in a manner similar to semiconductor crystals on electron waves. By a periodic modulation of the dielectric constant, light in the photonic crystal can propagate only in certain wavelength ranges, while in other wavelength ranges leads to a destructive interference of the light waves in all spatial directions. Light from this wavelength range can therefore not propagate because of lack of suitable modes of the electromagnetic field in the crystal, so that this wavelength range is referred to as a photonic band gap in analogy to the electronic band gap in semiconductors.

A perfect photonic crystal is a perfect reflector for light from the wavelength range of the band gap. Similar to semiconductors, the targeted incorporation of defects that disturb the periodic structure of the crystal and control its band structure in a controlled manner, within the bandgap defect modes are generated. Light from the forbidden area can be controlled in the crystal in such localized modes. Photonic crystals may consist, for example, of structured semiconductors, glasses or polymers. For further details on photonic crystals and their preparation, reference is made to the literature, for example, " Photonic Crystals - Advances in Design, Fabrication, and Characterization ", Kurt Busch, Stefan Lölkes, Ralf Wehrspohn, and Helmut Foll (Eds.), Wiley-VCH (Weinheim), (2004 ), in particular chapter 6 (pages 109-131) and 8 (pages 153-173).

In the invention, the selective reflection of the incident electromagnetic radiation is utilized by the feature area.

It is provided that the spectral range of selective reflection is in the visible spectral range. The feature area can then in particular appear optically variable, so that the viewer is given different color impressions at different viewing angles.

The feature area can be present in all the embodiments mentioned in the form of patterns, characters or codes, which can be visible or invisible depending on the selected reflection and absorption behavior and thus form visually and / or machine-detectable security features.

Furthermore, the feature area is embossed in partial regions, whereby the band gap of the platonic band gap material is changed by the embossment in order to create regions with different selective influencing of the incident electromagnetic radiation. In particular, the feature region in the non-embossed subregions can selectively reflect light of a first wavelength and light of a second, different wavelength in the embossed subregions reflect selectively. Furthermore, the feature region in the non-embossed partial regions can selectively absorb light of a first wavelength and selectively absorb light of a second, different wavelength in the embossed partial regions.

The material having a photonic band gap can be formed, in particular, by nanoparticles that are spherical in the undeformed state. The preparation of such nanoparticle structures is based on the self-organized arrangement of monodisperse spheres, for example of latex, PMMA, polystyrene or inorganic-polymer hybrid particles. These materials can be used, for example, by emulsion polymerization or by means of wet chemistry and subsequent sintering for the production of photonic bandgap material. For example, latex beads can be sedimented to lie in a three-dimensional hexagonal array. In addition, the system can be in a gas phase process are filled with a dielectric and the latex balls are then removed by dissolution, so that a periodic arrangement in the form of an artificial inverted opal, which has a photonic band gap.

In another synthetic route, an inverse opal structure is created by coating monodisperse SiO ₂ particles with photopolymers and then photopolymerizing them. The SiO ₂ is then dissolved by addition of hydrofluoric acid to give an inverse opal in a deformable acrylate matrix whose "holes" are filled with air.

The described piezochromic effects can thus be achieved both with direct structures in which photonic bandgap material is introduced into a matrix, as well as with inverse photonic crystals, which are also referred to as inverse opals in the context of this description and in which initially present balls in the course of Removed manufacturing process to produce a matrix with air-filled holes. An advantage of inverse photonic crystals is the large difference in the refractive index of air with n = 1 and the refractive index of organic polymers, which can be n = 1.3 to 1.5, so that materials with inverse photonic crystals have a high color brilliance.

Instead of using such a bottom-up approach, photonic crystals can also be produced with a top-down approach, that is, by artificial structuring of bulk material. For this purpose, suitable channels are etched or etched into the starting material, for example by lithographic techniques, which lead to a photonic bandgap in the remaining material.

In another embodiment of the invention, the photonic bandgap material may form a shell for a functional system such as a thermochromic leuco dye or thermochromic liquid crystals. The feature area can thus form a thermochromic, optically variable system. The functional systems can be introduced, for example, in an emulsion polymerization, wherein the embedding in the shells promises as a further advantage a consistency improvement. It is also conceivable to use inverse structures as a matrix, which are then also filled with functional systems.

In all designs, the photonic crystals can be encoded by laser exposure and / or ablated in subregions to provide further information.

The invention also includes a security paper and a security film for the production of security or value documents with a security element of the type described above. The feature area of the security element can be further developed in particular in the manner described above.

The feature area can be present in the interior of the security paper or the security film, or can be present in a layer applied to the security paper or the security film, in particular in a printed printing layer. The feature area can also be present in a separate security element of the type described above, which is introduced into or applied to the security paper or the security film.

The invention further comprises a data carrier, in particular a value document, such as a banknote, an identity card or the like, with a security element of the type described above. Also in this case, the feature area of the security element is advantageously designed further in the manner described in more detail above.

The feature area of the data carrier may be present in the interior of the data carrier, or in a layer applied to the data carrier, in particular in an imprinted print layer. The feature area may also be present in a separate security element of the type described above that has been introduced or applied to the data carrier.

In a preferred embodiment, the feature area is arranged at least partially over an information applied to the data carrier. Preferably, the feature area in a first state hinders the view of the underlying information. By stimulating with an external stimulus such as pressure, temperature, voltage, magnetism, light or sound, the feature area is transitioned to a second state where it releases the view of the underlying information.

The invention further includes a method for producing a security feature of a security element, a security paper, a security film or a data carrier, according to claim 19. The feature region can be produced in particular by printing on a printing ink containing photonic bandgap material by imprinting a printing ink containing interference pigments from photonic bandgap material or by introducing photonic bandgap material into the bulk of a substrate.

Further exemplary embodiments and advantages of the invention are explained below with reference to the figures, in the representation of which a representation true to scale and proportion has been dispensed with in order to increase the clarity.

Fig.1

eine schematische Darstellung einer Banknote mit einem Merkmalsbereich,

Fig. 2

einen Querschnitt durch eine Banknote mit einem aufgedruckten Merkmalsbereich,

Fig. 3

einen Querschnitt durch ein Wertdokument mit einem Merkmalsbereich,

Fig. 4

einen Querschnitt durch ein Wertdokument mit einem im Inneren eines Wertdokumentsubstrats angeordneten Merkmalsbereich,

Fig. 5

einen erfindungsgemäßen Merkmalsbereich eines Wertdokuments mit einem unverformten und einem verformten Teilbereich,

Fig. 6

einen piezochromen Merkmalsbereich, wobei in der linken Bildhälfte der Normalzustand und in der rechten Bildhälfte der Zustand unter Druck schematisch dargestellt sind,

Fig. 7

in einer Darstellung wie Fig. 6, einen piezochromen Merkmalsbereich,

Fig. 8

in einer Darstellung wie Fig. 6, einen thermochromen Merkmalsbereich, und

Fig. 9

eine Banknote mit einem Sicherheitselement nach einem weiteren Ausführungsbeispiel der Erfindung.

Show it:

Fig.1

a schematic representation of a banknote with a feature area,

Fig. 2

a cross section through a banknote with a printed feature area,

Fig. 3

a cross section through a value document with a feature area,

Fig. 4

a cross section through a value document with a feature area arranged inside a value document substrate,

Fig. 5

a feature range according to the invention of a value document with an undeformed and a deformed portion,

Fig. 6

a piezochromic feature area, the normal state being shown schematically in the left half of the picture and the state under pressure in the right half of the picture,

Fig. 7

in a presentation like Fig. 6 , a piezochromic feature area,

Fig. 8

in a presentation like Fig. 6 , a thermochromic feature area, and

Fig. 9

a banknote with a security element according to a further embodiment of the invention.

The invention will now be explained using the example of a banknote. Fig.1 shows a schematic representation of a banknote 10 with a feature area 12.

The feature area 12 is in the example shown in the form of an imprinted machine-readable barcode, which does not stand out in the visible spectral range due to a white body color of the ink used from the likewise white background. Due to the photonic band gap material contained in the feature area 12 exhibit the printed areas in the near infrared have a characteristic narrow-band absorption, which can easily be detected by machine.

The basic principle and the mode of action of these designs will now be described on the basis of Fig. 2 explained in more detail. Fig. 2 shows a cross section through a banknote 20, on the substrate 22 in a feature area, a print layer 24 is printed. The print layer 24 contains a binder matrix in which interference pigments of photonic bandgap material 26 are introduced. In the cross sections, the interference pigments or the photonic band gap material are represented schematically by an arrangement of circular disks. By suitable wet-chemical methods, such as by a sol-gel method or by emulsion polymerization, such interference pigments can be produced comparatively inexpensively. However, it is understood that all types of photonic band gap materials can be used. In particular, a dispersion varnish layer containing photonic bandgap material is also suitable. Preferably, this material is formed by spherical nanoparticles.

As discussed above, the reflection and absorption characteristics of the photonic bandgap material 26 can be made as desired by suitably adjusting the location and size of the photonic band gap, and optionally by introducing defect modes into the bandgap in a wide range. In the examples of Figures 1 and 2 For example, the bandgap of the material 26 and the defect modes in the bandgap are selected so that the material 26 of the incidental electromagnetic radiation 30 substantially completely reflects the visible and ultraviolet radiation component 32 and absorbs a very narrow band near infrared region from the infrared radiation component. The set absorption wavelength is preferably between 800 nm and 1000 nm, for example at about 850 nm.

Because of the high and uniform reflectivity of the photonic band gap material 26 in the visible spectral range, the printed print layer 24 has a white body color for the viewer. The narrow band near infrared absorption can be readily detected by illuminating the feature area with infrared radiation and recording the reflected radiation with a suitable detector, such as a silicon detector.

The feature area may be designed in particular in the form of patterns, characters or codes, as in FIG Fig.1 shown. Fig. 3 shows a cross section through a value document 40 with a feature area 42 containing a printed in the form of a pattern, a character or a coding photonic bandgap material 44. The feature area 42 may be combined with other printing or functional layers 46, 48 that are applied to the value document substrate above and / or below the feature area.

Again, the photonic bandgap material 44 may be selected to be colorless in the visible spectral region, or to have a white body color and to absorb only narrow band in the infrared. As a result of the combination with further printing or functional layers 46, 48, it is possible to realize machine-readable, extremely brilliant color shades on the value document 40, which can hardly be faked because of the specific IR absorption properties of the photonic band gap material 44.

According to other examples of the invention, the feature area may also be located inside a value document substrate, as in FIG Fig. 4 shown. The value document 50 shown there contains a security film 52 in whose volume in a feature area 54 a photonic bandgap material 56 is introduced, which in turn is designed for narrow-band absorption in the near infrared. The thus provided with an authenticity feature security film 52 is then combined in a conventional manner with other pressure and / or Funktionsschichen 58. Particularly advantageously, the body color of the band gap material 56 is matched to the body color of the security film 52 by the choice of the band gap and the defect structure, so that the feature region 54 visually does not appear. The printed or functional sheaths 58 may also be matched to the optical properties of the bandgap material 56 in order, for example, to enable a detection of the IR absorption of the bandgap material 56 from the top side of the value document 50.

If the photonic band gap material is adjusted so that it selectively reflects light from the visible spectral range, we obtain optically variable systems that change color when the viewing angle is changed.

In further designs, particularly impressive effects can be generated by a local deformation of the photonic band gap material, since such a deformation can change the band gap and thus also the optical properties of the material. Fig. 5 shows for illustration the feature area 60 of a value document which contains a photonic bandgap material in the form of spherical nanoparticles 64 in an undeformed portion 62. Corresponding to the selected band gap, the photonic bandgap material in the undeformed portion 62 has a reflection wavelength λ ₁ , which may be in the visible, ultraviolet or infrared spectral range.

In a second subregion 66, the order of the periodic nanoparticle structures has been permanently changed by a blind embossing, that is to say by local exertion of considerable pressure. For example, the embossing causes the nanoparticles 68 to be deformed and / or arranged with a changed intermediate spacing, as in FIG Fig. 5 shown schematically. The altered order of the nanoparticles 68 causes a change in the photonic bandgap and thus also a change in the reflection properties of the material, so that the photonic bandgap material in the deformed subregions 66 has a reflection wavelength λ ₂ different from λ ₁ .

The deformation by blind embossing can be carried out with very high accuracy, so that in this way detailed color cuts highest Create resolution. If IR-absorbing nanoparticles 64 are used, the wavelength of the narrow-band IR absorption due to the deformation can be shifted out of the sensitivity range of the selected IR detector or out of the passband of a suitably chosen filter. In this way, an extremely fine IR cut can be generated, which can be detected mechanically with corresponding sensors.

In the further example of the Fig. 6 For example, the photonic band gap material in the form of spherical nanoparticles 70 is embedded in a reversibly deformable matrix 72, for example in a gel, a soft lacquer or a soft color. In the in Fig. 6 in the normal state shown in the left half of the image, the photonic bandgap material according to the selected band gap on a reflection wavelength λ ₁ , which may be in the visible, ultraviolet or infrared spectral range.

By applying pressure 74 to the assembly, the shape and / or arrangement of the spherical nanoparticles changes, as in the right half of FIG Fig. 6 shown. With the shape and arrangement, the band gap and thus the reflection wavelength of the material changes, so that by applying pressure 74, a shift of the reflection wavelength can be achieved to a value λ ₂ different from λ ₁ . After relief 76 of the arrangement, the reversibly deformable matrix 72 restores the initial state and thus the original reflection wavelength λ ₁ . The feature area with the photonic bandgap material therefore exhibits piezochromic, optically variable behavior that can be triggered interactively by a user for authenticity testing. Instead of using a reversibly deformable matrix for embedding the active material, it is also possible to use a material with a photonic band gap which itself is reversibly deformable, as in US Pat Fig. 7 shown. In the left half of the picture Fig. 7 In this case, the initial state is represented by spherical rubber-elastic nanoparticles 80 in which the feature region has a reflection wavelength λ ₁ corresponding to the selected band gap. By applying pressure 82 to the array, the shape and / or arrangement of the nanoparticles 80 changes, so that the reflection wavelength of the material shifts to a value λ ₂ . At relief 84, the restoring force of the rubber-elastic nanoparticles 80 restores the initial state and thus the original reflection wavelength λ _{1 of} the feature region.

It is understood that the described deformations can be generated not only by pressure but also by other external stimuli, such as temperature, electrical voltage, magnetism, light or sound. For example, in the example of Fig. 6 Also, an embedding matrix with a high coefficient of thermal expansion may be used, such that the distance of the nanoparticles 70 changes with temperature. For example, embedding in thermoactive hydrogels is possible.

At the in Fig. 8 As shown, the spherical nanoparticles 90 form shells for a functional system. If these shells are filled, for example, with thermochromic leuco dye systems 92 or thermochromic liquid crystals, the result is a thermochromic, optically variable system whose reflection wavelength λ ₁ or λ ₂ changes with temperature 94. As indicated by the double arrow 94 in Fig. 8 implied, too this color change on return to the starting temperature reversible, so that a thermochromic, optically variable system is formed.

Another embodiment of the invention is in Fig. 9 shown. The banknote 100 is provided with a security element 102 which comprises a through-hole 103, an imprint 104 on the banknote substrate 101, a foil 105 covering the through-hole 103 and the imprint 104, and a photonic band-gap material feature region 106 according to the invention.

On the banknote substrate 101, first of all, the imprint 104 is imprinted with a color contrasting with the substrate, it being possible to use a method customary in banknote printing, such as offset printing or nyloprinting. Subsequently, the multi-part through hole 103 is punched out of the substrate to fit the imprint 104, so that the resulting recesses together with parts of the imprint 104 represent desired information, in this case the numerical sequence "20". As in Fig. 9 to recognize the imprint 104 encloses on the one hand the information "20" over the entire surface and contributes at the same time with individual components to represent the information. Not printed is an area 104 'immediately adjacent to the information "20". This area 104 'thereby forms a negative contour to the information shown.

The transparent film 105 is applied as a film strip extending over the entire banknote width. Regardless of the feature area 106, the information "20" is particularly clearly visible when the banknote 100 is viewed against a dark background, since then the printed parts 104 of the information complement the background visible through the through-hole 103 for the information "20". by virtue of However, the negative contour 104 ', the information is also visible against a light background, albeit with a lower contrast.

According to the invention, the feature area 106 is applied over the information "20". The properties of the photonic bandgap material are set such that the feature region 106 in an initial state obstructs the view of the underlying information "20", for example by appearing opaque in the relevant wavelength range. By a suitable stimulus, the band gap of the material in the feature area and thus the optical properties of the feature area 106 is changed, so that the view of the information "20" is released. The stimulation of the feature area can be done for example by applying pressure, a change in temperature or another external stimulus.

The substrate 101 further has a background pressure 107, which is indicated in the exemplary embodiment by arcuate lines and is typically realized as a guilloche pattern in the form of an intertwined line pattern. The imprint 104 and the background printing 107 can be produced in the same operation, for example in offset printing or Nyloprint. In turn, the film 105 may have line patterns 108 corresponding to the background printing 107, wherein care should be taken to ensure register-accurate application of the film 105, so that the patterns 107 and 108 complement or overlap with an exact fit. The line patterns 107 of the film 105 can be designed in particular as a metallization and thus on the one hand further increase the complexity and security against forgery of the arrangement, on the other hand provide a simple visual inspection possibility of tailor-made application of the film 105.

The photonic band gap material can be applied or introduced in various aggregation forms. A particularly simple possibility is the application of a dispersion varnish containing the photonic bandgap material. This method is particularly suitable for application to substrates with low surface roughness, so that in particular films as carriers come into question.

The pigment production can be based on the one hand on a direct spalling of the pigments of a film. Alternatively, a film can be coated with a lacquer which promotes peeling of the pigments or which itself can be dissolved in a suitable solvent without destroying the pigments to be prepared. The solvent may in particular also be water.

Claims (23)

1. A security element for security papers, value documents and the like, having a feature region that selectively influences incident electromagnetic radiation and that comprises a material having a photonic band gap, characterized in that the feature region selectively reflects incident electromagnetic radiation, the spectral range of selective reflection lying in the visible spectral range, and in that the feature region is embossed in sub-regions, the band gap of the photonic band gap material being changed by the embossing to create regions having different selective influence on the incident electromagnetic radiation.
2. The security element according to claim 1, characterized in that the feature region forms an optically variable layer that, under different viewing angles, conveys different color impressions to the viewer.
3. The security element according to claim 1 or 2, characterized in that the feature region is present in the form of patterns, characters or codes.
4. The security element according to at least one of claims 1 to 3, characterized in that, in the non-embossed sub-regions, the feature region selectively reflects light of a first wavelength, and in the embossed sub-regions, selectively reflects light of a second, different wavelength.
5. The security element according to at least one of claims 1 to 3, characterized in that, in the non-embossed sub-regions, the feature region selectively absorbs light of a first wavelength, and in the embossed sub-regions, selectively absorbs light of a second, different wavelength.
6. The security element according to at least one of claims 1 to 5, characterized in that the material having a photonic band gap is formed by nanoparticles which are spherical in their undeformed state.
7. The security element according to at least one of claims 1 to 6, characterized in that the material having a photonic band gap exhibits an inverse opal structure having air-filled holes.
8. The security element according to at least one of claims 1 to 7, characterized in that the material having a photonic band gap forms a shell for a functional system, such as a thermochromic leuco dye or a thermochromic liquid crystal.
9. A security paper or foil for manufacturing security or value documents, having a security element according to one of claims 1 to 8.
10. The security paper or foil according to claim 9, characterized in that the feature region is present in the interior of the security paper.
11. The security paper or foil according to claim 9, characterized in that the feature region is present in a layer applied to the security paper or the security foil, especially in an imprinted printing layer.
12. The security paper or foil according to claim 9, characterized in that the feature region is present in a separate security element, according to at least one of claims 1 to 8, that is introduced into or applied to the security paper or the security foil.
13. A data carrier, especially a value document, such as a banknote, identification card or the like, having a security element according to one of claims 1 to 8.
14. The data carrier according to claim 13, characterized in that the feature region is present in the interior of the data carrier.
15. The data carrier according to claim 13, characterized in that the feature region is present in a layer applied to the data carrier, especially in an imprinted printing layer.
16. The data carrier according to claim 13, characterized in that the feature region is present in a separate security element, according to at least one of claims 1 to 8, that is introduced into or applied to the data carrier.
17. The data carrier according to claim 13,15 or 16, characterized in that the feature region is at least partially arranged over a piece of information applied on the data carrier.
18. The data carrier according to claim 17, characterized in that, in a first state, the feature region impedes the view of the piece of information lying thereunder, and through stimulation with an external stimulus, such as pressure, temperature, electrical potential, magnetism, light or sound, is transferred to a second state in which it enables the view of the piece of information lying thereunder.
19. A method for manufacturing a security feature of a security element, security paper, security foil or data carrier, in which a feature region is provided with a material having a photonic band gap to create a feature region that selectively influences incident electromagnetic radiation, the feature region selectively reflecting incident electromagnetic radiation and the spectral range of selective reflection lying in the visible spectral range, and in which the feature region is embossed in sub-regions, the band gap of the photonic band gap material being changed by the embossing to create regions having different selective influence on the incident electromagnetic radiation.
20. The method according to claim 19, characterized in that the feature region is produced by imprinting a printing ink containing a photonic band gap material.
21. The method according to claim 19, characterized in that the feature region is produced by imprinting a printing ink that contains interference pigments composed of photonic band gap material.
22. The method according to claim 19, characterized in that the feature region is produced by introducing photonic band gap material into the volume of a substrate.
23. A use of a security element according to one of claims 1 to 8, of a security paper or security foil according to one of claims 9 to 12, or of a data carrier according to one of claims 13 to 18 for securing articles of any kind.

Images