SAFETY ELEMENT WITH LENS RATIO IMAGE

Description

[0001] The invention relates to a security element for protecting security documents, valuables, and other data carriers, comprising a lenticular image that displays at least two different appearances from different viewing angles. The invention also relates to a method for manufacturing such a security element and a data carrier equipped with such a security element.

[0002] Data carriers, such as valuables or identification documents, but also other valuables, such as branded goods, are often equipped with security elements for protection, which allow verification of the authenticity of the data carrier and also serve as protection against unauthorized reproduction.

[0003] Security features with viewing-angle-dependent effects play a particularly important role in ensuring authenticity, as these cannot be reproduced even with the most modern copying equipment. These security features are equipped with optically variable elements that convey a different visual impression to the viewer from different viewing angles, for example, displaying a different color or brightness impression and / or a different graphic motif depending on the viewing angle.

[0004] In this context, it is known to protect data carriers by applying laser-engraved reversible images. Two or more different markings, such as a serial number and an expiration date, are laser-engraved into the data carrier at different angles using an arrangement of cylindrical lenses. The laser radiation creates a local darkening of the data carrier, making the engraved markings visually apparent. When viewed from a particular angle, only the marking engraved from that direction is visible, so that tilting the data carrier perpendicular to the axis of the cylindrical lenses creates an optically variable reversible effect.

[0005] In the case of reversible images, it is further desirable to increase security against forgery if the images visible from different directions have different colors.

[0006] Several methods are known for producing ambiguous images, but each has certain disadvantages. The known methods can be fundamentally distinguished by whether the microimages present in a motif layer are generated with or without the aid of the lens array of the ambiguous image.

[0007] Without the use of the lenticular grid, the microimages can be printed or embossed, for example. These production methods are generally very cost-effective; however, especially with the very thin layer structures important in security printing, it is usually not possible to align the microimages so precisely with the lenticular grid that the different images always appear at the same angle. This means, for example, that when viewing several banknotes with the same ambiguous image side by side, all banknotes show the same image from a specific angle.

[0008] Other manufacturing processes utilize the lens array to structure the microimages. Laser engraving processes are particularly common, in which an image is inscribed into a motif layer through the lenses of the lens array using a laser. For this purpose, the motif layer is either exposed to laser radiation through a mask, or a laser beam is scanned across the motif layer to inscribe the desired motif. In both methods, the motif is inscribed under the lenses at focus and is therefore always perfectly registered with the lenses. Furthermore, it is ensured that the inscribed motif is later visible from precisely the direction from which it was exposed by the laser beam. However, a disadvantage is that laser engraving processes are often difficult to implement on an industrial scale.For example, laser engraving millimeter-sized motifs using a mask or scanner in film production presents a significant and costly technical challenge at the film widths and process speeds typical for security applications. This is especially true when, to achieve two or more different, directionally visible motifs, a different representation must be laser-engraved into the motif layer from two or more different directions.

[0009] From publication DE 10 2012 007 747 A1, an optically variable security element is known, comprising a transparent substrate with opposing first and second principal surfaces, an arrangement of microlenses on the first principal surface, and a laser-sensitive recording layer on the second principal surface of the substrate, the latter containing first and second sublayers arranged one above the other. The first sublayer is arranged between the substrate and the second sublayer and has a plurality of microholes generated by the action of laser radiation, each microhole being associated with a microlens.

[0010] German patent application DE 10 2014 004 700 A1 also describes a security element with a lenticular image that displays at least two different appearances from different viewing angles. The lenticular image comprises a lens grid consisting of a plurality of microlenses and a laser-sensitive motif layer spaced apart from the lens grid. This motif layer has different markings in two or more sub-areas, introduced by the action of laser radiation, which produce the two different appearances when the motif layer is viewed with the lens grid.

[0011] In application WO 2013 / 098513 A1, a laser-sensitive motif layer, into which a first reversible image is applied by laser through blackening, is applied over a printed motif layer of the second reversible image. According to EP 2 391 512 B1, two images are applied to an optically variable recording layer by means of a laser from two directions.

[0012] Publication WO 2005 / 052650 A2, in turn, concerns a film material in which a regular two-dimensional arrangement of non-cylindrical lenses is used to enlarge micro-images and to form a synthetically enlarged image through the combined power of a large number of individual image systems with lenses and micro-images.

[0013] Based on this, the invention aims to provide a safety element of the type mentioned above, the appearances of which can be generated in a simple yet highly accurate manner.

[0014] This problem is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

[0015] According to the invention, a security element for securing security documents, valuables, and other data carriers is provided, featuring a lenticular image that displays at least two different appearances from different viewing angles. The lenticular image comprises a lens grid consisting of a plurality of microlenses and a radiation-sensitive motif layer spaced apart from the lens grid by a transparent substrate of the security element. The radiation-sensitive motif layer contains a plurality of transparent areas generated by radiation exposure, each precisely aligned with the microlenses of the lens grid.The radiation-sensitive motif layer is opaque outside the transparency areas created by radiation exposure and is structured in the form of a first motif, so that the first motif is visible as the first appearance when viewing the security element from a first viewing direction through the lens grid.

[0016] On the side of the radiation-sensitive motif layer facing away from the lens grid, a second motif layer is arranged, which is structured in the form of a second motif, so that the second motif is visible as a second appearance when viewing the security element from a second viewing direction through the lens grid and the transparency areas of the radiation-sensitive motif layer.

[0017] When viewed from a second angle, the observer sees through the transparent areas of the radiation-sensitive motif layer. The radiation-sensitive motif layer is not visible from this angle, and the specific appearance of this second view depends on the further design of the security element in the transparent areas, as explained in more detail below.

[0018] Preferably, the radiation-sensitive motif layer comprises a metal layer. This metal layer can be combined with at least one other metal layer or with a color layer, or it can also be part of a thin-film interference layer system and, for example, represent the reflector or absorber layer of such a layer system.

[0019] In an advantageous embodiment, the radiation-sensitive motif layer comprises two radiation-sensitive, contrasting metal layers, in particular of different colors, wherein at least one of the metal layers is structured to form the first motif. For example, one metal layer can be silver-colored and made of aluminum or silver, and the other metal layer can be made of a non-ferrous metal or a colored precious metal, such as copper or gold. If a more subtle motif is desired, the two metal layers can differ not only in color, but also, for example, in their brightness or their reflectivity (glossy / matte).

[0020] In another, equally advantageous embodiment, the radiation-sensitive motif layer comprises a radiation-sensitive color layer and a radiation-sensitive metal layer, wherein at least one of the two layers is structured to form the first motif. The color layer can, for example, be carbon black or Milori blue, while any metal is suitable for the metal layer, since practically all metals exhibit a sufficiently high contrast to a printed color layer.

[0021] In another, equally advantageous embodiment, the radiation-sensitive motif layer comprises a radiation-sensitive metallized embossed structure that is structured to form the first motif.

[0022] Finally, according to a further advantageous embodiment, the radiation-sensitive motif layer can comprise a radiation-sensitive resist layer and a metal layer present on the resist layer, which is structured to form the first motif. The transparent areas are created, in particular, by removing only the exposed areas of the resist layer.

[0023] According to a further, also advantageous embodiment, the radiation-sensitive motif layer comprises two radiation-sensitive contrasting color layers, in particular of different colors, wherein at least one of the color layers is structured to form the first motif.

[0024] In a preferred embodiment, the radiation-sensitive motif layer is laser-sensitive and is in particular ablated by laser radiation or converted into a transparent modification.

[0025] The refractive effect of the microlenses in the lens array defines a focal plane, with the radiation-sensitive motif layer advantageously positioned essentially within this focal plane. The motif layer does not need to lie exactly within the focal plane; in some designs, it can be positioned up to half a focal length above or below it. Such a defocused arrangement of the motif layer can be particularly advantageous when a very thin security element is desired or when a particularly large area beneath the respective microlenses needs to be made transparent. By arranging the motif layer outside the focal plane, the viewing angles from which the designs are visible can also be influenced and, in particular, increased. A wide viewing angle range is a particularly desirable product characteristic of the described security elements.

[0026] In an advantageous embodiment, the lens array comprises or represents a one-dimensional arrangement of microlenses, in particular cylindrical lenses. It is also advantageous for the lens array to comprise or represent a two-dimensional arrangement of microlenses, in particular spherical or aspherical lenses.

[0027] For the purposes of this description, microlenses are defined as lenses whose size in at least one lateral direction is below the resolution limit of the naked eye. Microlenses can be cylindrical, but spherical or aspherical lenses are also suitable. The latter preferably have a diameter between 5 µm and 300 µm, particularly between 10 µm and 50 µm, and most preferably between 15 µm and 20 µm. Microcylindrical lenses preferably have a width between 5 µm and 300 µm, particularly between 10 µm and 50 µm, and most preferably between 15 µm and 20 µm. The length of the microcylindrical lenses is arbitrary; for example, when used in safety threads or transfer elements, it can correspond to the total width of the thread or transfer element and be several millimeters or several centimeters.

[0028] In this case, a second motif layer is arranged on the side of the radiation-sensitive motif layer facing away from the lens grid. This second motif is structured in the form of a second motif, so that when the security element is viewed from a second viewing angle, the second motif is visible through the lens grid and the transparent areas of the radiation-sensitive motif layer as a second appearance. The second motif layer can be formed, in particular, by a printed layer. The second motif layer can be formed across the entire surface, or it can be only partially present, in which case the security element can reveal a substrate lying beneath it outside the second motif layer.

[0029] According to a further, unclaimed embodiment, one or more transparent layers are arranged on the side of the radiation-sensitive motif layer facing away from the lens grid, so that when viewing the safety element from a second viewing direction through the lens grid and the transparency areas of the radiation-sensitive motif layer, a substrate lying below the safety element is visible as a second appearance.

[0030] The invention also includes a data carrier, in particular a security document, a security paper, an identity card, a branded article or the like, with a security element of the type described.

[0031] Such a data carrier can, in particular, contain an unclaimed security element without a second motif layer, in which one or more transparent layers are arranged on the side of the radiation-sensitive motif layer facing away from the lens array, as described above. It is further provided that the data carrier is provided in a partial area with a second motif layer structured in the form of a second motif. The security element is then arranged with the lens array and the transparent areas above the second motif layer, so that the second motif is visible as a second appearance when the security element is viewed from a second viewing direction through the lens array and the transparent areas of the radiation-sensitive motif layer.This makes it easy to create data carriers with reversible images that show a general, generic motif (first motif) from a first viewing direction and an individualized motif (second motif) from a second viewing direction, as explained in more detail below.

[0032] The invention also includes a method for manufacturing a security element with a lenticular image that shows at least two different appearances from different viewing directions, wherein the method A carrier substrate is provided and equipped with a lens grid consisting of a plurality of microlenses and a radiation-sensitive motif layer spaced apart from the lens grid. In the radiation-sensitive motif layer, a plurality of transparency areas precisely aligned with the microlenses of the lens grid are generated by radiation exposure through the lens grid. Outside the transparency areas generated by radiation exposure, the radiation-sensitive motif layer is opaque and structured in the form of a first motif, so that the first motif is visible as the first appearance when viewing the security element from a first viewing direction through the lens grid.

[0033] In this case, a second motif layer is arranged on the side of the radiation-sensitive motif layer facing away from the lens grid, which is structured in the form of a second motif, so that the second motif is visible as a second appearance when viewing the security element from a second viewing direction through the lens grid and the transparency areas of the radiation-sensitive motif layer.

[0034] In an advantageous process, the radiation-sensitive motif layer is exposed to laser radiation through the lens array to create the transparent areas. The radiation-sensitive motif layer is advantageously ablated by the laser radiation or converted into a transparent modification.

[0035] In an alternative, equally advantageous method variant, the radiation-sensitive motif layer has a radiation-sensitive resist layer that is exposed through the lens array. The transparent areas are then created by a subsequent step of removing only the exposed part of the resist layer.

[0036] In an advantageous embodiment of this process variant, it is provided that the areas of the resist layer remaining after the removal of the exposed areas form sticky resist lines, which are brought into contact with a structured metal layer to form the first motif.

[0037] A safety element according to the invention can also contain more than two representations that are visible from more than two different viewing directions.For example, to generate three representations for three different viewing directions, a multitude of transparency areas are created in the aforementioned (first) radiation-sensitive motif layer by radiation from a second and third different direction; a second, opaque, and radiation-sensitive motif layer, structured in the form of a second motif, is arranged on the side of the first radiation-sensitive motif layer facing away from the lens grid; a multitude of transparency areas are created in the second radiation-sensitive motif layer by radiation from the third direction; and finally, a third motif layer, structured in the form of a third motif, is arranged on the side of the second radiation-sensitive motif layer facing away from the lens grid.

[0038] From a first viewing angle, the viewer sees the first motif of the first radiation-sensitive motif layer; from a second viewing angle, through the transparent areas of the first motif layer, the second motif of the second radiation-sensitive motif layer; and from a third viewing angle, through the transparent areas of the first and second motif layers, the third motif of the third motif layer. Analogous to the above illustration, the third motif layer can also be omitted, and the safety element can reveal a substrate layer beneath it through the transparent areas of the first and second motif layers.

[0039] A higher opacity can also be achieved in certain areas by applying a laser to the security element. For example, with suitable doping of the substrate or another layer located beneath the lenses, local darkening or color conversion can be achieved through thermochromic or photochromic effects during laser exposure. Simultaneously with the darkening or color conversion, the residual energy of the laser beam can remove or render transparent the first motif layer.

[0040] Additional information can also be inscribed into the security element by laser beaming. This additional information can be written either with energy high enough to be visible from all directions, or with energy low enough to create a mark only at the focal point, making it visible only when viewed from the angle of incidence of the laser beam. The marks can be so small that they are only visible when viewed through a light source.

Claims

1. Security element (12) for securing security papers, valuable documents, and other data carriers (10), comprising a lenticular image that displays at least two different appearances (14A, 14B) when viewed from different viewing directions, wherein - the lenticular image comprises a lenticular array (24) consisting of a plurality of microlenses (26) and a radiation-sensitive motif layer (30) spaced apart from the lenticular array (24) by a transparent carrier substrate (22) of the security element (12), - the radiation-sensitive image layer (30) comprises a plurality of transparency areas (40) generated by radiation exposure, each of which is precisely aligned with the microlenses (26) of the lens array (24), and - the radiation-sensitive pattern layer (30) is opaque outside (42) the transparency areas generated by radiation exposure and is structured in the form of a first pattern, such that the first pattern is visible as a first image (14A) when the security element (12) is viewed from a first viewing direction through the lens array (24), wherein a second motif layer is arranged on the side of the radiation-sensitive motif layer facing away from the lens grating, which is structured in the form of a second motif, such that the second motif is visible as a second image when viewing the security element from a second viewing direction through the lens grating and the transparent areas of the radiation-sensitive motif layer.

2. Security element according to claim 1, characterized in that the radiation-sensitive pattern layer comprises a metal layer.

3. A security element according to claim 1 or 2, characterized in that the radiation-sensitive motif layer comprises two radiation-sensitive contrasting metal layers, in particular of different colors, wherein at least one of the metal layers is structured to form the first motif.

4. Security element according to claim 1 or 2, characterized in that the radiation-sensitive motif layer comprises a radiation-sensitive color layer and a radiation-sensitive metal layer, wherein at least one of the two layers is structured to form the first motif.

5. A security element according to claim 1 or 2, characterized in that the radiation-sensitive motif layer comprises a radiation-sensitive metallized embossed structure that is structured to form the first motif.

6. A security element according to claim 1 or 2, characterized in that the radiation-sensitive pattern layer comprises a radiation-sensitive resist layer and a metal layer disposed on the resist layer, which is patterned to form the first pattern.

7. A security element according to claim 1, characterized in that the radiation-sensitive pattern layer comprises two radiation-sensitive contrasting color layers, wherein at least one of the color layers is patterned to form the first pattern.

8. A security element according to at least one of claims 1 to 7, characterized in that the radiation-sensitive pattern layer is laser-sensitive.

9. A security element according to at least one of claims 1 to 8, characterized in that the refractive effect of the microlenses defines a focal plane and the radiation-sensitive image layer is arranged substantially in this focal plane.

10. A security element according to at least one of claims 1 to 9, characterized in that the lens array comprises or represents a one-dimensional arrangement of microlenses, in particular cylindrical lenses, and / or that the lens array comprises or represents a two-dimensional arrangement of microlenses, in particular spherical or aspherical lenses.

11. Security element according to at least one of claims 1 to 10, characterized in that the second motif layer is formed by a printing layer.

12. A security element according to claim 11, characterized in that the second motif layer is present only partially and the security element reveals a substrate lying beneath the security element outside the second motif layer.

13. Data carrier comprising a security element according to at least one of claims 1 to 12.

14. A method for manufacturing a security element (12) with a lenticular image that displays at least two different appearances (14A, 14B) when viewed from different directions, wherein - a transparent carrier substrate (22) is provided and is provided with a lenticular array (24) comprising a plurality of microlenses (26) and a radiation-sensitive image layer (30) arranged at a distance from the lenticular array (24), - in the radiation-sensitive image layer (30), a plurality of transparent areas (40) are generated by the action of radiation passing through the lens array (24), which are precisely aligned with the microlenses (26) of the lens array (24), and - the radiation-sensitive pattern layer (30) is formed to be opaque outside (42) the transparent areas created by the radiation and is structured in the form of a first pattern, such that the first pattern is visible as a first image (14A) when the security element (12) is viewed from a first viewing direction through the lens array (24), wherein a second motif layer is arranged on the side of the radiation-sensitive motif layer facing away from the lens grating, which is structured in the form of a second motif, such that the second motif is visible as a second image when viewing the security element from a second viewing direction through the lens grating and the transparent areas of the radiation-sensitive motif layer.

15. A method according to claim 14, characterized in that the radiation-sensitive pattern layer is irradiated with laser radiation through the lens grating to produce the transparent areas, in particular that the radiation-sensitive pattern layer is ablated by the laser radiation or converted into a transparent modification.

16. A method according to claim 14, characterized in that the radiation-sensitive image layer comprises a radiation-sensitive resist layer which is exposed through the lens grating, and the transparent areas are produced by a subsequent step of removing only the exposed areas of the resist layer.