Optically variable see-through security element, data carrier and manufacturing method

Abstract

The invention relates to an optically variable see-through security element (12) for protecting a data carrier (10), comprising: a lens grid (22) consisting of a plurality of microlenses (24) arranged in a first grid, the refractive action of which defines a focal plane; a color-changing coating (30) substantially located in the focal plane of the lenticular grid (22), which presents different colors in plan view and perspective; and a microstructure arrangement substantially located in the focal plane of the lenticular grid (22), consisting of a plurality of microstructures (40, 42) arranged in a second grid, which produce one or more images (16-T2, 16-T3) in a predetermined viewing direction when viewed through the lenticular grid (22). The microstructures (40, 42) are formed in the color changing coating (30) or directly on the color changing coating.

Description

[0001] The present invention relates to an optically variable see-through security element, to a data carrier having such a see-through security element and to a method for producing such a see-through security element.

[0002] Data carriers such as value documents or identification documents or other valuable items such as luxury goods are often equipped with security elements for protection against forgery, which allow the authenticity of the data carrier to be verified and at the same time protect against unauthorised copying.

[0003] Among these, see-through security features, for example see-through windows in banknotes, are increasingly important, since they are easy to recognise but difficult to forge.

[0004] It has therefore also been attempted to use lenticular features in see-through security elements, for example in see-through windows of banknotes. While these lenticular features are attractive in such see-through windows from a top view from the front, they are often blurred from the back and, under transmitted light, the attractiveness is rather weak due to the strong light refraction at the individual lenses and the associated overall scattering effect of the window. On the other hand, for pigmented lenticular features, the static optical impression is often easily reproduced by a colour copier, so that the security against forgery is not optimal.

[0005] Against this background, the technical problem addressed by the present invention is to provide an optically variable see-through security element having an attractive visual appearance and a high security against forgery. The present invention should also provide a value document having such a see-through security element and a production method for such a see-through security element.

[0006] The technical problem is solved by the features of the independent claims. The embodiments of the invention are the technical solutions of the dependent claims.

[0007] The present invention provides an optically variable see-through security element for protecting data carriers, in particular banknotes and other value documents.

[0008] The see-through security element comprises a lenticular grid consisting of a plurality of micro-lenses arranged in a first grid, the refractive action of which defines a focal plane; a colour-shifting coating which is located substantially in the focal plane of the lenticular grid, which colour-shifting coating exhibits different colours under a top view and under see-through; and a micro-structure arrangement which is arranged substantially in the focal plane of the lenticular grid, which micro-structure arrangement consists of a plurality of micro-structures arranged in a second grid, which micro-structures produce one or more images in a predetermined viewing direction when viewed through the lenticular grid under see-through. The micro-structures are formed in the colour-shifting coating or directly on the colour-shifting coating.

[0009] The see-through security element according to the present application is based on the combination of at least two interwoven optically variable effects, namely on the one hand a colorshift effect upon switching between a planar view and a see-through view, and on the other hand an optically variable lenticular feature which can be hidden in planar view and which surprisingly appears only upon see-through view and tilting of the security element. In addition, the colorshift effect is also visible upon back view and upon switching from planar view to see-through view, so that the security element presents a visually appealing appearance in all viewing situations.

[0010] In a preferred embodiment, the microstructure is at least partially constituted by microscopic openings in the colorshift coating. By microscopic openings is meant openings which are hardly or completely indistinguishable to the naked eye compared to the larger area negative indicia. Typically, the microscopic openings have a diameter in the range of a few micrometers, in particular in the range of 1 pm to 10 pm.

[0011] The combination of a microstructure in the form of microscopic openings and a larger area negative indicium represents a particularly preferred embodiment - the negative indicium being perceived by the observer as static, while the lenticular effect resulting from the interaction of the microscopic openings with the lenticules changes or moves upon tilting. These movements are particularly clearly perceived in relation to the static reference point created by the negative indicium.

[0012] Advantageously, the microstructure is at least partially formed by laser-ablated local areas or by local areas of the colorshift coating which are transformed into transparent modifications by laser radiation. In order to obtain the best ablation or transformation effect, the wavelength of the laser used can be adapted to the thickness of the dielectric spacer layer in the colorshift coating which will be discussed in detail below.

[0013] According to another equally advantageous embodiment, the microstructure is at least partially formed by colored microstructured elements on or in the colorshift coating.

[0014] Advantageously, the microstructure can also be at least partially formed by raised or recessed local areas of the colorshift coating. In a particularly simple embodiment, the microstructure is constituted by an embossed structure which is completely provided with the colorshift coating. The embossed structure can in particular be embossed into a thermoplastic lacquer or a radiation-curable lacquer, preferably a UV lacquer. The raised and recessed local areas can take a variety of forms and geometrical shapes, including but not limited to structures with asymmetric or symmetric cross-sectional profiles, structures with trapezoidal cross-sectional profiles, binary structures, structures with stepped reliefs, and / or concave or convex structures, wherein the cross-sectional profiles can also have rounded edges.

[0015] The embodiments of the microstructure described above can also be combined, for example, the raised or recessed partial areas of the colorshift coating or the openings in the colorshift coating can be filled with a suitable color. Furthermore, for example, the first image of the security element can be formed by the microstructure in the form of microscopic openings and the second image can be formed by the colored microstructure elements.

[0016] If the microstructure is not a purely open or demetallized area of the colorshift coating, but comprises an additional embossed height difference, which is optionally filled with a contrasting color, the lenticular features are well perceived not only in perspective, but also in plan view, by the contours or edges of the image-generating microstructure. In plan view from the front, the optically variable lenticular effect is visible in the plan view color of the colorshift coating. In perspective, the same lenticular effect is visible in the perspective color of the colorshift coating. When viewed from the back, although the lenticular features can only be seen in reduced clarity and altered form depending on the lighting situation, the color change typical for the colorshift coating when switching from the plan view situation to the perspective view situation is also clearly visible in this case.

[0017] In an advantageous embodiment, the first grid of lenticules and the second grid of microstructures have the same grid spacing and the same orientation. This does not exclude that the two grids are offset to each other in the plane, so that the image is not visible in perpendicular view. At this time, the working principle of the lenticular features essentially corresponds to the working principle of a tilted lens image.

[0018] In another equally advantageous embodiment, the grid spacing of the first grid and the second grid is different and / or the first grid and the second grid are rotated relative to each other. The difference in grid spacing is preferably at most a few percent, and the rotation of the grids relative to each other is preferably at most a few degrees. For such grids, the working principle of the lenticular features corresponds to the working principle of a Moire magnification device or so-called modulo magnification device. The basic principle of such micro-optical display devices is described in document WO 2009 / 000528 A1, the disclosure of which is incorporated into the present specification in this respect.

[0019] The grid of lenses is advantageously a one-dimensional grid with a grid spacing or a regular two-dimensional grid, in particular a hexagonal, square, rectangular or parallelogram grid. The grid spacing or grid period is typically between 500 µm and 3 µm, preferably between 50 µm and 5 µm, particularly preferably between 30 µm and 30 µm, very particularly preferably between 30 µm and 8 µm.

[0020] The pitch of the adjacent microlenses is preferably small in order to ensure a high coverage and thus a high-contrast display. The microlenses of spherical or aspherical design preferably have a diameter of between 5 pm and 50 pm, in particular only between 10 pm and 35 pm, and thus cannot be recognized by the naked eye. The microlenses of rod design advantageously have a width of between 5 pm and 50 pm, in particular between 10 pm and 35 pm. The length of the rod lenses can be much greater, up to several millimeters or even centimeters.

[0021] The lens grid and the color-shifting coating are advantageously formed on opposite sides of a transparent carrier foil, for example a PET foil. This carrier foil serves both as a mechanical carrier and as an optical spacer.

[0022] The color-shifting coating is preferably formed by a three-layer layer system with two semitransparent metal layers and a dielectric spacer layer between them. The dielectric spacer layer expediently has a layer thickness of between 50 nm and 600 nm, preferably between 100 nm and 400 nm, and / or is formed from one of the materials ZnS, Si02, MgF2 and Al203. The semitransparent metal layers expediently have a layer thickness of between 3 nm and 20 nm, preferably between 5 nm and 10 nm, and / or are formed from the material Al, Cr, Ag, Cu, Fe, Ni, Au or an alloy containing one or more of these elements. Such a three-layer layer system is particularly suitable for producing a color-shifting effect in plan view / perspective. The thickness of the two semitransparent metal layers can be the same, but does not have to be.

[0023] Although a three-layer layer system is currently preferred, the color-shifting layer can in principle also be formed by a thin silicon layer alone or in combination with a semitransparent metal layer, with layer thicknesses in the order of magnitude of 10 nm. A further option is to use a single dielectric layer whose refractive index differs sufficiently from the refractive indices of the materials of the two layers surrounding it.

[0024] In an advantageous development of the application, the color-shifting coating is left free in local regions of the security element, preferably in the form of a negative marking, and particularly preferably in the form of a negative text of small alphanumeric characters which are still distinguishable to the naked eye.

[0025] The position and shape of the microstructures are preferably chosen exactly such that the desired optically variable effect is visible when an observer looks through the microlens arrangement towards the plane of the microstructures. For example, the following effects can be realized: a tilt effect between two images that are meaningfully related to each other, a tilt effect between two images that are not meaningfully related to each other, a tilt effect between an arbitrary number of images that are meaningfully related to each other, a tilt effect between an arbitrary number of images that are not meaningfully related to each other, a magnification, shift and depth effect, a distortion effect or a pumping effect. A depth effect is understood to mean a different effect that is perceived in three dimensions, in particular including those patterns that are perceived in a plane that is at a certain distance in the z direction from the plane of observation, patterns that are located in different discrete z planes, and objects that are themselves perceived in three dimensions in a region that extends continuously in the z direction.

[0026] The microlens effect can occur when the security element is tilted around different axes that lie in the plane of the security element. Combinations of these effects are also possible and in many cases are particularly visually appealing. As mentioned above, in an advantageous embodiment, the arrangement of the microstructures essentially follows the arrangement of the microlenses and thus also has the same grid type.

[0027] The area of the face that is provided with the microstructures can cover the entire area of the colorshifting coating, but can also only occupy a partial area of arbitrary shape. The area of the face that contains the microstructures can coincide or approximately coincide with the area of the face that is provided with the microlenses, but they can also be smaller or larger, or in some places extend beyond or recede from the microlens area. It is advantageous, however, that there is always an overlap that is clearly visible to the naked eye.

[0028] An advantageous possibility for making the window area covered by the see-through security element more recognizable consists in making the area of the face that is filled with microlenses approximately coincide with the area of the face that is provided with the colorshifting coating. This is technically extremely challenging, since the embossing of the microlenses or the coating of the paint that can be embossed for this purpose, on the one hand, and the demetallization of the colorshifting coating, on the other hand, are carried out in different and independent working steps. Nevertheless, the complete or at least approximately complete registration of the area containing the microlenses with the colorshifting coating requires complex technical equipment, thereby further increasing the protection against forgery of the security element.

[0029] At the same time, the window area becomes more recognizable, since the light scattering effect of the microlenses is missing in the transparent areas without colorshifting coating, so that the observer not only perceives these areas with full brightness, but can also clearly see objects through the window area.

[0030] In another advantageous embodiment, the optically variable microlens effect is designed so as to be invisible or very difficult to perceive in plan view. The observer then sees only the window area and the colorshifting coating with its special contour shape. As soon as the observer changes the viewing conditions so that sufficient light of sufficient brightness penetrates the security element from behind into his eye, he not only recognizes the colorshifting effect of the colorshifting coating with the pattern represented by its contour shape, but also, unexpectedly, the microlens effect and possibly the negative marking.

[0031] This is achieved in particular when the microstructures are formed by pure openings in the colorshifting coating, for example by laser ablation, and are advantageously small openings, i.e. only a small fraction of the total area in terms of area. Under reflected light, the small openings are masked by the largely reflecting action of the semi-transparent mirror surface, so that they cannot be perceived by the observer. Only when a strong light source behind the security feature illuminates the security element with so much light that it exceeds the portion of light incident and reflected from the front, do these small openings become recognizable. This embodiment is particularly suitable for a tilt effect, in which the pattern can only be seen in a small solid angle. In order to achieve a small solid angle, the colorshifting coating should be located as well as possible in the focal plane of the laser.

[0032] The application also comprises a data carrier having a see-through security element of the type described above, which is arranged in or on a light-transmitting partial area of the data carrier. The data carrier can be in particular a value document, such as a banknote, in particular a paper banknote, a polymer banknote or a film composite banknote, or a share, a bond, a certificate, a gift voucher, a check, a seal, a stamp duty, a high-quality admission ticket, but also an identification document, for example a credit card, a bank card, a cash payment card, an authorization card, an identity card or a passport personal information page. The light-transmitting partial area is in particular a continuous opening in the data carrier, for example a hole in a paper banknote, which is covered by the see-through security element.

[0033] Finally, the application also comprises a method for producing an optically variable see-through security element of the type described above, in which:

[0034] - a lens grid consisting of a plurality of microlenses arranged in a first grid is produced,

[0035] - a colorshifting coating which appears in different colors in plan view and in see-through view is arranged essentially in the focal plane of the lens grid, and

[0036] - a microstructure device (or microstructure array) consisting of a plurality of microstructures arranged in a second grid is formed in or on the colorshifting coating.

[0037] The microlenses are preferably produced by hot embossing in a thermoplastic material or by embossing in a UV-curing material with concomitant and / or subsequent UV exposure. In order to protect them from contamination or other environmental influences, the lenses can be embedded in a material having a different refractive index, wherein the difference in refractive index between the lens material and the embedding material influences the focal length in addition to the radius of curvature of the lens, which must be taken into account when designing the security element.

[0038] The layer system preferably used for the color-shifting coating is generally produced over the full surface, with physical vapor deposition (PVD) processes being predominantly used. For example, electron beam evaporation, boat evaporation, sputtering, etc. can be considered. In a preferred embodiment, the layers applied over the full surface are subsequently structured laterally in order to impart a visually appealing contour shape, for example in the form of alphanumeric characters or other patterns. The lateral, partial removal of this layer system can be carried out by means of etching processes or peeling processes, which are known in the art. Transparent segments are thereby produced, which are visible to the naked eye and are also referred to as negative indicia in the present description.

[0039] For the production of the microstructures, the following methods are considered in particular:

[0040] Exposure with a laser: If the color-shifting coating, which is located substantially in the focal plane, is irradiated with a laser through the microlenses, the coating is ablated at the focal point (spherical lens) or the focal line (cylindrical lens), or the metal is converted into a transparent modification. In this way, different images can also be exposed from different directions, so that a tilted image is formed. Instead of exposure in the focal plane, it is also possible to expose slightly outside the focal plane. In this way, the ablated circular faces or lines will be slightly larger, so that they can also be visible over a larger angular range.

[0041] The microstructures forming microscopically open pores can also be (pre)defined by embossing into a UV lacquer, wherein the regions to be removed are provided by a fine structure, preferably having a high aspect ratio. After the color-shifting coating has been applied, an etching process is carried out, which removes the coating in the fine-structured regions or removes at least one of the metal layers, while the coating in the non-structured regions is retained.

[0042] The selective metal transfer is also suitable for producing microstructures forming microscopically open pores: By means of UV embossing, a microstructure having protrusions or recesses relative to the surrounding region is produced on a first foil. After the color-shifting coating has been applied, which is applied non-stably, the first foil is bonded to a second foil having an adhesion layer applied over the full surface. When the second foil is peeled off, the color-shifting coating parts located on the protrusion regions of the first foil (donor foil) or the background (for recess structures) are peeled off and remain on the second foil (acceptor foil). Both foils can be equipped with microlenses and further processed into a security element according to the invention.

[0043] In another preferred embodiment, the microstructure forms a contrast in color with respect to the plan view color and / or the perspective view color of the color shifting coating. In this embodiment, the microstructure can be defined by embossing into the UV lacquer, resulting in a surface relief consisting of raised and recessed areas. Subsequently, the recesses are filled with a suitable contrasting color using known microstructure color filling methods, and then the color shifting coating is applied. Depending on the construction of the security element, it is sometimes also reasonable to reverse the order of color filling and coating.

[0044] In a variant of this embodiment, the recesses are filled with a color that absorbs light so as to present an opaque effect in perspective view. In this case, the color used does not necessarily form a color contrast with the perspective view color of the color shifting coating, since the contrast is already achieved by the different opacity. For embodiments in which the optically variable micro-lens feature should be hidden in plan view, the color used is suitably chosen so as to be colorless with respect to the plan view color.

[0045] Further embodiments and advantages of the application are described below with reference to the accompanying drawings, which are not true to scale for greater clarity.

[0046] In the drawings:

[0047] Figure 1 a schematic view of a banknote having an optically variable security element according to the application is shown,

[0048] Figure 2 a cross-section of a portion of a security element according to the application is shown,

[0049] Figure 3 a cross-section of a portion of a security element according to another embodiment of the application is shown, and

[0050] Figure 4 a cross-section of a portion of a security element according to yet another embodiment of the application is shown.

[0051] The application will now be explained by way of example with a security element for a banknote. To this end, Figure 1A schematic view of a banknote 10 is shown, which has an optically variable security element 12 according to the present application in the form of a pasted transfer element. However, it is to be understood that the present application is not limited to transfer elements and banknotes, but can be used for all types of security elements, for example for labels on goods and packaging, or for the protection of documents, identity cards, passports, credit cards, health cards, etc. For banknotes and similar documents, in addition to transfer elements, for example, security threads or security strips can also be considered. The present application is preferably suitable for patches and so-called LEAD (Long Lasting Economical Anticopy Device) strips. In the case of a paper substrate, these are present in the form of L-shaped patches and L-shaped LEAD strips, in the case of a polymer substrate, also a transfer variant (T-shaped LEAD) is present. The main difference between L-shaped LEAD strips and T-shaped LEAD strips is that for T-shaped LEAD strips, the carrier foil, if present, is removed after application to the valuable document substrate, if necessary, whereas for L-shaped LEAD strips, at least the stabilizing foil remains in the foil structure. The valuable document substrate can also be a paper / polymer composite substrate in addition to a paper base or a polymer base.

[0052] Figure 1 The shown security element 12 is arranged in a window area 14 of the banknote 10 and covers there a continuous opening or a transparent partial area of the banknote. When the banknote 10 is viewed in plan view, especially against a dark background, the security element 12 appears uniformly metallically reflective gold to the observer (viewing situation R in Fig. 16-R). Figure 1 This plan view appearance 16-R remains essentially unchanged in a back-and-forth tilt 18 of the security element 12.

[0053] However, if the banknote 10 is viewed in perspective against a light background, the appearance of the security element 12 changes significantly: the security element 12 now appears blue instead of gold, and upon tilting also shows different images in different viewing directions. For example, the security element 12 appears uniformly blue in a first angular range around the vertical viewing direction (viewing situation T1 in Fig. 16-T1). Figure 1 When the banknote 10 is tilted downwards, an image 16-T2 with a bright colored denomination number "10" and a blue background appears in a second angular range around the oblique viewing angle (viewing situation T2 in Fig. 16-T2). Figure 1 When the banknote 10 is tilted upwards, an image 16-T3 with a number of bright stars and a blue background appears in a third angular range around the oblique viewing angle from below (viewing situation T3 in Fig. 16-T3). Figure 1

[0054] ​Thus, the security element 12 combines a plurality of interacting variable optical effects, namely, on the one hand, the gold / blue color shift effect when switching from an overhead view to a perspective view, and, on the other hand, the tilted image effect (uniform blue - denomination number "10" - bright star) based on the lenticular features, which is not visible in an overhead view, but which surprisingly only appears to the observer when viewing in perspective and tilting the security element. The security element 12 also presents a visual attraction when viewing the banknote 10 from the back side, since the color shift effect is also visible in a back side view and can further increase the visual attraction, for example, by combination with negative text.

[0055] The special structure and function of the security element according to the present application will now be explained further with reference to the following figures, which show a cross-section of a portion of a security element according to the present application, respectively. Figures 2 to 4 The special structure and function of the security element according to the present application will now be explained further with reference to the following figures, which show a cross-section of a portion of a security element according to the present application, respectively.

[0056] Firstly, reference is made to Figure 2 The security element 20 comprises an (optional) transparent carrier foil 26, the upper side of which is provided with a lenticular grid 22 consisting of a plurality of lenticules 24 arranged in a grid. In this embodiment, the lenticules 24 are arranged two-dimensionally in a regular hexagonal grid with a grid period of 20 pm.

[0057] On the lower side of the carrier foil 26, a color shift coating 30 is applied, which is formed by a semi-transparent three-layer layer system consisting of a 5 nm thick aluminum layer 32, a 240 nm thick Si02 layer 34 and a further 5 nm thick aluminum layer 36.

[0058] The security element 20 typically also comprises further layers, such as primer layers, protective layers, cover layers or additional functional layers, which are not critical here and are therefore not described in detail.

[0059] In Figure 2 In the subsequent figures, the layer thicknesses of the layers 32, 34, 36 of the layer system of the color shift coating 30 are greatly exaggerated for illustration. In practice, for a three-layer layer system with two semi-transparent metal layers and a dielectric spacer layer therebetween, the layer thicknesses are suitably between 50 nm and 600 nm (dielectric spacer layer) and between 3 nm and 20 nm (semi-transparent metal layers), thus only a small fraction of the size of the lenticules 24 or the carrier foil 26.

[0060] By the interaction of the two semi-transparent aluminum layers 32, 36 and the dielectric spacer layer 34, the layer system constitutes the color shift coating 30, which appears gold in an overhead view or reflection, and blue in a perspective view, i.e. transmission.

[0061] By varying the thickness of the dielectric SiO2 layer 34, other color-shifting effects for planar or perspective viewing can also be produced. For example, when the thickness of the SiO2 layer is 270 nm, the color-shifting coating appears purple in planar viewing and green in perspective viewing. By further varying the thickness of the dielectric layer, other color combinations can also be achieved.

[0062] For the security element 20, the thickness of the carrier foil 26 and the focal length of the microlenses 24 are coordinated with each other such that the color-shifting coating 30 is located substantially in the focal plane of the microlenses 24. This can be easily achieved since the thickness of the color-shifting coating 30 (250 nm) is much smaller than the focal length of the microlenses (typically 10 pm to 40 pm). The carrier foil 26 at the same time acts as a mechanical carrier and an optical spacer.

[0063] In order to produce the images 16-T2, 16-T3, microstructures 40 or 42 are formed in the color-shifting coating 30, which are arranged in the same grid as the microlenses 22, respectively.

[0064] In the embodiment of Fig. 1, the microstructures 40 and 42 are formed by microscopic openings in the color-shifting coating 30, which appear bright when illuminated in perspective from the underside of the security element 20, i.e. from the opposite side of the lens grid. Figure 2

[0065] The microstructures 40 and 42, as is known from the principle of lens tilt images, produce the desired pattern by their spatial arrangement, here the denomination number “10” (microstructures 40) or a bright star (microstructures 42).

[0066] The microstructures 40 and 42 are slightly offset with respect to the center of the microlenses 22, so that in vertical perspective viewing, neither of the images 16-T2, 16-T3 is visible, and the security element 20 appears uniformly blue (appearance 16-T1). Only when the security element 20 is tilted, the observer looks through the microlenses 24 or lens grid 22 at the microscopic openings of the microstructures 40 (viewing situation T2) or 42 (viewing situation T3), which appear bright in transmitted light, the images unexpectedly emerge.

[0067] Due to the larger diameter of the microstructures 42, the visible angular range of the image 16-T3 is larger than that of the denomination number “10” of the image 16-T2, which flashes only essentially when the observer looks through the security element 20 exactly from the tilt angle of the viewing situation T2.

[0068] As Figure 2 ​As also shown, the microstructure micro-openings can either run through the entire colorshift coating 30 (as microstructure 40) or only cover part of the layer (as microstructure 42). Since the color effect of the colorshift coating 30 is based on the combined effect of all three sub-layers 32, 34, 36, even if only the upper aluminum layer 36 is hollowed out, the blue perspective color is suppressed, so that the microstructure 42 appears bright against the blue background of the complete colorshift coating 30. However, since the remaining layer 32 reflects or absorbs part of the light, the microstructure 42 appears slightly darker than the microstructure 40, since the microstructure 40 also contains hollows in the lower aluminum layer 32 and the microstructure 40 runs through the entire colorshift coating 30.

[0069] The microstructures 40, 42 can be exposed by, for example, laser irradiation. If a laser beam is used to irradiate the colorshift coating 30 located in the focal plane through the micro-lens 24, the colorshift coating is ablated at the focal point or the metal is converted into a transparent modification. By exposing from different directions, different images 16-T2, 16-T3 can be exposed, so that inclined images are formed.

[0070] Instead of exposing exactly on the focal plane, it is also possible to expose slightly outside the focal plane. In this way, the circular ablation face is slightly larger, so that it is also visible over a larger angular range (microstructure 42). Alternatively, the generation of the microstructures 40, 42 can also be achieved by embossing and etching or selective metal transfer, as described in more detail above.

[0071] Figure 3 A security element 50 according to another embodiment of the application is shown, which has a similar basic structure to the security element of Figure 2 but the microstructure for generating the image is not formed by openings in the colorshift coating, but by small colored microstructure elements 52 arranged on top of the colorshift coating (between the carrier foil 26 and the colorshift coating 30). For simplicity, only one image's microstructure element 52 is shown, but it is understood that microstructure elements for multiple images can also be generated in this way.

[0072] In the embodiment of Figure 3 a layer of UV embossing lacquer 54 is applied on the carrier foil 26 and embossed in the form of the desired microstructure elements, so that a surface relief consisting of raised and recessed areas is formed. The embossed recesses, which are usually a few micrometers deep, are filled with a suitable contrasting color using a microstructure color filling method known per se, and then the colorshift coating 30 is applied.

[0073] When viewed through the lens grid 22, the microstructure elements 52 contrast in color both with the viewing color of the colorshift coating 30 and with the perspective color. Thus, when viewed from above, the observer perceives an optically variable lenticular effect with a background in the viewing color (gold color) of the colorshift coating 30. The image produced by the color-filled recesses appears in the color of the color filling. In perspective, the background color then corresponds to the perspective color (blue color in the embodiment) of the colorshift coating 30, while the image produced by the color-filled recesses is perceived through the colorshift coating 30 and the color of the color filling (possibly with a certain reflection color component). When viewed from the back, the image produced by the color-filled recesses is only weakly visible in the viewing color (gold color) when viewed from above. When viewed in perspective, the observer perceives a background with the perspective color and an image filtered through the color of the color filling and the colorshift coating 30 (the more directional the illumination, the more clearly).

[0074] In a variant of this embodiment, the microstructure elements use a color that absorbs light and thus appears opaque in perspective. In this case, the color used does not have to contrast in color with the perspective color of the colorshift coating 30, since the contrast is already achieved by the different opacity. If the optically variable lenticular effect should remain hidden in the viewing from above, the color used is selected to be color-contrasting with the viewing color.

[0075] Figure 4 Another principle for the formation of the microstructure producing an image in a security element according to the application is illustrated. Figure 4 The security element 60 has a basic structure similar to the security element of Figure 2 but the microstructure 62 producing an image is formed by embossed height differences in the colorshift coating. For simplicity, only one microstructure element 62 of an image is shown, but it is understood that microstructure elements for multiple images can also be produced in this way.

[0076] In this variant, a UV embossing lacquer layer 64 can also be applied to the carrier foil 26 for this purpose and embossed in the form of the desired microstructure elements, thus forming a surface relief composed of raised and recessed areas. When the colorshift coating 30 is applied to the embossed lacquer layer 64, the surface relief is transferred into the colorshift coating 30.

[0077] For illustration, the layer thicknesses of the layers 32, 34, 36 of the layer system of the colorshift coating are also greatly exaggerated here. In reality, the typical height differences of the surface relief are in the range of a few micrometers, while the layer thicknesses of the layer system 32, 34, 36 are only about 250 nm, for example.

[0078] The embossed height differences can also be combined with the openings and the de- metallized areas according to Figure 2 and / or with the recesses according to Figure 3The color filling of the recesses in combination with the micro-lens features is also well perceived in planar view. When viewed from above, the observer sees the optically variable micro-lens effect through the micro-lenses 24, which presents the planar color of the colorshift coating 30 (in the embodiment a gold color), wherein the image is defined by the contours or edges of the embossed image-producing microstructures 62. In perspective, the same micro-lens effect is visible in the perspective color or background color of the colorshift coating 30 (in the embodiment a blue color), wherein in this case the image is likewise defined by the contours or edges of the embossed image-producing microstructures 62. When viewed from the back, the micro-lens features can only be seen in reduced clarity and altered form depending on the lighting situation, but the color change typical for the colorshift coating 30 when switching from the planar view situation to the perspective view situation is also clearly visible in this case.

[0079] The security elements 20, 50, 60 can further enhance their visual appeal by employing a transparent design in local areas of the window area 14. To this end, the colorshift coating is removed in these local areas, enabling the observer to immediately recognize the window 14 as a window. In order to increase the appeal and the security against forgery of the security element, the transparent local areas can in particular be composed of negative indicia, for example in the form of small alphanumeric characters or other patterns still discernible to the naked eye.

[0080] On the underside of the security elements 20, 50, 60 other layers can be included, for example a primer layer, a protective lacquer layer, a cover layer or an adhesive layer, in particular a UV-cured hot-seal adhesive layer for connecting the security element to a target substrate such as the banknote 10.

[0081] The micro-lenses 24 can also be equipped with further layers, in particular a protective lacquer layer not shown in the figures, the refractive index of which preferably differs from the refractive index of the micro-lenses 24 by at least 0.3. In this case, the protective lacquer layer changes the focal length of the lenses, which must be taken into account when determining the lens radius of curvature and / or the thickness of the spacer layer. In addition to protection from the environment, such a protective layer also prevents easy copying of the micro-lenses 24 of the lens grid for counterfeiting purposes.

[0082] List of reference signs

[0083] 10 banknote

[0084] 12 security element

[0085] 14 window area

[0086] 16-R viewing situation, reflective

[0087] 16-T1, 16-T2, 16-T3 viewing situation, transmissive

[0088] 20 security element

[0089] 22 lens grid

[0090] 24 microlenses

[0091] 26 carrier foil

[0092] 30 color-shifting coating

[0093] 32 aluminum layer

[0094] 34 SiO2 layer

[0095] 36 aluminum layer

[0096] 40 microstructure

[0097] 42 microstructure

[0098] 50 security element

[0099] 52 colored microstructure element

[0100] 54 embossed lacquer layer

[0101] 60 security element

[0102] 62 image-generating microstructure

[0103] 64 embossed lacquer layer

Claims

1. An optically variable see-through security element for protecting a data carrier, comprising - a lens grid composed of a plurality of microlenses arranged in a first grid, the refractive action of which microlenses defines a focal plane, - a colorshifting coating which is located substantially in the focal plane of the lens grid, which colorshifting coating exhibits different colors in plan view and in see-through view, and - a microstructure arrangement which is located substantially in the focal plane of the lens grid, which microstructure arrangement is composed of a plurality of microstructures arranged in a second grid, which microstructures produce one or more images in a preset viewing direction when viewed in see-through view through the lens grid, - wherein the microstructures are formed in or directly on the colorshifting coating.

2. The see-through security element of claim 1, wherein, The microstructures are formed at least partially by microscopic openings in the colorshifting coating.

3. A see-through security element according to claim 1 or 2, characterised in that, The microstructures are formed at least partially by laser-ablated local regions or by local regions of the colorshifting coating which are converted into transparent modifications by laser radiation.

4. The see-through security element according to at least one of claims 1 to 3, characterized in that The microstructures are formed at least partially by colored microstructure elements on or in the colorshifting coating.

5. The see-through security element according to at least one of claims 1 to 4, characterized in that The microstructures are formed at least partially by raised or recessed local regions of the colorshifting coating.

6. The see-through security element according to at least one of claims 1 to 5, characterized in that The position and shape of the microstructures are selected such that, when the microstructure arrangement is viewed through the lens grid, optically variable microlens effects, in particular tilting effects, magnification effects, movement effects, depth effects, distortion effects and / or pumping effects, can be perceived.

7. The see-through security element according to at least one of claims 1 to 6, characterized in that The first grid and the second grid have the same grid spacing and the same orientation.

8. The see-through security element according to at least one of claims 1 to 6, characterized in that The grid spacing of the first grid and the second grid is different, and / or the first grid and the second grid are rotated relative to one another.

9. The see-through security element according to any one of claims 1 to 8, characterized in that The lens grid is a one-dimensional grid with a defined grid spacing, or a regular two-dimensional grid, in particular a hexagonal, square, rectangular or parallelogram grid.

10. The see-through security element according to any one of claims 1 to 9, characterized in that The lens grid and the colorshifting coating are formed on opposite sides of a transparent carrier foil.

11. The see-through security element according to any one of claims 1 to 10, characterized in that The colorshifting coating is formed from a three-layer layer system with two semitransparent metal layers and a dielectric spacer layer located therebetween.

12. The see-through security element of claim 11, wherein, The dielectric spacer layer has a layer thickness of between 50 nm and 600 nm, preferably between 100 nm and 400 nm, and / or is formed from one of the materials ZnS, SiO2, MgF2 and Al2O3.

13. A see-through security element according to claim 11 or 12, characterised in that, The semitransparent metal layers have a layer thickness of between 3 nm and 20 nm, preferably between 5 nm and 10 nm, and / or are formed from Al, Cr, Ag, Cu, Fe, Ni, Au or an alloy containing one or more of these elements.

14. The see-through security element according to any one of claims 1 to 13, characterized in that The colorshifting coating is left free in local regions of the security element, preferably in the form of negative indicia, particularly preferably in the form of small alphanumeric characters which are still distinguishable to the naked eye.

15. A data carrier having a see-through security element according to any one of claims 1 to 14, which see-through security element is arranged in or on a light-transmissive local region of the data carrier.

16. A method for producing an optically variable see-through security element, in particular according to any one of claims 1 to 14, wherein - a lens grid composed of a plurality of microlenses arranged in a first grid is produced, - a color-shifting coating which appears different in plan view and in perspective is essentially arranged in the focal plane of the lens grid, and - a microstructure arrangement consisting of a plurality of microstructures arranged in a second grid is formed in or directly on the color-shifting coating.

17. The method of claim 16, wherein, The microstructures are defined at least partially by embossing into the UV lacquer in such a way that the regions to be removed are provided with a fine structure, preferably with a high aspect ratio, wherein after the application of the color-shifting coating, at least one of the color-shifting coating or the semi-transparent metal layers of the color-shifting coating is removed in the fine-structured regions, while the color-shifting coating is retained in the unstructured regions.

18. The method of claim 16 or 17, wherein, The microstructures are defined at least partially by embossing into the UV lacquer, resulting in a surface relief consisting of raised and recessed regions, wherein the recessed regions are filled with a particularly contrasting color, and subsequently the color-shifting coating is applied, or wherein the color-shifting coating is applied to the surface relief consisting of raised and recessed regions, and subsequently the recessed regions are optionally filled with a particularly contrasting color.

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