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

Abstract

The invention relates to an optically variable see-through security element (12) for safeguarding data carriers (10), comprising a lens grid (22) composed of a plurality of microlenses (24) which are arranged in a first grid and the refractive effect of which defines a focal plane, a color change coating (30), which is substantially arranged in the focal plane of the lens grid (22) and exhibits different colors in a plan view and in a see-through view, and a microstructure arrangement substantially arranged in the focal plane of the lens grid (22) and composed of a plurality of microstructures (40, 42) which are arranged in a second grid and generate one or more motif images (16-T2, 16-T3) when viewed through the lens grid (22) in a see-through view in predefined viewing directions. In this case, the microstructures (40, 42) are formed in or directly on the color change coating (30).

Description

[0001] Optically variable see-through security element,

[0002] Data carriers and manufacturing processes

[0003] The invention relates to an optically variable see-through security element, a data carrier with such a see-through security element, and a method for producing such a see-through security element.

[0004] Data storage media, such as valuables or identification documents, but also other valuable items, such as branded goods, are often provided with security elements for security purposes. These elements allow the authenticity of the data storage media to be verified and at the same time serve as protection against unauthorized reproduction.

[0005] See-through security features, such as see-through windows in banknotes, are becoming increasingly important because they are easy to detect but difficult to counterfeit.

[0006] Attempts have already been made to use microlens features in see-through security elements, such as the see-through windows of banknotes. While the microlens features in such see-through windows appear quite attractive when viewed from the front, they are often blurred from the back and, due to the strong light refraction at the individual lenses and the associated scattering effect of the window as a whole, are rather unattractive in transmitted light. On the other hand, with colored microlens features, the static optical impression can often be easily reproduced even with a color copier, so the counterfeit security is not optimal.

[0007] Based on this, the invention is based on the object of providing an optically variable see-through security element with an attractive visual appearance and a high level of forgery protection. The invention also aims to provide a valuable document with such a see-through security element and a manufacturing method for such a see-through security element.

[0008] This object is achieved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

[0009] The invention provides an optically variable see-through security element for securing data carriers, in particular banknotes and other value documents.

[0010] The see-through security element contains a lenticular array composed of a plurality of microlenses arranged in a first array, the refractive power of which defines a focal plane. It contains a color-changing coating arranged substantially in the focal plane of the lenticular array, which displays different colors in plan and transmitted view. It also contains a microstructure arrangement arranged substantially in the focal plane of the lenticular array, composed of a plurality of microstructures arranged in a second array, which generate one or more motif images when viewed through the lenticular array in transmitted view in predetermined viewing directions. The microstructures are formed in or directly on the color-changing coating.

[0011] The see-through security element according to the invention is based on a combination of at least two interwoven, optically variable effects: a color-changing effect when switching between top and bottom view, and an optically variable microlens feature, which can be concealed, particularly in top view, and only surprisingly reveals itself when viewing and tilting the security element in the view through. Furthermore, the color-changing effect is also visible when viewed from the back when switching from top view to bottom view, so that the security element presents a visually attractive appearance in all viewing situations.

[0012] In a preferred embodiment, the microstructures are formed at least partially by microscopic openings in the color-change coating. Microscopic openings are those openings that, in contrast to larger-area negative markings, are difficult or impossible to resolve with the naked eye. Typically, the microscopic openings have diameters of a few micrometers, specifically from 1 μm to 10 μm.

[0013] A combination of microstructures in the form of microscopic openings and larger-area negative marks represents a particularly preferred embodiment. The negative marks are perceived by the viewer as static, while the microlensing effects created by the microscopic openings in conjunction with the microlenses change or move when tilted. These movements are particularly clearly perceived against the stationary reference points created by the negative marks.

[0014] Advantageously, the microstructures are formed at least partially by laser-ablated sections or by sections of the color-change coating that have been converted into a transparent modification using laser radiation. For optimal ablation or conversion, the wavelength of the laser used can be adapted to the thickness of a dielectric spacer layer of the color-change coating, which will be discussed in more detail later.

[0015] According to another, likewise advantageous embodiment, the microstructures are at least partially formed by colored microstructural elements above or in the color-change coating.

[0016] Advantageously, the microstructures can also be formed at least partially by raised or recessed sections of the color-changing coating. In a particularly simple embodiment, the microstructures consist of embossed structures provided with the color-changing coating over their entire surface. The embossed structures can be embossed, in particular, into a thermoplastic lacquer or a radiation-curing lacquer, preferably a UV lacquer. The raised and recessed sections can take on a variety of shapes and geometries, including, but not limited to, structures with asymmetrical or symmetrical cross-sectional profiles, structures with trapezoidal cross-sectional profiles, binary structures, structures with stepped relief, and / or concave or convex structures, whereby the cross-sectional profile can also be formed with rounded edges.

[0017] The aforementioned designs of the microstructures can also be combined; for example, raised or depressed sections of the color-change coating or openings in the color-change coating can be filled with a suitable color. For example, a first motif image of the security element can be formed by microstructures in the form of microscopic openings, and a second motif image by colored microstructural elements. If the microstructures are not pure openings or demetallized areas in the color-change coating, but additionally contain embossed height differences, which are optionally filled with a contrasting color, the microlens feature is clearly visible not only when viewed through, but also when viewed from above via the outlines or edges of the microstructures that create a motif image. When viewed from the front, the optically variable microlens effect is then visible in the surface color of the color-change coating.When viewed through the lens, the same microlens effect is visible in the transparent color of the color-change coating. Viewed from the back, the microlens feature may be seen with reduced sharpness and in a modified form depending on the lighting conditions, but the color change typical of the color-change coating when transitioning from a top-down to a translucent viewing situation is still clearly visible.

[0018] In an advantageous embodiment, the first grid of microlenses and the second grid of microstructures have the same grid width and the same orientation. This does not preclude the two grids from being offset from each other in the plane, so that no motif image is visible when viewed perpendicularly. The functionality of the microlens feature then essentially corresponds to the functionality of a lens tilt image.

[0019] In another, equally advantageous embodiment, the grid widths of the first and second grids differ and / or the first and second grids are rotated relative to one another. The differences in the grid width are advantageously a few percent at most, and the rotation of the grids relative to one another is advantageously a few degrees at most. The functionality of the microlens feature in such grids corresponds to the functionality of a moiré magnification arrangement or a so-called modulo magnification arrangement. The basic principles of such micro-optical display arrangements are explained in the publication WO 2009 / 000528 A1, the disclosure of which is incorporated into the present description in this respect.

[0020] The lenticular grid is advantageously a one-dimensional grid with a defined grid width or a regular two-dimensional grid, in particular a hexagonal, square, rectangular, or parallelogram-shaped grid. The grid width or grid period is typically between 500 μm and 3 μm, preferably between 50 μm and 5 μm, particularly preferably between 30 μm and 8 μm.

[0021] The spacing between adjacent microlenses is preferably small to ensure high surface coverage and thus a high-contrast image. Spherically or aspherically designed microlenses preferably have a diameter between 5 gm and 50 gm, and in particular a diameter between only 10 gm and 35 gm, and are therefore not visible to the naked eye. Rod-shaped microlenses advantageously have a width between 5 gm and 50 gm, in particular between 10 gm and 35 gm. The length of rod lenses can be considerably greater, reaching several millimeters or even centimeters.

[0022] The lenticular grid and the color-change coating are advantageously formed on opposite sides of a transparent carrier film, such as a PET film. The carrier film serves both as a mechanical support and as an optical spacer.

[0023] The color-change coating is advantageously formed by a three-layer system with two semi-transparent metal layers and an intermediate dielectric spacer layer. The dielectric spacer layer expediently has a layer thickness between 50 nm and 600 nm, preferably between 100 nm and 400 nm, and / or is formed from one of the materials ZnS, SiCb, MgF?, and Al2O3. The semi-transparent metal layers expediently have a layer thickness 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 alloys containing one or more of these elements. Such three-layer systems are particularly well suited to creating a color-change effect in top view / transparent view. The thicknesses of the two semi-transparent metal layers can, but do not necessarily have to, be the same.

[0024] Although three-layer systems are currently preferred, the color-change layer can in principle also be formed by a thin Si layer with a thickness on the order of 10 nm, alone or in combination with a semitransparent metal layer. Another alternative is the use of a single dielectric layer whose refractive index is sufficiently different from the refractive indices of the two surrounding layers.

[0025] In an advantageous development of the invention, the color-changing coating is recessed in a partial area of ​​the security element, preferably in the form of negative characters and particularly preferably in the form of negative writing in the form of small alphanumeric characters that can still be resolved with the naked eye.

[0026] The position and shape of the microstructures are preferably selected so that a viewer of the security feature sees the desired optically variable effects when looking through the microlens array onto the microstructure level. For example, the following effects can be realized: a tilt effect between two images with a meaningful connection between the two images, a tilt effect between two images without a meaningful connection between the two images, a tilt effect between any number of images with a meaningful connection between the individual images, a tilt effect between any number of images without a meaningful connection between the individual images, magnification, movement, and depth effects, morph effects, or pump effects.Depth effects are understood to mean different three-dimensionally perceptible effects, in particular they include motifs that are perceptible in a specific plane spaced from the viewing plane in the z-direction, motifs in different, discrete z-planes, as well as three-dimensionally perceptible objects in areas that extend continuously in the z-direction.

[0027] The microlensing effects can occur when the security feature is tilted around various axes lying 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 grating type.

[0028] The surface area provided with microstructures can extend over the entire area of ​​the color-change coating, but it can also occupy only a portion of it of any shape. The surface areas containing microstructures can be congruent or almost congruent with the surface areas provided with microlenses, but they can also be smaller or larger, or extend beyond the microlens surface in some places or recede behind it. However, it is always advantageous to have an overlap that is clearly visible to the naked eye.

[0029] An advantageous option for making a window area covered by a see-through security element even more recognizable is to overlay the microlens-filled surface areas approximately congruent with the surface areas coated with the color-change coating. This is technologically very challenging, since the microlens embossing or coating with the embossable coating, on the one hand, and the demetallization of the color-change coating, on the other, take place in different and independent processes. Therefore, registering the microlens-containing surfaces congruently, or at least almost congruently, with the color-change coating requires complex technical equipment, thereby further increasing the security element's counterfeit protection.

[0030] At the same time, the window area becomes more visible because the light-scattering effect of the microlenses is eliminated in the transparent areas without the color-change coating, so that a viewer not only perceives these areas in full brightness, but can also see objects through the window area in good sharpness.

[0031] In a further advantageous embodiment, the optically variable microlens effect is designed so that it is either not perceptible or very difficult to perceive when viewed from above. A viewer then sees only the window area and the color-changing coating with its special outline. As soon as the viewer changes the viewing situation so that light of sufficient brightness falls from behind through the security element into their eye, they not only perceive the color-changing effect of the color-changing coating in the form of the motif represented by its outline, but also, surprisingly, the microlens effect and any negative markings.

[0032] This is particularly successful when the microstructures are formed purely from openings in the color-change coating, which are produced, for example, by laser ablation, and are advantageously small, i.e. they only take up a small proportion of the total area. In incident light, the small openings are then outshone by the reflective effect of the predominantly semi-transparent mirrored surface, so that the viewer does not notice them. The small openings only become visible when a strong light source behind the security feature shines so much light onto the security element that it dominates the portion incident from the front and reflected. Tilt effects, in which the motifs are only visible over small solid angles, are particularly suitable for this embodiment. To achieve small solid angles, the color-change coating should be located as closely as possible in the focal plane of the laser.

[0033] The invention also includes a data carrier with a see-through security element of the type described, which is arranged in or above a translucent partial region 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 composite film banknote, a share, a bond, a certificate, a voucher, a check, a seal, a tax stamp, a high-value admission ticket, or even an identification card, such as a credit card, a bank card, a cash payment card, an authorization card, an identity card, or a passport personalization page. The translucent partial region is, in particular, a through-opening in the data carrier, for example, a hole in a paper banknote, which is covered by the see-through security element.

[0034] Finally, the invention also includes a method for producing an optically variable see-through security element of the type described, in which a lenticular grid is produced from a plurality of microlenses arranged in a first grid, a color-changing coating which shows different colors in plan and transmitted view is arranged substantially in the focal plane of the lenticular grid, and a microstructure arrangement from a plurality of microstructures arranged in a second grid is formed in or directly on the color-changing coating.

[0035] The microlenses are preferably produced by hot stamping into a thermoplastic material or by embossing into a UV-curable material, accompanied and / or followed by UV exposure. To protect them from contamination or other environmental influences, the lenses can be embedded in a material with a different refractive index. The difference in refractive index between the lens material and the embedding material, in addition to the radius of curvature of the lenses, affects the focal length, which must be taken into account when designing the security element. The layer systems advantageously used for the color-change layer are usually produced over the entire surface, with PVD processes being the most common. Examples include electron beam vapor deposition, boat vapor deposition, sputtering, and the like.In preferred embodiments, the fully applied layer is subsequently laterally structured to give it visually attractive outlines, for example, in the form of alphanumeric characters or other motifs. This partial lateral removal of the layer system can be carried out using etching or lift-off processes known from the prior art. This creates transparent sections that are visible to the naked eye and are also referred to as negative markings in this description.

[0036] The following processes are particularly suitable for the production of microstructures:

[0037] Laser exposure: If a laser is used to illuminate the color-change coating, which is essentially located in the focal plane, through the microlenses, this coating is ablated at the focal points (in the case of spherical lenses) or the focal lines (cylindrical lenses), or the metal is converted into a transparent modification. In this way, different images can be exposed from different directions, creating a tilted image. Instead of exposing into the focal plane, exposure can also be made slightly outside the focal plane. This makes the ablated circular areas or lines somewhat larger and therefore visible from a wider angle. The microstructures forming the microscopic openings can also be (pre)defined by embossing into a UV varnish, whereby the areas to be removed are provided with fine structures, preferably with a high aspect ratio.After coating with the color change coating, an etching process is carried out which removes the coating, or at least one of the metal layers, in the finely structured areas, while the coating remains in the non-structured areas.

[0038] Selective metal transfer can also be used to produce the microstructures forming the microscopic openings: UV embossing is used to create microstructures on a first film with raised or depressed areas relative to the surroundings. After coating with the color-change coating, which is not adhesive, the first film is bonded to a second film with a fully applied adhesive layer. When the second film is peeled off, the parts of the color-change coating located on the raised areas of the first film (the donor film) or the background (in the case of depressed structures) are also peeled off and remain on the second film (the acceptor film). Both films can be equipped with microlenses and further processed into a security element according to the invention.

[0039] In another preferred embodiment, the microstructures contrast in color with the visible and / or transparent color of the color-change coating. In this embodiment, the microstructures can be defined by embossing with UV varnish, creating a surface relief consisting of raised and depressed areas. Subsequently, the depressions are filled with a suitably contrasting color using known color-filling processes for microstructures, and then the color-change coating is applied. Depending on the structure of the security element, it may also be useful to reverse the order of color filling and coating.

[0040] In a variation of this design, a color that absorbs light and thus appears opaque when viewed through the coating is used to fill the recesses. In this case, the color used does not need to contrast with the transparent color of the color-change coating, as the contrast is already achieved through the different opacity. In designs where the optically variable microlens feature is intended to be concealed when viewed through the coating, the color used is preferably chosen without contrasting with the visible color.

[0041] Further embodiments and advantages of the invention are explained below with reference to the figures, in which a true-to-scale and true-to-proportion reproduction has been omitted in order to increase clarity.

[0042] They show:

[0043] Fig. 1 is a schematic representation of a banknote with an optically variable security element according to the invention,

[0044] Fig. 2 shows a section of a security element according to the invention in cross section,

[0045] Fig. 3 shows a section of a security element according to another embodiment of the invention in cross section, and Fig. 4 shows a section of a security element according to a further embodiment of the invention in cross section.

[0046] The invention will now be explained using the example of security elements for banknotes. Figure 1 shows a schematic representation of a banknote 10 with an optically variable security element 12 according to the invention in the form of an adhesive-applied transfer element. It is understood, however, that the invention is not limited to transfer elements and banknotes, but can be used for all types of security elements, for example, labels on goods and packaging or for securing documents, ID cards, passports, credit cards, health cards, and the like. For banknotes and similar documents, in addition to transfer elements, security threads or security strips, for example, are also possible. The invention is preferably intended for patches and so-called LEAD (Longlasting Economical Anticopy Device) strips.In the case of paper substrates, these are available in the form of L-patches and L-LEAD strips, and in the case of polymer substrates, also in transfer variants (T-LEAD). L-LEAD strips differ from T-LEAD strips primarily in that, with a T-LEAD strip, any carrier film is usually removed after application to a security document substrate, whereas with an L-LEAD strip, at least one stabilizing film remains in the film structure. Security document substrates can be paper or polymer substrates, as well as paper / polymer composite substrates.

[0047] The security element 12 shown in Fig. 1 is arranged in a window area 14 of the banknote 10 and covers a continuous opening or a transparent portion of the banknote. When viewing the banknote 10 from above, particularly against a dark background, the security element 12 appears to an observer to be uniform with a metallically reflective gold color (Figure 16-R, viewing situation R in Fig. 1). This top-view appearance 16-R remains essentially unchanged when the security element 12 is tilted back and forth 18.

[0048] However, if the banknote 10 is viewed through a light background, the appearance of the security element 12 changes significantly: Instead of gold, the security element 12 now appears blue and, when tilted, also displays different image motifs in different viewing directions. For example, the security element 12 appears uniformly blue in a first angular range around the vertical viewing direction (image 16-T1, viewing situation T1 in Fig. 1). When the banknote 10 is tilted downward, an image 16-T2 with the bright value number "10" appears against a blue background in a second angular range around an oblique viewing angle (viewing situation T2 in Fig. 1). While when the banknote 10 is tilted upward, an image 16-T3 with several bright stars appears against a blue background in a third angular range around an oblique viewing angle from below (viewing situation T3 in Fig. 1).

[0049] The security element 12 therefore combines several interacting optical variable effects, namely, on the one hand, a gold / blue color change effect when changing from top view to back view and, on the other hand, a tilting image effect based on a microlens feature (uniform blue - value number "10" - bright stars), which is not visible when viewed from top view but, to the viewer's surprise, only becomes apparent when viewing and tilting the security element in back view. The security element 12 also appears visually attractive when viewing banknote 10 from the reverse, since the color change effect is also visible when viewed from the reverse, and can be further visually enhanced, for example, by combining it with a negative text.

[0050] The special structure and functioning of security elements according to the invention will now be explained in more detail with reference to Figures 2 to 4, each of which shows a section of a security element according to the invention in cross section.

[0051] Referring first to Fig. 2, the security element 20 contains an (optional) transparent carrier film 26, which is provided on its upper side with a lenticular array 22 comprising a plurality of microlenses 24 arranged in a grid. In the exemplary embodiment, the microlenses 24 are arranged two-dimensionally in a regular hexagonal grid with a grid period of 20 μm.

[0052] A color-changing coating 30 is applied to the underside of the carrier film 26, which is formed by a semi-transparent, three-layer system consisting of a 5 nm thick aluminum layer 32, a 240 nm thick SiO2 layer 34 and a further 5 nm thick aluminum layer 36.

[0053] The security element 20 typically contains further layers, such as primer, protective, covering or additional functional layers, which, however, are not essential here and are therefore not described in detail.

[0054] In Fig. 2 and the other figures, the layer thicknesses of layers 32, 34, and 36 of the layer system of the color-change coating 30 are greatly exaggerated for illustrative purposes. In fact, the layer thicknesses for a three-layer system with two semitransparent metal layers and an intermediate dielectric spacer layer are advantageously between 50 nm and 600 nm (dielectric spacer layer) and between 3 nm and 20 nm (semitransparent metal layer), respectively, and thus amount to only a fraction of the dimensions of the microlenses 24 and the carrier film 26, respectively.

[0055] Through the interaction of the two semi-transparent aluminum layers 32, 36 and the dielectric spacer layer 34, the layer system forms a color-changing coating 30, which appears gold-colored when viewed from above or in reflection and blue when viewed in transmission.

[0056] By varying the thickness of the SiCh dielectric layer 34, different color changes can also be created for top-down and transverse viewing. For example, with a SiCh layer thickness of 270 nm, the color-change coating appears violet in top-down view, while appearing green in transverse view. Other color combinations are also possible by further varying the thickness of the dielectric layer.

[0057] The thickness of the carrier film 26 and the focal length of the microlenses 24 in the security element 20 are coordinated such that the color-change coating 30 lies essentially in the focal plane of the microlenses 24. This is easily possible because the thickness of the color-change coating 30 (250 nm) is significantly smaller than the focal length of the microlenses (typically 10 μm to 40 μm). The carrier film 26 acts simultaneously as a mechanical support and optical spacer. To generate the motif images 16-T2, 16-T3, microstructures 40 and 42, respectively, are formed in the color-change coating 30, each arranged in the same grid as the microlenses 22.

[0058] In the embodiment of Fig. 2, the microstructures 40 and 42 are each formed by microscopic openings in the color-changing layer 30, which, when viewed through, are illuminated from the underside, i.e. the side of the security element 20 opposite the ones grid, and therefore appear bright.

[0059] As is generally known from lens tilt images, the microstructures 40 and 42 create a desired motif through their spatial arrangement, here the representation of the value number "10" (microstructures 40) or the bright stars (microstructures 42).

[0060] The microstructures 40 and 42 are slightly offset from the center of the microlenses 22, so that when viewed vertically through the lens, none of the motif images 16-T2, 16-T3 are visible, but the security element 20 appears uniformly blue (appearance 16-T1). Surprisingly, the motif images only become visible after tilting the security element 20, when the observer looks through the microlenses 24 or the lenticular grid 22 at the microscopic openings of the microstructures 40 (viewing situation T2) or 42 (viewing situation T3), which appear bright in transmitted light.

[0061] Due to the larger diameter of the microstructures 42, the motif image 16-T3 is visible in a larger angular range than the value number "10" of the motif image 16-T2, which practically only flashes when the observer looks through the security element 20 at exactly the oblique angle of the viewing situation T2.

[0062] As also illustrated in Fig. 2, the microscopic openings of the microstructures can extend through the entire color-change layer 30 (as with the microstructures 40), but they can also cover only a portion of the layers (as with the microstructures 42). Since the color effect of the color-change layer 30 is based on the interaction of all three sub-layers 32, 34, 36, the blue transparent color is suppressed by recesses, for example, only in the upper aluminum layer 36, so that the microstructures 42 also appear bright against the blue background of the complete color-change layer 30. However, since the remaining layer 32 reflects or absorbs some of the light, the microstructures 42 appear somewhat darker than the microstructures 40, in which the lower aluminum layer 32 also contains recesses and the microstructures 40 extend through the entire color-change layer 30.

[0063] The microstructures 40, 42 can be exposed, for example, by laser irradiation. If, for example, a laser beam is used to illuminate the color-change layer 30 located in the focal plane through the microlenses 24, the color-change layer is ablated at the focal points or the metal is converted into a transparent modification. By illuminating from different directions, different images 16-T2, 16-T3 can be exposed, creating a tilted image.

[0064] Instead of exposing precisely into the focal plane, exposure can also be performed slightly outside the focal plane. The ablated circular areas are then somewhat larger and thus visible at a wider angle (microstructures 42). Alternatively, the microstructures 40, 42 can be created by embossing and etching or selective metal transfer, as described in more detail above.

[0065] Figure 3 shows a security element 50 according to a further embodiment of the invention, which is fundamentally constructed like the security element of Figure 2, but in which the image-generating microstructures are not formed by openings in the color-change layer, but rather by small colored microstructure elements 52 arranged above the color-change layer (between the carrier film 26 and the color-change layer 30). For the sake of simplicity, only the microstructure elements 52 of one motif image are shown; however, it is understood that microstructure elements for multiple motif images can also be generated in this way.

[0066] In the embodiment shown in Fig. 3, a UV embossing lacquer layer 54 was applied to the carrier film 26 and embossed in the shape of the desired microstructure elements, creating a surface relief consisting of raised and depressed areas. The embossed depressions, whose depth is typically a few micrometers, were filled with a suitably contrasting color using conventional color-filling processes for microstructures, and then the color-change layer 30 was applied.

[0067] When viewed through the ones-grid 22, the microstructural elements 52 stand out in color against both the surface and the transparent color of the color-change layer 30. Accordingly, when viewed from above through the microlenses 24, a viewer perceives the optically variable microlens effect with the surface color (gold) of the color-change layer 30 as the background. The motif image created by the color-filled depressions appears in the color of the color fill. When viewed through the microlenses 24, the background color then corresponds to the transparent color (blue in the exemplary embodiment) of the color-change layer 30, while the motif image created by the color-filled depressions is perceived as color-filtered by the color-change layer 30 and the color of the color fill (possibly with a certain color component due to reflection). When viewed from the back, the motif image created by the color-filled depressions is only faintly visible in the surface color (gold).When viewed in transmission, the viewer perceives the background with the transmission color and the subject image color-filtered by the color of the color fill and the color change layer 30 (the sharper the more directed the lighting is).

[0068] In a modification of this embodiment, a color that absorbs light and thus appears opaque when viewed through is used for the microstructure elements. In this case, the color used does not need to exhibit a color contrast to the transparent color of the color-change layer 30, since the contrast is already achieved through the different opacity. If the optically variable microlens effect is intended to remain concealed when viewed through, the color used is selected without a color contrast to the viewed color.

[0069] A further principle for forming the image-generating microstructures in security elements according to the invention is illustrated in Fig. 4. The security element 60 of Fig. 4 is fundamentally constructed in the same way as the security element of Fig. 2, but the image-generating microstructures 62 are formed by embossed height differences in the color-change layer. For the sake of simplicity, only the microstructure elements 62 of one motif image are shown; however, it is understood that microstructure elements for multiple motif images can also be created in this way. In this variant, too, a UV embossing lacquer layer 64 can be applied to the carrier film 26 for this purpose and embossed in the form of the desired microstructure elements, creating a surface relief consisting of raised and depressed areas. When the color-change layer 30 is applied to the embossing lacquer layer 64, the surface relief is transferred into the color-change layer 30.

[0070] For illustration purposes, the layer thicknesses of layers 32, 34, and 36 of the layer system of the color-change coating 30 are also greatly exaggerated. In fact, typical height differences in the surface relief are in the range of a few micrometers, while the layer thickness of the layer system 32, 34, 36, for example, is only approximately 250 nm.

[0071] The embossed height differences can additionally be combined with openings and demetallized regions according to Fig. 2 and / or with color-filled depressions according to Fig. 3. Such a microlens feature is also clearly visible in plan view. Viewed from above through the microlenses 24, an observer sees the optically variable microlens effect in the view color (gold in the exemplary embodiment) of the color-change layer 30, with the motif image being defined by the outlines or edges of the embossed image-generating microstructures 62. In view through the microlenses 24, the same microlens effect is visible in the view color or background color (blue in the exemplary embodiment) of the color-change layer 30, with the motif image also being defined by the outlines or edges of the embossed image-generating microstructures 62.When viewed from the rear side, the microlens feature can only be seen with reduced sharpness and in a modified form depending on the lighting situation; however, the color change typical for the color change layer 30 when transitioning from a top-view viewing situation to a through-view viewing situation is also clearly visible in this case.

[0072] The security elements 20, 50, 60 can be further visually enhanced by a transparent design in partial areas of the window area 14. For this purpose, the color-changing layer is removed in these partial areas, allowing the viewer to immediately recognize the window 14 as such.

[0073] To increase the attractiveness and forgery protection of the security elements, the transparent partial areas can be formed in particular by negative markings in the form of small, but still resolvable with the naked eye, alphanumeric characters or other motifs.

[0074] On their underside, the security elements 20, 50, 60 may contain further layers, for example a primer layer, a protective lacquer layer, a cover layer or an adhesive layer, in particular a layer of a UV-curable heat-seal adhesive, for connecting the security element to a target substrate, such as the banknote 10.

[0075] The microlenses 24 can also be provided with additional layers, and in particular with a protective lacquer layer (not shown here), whose refractive index preferably deviates by at least 0.3 from the refractive index of the microlenses 24. In this case, the protective lacquer layer changes the focal length of the lenses, which must be taken into account when dimensioning the lens curvature radii and / or the thickness of the spacer layer. In addition to providing protection against environmental influences, such a protective layer also prevents the microlenses 24 of the lenticular array from being easily molded for counterfeiting purposes.

Claims

Patent claims 1. Optically variable see-through security element for securing data carriers, with a lenticular grid consisting of a plurality of microlenses arranged in a first grid, the refractive effect of which defines a focal plane, a color-changing coating arranged substantially in the focal plane of the lenticular grid, which shows different colors in plan and transmitted view, and a microstructure arrangement arranged substantially in the focal plane of the lenticular grid, consisting of a plurality of microstructures arranged in a second grid, which produce one or more motif images when viewed through the lenticular grid in transmitted view in predetermined viewing directions, wherein the microstructures are formed in or directly on the color-changing coating.

2. See-through security element according to claim 1, characterized in that the microstructures are at least partially formed by microscopic openings in the color-change coating.

3. See-through security element according to claim 1 or 2, characterized in that the microstructures are formed at least partially by laser-ablated partial areas or by means of laser radiation into a transparent modification converted parts of the color change coating are formed.

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

5. See-through security element according to at least one of claims 1 to 4, characterized in that the microstructures are at least partially formed by raised or recessed partial regions of the color-change coating.

6. 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 lenticular grid, an optically variable microlens effect, in particular a tilt effect, a magnification effect, a movement effect, a depth effect, a morphing effect and / or a pumping effect is perceptible.

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

8. See-through security element according to at least one of claims 1 to 6, characterized in that the grid widths of the first and second grids differ and / or that the first and second grids are rotated relative to one another.

9. See-through security element according to one of claims 1 to 8, characterized in that the lenticular grid is a one-dimensional grid with a defined grid width, or a regular two-dimensional grid, in particular a hexagonal, square, rectangular or parallelogram-shaped grid.

10. A see-through security element according to one of claims 1 to 9, characterized in that the lenticular pattern and the color-change coating are formed on opposite sides of a transparent carrier film.

11. A see-through security element according to one of claims 1 to 10, characterized in that the color-change coating is formed by a three-layer system with two semi-transparent metal layers and an intermediate dielectric spacer layer.

12. See-through security element according to claim 11, characterized in that the dielectric spacer layer has a layer thickness between 50 nm and 600 nm, preferably between 100 nm and 400 nm and / or is formed from one of the materials ZnS, SiCb, MgF? and Al2O3.

13. See-through security element according to claim 11 or 12, characterized in that the semi-transparent metal layers have a layer thickness 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 alloys containing one or more of these elements.

14. See-through security element according to one of claims 1 to 13, characterized in that the color change coating is in a Part of the security element is left out, preferably in the form of negative markings, particularly preferably in the form of small alphanumeric characters that can still be resolved with the naked eye.

15. A data carrier with a see-through security element according to one of claims 1 to 14, which is arranged in or above a translucent portion of the data carrier.

16. A method for producing an optically variable see-through security element, in particular according to one of claims 1 to 14, in which a lenticular grid is produced from a plurality of microlenses arranged in a first grid, a color-changing coating which shows different colors in plan and seen through is arranged substantially in the focal plane of the lenticular grid, and a microstructure arrangement from a plurality of microstructures arranged in a second grid is formed in or directly on the color-changing coating.

17. The method according to claim 16, characterized in that the microstructures are defined at least partially by embossing into a UV lacquer by providing the areas to be removed with fine structures, preferably with a high aspect ratio, wherein after coating with the color change coating, the color change coating, or at least one of the semi-transparent metal layers of the color change coating, is removed in the finely structured areas, while the color change coating is retained in the non-structured areas.

18. The method according to claim 16 or 17, characterized in that the microstructures are at least partially defined by embossing in UV varnish, so that a surface relief of raised and depressed areas is created, wherein the depressed areas are filled with a particularly contrasting color and then the color-changing coating is applied, or wherein the color-changing coating is applied to the surface relief of raised and depressed areas and then optionally the depressed areas are filled with a particularly contrasting color.

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