METHOD FOR PRODUCING AN OPTICALLY VARIABLE SECURITY ELEMENT

Abstract

A method for manufacturing an optically variable security element, so that for a viewer of the security element, a first color impression is created through the combination of at least the color effects of a first embossing lacquer layer and the coating, and a second, different color impression is created through the combination of the color effects of at least the first embossing lacquer layer, a second embossing lacquer layer and a coating.

Claims

1.-16. (canceled)

17. A method for manufacturing an optically variable security element, in which a carrier is made available, the area extension of which defines a z axis standing perpendicularly thereon, wherein: (A1) a first embossing lacquer layer is applied to the carrier in an area region, (P1) a first relief structure is embossed into the first embossing lacquer layer, (A2) a second, dyed embossing lacquer layer is applied to the first embossing lacquer layer, wherein a color effect of the second embossing lacquer layer differs from a color effect of the first embossing lacquer layer, and wherein the first relief structure is partially covered by the second, dyed embossing lacquer layer and is partially not covered, (P2) into the second embossing lacquer layer there is embossed a second relief structure, which differs from the first relief structure, so that the first relief structure and the second relief structure in the z-direction are arranged at different height levels with reference to the carrier, and (M) a coating is applied to a non-covered portion of the first relief structure and to the second relief structure, so that for a viewer of the security element a first color impression is created through the combination of at least the color effects of the first embossing lacquer layer and the coating, and a second, different color impression is created through the combination of the color effects of at least the first embossing lacquer layer, the second embossing lacquer layer and the coating.

18. The method according to claim 17, wherein the first and/or second embossing lacquer layer is applied by means of screen printing, offset printing, flexographic printing or gravure printing.

19. The method according to claim 17, wherein the second embossing lacquer layer is applied in register with the first relief structure in step (A2).

20. The method according to claim 17, wherein the coating is supplied with recesses after step (M), preferably by either before step (M) printing a washing ink onto the first and/or second embossing lacquer layer and washing out the washing ink together with the coating after step (M), or after step (M) applying a resist lacquer to the coating and removing the coating in the regions not supplied with resist by an etching step.

21. The method according to claim 17, wherein the coating is formed by a, preferably chromatic, color coating, by a metallization with a glazing ink layer, a chromatic metallization or a thin-film structure containing a metal layer.

22. The method according to claim 17, wherein the coating is formed by an achromatic coating, by a metallization, as an achromatic color coating, or by a transparent reflection-increasing layer.

23. The method according to claim 17, wherein the first embossing lacquer layer is colorless, and the second embossing lacquer layer is dyed with a glazing chromatic ink or achromatic ink.

24. The method according to claim 17, wherein on the side of the carrier opposite the embossing lacquer layers, or between the carrier and the first embossing lacquer layer there is applied a further color coating, a glazing color coating.

25. The method according to claim 17, wherein the first and/or second relief structure are formed by micromirror arrangements with directional micromirrors, wherein the lateral dimensions of the micromirrors are advantageously below 20 μm, preferably below 10 μm.

26. The method according to claim 17, wherein the second embossing lacquer layer is applied at least in a partial region in the form of a regular or irregular grid with grid elements and grid spaces, wherein the dimensions of the grid elements and/or grid spaces are at least in one direction between 20 μm and 200 μm.

27. The method according to claim 17, wherein the second embossing lacquer layer is applied in partial regions which have lateral dimensions of more than 140 μm, and/or in which the second embossing lacquer layer is applied with recesses that have lateral dimensions of more than 140 μm.

28. The method according to claim 27, wherein the lateral dimensions of at least a partial region and/or at least one recess are more than 250 μm.

29. The method according to claim 17, wherein the first and the second color impression are perceivable separately from one another, are perceivable separately from one another in dependence on the viewing angle and/or in certain regions.

30. The method according to claim 17, wherein the two relief structures, depending on the viewing angle, make available a color change for an unchanged motif or make available a color change together with a motif change, wherein the motifs of the two relief structures differ with regard to shape, movement and/or dimensionality of the motif.

31. The method according to claim 17, wherein the first relief structure produces a first motif that is visible from a first viewing angle range with a first color impression, which is created through the combination of the color effects of the first embossing lacquer layer and the color coating, and that the second relief structure produces a second motif that is visible from a second viewing angle range with a second, different color impression, which is created through the combination of the color effects of the first embossing lacquer layer, the second embossing lacquer layer and the color coating, wherein the first and the second viewing angle ranges do not overlap.

32. The method according to claim 17, wherein the first relief structure produces a first movement motif with a first color impression and the second relief structure produces a second movement motif with a second, different color impression, wherein the first and second movement motive, upon tilting the security element move in a manner offset to one another or in a manner against one another and, in an overlap position in which both movement motifs are visible, cross each other and/or move consecutively through the same portion of the common region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Further embodiment examples as well as advantages of the invention will be explained hereinafter with reference to the figures, in the representation of which a rendition that is true to scale and proportion has been dispensed with in order to increase clarity.

[0044] There are shown:

[0045] FIG. 1 a schematic representation of a banknote with two security elements according to the invention,

[0046] FIG. 2 schematically a detail of the first security element of FIG. 1 in cross section,

[0047] FIG. 3, including FIGS. 3(a) to 3(d), intermediate steps of the manufacture of the security element of FIG. 2,

[0048] FIG. 4, including FIGS. 4(a) to 4(d) some concrete advantageous embodiments of the grid of the embossed structure of the security element of FIG. 2 in plan view,

[0049] FIG. 5 schematically a detail of the second security element of FIG. 1 in cross section,

[0050] FIG. 6, including FIGS. 6(a) to 6(f) intermediate steps of the manufacture of the security element of FIG. 5, and

[0051] FIG. 7 a variant of the security element of FIG. 2 in cross section.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

[0052] The invention will now be explained by the example of security elements for banknotes. FIG. 1 shows a schematic representation of a banknote 10 with two optically variable security elements 12 and 62, each of which is configured in the form of an adhesively bonded transfer element. It goes without saying, however, that the invention 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 packagings or for securing documents, identity documents, passports, credit cards, health cards and the like. In the case of banknotes and similar documents, in addition to transfer elements, security threads or security strips can also be considered, for example. The two security elements 12, 62 of FIG. 1 are themselves configured to be very flat, but nevertheless convey a three-dimensional impression to the viewer.

[0053] The first security element 12 in addition to the three-dimensional appearance shows a binary color and effect change upon tilting the banknote 10, in which, from a first viewing direction, a first motif 14-A appears that apparently bulges out of the plane of the banknote 10, for example a curved representation of the value number “10”, with a first, for example silvery lustrous, color impression. From a second viewing direction, a second motif 14-B shows that appears to bulge out of the plane of the banknote 10, for example a curved representation of a coat of arms with a second color impression, for example a lustrous red color impression.

[0054] When tilting 16 the banknote 10 or a corresponding change in the viewing direction, the appearance of the security element 12 suddenly switches from the first to the second appearance or upon tilting back from the second to the first appearance. The change of the motif and the color takes place simultaneously and without an intermediate or transitional stage in which both motifs or colors would be visible at the same time, or a motif would be visible in the color of the other motif. The appearance therefore switches seamlessly between two appearances 14-A, 14-B and is therefore referred to as a binary color and effect change.

[0055] The particular structure and the manufacture according to the invention of the first security element 12 will now be explained in more detail with reference to FIGS. 2 and 3, wherein FIG. 2 schematically shows a section of the security element 12 applied to the banknote 10 in cross section and FIG. 3 shows various intermediate steps of the manufacture of the security element 12.

[0056] The security element 12 contains a flat, transparently colorless carrier 18, the area extension of which defines an x-y plane and a z-axis standing perpendicular thereon. A multicolored reflective area region is arranged on the carrier 18, said region containing an embossed structure region 25 with two nested micromirror embossings 24, 34 at two different height levels. A first embossed region 24 is given by micromirror embossings, the base areas of which are at a height H.sub.1 above the carrier 18. A second embossed region 34 is given by micromirror embossings, the base areas of which are at a height H.sub.2>H.sub.1 above the carrier 18. The height as well as the direction of the positive z-axis is always measured starting from the carrier 18. Since the security element 12 is intended to be viewed from the lower side, i.e. the side of the carrier 18, the z-axis in the representation of FIG. 2 extends away from the carrier downwards.

[0057] The micromirror embossings 24, 34 (hereinafter also referred to as micromirror arrangements) each contain a multiplicity of micromirrors inclined relative to the x-y plane, the local inclination angles of which are selected so that the relief structures of the micromirror embossings 24, 34, in interaction with the color effects of the embossing lacquer layers 22, 32 and the color effect of a uniform color coating 26, produce a desired optical appearance.

[0058] Concretely, the inclination angles of the micromirrors in the embodiment example are selected so that the micromirror arrangement 24 produces the curved representation of the value number “10” in a viewing angle range of +5° to +20° (viewing position 40-A) with reference to the surface normal, and the micromirror arrangement 34 produces the curved representation of the coat of arms in a viewing angle range of −5° to −20° (viewing position 40-B). In the embodiment example, the micromirrors of the micromirror embossings 24, 34 themselves have a lateral dimension of 10×10 μm.sup.2 and a maximum height h of 3.5 μm. The height offset ΔH=H.sub.2− H.sub.1 with reference to the base area can be for example ΔH=6 μm.

[0059] As explained in more detail in connection with FIG. 3, the micromirror arrangements 24, 34 are produced by embossing two different embossing lacquer layers 22, 32 with different color effects. While the embossing lacquer layer 22 in which the micromirror arrangement 24 is embossed is transparently colorless, the embossing lacquer layer 32 in which the micromirror arrangement 34 is embossed is dyed in a glazing red. Both micromirror arrangements 32, 34 are supplied with a uniform color coating 26, which in the embodiment example is formed by a metal coating, concretely by a thin, vapor-deposited aluminum layer, which has a silvery metallic, and thus achromatic color effect.

[0060] The desired visual contrast of the micromirror arrangements 24, 34 from the viewing positions 40-A or 40-B of the viewer 40 is created by the interaction of the different color effects of the embossing lacquer layers 22, 32 with the color effect of the uniform color coating 26.

[0061] In the embodiment example of FIG. 2, the two micromirror arrangements 24, 34 are nested in one another in the form of a regular grid 50 in the entire area region of the security element 12, wherein only the micromirror embossings 24 of the height level H.sub.1 are present in the first grid regions 52, while in the complementary second grid regions 54, the covered region, the second embossing lacquer layer 32 with the micromirror embossings 34 are additionally present at the height level H.sub.2 and are optically effective. Concretely, the grid regions 52, 54 in the embodiment example form a checkerboard pattern in which each field, i.e. each grid region 52, 54, has a dimension of 100 μm×100 μm. Since the micromirrors are generally significantly smaller, here for example have an edge length of only 10 the grid 50, unlike in the simplified schematic representation of FIGS. 2 and 3, is generally not congruent with the grid of the micromirrors of the micromirror arrangements 24, 34.

[0062] Overall, the described arrangement results in the desired appearances. Since the carrier 18 and the first embossing lacquer layer 22 are configured to be transparently colorless, the micromirror arrangement 24 with the silvery metallic appearance of the aluminum layer 26 which shows the curved representation 14-A of the value number “10” is visible from the viewing position 40-A. Due to the glazing red dyeing of the second embossing lacquer layer 32 and the underlaying of the second embossing lacquer layer with the aluminum layer 26, the coat of arms 14-B appears with a lustrous red appearance from the viewing position 40-B.

[0063] The manufacture of the security element 12 according to the invention will now be described in more detail with reference to FIG. 3, wherein (a) to (d) each show intermediate steps of the manufacture of the security element.

[0064] First, with reference to FIG. 3 (a), a transparent carrier 18, for example a transparently colorless PET foil, is made available and supplied with a first, transparent and colorless embossing lacquer layer 22. The micromirror embossing 24, which produces the representation 14-A of the value number “10”, is embossed into the first embossing lacquer layer 22 with an embossing tool (not shown). When using a UV embossing lacquer, the embossing lacquer layer 22 is subsequently cured.

[0065] A second embossing lacquer layer 32 dyed in a glazing red is then printed onto the first embossing lacquer layer 22 in a regular grid 50, as shown in FIG. 3 (b), with a printing cylinder (not shown). The grid 50 is configured in the form of grid elements 54 and grid spaces 52 and corresponds, for example, to the checkerboard pattern described above with field dimensions of 100 μm×100 μm. In this embodiment example, the grid elements 54 produce the covered portion or the covered region mentioned above, in which the second embossing lacquer layer 32 is applied to the first embossing lacquer layer 22.

[0066] The second embossing lacquer layer 32 is then supplied with the micromirror embossing 34, which shows the representation of the coat of arms 14-B, as shown in FIG. 3 (c), with an embossing tool (not shown). When using a UV embossing lacquer, the embossing lacquer layer 32 is subsequently cured.

[0067] To the overall relief structure 25 formed in this manner, which is formed by the first relief structure 24 of the first embossing lacquer layer 22 and the second relief structure 34 of the second embossing lacquer layer 32, there is then applied a full-area metal coating 26, for example an aluminum layer, as shown in FIG. 3 (d). Finally, the structure side of the metalized overall relief structure 25 is supplied with a lacquer coating 48 and, possibly, further coatings, and the security element 12 is thereby completed.

[0068] A substantial advantage of the manufacturing method according to the invention is the very small number of working steps required in comparison to conventional methods. The proposed layer structure also results in very small product thicknesses of less than 45 μm, which is of great importance in particular for the use of the security elements in banknotes and other value documents. In addition, with the method described, the security elements can also be supplied with transparent or colored negative markings in a simple manner, as explained in more detail elsewhere.

[0069] FIG. 4 shows some concrete advantageous configurations of the grid 50 of the second embossing lacquer layer 32 in plan view. The grid elements 54 are each represented with a hatching and the grid spaces 52 are each represented without hatching. FIG. 4 (a) shows a grid 50 as employed in FIGS. 2 and 3, in which the grid elements 54 and the grid spaces 52 form a checkerboard pattern. The dimensions of the grid regions are advantageously between 20×20 μm.sup.2 and 140×140 μm.sup.2, in particular between 20×20 μm.sup.2 and 60×60 μm.sup.2; the area coverage is 50%. If an area coverage that deviates from 50% is to be produced, part of the grid elements 54 can be omitted or part of the grid spaces 52 can be occupied by grid elements.

[0070] In this, but also in the configurations described in the following, the area coverage of the grid with grid elements 54 is preferably between 30% and 70%, in particular between 40% and 60%. The brightness of the appearances produced in each case can be adjusted as desired by the area coverage of the first and second grid regions.

[0071] FIG. 4 (b) shows a grid 50 with alternately arranged strip-shaped grid elements 54 and grid spaces 52. The width of the grid regions is advantageously between 20 μm and 140 μm, in particular between 20 μm and 60 μm. The length of the grid regions is arbitrary and can be several millimeters or even some centimeters. The area coverage can easily be adjusted via the relative width of the grid elements and grid spaces.

[0072] The grid elements and grid spaces can also have other polygonal shapes or irregular shapes. By way of example, FIG. 4 (c) shows an embodiment in which the grid elements 54 and grid spaces 52 of the grid 50 are formed by triangles. In the grid 50 of FIG. 4 (d), the grid elements 54 and grid spaces 52 are formed by irregular shapes. The grid elements and/or grid spaces can form a coherent structure, as shown for example of FIG. 4 (d) for the grid spaces 52.

[0073] Returning to the representation in FIG. 1, the second security element 62 transferred to the banknote 10 is also very flat itself, but nevertheless conveys to the viewer the three-dimensional impression of a motif 64 appearing to bulge out of the plane of the banknote 10, which appears with a first color impression. The motif 64 can represent, for example, a value number, a portrait or another graphic motif. Within the motif 64 with the first color impression, a movement effect with a second color impression is visible in a partial region 66. For example, upon tilting the banknote 10, a bright bar can move up and down along the partial region 66 and produce a so-called rolling bar effect. As a substantial special feature, the regions of different color impressions (first and second color impression) and different effects (three-dimensional motif or running bar) therein are disposed in exact mutual register. This registration is therefore also referred to as color-to-effect registration in the following.

[0074] In addition, the security element 62 contains a negative writing 68 in the form of the value number “10”, which is formed by a transparent partial region of the security element 62. If the security element 62 is arranged over an opaque region of the banknote 10, the surface of the banknote, for example the white banknote paper, becomes visible there. If the security element 62 is arranged over a window region of the banknote, the negative writing 68 forms a transparent see-through region in the security element 62, which lights up brightly when viewed in transmitted light.

[0075] The special structure and the manufacture according to the invention of the security element 62 will now be explained in more detail with reference to FIGS. 5 and 6, wherein FIG. 5 schematically shows a detail of the security element 62 applied to the banknote 10 in cross section and FIG. 6 shows various intermediate steps of the manufacture of the security element 62.

[0076] The security element 62 is constructed similarly to the security element 12 already described in connection with FIG. 2, so that elements that correspond to one another are each designated with the same reference numerals. The security element 62 contains a flat, transparently colorless carrier 18, the area extension of which defines an x-y plane and a z-axis standing perpendicularly thereon. On the carrier 18 there is arranged a multicolored reflective area region which contains an embossed structure region with micromirror embossings with two different height levels.

[0077] Like in FIG. 2, a first embossed region 24 is given by micromirror embossings, the base areas of which are at a height H.sub.1 above the carrier 18, while a second embossed region is given by micromirror embossings 34, the base areas of which are at a height H.sub.2>H.sub.1 above the carrier 18. The micromirror embossings or micromirror arrangements 24, 34 each contain, like in the embodiment example of FIG. 2, a multiplicity of micromirrors inclined relative to the x-y plane, the local inclination angles of which are selected so that the relief structures of the micromirror embossings 24, 34, in interaction with the color effects of the embossing lacquer layers 22, 32 and the color effect of a uniform color coating 26, produce a desired optical appearance.

[0078] Concretely, the inclination angles of the micromirrors in the embodiment example are selected such that the micromirror arrangements 24, 26 produce the bulging three-dimensional impression of the motif 64 and the rolling bar effect of the partial region 66. The sizes and heights of the micromirrors can be selected like in the embodiment example of FIG. 2.

[0079] While the embossing lacquer layer 22 in which the micromirror arrangement 24 is embossed is transparently colorless, the embossing lacquer layer 32 in which the micromirror arrangement 34 is embossed is dyed in a glazing blue. Both micromirror arrangements 32, 34 are supplied with a uniform color coating 26, which in the embodiment example of FIG. 5 is formed by a metal coating, concretely by a thin, vapor-deposited silver layer that has a silvery metallic and thus achromatic color effect.

[0080] The desired visual contrast of the micromirror arrangements 24, 34 from the different viewing positions of the viewer is created by the interaction of the different color effects of the embossing lacquer layers 22, 32 with the color effect of the uniform color coating 26.

[0081] In the embodiment example of FIG. 5, the two micromirror arrangements 24, 34 are each arranged directly adjacent to one another in the area region of the security element 62. The partial region 66 is formed, for example, by a 5 mm wide and 2 cm long curving strip within a 2.5×2.5 cm.sup.2 large area region 64. While in the partial region 66, which represents the above-mentioned covered region, the viewer looks through the glazing blue embossing lacquer layer 32 at the micromirror arrangement 34 with the silver layer 26 disposed at the height level H.sub.2, the visual impression in the region 64, i.e. outside the covered region 66, is determined by the micromirror arrangement 24 disposed at the height level H.sub.1 and thus only by the color effect of the silver layer 26.

[0082] In the region 64, the viewer therefore perceives the silvery lustrous motif 64 produced by the micromirror arrangement 24, while within the partial region 66 the blue-metallic rolling bar effect appears, in which, upon tilting the banknote 10, a blue reflective bar appears to run back and forth along the curving strip. Since the height difference between the two micromirror arrangements 24, 34 is in the range of a few micrometers, it is imperceptible to the viewer, so that the two differently colored motifs and the different effects 64, 66 appear to be arranged next to one another in exact register.

[0083] The security element 62 additionally has a smaller partial region 68 in the region 64, which is configured in the form of the value number “10” and in which the color coating 26 is omitted. Due to the lack of color coating and the transparency of the other layers present in the partial region 68, a negative marking is created there in the security element 62. Depending on the arrangement of the security element, the partial region 68 forms a transparent see-through window in the banknote or it reveals the view of the surface of the banknote.

[0084] The manufacture of the security element 62 according to the invention will now be described in more detail with reference to FIG. 6, wherein (a) to (f) each show intermediate steps in the manufacture of the security element.

[0085] First, with reference to FIG. 6 (a), a transparent carrier 18, for example a transparently colorless PET foil, is made available and supplied with a first, transparent and colorless embossing lacquer layer 22. The micromirror embossing 24, which produces the motif 64 of the security element 62, is embossed into the first embossing lacquer layer 22 with an embossing tool (not shown). When using a UV embossing lacquer, the embossing lacquer layer 22 is subsequently cured.

[0086] A second embossing lacquer layer 32 dyed in a glazing blue is printed onto the first embossing lacquer layer 22 in the desired covered region 66 of the running bar, as shown in FIG. 6 (b), with a printing cylinder (not shown). With reference to FIG. 6 (c), the second embossing lacquer layer 32 is then supplied with the micromirror embossing 34 which produces the rolling bar effect using an embossing tool (not shown). When using a UV embossing lacquer, the embossing lacquer layer 32 is subsequently cured.

[0087] In order to produce the negative writing, washing ink 70 is printed on in the partial regions 68 which are to be demetalized subsequently, as shown in FIG. 6 (d).

[0088] To the overall structure produced in this manner, which is formed by the first relief structure 24 of the first embossing lacquer layer 22, the second relief structure 34 of the second embossing lacquer layer 32 present in the overlap region 66 and the washing ink 70 printed in the partial regions 68, there is then applied a uniform, full-area metal coating 26, for example, the mentioned silver layer, as shown in FIG. 6 (e).

[0089] Subsequently, the washing ink 70 is washed out together with the portion of the metal coating 26 disposed on the washing ink and there is obtained the area region 68 demetalized in certain regions, represented in FIG. 6 (f). Finally, the structure side of the partially metalized relief structure is supplied with a lacquer coating 48 and, possibly, further coatings, and the security element 62 is thereby completed. The color variety of the appearances of the two micromirror embossings can be further increased within the scope of the invention. For illustration, FIG. 7 shows a modification of the embodiment example of FIG. 2, in which both the motif 14-A (value number “10”) and the coat of arms motif 14-B appear with a chromatic impression. For this purpose, in the case of the security element 80, in addition to the elements already described in FIG. 2, on the side of the carrier 18 facing away from the micromirror embossings 24, 34, a continuous glazing ink layer 82 is provided.

[0090] When viewed, the motif 14-A of the micromirror embossing 24 then appears lustrous with a first chromatic color, due to the combined effect of the ink layer 82 and the metallization 26, and the motif 14-B of the micromirror embossing 34 appears lustrous with a second chromatic color, due to the combined effect of the ink layer 82, the dyed embossing lacquer layer 32 and the metallization 26, said second chromatic color being created by subtractive color mixture of the colors of the ink layer 82 and the embossing lacquer layer 32. If, for example, the embossing lacquer layer 32 is dyed in glazing cyan and the ink layer 82 is dyed in glazing yellow, then the motif 14-A appears with a yellow lustrous color and the motif 14-B appears with a green lustrous color due to the subtractive color mixture of cyan and yellow.

[0091] Alternatively, the ink layer 82 can also be provided between the carrier 18 and the first embossing lacquer layer 22. Instead of providing an additional ink layer 82, a first embossing lacquer layer 22 dyed in glazing manner or a carrier foil 18 dyed in glazing manner can also be employed. These measures can also increase the color variety of the appearances.

[0092] Even if the embodiment examples were concretely described with metal layers and glazing chromatic inks for illustration purposes, it is understood that the other inks mentioned above can also be used for the color coating 26 and the embossing lacquer layers 22, 32.