AU2017200729A1

AU2017200729A1 - Optically Variable Security Element

Info

Publication number: AU2017200729A1
Application number: AU2017200729A
Authority: AU
Inventors: Annett Baehr; Georg Depta; Walter Doerfler; Simon Freutsmiedl; Andre Gregarek; Michael Rahm; Harald Reiner
Original assignee: Giesecke and Devrient GmbH
Current assignee: Giesecke and Devrient GmbH
Priority date: 2012-04-18
Filing date: 2017-02-03
Publication date: 2017-02-23
Also published as: CN104245346A; AU2013248632A1; EP2838737B1; EP2838737A1; CN104245346B; AU2013248632B2; TWI574211B; DE102012007747A1; WO2013156149A1; TW201344588A; IN2014KN02263A

Abstract

Abstract The invention relates to an optically variable security element for security papers, documents of value and other data carriers, having a substantially transparent carrier with first and second main surfaces located 5 opposite one another, having an arrangement of microlenses on the first main surface of the carrier, having a laser-sensitive recording layer, which is arranged on the second main surface of the carrier and contains first and second sub-layers arranged one above the other, wherein the first sub-layer is arranged between the carrier and the second sub-layer, and having a 10 multiplicity of microholes which are generated in the laser-sensitive recording layer by the action of laser radiation and of which each microhole is assigned to a microlens and, with the security elements being viewed from a certain viewing angle, can be seen through the associated microlens, wherein the multiplicity of microholes comprise a multiplicity of first and a multiplicity of 15 second microholes wherein the first microholes are present in the first sub layer, and do not pass through the recording layer, and the second microholes pass through the recording layer with the first and second sub-layer, and wherein the diameter of the first microholes is larger than the diameter of the second microholes.

Description

-1- 2017200729 03 Feb 2017

Optically Variable Security Element

Field of the Invention

The present invention relates to an optically variable security element for security 5 papers, value documents and other data carriers, a method for manufacturing such a security element, and a data carrier having such a security element.

Background

For protection, data carriers, such as value or identification documents, but also other 0 valuable articles, such as branded articles, are often provided with security elements that permit the authenticity of the data carrier to be verified, and that simultaneously serve as protection against unauthorized reproduction.

Security elements having viewing-angle-dependent effects play a special role in 5 safeguarding authenticity, as these cannot be reproduced even with the most modern copiers. Here, the security elements are furnished with optically variable elements that, from different viewing angles, convey to the viewer a different image impression and, depending on the viewing angle, display for example another color or brightness impression and/or another graphic motif. !0

For example, identification cards, such as credit cards or personal identity cards, have long been personalized by means of laser engraving. In personalization by laser engraving, the optical properties of the substrate material are irreversibly changed through suitable guidance of a laser beam in the form of a desired marking. Such a 25 laser marking makes it possible to combine the individualization of the data carriers with security elements and to integrate them into the print image more freely than with conventional individualizations, for example with known numbering methods.

Patent document EP 0 219 012 A1 describes an identification card having a partial 30 lens grid pattern. Through this lens pattern, pieces of information are inscribed in the card with a laser under different angles. Subsequently, these pieces of information -2- 2017200729 03 Feb 2017 can also be perceived only under this angle, such that, when the card is tilted, the different pieces of information appear.

It is a preferred aim of the present invention to provide a security element of the kind 5 cited above having an attractive visual appearance and high counterfeit security.

Summary of the Invention

According to the present invention, a generic security element comprises a substantially transparent substrate having opposing first and second main 0 surfaces, an arrangement composed of microlenses arranged on the first main surface of the substrate, arranged on the second main surface of the substrate, a laser-sensitive recording layer that includes stacked first and second sub-layers, the first sub-5 layer being arranged between the substrate and the second sub-layer, a plurality of microholes produced in the laser-sensitive recording layer by the action of laser radiation, of which each microhole is associated with a microlens and is visible through the associated microlens when the security element is viewed from a certain viewing angle, !0 - the plurality of microholes comprising a plurality of first and a plurality of second microholes, the first microholes being present in the first sub-layer and not going through the recording layer, and the second microholes going through the recording layer with the first and second sub-layer, and the diameter of the first microholes being larger than the diameter of the 25 second microholes.

Lenses whose size lies below the resolution limit of the naked eye are referred to as microlenses. The microlenses are preferably developed to be spherical or aspherical and, for example in banknotes, advantageously have a diameter between 5 pm and 30 100 pm, preferably between 10 pm and 50 pm, particularly preferably between 15 pm and 20 pm. For card applications, the microlenses can also be larger andhave, for 2017200729 03 Feb 2017 -3- example, a diameter between 100 pm and 300 pm. In all designs, the microlenses can also be developed to be cylinder lenses.

The diameter of the first microholes is preferably more than 10%, especially more 5 than 20%, and particularly preferably more than 30% larger than the diameter of the second microholes. However, the diameter of the first microholes is expediently not more than 4 times, especially not more than 3 times, the diameter of the second microholes. Due to the magnifying effect of the microlenses, even a minor difference in the hole size of the first and second microholes leads to a good contrast difference 0 of the reflected light effect or transmitted light effect, as explained in greater detail below.

In expedient embodiments, the diameter of the second microholes lies between 2 pm and 4 pm, and the diameter of the first microholes between 3 pm and 8 pm. For a 5 good contrast difference, the diameters of the first microholes are, for example, 0.5 pm to 4 pm larger than the diameter of the second microholes.

In advantageous embodiments, the microholes are each smaller than the associated microlenses. Here, the area ratio of microholes and associated microlens can lie !0 below 1.0 or below 0.5, below 0.2, or even below 0.1.

In simple designs, the first and second microholes are each developed to be substantially circular or linear. However, it is also possible to develop the first and/or second microholes to be pattern-shaped, for example in geometric shapes, 25 such as squares, triangles or stars, or in the form of microcharacters, such as letters, numerals or the like, in order to integrate an additional, hidden security feature into the security element. A pattern-shaped development is appropriate especially for the larger first microholes. -4- 2017200729 03 Feb 2017

While the first microholes differ at least in their size and, if appropriate, also in their shape from the second microholes, the first microholes themselves advantageously all have the same shape and size, and the second microholes likewise. 5 The first microholes advantageously form, in the form of patterns, characters or a code, a first motif that is perceptible when the security element is viewed from a prechosen first viewing direction in reflected light, and in that the second microholes form, in the form of patterns, characters or a code, a second motif that is perceptible when the security element is viewed from a prechosen second viewing direction in 0 transmitted light. The first and second motif are normally different, but can also be identical. Also the first and second viewing direction are preferably different, but can also be identical.

In advantageous designs, the first and second microholes are arranged 5 independently of one another. In other, likewise advantageous designs, at least a portion of the second microholes lies completely within the first microholes. For example, more than 50%, more than 75%, or also all second micro holes can lie completely within the first microholes. In this way, a "motif within a motif' can be produced in which a transmitted-light motif appears within a reflected-light motif. !0 For example, the security element can include a crest that is visible in reflected light and that is formed by the first microholes, and in whose interior, when changing to viewing in transmitted light, a logo is visible that is formed by the second microholes. In this case, the first and second viewing direction are expediently chosen to be identical. 25

In expedient embodiments, the first and/or second microholes are introduced into the recording layer through the microlens arrangement from different directions with laser radiation. When viewed later, the microholes are then perceptible, in reflected light or transmitted light, from the respective viewing direction from which 30 they were introduced. Here, as already described above, the first microholes can each -5- 2017200729 03 Feb 2017 be perceptible from a first viewing direction, and the second microholes each from a second, different viewing direction.

However, it is also possible that a group of first microholes is introduced from one 5 direction, and another group of first microholes from another direction. The first motif formed by the first microholes then displays a tilt image or alternating image whose sub-images are formed by the different groups of first microholes. Also embodiments having more than two introduction directions or continuous direction changes are possible. Alternatively or additionally, in the same way, also the second 0 microholes can be introduced from two or more different directions.

The motif portions or sub-images that are visible from different viewing directions can be associated in meaning and, for example, as in a flip-book, depict an image sequence that proceeds before the eye of the viewer when the security element is 5 tilted. If the introduction angle, and thus also the viewing angle, changes continuously, then the degree of transparency, and thus the brightness in which the motif appears when the security element is tilted, changes continuously.

The first and second sub-layer of the recording layer are advantageously formed by !0 metal layers, for example by layers composed of aluminum, copper, silver, gold, chrome, nickel, tungsten, palladium or an alloy of these metals, such as an Al-Cu alloy. The first and second sub-layer are advantageously formed by metal layers of different colors, such as aluminum and copper. To ensure particularly good visibility of the reflected-light motif, the second sub-layer is advantageously formed by a 25 highly reflective metal layer having a reflectivity of 90% or more, for example by a vapor-deposited aluminum or silver layer.

The first and/ or second sub-layer is advantageously opaque, a layer being referred to as opaque when its transmission in the visible is less than 1%, especially less than 30 0.1%. -6- 2017200729 03 Feb 2017

In advantageous designs, the recording layer consists of the first and second sublayer, so includes no further layers.

However, also embodiments are conceivable in which one or more further layers are 5 arranged between the first and the second sub-layer of the recording layer. In particular, one or more layers that are transparent for the laser can be present between the first and second sub-layer, e.g. dielectric layer(s) composed of S1O2 (silicon dioxide). Such additional layers can be used, for example, to produce a certain color and/or color-shift effects, and/or serve as adhesive-boosting layer(s). 0 Besides this, also the sub-layers as such can each consist of multiple individual layers that can likewise include neutral layers.

As explained yet in detail below, the difference in the diameter or in the surface area of the micro holes in the same recording layer permits coding two independent 5 appearances of the security element for reflected-light viewing and transmitted-light viewing. Summarized briefly, when viewing in reflected light, a viewer looks through the comparatively large first microholes at the highly reflective second sublayer, while the smaller second microholes are not perceptible in reflected light, especially due to their small size. Thus, due to the high reflectivity of the second sub-!0 layer, the first motif formed by the first microholes is well perceptible in reflected light, while the second motif remains hidden.

In transmitted light, sufficient light also passes through the comparatively small second microholes to be able to perceive the second motif formed by said second 25 microholes, while the first motif composed of the first microholes that are present in the first sub-layer remains hidden due to the opacity of the second sub-layer.

The first microholes that are present in the first sub-layer preferably do not extend into the second sub-layer. In practice, however, if the first and second sub-layer are 30 stacked immediately on top of one another, it is harmless if, for production reasons, the holes extend slightly into the second sub-layer, that is, less than 1/10 or even less -7- 2017200729 03 Feb 2017 than 1/20 of the layer thickness. However, the remaining layer thickness of the second sub-layer should have a sufficiently high reflectivity and a sufficiently high opacity. 5 In an advantageous development of the present invention, the security element simultaneously includes a micro-optical depiction arrangement, especially a moire magnification arrangement, a moire-type micro-optical magnification arrangement, or a modulo magnification arrangement. The basic principle of such micro-optical depiction arrangements is explained in document WO 2009/000528 Al, the 0 disclosure of which is incorporated in the present description by reference. In this case, the security element preferably has, between the substrate and the recording layer, a motif image that is divided into a plurality of cells, in each of which are arranged imaged regions of a predetermined background motif, the microlens arrangement forming a microlens grid that, when the motif image is viewed, 5 reconstructs the background motif from the imaged regions arranged in the cells.

The motif image is advantageously present as a relief pattern in an embossing lacquer layer that is arranged between the substrate and the recording layer. Here, it can especially be provided that the first and second sub-layer follow the relief of the !0 embossing lacquer layer, that is, have substantially the same relief pattern.

In one variant of the present invention, the microlens arrangement can be provided with a semitransparent cover layer and/ or a cover layer that is present only in some regions. Currently, however, it is preferred that the microlens arrangement be free 25 from applied layers that impair or cancel the optical effect of the microlenses.

The present invention also comprises a data carrier, especially a value document, such as a banknote, a passport, a certificate, an identification card or the like, that is furnished with a security element of the kind described. In one advantageous variant 30 of the present invention, the security element can especially be arranged in or over a window region or a through opening in the data carrier. -8- 2017200729 03 Feb 2017

The present invention further includes a method for manufacturing an optically variable security element for security papers, value documents and other data carriers, in which 5 - a substantially transparent substrate having opposing first and second main surfaces is provided, an arrangement composed of microlenses being arranged on the first main surface of the substrate, on the second main surface of the substrate is arranged a laser-sensitive recording layer that includes stacked first and second sub-layers, the first sub-0 layer being arranged between the substrate and the second sub-layer, by the action of laser radiation is produced in the laser-sensitive recording layer a plurality of microholes, of which each microhole is associated with a microlens and is visible through the associated microlens when the security element is viewed from a certain viewing angle, 5 - the plurality of microholes comprising a plurality of first and a plurality of second microholes, the first microholes being produced in the first sub-layer and not going through the recording layer, and the second microholes being produced going through the recording layer with the first and second sublayer, and !0 - the first microholes being produced having a larger diameter than the second microholes.

In one advantageous development of the method, the first and/ or second microholes are introduced into the recording layer through the microlens arrangement from 25 different directions with laser radiation.

In one advantageous method variant, in a first step, initially only the first sub-layer of the laser-sensitive recording layer is produced on the second main surface of the substrate and provided with the plurality of first microholes by the action of laser 30 radiation. In a second step, the second sub-layer of the laser-sensitive recording layer -9- 2017200729 03 Feb 2017 is then arranged on the first sub-layer, and the second microholes are produced going through the recording layer with the first and second sub-layer.

Another optically variable security element for security papers, value documents and 5 other data carriers includes a substantially transparent substrate having opposing first and second main surfaces, an arrangement composed of microlenses arranged on the first main surface of the substrate, 0 - a laser-sensitive recording layer, especially a metal layer, arranged on the second main surface of the substrate, a printing layer, especially an ink layer, arranged on the recording layer, a plurality of microholes produced in the laser-sensitive recording layer by the action of laser radiation, of which each microhole is associated with a 5 microlens and is visible through the associated microlens when the security element is viewed from a certain viewing angle, each microhole being smaller than the associated microlens, produced in the recording layer by the action of laser radiation, at least one gap region whose dimension is larger than the dimension of the microlenses, !0 - the at least one gap region forming, in the form of patterns, characters or a code, a first motif that, when the security element is viewed in reflected light and transmitted light, is perceptible having the appearance of the printing layer, and the microholes forming, in the form of patterns, characters or a code, a second 25 motif that is perceptible only when the security element is viewed in transmitted light from a prechosen viewing direction, and from this viewing direction, complements the first motif to form a complete motif.

The at least one gap region forms a macroscopic motif that is visible through the 30 microlenses with the naked eye without auxiliary means, especially without magnification. Its smallest dimensions usually lie above 0.5 mm, typically at a few -10- 2017200729 03 Feb 2017 millimeters. The material of the printing layer can, but need not, penetrate into the microholes and/or the gap regions. The microlens arrangement is preferably free from applied layers that impair or cancel the optical effect of the microlenses. The recording layer can be, for example, a 50 nm thick aluminum layer, with the printing 5 layer, for example, an imprinted solvent-based red lacquer layer. The security element can be applied on a data carrier having a certain transmittance in transmitted light, such as banknote paper. In advantageous designs, the security element is arranged in or over a window region or a through opening in a data carrier. 0

Further exemplary embodiments and advantages of the present invention are explained below by reference to the drawings, in which a depiction to scale and proportion was omitted in order to improve their clarity. 5 Brief Description of the Drawines Shown are: Fig. 1 a schematic depiction of a banknote having an inventive optically variable security element that is arranged over a through opening in the banknote, !0 Fig. 2 schematically, the layer structure of a security element according to the present invention, in cross section, Fig. 3 in (a) and (b), two intermediate steps in the manufacture of the security element in fig. 2, Fig. 4 25 the visual appearance of the security element in fig. 2 when viewed from the front, (a) and (b) showing the appearance from two viewing directions in reflected light, and (c) and (d) the appearance from two viewing directions in transmitted light, and Fig. 5 the visual appearance of the security element in fig. 2 when viewed from the back, in (a) in reflected light and in (b) in transmitted light. 30 -11- 2017200729 03 Feb 2017

Description of Embodiment(s) of the Invention

The invention will now be explained using the example of security elements for banknotes. For this, figure 1 shows a schematic depiction of a banknote 10 having an inventive optically variable security element 12 that is arranged over a through 5 opening 14 in the banknote 10. In transmitted light, independently of the viewing direction, the security element 12 appears to be semitransparent in sub-regions and can, due to its application over the opening 14, be viewed from its front and from its back, in each case both in reflected light and in transmitted light. 0 From each of these different viewing directions, the security element 12 displays different visual appearances, which leads to a high attention and recognition value.

Figure 2 shows, schematically, the layer structure of the security element 12 according to an embodiment of the present invention, in cross section, with only the 5 portions of the layer structure that are required to explain the functional principle being depicted.

The security element 12 includes a substantially transparent substrate 20 that typically is formed by a transparent plastic foil, for example an about 20 pm thick !0 polyethylene terephthalate (PET) foil. The substrate 20 has opposing first and second main surfaces, the first main surface 22 being provided with an arrangement of microlenses 26. In the exemplary embodiment shown, the microlenses 26 are arranged regularly in the form of a microlens grid and form on the surface of the substrate foil a two-dimensional Bravais lattice having a prechosen symmetry. The 25 Bravais lattice of the microlenses 26 canhave, for example, a hexagonal grating symmetry or also a lower symmetry, such as the symmetry of a parallelogram grating.

In the exemplary embodiment, the spherically or aspherically designed microlenses 30 26 preferably have a diameter between 15 pm and 30 pm and are thus not perceptible with the naked eye. The thickness of the substrate 20 and the curvature of the -12- 2017200729 03 Feb 2017 microlenses 26 are coordinated with each other in such a way that the focal length of the microlenses 26 substantially corresponds to the thickness of the substrate 20.

On the second main surface 24 of the substrate 20 is arranged a laser-sensitive 5 recording layer 30 that consists of two stacked sub-layers, the first sub-layer 32 being arranged between the substrate 20 and the second sub-layer 34. The first and second sub-layer 32,34 are preferably formed from metal layers of different colors, and the second sub-layer has a particularly high reflectivity of 90% or more. For this, in the exemplary embodiment shown, the first sub-layer 32 is formed by a 100 nm thick 0 copper layer, and the second sub-layer 34 by a 50 nm thick aluminum layer, which were vapor deposited in succession on the substrate 20.

Further, a plurality of circular microholes 40 was introduced into the recording layer 30 by the action of laser radiation. Here, a portion of the microholes (called first 5 microholes 42 in the following) is present only in the first sub-layer 32 and does not go through the recording layer 30. Another portion of the microholes (called second microholes 44 in the following) goes through the recording layer 30 with the first and second sub-layer 32, 34. !0 Together, the plurality of the first microholes 42 form a first motif 46, in the exemplary embodiment the logo "G+D", that is perceptible when the security element is viewed from a prechosen first viewing direction in reflected light (fig. 4(b)). Together, the plurality of second microholes 44 forms a second motif 48, in the exemplary embodiment the letter pair "PL", that is perceptible when the security 25 element is viewed from a prechosen second viewing direction in transmitted light (fig. 5(b)).

Here, the first microholes 42 have a diameter of 6 gm, the second microholes a diameter of only 4 gm. The diameter of the first microholes 42 is thus (6 gm/4 gm) = 30 1.5 times as large as the diameter of the second microholes 44. Accordingly, the surface area of the first microholes 42 is (6 gm/4 gm)2 = 2.25 times as large as the -13- 2017200729 03 Feb 2017 surface area of the second microholes 44. In this way, it is achieved, on the one hand, that only the first motif 46, but not the second motif 48, is visible in reflected light. On the other hand, through the large first microholes 42, in connection with the high reflectivity of the second sub-layer 34, a light appearance of the first motif is ensured. 5

The visibility of the first and second motif only from certain prechosen viewing directions is an immediate result of the production of the microholes through the microlenses 26. With reference to fig. 3, to manufacture the security element 12, a 100 nm thick copper layer 32 is first applied to the second main surface of the 0 substrate 20 and, to this, a 50 nm thick aluminum layer 34, preferably in a vacuum vapor deposition process. At these layer thicknesses, both the copper layer 32 and the aluminum layer 34 are opaque. Moreover, the aluminum layer 34 has a particularly high reflectivity of more than 90%. 5 The coated substrate is then impinged on from the side of the microlenses 26 from the desired later viewing direction 50 of the second motif with laser radiation, for example with the radiation of a Nd:YAG, Nd:YV04 or fiber laser. The microlenses 26 focus the laser radiation on the recording layer 30, as indicated in fig. 3(a) by the reference sign 52. Here, the laser energy or laser power is chosen such that both the !0 first sub-layer 32 and the second sub-layer 34 are ablated, such that circular second microholes 44 having a diameter of 2 to 4 pm and going through the recording layer are created. Here, the laser beam travels the surface area of the second motif 48, such that the entirety of the second microholes 44 forms the second motif 48. 25 Then the coated substrate, in turn, is impinged on from the side of the microlenses 26 from the desired later viewing direction 54 of the first motif with laser radiation. The microlenses 26 focus the laser radiation on the recording layer 30, as indicated in fig. 3(b) by the reference sign 56. For laser energy or laser power, in this step, a choice is made such that substantially only the first sub-layer 32, but not the second sub-layer 30 34, is ablated. To produce the larger surface area of the first microholes 42, for example, the irradiation direction of the laser can be tilted circularly about the -14- 2017200729 03 Feb 2017 desired viewing direction 54 with a small amplitude. In this way, circular first microholes having a diameter of 3 to 8 pm are produced. Moreover, the laser beam travels the surface of the first motif 46, such that the entirety of the first microholes 42 forms the first motif 46. 5

Through this approach, it is achieved that, with each of the microholes 42,44, a microlens 26 is associated through which the microhole 42,44 is produced upon laser impingement, and through which, due to the reversibility of the beam path, the microhole is visible when the security element is viewed later. 0

In one alternative method variant, not shown here, to manufacture the security element 12, a 100 nm thick copper layer 32 is first applied to the second main surface of the substrate 20, preferably in a vacuum vapor deposition process. The substrate coated with the copper layer 32 is then impinged on from the side of the microlenses 5 26 from the desired later viewing direction 54 of the first motif with laser radiation, for example with the radiation of a Nd:YAG, Nd:WO4 or fiber laser. The microlenses 26 focus the laser radiation on the first sub-layer 32. Here, the laser energy or laser power is chosen such that the first sub-layer 32 is ablated and circular first microholes having a diameter of 3 to 8 pm are produced. To produce the larger !0 surface area of the first microholes 42, for example, the irradiation direction of the laser can be tilted circularly about the desired viewing direction 54 with a small amplitude. Here, the laser beam travels the surface area of the first motif 46, such that the entirety of the first microholes 42 forms the first motif 46. 25 Thereafter, a 50 nm thick aluminum layer 34 is applied to the copper layer 32, preferably vapor deposited. The coated substrate is then impinged on from the side of the micro lenses 26 from the desired later viewing direction 50 of the second motif with laser radiation. The microlenses 26 focus the laser radiation on the recording layer 30. Here, the laser energy or laser power is chosen such that both the first sub-30 layer 32 and the second sub-layer 34 are ablated, such that circular second microholes 44 (having a diameter of 2 to 4 pm) that go through the complete recording layer 30 -15- 2017200729 03 Feb 2017 are created. Here, the laser beam travels the surface of the second motif 48, such that the entirety of the second microholes 44 forms the second motif 48.

Figure 4 shows the visual appearance of the security element 12 produced in this 5 way when viewed from the side of the first main surface 22 (front), fig. 4(a) and 4(b) showing the appearance from two viewing directions in reflected light, that is, in reflection, and fig. 4(c) and 4(d) showing the appearance from two viewing directions in transmitted light, that is, in transmission. 0 In reflected light, a viewer looks from viewing direction 54 (fig. 3(b)) through the microlenses 26 at the microholes 42 of the first sub-layer 32, and thus at the underlying second sub-layer 34. Due to the high reflectivity of the second sub-layer 34 and the comparatively large surface area of the first microholes 42, from direction 54, the first motif (logo "G+D") is brightly visible with good contrast and silver-5 colored in front of the copper-colored background of the first sub-layer 32, as depicted in fig. 4(b).

From another viewing direction that does not correspond to the prechosen viewing direction 54 of the first motif, the first microholes 42 are not visible in reflected light, !0 since the viewer in this case looks through the microlenses 26 at a site of the first sublayer 32 that lies outside the microholes 42. Due to their considerably smaller surface area in reflected light, the second microholes 44 are less conspicuous or not perceptible at all. Overall, from such a viewing direction, the security element 12 thus appears as a homogeneous, copper surface, as depicted in fig. 4(a). By tilting the 25 security element 12 back and forth, in reflected light, the viewer can change between the appearances in figures 4(a) and 4(b).

In transmitted light, independently of the viewing direction, the recording layer 30 is semitransparent due to the plurality of second microholes 44. Since, in this viewing 30 direction, the microholes 44 are viewed through the microlenses 26, the light that is incident from the back shines in each case through the microholes 44 substantially at -16- 2017200729 03 Feb 2017 that angle at which said microholes were introduced when produced with the laser beam. Thus, from viewing direction 50 (fig. 3(a)), in transmission, the second motif (letter string "PL") formed by the second microholes is visible light against the dark background of the metallic recording layer 30, as depicted in fig. 4(d). 5

From another viewing direction that does not correspond to the prechosen viewing direction 50 of the second motif, the second microholes 44 are not visible in transmitted light, since the viewer in this case looks through the microlenses 26 at a site of the first or second sub-layer that lies outside the microholes 44. Both the first 0 and the second sub-layer are opaque, such that the security element 12 appears from such a viewing direction as a homogeneous, dark surface, as depicted in fig. 4(c). By tilting the security element 12 back and forth, in transmitted light, the viewer can change between the appearances in figures 4(c) and 4(d). 5 The different appearance in reflected light and transmitted light is unusual and surprising for a viewer and thus leads to a visually attractive and conspicuous overall impression having a high attention and recognition value.

Figure 5 shows the visual appearance of the security element 12 when viewed from !0 the side of the second main surface 24 (back), fig. 5(a) illustrating the appearance in reflected light and fig. 5(b) the appearance in transmitted light.

In reflected light, from the back, merely the silver-colored second sub-layer 34 is visible, since the through second microholes 44 are not perceptible in reflected light 25 due to their small size. From the back, in reflected light, the viewer thus sees the homogeneous silver-colored metal layer 34, as illustrated in fig. 5(a).

When viewed in transmitted light, the security element 12 appears semitransparent in a large angle range through the plurality of the second microholes 44. In constrast 30 to viewing from the front, when viewed from the back, the second microholes 44 are not viewed through microlenses 26. Rather, the microlenses 26 collect the light 2017200729 03 Feb 2017 -17- incident from the first main surface 22 and focus it on the second microholes 44, such that a broad angle range results in which the second motif 48 formed by the microholes 44 appears light from the back. 5 The first microholes 42 do not go through the recording layer 30, such that the first motif 46 is not perceptible from the back also in transmitted light due to the opaque second sub-layer 34. Altogether, the viewer thus sees, in a wide angle range, the brightly shining letter string "PL" against a dark background, as illustrated in fig. 5(b). Since the second motif appears mirror reversed when viewed from the back, a 0 mirror-symmetric motif is preferably chosen as the second motif, or a mirror-neutral motif, that is, a motif whose perceptibility is not affected by the mirroring, such as a geometric pattern, an architectural, technical or natural motif.

In one variant, the introduction angle and thus also the viewing angle of the first 5 and/or second microholes can be varied continuously over the dimension of the first or second motif 46,48 in one or even in two spatial directions. Such a continuous variation can be realized, for example, through a suitable deflection system for the laser radiation. The brightness of the first or second motif 46,48 then changes continuously when viewed in reflected light or transmitted light when the security !0 element is tilted.

Reference to background art or other prior art in this specification is not an admission that such background art or other prior art is common general knowledge in Australia or elsewhere. -18- 2017200729 03 Feb 2017

List of reference signs 10 Banknote 12 Security element 14 Opening 20 Support 22,24 Main surfaces 26 Microlenses 30 Recording layer 32,34 First and second sub-layer 40 Microholes 42,44 First and second microholes 46, 48 First and second motif 50 Viewing direction 52 Focused laser radiation 54 Viewing direction 56 Focused laser radiation

Claims

Claims

1. An optically variable security element for security papers, value documents and other data carriers, having - a substantially transparent substrate having opposing first and second main surfaces, - an arrangement composed of microlenses arranged on the first main surface of the substrate, - arranged on the second main surface of the substrate, a laser-sensitive recording layer that includes stacked first and second sub-layers, the first sublayer being arranged between the substrate and the second sub-layer, - a plurality of microholes produced in the laser-sensitive recording layer by the action of laser radiation, of which each microhole is associated with a microlens and is visible through the associated microlens when the security element is viewed from a certain viewing angle, - the plurality of microholes comprising a plurality of first and a plurality of second microholes, the first microholes being present in the first sub-layer and not going through the recording layer, and the second microholes going through the recording layer with the first and second sub-layer, and - the diameter of the first microholes being larger than the diameter of the second microholes.
2. The security element according to claim 1, characterized in that the diameter of the first microholes is more than 10%, especially more than 20%, and particularly preferably more than 30% larger than the diameter of the second microholes.
3. The security element according to claim 1 or 2, characterized in that the first microholes form, in the form of patterns, characters or a code, a first motif that is perceptible when the security element is viewed from a prechosen first viewing direction in reflected light, and in that the second microholes form, in the form of patterns, characters or a code, a second motif that is perceptible when the security element is viewed from a prechosen second viewing direction in transmitted light.
4. The security element according to any one of claims 1 to 3, characterized in that the first and/ or second microholes are introduced into the recording layer through the microlens arrangement from different directions with laser radiation, and in that the microholes are perceptible in reflected light or in transmitted light when viewed from the respective viewing direction.
5. The security element according to any one of claims 1 to 4, characterized in that the first and second microholes are each substantially circular or pattern-shaped.
6. The security element according to any one of claims 1 to 5, characterized in that the microholes are each smaller than the associated microlenses.
7. The security element according to any one of claims 1 to 6, characterized in that the area ratio of microholes and associated microlenses lies below 1.0 or below 0.5 or even below 0.2.
8. The security element according to any one of claims 1 to 7, characterized in that more than 50%, and preferably more than 75% of the second microholes lie within the first microholes.
9. The security element according to any one of claims 1 to 8, characterized in that the first and second sub-layer are formed by metal layers of different colors.
10. The security element according to any one of claims 1 to 9, characterized in that the second sub-layer is formed by a highly reflective metal layer having a reflectivity of 90% or more.
11. The security element according to any one of claims 1 to 10, characterized in that the first and/ or second sub-layer is opaque.
12. The security element according to any one of claims 1 to 11, characterized in that, between the substrate and the recording layer, a motif image is provided that is divided into a plurality of cells, in each of which are arranged imaged regions of a predetermined background motif, the microlens arrangement forming a microlens grid that, when the motif image is viewed, reconstructs the background motif from the imaged regions arranged in the cells.
13. The security element according to claim 12, characterized in that the motif image is present as a relief pattern in an embossing lacquer layer arranged between the substrate and the recording layer.
14. The security element according to claim 13, characterized in that the first and second sub-layer follow the relief of the embossing lacquer layer.
15. The security element according to any one of claims 1 to 14, characterized in that the microlens arrangement is provided with a semitransparent cover layer and/ or a cover layer that is present only in some regions.
16. The security element according to any one of claims 1 to 14, characterized in that the microlens arrangement is free from applied layers that impair or cancel the optical effect of the microlenses.
17. A data carrier having a security element according to any one of claims 1 to 16.
18. The data carrier according to claim 17, characterized in that the security element is arranged in or over a window region or a through opening in the data carrier.
19. A method for manufacturing an optically variable security element for security papers, value documents and other data carriers, in which - a substantially transparent substrate having opposing first and second main surfaces is provided, an arrangement composed of microlenses being arranged on the first main surface of the substrate, - on the second main surface of the substrate is arranged a laser-sensitive recording layer that includes stacked first and second sub-layers, the first sublayer being arranged between the substrate and the second sub-layer, - by the action of laser radiation is produced in the laser-sensitive recording layer a plurality of microholes, of which each micro hole is associated with a microlens and is visible through the associated microlens when the security element is viewed from a certain viewing angle, - the plurality of microholes comprising a plurality of first and a plurality of second microholes, the first microholes being produced in the first sub-layer and not going through the recording layer, and the second microholes being produced going through the recording layer with the first and second sublayer, and - the first microholes being produced having a larger diameter than the second microholes.
20. The method according to claim 19, characterized in that the first and/ or second microholes are introduced into the recording layer through the microlens arrangement from different directions with laser radiation.
21. The method according to claim 19 or 20, characterized in that, on the second main surface of the substrate, in a first step, only the first sub-layer of the laser-sensitive recording layer is produced and provided with the plurality of first microholes by the action of laser radiation, and in a second step, the second sub-layer of the laser-sensitive recording layer is arranged on the first sub-layer, the second microholes being produced going through the recording layer with the first and second sublayer.