EP3233512B1 - Optically variable transparent security element - Google Patents

Description

The invention relates to an optically variable see-through security element for securing valuables, having a planar, optically variable surface pattern, which shows a colored appearance with a viewing angle-dependent multicolor color change.

Data carriers, such as valuables or identity documents, but also other valuables, such as branded goods, are often provided with security elements for the purpose of security, which permit verification of the authenticity of the data carrier and at the same time serve as protection against unauthorized reproduction. Increasingly transparent security features, such as transparent windows in banknotes, are becoming increasingly attractive.

However, conventional transparent or semitransparent security elements with a viewing angle-dependent multicolor color change in transmitted light have various disadvantages. It is known, for example, to produce diffraction colors with translucent or semitransparent coated hologram gratings or transmission gratings in the transmitted light, whereby it can be achieved by suitable choice of the grating periods and the azimuth angle of the grating that different representations with changing colors result under different viewing angles. The appearance of such lattice images, however, strongly depends on the lighting conditions. When illuminated with a point light source, individual subregions can flash very brightly at certain angles and quickly disappear, whereas in diffuse ambient light only a very weak or possibly even no diffraction effect can be visible. Also, the perceived color depends not only on the viewing angle to the security element, but also on the direction to the light source, and also a corresponding security element for viewing the diffraction colors of the first order not directly in front of a light source may be held, but the security element must be kept something out of the direct line of connection. Furthermore, when the security element is tilted, all the rainbow colors are passed through, so that the color changes that occur are largely undefined and the observed color effects are often simply perceived by the untrained viewer as colorful. Finally, holographic techniques are now also used outside the security area and therefore offer only limited protection against counterfeiting.
In another solution, thin-film systems produce colors that change as a function of viewing angle due to interference in reflected light and transmitted light. Different colors are usually realized by a variation of the layer thicknesses, for example the thickness of a dielectric spacer layer in a three-layer structure absorber / dielectric / absorber. The adjustment of a desired color on the adaptation of the layer thicknesses, however, is technologically very expensive. One possibility is to print one or more dielectric layers in sections, but very high demands are placed on the uniformity of the printed layers and the lateral resolution is limited to the resolution achievable with the corresponding printing methods. In addition, motif changes when tilting with such thin film systems are practically unrealizable.
A further solution consists of producing colors with transparent or semitransparently coated subwavelength structures in the transmitted and transmitted light which change when the structures are tilted. However, such subwavelength structures are very demanding in their production and difficult to produce in the required large-scale industrial scale.
DE 10 2009 053 925 A1 relates to a security element according to the preamble of claim 1, wherein through an opaque louver-like structure through an underlying motif image in view viewing angle is dependent visible or not visible. In one variant, an additional motif may be different by area Orientation of the shutter elements are displayed. In another variant, an additional motif may be formed by a thin-film element on the opaque layer.
Proceeding from this, the present invention seeks to provide a see-through security element of the type mentioned, which avoids the disadvantages of the prior art. In particular, the see-through security element should combine an appealing visual appearance with high security against counterfeiting and ideally be able to be produced in the commercial scale required in the security area.
This object is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.
Since the angle of inclination and the azimuth angle in the mentioned subareas of the optically variable area pattern are the same for all facets in each case, the subareas represent in each case just the areas of similarly oriented facets.

In an advantageous embodiment, the facets of a subarea have not only the same orientation but also the same shape and size. The area occupied by each subarea on the optically variable surface pattern is in advantageous embodiments at least 50 times, preferably at least 100 times, more preferably at least 1000 times larger than the area occupied by a single facet of this surface area on average. The sections usually contain a very large number of individual facets.

In an advantageous embodiment, the facets of the at least two partial regions differ in inclination angle against the plane by 5 ° or more, preferably by 10 ° or more, particularly preferably by 20 ° or more. Alternatively or additionally, the facets of the at least two partial regions differ in the azimuth angle in the plane by 45 ° or more, preferably by 90 ° or more, in particular by 180 °.

The facets of the surface pattern are preferably formed by flat surface pieces, which are each characterized by their shape, size and orientation. The orientation of a facet is indicated by the inclination α against the plane of the surface pattern and by an azimuth angle θ in the plane of the surface pattern. The azimuth angle θ is the angle between the projection of the normal vector of the facet on the plane of the surface pattern and a reference direction in the plane. Since the azimuth angle θ depends on the choice of the reference direction, its absolute value has no meaning, but the difference of the azimuth angle of different sub-ranges, since this describes the different relative orientation of the facets in the associated sub-areas. In principle, it is also possible, although not currently preferred, to provide curved facets. Even with these curved facets, the orientation can be through a normal vector averaged over its surface and thus an averaged angle of inclination α and an average azimuth angle θ can be specified.

The dimension of the facets is preferably so large that no or hardly diffraction effects occur, so that the facets essentially act only radiation-optical. In particular, the facets advantageously have a smallest dimension of more than 2 μm, preferably more than 5 μm, in particular more than 10 μm. In particular, for use in banknotes and other documents of value, the facets preferably have a height below 100 μm, preferably below 50 μm, in particular below 10 μm. The facets can be arranged regularly, for example in the form of a 1- or 2-dimensional periodic grid, for example a sawtooth grid, or else aperiodically.

Another possibility to suppress unwanted diffraction effects is to aperiodically offset the facets in their height above the surface area. With an aperiodic displacement of the facets, there is no simple, regular relationship between the heights of adjacent facets, so that constructive interference of the light reflected at neighboring facets and thus the emergence of a superimposed diffraction pattern are reliably prevented. Details of such aperiodic displacement of the document WO 2012/055506 A1 are removed, the disclosure content of which is included in the present application in this respect.

In principle, all coatings which show a viewing angle-dependent color change in transmitted light can be used as the interference layer. A first example of an advantageous interference layer is a thin-film element with semitransparent metal layers and a dielectric spacer layer, in particular with a structure absorber / dielectric / absorber, wherein for example metals such as Ag, Au, Cr or Al can be used as absorber layers and SiO ₂ , MgF ₂ or polymers can be used as the dielectric layer. Dielectric layer systems, in particular multilayer systems, are also suitable as interference layer, in particular layer structures with at least one high-index layer, such as TiO ₂ or ZnS, preferably combined with at least one low-index layer, such as SiO ₂ or MgF ₂ . The thin-film element may also contain semiconductive layers, such as Si, for example, a thin-film structure of the Si / SiO ₂ / Si layer sequence may be used. As dielectric spacer layers, it is also possible, for example, to use polymers instead of oxides. Finally, it is also possible to use liquid-crystalline layers, in particular with color-changing cholesteric liquid crystals, as the interference layer.

The entire optically variable surface pattern is advantageously provided with the same interference layer, which is applied simultaneously to all facets. After application, the interference layer can be further structured by subsequent process steps in order to produce interference-layer-free regions. Also, the interference layer depending on the inclination of the facets may have a locally different thickness, as explained in more detail below.

In an advantageous embodiment, the interference layer has a layer thickness which does not depend significantly on the angle of inclination of the coated facets. Such a substantially constant layer thickness can be achieved, for example, with non-directional coating methods be achieved or results in a coating with cholesteric liquid crystals in the form of constant distances of the planes with the same refractive index.

In another, particularly advantageous embodiment, the facets are provided with an interference layer whose layer thickness varies with the inclination angle α of the facets, in particular decreases with increasing inclination angle α. The present inventors have surprisingly found that such an interference layer can produce particularly strong color differences between facets of different inclinations. As a result, on the one hand, a particularly large color palette for the colored appearances is available, which even allows the production of true color images, on the other hand can be realized in this way strong color change when tilting the surface pattern. Such a varying layer thickness of the interference layer can be achieved, for example, by directional coating methods, such as vacuum evaporation methods. In such processes, the angle of inclination of the facets leads to an increase in the effective surface area, so that less material per unit area is deposited on inclined facets, and the resulting layer thickness thus strongly depends on the angle of inclination of the facets.

The facets are advantageously embossed in an embossing lacquer layer having a first refractive index. A lacquer layer having a second refractive index, which differs from the first refractive index of the embossing lacquer layer by less than 0.3, in particular by less than 0.1, is applied over the interference layer. Due to this essentially identical refractive index of the two paint layers, incident light traverses the security element independently of the local inclination angle α of the facets essentially without directional deflection, thus ensuring a uniform distribution of brightness in the plane of the surface pattern.

In an advantageous embodiment, the at least two partial regions are arranged in the form of a motif, wherein the optically variable surface pattern shows the motif formed by the partial regions in review, at least in certain tilted positions of the security element with two or more different colors. For this purpose, the inclination angles α and the azimuth angles θ of the facets and the interference layer in the two subregions are advantageously matched to one another in such a way that the subregions display the same colors in a certain tilted position and different colors in other tilted positions. Overall, the security element then shows a motif that arises when tilted from a homogeneous appearing surface or disappears into a seemingly homogeneous surface.

Since the complete color effect of the coated facets depends not only on their orientation, but also on the properties of the interference layer selected, both the inclination angles α of the facets, the azimuth angles θ of the facets and the interference layer must be coordinated in the subregions such that the desired color effect is achieved.

• in einer ersten Kippstellung ein erstes Motiv zeigt, bei dem der erste Vordergrundbereich mit einer Motivfarbe und der zweite Vordergrundbereich und der Hintergrundbereich mit einer von der Motivfarbe unterschiedlichen Hintergrundfarbe erscheinen, und
• in einer zweiten Kippstellung ein zweites Motiv zeigt, bei dem der zweite Vordergrundbereich mit der Motivfarbe und der erste Vordergrundbereich und der Hintergrundbereich mit der Hintergrundfarbe erscheinen.

In an advantageous development, the optically variable surface pattern contains at least three partial regions, which are arranged in the form of a background region and two foreground regions, and in which the inclination angles α and the azimuth angles θ of the facets and the interference layer are matched to one another such that the optically variable surface pattern in review

• in a first tilted position shows a first motif, in which the first foreground area with a subject color and the second foreground area and the background area appear with a different background color of the subject color, and
• in a second tilt position, a second motif is shown, in which the second foreground area with the subject color and the first foreground area and the background area with the background color appear.

• in einer ersten Kippstellung ein erstes Motiv zeigt, bei dem der erste Vordergrundbereich und der Überlappungsbereich mit einer Motivfarbe und der zweite Vordergrundbereich und der Hintergrundbereich mit einer von der Motivfarbe unterschiedlichen Hintergrundfarbe erscheinen, und
• in einer zweiten Kippstellung ein zweites Motiv zeigt, bei dem der zweite Vordergrundbereich und der Überlappungsbereich mit der Motivfarbe und der erste Vordergrundbereich und der Hintergrundbereich mit der Hintergrundfarbe erscheinen.

Advantageously, in one development, the optically variable surface pattern contains at least four partial regions which are arranged in the form of a background region, two foreground regions and an overlap region, and in which the inclination angles α and the azimuth angles θ of the facets and the interference layer are coordinated with one another such that the optically variable surface pattern in transparency

• in a first tilted position, showing a first motif in which the first foreground area and the overlapping area with a subject color and the second foreground area and the background area with a background color different from the subject color appear, and
• in a second tilt position, a second motif is shown, where the second foreground area and the overlap area with the subject color and the first foreground area and the background area with the background color appear.

In all configurations, the optically variable surface pattern advantageously contains at least two partial regions in which the facets have the same inclination angle a but azimuth angles θ differing by 180 °. The inclination angles α are advantageously greater than 5 °, particularly preferably greater than 10 °, and are for example 15 °, 20 ° or 25 °. As explained in more detail below, in this way, a tilt image with one of a homogeneous surface herauskippendem or eininkippendem in a homogeneous surface motif can be realized.

If the optically variable surface pattern contains at least four partial regions, it is advantageously provided that the optically variable surface pattern contains a first and second partial region in which the facets have the same inclination angle ao but azimuth angles θ differing by 180 °, and further a third and fourth sub-area, in which the facets have different inclination angles α ₁ and α ₂ and in which the azimuth angle θ differs by 90 ° or 270 ° from the azimuth angle of the first and second sub-area. The inclination angles α ₀ are advantageously greater than 5 °, particularly preferably greater than 10 °, and are for example 15 °, 20 ° or 25 °. As explained in more detail below, can be realized in this way in a particularly simple manner, a tilt image with two different motifs.

In principle, tilt images with two different, even overlapping motifs can already be realized with an optically variable surface pattern with only three partial areas. In the case of at least partially overlapping motifs, however, this usually requires an interleaving of the subregions assigned to the motifs, in which, as described in more detail below, the surface pattern is decomposed into narrow strips or small pixels.

In an advantageous development, the optically variable surface pattern contains at least three subregions in which the inclination angle α and the azimuth angle θ of the facets and the interference layer are matched to one another so that the subregions appear in a tilted position as viewed in red, green or blue. Preferably, these colors are not tipped Security element, that is generated in vertical viewing. In an advantageous development, the optically variable surface pattern may additionally have in the subregions a black mask which has been matched to the inclined facets and which serves to adjust the translucent brightness of the facets in the respective subregions. The three subareas may, optionally together with the black mask, thereby advantageously represent the color separations of a true color image. In this way can be displayed in the selected tilt position in perspective realistic appearing true color images.

The invention also includes a data carrier with a see-through security element of the type described, wherein the see-through security element is preferably arranged in or over a window region or a through opening of the data carrier. The data carrier may in particular be a value document, such as a banknote, in particular a paper banknote, a polymer banknote or a film composite banknote, but also an identity card, such as a credit card, bank card, cash card, authorization card, identity card or a Trade personalization page.

The invention further includes a method of fabricating an optically variable see-through security element in which a substrate is provided and the substrate is provided with a planar, optically variable area pattern which shows in phantom a colored appearance with a viewing angle dependent multicolor color change. According to the invention, the optically variable surface pattern is generated with a plurality of substantially radiation-optical facets whose orientation is in each case by an inclination angle α against the plane of the surface pattern, which lies between 0 ° and 45 °, and by a Azimuth angle θ is characterized in the plane of the surface pattern, the facets are provided with an interference layer with a viewing angle-dependent color change, and the optically variable surface pattern is generated with at least two subregions, each having a plurality of identically oriented facets, wherein the facets of the at least two Divide sections from each other in the angle of inclination against the plane and / or in the azimuth angle in the plane.

In an advantageous variant of the method, the facets are coated with the interference layer in a directional coating process, in particular in a vacuum vapor deposition process.

Further exemplary embodiments and advantages of the invention are explained below with reference to the figures, in the representation of which a representation true to scale and proportion has been dispensed with in order to increase the clarity.

Fig. 1

eine schematische Darstellung einer Banknote mit einem erfindungsgemäßen optisch variablen Durchsichtsicherheitselement,

Fig. 2

schematisch den Schichtaufbau des Sicherheitselements der Fig. 1 im Querschnitt,

Fig. 3

schematisch ein berechnetes Farbspektrum von Facetten mit einer dreischichtigen Interferenzbeschichtung mit einer ersten, 25 nm dicken Ag-Schicht, einer SiO₂-Abstandsschicht der Dicke d und einer zweiten, ebenfalls 25 nm dicken Ag-Schicht, aufgetragen in Abhängigkeit von der Dicke d und dem Winkel φ des Lichteinfalls auf die Interferenzbeschichtung,

Fig. 4

zur Erläuterung des auftretenden Kippeffekts das Sicherheitselement der Fig. 2 mit der Interferenzbeschichtung der Fig. 3, in (a) in nicht verkippter Lage und in (b) in einer um β = 20° nach rechts gekippten Lage,

Fig. 5

ein Sicherheitselement nach einem weiteren Ausführungsbeispiel der Erfindung, bei dem in unterschiedlichen Kippstellungen unterschiedliche Motive sichtbar sind, wobei (a) in Aufsicht die Aufteilung des optisch variablen Flächenmusters des Sicherheitselements in drei Teilbereiche zeigt, und (b) bis (d) das Sicherheitselement im Querschnitt in verschiedenen Kippstellungen zeigen,

Fig. 6

ein Sicherheitselement nach einem weiteren Ausführungsbeispiel der Erfindung, dessen optisch variables Flächenmuster in vier Teilbereiche aufgeteilt ist,

Fig. 7

schematisch ein berechnetes Farbspektrum von beschichteten Facetten bei senkrechtem Lichteinfall auf die Ebene des Flächenmusters, wobei die Interferenzbeschichtung durch eine dreischichtige Interferenzbeschichtung mit einer ersten, 25 nm dicken Ag-Schicht, einer SiO₂-Abstandsschicht der nominellen Dicke d₀ und einer zweiten, ebenfalls 25 nm dicken Ag-Schicht gebildet ist, und die Schichtdicke d der Abstandsschicht mit dem Neigungswinkel α gemäß der Beziehung d = d₀ cos α abnimmt, wobei das Farbspektrum in Abhängigkeit von der nominellen Dicke d₀ der Abstandsschicht und dem Neigungswinkel α der Facetten aufgetragen ist, und

Fig. 8

in (a) bis (e) im Querschnitt verschiedene Zwischenstadien bei der Herstellung eines optisch variablen Flächenmusters zur Darstellung eines Echtfarbbilds mit einer passergenauen Schwarzmaske.

Show it:

Fig. 1

a schematic representation of a banknote with an optically variable transparent security element according to the invention,

Fig. 2

schematically the layer structure of the security element of Fig. 1 in cross section,

Fig. 3

schematically a calculated color spectrum of facets with a three-layer interference coating with a first, 25 nm thick Ag layer, a SiO ₂ spacer layer of thickness d and a second, likewise 25 nm thick Ag layer, applied as a function of the thickness d and the angle φ of the light incident on the interference coating,

Fig. 4

to explain the occurring tilting the security element of Fig. 2 with the interference coating of Fig. 3 , in (a) in a non-tilted position and in (b) in a position tilted β = 20 ° to the right,

Fig. 5

a security element according to a further embodiment of the invention, in which different motifs are visible in different tilt positions, wherein (a) shows in plan the division of the optically variable surface pattern of the security element into three sections, and (b) to (d) the security element in cross section show in different tilt positions,

Fig. 6

a security element according to a further exemplary embodiment of the invention, whose optically variable area pattern is divided into four partial areas,

Fig. 7

schematically a calculated color spectrum of coated facets at normal incidence of light on the plane of the surface pattern, wherein the interference coating by a three-layer interference coating with a first, 25 nm thick Ag layer, a SiO ₂ spacer layer of nominal thickness d ₀ and a second, also 25 nm thick Ag layer is formed, and the layer thickness d of the spacer layer decreases with the inclination angle α according to the relationship d = d ₀ cos α, wherein the color spectrum is plotted against the nominal thickness d _{0 of} the spacer layer and the inclination angle α of the facets, and

Fig. 8

in (a) to (e) in cross-section different intermediate stages in the production of an optically variable surface pattern to represent a true color image with a register-accurate black mask.

The invention will now be explained using the example of security elements for banknotes. Fig. 1 shows a schematic representation of a banknote 10 with an optically variable see-through security element 12 according to the invention, which is arranged over a continuous opening 14 of the banknote 10. The security element 12 shows in phantom a colored appearance with a motif 16, 18 which has a viewing angle-dependent multicolor color change.

In the embodiment of the Fig. 1 shows the security element 12 in a vertical viewing perspective, a homogeneous, monochrome yellow area in which the value "10" of the foreground area 16 is not recognizable because of the lack of color difference to the background 18. However, when the security element 12 is tilted to the right or left (reference numerals 20-R, 20-L) and viewed at an oblique angle, the colors of the foreground 16 and the background 18 change in different ways, so that the value "10" clearly stands out in the tilted position due to the color difference. For example, when the right-hand 20-R tilted, the see-through color of the background area 18 changes from yellow to green, while the see-through color of the foreground area 16 changes from yellow to red. Tilting to the left 20-L results in reverse color changes, that is, the see-through color of the background area 18 changes from yellow to red, while the see-through color of the foreground area 16 changes from yellow to green. The security element 12 thus shows in review from different viewing directions very different visual appearances, which is unexpected especially for transparency elements for the viewer and therefore has a high attention and recognition value.

Fig. 2 schematically shows the layer structure of the security element 12 according to the invention in cross section, wherein only the parts of the layer structure required for the explanation of the principle of operation are shown.

The security element 12 has a planar, optically variable surface pattern which contains a multiplicity of essentially radiation-optical facets 32. The facets 32 are formed by flat surface pieces and are each characterized by their shape, size and orientation. As already generally explained above, the orientation of a facet 32 is indicated by the inclination α to the plane 30 of the surface area and by an azimuth angle θ in the plane 30, the azimuth angle θ being the angle between the projection of the normal vector 46, 48 of a facet 32 the level 30 and a reference direction is Ref.

As in Fig. 2 11, the azimuth angles θ differ, however, by 180 °, so that the facets 32 are tilted to the left in the partial region 16, while the facets 32 are tilted to the left are tilted in the partial area 18 to the right.

The facets 32 of the surface pattern are embossed into a preferably transparent embossing lacquer 34 and, in the exemplary embodiment, have a square outline with a dimension of 20 μm × 20 μm. The facets 32 are further provided with an almost transparent or at least semitransparent interference coating 36 which, when viewed, produces a color impression dependent on the viewing angle.

The interference coating 36 may be formed, for example, of a three-layer thin-film structure having two metallic semitransparent layers, such as aluminum, silver, chromium, gold, or copper, and an intervening dielectric spacer layer, such as SiO ₂ , MgF _2, or a polymer. In the embodiments described above, the thickness of the interference coating 36 is independent of the inclination angle α of the facets 32.

Over the interference coating 36, a further resist layer 38 is applied, which has substantially the same refractive index as the resist layer 34, which ensures that incident light passes through the layer sequence of the security element 12 regardless of the local inclination angle α of the facets 32 substantially without directional deflection and thus a uniform Brightness distribution generated in the plane of the surface pattern.

The interference coating 36 of the facets produces a color impression in transmitted light that depends on both the direction of incidence of the light relative to the plane normal of the optically variable area pattern and the individual inclination angle of the facets 32, since both factors influence the angle of incidence of the light relative to the normal of the interference coating 36 ,

Fig. 3 schematically shows a calculated color spectrum of facets 32 with a three-layer interference coating 36 having a first, 25 nm thick silver layer, a SiO ₂ spacer layer of thickness d and a second, 25 nm thick silver layer. The thickness of the spacer layer is plotted on the abscissa, while plotted on the ordinate, the angle φ of the light incident on the interference coating, based on vertical incidence of light (φ = 0 °). As in Fig. 3 In the case of very thin spacer layers, the transparency is initially outside the visible spectral range and then changes to blue (B), green (G) and yellow (Y) to red (R) for spacer layers with layer thicknesses in the range of about 130 nm After a region without visible see-through color, this sequence is repeated at higher layer thicknesses from 200 nm to about 350 nm.

If one uses in the embodiment of Figures 1 and 2 Such an interference coating 36 with a SiO ₂ spacer layer of thickness d = 130 nm, resulting in normal incidence of light 40 depending on the tilting state of the security element 12 in 4 (a) and (b) shown situations.

Fig. 4 (a) shows the security element 12 initially in a non-tilted position in which the light 40 is incident parallel to the plane normal 42. Because of the angle of inclination of the facets 32 in the subregions 16, 18 of α = 20 °, the light 40 equally falls in both subregions at an angle of φ = 20 ° with respect to the interference layer normal 46 and 48, respectively. Again Fig. 3 can be taken at point 50, the interference coating 36 generates a yellow see-through color in both partial areas 16, 18. The different azimuth angle of the facets 32 has no effect on the see-through color, since it does not lead to a change in the light incidence angle leads. Due to the lack of color contrast, the subregions 16, 18 can therefore not be distinguished in a transparent view, and the security element 12 appears as a monochrome, homogeneous surface.

In Fig. 4 (b) is the security element 12 tilted by β = 20 ° to the right, so that the light 40 is no longer parallel to the plane normal 42 incident, but with this an angle of β = 20 ° includes. Due to the different azimuth angle, the tilting of the security element 12 has different effects on the facets 32 in the subregions 16 and 18, respectively.

In the partial region 16, the angle between the incident light 40 and the interference layer normal 46 is reduced by β = 20 ° due to the tilting to the right, so that the light 40 there is now perpendicular to the interference layer 36 (φ = 0 °). Again Fig. 3 At point 54, the interference coating 36 therefore generates a red transmission color in the partial region 16. On the other hand, in the partial region 18, the inclination increases the angle between the incident light 40 and the interference layer normal 48 by β = 20 °, so that the light 40 there now impinges on the interference layer 36 at an angle of φ = 40 °. Again Fig. 3 at point 52, the interference coating 36 therefore produces a green see-through color in the subregion 18.

With a tilt by 20 ° to the left, the conditions are reversed accordingly, so that then the light 40 in the partial region 18 is incident perpendicular to the interference layer 36 and generates a red see-through color, while in the partial region 16 at an angle of φ = 40 ° incident on the interference layer 36 and generates a green see-through color.

The monochrome homogeneous color impression at normal incidence of light in Fig. 4 (a) is a consequence of the equality of the inclination angle α in the two sub-areas 16,18 with simultaneous azimuth angle difference of 180 °. By another choice of the inclination angle and / or azimuth angle can also be achieved that adjusts the homogeneous color impression in other viewing directions. If, for example, the angle of inclination α = 30 ° to the left and the partial region 16 α = 0 ° are selected at unchanged azimuth angles in the partial region 18, the result is a monochrome homogeneous color impression at a tilt angle of 15 ° to the left.

A security element 60 according to the invention can also show a tilted image in which different motifs are visible in different tilt positions, as is now the case with reference to FIG Fig. 5 explained. Fig. 5 (a) first shows in plan the division of the optically variable surface pattern of the security element 60 into three sub-areas 62, 64, 66, which are arranged in the form of a background area 62, a first foreground area 64 (triangle) and a second foreground area 66 (circle).

Fig. 5 further shows in (b) to (d) the security element 60 in cross section in different tilted positions. The security element 60 is basically like the security element 12 of Fig. 2 However, in the foreground regions 64 and 66 the facets have the same inclination angle α against the plane 30, for example α = 20 °, but the azimuth angles θ of the two foreground regions differ by 180 °, so that the facets 32 in the partial area 64 are tilted to the right, while the facets 32 in the partial area 66 are tilted to the left. In the background region 62, the facets 32 are aligned parallel to the plane of the surface element, ie have an inclination angle of α = 0 °.

In this exemplary embodiment, the interference layer 36 is selected such that it produces an orange transmission color at normal incidence (φ = 0 °), a yellow transmission color at incidence below φ = 10 °, a transparent green color at incidence below φ = 20 °, and incident light under φ = 30 ° a blue transparent color.

In the not tilted location of Fig. 5 (b) incident light parallel to the plane normal 42 and therefore also falls perpendicular to the facets 32 of the background region 62, while including both with the facets 32 of the first foreground area 64 and with facets 32 of the second foreground area 66 each having an angle of 20 °. The background region 62 therefore appears orange in transmitted light, while the two foreground regions 64, 66 appear green.

In the position of Fig. 5 (c) If the security element 60 is tilted by β = 10 ° to the left, so that the light 40 is no longer incident parallel to the plane normal 42, but with this an angle β = 10 ° includes. In the background region 62, the inclination increases the angle between the incident light 40 and the interference layer normal 72 by β = 10 °, so that the light 40 there is now incident at an angle of φ = 10 ° and produces a yellow transmission color as the background color. By contrast, in the first foreground area 64, the inclination reduces the angle between the incident light 40 and the interference layer normal 74 by β = 10 °, so that the light 40 there now likewise falls at an angle of φ = 10 ° and therefore, as in the background area 62 creates a yellow transparency (the background color). On the other hand, in the second foreground area 66, the inclination causes the angle between the incident light 40 and the interference layer normal 76 to be β = 10 ° increases, so that the light 40 there now at an angle of φ = 30 ° incident on the interference layer 36 and therefore produces a blue transparency color (the subject color). As a result, in this tilted position, only the motif of the second foreground region 66 is visible, since the motif of the first foreground region 64 merges with the background region 62 in the same color.

Conversely, in the position of the Fig. 5 (d) the security element 60 tilted by β = 10 ° to the right. In the background region 62, this tilt increases the angle between the incident light 40 and the interference layer normal 72 again by β = 10 °, so that the light 40 is incident there at an angle of φ = 10 ° and again a yellow transparent color (the background color). generated. The first and second foreground areas now exchange their roles. In the first foreground area 64, the inclination increases the angle between the incident light 40 and the interference layer normal 74 by β = 10 °, so that the light 40 there is now incident at an angle of φ = 30 ° and a blue transparent color (the subject color). generated. On the other hand, in the second foreground area 66, the inclination reduces the angle between the incident light 40 and the interference layer normal 76 by β = 10 °, so that the light 40 is incident there on the interference layer 36 at an angle of φ = 10 ° and therefore as in FIG Background area 62 generates a yellow transparency (the background color). As a result, in this tilted position, only the motif of the first foreground region 64 is visible, since the motif of the second foreground region 66 merges with the background region 62 in the same color.

In the embodiments of the Figures 2 and 5 has been illustrated by a color change in a right / left tilt of the security element went out. Of course, depending on the azimuth angle of the facets 32, other tilting directions, for example an up / down tilting, can also be used for the color change.

In the embodiment of the Fig. 5 For example, the foreground regions 64, 66 are spatially separated from each other in the plane of the surface pattern, and thus have no overlap. If tipping motives are to be realized with overlaps, this can be achieved, for example, by interleaving the subareas assigned to the motifs. For this purpose, the surface pattern is decomposed into narrow strips or small pixels, alternately the first foreground motif 64 and the background motif 62 on the one hand and the second foreground motif 66 on the other hand and the background image 62 included. The dimensions of the small strips or pixels are in particular below 300 .mu.m or even below 100 .mu.m, so that the division of the surface pattern with the naked eye is not recognizable or at least not noticeable.

However, the interleaving of overlapping representations with three subregions with different facet orientations usually leads to the fact that the chroma or the contrast of the see-through colors does not reach the maximum possible values, since the interleaving can in part only produce mixed colors, and mixed colors in general have a lower chroma than the original colors.

However, very high-contrast and colorful tilting pictures can be realized by using four sections with different facet orientations, as in Fig. 6 shown schematically.

In the security element 80, the optically variable area pattern is divided into four subareas 82, 84, 86, 88, which are in the form of a background area 82, a first foreground area 84 (square without circle segment 88), a second foreground area 86 (circular disk without circle segment 88) and an overlap region 88 (circle segment) are arranged. The first foreground area 84 forms, together with the circle segment 88, the complete square as the first motif to be displayed, the second foreground area 86 together with the circle segment 88 as the second motif to be represented forms the complete circular disk. Although the two motifs to be displayed overlap in the overlapping area 88, their see through color is not due to color mixing.

The inclinations and azimuth angles of the facets in the four subregions are selected so that the security element 80 in a first tilted position in the transmitted light as the first motif to be displayed the complete square (first foreground area 84 and circle segment 88 together) with a uniform subject color and the remaining area pattern ( second foreground area 86 and background area 82) with a background color different from the subject color. In a second tilted position, the security element 80 shows in transmitted light as the second motif to be displayed the complete circle (second foreground area 86 and circle segment 88 together) with the uniform subject color, while the remaining area pattern (first foreground area 84 and background area 82) appears with the background color.

In order to achieve this, the inclination and the azimuth angle of the facets in the background region 82 are thus selected such that they produce the background color both in the first and in the second tilt position. The slope and azimuth angle of the facets in the first foreground area 84 are selected such that they produce the motif color in the first tilted position and the background color in the second tilted position, while the facets in the second foreground region 86 are selected such that they produce the background color in the first tilted position and the subject color in the second tilted position. Finally, in the overlapping area 88, the inclination and the azimuth angle of the facets are selected such that they produce the motif color both in the first and in the second tilt position. Overall, therefore, four partial areas with different orientations of the facets are required.

The required inclinations and azimuth angles in the various subregions can be determined, for example, by the following procedure, wherein it is concretely assumed that the first tilted position results from a tilting 90-0 of the security element 80 upwards at a certain angle, while the second tilted position by tilting 90-U of the security element 80 by the same angle down.

First, for the facets of the first and second foreground areas 84, 86, the azimuth angle in the tilting direction 90-0, 90-U, that is, θ = 270 ° and θ = 90 °, respectively, is set relative to the reference direction Ref shown in the figure. As the angle of inclination α, that angle is defined for both foreground areas, which generates the desired subject color when the mirrors are inclined upwards or downwards in the first or second tilted position. This essentially corresponds to that already related to Fig. 2 described procedure. By way of illustration, in Fig. 6 In each of the different subareas, the projections of the normal vectors of the facets are also drawn onto the plane of the surface pattern. For example, the facets in the first foreground area 84 have one Inclination angle α = 25 ° and an azimuth angle of θ = 270 ° with respect to the reference direction Ref on, as shown by the projected normal vector 94 (the azimuth angle is measured counterclockwise from the reference direction as usual). Accordingly, the facets in the second foreground area 86 also have an inclination angle α = 25 °, but an azimuth angle of θ = 90 ° with respect to the reference direction Ref, as shown by the projected normal vector 96.

Similar to Fig. 2 For example, the facets in the portions 84, 86 have the same inclination angles α, while the azimuth angles θ differ by 180 °. Because of the symmetry of the arrangement, this ensures that the first foreground area 84 in the first tilted position shows the same see-through color (subject color) as the second foreground area 86 in the second tilted position. The first foreground area 84 shows the background color in the second tilted position, as does the second foreground area 86 in the first tilted position.

It was also determined in a series of experiments at which angles of inclination coated with the selected interference coating facets at an azimuth angle of 0 ° or 180 ° in the first tilt position, the subject color or the background color. These angles of inclination generally depend on the type of interference coating, the dependence of the interference layer thickness on the angle of inclination of the facets and the refractive indices of the embedding lacquer layers, but can easily be determined by a simple series of experiments. For example, it follows that the facets in the first tilt position at an azimuth angle of 0 ° and an inclination angle α _M show the subject color and at an inclination angle α _H show the background color. Because of the symmetry of the arrangement is then ensured that the facets this Show colors even in the second tilted position, as this is achieved by tilting the security element by the same angular amount as the first tilted position.

The facets in the overlap area 88 are then formed with an angle of inclination α = α _M and an azimuth angle of θ = 0 ° or θ = 180 °, while the facets in the background area 82 with an inclination angle α = α _H and an azimuth angle of θ = 0 ° or θ = 180 °. The associated projected normal vectors 98 and 92 are for θ = 0 ° in Fig. 6 located. Due to the choice of the orientation of the facets in the different subregions 82, 84, 86, 88, the above-described visual appearances in the two tilted positions are then realized.

mit der nominellen Schichtdicke d₀, die bei ungeneigten Facetten erhalten wird. Wie die Erfinder überraschend gefunden haben, können durch die mit zunehmender Neigung abnehmende Schichtdicke die in Fig. 3 gezeigten Farbunterschiede zwischen unterschiedlich gezeigten Facetten noch deutlich verstärkt werden.In the embodiments described so far, the thickness of the interference coating was independent of the tilt angle of the facets. However, particularly strong color differences can be produced if, for applying the interference coating, a coating method is selected in which the layer thickness achieved depends on the inclination of the facets. This can be achieved, for example, by a directional vacuum deposition of the facets, with a layer thickness resulting from vertical vapor deposition which is essentially proportional to the cosine of the angle of inclination α, ie $$\mathrm{d}={\mathrm{<figure-callout\; id="0"\; label="d"\; filenames="imgf0004.png"\; state="\{\{state\}\}">d</figure-callout>}}_0\mathrm{cos\; \alpha }$$

with the nominal layer thickness d ₀ , which is obtained at non-faceted facets. As the inventors have surprisingly found, by decreasing with increasing inclination layer thickness in Fig. 3 shown color differences between different facets shown are significantly enhanced.

Fig. 7 schematically shows a calculated color spectrum of coated facets at normal incidence of light on the plane of the surface pattern, wherein the interference coating by a three-layer interference coating with a first 25 nm thick silver layer, a SiO ₂ spacer layer of nominal thickness do and a second, also 25 nm thick silver layer is formed. In this case, it is assumed that the real layer thickness d of the spacer layer decreases with the inclination angle for a facet with an inclination angle α in accordance with the relationship d = d ₀ cos α. The nominal thickness d ₀ is plotted on the abscissa, while the inclination angle α of the facets is plotted on the ordinate.

Like a comparison of Figures 3 and 7 shows, the pitch-dependent layer thickness significantly greater color differences are achieved. Since facets of different inclinations can be produced simply by embossing into an embossing lacquer layer 34, subareas of very different colors can be arranged with a high accuracy of a few micrometers to each other.

The embodiments described above can be realized not only with interference coating constant thickness, but advantageously also with an interference coating with tilt-dependent thickness, which can be generated, for example, tilt images with particularly strong color contrasts.

It is particularly remarkable and surprising that there are certain layer thicknesses in some interference layer systems in which the primary colors red, green and blue are produced with the same interference coating depending on the angle of inclination of the facets as see-through colors can. Im in Fig. 7 shown layer system is, for example, at a nominal thickness of the spacer layer of d ₀ = 330 nm at an inclination angle of α = 0 °, the see-through color red (point 100), at an inclination angle of α = 25 °, the see-through color green (point 102) and at Inclination angle of α = 40 ° produces the transmission color blue (point 104).

In this way, by suitable arrangement of small red, green and blue color areas in view true color images can be generated because any color can be represented as additive color mixing of these three primary colors. The subregions are formed for this purpose, for example, as in a conventional RGB display in the form of small pixels or stripes.

In order to be able to produce realistic true color images, the brightness of the color areas in the individual pixels must be able to be specifically adjusted. For example, the color areas of individual pixels can be overprinted black or coated with an opaque metallization, the technological challenge being the exact registration of overprinting or of the coating.

Specifically, an optically variable area pattern for representing a true color image with a registration-accurate black mask can be used with reference to FIG Fig. 8 be prepared manner described. Fig. 8 shows in (a) to (e) in cross section various intermediate stages in the production of the optically variable surface pattern 110, wherein only a small portion of the surface pattern is shown, namely just a single color pixel 112 with a red color range 114-R, a green color range 114-G and one blue color range 114-B. The size of the color pixel 112 is, for example, 100 μm × 100 μm.

Regarding Fig. 8 (a) are in the red color region 114-R facets 32 having an inclination angle α = 0 ° (corresponding to point 100 in FIG Fig. 7 ), in the green color region 114-G facets 32 having an inclination angle α = 25 ° (corresponding to point 102 in FIG Fig. 7 ) and in the blue color region 114-B facets 32 with an inclination angle α = 40 ° (corresponding to point 104 in FIG Fig. 7 ) embossed in the lacquer layer 34. Between the facets 32, elevations 116 are provided which later form the black area for each color area and whose area ratio to the facets is selected according to the desired brightness of the respective color area. If, for example, the red component in the color pixel 112 shown is to have a brightness of 70%, the facets occupy 70% and the elevations 30% of the total area of the color region 112-R.

Subsequently, the embossed lacquer layer 34, as in Fig. 8 (b) shown, over the entire surface with the selected interference coating 36 provided, such as the above-mentioned three-layer system of a first 25 nm thick silver layer, a nominally 330 nm thick SiO ₂ spacer layer and a second 25 nm thick silver layer. At least the SiO ₂ spacer layer is produced by directional coating methods, for example by vertical vapor deposition, so that the described dependence of the actual layer thickness of the spacer layer on the angle of inclination α of the facets is established.

Then, as in Fig. 8 (c) shown, the interference coating 36 removed only on the elevations 116. This can be done for example with a metal transfer method, as described in the document DE 10 2010 019 766 A1 For example, an etch resist may be printed over the entire surface of the coated resist layer and doctored so that the resist remains only in the faceted depressions and the interference coating 36 may be etched away from the non-resist covered bumps.

Now, a blackened photoresist 118 is applied to the opposite side of the surface pattern as in FIG Fig. 8 (d) and exposed from the upper side through the partially coated surface pattern (reference numeral 120) as shown in FIG Fig. 8 (e) shown. The exposure dose is chosen so that the photoresist is removed during the exposure by the interference layer during development, the remains of the elevations 116 without interference layer exposed photoresist but stops. After development, a black mask 122 is obtained in this way on the back of the surface pattern, which is blackened exactly at the locations where there are no facets 32 provided with an interference layer 36, as in FIG Fig. 8 (f) shown. The surface pattern of Fig. 8 (f) is then further processed by further process steps to the finished security element, for example by applying a further lacquer layer 38 to the interference coating 36 and by applying further protective or functional layers.

In another variant of the method can in the step of Fig. 8 (b) Instead of the interference coating, an auxiliary layer, for example an opaque aluminum layer, which only serves to structure the photoresist 118, is also initially applied. After patterning the photoresist 118 to create the black mask in the step of Fig. 8 (f) the auxiliary layer is completely removed and the desired interference layer 36 is applied over the entire surface. This variant offers the advantage that the interference coating neither in the exposure step ( Fig. 8 (e) ) can serve as a reliable exposure mask, nor that the interference coating etched away well ( Fig. 8 (c) ) must be. Rather, an auxiliary layer optimized for these requirements can be selected, while the interference coating is selected only on the basis of the desired coloring properties.

In principle, however, the black mask can also be produced by other methods, for example by metal transfer methods, etching methods or else directly or indirectly via laser ablation controlled by embossed structures.

LIST OF REFERENCE NUMBERS

10

bill

12

Through security element

14

through opening

16

foreground

18

background

20-R, 20-L

tilt directions

30

Plane of the surface area

32

facets

34

embossing lacquer

36

interference coating

38

paint layer

40

incident light

42

plane normal

46, 48

Interference layer normal

50, 52, 54

Points in Fig. 3

60

security element

62, 64, 66

subregions

72, 74, 76

Interference layer normal

80

security element

82, 84, 86, 88

subregions

90-O, 90-U

tilt directions

92, 94, 96, 98

projected normal vectors

100, 102, 104

Points in Fig. 7

110

optically variable surface pattern

112

color pixels

114-R, 114-G, 114-B

color ranges

116

increases

118

photoresist

120

exposure

122

Black mask

Ref

reference direction

Claims (15)

1. An optically variable see-through security element (12) for securing objects of value (10) with a planar, optically variable area pattern (16, 18),
   wherein the optically variable area pattern includes a multiplicity of facets (32) which have a substantially ray-optical effect and the orientation of which is distinguished respectively by an inclination angle α relative to the plane (30) of the area pattern, and by an azimuth angle θ in the plane of the area pattern,
   wherein the optically variable area pattern includes at least two subregions (16, 18) respectively having a multiplicity of identically oriented facets, wherein the facets of the at least two subregions differ from each other with respect to the inclination angle relative to the plane and/or the azimuth angle in the plane,
   the inclination angle α is between 0° and 45°,
   characterized in that
   the facets of the at least two subregions are supplied with an interference layer (36), the interference layer has a viewing-angle-dependent color change in transmitted light, and
   the optically variable area pattern shows a colored appearance with a viewing-angle-dependent, polychrome color change in transmission.
2. The see-through security element according to claim 1, characterized in that the area occupied by each subregion on the optically variable area pattern is at least 50 times, preferably at least 100 times, particularly preferably at least 1000 times greater than the area occupied on average by one individual facet of this area region.
3. The see-through security element according to claim 1 or 2, characterized in that the facets of the at least two subregions differ with respect to the inclination angle relative to the plane by 5° or more, preferably by 10° or more, particularly preferably by 20° or more, and/or that the facets of the at least two subregions differ with respect to the azimuth angle in the plane by 45° or more, preferably by 90° or more, in particular by 180°.
4. The see-through security element according to at least one of claims 1 to 3, characterized in that the facets are each supplied with an interference layer the thickness of which varies with the inclination angle α of the facets, preferably decreases with an increasing inclination angle α.
5. The see-through security element according to at least one of claims 1 to 4, characterized in that the at least two subregions are arranged in the form of a motif, so that the optically variable area pattern shows the motif formed by the subregions with two or more different colors in transmission at least in certain tilted positions of the security element.
6. The see-through security element according to at least one of claims 1 to 5, characterized in that the inclination angles α and the azimuth angles θ of the facets and the interference layer are mutually coordinated in the subregions such that the subregions show the same colors in one certain tilted position and different colors in other tilted positions.
7. The see-through security element according to at least one of claims 1 to 6, characterized in that the optically variable area pattern includes at least three subregions which are arranged in the form of a background region and of two foreground regions and in which the inclination angles α and the azimuth angles θ of the facets and the interference layer are so mutually coordinated that the optically variable area pattern in transmission

   - in a first tilted position shows a first motif, in which the first foreground region appears with a motif color and the second foreground region and the background region appear with a background color different from the motif color, and

   - in a second tilted position shows a second motif, in which the second foreground region appears with the motif color and the first foreground region and the background region appear with the background color.
8. The see-through security element according to at least one of claims 1 to 6, characterized in that the optically variable area pattern includes at least four subregions which are arranged in the form of a background region, of two foreground regions and an overlap region, and in which the inclination angles α and the azimuth angles θ of the facets and the interference layer are so mutually coordinated that the optically variable area pattern in transmission

   - in a first tilted position shows a first motif, in which the first foreground region and the overlap region appear with a motif color and the second foreground region and the background region appear with a background color different from the motif color, and

   - in a second tilted position shows a second motif, in which the second foreground region and the overlap region appear with the motif color and the first foreground region and the background region appear with the background color.
9. The see-through security element according to at least one of claims 1 to 7, characterized in that the optically variable area pattern includes at least two subregions in which the facets have the same inclination angle α, but azimuth angles θ which differ by 180°.
10. The see-through security element according to at least one of claims 1 to 9, characterized in that the optically variable area pattern includes a first and a second subregion in which the facets have the same inclination angle α₀, but azimuth angles θ which differ by 180°, and a third and a fourth subregion in which the facets have different inclination angles α₁ and α₂ and in which the azimuth angle θ differs from the azimuth angle of the first and the second subregion by 90° or 270°.
11. The see-through security element according to at least one of claims 1 to 10, characterized in that the optically variable area pattern includes at least three subregions in which the inclination angles α and the azimuth angles θ of the facets and the interference layer are mutually coordinated such that the subregions in a tilted position appear in red, green or blue in transmission.
12. The see-through security element according to at least one of claims 1 to 11, characterized in that the facets are embossed into an embossing lacquer layer with a first refractive index, and over the interference layer there is applied a lacquer layer with a second refractive index that differs from the first refractive index by less than 0.3, in particular by less than 0.1.
13. The see-through security element according to at least one of claims 1 to 12, characterized in that the interference layer is formed by a thin film element with semitransparent metal layers and a dielectric spacer layer, by a dielectric layer structure with at least one highly refractive layer, preferably combined with at least one lowly refractive layer, or includes at least one cholesteric liquid crystal layer.
14. The see-through security element according to at least one of claims 1 to 13, characterized in that the facets are configured substantially as planar area elements; and/or the facets are arranged in a periodical grid and in particular form a sawtooth grating, or that the facets are arranged aperiodically.
15. A method for manufacturing an optically variable see-through security element in which a substrate is made available and the substrate is supplied with a planar, optically variable area pattern which shows a colored appearance with a viewing-angle-dependent, polychrome color change in transmission, wherein

    - the optically variable area pattern is formed with a multiplicity of facets which have a substantially ray-optical effect and the orientation of which is distinguished respectively by an inclination angle α relative to the plane of the area pattern which is between 0° and 45°, and by an azimuth angle θ in the plane of the area pattern,

    - the optically variable area pattern is produced with at least two subregions respectively having a multiplicity of identically oriented facets, wherein the facets of the at least two subregions differ from each other with respect to the inclination angle relative to the plane and/or the azimuth angle in the plane, and

    - the facets of the at least two subregions are supplied with an interference layer with a viewing-angle-dependent color change in transmitted light.

Images