DE102019003518A1 - Security element with optically variable surface pattern - Google Patents

Abstract

The invention relates to a security element (12) for securing objects of value, with an optically variable surface pattern (14) which, when viewed in reflected light at a predetermined viewing angle (16-A), generates a predetermined gray-scale image (18-A) with different brightness values, wherein- the optically variable surface pattern (14) is formed from a plurality of essentially ray-optically acting facets (20), the lateral dimensions of which are below 100 μm and their orientation in each case by an angle of inclination α to the plane of the surface pattern (14) and through an azimuth angle φ is characterized in the plane of the surface pattern (14), the orientation of a facet each corresponding to an associated characteristic viewing angle (24), and the gray-scale image (18-A) of a plurality of facets (20) of the optically variable surface pattern (14) is generated, the different brightness values of the gray level nimage (18-A) are generated by differently large angle differences (δ) between the characteristic viewing angle (24) of the facets (20) involved in the image generation and the specified viewing angle (16-A), with smaller angle differences lighter gray levels and larger angle differences darker Correspond to grayscale.

Description

The invention relates to security elements for protecting objects of value with an optically variable surface pattern, as well as data carriers equipped with such security elements.

Data carriers, such as value or identity documents, or other objects of value, such as branded goods and packaging or outer packaging of high-quality branded goods, are often provided with security elements that allow the authenticity of the data carrier to be checked and at the same time serve as protection against unauthorized reproduction.

Security elements with viewing angle-dependent effects play a special role in securing authenticity, since these cannot be reproduced even with the most modern copiers. The security elements are equipped with optically variable elements which give the viewer a different image impression from different viewing angles and, for example, show a different color or brightness impression and / or a different graphic motif depending on the viewing angle.

In the case of security elements and in particular bank notes, portraits of well-known personalities or dignitaries, images of coats of arms or other heraldic symbols and emblems are often used as graphic motifs. Hologram effects, microlens features or micromirror elements are often used for the physical realization. Hologram effects allow the implementation of filigree motifs with high resolution, but they are comparatively less brilliant and therefore depend on good lighting. In addition, even slight changes in the viewing angle lead to false colors, which are not particularly attractive for portraits. For technical reasons, only symbols with limited resolution can currently be displayed for microlens features; the implementation of filigree motifs is not possible. The micromirror elements known to date are clearly visible regardless of the lighting, but the creation of the individual motifs is very complex. Also, the three-dimensional warping effects generated by the micromirrors do not always appear visually attractive enough, since brightness variations cannot be realized or only with great effort by light-absorbing nanostructures.

Taking this as a starting point, the invention is based on the object of specifying a security element of the type mentioned at the outset that is easy to manufacture and has an attractive appearance and a high level of security against forgery.

This object is achieved by the features of the independent claims. Developments of the invention are the subject of the dependent claims.

• - das optisch variable Flächenmuster aus einer Mehrzahl von im Wesentlichen strahlenoptisch wirkenden Facetten gebildet ist, deren laterale Abmessungen unterhalb von 100 µm liegen und deren Orientierung jeweils durch einen Neigungswinkel α gegen die Ebene des Flächenmusters und durch einen Azimutwinkel φ in der Ebene des Flächenmusters charakterisiert ist, wobei die Orientierung einer Facette jeweils einem zugehörigen charakteristischen Betrachtungswinkel entspricht, und
• - das Graustufenbild von einer Vielzahl von Facetten des optisch variablen Flächenmusters erzeugt wird, wobei die unterschiedlichen Helligkeitswerte des Graustufenbilds durch unterschiedlich große Winkeldifferenzen zwischen dem charakteristischen Betrachtungswinkel der an der Bilderzeugung beteiligten Facetten und dem vorgegebenen Betrachtungswinkel erzeugt werden, wobei kleinere Winkeldifferenzen helleren Graustufen und größere Winkeldifferenzen dunkleren Graustufen entsprechen.

According to a first aspect of the invention, a security element of the type mentioned at the outset generates a predetermined gray-scale image with different brightness values when viewed in reflected light at a predetermined viewing angle. It is provided that

• the optically variable surface pattern is formed from a plurality of essentially ray-optically acting facets, the lateral dimensions of which are below 100 μm and their orientation in each case by an angle of inclination α against the plane of the surface pattern and through an azimuth angle φ is characterized in the plane of the surface pattern, the orientation of a facet each corresponding to an associated characteristic viewing angle, and
• - The grayscale image is generated from a large number of facets of the optically variable surface pattern, the different brightness values of the grayscale image being generated by differently large angle differences between the characteristic viewing angle of the facets involved in the image generation and the specified viewing angle, with smaller angle differences lighter gray levels and larger angle differences correspond to darker shades of gray.

In this aspect, the invention is based on the idea that, in practice, facets which act optically do not reflect in a single, infinitely sharp angle, but always in a certain solid angle range around this characteristic viewing angle. This reflection can also and / or be caused by light sources with a spatial extent and / or by scattered light. If the viewing angle corresponds to the characteristic viewing angle for which a facet is designed due to its orientation, it appears with the maximum possible brightness. With increasing deviation of the viewing angle from the characteristic viewing angle, the brightness of the facet decreases until finally no more light is reflected in the viewing direction. Through targeted misorientation, i.e. the targeted setting of angle differences between the characteristic viewing angle of a facet and the intended viewing direction, it is possible to generate brightness gradations in a grayscale image without changing the surface of the facets or having to cover them with additional absorbent structures.

In a preferred embodiment of the invention, the facets having a given angle difference have different combinations of azimuth angle and angle of inclination in order to generate the given angle difference. Azimuth angles and / or angles of inclination which generate a given angle difference are advantageously distributed irregularly, in particular randomly or quasi-randomly.

In another, likewise advantageous embodiment, the surface pattern is subdivided into several zones, the facets having a given angle difference within each zone of the surface pattern each having the same azimuth angle and angle of inclination. However, azimuth angles and / or angles of inclination preferably differ significantly between different zones, in particular between adjacent zones, so that the zones appear in contrast to one another apart from the predetermined viewing angle.

The named zones can in particular be designed in the form of characters or patterns, so that an additional graphic pattern or additional information becomes visible away from the specified viewing angle. The additional pattern or the additional information can, in particular, cover undesired negative images of the gray-scale image and make them unrecognizable.

• - das optisch variable Flächenmuster neben dem in dem genannten ersten Betrachtungswinkel erzeugten ersten Graustufenbild ein in einem zweiten, unterschiedlichen, vorgegebenen Betrachtungswinkel ein zweites vorgegebenes Graustufenbild mit unterschiedlichen Helligkeitswerten erzeugt, wobei
• - das erste und zweite Graustufenbild jeweils von einer Vielzahl von Facetten des optisch variablen Flächenmusters erzeugt werden, wobei die unterschiedlichen Helligkeitswerte des ersten bzw. zweiten Graustufenbilds durch unterschiedlich große Winkeldifferenzen zwischen dem charakteristischen Betrachtungswinkel der an der Bilderzeugung jeweils beteiligten Facetten und dem vorgegebenen ersten bzw. zweiten Betrachtungswinkel erzeugt werden, wobei kleinere Abweichungen helleren Graustufen und größere Abweichungen dunkleren Graustufen entsprechen.

In an advantageous development of the invention it is provided that

• the optically variable surface pattern, in addition to the first gray-level image generated in the said first viewing angle, generates a second predetermined gray-level image with different brightness values in a second, different, predetermined viewing angle, wherein
• - the first and second gray-scale image are each generated from a plurality of facets of the optically variable surface pattern, the different brightness values of the first and second gray-scale image due to differently large angle differences between the characteristic viewing angle of the facets involved in the image generation and the specified first or Second viewing angle are generated, with smaller deviations corresponding to lighter gray levels and larger deviations correspond to darker gray levels.

The facets involved in the generation of the first or second gray level image are arranged in an advantageous embodiment regularly, in particular in a grid-like manner, nested. Alternatively, the facets involved in the generation of the first or second gray level image can also advantageously be arranged irregularly, in particular randomly or quasi-randomly distributed.

In a preferred embodiment, the facets involved in the generation of the first gray level image each have a large, preferably even the maximum, angle difference with respect to the second viewing angle. Conversely, the facets involved in the generation of the second grayscale image also each have a large, preferably even the maximum, angle difference in relation to the first viewing angle.

It goes without saying that the optically variable surface pattern can also generate further gray-scale images in an analogous manner in addition to the second gray-scale image.

• - das optisch variable Flächenmuster aus einer Mehrzahl von im Wesentlichen strahlenoptisch wirkenden Facetten gebildet ist, deren laterale Abmessungen unterhalb von 100 µm liegen und deren Orientierung jeweils durch einen Neigungswinkel α gegen die Ebene des Flächenmusters und durch einen Azimutwinkel φ in der Ebene des Flächenmusters charakterisiert ist, wobei die Orientierung einer Facette jeweils einem zugehörigen charakteristischen Betrachtungswinkel entspricht,
• - jedes Graustufenbild von einer Vielzahl von Facetten des optisch variablen Flächenmusters erzeugt wird, wobei die unterschiedlichen Helligkeitswerte eines Bildpunkts des jeweiligen Graustufenbilds durch den Flächenanteil der diesem Bildpunkt zugeordneten Facetten erzeugt wird, deren charakteristischen Betrachtungswinkel dem vorgegebenen Betrachtungswinkel des Graustufenbilds entspricht, wobei größere Flächenanteile helleren Graustufen und kleinere Flächenanteile dunkleren Graustufen entsprechen, und
• - der charakteristische Betrachtungswinkel derjenigen Facetten, die keinem der vorgegebenen Betrachtungswinkel eines Graustufenbilds entsprechen, für alle Graustufenbilder einem gemeinsamen, vorgegebenen Nebenwinkel entsprechen.

According to a second aspect of the invention, a security element of the type mentioned at the beginning generates two or more predetermined gray-scale images with different brightness values when viewed in reflected light at a predetermined viewing angle. It is provided that

• the optically variable surface pattern is formed from a plurality of essentially ray-optically acting facets, the lateral dimensions of which are below 100 μm and their orientation in each case by an angle of inclination α against the plane of the surface pattern and through an azimuth angle φ is characterized in the plane of the surface pattern, the orientation of a facet each corresponding to an associated characteristic viewing angle,
• - Each grayscale image is generated from a large number of facets of the optically variable surface pattern, the different brightness values of a pixel of the respective grayscale image being generated by the area portion of the facets assigned to this pixel, the characteristic viewing angle of which corresponds to the specified viewing angle of the gray scale image, with larger surface portions being lighter gray levels and smaller areas correspond to darker shades of gray, and
• the characteristic viewing angle of those facets which do not correspond to any of the predetermined viewing angles of a gray level image correspond to a common, predetermined secondary angle for all gray level images.

In this aspect, the invention is based on the idea of increasing the brightness of the pixels Set grayscale images by the area proportion of facets that reflect in the associated predetermined viewing angle. The area portion can be 100% for the brightest image points and 0% for the darkest image points and assume corresponding intermediate values between 0% and 100% for gray image points. The special feature here is that all facets that do not reflect into one of the specified viewing angles are aligned in the same way, in such a way that they all reflect into a common secondary angle. While the grayscale images are thus all individually visible in the associated viewing angles, the undesirable negative representations are all superimposed in the secondary angle and are thereby made very unrecognizable.

The secondary angle preferably differs as much as possible from the specified viewing directions. For example, the angle between the secondary angle and each of the predetermined viewing directions can be more than 40 °, in particular more than 50 ° or even more than 60 °.

In both aspects of the invention, the facets advantageously have lateral dimensions below 50 μm, preferably below 30 μm, particularly preferably below 15 μm.

In both aspects of the invention, at least one of the predefined gray-scale images advantageously has sharply delimited subject areas. The motif areas preferably have a resolution of more than 170 dpi, in particular more than 500 dpi, preferably more than 2000 dpi. The achievable resolution is limited to a line width of around 150 µm. With the security elements described above, clearly finer line widths down to less than 10 µm can be produced. This not only gives the designer much greater freedom of design, it also significantly improves protection against forgery.

If the surface pattern contains several gray-scale images, then the respective predetermined viewing directions advantageously differ from one another as much as possible. For example, the angle between the predetermined viewing directions of two gray-scale images can be more than 40 °, in particular more than 50 ° or even more than 60 °.

In both aspects of the invention it can be provided that the angle difference between the first and second viewing angles of two gray-scale images is very large, and is preferably greater than 70 °. Thus there is a minor angle, i.e. the viewing angle of the common negative of the grayscale images between the respective grayscale images. The respective grayscale image can be recognized very well when viewed from its viewing angle without being disturbed by the negative of the other grayscale image or the other grayscale images. In particular, by overlaying the respective negative representations of the gray-scale images, these can be made very unrecognizable.

The negative representations of the grayscale images can be divided into several secondary angles with the help of several groups of facets, which are each aligned differently. The groups of facets are preferably formed, oriented and / or arranged randomly and can have a specific, preferably random shape, in particular a random pattern. Thus, for example, a combined representation of a negative representation would be possible, after which the respective negative representations become almost unrecognizable for the viewer.

In both aspects of the invention, at least one facet, in particular a group of facets, and / or a surface pattern has a coating. In one embodiment, the coating can be a color shift coating, ie a coating that changes color in accordance with the viewing angle. The color shift coating comprises, for example, several layers, an absorber layer and a dielectric and optionally a reflector layer. The absorber layer has, for example, a layer based on chromium, aluminum and / or silver, the layer of the dielectric is a layer comprising, for example, SiO ₂ . The surface of the facet on which the coating is applied can already serve as a reflector. In one embodiment, the coating can additionally comprise the reflector layer based on chromium, aluminum and / or silver. In one embodiment, the coating can comprise a combination of at least one metal, inorganic material and / or one translucent printing ink, wherein a combination of metals and / or inorganic materials and / or translucent printing inks can be provided alone or with one another.

In one embodiment of both aspects of the invention, it can be provided that a group of facets and / or a surface pattern of facets in combination with a hologram and / or micromirrors and / or microlenses is present. Different optical effects can thus be combined with one another, so that, for example, additional diffractive effects can be generated. The security element's security against forgery is thereby significantly increased, since several complex steps and processes are necessary for production.

In one embodiment of both aspects of the invention, it can be provided that a group of facets and / or a surface pattern of facets is interleaved with a hologram and / or micromirrors and / or microlenses. Here, too, the security element's security against counterfeiting is significantly increased because several complex steps and processes are necessary for production. The individual surface patterns and hologram, microgame gel and / or micro lens surface areas are selected to be so small that not every surface area can be seen individually by the viewer, but in combination with one another. The surface areas and / or surface patterns preferably have an average length and width of at most 100 μm. The surface areas and / or surface patterns are preferably arranged in a checkerboard manner to one another.

In addition to the described security elements themselves, the invention also contains a data carrier with one of the security elements of the type described, wherein the security element can be arranged both in an opaque area of the data carrier and in or above a transparent window area or a continuous opening in the data carrier. The data carrier can in particular be a value document, such as a bank note, in particular a paper bank note, a polymer bank note or a film composite bank note, a share, a bond, a certificate, a voucher, a check, a high-quality admission ticket, but also an identity card such as a credit card, a bank card, a cash card, an authorization card, an identity card or a passport personalization page.

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

• 1 eine schematische Darstellung einer Banknote mit einem erfindungsgemäßen, optisch variablen Sicherheitselement,
• 2 eine Veranschaulichung der bei der Reflexion an einer Facette in der vorliegenden Erfindung relevanten Richtungen mit einer den Beobachtungsraum darstellenden Halbsphäre,
• 3 in (a) den visuellen Eindruck eines Graustufenbilds bei Betrachtung aus dem zugehörigen vorgegebenen Betrachtungswinkel, und in (b) den visuellen Eindruck des Graustufenbilds aus einem stark verkippten Betrachtungswinkel,
• 4 in (a) und (b) eine Darstellung wie in 3 für ein anderes Ausführungsbeispiel der Erfindung,
• 5 in (a) und (b) eine Darstellung wie in 3 und 4 für ein weiteres Ausführungsbeispiel der Erfindung,
• 6 eine Veranschaulichung der Wahl der charakteristischen Betrachtungswinkel der Facetten in einem Ausführungsbeispiel mit zwei Graustufenbildern,
• 7 eine Veranschaulichung der Ausrichtung der Facetten in einem weiteren Ausführungsbeispiel der Erfindung, und
• 8 eine Veranschaulichung der Ausrichtung der Facetten in einem weiteren Ausführungsbeispiel der Erfindung.

Show it:

• 1 a schematic representation of a bank note with an optically variable security element according to the invention,
• 2 an illustration of the directions relevant for the reflection on a facet in the present invention with a hemisphere representing the observation space,
• 3 in (a) the visual impression of a grayscale image when viewed from the associated specified viewing angle, and in (b) the visual impression of the grayscale image from a strongly tilted viewing angle,
• 4th in (a) and (b) a representation as in 3 for another embodiment of the invention,
• 5 in (a) and (b) a representation as in 3 and 4th for a further embodiment of the invention,
• 6th an illustration of the choice of the characteristic viewing angles of the facets in an exemplary embodiment with two gray-scale images,
• 7th an illustration of the orientation of the facets in a further embodiment of the invention, and
• 8th an illustration of the orientation of the facets in a further embodiment of the invention.

The invention will now be explained using the example of security elements for bank notes. 1 shows a schematic representation of a bank note 10 with an optically variable security element according to the invention 12 in the form of a glued-on transfer element. It goes without saying, however, that the invention is not limited to transfer elements and banknotes, but can be used with all types of security elements, for example with labels on goods and packaging or with the protection of documents, ID cards, passports, credit cards, health cards and the like. In the case of banknotes and similar documents, in addition to transfer elements, security threads or security strips can also be considered.

This in 1 shown security element 12 contains an optically variable surface pattern 14th that when viewed in reflected light at a first predetermined viewing angle 16-A a first grayscale image 18-A and from a second, different viewing angle 16-B a second grayscale image 18-B generated. The grayscale images each contain several, for example 16, 32 or more different brightness values (grayscale), so that the images shown appear very realistic. In particular, the grayscale images can be portraits 18-A , heraldic symbols 18-B or represent national emblems.

The optically variable surface pattern 14th is in a manner known per se from a plurality of essentially ray-optically acting facets 20th formed whose lateral dimensions are below 100 μm and whose orientation is characterized in each case by an angle of inclination with respect to the plane of the surface pattern and by an azimuth angle in the plane of the surface pattern. Such a facet 20th is in 2 shown schematically. Those relevant to the present invention Directions are with the help of the hemisphere S. illustrates, which represents the available observation space.

The grayscale image 18-A is with vertical lighting 22nd on viewing from one angle 16-A designed, which in the exemplary embodiment an angle of 25 ° with the perpendicular direction of illumination 22nd forms. The grayscale image is the same 18-B on viewing from one angle 16-B designed (in 2 not shown), which in the exemplary embodiment in to the angle 16-A opposite tilt direction also an angle of 25 ° with the vertical direction of illumination 22nd forms. The change between the two grayscale images 18-A , 18-B therefore requires tilting 15th of the banknote 10 by 2 * 25 ° = 50 ° or a corresponding change in the viewing direction.

The principle of the invention will now be explained first on the basis of a single grayscale image 18-A explained in more detail.

Regarding 2 is each of the facets 20th of the surface pattern 14th by an angle of inclination α against the plane of the surface pattern and through an azimuth angle φ in the plane of the surface pattern based on a reference direction R. characterized. The inclination angle and azimuth angle of a facet 20th each place an associated characteristic viewing angle 24 the facet firmly. As described above, the present inventors have recognized that by selecting the angle difference δ between the characteristic viewing angle 24 one facet 20th and the viewing angle 16-A of the grayscale image, the brightness value of this facet 20th can be set in the grayscale image. Smaller angle differences δ generated lighter shades of gray, while larger angle differences δ produce darker shades of gray.

As with the hemisphere S. the 2 can be seen, there is a desired angular difference δ to the observation angle 16-A not just a suitable characteristic viewing angle 24 of the associated facet, but there is a multitude of such characteristic viewing angles which are on the hemisphere S. in a circle 26th around the viewing angle 16-A are arranged around.

Using this knowledge, surface patterns 14th can be generated with grayscale images, which have a particularly advantageous behavior when tilted strongly from the specified viewing angle.

First shows 3 in (a) schematically the visual impression of a grayscale image 30th when viewed from the specified viewing angle. For illustration, it is assumed that the viewing angle corresponds to a tilt of + 25 ° in the direction of the positive x-axis of the surface pattern. The brightness values of the various pixels range from very bright (pixels 32 ) to very dark (pixels 34 ) and are created by facets, their angular difference δ range from a very small value (for example 0 °) to a very large value (for example 50 °) for the given viewing angle. Unlike the simplified representation of the 3 (a) there are also many intermediate gray values between the lightest and darkest image points 32, 34 in the grayscale image.

I'm depicting the 3 are the facets 20th to generate the different gray levels in the direction of the negative x-axis by the required angle difference δ tilted. The user looks at the security element 12 now at an actual viewing angle which differs greatly from the specified viewing angle, the appearance of the original gray-scale image changes 30th strong. When tilting from the specified viewing angle in the direction of the negative x-axis, a representation essentially arises after several intermediate images 36 with inverted brightnesses, as shown schematically in 3 (b) shown. The strongly tilted facets of the pixels 34 that appear dark from the specified viewing direction then appear light, while the facets of the image points that essentially point in the specified viewing direction 32 that appear light from the specified viewing direction now appear dark.

In the embodiment of 4th are the facets 20th to generate the various gray levels of the gray level image 40 for a desired angle difference δ provided with different combinations of azimuth and tilt angles. For example, the characteristic viewing angle 24 for a desired angle difference δ irregular or quasi-random along the circle 26th the 2 be distributed so that all points of the circle 26th are occupied with approximately the same probability. All the facets generated in this way have the same angle difference δ at the given viewing angle 16-A they all appear with the same gray level from this viewing angle.

If this is the procedure for all gray levels or for all associated angle differences, the in 4 (a) schematically shown image impression 40 of the grayscale image from the specified viewing angle is identical to the image impression 30th of the grayscale image of the 3 (a) .

However, there is a clear difference when viewing the grayscale image away from the specified viewing angle, as in 4 (b) illustrated. The strongly tilted facets of the pixels 34 from the specified viewing direction of the 4 (a) appear dark, appear significantly less bright than in the exemplary embodiment of 3 (b) as their characteristic viewing angle for each angle difference δ a wide distribution along the curve 26th exhibit. Similarly, the facets that appear light from the specified viewing direction also appear less dark than in 3 (b) , since they too have an angular distribution, albeit a less extensive one. Overall, a significantly less noticeable appearance results in the event of severe tilting 46 with more closely aligned brightnesses. Such an inconspicuous appearance is particularly desirable for portraits or depictions of nature, which often appear unnatural in inverted depictions.

With the design according to 4th is now based on the representation when viewing the grayscale image away from the specified viewing angle 30th the 3a or representation 40 according to 4a largely no representation 36 with inverted brightnesses, as shown schematically in 3 (b) shown, visible to the viewer, but it only results in the much more inconspicuous appearance 46 according to 4b .

Regarding 5 a strong weakening of the disturbing inverted display in the case of strong tilting can also be achieved by the surface pattern 14th is divided into different zones according to the motif. The facets that lead to a given angular difference δ belong, will then each be formed with the same azimuth angle and angle of inclination within a zone, but the alignment of the azimuth angle and / or angle of inclination in adjacent zones differs as much as possible. For example, the surface pattern is divided into two nested, cross-shaped zones 52 , 54 split as in 5 (b) shown. The tilting of the facets 20th takes place in the first zone 52 in the direction of the positive y-axis, in the zone 54 however, in the direction of the negative y-axis, in each case by the required angle difference δ .

Because the facets created in this way all have the same angular difference δ at the specified viewing angle, they appear again with the same gray level from the specified viewing angle, so that the in 5 (a) schematically shown image impression 50 of the grayscale image does not depend on the image impression 30th or. 40 the grayscale images of the 3 (a) or. 4 (a) differs.

However, if the grayscale image is tilted from the specified viewing angle, this results in 5 (b) appearance shown schematically 56 . The facets are in the zones 52 , 54 each oriented very differently and thus have different brightnesses apart from the specified viewing angle, so that the inverted portrait 58 a clearly visible cross pattern 52 , 54 is superimposed. The cross pattern can also dominate the impression of the picture in the event of a strong tilt and move the disturbing inverted appearance of the portrait into the background.

In the illustrated embodiment, the two are zones 52 and 54 so differently oriented that the inverted portrait at the viewing angle shown 58 only in the zones 52 is recognizable, the zones 54 but dominate the appearance 56 such that essentially these zones 54 are recognizable. The viewer will therefore only essentially see the pattern with the darkly patterned crosses, ie the pattern of the zones 54 , detect.

In another exemplary embodiment, not shown, the inverted portrait could be used at one viewing angle 58 only (essentially) in the zones 54 be recognizable, the zones 52 are designed to match the appearance 56 dominate, so that essentially the design of the zones 52 are recognizable and not the zones 54 with inverted portrait.

In an embodiment not shown, the two zones 52 , 54 be designed in such a way that they have the inverted portrait 58 according to the area of the zones 52 , 54 represent, but only from a corresponding viewing angle. The inverted portrait 58 is therefore never completely visible but only part of it. The inverted portrait 58 is therefore only barely visible.

In a further, not shown, embodiment, instead of two zones 52 , 54 three or more zones can be provided. Each of these zones has facets which are oriented differently with respect to the facets in the other zones. As in the case of the exemplary embodiment with two zones, the portrait is thus inverted 58 divided into the three or more zones so that the viewer does not see the full inverted portrait 58 can see but only a fraction of it. In particular, the visible part of the inverted portrait 58 so incomplete and so small in size that the inverted portrait 58 is not visible to the viewer for the naked eye.

Further design options arise when the optically variable surface pattern 14th two or more predetermined gray-scale images are generated at different viewing angles, such as the gray-scale images 18-A , 18-B the 1 .

The facets involved in the generation of the various gray-scale images can for this purpose, for example, be nested in a grid-like manner. For example, you can use the facets to create two grayscale images 18-A , 18-B be arranged like a checkerboard, with the "white" fields generating the first grayscale image 18-A , the "black" fields of the generation of the second grayscale image 18-B serve. However, it is also possible to arrange the facets for the generation of the different gray-scale images in an irregular manner, for example in a random manner. For this purpose, a random number Z can be generated from the interval [0,1 [for each facet position and the position with a facet for the first gray level image 18-A can be assigned if Z <0.5, otherwise with a facet for the second grayscale image 18-B .

The given viewing angles of the various grayscale images 18-A , 18-B advantageously differ from one another as much as possible.

6th illustrates the choice of the characteristic viewing angles of the facets 20th of the surface pattern 14th in one embodiment with two grayscale images 18-A , 18-B each based on viewing from a given viewing angle 16-A or. 16-B are designed. As related to 2 explained, there is the choice of the characteristic viewing angle of a facet 20th of the first grayscale image 18-A basically for any desired angle difference δ a multitude of possible characteristic viewing angles which are on the hemisphere S. on a circle 26th with opening angle δ around the viewing angle 16-A are arranged around.

Now to the representation of the second grayscale image 18-B in its given viewing angle 16-B To disturb as little as possible, it has proven to be advantageous if for the facets 20th of the first grayscale image 18-A based on the second viewing angle 16-B each a characteristic viewing angle from one area 60 is chosen which has a large, preferably even the maximum, angle difference to the second viewing angle 16-B having. In this case the facet appears 20th namely when viewing the second grayscale image 18-B from the viewing angle 16-B dark and only a little disturbing. Would be the characteristic viewing angle of the facet 20th however, from one area 62 chosen that is close to the viewing angle 16-B lies, so reflects the facet 20th strong in the direction of the viewing angle 16-B and creates a bright, disruptive light reflex there.

This selection is not just made with respect to the facets of the first grayscale image 18-A based on the second viewing angle 16-B but also vice versa for the facets of the second grayscale image 18-B based on the first viewing angle 16-A performed so that the two grayscale images interfere as little as possible.

Regarding 7th becomes an alternative way of aligning the facets 20th for the generation of gray levels and for the display of several gray level images in a surface pattern. In this embodiment, each facet 20th with a probability W according to the given viewing angle 16-A or. 16-B of the associated grayscale image 18-A or. 18-B aligned with the brightness of the associated pixel in the grayscale image 18-A or. 18-B corresponds. For example, the probability W can be 1 for the brightest pixels, 0 for the darkest pixels and assume corresponding intermediate values between 0 and 1 for gray pixels.

The specified viewing angles of the individual representations should also differ from one another as much as possible here. All facets 20th that are not according to the given viewing angle 16-A , 16-B of their respective grayscale image are aligned in the direction of a predetermined secondary angle 16-C to reflect, which is the same for all grayscale images, but differs from the given viewing angles 16-A , 16-B differs as much as possible.

This way, all of the images will be grayscale 18-A , 18-B under their respective given viewing angles 16-A , 16-B individually visible, while the inverted representations of all grayscale images only together as an overlay 18-C in the side corner 16-C become visible. The negative representations of the grayscale images are due to the overlay 18-A , 18-B made very unrecognizable and comparatively little disturbing.

In the 8th is another embodiment, similar to FIG 6th and 7th shown. However, it is provided that the angle difference between the first and second viewing angles 16-A and 16-B the grayscale images 18-A or. 18-B is very large, and is preferably greater than 70 °. The secondary angle is thus located 16-C , ie the viewing angle of the common negative of the grayscale images 18-A or. 18-B between the respective grayscale images 18-A or. 18-B . Thus, the respective grayscale image 18-A or. 18-B can be recognized very well without being affected by the negative of the other grayscale image 18-B or. 18-A to be disturbed. In particular, by superimposing the respective negative representations of the gray-scale images 18-A , 18-B this made highly unrecognizable.

The negative representations of the grayscale images 18-A , 18-B can be divided into several minor angles using several groups of facets, each oriented differently. The groups of facets are preferably formed, oriented and / or arranged randomly and can have a specific, preferably random shape, in particular a random pattern. A combined representation of a negative representation according to FIGS 4th and 5 possible, after which the respective negative representations are almost unrecognizable for the viewer.

List of reference symbols

10

Banknote

12

Security element

14th

optically variable surface pattern

15th

Tilt

16-A, 16-B

predetermined viewing angles

16-C

Secondary angle

18-A, 18-B

Grayscale images

20th

facet

22nd

vertical direction of illumination

24

characteristic viewing angle

26th

Circle around observation angle

30th

Grayscale image

32, 34

Pixels

36

Grayscale image when tilted

40

Grayscale image

46

Grayscale image when tilted

50

Grayscale image

52.54

Zones

56

Grayscale image when tilted

58

inverted portrait

60.62

Areas

S.

Hemisphere

R.

Reference direction

α

Inclination angle

φ

Azimuth angle

δ

Angular difference

Claims (13)

Security element for protecting objects of value, with an optically variable surface pattern which, when viewed in reflected light at a predetermined viewing angle, generates a predetermined gray-scale image with different brightness values, wherein - The optically variable surface pattern is formed from a plurality of essentially ray-optically acting facets whose lateral dimensions are below 100 µm and whose orientation is characterized in each case by an angle of inclination α against the plane of the surface pattern and by an azimuth angle φ in the plane of the surface pattern , wherein the orientation of a facet corresponds in each case to an associated characteristic viewing angle, and - The grayscale image is generated from a large number of facets of the optically variable surface pattern, the different brightness values of the grayscale image being generated by differently large angle differences between the characteristic viewing angle of the facets involved in the image generation and the specified viewing angle, with smaller angle differences lighter gray levels and larger angle differences correspond to darker shades of gray. Security element after Claim 1 , characterized in that the facets having a given angular difference have different combinations of azimuth angle and tilt angle in order to generate the given angular difference. Security element after Claim 2 , characterized in that azimuth angles and / or angles of inclination, which generate a given angle difference, are distributed irregularly, in particular randomly or quasi-randomly. Security element after Claim 2 , characterized in that the surface pattern is divided into several zones, the facets having a given angle difference within each zone of the surface pattern each having the same azimuth angle and angle of inclination, and the azimuth angle and / or angle of inclination advantageously differ significantly between different zones, so that the zones away from the appear in contrast to one another at a given viewing angle. Security element after Claim 4 , characterized in that the zones are designed in the form of characters or patterns. Security element according to at least one of the Claims 1 to 5 , characterized in that - the optically variable surface pattern, in addition to the first gray-scale image generated in the said first viewing angle, generates a second predetermined gray-scale image with different brightness values in a second, different, predetermined viewing angle, the first and second gray-scale image each from a plurality of Facets of the optically variable surface pattern are generated, the different brightness values of the first and second gray scale image being generated by differently large angle differences between the characteristic viewing angle of the respective facets involved in the generation of the image and the specified first or second viewing angle, with smaller deviations lighter gray levels and larger deviations correspond to darker shades of gray. Security element after Claim 6 , characterized in that the facets involved in the generation of the first or second gray level image are arranged regularly, in particular nested in a grid-like manner. Security element after Claim 6 , characterized in that the facets involved in the generation of the first or second gray level image are distributed irregularly, in particular randomly or quasi-randomly. Security element according to at least one of the Claims 6 to 8th , characterized in that the facets involved in the generation of the first grayscale image each have a large, preferably even the maximum angle difference with respect to the second viewing angle, and vice versa. Security element for securing objects of value, with an optically variable surface pattern which, when viewed in reflected light at a predetermined viewing angle, generates two or more predetermined gray-scale images with different brightness values, wherein - The optically variable surface pattern is formed from a plurality of essentially ray-optically acting facets whose lateral dimensions are below 100 µm and whose orientation is characterized in each case by an angle of inclination α against the plane of the surface pattern and by an azimuth angle φ in the plane of the surface pattern , whereby the orientation of a facet corresponds to an associated characteristic viewing angle, - Each grayscale image is generated from a large number of facets of the optically variable surface pattern, the different brightness values of a pixel of the respective grayscale image being generated by the area portion of the facets assigned to this pixel, the characteristic viewing angle of which corresponds to the specified viewing angle of the gray scale image, with larger surface portions being lighter gray levels and smaller areas correspond to darker shades of gray, and the characteristic viewing angle of those facets which do not correspond to any of the predetermined viewing angles of a gray level image correspond to a common, predetermined secondary angle for all gray level images. Security element according to at least one of the Claims 1 to 10 , characterized in that the facets have lateral dimensions below 50 µm, preferably below 30 µm, particularly preferably below 15 µm. Security element according to at least one of the Claims 1 to 11 , characterized in that at least one of the specified gray scale images has sharply delimited motif areas with an edge line with a width of less than 100 µm, in particular less than 50 µm. Data carrier with a security element according to one of the Claims 1 to 12 .

Images